1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
156 @section Option Summary
158 Here is a summary of all the options, grouped by type. Explanations are
159 in the following sections.
162 @item Overall Options
163 @xref{Overall Options,,Options Controlling the Kind of Output}.
164 @gccoptlist{-c -S -E -o @var{file} -combine -no-canonical-prefixes @gol
165 -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
167 --version -wrapper@@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg}}
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -fno-pretty-templates @gol
193 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
194 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
195 -fno-default-inline -fvisibility-inlines-hidden @gol
196 -fvisibility-ms-compat @gol
197 -Wabi -Wctor-dtor-privacy @gol
198 -Wnon-virtual-dtor -Wreorder @gol
199 -Weffc++ -Wstrict-null-sentinel @gol
200 -Wno-non-template-friend -Wold-style-cast @gol
201 -Woverloaded-virtual -Wno-pmf-conversions @gol
204 @item Objective-C and Objective-C++ Language Options
205 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
206 Objective-C and Objective-C++ Dialects}.
207 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
208 -fgnu-runtime -fnext-runtime @gol
209 -fno-nil-receivers @gol
210 -fobjc-call-cxx-cdtors @gol
211 -fobjc-direct-dispatch @gol
212 -fobjc-exceptions @gol
214 -freplace-objc-classes @gol
217 -Wassign-intercept @gol
218 -Wno-protocol -Wselector @gol
219 -Wstrict-selector-match @gol
220 -Wundeclared-selector}
222 @item Language Independent Options
223 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
224 @gccoptlist{-fmessage-length=@var{n} @gol
225 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
226 -fdiagnostics-show-option}
228 @item Warning Options
229 @xref{Warning Options,,Options to Request or Suppress Warnings}.
230 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
231 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
232 -Wno-attributes -Wno-builtin-macro-redefined @gol
233 -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
234 -Wchar-subscripts -Wclobbered -Wcomment @gol
235 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
236 -Wno-deprecated-declarations -Wdisabled-optimization @gol
237 -Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol
238 -Werror -Werror=* @gol
239 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
240 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
241 -Wformat-security -Wformat-y2k @gol
242 -Wframe-larger-than=@var{len} -Wjump-misses-init -Wignored-qualifiers @gol
243 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
244 -Winit-self -Winline @gol
245 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
246 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
247 -Wlogical-op -Wlong-long @gol
248 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
249 -Wmissing-format-attribute -Wmissing-include-dirs @gol
250 -Wmissing-noreturn -Wno-mudflap @gol
251 -Wno-multichar -Wnonnull -Wno-overflow @gol
252 -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol
253 -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
254 -Wpointer-arith -Wno-pointer-to-int-cast @gol
255 -Wredundant-decls @gol
256 -Wreturn-type -Wsequence-point -Wshadow @gol
257 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
258 -Wstrict-aliasing -Wstrict-aliasing=n @gol
259 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
260 -Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol
261 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
262 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
263 -Wunsuffixed-float-constants -Wunused -Wunused-function @gol
264 -Wunused-label -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable @gol
265 -Wvariadic-macros -Wvla @gol
266 -Wvolatile-register-var -Wwrite-strings}
268 @item C and Objective-C-only Warning Options
269 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
270 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
271 -Wold-style-declaration -Wold-style-definition @gol
272 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
273 -Wdeclaration-after-statement -Wpointer-sign}
275 @item Debugging Options
276 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
277 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
278 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
279 -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
280 -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
281 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
282 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
283 -fdump-statistics @gol
285 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
289 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
295 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
298 -fdump-tree-nrv -fdump-tree-vect @gol
299 -fdump-tree-sink @gol
300 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
301 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
302 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
303 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
304 -ftree-vectorizer-verbose=@var{n} @gol
305 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
306 -fdump-final-insns=@var{file} @gol
307 -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
308 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
309 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
310 -fenable-icf-debug @gol
311 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
312 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
313 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
314 -ftest-coverage -ftime-report -fvar-tracking @gol
315 -fvar-tracking-assigments -fvar-tracking-assignments-toggle @gol
316 -g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol
317 -ggdb -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
318 -gvms -gxcoff -gxcoff+ @gol
319 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
320 -fdebug-prefix-map=@var{old}=@var{new} @gol
321 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
322 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
323 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
324 -print-multi-directory -print-multi-lib -print-multi-os-directory @gol
325 -print-prog-name=@var{program} -print-search-dirs -Q @gol
326 -print-sysroot -print-sysroot-headers-suffix @gol
327 -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
329 @item Optimization Options
330 @xref{Optimize Options,,Options that Control Optimization}.
332 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
333 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
334 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
335 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
336 -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping @gol
337 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
338 -fdata-sections -fdce -fdce @gol
339 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
340 -fearly-inlining -fipa-sra -fexpensive-optimizations -ffast-math @gol
341 -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
342 -fforward-propagate -ffunction-sections @gol
343 -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
344 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
345 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
346 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta @gol
347 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
348 -fipa-type-escape -fira-algorithm=@var{algorithm} @gol
349 -fira-region=@var{region} -fira-coalesce @gol
350 -fira-loop-pressure -fno-ira-share-save-slots @gol
351 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
352 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
353 -floop-block -floop-interchange -floop-strip-mine -fgraphite-identity @gol
354 -floop-parallelize-all -flto -flto-compression-level -flto-report -fltrans @gol
355 -fltrans-output-list -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
356 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
357 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
358 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
359 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
360 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
361 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
362 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
363 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
364 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
365 -fprofile-generate=@var{path} @gol
366 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
367 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
368 -freorder-blocks-and-partition -freorder-functions @gol
369 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
370 -frounding-math -fsched2-use-superblocks @gol
371 -fsched2-use-traces -fsched-pressure @gol
372 -fsched-spec-load -fsched-spec-load-dangerous @gol
373 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
374 -fsched-group-heuristic -fsched-critical-path-heuristic @gol
375 -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
376 -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
377 -fschedule-insns -fschedule-insns2 -fsection-anchors @gol
378 -fselective-scheduling -fselective-scheduling2 @gol
379 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
380 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
381 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
382 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
383 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
384 -ftree-copyrename -ftree-dce @gol
385 -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-loop-im @gol
386 -ftree-phiprop -ftree-loop-distribution @gol
387 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
388 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-pta -ftree-reassoc @gol
389 -ftree-sink -ftree-sra -ftree-switch-conversion @gol
390 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
391 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
392 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
393 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
394 -fwhole-program -fwhopr -fwpa -fuse-linker-plugin @gol
395 --param @var{name}=@var{value}
396 -O -O0 -O1 -O2 -O3 -Os}
398 @item Preprocessor Options
399 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
400 @gccoptlist{-A@var{question}=@var{answer} @gol
401 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
402 -C -dD -dI -dM -dN @gol
403 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
404 -idirafter @var{dir} @gol
405 -include @var{file} -imacros @var{file} @gol
406 -iprefix @var{file} -iwithprefix @var{dir} @gol
407 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
408 -imultilib @var{dir} -isysroot @var{dir} @gol
409 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
410 -P -fworking-directory -remap @gol
411 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
412 -Xpreprocessor @var{option}}
414 @item Assembler Option
415 @xref{Assembler Options,,Passing Options to the Assembler}.
416 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
419 @xref{Link Options,,Options for Linking}.
420 @gccoptlist{@var{object-file-name} -l@var{library} @gol
421 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
422 -s -static -static-libgcc -static-libstdc++ -shared @gol
423 -shared-libgcc -symbolic @gol
424 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
427 @item Directory Options
428 @xref{Directory Options,,Options for Directory Search}.
429 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
430 -specs=@var{file} -I- --sysroot=@var{dir}}
433 @c I wrote this xref this way to avoid overfull hbox. -- rms
434 @xref{Target Options}.
435 @gccoptlist{-V @var{version} -b @var{machine}}
437 @item Machine Dependent Options
438 @xref{Submodel Options,,Hardware Models and Configurations}.
439 @c This list is ordered alphanumerically by subsection name.
440 @c Try and put the significant identifier (CPU or system) first,
441 @c so users have a clue at guessing where the ones they want will be.
444 @gccoptlist{-EB -EL @gol
445 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
446 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
449 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
450 -mabi=@var{name} @gol
451 -mapcs-stack-check -mno-apcs-stack-check @gol
452 -mapcs-float -mno-apcs-float @gol
453 -mapcs-reentrant -mno-apcs-reentrant @gol
454 -msched-prolog -mno-sched-prolog @gol
455 -mlittle-endian -mbig-endian -mwords-little-endian @gol
456 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
457 -mfp16-format=@var{name}
458 -mthumb-interwork -mno-thumb-interwork @gol
459 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
460 -mstructure-size-boundary=@var{n} @gol
461 -mabort-on-noreturn @gol
462 -mlong-calls -mno-long-calls @gol
463 -msingle-pic-base -mno-single-pic-base @gol
464 -mpic-register=@var{reg} @gol
465 -mnop-fun-dllimport @gol
466 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
467 -mpoke-function-name @gol
469 -mtpcs-frame -mtpcs-leaf-frame @gol
470 -mcaller-super-interworking -mcallee-super-interworking @gol
472 -mword-relocations @gol
473 -mfix-cortex-m3-ldrd}
476 @gccoptlist{-mmcu=@var{mcu} -mno-interrupts @gol
477 -mcall-prologues -mtiny-stack -mint8}
479 @emph{Blackfin Options}
480 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
481 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
482 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
483 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
484 -mno-id-shared-library -mshared-library-id=@var{n} @gol
485 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
486 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
487 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
491 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
492 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
493 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
494 -mstack-align -mdata-align -mconst-align @gol
495 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
496 -melf -maout -melinux -mlinux -sim -sim2 @gol
497 -mmul-bug-workaround -mno-mul-bug-workaround}
500 @gccoptlist{-mmac -mpush-args}
502 @emph{Darwin Options}
503 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
504 -arch_only -bind_at_load -bundle -bundle_loader @gol
505 -client_name -compatibility_version -current_version @gol
507 -dependency-file -dylib_file -dylinker_install_name @gol
508 -dynamic -dynamiclib -exported_symbols_list @gol
509 -filelist -flat_namespace -force_cpusubtype_ALL @gol
510 -force_flat_namespace -headerpad_max_install_names @gol
512 -image_base -init -install_name -keep_private_externs @gol
513 -multi_module -multiply_defined -multiply_defined_unused @gol
514 -noall_load -no_dead_strip_inits_and_terms @gol
515 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
516 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
517 -private_bundle -read_only_relocs -sectalign @gol
518 -sectobjectsymbols -whyload -seg1addr @gol
519 -sectcreate -sectobjectsymbols -sectorder @gol
520 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
521 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
522 -segprot -segs_read_only_addr -segs_read_write_addr @gol
523 -single_module -static -sub_library -sub_umbrella @gol
524 -twolevel_namespace -umbrella -undefined @gol
525 -unexported_symbols_list -weak_reference_mismatches @gol
526 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
527 -mkernel -mone-byte-bool}
529 @emph{DEC Alpha Options}
530 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
531 -mieee -mieee-with-inexact -mieee-conformant @gol
532 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
533 -mtrap-precision=@var{mode} -mbuild-constants @gol
534 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
535 -mbwx -mmax -mfix -mcix @gol
536 -mfloat-vax -mfloat-ieee @gol
537 -mexplicit-relocs -msmall-data -mlarge-data @gol
538 -msmall-text -mlarge-text @gol
539 -mmemory-latency=@var{time}}
541 @emph{DEC Alpha/VMS Options}
542 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
545 @gccoptlist{-msmall-model -mno-lsim}
548 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
549 -mhard-float -msoft-float @gol
550 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
551 -mdouble -mno-double @gol
552 -mmedia -mno-media -mmuladd -mno-muladd @gol
553 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
554 -mlinked-fp -mlong-calls -malign-labels @gol
555 -mlibrary-pic -macc-4 -macc-8 @gol
556 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
557 -moptimize-membar -mno-optimize-membar @gol
558 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
559 -mvliw-branch -mno-vliw-branch @gol
560 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
561 -mno-nested-cond-exec -mtomcat-stats @gol
565 @emph{GNU/Linux Options}
566 @gccoptlist{-muclibc}
568 @emph{H8/300 Options}
569 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
572 @gccoptlist{-march=@var{architecture-type} @gol
573 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
574 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
575 -mfixed-range=@var{register-range} @gol
576 -mjump-in-delay -mlinker-opt -mlong-calls @gol
577 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
578 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
579 -mno-jump-in-delay -mno-long-load-store @gol
580 -mno-portable-runtime -mno-soft-float @gol
581 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
582 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
583 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
584 -munix=@var{unix-std} -nolibdld -static -threads}
586 @emph{i386 and x86-64 Options}
587 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
588 -mfpmath=@var{unit} @gol
589 -masm=@var{dialect} -mno-fancy-math-387 @gol
590 -mno-fp-ret-in-387 -msoft-float @gol
591 -mno-wide-multiply -mrtd -malign-double @gol
592 -mpreferred-stack-boundary=@var{num}
593 -mincoming-stack-boundary=@var{num}
594 -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip @gol
595 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
596 -maes -mpclmul -mfused-madd @gol
597 -msse4a -m3dnow -mpopcnt -mabm -mfma4 -mxop -mlwp @gol
598 -mthreads -mno-align-stringops -minline-all-stringops @gol
599 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
600 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
601 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
602 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
603 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
604 -mcmodel=@var{code-model} -mabi=@var{name} @gol
605 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
609 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
610 -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
611 -mconstant-gp -mauto-pic -mfused-madd @gol
612 -minline-float-divide-min-latency @gol
613 -minline-float-divide-max-throughput @gol
614 -mno-inline-float-divide @gol
615 -minline-int-divide-min-latency @gol
616 -minline-int-divide-max-throughput @gol
617 -mno-inline-int-divide @gol
618 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
619 -mno-inline-sqrt @gol
620 -mdwarf2-asm -mearly-stop-bits @gol
621 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
622 -mtune=@var{cpu-type} -milp32 -mlp64 @gol
623 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
624 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
625 -msched-spec-ldc -msched-spec-control-ldc @gol
626 -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
627 -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
628 -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
629 -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
631 @emph{IA-64/VMS Options}
632 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
635 @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
636 -msign-extend-enabled -muser-enabled}
638 @emph{M32R/D Options}
639 @gccoptlist{-m32r2 -m32rx -m32r @gol
641 -malign-loops -mno-align-loops @gol
642 -missue-rate=@var{number} @gol
643 -mbranch-cost=@var{number} @gol
644 -mmodel=@var{code-size-model-type} @gol
645 -msdata=@var{sdata-type} @gol
646 -mno-flush-func -mflush-func=@var{name} @gol
647 -mno-flush-trap -mflush-trap=@var{number} @gol
651 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
653 @emph{M680x0 Options}
654 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
655 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
656 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
657 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
658 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
659 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
660 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
661 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
664 @emph{M68hc1x Options}
665 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
666 -mauto-incdec -minmax -mlong-calls -mshort @gol
667 -msoft-reg-count=@var{count}}
670 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
671 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
672 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
673 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
674 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
677 @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
678 -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
679 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
680 -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
684 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
685 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
686 -mips64 -mips64r2 @gol
687 -mips16 -mno-mips16 -mflip-mips16 @gol
688 -minterlink-mips16 -mno-interlink-mips16 @gol
689 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
690 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
691 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
692 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
693 -mfpu=@var{fpu-type} @gol
694 -msmartmips -mno-smartmips @gol
695 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
696 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
697 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
698 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
699 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
700 -membedded-data -mno-embedded-data @gol
701 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
702 -mcode-readable=@var{setting} @gol
703 -msplit-addresses -mno-split-addresses @gol
704 -mexplicit-relocs -mno-explicit-relocs @gol
705 -mcheck-zero-division -mno-check-zero-division @gol
706 -mdivide-traps -mdivide-breaks @gol
707 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
708 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
709 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
710 -mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol
711 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
712 -mflush-func=@var{func} -mno-flush-func @gol
713 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
714 -mfp-exceptions -mno-fp-exceptions @gol
715 -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
716 -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address}
719 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
720 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
721 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
722 -mno-base-addresses -msingle-exit -mno-single-exit}
724 @emph{MN10300 Options}
725 @gccoptlist{-mmult-bug -mno-mult-bug @gol
726 -mam33 -mno-am33 @gol
727 -mam33-2 -mno-am33-2 @gol
728 -mreturn-pointer-on-d0 @gol
731 @emph{PDP-11 Options}
732 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
733 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
734 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
735 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
736 -mbranch-expensive -mbranch-cheap @gol
737 -msplit -mno-split -munix-asm -mdec-asm}
739 @emph{picoChip Options}
740 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N}
741 -msymbol-as-address -mno-inefficient-warnings}
743 @emph{PowerPC Options}
744 See RS/6000 and PowerPC Options.
746 @emph{RS/6000 and PowerPC Options}
747 @gccoptlist{-mcpu=@var{cpu-type} @gol
748 -mtune=@var{cpu-type} @gol
749 -mpower -mno-power -mpower2 -mno-power2 @gol
750 -mpowerpc -mpowerpc64 -mno-powerpc @gol
751 -maltivec -mno-altivec @gol
752 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
753 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
754 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
755 -mfprnd -mno-fprnd @gol
756 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
757 -mnew-mnemonics -mold-mnemonics @gol
758 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
759 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
760 -malign-power -malign-natural @gol
761 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
762 -msingle-float -mdouble-float -msimple-fpu @gol
763 -mstring -mno-string -mupdate -mno-update @gol
764 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
765 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
766 -mstrict-align -mno-strict-align -mrelocatable @gol
767 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
768 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
769 -mdynamic-no-pic -maltivec -mswdiv @gol
770 -mprioritize-restricted-insns=@var{priority} @gol
771 -msched-costly-dep=@var{dependence_type} @gol
772 -minsert-sched-nops=@var{scheme} @gol
773 -mcall-sysv -mcall-netbsd @gol
774 -maix-struct-return -msvr4-struct-return @gol
775 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
776 -misel -mno-isel @gol
777 -misel=yes -misel=no @gol
779 -mspe=yes -mspe=no @gol
781 -mgen-cell-microcode -mwarn-cell-microcode @gol
782 -mvrsave -mno-vrsave @gol
783 -mmulhw -mno-mulhw @gol
784 -mdlmzb -mno-dlmzb @gol
785 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
786 -mprototype -mno-prototype @gol
787 -msim -mmvme -mads -myellowknife -memb -msdata @gol
788 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
791 @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
793 -mbig-endian-data -mlittle-endian-data @gol
796 -mas100-syntax -mno-as100-syntax@gol
798 -mmax-constant-size=@gol
800 -msave-acc-in-interrupts}
802 @emph{S/390 and zSeries Options}
803 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
804 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
805 -mlong-double-64 -mlong-double-128 @gol
806 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
807 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
808 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
809 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
810 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
813 @gccoptlist{-meb -mel @gol
817 -mscore5 -mscore5u -mscore7 -mscore7d}
820 @gccoptlist{-m1 -m2 -m2e @gol
821 -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
823 -m4-nofpu -m4-single-only -m4-single -m4 @gol
824 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
825 -m5-64media -m5-64media-nofpu @gol
826 -m5-32media -m5-32media-nofpu @gol
827 -m5-compact -m5-compact-nofpu @gol
828 -mb -ml -mdalign -mrelax @gol
829 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
830 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
831 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
832 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
833 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
837 @gccoptlist{-mcpu=@var{cpu-type} @gol
838 -mtune=@var{cpu-type} @gol
839 -mcmodel=@var{code-model} @gol
840 -m32 -m64 -mapp-regs -mno-app-regs @gol
841 -mfaster-structs -mno-faster-structs @gol
842 -mfpu -mno-fpu -mhard-float -msoft-float @gol
843 -mhard-quad-float -msoft-quad-float @gol
844 -mimpure-text -mno-impure-text -mlittle-endian @gol
845 -mstack-bias -mno-stack-bias @gol
846 -munaligned-doubles -mno-unaligned-doubles @gol
847 -mv8plus -mno-v8plus -mvis -mno-vis
848 -threads -pthreads -pthread}
851 @gccoptlist{-mwarn-reloc -merror-reloc @gol
852 -msafe-dma -munsafe-dma @gol
854 -msmall-mem -mlarge-mem -mstdmain @gol
855 -mfixed-range=@var{register-range} @gol
857 -maddress-space-conversion -mno-address-space-conversion @gol
858 -mcache-size=@var{cache-size} @gol
859 -matomic-updates -mno-atomic-updates}
861 @emph{System V Options}
862 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
865 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
866 -mprolog-function -mno-prolog-function -mspace @gol
867 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
868 -mapp-regs -mno-app-regs @gol
869 -mdisable-callt -mno-disable-callt @gol
875 @gccoptlist{-mg -mgnu -munix}
877 @emph{VxWorks Options}
878 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
879 -Xbind-lazy -Xbind-now}
881 @emph{x86-64 Options}
882 See i386 and x86-64 Options.
884 @emph{i386 and x86-64 Windows Options}
885 @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll
886 -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows
887 -fno-set-stack-executable}
889 @emph{Xstormy16 Options}
892 @emph{Xtensa Options}
893 @gccoptlist{-mconst16 -mno-const16 @gol
894 -mfused-madd -mno-fused-madd @gol
895 -mserialize-volatile -mno-serialize-volatile @gol
896 -mtext-section-literals -mno-text-section-literals @gol
897 -mtarget-align -mno-target-align @gol
898 -mlongcalls -mno-longcalls}
900 @emph{zSeries Options}
901 See S/390 and zSeries Options.
903 @item Code Generation Options
904 @xref{Code Gen Options,,Options for Code Generation Conventions}.
905 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
906 -ffixed-@var{reg} -fexceptions @gol
907 -fnon-call-exceptions -funwind-tables @gol
908 -fasynchronous-unwind-tables @gol
909 -finhibit-size-directive -finstrument-functions @gol
910 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
911 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
912 -fno-common -fno-ident @gol
913 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
914 -fno-jump-tables @gol
915 -frecord-gcc-switches @gol
916 -freg-struct-return -fshort-enums @gol
917 -fshort-double -fshort-wchar @gol
918 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
919 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
920 -fno-stack-limit -fargument-alias -fargument-noalias @gol
921 -fargument-noalias-global -fargument-noalias-anything @gol
922 -fleading-underscore -ftls-model=@var{model} @gol
923 -ftrapv -fwrapv -fbounds-check @gol
928 * Overall Options:: Controlling the kind of output:
929 an executable, object files, assembler files,
930 or preprocessed source.
931 * C Dialect Options:: Controlling the variant of C language compiled.
932 * C++ Dialect Options:: Variations on C++.
933 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
935 * Language Independent Options:: Controlling how diagnostics should be
937 * Warning Options:: How picky should the compiler be?
938 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
939 * Optimize Options:: How much optimization?
940 * Preprocessor Options:: Controlling header files and macro definitions.
941 Also, getting dependency information for Make.
942 * Assembler Options:: Passing options to the assembler.
943 * Link Options:: Specifying libraries and so on.
944 * Directory Options:: Where to find header files and libraries.
945 Where to find the compiler executable files.
946 * Spec Files:: How to pass switches to sub-processes.
947 * Target Options:: Running a cross-compiler, or an old version of GCC.
950 @node Overall Options
951 @section Options Controlling the Kind of Output
953 Compilation can involve up to four stages: preprocessing, compilation
954 proper, assembly and linking, always in that order. GCC is capable of
955 preprocessing and compiling several files either into several
956 assembler input files, or into one assembler input file; then each
957 assembler input file produces an object file, and linking combines all
958 the object files (those newly compiled, and those specified as input)
959 into an executable file.
961 @cindex file name suffix
962 For any given input file, the file name suffix determines what kind of
967 C source code which must be preprocessed.
970 C source code which should not be preprocessed.
973 C++ source code which should not be preprocessed.
976 Objective-C source code. Note that you must link with the @file{libobjc}
977 library to make an Objective-C program work.
980 Objective-C source code which should not be preprocessed.
984 Objective-C++ source code. Note that you must link with the @file{libobjc}
985 library to make an Objective-C++ program work. Note that @samp{.M} refers
986 to a literal capital M@.
989 Objective-C++ source code which should not be preprocessed.
992 C, C++, Objective-C or Objective-C++ header file to be turned into a
997 @itemx @var{file}.cxx
998 @itemx @var{file}.cpp
999 @itemx @var{file}.CPP
1000 @itemx @var{file}.c++
1002 C++ source code which must be preprocessed. Note that in @samp{.cxx},
1003 the last two letters must both be literally @samp{x}. Likewise,
1004 @samp{.C} refers to a literal capital C@.
1008 Objective-C++ source code which must be preprocessed.
1010 @item @var{file}.mii
1011 Objective-C++ source code which should not be preprocessed.
1015 @itemx @var{file}.hp
1016 @itemx @var{file}.hxx
1017 @itemx @var{file}.hpp
1018 @itemx @var{file}.HPP
1019 @itemx @var{file}.h++
1020 @itemx @var{file}.tcc
1021 C++ header file to be turned into a precompiled header.
1024 @itemx @var{file}.for
1025 @itemx @var{file}.ftn
1026 Fixed form Fortran source code which should not be preprocessed.
1029 @itemx @var{file}.FOR
1030 @itemx @var{file}.fpp
1031 @itemx @var{file}.FPP
1032 @itemx @var{file}.FTN
1033 Fixed form Fortran source code which must be preprocessed (with the traditional
1036 @item @var{file}.f90
1037 @itemx @var{file}.f95
1038 @itemx @var{file}.f03
1039 @itemx @var{file}.f08
1040 Free form Fortran source code which should not be preprocessed.
1042 @item @var{file}.F90
1043 @itemx @var{file}.F95
1044 @itemx @var{file}.F03
1045 @itemx @var{file}.F08
1046 Free form Fortran source code which must be preprocessed (with the
1047 traditional preprocessor).
1049 @c FIXME: Descriptions of Java file types.
1055 @item @var{file}.ads
1056 Ada source code file which contains a library unit declaration (a
1057 declaration of a package, subprogram, or generic, or a generic
1058 instantiation), or a library unit renaming declaration (a package,
1059 generic, or subprogram renaming declaration). Such files are also
1062 @item @var{file}.adb
1063 Ada source code file containing a library unit body (a subprogram or
1064 package body). Such files are also called @dfn{bodies}.
1066 @c GCC also knows about some suffixes for languages not yet included:
1077 @itemx @var{file}.sx
1078 Assembler code which must be preprocessed.
1081 An object file to be fed straight into linking.
1082 Any file name with no recognized suffix is treated this way.
1086 You can specify the input language explicitly with the @option{-x} option:
1089 @item -x @var{language}
1090 Specify explicitly the @var{language} for the following input files
1091 (rather than letting the compiler choose a default based on the file
1092 name suffix). This option applies to all following input files until
1093 the next @option{-x} option. Possible values for @var{language} are:
1095 c c-header c-cpp-output
1096 c++ c++-header c++-cpp-output
1097 objective-c objective-c-header objective-c-cpp-output
1098 objective-c++ objective-c++-header objective-c++-cpp-output
1099 assembler assembler-with-cpp
1101 f77 f77-cpp-input f95 f95-cpp-input
1106 Turn off any specification of a language, so that subsequent files are
1107 handled according to their file name suffixes (as they are if @option{-x}
1108 has not been used at all).
1110 @item -pass-exit-codes
1111 @opindex pass-exit-codes
1112 Normally the @command{gcc} program will exit with the code of 1 if any
1113 phase of the compiler returns a non-success return code. If you specify
1114 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1115 numerically highest error produced by any phase that returned an error
1116 indication. The C, C++, and Fortran frontends return 4, if an internal
1117 compiler error is encountered.
1120 If you only want some of the stages of compilation, you can use
1121 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1122 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1123 @command{gcc} is to stop. Note that some combinations (for example,
1124 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1129 Compile or assemble the source files, but do not link. The linking
1130 stage simply is not done. The ultimate output is in the form of an
1131 object file for each source file.
1133 By default, the object file name for a source file is made by replacing
1134 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1136 Unrecognized input files, not requiring compilation or assembly, are
1141 Stop after the stage of compilation proper; do not assemble. The output
1142 is in the form of an assembler code file for each non-assembler input
1145 By default, the assembler file name for a source file is made by
1146 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1148 Input files that don't require compilation are ignored.
1152 Stop after the preprocessing stage; do not run the compiler proper. The
1153 output is in the form of preprocessed source code, which is sent to the
1156 Input files which don't require preprocessing are ignored.
1158 @cindex output file option
1161 Place output in file @var{file}. This applies regardless to whatever
1162 sort of output is being produced, whether it be an executable file,
1163 an object file, an assembler file or preprocessed C code.
1165 If @option{-o} is not specified, the default is to put an executable
1166 file in @file{a.out}, the object file for
1167 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1168 assembler file in @file{@var{source}.s}, a precompiled header file in
1169 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1174 Print (on standard error output) the commands executed to run the stages
1175 of compilation. Also print the version number of the compiler driver
1176 program and of the preprocessor and the compiler proper.
1180 Like @option{-v} except the commands are not executed and all command
1181 arguments are quoted. This is useful for shell scripts to capture the
1182 driver-generated command lines.
1186 Use pipes rather than temporary files for communication between the
1187 various stages of compilation. This fails to work on some systems where
1188 the assembler is unable to read from a pipe; but the GNU assembler has
1193 If you are compiling multiple source files, this option tells the driver
1194 to pass all the source files to the compiler at once (for those
1195 languages for which the compiler can handle this). This will allow
1196 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1197 language for which this is supported is C@. If you pass source files for
1198 multiple languages to the driver, using this option, the driver will invoke
1199 the compiler(s) that support IMA once each, passing each compiler all the
1200 source files appropriate for it. For those languages that do not support
1201 IMA this option will be ignored, and the compiler will be invoked once for
1202 each source file in that language. If you use this option in conjunction
1203 with @option{-save-temps}, the compiler will generate multiple
1205 (one for each source file), but only one (combined) @file{.o} or
1210 Print (on the standard output) a description of the command line options
1211 understood by @command{gcc}. If the @option{-v} option is also specified
1212 then @option{--help} will also be passed on to the various processes
1213 invoked by @command{gcc}, so that they can display the command line options
1214 they accept. If the @option{-Wextra} option has also been specified
1215 (prior to the @option{--help} option), then command line options which
1216 have no documentation associated with them will also be displayed.
1219 @opindex target-help
1220 Print (on the standard output) a description of target-specific command
1221 line options for each tool. For some targets extra target-specific
1222 information may also be printed.
1224 @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
1225 Print (on the standard output) a description of the command line
1226 options understood by the compiler that fit into all specified classes
1227 and qualifiers. These are the supported classes:
1230 @item @samp{optimizers}
1231 This will display all of the optimization options supported by the
1234 @item @samp{warnings}
1235 This will display all of the options controlling warning messages
1236 produced by the compiler.
1239 This will display target-specific options. Unlike the
1240 @option{--target-help} option however, target-specific options of the
1241 linker and assembler will not be displayed. This is because those
1242 tools do not currently support the extended @option{--help=} syntax.
1245 This will display the values recognized by the @option{--param}
1248 @item @var{language}
1249 This will display the options supported for @var{language}, where
1250 @var{language} is the name of one of the languages supported in this
1254 This will display the options that are common to all languages.
1257 These are the supported qualifiers:
1260 @item @samp{undocumented}
1261 Display only those options which are undocumented.
1264 Display options which take an argument that appears after an equal
1265 sign in the same continuous piece of text, such as:
1266 @samp{--help=target}.
1268 @item @samp{separate}
1269 Display options which take an argument that appears as a separate word
1270 following the original option, such as: @samp{-o output-file}.
1273 Thus for example to display all the undocumented target-specific
1274 switches supported by the compiler the following can be used:
1277 --help=target,undocumented
1280 The sense of a qualifier can be inverted by prefixing it with the
1281 @samp{^} character, so for example to display all binary warning
1282 options (i.e., ones that are either on or off and that do not take an
1283 argument), which have a description the following can be used:
1286 --help=warnings,^joined,^undocumented
1289 The argument to @option{--help=} should not consist solely of inverted
1292 Combining several classes is possible, although this usually
1293 restricts the output by so much that there is nothing to display. One
1294 case where it does work however is when one of the classes is
1295 @var{target}. So for example to display all the target-specific
1296 optimization options the following can be used:
1299 --help=target,optimizers
1302 The @option{--help=} option can be repeated on the command line. Each
1303 successive use will display its requested class of options, skipping
1304 those that have already been displayed.
1306 If the @option{-Q} option appears on the command line before the
1307 @option{--help=} option, then the descriptive text displayed by
1308 @option{--help=} is changed. Instead of describing the displayed
1309 options, an indication is given as to whether the option is enabled,
1310 disabled or set to a specific value (assuming that the compiler
1311 knows this at the point where the @option{--help=} option is used).
1313 Here is a truncated example from the ARM port of @command{gcc}:
1316 % gcc -Q -mabi=2 --help=target -c
1317 The following options are target specific:
1319 -mabort-on-noreturn [disabled]
1323 The output is sensitive to the effects of previous command line
1324 options, so for example it is possible to find out which optimizations
1325 are enabled at @option{-O2} by using:
1328 -Q -O2 --help=optimizers
1331 Alternatively you can discover which binary optimizations are enabled
1332 by @option{-O3} by using:
1335 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1336 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1337 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1340 @item -no-canonical-prefixes
1341 @opindex no-canonical-prefixes
1342 Do not expand any symbolic links, resolve references to @samp{/../}
1343 or @samp{/./}, or make the path absolute when generating a relative
1348 Display the version number and copyrights of the invoked GCC@.
1352 Invoke all subcommands under a wrapper program. It takes a single
1353 comma separated list as an argument, which will be used to invoke
1357 gcc -c t.c -wrapper gdb,--args
1360 This will invoke all subprograms of gcc under "gdb --args",
1361 thus cc1 invocation will be "gdb --args cc1 ...".
1363 @item -fplugin=@var{name}.so
1364 Load the plugin code in file @var{name}.so, assumed to be a
1365 shared object to be dlopen'd by the compiler. The base name of
1366 the shared object file is used to identify the plugin for the
1367 purposes of argument parsing (See
1368 @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
1369 Each plugin should define the callback functions specified in the
1372 @item -fplugin-arg-@var{name}-@var{key}=@var{value}
1373 Define an argument called @var{key} with a value of @var{value}
1374 for the plugin called @var{name}.
1376 @include @value{srcdir}/../libiberty/at-file.texi
1380 @section Compiling C++ Programs
1382 @cindex suffixes for C++ source
1383 @cindex C++ source file suffixes
1384 C++ source files conventionally use one of the suffixes @samp{.C},
1385 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1386 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1387 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1388 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1389 files with these names and compiles them as C++ programs even if you
1390 call the compiler the same way as for compiling C programs (usually
1391 with the name @command{gcc}).
1395 However, the use of @command{gcc} does not add the C++ library.
1396 @command{g++} is a program that calls GCC and treats @samp{.c},
1397 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1398 files unless @option{-x} is used, and automatically specifies linking
1399 against the C++ library. This program is also useful when
1400 precompiling a C header file with a @samp{.h} extension for use in C++
1401 compilations. On many systems, @command{g++} is also installed with
1402 the name @command{c++}.
1404 @cindex invoking @command{g++}
1405 When you compile C++ programs, you may specify many of the same
1406 command-line options that you use for compiling programs in any
1407 language; or command-line options meaningful for C and related
1408 languages; or options that are meaningful only for C++ programs.
1409 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1410 explanations of options for languages related to C@.
1411 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1412 explanations of options that are meaningful only for C++ programs.
1414 @node C Dialect Options
1415 @section Options Controlling C Dialect
1416 @cindex dialect options
1417 @cindex language dialect options
1418 @cindex options, dialect
1420 The following options control the dialect of C (or languages derived
1421 from C, such as C++, Objective-C and Objective-C++) that the compiler
1425 @cindex ANSI support
1429 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1430 equivalent to @samp{-std=c++98}.
1432 This turns off certain features of GCC that are incompatible with ISO
1433 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1434 such as the @code{asm} and @code{typeof} keywords, and
1435 predefined macros such as @code{unix} and @code{vax} that identify the
1436 type of system you are using. It also enables the undesirable and
1437 rarely used ISO trigraph feature. For the C compiler,
1438 it disables recognition of C++ style @samp{//} comments as well as
1439 the @code{inline} keyword.
1441 The alternate keywords @code{__asm__}, @code{__extension__},
1442 @code{__inline__} and @code{__typeof__} continue to work despite
1443 @option{-ansi}. You would not want to use them in an ISO C program, of
1444 course, but it is useful to put them in header files that might be included
1445 in compilations done with @option{-ansi}. Alternate predefined macros
1446 such as @code{__unix__} and @code{__vax__} are also available, with or
1447 without @option{-ansi}.
1449 The @option{-ansi} option does not cause non-ISO programs to be
1450 rejected gratuitously. For that, @option{-pedantic} is required in
1451 addition to @option{-ansi}. @xref{Warning Options}.
1453 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1454 option is used. Some header files may notice this macro and refrain
1455 from declaring certain functions or defining certain macros that the
1456 ISO standard doesn't call for; this is to avoid interfering with any
1457 programs that might use these names for other things.
1459 Functions that would normally be built in but do not have semantics
1460 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1461 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1462 built-in functions provided by GCC}, for details of the functions
1467 Determine the language standard. @xref{Standards,,Language Standards
1468 Supported by GCC}, for details of these standard versions. This option
1469 is currently only supported when compiling C or C++.
1471 The compiler can accept several base standards, such as @samp{c89} or
1472 @samp{c++98}, and GNU dialects of those standards, such as
1473 @samp{gnu89} or @samp{gnu++98}. By specifying a base standard, the
1474 compiler will accept all programs following that standard and those
1475 using GNU extensions that do not contradict it. For example,
1476 @samp{-std=c89} turns off certain features of GCC that are
1477 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1478 keywords, but not other GNU extensions that do not have a meaning in
1479 ISO C90, such as omitting the middle term of a @code{?:}
1480 expression. On the other hand, by specifying a GNU dialect of a
1481 standard, all features the compiler support are enabled, even when
1482 those features change the meaning of the base standard and some
1483 strict-conforming programs may be rejected. The particular standard
1484 is used by @option{-pedantic} to identify which features are GNU
1485 extensions given that version of the standard. For example
1486 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1487 comments, while @samp{-std=gnu99 -pedantic} would not.
1489 A value for this option must be provided; possible values are
1494 Support all ISO C90 programs (certain GNU extensions that conflict
1495 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1497 @item iso9899:199409
1498 ISO C90 as modified in amendment 1.
1504 ISO C99. Note that this standard is not yet fully supported; see
1505 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1506 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1509 GNU dialect of ISO C90 (including some C99 features). This
1510 is the default for C code.
1514 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1515 this will become the default. The name @samp{gnu9x} is deprecated.
1518 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1522 GNU dialect of @option{-std=c++98}. This is the default for
1526 The working draft of the upcoming ISO C++0x standard. This option
1527 enables experimental features that are likely to be included in
1528 C++0x. The working draft is constantly changing, and any feature that is
1529 enabled by this flag may be removed from future versions of GCC if it is
1530 not part of the C++0x standard.
1533 GNU dialect of @option{-std=c++0x}. This option enables
1534 experimental features that may be removed in future versions of GCC.
1537 @item -fgnu89-inline
1538 @opindex fgnu89-inline
1539 The option @option{-fgnu89-inline} tells GCC to use the traditional
1540 GNU semantics for @code{inline} functions when in C99 mode.
1541 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1542 is accepted and ignored by GCC versions 4.1.3 up to but not including
1543 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1544 C99 mode. Using this option is roughly equivalent to adding the
1545 @code{gnu_inline} function attribute to all inline functions
1546 (@pxref{Function Attributes}).
1548 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1549 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1550 specifies the default behavior). This option was first supported in
1551 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1553 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1554 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1555 in effect for @code{inline} functions. @xref{Common Predefined
1556 Macros,,,cpp,The C Preprocessor}.
1558 @item -aux-info @var{filename}
1560 Output to the given filename prototyped declarations for all functions
1561 declared and/or defined in a translation unit, including those in header
1562 files. This option is silently ignored in any language other than C@.
1564 Besides declarations, the file indicates, in comments, the origin of
1565 each declaration (source file and line), whether the declaration was
1566 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1567 @samp{O} for old, respectively, in the first character after the line
1568 number and the colon), and whether it came from a declaration or a
1569 definition (@samp{C} or @samp{F}, respectively, in the following
1570 character). In the case of function definitions, a K&R-style list of
1571 arguments followed by their declarations is also provided, inside
1572 comments, after the declaration.
1576 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1577 keyword, so that code can use these words as identifiers. You can use
1578 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1579 instead. @option{-ansi} implies @option{-fno-asm}.
1581 In C++, this switch only affects the @code{typeof} keyword, since
1582 @code{asm} and @code{inline} are standard keywords. You may want to
1583 use the @option{-fno-gnu-keywords} flag instead, which has the same
1584 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1585 switch only affects the @code{asm} and @code{typeof} keywords, since
1586 @code{inline} is a standard keyword in ISO C99.
1589 @itemx -fno-builtin-@var{function}
1590 @opindex fno-builtin
1591 @cindex built-in functions
1592 Don't recognize built-in functions that do not begin with
1593 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1594 functions provided by GCC}, for details of the functions affected,
1595 including those which are not built-in functions when @option{-ansi} or
1596 @option{-std} options for strict ISO C conformance are used because they
1597 do not have an ISO standard meaning.
1599 GCC normally generates special code to handle certain built-in functions
1600 more efficiently; for instance, calls to @code{alloca} may become single
1601 instructions that adjust the stack directly, and calls to @code{memcpy}
1602 may become inline copy loops. The resulting code is often both smaller
1603 and faster, but since the function calls no longer appear as such, you
1604 cannot set a breakpoint on those calls, nor can you change the behavior
1605 of the functions by linking with a different library. In addition,
1606 when a function is recognized as a built-in function, GCC may use
1607 information about that function to warn about problems with calls to
1608 that function, or to generate more efficient code, even if the
1609 resulting code still contains calls to that function. For example,
1610 warnings are given with @option{-Wformat} for bad calls to
1611 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1612 known not to modify global memory.
1614 With the @option{-fno-builtin-@var{function}} option
1615 only the built-in function @var{function} is
1616 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1617 function is named that is not built-in in this version of GCC, this
1618 option is ignored. There is no corresponding
1619 @option{-fbuiltin-@var{function}} option; if you wish to enable
1620 built-in functions selectively when using @option{-fno-builtin} or
1621 @option{-ffreestanding}, you may define macros such as:
1624 #define abs(n) __builtin_abs ((n))
1625 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1630 @cindex hosted environment
1632 Assert that compilation takes place in a hosted environment. This implies
1633 @option{-fbuiltin}. A hosted environment is one in which the
1634 entire standard library is available, and in which @code{main} has a return
1635 type of @code{int}. Examples are nearly everything except a kernel.
1636 This is equivalent to @option{-fno-freestanding}.
1638 @item -ffreestanding
1639 @opindex ffreestanding
1640 @cindex hosted environment
1642 Assert that compilation takes place in a freestanding environment. This
1643 implies @option{-fno-builtin}. A freestanding environment
1644 is one in which the standard library may not exist, and program startup may
1645 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1646 This is equivalent to @option{-fno-hosted}.
1648 @xref{Standards,,Language Standards Supported by GCC}, for details of
1649 freestanding and hosted environments.
1653 @cindex openmp parallel
1654 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1655 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1656 compiler generates parallel code according to the OpenMP Application
1657 Program Interface v3.0 @w{@uref{http://www.openmp.org/}}. This option
1658 implies @option{-pthread}, and thus is only supported on targets that
1659 have support for @option{-pthread}.
1661 @item -fms-extensions
1662 @opindex fms-extensions
1663 Accept some non-standard constructs used in Microsoft header files.
1665 Some cases of unnamed fields in structures and unions are only
1666 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1667 fields within structs/unions}, for details.
1671 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1672 options for strict ISO C conformance) implies @option{-trigraphs}.
1674 @item -no-integrated-cpp
1675 @opindex no-integrated-cpp
1676 Performs a compilation in two passes: preprocessing and compiling. This
1677 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1678 @option{-B} option. The user supplied compilation step can then add in
1679 an additional preprocessing step after normal preprocessing but before
1680 compiling. The default is to use the integrated cpp (internal cpp)
1682 The semantics of this option will change if "cc1", "cc1plus", and
1683 "cc1obj" are merged.
1685 @cindex traditional C language
1686 @cindex C language, traditional
1688 @itemx -traditional-cpp
1689 @opindex traditional-cpp
1690 @opindex traditional
1691 Formerly, these options caused GCC to attempt to emulate a pre-standard
1692 C compiler. They are now only supported with the @option{-E} switch.
1693 The preprocessor continues to support a pre-standard mode. See the GNU
1694 CPP manual for details.
1696 @item -fcond-mismatch
1697 @opindex fcond-mismatch
1698 Allow conditional expressions with mismatched types in the second and
1699 third arguments. The value of such an expression is void. This option
1700 is not supported for C++.
1702 @item -flax-vector-conversions
1703 @opindex flax-vector-conversions
1704 Allow implicit conversions between vectors with differing numbers of
1705 elements and/or incompatible element types. This option should not be
1708 @item -funsigned-char
1709 @opindex funsigned-char
1710 Let the type @code{char} be unsigned, like @code{unsigned char}.
1712 Each kind of machine has a default for what @code{char} should
1713 be. It is either like @code{unsigned char} by default or like
1714 @code{signed char} by default.
1716 Ideally, a portable program should always use @code{signed char} or
1717 @code{unsigned char} when it depends on the signedness of an object.
1718 But many programs have been written to use plain @code{char} and
1719 expect it to be signed, or expect it to be unsigned, depending on the
1720 machines they were written for. This option, and its inverse, let you
1721 make such a program work with the opposite default.
1723 The type @code{char} is always a distinct type from each of
1724 @code{signed char} or @code{unsigned char}, even though its behavior
1725 is always just like one of those two.
1728 @opindex fsigned-char
1729 Let the type @code{char} be signed, like @code{signed char}.
1731 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1732 the negative form of @option{-funsigned-char}. Likewise, the option
1733 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1735 @item -fsigned-bitfields
1736 @itemx -funsigned-bitfields
1737 @itemx -fno-signed-bitfields
1738 @itemx -fno-unsigned-bitfields
1739 @opindex fsigned-bitfields
1740 @opindex funsigned-bitfields
1741 @opindex fno-signed-bitfields
1742 @opindex fno-unsigned-bitfields
1743 These options control whether a bit-field is signed or unsigned, when the
1744 declaration does not use either @code{signed} or @code{unsigned}. By
1745 default, such a bit-field is signed, because this is consistent: the
1746 basic integer types such as @code{int} are signed types.
1749 @node C++ Dialect Options
1750 @section Options Controlling C++ Dialect
1752 @cindex compiler options, C++
1753 @cindex C++ options, command line
1754 @cindex options, C++
1755 This section describes the command-line options that are only meaningful
1756 for C++ programs; but you can also use most of the GNU compiler options
1757 regardless of what language your program is in. For example, you
1758 might compile a file @code{firstClass.C} like this:
1761 g++ -g -frepo -O -c firstClass.C
1765 In this example, only @option{-frepo} is an option meant
1766 only for C++ programs; you can use the other options with any
1767 language supported by GCC@.
1769 Here is a list of options that are @emph{only} for compiling C++ programs:
1773 @item -fabi-version=@var{n}
1774 @opindex fabi-version
1775 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1776 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1777 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1778 the version that conforms most closely to the C++ ABI specification.
1779 Therefore, the ABI obtained using version 0 will change as ABI bugs
1782 The default is version 2.
1784 @item -fno-access-control
1785 @opindex fno-access-control
1786 Turn off all access checking. This switch is mainly useful for working
1787 around bugs in the access control code.
1791 Check that the pointer returned by @code{operator new} is non-null
1792 before attempting to modify the storage allocated. This check is
1793 normally unnecessary because the C++ standard specifies that
1794 @code{operator new} will only return @code{0} if it is declared
1795 @samp{throw()}, in which case the compiler will always check the
1796 return value even without this option. In all other cases, when
1797 @code{operator new} has a non-empty exception specification, memory
1798 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1799 @samp{new (nothrow)}.
1801 @item -fconserve-space
1802 @opindex fconserve-space
1803 Put uninitialized or runtime-initialized global variables into the
1804 common segment, as C does. This saves space in the executable at the
1805 cost of not diagnosing duplicate definitions. If you compile with this
1806 flag and your program mysteriously crashes after @code{main()} has
1807 completed, you may have an object that is being destroyed twice because
1808 two definitions were merged.
1810 This option is no longer useful on most targets, now that support has
1811 been added for putting variables into BSS without making them common.
1813 @item -fno-deduce-init-list
1814 @opindex fno-deduce-init-list
1815 Disable deduction of a template type parameter as
1816 std::initializer_list from a brace-enclosed initializer list, i.e.
1819 template <class T> auto forward(T t) -> decltype (realfn (t))
1826 forward(@{1,2@}); // call forward<std::initializer_list<int>>
1830 This option is present because this deduction is an extension to the
1831 current specification in the C++0x working draft, and there was
1832 some concern about potential overload resolution problems.
1834 @item -ffriend-injection
1835 @opindex ffriend-injection
1836 Inject friend functions into the enclosing namespace, so that they are
1837 visible outside the scope of the class in which they are declared.
1838 Friend functions were documented to work this way in the old Annotated
1839 C++ Reference Manual, and versions of G++ before 4.1 always worked
1840 that way. However, in ISO C++ a friend function which is not declared
1841 in an enclosing scope can only be found using argument dependent
1842 lookup. This option causes friends to be injected as they were in
1845 This option is for compatibility, and may be removed in a future
1848 @item -fno-elide-constructors
1849 @opindex fno-elide-constructors
1850 The C++ standard allows an implementation to omit creating a temporary
1851 which is only used to initialize another object of the same type.
1852 Specifying this option disables that optimization, and forces G++ to
1853 call the copy constructor in all cases.
1855 @item -fno-enforce-eh-specs
1856 @opindex fno-enforce-eh-specs
1857 Don't generate code to check for violation of exception specifications
1858 at runtime. This option violates the C++ standard, but may be useful
1859 for reducing code size in production builds, much like defining
1860 @samp{NDEBUG}. This does not give user code permission to throw
1861 exceptions in violation of the exception specifications; the compiler
1862 will still optimize based on the specifications, so throwing an
1863 unexpected exception will result in undefined behavior.
1866 @itemx -fno-for-scope
1868 @opindex fno-for-scope
1869 If @option{-ffor-scope} is specified, the scope of variables declared in
1870 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1871 as specified by the C++ standard.
1872 If @option{-fno-for-scope} is specified, the scope of variables declared in
1873 a @i{for-init-statement} extends to the end of the enclosing scope,
1874 as was the case in old versions of G++, and other (traditional)
1875 implementations of C++.
1877 The default if neither flag is given to follow the standard,
1878 but to allow and give a warning for old-style code that would
1879 otherwise be invalid, or have different behavior.
1881 @item -fno-gnu-keywords
1882 @opindex fno-gnu-keywords
1883 Do not recognize @code{typeof} as a keyword, so that code can use this
1884 word as an identifier. You can use the keyword @code{__typeof__} instead.
1885 @option{-ansi} implies @option{-fno-gnu-keywords}.
1887 @item -fno-implicit-templates
1888 @opindex fno-implicit-templates
1889 Never emit code for non-inline templates which are instantiated
1890 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1891 @xref{Template Instantiation}, for more information.
1893 @item -fno-implicit-inline-templates
1894 @opindex fno-implicit-inline-templates
1895 Don't emit code for implicit instantiations of inline templates, either.
1896 The default is to handle inlines differently so that compiles with and
1897 without optimization will need the same set of explicit instantiations.
1899 @item -fno-implement-inlines
1900 @opindex fno-implement-inlines
1901 To save space, do not emit out-of-line copies of inline functions
1902 controlled by @samp{#pragma implementation}. This will cause linker
1903 errors if these functions are not inlined everywhere they are called.
1905 @item -fms-extensions
1906 @opindex fms-extensions
1907 Disable pedantic warnings about constructs used in MFC, such as implicit
1908 int and getting a pointer to member function via non-standard syntax.
1910 @item -fno-nonansi-builtins
1911 @opindex fno-nonansi-builtins
1912 Disable built-in declarations of functions that are not mandated by
1913 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1914 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1916 @item -fno-operator-names
1917 @opindex fno-operator-names
1918 Do not treat the operator name keywords @code{and}, @code{bitand},
1919 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1920 synonyms as keywords.
1922 @item -fno-optional-diags
1923 @opindex fno-optional-diags
1924 Disable diagnostics that the standard says a compiler does not need to
1925 issue. Currently, the only such diagnostic issued by G++ is the one for
1926 a name having multiple meanings within a class.
1929 @opindex fpermissive
1930 Downgrade some diagnostics about nonconformant code from errors to
1931 warnings. Thus, using @option{-fpermissive} will allow some
1932 nonconforming code to compile.
1934 @item -fno-pretty-templates
1935 @opindex fno-pretty-templates
1936 When an error message refers to a specialization of a function
1937 template, the compiler will normally print the signature of the
1938 template followed by the template arguments and any typedefs or
1939 typenames in the signature (e.g. @code{void f(T) [with T = int]}
1940 rather than @code{void f(int)}) so that it's clear which template is
1941 involved. When an error message refers to a specialization of a class
1942 template, the compiler will omit any template arguments which match
1943 the default template arguments for that template. If either of these
1944 behaviors make it harder to understand the error message rather than
1945 easier, using @option{-fno-pretty-templates} will disable them.
1949 Enable automatic template instantiation at link time. This option also
1950 implies @option{-fno-implicit-templates}. @xref{Template
1951 Instantiation}, for more information.
1955 Disable generation of information about every class with virtual
1956 functions for use by the C++ runtime type identification features
1957 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1958 of the language, you can save some space by using this flag. Note that
1959 exception handling uses the same information, but it will generate it as
1960 needed. The @samp{dynamic_cast} operator can still be used for casts that
1961 do not require runtime type information, i.e.@: casts to @code{void *} or to
1962 unambiguous base classes.
1966 Emit statistics about front-end processing at the end of the compilation.
1967 This information is generally only useful to the G++ development team.
1969 @item -ftemplate-depth-@var{n}
1970 @opindex ftemplate-depth
1971 Set the maximum instantiation depth for template classes to @var{n}.
1972 A limit on the template instantiation depth is needed to detect
1973 endless recursions during template class instantiation. ANSI/ISO C++
1974 conforming programs must not rely on a maximum depth greater than 17
1975 (changed to 1024 in C++0x).
1977 @item -fno-threadsafe-statics
1978 @opindex fno-threadsafe-statics
1979 Do not emit the extra code to use the routines specified in the C++
1980 ABI for thread-safe initialization of local statics. You can use this
1981 option to reduce code size slightly in code that doesn't need to be
1984 @item -fuse-cxa-atexit
1985 @opindex fuse-cxa-atexit
1986 Register destructors for objects with static storage duration with the
1987 @code{__cxa_atexit} function rather than the @code{atexit} function.
1988 This option is required for fully standards-compliant handling of static
1989 destructors, but will only work if your C library supports
1990 @code{__cxa_atexit}.
1992 @item -fno-use-cxa-get-exception-ptr
1993 @opindex fno-use-cxa-get-exception-ptr
1994 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1995 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1996 if the runtime routine is not available.
1998 @item -fvisibility-inlines-hidden
1999 @opindex fvisibility-inlines-hidden
2000 This switch declares that the user does not attempt to compare
2001 pointers to inline methods where the addresses of the two functions
2002 were taken in different shared objects.
2004 The effect of this is that GCC may, effectively, mark inline methods with
2005 @code{__attribute__ ((visibility ("hidden")))} so that they do not
2006 appear in the export table of a DSO and do not require a PLT indirection
2007 when used within the DSO@. Enabling this option can have a dramatic effect
2008 on load and link times of a DSO as it massively reduces the size of the
2009 dynamic export table when the library makes heavy use of templates.
2011 The behavior of this switch is not quite the same as marking the
2012 methods as hidden directly, because it does not affect static variables
2013 local to the function or cause the compiler to deduce that
2014 the function is defined in only one shared object.
2016 You may mark a method as having a visibility explicitly to negate the
2017 effect of the switch for that method. For example, if you do want to
2018 compare pointers to a particular inline method, you might mark it as
2019 having default visibility. Marking the enclosing class with explicit
2020 visibility will have no effect.
2022 Explicitly instantiated inline methods are unaffected by this option
2023 as their linkage might otherwise cross a shared library boundary.
2024 @xref{Template Instantiation}.
2026 @item -fvisibility-ms-compat
2027 @opindex fvisibility-ms-compat
2028 This flag attempts to use visibility settings to make GCC's C++
2029 linkage model compatible with that of Microsoft Visual Studio.
2031 The flag makes these changes to GCC's linkage model:
2035 It sets the default visibility to @code{hidden}, like
2036 @option{-fvisibility=hidden}.
2039 Types, but not their members, are not hidden by default.
2042 The One Definition Rule is relaxed for types without explicit
2043 visibility specifications which are defined in more than one different
2044 shared object: those declarations are permitted if they would have
2045 been permitted when this option was not used.
2048 In new code it is better to use @option{-fvisibility=hidden} and
2049 export those classes which are intended to be externally visible.
2050 Unfortunately it is possible for code to rely, perhaps accidentally,
2051 on the Visual Studio behavior.
2053 Among the consequences of these changes are that static data members
2054 of the same type with the same name but defined in different shared
2055 objects will be different, so changing one will not change the other;
2056 and that pointers to function members defined in different shared
2057 objects may not compare equal. When this flag is given, it is a
2058 violation of the ODR to define types with the same name differently.
2062 Do not use weak symbol support, even if it is provided by the linker.
2063 By default, G++ will use weak symbols if they are available. This
2064 option exists only for testing, and should not be used by end-users;
2065 it will result in inferior code and has no benefits. This option may
2066 be removed in a future release of G++.
2070 Do not search for header files in the standard directories specific to
2071 C++, but do still search the other standard directories. (This option
2072 is used when building the C++ library.)
2075 In addition, these optimization, warning, and code generation options
2076 have meanings only for C++ programs:
2079 @item -fno-default-inline
2080 @opindex fno-default-inline
2081 Do not assume @samp{inline} for functions defined inside a class scope.
2082 @xref{Optimize Options,,Options That Control Optimization}. Note that these
2083 functions will have linkage like inline functions; they just won't be
2086 @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
2089 Warn when G++ generates code that is probably not compatible with the
2090 vendor-neutral C++ ABI@. Although an effort has been made to warn about
2091 all such cases, there are probably some cases that are not warned about,
2092 even though G++ is generating incompatible code. There may also be
2093 cases where warnings are emitted even though the code that is generated
2096 You should rewrite your code to avoid these warnings if you are
2097 concerned about the fact that code generated by G++ may not be binary
2098 compatible with code generated by other compilers.
2100 The known incompatibilities at this point include:
2105 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
2106 pack data into the same byte as a base class. For example:
2109 struct A @{ virtual void f(); int f1 : 1; @};
2110 struct B : public A @{ int f2 : 1; @};
2114 In this case, G++ will place @code{B::f2} into the same byte
2115 as@code{A::f1}; other compilers will not. You can avoid this problem
2116 by explicitly padding @code{A} so that its size is a multiple of the
2117 byte size on your platform; that will cause G++ and other compilers to
2118 layout @code{B} identically.
2121 Incorrect handling of tail-padding for virtual bases. G++ does not use
2122 tail padding when laying out virtual bases. For example:
2125 struct A @{ virtual void f(); char c1; @};
2126 struct B @{ B(); char c2; @};
2127 struct C : public A, public virtual B @{@};
2131 In this case, G++ will not place @code{B} into the tail-padding for
2132 @code{A}; other compilers will. You can avoid this problem by
2133 explicitly padding @code{A} so that its size is a multiple of its
2134 alignment (ignoring virtual base classes); that will cause G++ and other
2135 compilers to layout @code{C} identically.
2138 Incorrect handling of bit-fields with declared widths greater than that
2139 of their underlying types, when the bit-fields appear in a union. For
2143 union U @{ int i : 4096; @};
2147 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2148 union too small by the number of bits in an @code{int}.
2151 Empty classes can be placed at incorrect offsets. For example:
2161 struct C : public B, public A @{@};
2165 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2166 it should be placed at offset zero. G++ mistakenly believes that the
2167 @code{A} data member of @code{B} is already at offset zero.
2170 Names of template functions whose types involve @code{typename} or
2171 template template parameters can be mangled incorrectly.
2174 template <typename Q>
2175 void f(typename Q::X) @{@}
2177 template <template <typename> class Q>
2178 void f(typename Q<int>::X) @{@}
2182 Instantiations of these templates may be mangled incorrectly.
2186 It also warns psABI related changes. The known psABI changes at this
2192 For SYSV/x86-64, when passing union with long double, it is changed to
2193 pass in memory as specified in psABI. For example:
2203 @code{union U} will always be passed in memory.
2207 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2208 @opindex Wctor-dtor-privacy
2209 @opindex Wno-ctor-dtor-privacy
2210 Warn when a class seems unusable because all the constructors or
2211 destructors in that class are private, and it has neither friends nor
2212 public static member functions.
2214 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2215 @opindex Wnon-virtual-dtor
2216 @opindex Wno-non-virtual-dtor
2217 Warn when a class has virtual functions and accessible non-virtual
2218 destructor, in which case it would be possible but unsafe to delete
2219 an instance of a derived class through a pointer to the base class.
2220 This warning is also enabled if -Weffc++ is specified.
2222 @item -Wreorder @r{(C++ and Objective-C++ only)}
2224 @opindex Wno-reorder
2225 @cindex reordering, warning
2226 @cindex warning for reordering of member initializers
2227 Warn when the order of member initializers given in the code does not
2228 match the order in which they must be executed. For instance:
2234 A(): j (0), i (1) @{ @}
2238 The compiler will rearrange the member initializers for @samp{i}
2239 and @samp{j} to match the declaration order of the members, emitting
2240 a warning to that effect. This warning is enabled by @option{-Wall}.
2243 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2246 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2249 Warn about violations of the following style guidelines from Scott Meyers'
2250 @cite{Effective C++} book:
2254 Item 11: Define a copy constructor and an assignment operator for classes
2255 with dynamically allocated memory.
2258 Item 12: Prefer initialization to assignment in constructors.
2261 Item 14: Make destructors virtual in base classes.
2264 Item 15: Have @code{operator=} return a reference to @code{*this}.
2267 Item 23: Don't try to return a reference when you must return an object.
2271 Also warn about violations of the following style guidelines from
2272 Scott Meyers' @cite{More Effective C++} book:
2276 Item 6: Distinguish between prefix and postfix forms of increment and
2277 decrement operators.
2280 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2284 When selecting this option, be aware that the standard library
2285 headers do not obey all of these guidelines; use @samp{grep -v}
2286 to filter out those warnings.
2288 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2289 @opindex Wstrict-null-sentinel
2290 @opindex Wno-strict-null-sentinel
2291 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2292 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2293 to @code{__null}. Although it is a null pointer constant not a null pointer,
2294 it is guaranteed to be of the same size as a pointer. But this use is
2295 not portable across different compilers.
2297 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2298 @opindex Wno-non-template-friend
2299 @opindex Wnon-template-friend
2300 Disable warnings when non-templatized friend functions are declared
2301 within a template. Since the advent of explicit template specification
2302 support in G++, if the name of the friend is an unqualified-id (i.e.,
2303 @samp{friend foo(int)}), the C++ language specification demands that the
2304 friend declare or define an ordinary, nontemplate function. (Section
2305 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2306 could be interpreted as a particular specialization of a templatized
2307 function. Because this non-conforming behavior is no longer the default
2308 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2309 check existing code for potential trouble spots and is on by default.
2310 This new compiler behavior can be turned off with
2311 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2312 but disables the helpful warning.
2314 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2315 @opindex Wold-style-cast
2316 @opindex Wno-old-style-cast
2317 Warn if an old-style (C-style) cast to a non-void type is used within
2318 a C++ program. The new-style casts (@samp{dynamic_cast},
2319 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2320 less vulnerable to unintended effects and much easier to search for.
2322 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2323 @opindex Woverloaded-virtual
2324 @opindex Wno-overloaded-virtual
2325 @cindex overloaded virtual fn, warning
2326 @cindex warning for overloaded virtual fn
2327 Warn when a function declaration hides virtual functions from a
2328 base class. For example, in:
2335 struct B: public A @{
2340 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2348 will fail to compile.
2350 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2351 @opindex Wno-pmf-conversions
2352 @opindex Wpmf-conversions
2353 Disable the diagnostic for converting a bound pointer to member function
2356 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2357 @opindex Wsign-promo
2358 @opindex Wno-sign-promo
2359 Warn when overload resolution chooses a promotion from unsigned or
2360 enumerated type to a signed type, over a conversion to an unsigned type of
2361 the same size. Previous versions of G++ would try to preserve
2362 unsignedness, but the standard mandates the current behavior.
2367 A& operator = (int);
2377 In this example, G++ will synthesize a default @samp{A& operator =
2378 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2381 @node Objective-C and Objective-C++ Dialect Options
2382 @section Options Controlling Objective-C and Objective-C++ Dialects
2384 @cindex compiler options, Objective-C and Objective-C++
2385 @cindex Objective-C and Objective-C++ options, command line
2386 @cindex options, Objective-C and Objective-C++
2387 (NOTE: This manual does not describe the Objective-C and Objective-C++
2388 languages themselves. See @xref{Standards,,Language Standards
2389 Supported by GCC}, for references.)
2391 This section describes the command-line options that are only meaningful
2392 for Objective-C and Objective-C++ programs, but you can also use most of
2393 the language-independent GNU compiler options.
2394 For example, you might compile a file @code{some_class.m} like this:
2397 gcc -g -fgnu-runtime -O -c some_class.m
2401 In this example, @option{-fgnu-runtime} is an option meant only for
2402 Objective-C and Objective-C++ programs; you can use the other options with
2403 any language supported by GCC@.
2405 Note that since Objective-C is an extension of the C language, Objective-C
2406 compilations may also use options specific to the C front-end (e.g.,
2407 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2408 C++-specific options (e.g., @option{-Wabi}).
2410 Here is a list of options that are @emph{only} for compiling Objective-C
2411 and Objective-C++ programs:
2414 @item -fconstant-string-class=@var{class-name}
2415 @opindex fconstant-string-class
2416 Use @var{class-name} as the name of the class to instantiate for each
2417 literal string specified with the syntax @code{@@"@dots{}"}. The default
2418 class name is @code{NXConstantString} if the GNU runtime is being used, and
2419 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2420 @option{-fconstant-cfstrings} option, if also present, will override the
2421 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2422 to be laid out as constant CoreFoundation strings.
2425 @opindex fgnu-runtime
2426 Generate object code compatible with the standard GNU Objective-C
2427 runtime. This is the default for most types of systems.
2429 @item -fnext-runtime
2430 @opindex fnext-runtime
2431 Generate output compatible with the NeXT runtime. This is the default
2432 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2433 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2436 @item -fno-nil-receivers
2437 @opindex fno-nil-receivers
2438 Assume that all Objective-C message dispatches (e.g.,
2439 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2440 is not @code{nil}. This allows for more efficient entry points in the runtime
2441 to be used. Currently, this option is only available in conjunction with
2442 the NeXT runtime on Mac OS X 10.3 and later.
2444 @item -fobjc-call-cxx-cdtors
2445 @opindex fobjc-call-cxx-cdtors
2446 For each Objective-C class, check if any of its instance variables is a
2447 C++ object with a non-trivial default constructor. If so, synthesize a
2448 special @code{- (id) .cxx_construct} instance method that will run
2449 non-trivial default constructors on any such instance variables, in order,
2450 and then return @code{self}. Similarly, check if any instance variable
2451 is a C++ object with a non-trivial destructor, and if so, synthesize a
2452 special @code{- (void) .cxx_destruct} method that will run
2453 all such default destructors, in reverse order.
2455 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2456 thusly generated will only operate on instance variables declared in the
2457 current Objective-C class, and not those inherited from superclasses. It
2458 is the responsibility of the Objective-C runtime to invoke all such methods
2459 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2460 will be invoked by the runtime immediately after a new object
2461 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2462 be invoked immediately before the runtime deallocates an object instance.
2464 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2465 support for invoking the @code{- (id) .cxx_construct} and
2466 @code{- (void) .cxx_destruct} methods.
2468 @item -fobjc-direct-dispatch
2469 @opindex fobjc-direct-dispatch
2470 Allow fast jumps to the message dispatcher. On Darwin this is
2471 accomplished via the comm page.
2473 @item -fobjc-exceptions
2474 @opindex fobjc-exceptions
2475 Enable syntactic support for structured exception handling in Objective-C,
2476 similar to what is offered by C++ and Java. This option is
2477 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2486 @@catch (AnObjCClass *exc) @{
2493 @@catch (AnotherClass *exc) @{
2496 @@catch (id allOthers) @{
2506 The @code{@@throw} statement may appear anywhere in an Objective-C or
2507 Objective-C++ program; when used inside of a @code{@@catch} block, the
2508 @code{@@throw} may appear without an argument (as shown above), in which case
2509 the object caught by the @code{@@catch} will be rethrown.
2511 Note that only (pointers to) Objective-C objects may be thrown and
2512 caught using this scheme. When an object is thrown, it will be caught
2513 by the nearest @code{@@catch} clause capable of handling objects of that type,
2514 analogously to how @code{catch} blocks work in C++ and Java. A
2515 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2516 any and all Objective-C exceptions not caught by previous @code{@@catch}
2519 The @code{@@finally} clause, if present, will be executed upon exit from the
2520 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2521 regardless of whether any exceptions are thrown, caught or rethrown
2522 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2523 of the @code{finally} clause in Java.
2525 There are several caveats to using the new exception mechanism:
2529 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2530 idioms provided by the @code{NSException} class, the new
2531 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2532 systems, due to additional functionality needed in the (NeXT) Objective-C
2536 As mentioned above, the new exceptions do not support handling
2537 types other than Objective-C objects. Furthermore, when used from
2538 Objective-C++, the Objective-C exception model does not interoperate with C++
2539 exceptions at this time. This means you cannot @code{@@throw} an exception
2540 from Objective-C and @code{catch} it in C++, or vice versa
2541 (i.e., @code{throw @dots{} @@catch}).
2544 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2545 blocks for thread-safe execution:
2548 @@synchronized (ObjCClass *guard) @{
2553 Upon entering the @code{@@synchronized} block, a thread of execution shall
2554 first check whether a lock has been placed on the corresponding @code{guard}
2555 object by another thread. If it has, the current thread shall wait until
2556 the other thread relinquishes its lock. Once @code{guard} becomes available,
2557 the current thread will place its own lock on it, execute the code contained in
2558 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2559 making @code{guard} available to other threads).
2561 Unlike Java, Objective-C does not allow for entire methods to be marked
2562 @code{@@synchronized}. Note that throwing exceptions out of
2563 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2564 to be unlocked properly.
2568 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2570 @item -freplace-objc-classes
2571 @opindex freplace-objc-classes
2572 Emit a special marker instructing @command{ld(1)} not to statically link in
2573 the resulting object file, and allow @command{dyld(1)} to load it in at
2574 run time instead. This is used in conjunction with the Fix-and-Continue
2575 debugging mode, where the object file in question may be recompiled and
2576 dynamically reloaded in the course of program execution, without the need
2577 to restart the program itself. Currently, Fix-and-Continue functionality
2578 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2583 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2584 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2585 compile time) with static class references that get initialized at load time,
2586 which improves run-time performance. Specifying the @option{-fzero-link} flag
2587 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2588 to be retained. This is useful in Zero-Link debugging mode, since it allows
2589 for individual class implementations to be modified during program execution.
2593 Dump interface declarations for all classes seen in the source file to a
2594 file named @file{@var{sourcename}.decl}.
2596 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2597 @opindex Wassign-intercept
2598 @opindex Wno-assign-intercept
2599 Warn whenever an Objective-C assignment is being intercepted by the
2602 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2603 @opindex Wno-protocol
2605 If a class is declared to implement a protocol, a warning is issued for
2606 every method in the protocol that is not implemented by the class. The
2607 default behavior is to issue a warning for every method not explicitly
2608 implemented in the class, even if a method implementation is inherited
2609 from the superclass. If you use the @option{-Wno-protocol} option, then
2610 methods inherited from the superclass are considered to be implemented,
2611 and no warning is issued for them.
2613 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2615 @opindex Wno-selector
2616 Warn if multiple methods of different types for the same selector are
2617 found during compilation. The check is performed on the list of methods
2618 in the final stage of compilation. Additionally, a check is performed
2619 for each selector appearing in a @code{@@selector(@dots{})}
2620 expression, and a corresponding method for that selector has been found
2621 during compilation. Because these checks scan the method table only at
2622 the end of compilation, these warnings are not produced if the final
2623 stage of compilation is not reached, for example because an error is
2624 found during compilation, or because the @option{-fsyntax-only} option is
2627 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2628 @opindex Wstrict-selector-match
2629 @opindex Wno-strict-selector-match
2630 Warn if multiple methods with differing argument and/or return types are
2631 found for a given selector when attempting to send a message using this
2632 selector to a receiver of type @code{id} or @code{Class}. When this flag
2633 is off (which is the default behavior), the compiler will omit such warnings
2634 if any differences found are confined to types which share the same size
2637 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2638 @opindex Wundeclared-selector
2639 @opindex Wno-undeclared-selector
2640 Warn if a @code{@@selector(@dots{})} expression referring to an
2641 undeclared selector is found. A selector is considered undeclared if no
2642 method with that name has been declared before the
2643 @code{@@selector(@dots{})} expression, either explicitly in an
2644 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2645 an @code{@@implementation} section. This option always performs its
2646 checks as soon as a @code{@@selector(@dots{})} expression is found,
2647 while @option{-Wselector} only performs its checks in the final stage of
2648 compilation. This also enforces the coding style convention
2649 that methods and selectors must be declared before being used.
2651 @item -print-objc-runtime-info
2652 @opindex print-objc-runtime-info
2653 Generate C header describing the largest structure that is passed by
2658 @node Language Independent Options
2659 @section Options to Control Diagnostic Messages Formatting
2660 @cindex options to control diagnostics formatting
2661 @cindex diagnostic messages
2662 @cindex message formatting
2664 Traditionally, diagnostic messages have been formatted irrespective of
2665 the output device's aspect (e.g.@: its width, @dots{}). The options described
2666 below can be used to control the diagnostic messages formatting
2667 algorithm, e.g.@: how many characters per line, how often source location
2668 information should be reported. Right now, only the C++ front end can
2669 honor these options. However it is expected, in the near future, that
2670 the remaining front ends would be able to digest them correctly.
2673 @item -fmessage-length=@var{n}
2674 @opindex fmessage-length
2675 Try to format error messages so that they fit on lines of about @var{n}
2676 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2677 the front ends supported by GCC@. If @var{n} is zero, then no
2678 line-wrapping will be done; each error message will appear on a single
2681 @opindex fdiagnostics-show-location
2682 @item -fdiagnostics-show-location=once
2683 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2684 reporter to emit @emph{once} source location information; that is, in
2685 case the message is too long to fit on a single physical line and has to
2686 be wrapped, the source location won't be emitted (as prefix) again,
2687 over and over, in subsequent continuation lines. This is the default
2690 @item -fdiagnostics-show-location=every-line
2691 Only meaningful in line-wrapping mode. Instructs the diagnostic
2692 messages reporter to emit the same source location information (as
2693 prefix) for physical lines that result from the process of breaking
2694 a message which is too long to fit on a single line.
2696 @item -fdiagnostics-show-option
2697 @opindex fdiagnostics-show-option
2698 This option instructs the diagnostic machinery to add text to each
2699 diagnostic emitted, which indicates which command line option directly
2700 controls that diagnostic, when such an option is known to the
2701 diagnostic machinery.
2703 @item -Wcoverage-mismatch
2704 @opindex Wcoverage-mismatch
2705 Warn if feedback profiles do not match when using the
2706 @option{-fprofile-use} option.
2707 If a source file was changed between @option{-fprofile-gen} and
2708 @option{-fprofile-use}, the files with the profile feedback can fail
2709 to match the source file and GCC can not use the profile feedback
2710 information. By default, GCC emits an error message in this case.
2711 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2712 error. GCC does not use appropriate feedback profiles, so using this
2713 option can result in poorly optimized code. This option is useful
2714 only in the case of very minor changes such as bug fixes to an
2719 @node Warning Options
2720 @section Options to Request or Suppress Warnings
2721 @cindex options to control warnings
2722 @cindex warning messages
2723 @cindex messages, warning
2724 @cindex suppressing warnings
2726 Warnings are diagnostic messages that report constructions which
2727 are not inherently erroneous but which are risky or suggest there
2728 may have been an error.
2730 The following language-independent options do not enable specific
2731 warnings but control the kinds of diagnostics produced by GCC.
2734 @cindex syntax checking
2736 @opindex fsyntax-only
2737 Check the code for syntax errors, but don't do anything beyond that.
2741 Inhibit all warning messages.
2746 Make all warnings into errors.
2751 Make the specified warning into an error. The specifier for a warning
2752 is appended, for example @option{-Werror=switch} turns the warnings
2753 controlled by @option{-Wswitch} into errors. This switch takes a
2754 negative form, to be used to negate @option{-Werror} for specific
2755 warnings, for example @option{-Wno-error=switch} makes
2756 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2757 is in effect. You can use the @option{-fdiagnostics-show-option}
2758 option to have each controllable warning amended with the option which
2759 controls it, to determine what to use with this option.
2761 Note that specifying @option{-Werror=}@var{foo} automatically implies
2762 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2765 @item -Wfatal-errors
2766 @opindex Wfatal-errors
2767 @opindex Wno-fatal-errors
2768 This option causes the compiler to abort compilation on the first error
2769 occurred rather than trying to keep going and printing further error
2774 You can request many specific warnings with options beginning
2775 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2776 implicit declarations. Each of these specific warning options also
2777 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2778 example, @option{-Wno-implicit}. This manual lists only one of the
2779 two forms, whichever is not the default. For further,
2780 language-specific options also refer to @ref{C++ Dialect Options} and
2781 @ref{Objective-C and Objective-C++ Dialect Options}.
2786 Issue all the warnings demanded by strict ISO C and ISO C++;
2787 reject all programs that use forbidden extensions, and some other
2788 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2789 version of the ISO C standard specified by any @option{-std} option used.
2791 Valid ISO C and ISO C++ programs should compile properly with or without
2792 this option (though a rare few will require @option{-ansi} or a
2793 @option{-std} option specifying the required version of ISO C)@. However,
2794 without this option, certain GNU extensions and traditional C and C++
2795 features are supported as well. With this option, they are rejected.
2797 @option{-pedantic} does not cause warning messages for use of the
2798 alternate keywords whose names begin and end with @samp{__}. Pedantic
2799 warnings are also disabled in the expression that follows
2800 @code{__extension__}. However, only system header files should use
2801 these escape routes; application programs should avoid them.
2802 @xref{Alternate Keywords}.
2804 Some users try to use @option{-pedantic} to check programs for strict ISO
2805 C conformance. They soon find that it does not do quite what they want:
2806 it finds some non-ISO practices, but not all---only those for which
2807 ISO C @emph{requires} a diagnostic, and some others for which
2808 diagnostics have been added.
2810 A feature to report any failure to conform to ISO C might be useful in
2811 some instances, but would require considerable additional work and would
2812 be quite different from @option{-pedantic}. We don't have plans to
2813 support such a feature in the near future.
2815 Where the standard specified with @option{-std} represents a GNU
2816 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2817 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2818 extended dialect is based. Warnings from @option{-pedantic} are given
2819 where they are required by the base standard. (It would not make sense
2820 for such warnings to be given only for features not in the specified GNU
2821 C dialect, since by definition the GNU dialects of C include all
2822 features the compiler supports with the given option, and there would be
2823 nothing to warn about.)
2825 @item -pedantic-errors
2826 @opindex pedantic-errors
2827 Like @option{-pedantic}, except that errors are produced rather than
2833 This enables all the warnings about constructions that some users
2834 consider questionable, and that are easy to avoid (or modify to
2835 prevent the warning), even in conjunction with macros. This also
2836 enables some language-specific warnings described in @ref{C++ Dialect
2837 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2839 @option{-Wall} turns on the following warning flags:
2841 @gccoptlist{-Waddress @gol
2842 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2844 -Wchar-subscripts @gol
2845 -Wenum-compare @r{(in C/Objc; this is on by default in C++)} @gol
2847 -Wimplicit-function-declaration @gol
2850 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2851 -Wmissing-braces @gol
2857 -Wsequence-point @gol
2858 -Wsign-compare @r{(only in C++)} @gol
2859 -Wstrict-aliasing @gol
2860 -Wstrict-overflow=1 @gol
2863 -Wuninitialized @gol
2864 -Wunknown-pragmas @gol
2865 -Wunused-function @gol
2868 -Wunused-variable @gol
2869 -Wvolatile-register-var @gol
2872 Note that some warning flags are not implied by @option{-Wall}. Some of
2873 them warn about constructions that users generally do not consider
2874 questionable, but which occasionally you might wish to check for;
2875 others warn about constructions that are necessary or hard to avoid in
2876 some cases, and there is no simple way to modify the code to suppress
2877 the warning. Some of them are enabled by @option{-Wextra} but many of
2878 them must be enabled individually.
2884 This enables some extra warning flags that are not enabled by
2885 @option{-Wall}. (This option used to be called @option{-W}. The older
2886 name is still supported, but the newer name is more descriptive.)
2888 @gccoptlist{-Wclobbered @gol
2890 -Wignored-qualifiers @gol
2891 -Wmissing-field-initializers @gol
2892 -Wmissing-parameter-type @r{(C only)} @gol
2893 -Wold-style-declaration @r{(C only)} @gol
2894 -Woverride-init @gol
2897 -Wuninitialized @gol
2898 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2901 The option @option{-Wextra} also prints warning messages for the
2907 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2908 @samp{>}, or @samp{>=}.
2911 (C++ only) An enumerator and a non-enumerator both appear in a
2912 conditional expression.
2915 (C++ only) Ambiguous virtual bases.
2918 (C++ only) Subscripting an array which has been declared @samp{register}.
2921 (C++ only) Taking the address of a variable which has been declared
2925 (C++ only) A base class is not initialized in a derived class' copy
2930 @item -Wchar-subscripts
2931 @opindex Wchar-subscripts
2932 @opindex Wno-char-subscripts
2933 Warn if an array subscript has type @code{char}. This is a common cause
2934 of error, as programmers often forget that this type is signed on some
2936 This warning is enabled by @option{-Wall}.
2940 @opindex Wno-comment
2941 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2942 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2943 This warning is enabled by @option{-Wall}.
2948 @opindex ffreestanding
2949 @opindex fno-builtin
2950 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2951 the arguments supplied have types appropriate to the format string
2952 specified, and that the conversions specified in the format string make
2953 sense. This includes standard functions, and others specified by format
2954 attributes (@pxref{Function Attributes}), in the @code{printf},
2955 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2956 not in the C standard) families (or other target-specific families).
2957 Which functions are checked without format attributes having been
2958 specified depends on the standard version selected, and such checks of
2959 functions without the attribute specified are disabled by
2960 @option{-ffreestanding} or @option{-fno-builtin}.
2962 The formats are checked against the format features supported by GNU
2963 libc version 2.2. These include all ISO C90 and C99 features, as well
2964 as features from the Single Unix Specification and some BSD and GNU
2965 extensions. Other library implementations may not support all these
2966 features; GCC does not support warning about features that go beyond a
2967 particular library's limitations. However, if @option{-pedantic} is used
2968 with @option{-Wformat}, warnings will be given about format features not
2969 in the selected standard version (but not for @code{strfmon} formats,
2970 since those are not in any version of the C standard). @xref{C Dialect
2971 Options,,Options Controlling C Dialect}.
2973 Since @option{-Wformat} also checks for null format arguments for
2974 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2976 @option{-Wformat} is included in @option{-Wall}. For more control over some
2977 aspects of format checking, the options @option{-Wformat-y2k},
2978 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2979 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2980 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2983 @opindex Wformat-y2k
2984 @opindex Wno-format-y2k
2985 If @option{-Wformat} is specified, also warn about @code{strftime}
2986 formats which may yield only a two-digit year.
2988 @item -Wno-format-contains-nul
2989 @opindex Wno-format-contains-nul
2990 @opindex Wformat-contains-nul
2991 If @option{-Wformat} is specified, do not warn about format strings that
2994 @item -Wno-format-extra-args
2995 @opindex Wno-format-extra-args
2996 @opindex Wformat-extra-args
2997 If @option{-Wformat} is specified, do not warn about excess arguments to a
2998 @code{printf} or @code{scanf} format function. The C standard specifies
2999 that such arguments are ignored.
3001 Where the unused arguments lie between used arguments that are
3002 specified with @samp{$} operand number specifications, normally
3003 warnings are still given, since the implementation could not know what
3004 type to pass to @code{va_arg} to skip the unused arguments. However,
3005 in the case of @code{scanf} formats, this option will suppress the
3006 warning if the unused arguments are all pointers, since the Single
3007 Unix Specification says that such unused arguments are allowed.
3009 @item -Wno-format-zero-length @r{(C and Objective-C only)}
3010 @opindex Wno-format-zero-length
3011 @opindex Wformat-zero-length
3012 If @option{-Wformat} is specified, do not warn about zero-length formats.
3013 The C standard specifies that zero-length formats are allowed.
3015 @item -Wformat-nonliteral
3016 @opindex Wformat-nonliteral
3017 @opindex Wno-format-nonliteral
3018 If @option{-Wformat} is specified, also warn if the format string is not a
3019 string literal and so cannot be checked, unless the format function
3020 takes its format arguments as a @code{va_list}.
3022 @item -Wformat-security
3023 @opindex Wformat-security
3024 @opindex Wno-format-security
3025 If @option{-Wformat} is specified, also warn about uses of format
3026 functions that represent possible security problems. At present, this
3027 warns about calls to @code{printf} and @code{scanf} functions where the
3028 format string is not a string literal and there are no format arguments,
3029 as in @code{printf (foo);}. This may be a security hole if the format
3030 string came from untrusted input and contains @samp{%n}. (This is
3031 currently a subset of what @option{-Wformat-nonliteral} warns about, but
3032 in future warnings may be added to @option{-Wformat-security} that are not
3033 included in @option{-Wformat-nonliteral}.)
3037 @opindex Wno-format=2
3038 Enable @option{-Wformat} plus format checks not included in
3039 @option{-Wformat}. Currently equivalent to @samp{-Wformat
3040 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
3042 @item -Wnonnull @r{(C and Objective-C only)}
3044 @opindex Wno-nonnull
3045 Warn about passing a null pointer for arguments marked as
3046 requiring a non-null value by the @code{nonnull} function attribute.
3048 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
3049 can be disabled with the @option{-Wno-nonnull} option.
3051 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
3053 @opindex Wno-init-self
3054 Warn about uninitialized variables which are initialized with themselves.
3055 Note this option can only be used with the @option{-Wuninitialized} option.
3057 For example, GCC will warn about @code{i} being uninitialized in the
3058 following snippet only when @option{-Winit-self} has been specified:
3069 @item -Wimplicit-int @r{(C and Objective-C only)}
3070 @opindex Wimplicit-int
3071 @opindex Wno-implicit-int
3072 Warn when a declaration does not specify a type.
3073 This warning is enabled by @option{-Wall}.
3075 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
3076 @opindex Wimplicit-function-declaration
3077 @opindex Wno-implicit-function-declaration
3078 Give a warning whenever a function is used before being declared. In
3079 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
3080 enabled by default and it is made into an error by
3081 @option{-pedantic-errors}. This warning is also enabled by
3086 @opindex Wno-implicit
3087 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
3088 This warning is enabled by @option{-Wall}.
3090 @item -Wignored-qualifiers @r{(C and C++ only)}
3091 @opindex Wignored-qualifiers
3092 @opindex Wno-ignored-qualifiers
3093 Warn if the return type of a function has a type qualifier
3094 such as @code{const}. For ISO C such a type qualifier has no effect,
3095 since the value returned by a function is not an lvalue.
3096 For C++, the warning is only emitted for scalar types or @code{void}.
3097 ISO C prohibits qualified @code{void} return types on function
3098 definitions, so such return types always receive a warning
3099 even without this option.
3101 This warning is also enabled by @option{-Wextra}.
3106 Warn if the type of @samp{main} is suspicious. @samp{main} should be
3107 a function with external linkage, returning int, taking either zero
3108 arguments, two, or three arguments of appropriate types. This warning
3109 is enabled by default in C++ and is enabled by either @option{-Wall}
3110 or @option{-pedantic}.
3112 @item -Wmissing-braces
3113 @opindex Wmissing-braces
3114 @opindex Wno-missing-braces
3115 Warn if an aggregate or union initializer is not fully bracketed. In
3116 the following example, the initializer for @samp{a} is not fully
3117 bracketed, but that for @samp{b} is fully bracketed.
3120 int a[2][2] = @{ 0, 1, 2, 3 @};
3121 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
3124 This warning is enabled by @option{-Wall}.
3126 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
3127 @opindex Wmissing-include-dirs
3128 @opindex Wno-missing-include-dirs
3129 Warn if a user-supplied include directory does not exist.
3132 @opindex Wparentheses
3133 @opindex Wno-parentheses
3134 Warn if parentheses are omitted in certain contexts, such
3135 as when there is an assignment in a context where a truth value
3136 is expected, or when operators are nested whose precedence people
3137 often get confused about.
3139 Also warn if a comparison like @samp{x<=y<=z} appears; this is
3140 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
3141 interpretation from that of ordinary mathematical notation.
3143 Also warn about constructions where there may be confusion to which
3144 @code{if} statement an @code{else} branch belongs. Here is an example of
3159 In C/C++, every @code{else} branch belongs to the innermost possible
3160 @code{if} statement, which in this example is @code{if (b)}. This is
3161 often not what the programmer expected, as illustrated in the above
3162 example by indentation the programmer chose. When there is the
3163 potential for this confusion, GCC will issue a warning when this flag
3164 is specified. To eliminate the warning, add explicit braces around
3165 the innermost @code{if} statement so there is no way the @code{else}
3166 could belong to the enclosing @code{if}. The resulting code would
3183 This warning is enabled by @option{-Wall}.
3185 @item -Wsequence-point
3186 @opindex Wsequence-point
3187 @opindex Wno-sequence-point
3188 Warn about code that may have undefined semantics because of violations
3189 of sequence point rules in the C and C++ standards.
3191 The C and C++ standards defines the order in which expressions in a C/C++
3192 program are evaluated in terms of @dfn{sequence points}, which represent
3193 a partial ordering between the execution of parts of the program: those
3194 executed before the sequence point, and those executed after it. These
3195 occur after the evaluation of a full expression (one which is not part
3196 of a larger expression), after the evaluation of the first operand of a
3197 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3198 function is called (but after the evaluation of its arguments and the
3199 expression denoting the called function), and in certain other places.
3200 Other than as expressed by the sequence point rules, the order of
3201 evaluation of subexpressions of an expression is not specified. All
3202 these rules describe only a partial order rather than a total order,
3203 since, for example, if two functions are called within one expression
3204 with no sequence point between them, the order in which the functions
3205 are called is not specified. However, the standards committee have
3206 ruled that function calls do not overlap.
3208 It is not specified when between sequence points modifications to the
3209 values of objects take effect. Programs whose behavior depends on this
3210 have undefined behavior; the C and C++ standards specify that ``Between
3211 the previous and next sequence point an object shall have its stored
3212 value modified at most once by the evaluation of an expression.
3213 Furthermore, the prior value shall be read only to determine the value
3214 to be stored.''. If a program breaks these rules, the results on any
3215 particular implementation are entirely unpredictable.
3217 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3218 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3219 diagnosed by this option, and it may give an occasional false positive
3220 result, but in general it has been found fairly effective at detecting
3221 this sort of problem in programs.
3223 The standard is worded confusingly, therefore there is some debate
3224 over the precise meaning of the sequence point rules in subtle cases.
3225 Links to discussions of the problem, including proposed formal
3226 definitions, may be found on the GCC readings page, at
3227 @w{@uref{http://gcc.gnu.org/readings.html}}.
3229 This warning is enabled by @option{-Wall} for C and C++.
3232 @opindex Wreturn-type
3233 @opindex Wno-return-type
3234 Warn whenever a function is defined with a return-type that defaults
3235 to @code{int}. Also warn about any @code{return} statement with no
3236 return-value in a function whose return-type is not @code{void}
3237 (falling off the end of the function body is considered returning
3238 without a value), and about a @code{return} statement with an
3239 expression in a function whose return-type is @code{void}.
3241 For C++, a function without return type always produces a diagnostic
3242 message, even when @option{-Wno-return-type} is specified. The only
3243 exceptions are @samp{main} and functions defined in system headers.
3245 This warning is enabled by @option{-Wall}.
3250 Warn whenever a @code{switch} statement has an index of enumerated type
3251 and lacks a @code{case} for one or more of the named codes of that
3252 enumeration. (The presence of a @code{default} label prevents this
3253 warning.) @code{case} labels outside the enumeration range also
3254 provoke warnings when this option is used (even if there is a
3255 @code{default} label).
3256 This warning is enabled by @option{-Wall}.
3258 @item -Wswitch-default
3259 @opindex Wswitch-default
3260 @opindex Wno-switch-default
3261 Warn whenever a @code{switch} statement does not have a @code{default}
3265 @opindex Wswitch-enum
3266 @opindex Wno-switch-enum
3267 Warn whenever a @code{switch} statement has an index of enumerated type
3268 and lacks a @code{case} for one or more of the named codes of that
3269 enumeration. @code{case} labels outside the enumeration range also
3270 provoke warnings when this option is used. The only difference
3271 between @option{-Wswitch} and this option is that this option gives a
3272 warning about an omitted enumeration code even if there is a
3273 @code{default} label.
3275 @item -Wsync-nand @r{(C and C++ only)}
3277 @opindex Wno-sync-nand
3278 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
3279 built-in functions are used. These functions changed semantics in GCC 4.4.
3283 @opindex Wno-trigraphs
3284 Warn if any trigraphs are encountered that might change the meaning of
3285 the program (trigraphs within comments are not warned about).
3286 This warning is enabled by @option{-Wall}.
3288 @item -Wunused-function
3289 @opindex Wunused-function
3290 @opindex Wno-unused-function
3291 Warn whenever a static function is declared but not defined or a
3292 non-inline static function is unused.
3293 This warning is enabled by @option{-Wall}.
3295 @item -Wunused-label
3296 @opindex Wunused-label
3297 @opindex Wno-unused-label
3298 Warn whenever a label is declared but not used.
3299 This warning is enabled by @option{-Wall}.
3301 To suppress this warning use the @samp{unused} attribute
3302 (@pxref{Variable Attributes}).
3304 @item -Wunused-parameter
3305 @opindex Wunused-parameter
3306 @opindex Wno-unused-parameter
3307 Warn whenever a function parameter is unused aside from its declaration.
3309 To suppress this warning use the @samp{unused} attribute
3310 (@pxref{Variable Attributes}).
3312 @item -Wno-unused-result
3313 @opindex Wunused-result
3314 @opindex Wno-unused-result
3315 Do not warn if a caller of a function marked with attribute
3316 @code{warn_unused_result} (@pxref{Variable Attributes}) does not use
3317 its return value. The default is @option{-Wunused-result}.
3319 @item -Wunused-variable
3320 @opindex Wunused-variable
3321 @opindex Wno-unused-variable
3322 Warn whenever a local variable or non-constant static variable is unused
3323 aside from its declaration.
3324 This warning is enabled by @option{-Wall}.
3326 To suppress this warning use the @samp{unused} attribute
3327 (@pxref{Variable Attributes}).
3329 @item -Wunused-value
3330 @opindex Wunused-value
3331 @opindex Wno-unused-value
3332 Warn whenever a statement computes a result that is explicitly not
3333 used. To suppress this warning cast the unused expression to
3334 @samp{void}. This includes an expression-statement or the left-hand
3335 side of a comma expression that contains no side effects. For example,
3336 an expression such as @samp{x[i,j]} will cause a warning, while
3337 @samp{x[(void)i,j]} will not.
3339 This warning is enabled by @option{-Wall}.
3344 All the above @option{-Wunused} options combined.
3346 In order to get a warning about an unused function parameter, you must
3347 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3348 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3350 @item -Wuninitialized
3351 @opindex Wuninitialized
3352 @opindex Wno-uninitialized
3353 Warn if an automatic variable is used without first being initialized
3354 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3355 warn if a non-static reference or non-static @samp{const} member
3356 appears in a class without constructors.
3358 If you want to warn about code which uses the uninitialized value of the
3359 variable in its own initializer, use the @option{-Winit-self} option.
3361 These warnings occur for individual uninitialized or clobbered
3362 elements of structure, union or array variables as well as for
3363 variables which are uninitialized or clobbered as a whole. They do
3364 not occur for variables or elements declared @code{volatile}. Because
3365 these warnings depend on optimization, the exact variables or elements
3366 for which there are warnings will depend on the precise optimization
3367 options and version of GCC used.
3369 Note that there may be no warning about a variable that is used only
3370 to compute a value that itself is never used, because such
3371 computations may be deleted by data flow analysis before the warnings
3374 These warnings are made optional because GCC is not smart
3375 enough to see all the reasons why the code might be correct
3376 despite appearing to have an error. Here is one example of how
3397 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3398 always initialized, but GCC doesn't know this. Here is
3399 another common case:
3404 if (change_y) save_y = y, y = new_y;
3406 if (change_y) y = save_y;
3411 This has no bug because @code{save_y} is used only if it is set.
3413 @cindex @code{longjmp} warnings
3414 This option also warns when a non-volatile automatic variable might be
3415 changed by a call to @code{longjmp}. These warnings as well are possible
3416 only in optimizing compilation.
3418 The compiler sees only the calls to @code{setjmp}. It cannot know
3419 where @code{longjmp} will be called; in fact, a signal handler could
3420 call it at any point in the code. As a result, you may get a warning
3421 even when there is in fact no problem because @code{longjmp} cannot
3422 in fact be called at the place which would cause a problem.
3424 Some spurious warnings can be avoided if you declare all the functions
3425 you use that never return as @code{noreturn}. @xref{Function
3428 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3430 @item -Wunknown-pragmas
3431 @opindex Wunknown-pragmas
3432 @opindex Wno-unknown-pragmas
3433 @cindex warning for unknown pragmas
3434 @cindex unknown pragmas, warning
3435 @cindex pragmas, warning of unknown
3436 Warn when a #pragma directive is encountered which is not understood by
3437 GCC@. If this command line option is used, warnings will even be issued
3438 for unknown pragmas in system header files. This is not the case if
3439 the warnings were only enabled by the @option{-Wall} command line option.
3442 @opindex Wno-pragmas
3444 Do not warn about misuses of pragmas, such as incorrect parameters,
3445 invalid syntax, or conflicts between pragmas. See also
3446 @samp{-Wunknown-pragmas}.
3448 @item -Wstrict-aliasing
3449 @opindex Wstrict-aliasing
3450 @opindex Wno-strict-aliasing
3451 This option is only active when @option{-fstrict-aliasing} is active.
3452 It warns about code which might break the strict aliasing rules that the
3453 compiler is using for optimization. The warning does not catch all
3454 cases, but does attempt to catch the more common pitfalls. It is
3455 included in @option{-Wall}.
3456 It is equivalent to @option{-Wstrict-aliasing=3}
3458 @item -Wstrict-aliasing=n
3459 @opindex Wstrict-aliasing=n
3460 @opindex Wno-strict-aliasing=n
3461 This option is only active when @option{-fstrict-aliasing} is active.
3462 It warns about code which might break the strict aliasing rules that the
3463 compiler is using for optimization.
3464 Higher levels correspond to higher accuracy (fewer false positives).
3465 Higher levels also correspond to more effort, similar to the way -O works.
3466 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3469 Level 1: Most aggressive, quick, least accurate.
3470 Possibly useful when higher levels
3471 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3472 false negatives. However, it has many false positives.
3473 Warns for all pointer conversions between possibly incompatible types,
3474 even if never dereferenced. Runs in the frontend only.
3476 Level 2: Aggressive, quick, not too precise.
3477 May still have many false positives (not as many as level 1 though),
3478 and few false negatives (but possibly more than level 1).
3479 Unlike level 1, it only warns when an address is taken. Warns about
3480 incomplete types. Runs in the frontend only.
3482 Level 3 (default for @option{-Wstrict-aliasing}):
3483 Should have very few false positives and few false
3484 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3485 Takes care of the common punn+dereference pattern in the frontend:
3486 @code{*(int*)&some_float}.
3487 If optimization is enabled, it also runs in the backend, where it deals
3488 with multiple statement cases using flow-sensitive points-to information.
3489 Only warns when the converted pointer is dereferenced.
3490 Does not warn about incomplete types.
3492 @item -Wstrict-overflow
3493 @itemx -Wstrict-overflow=@var{n}
3494 @opindex Wstrict-overflow
3495 @opindex Wno-strict-overflow
3496 This option is only active when @option{-fstrict-overflow} is active.
3497 It warns about cases where the compiler optimizes based on the
3498 assumption that signed overflow does not occur. Note that it does not
3499 warn about all cases where the code might overflow: it only warns
3500 about cases where the compiler implements some optimization. Thus
3501 this warning depends on the optimization level.
3503 An optimization which assumes that signed overflow does not occur is
3504 perfectly safe if the values of the variables involved are such that
3505 overflow never does, in fact, occur. Therefore this warning can
3506 easily give a false positive: a warning about code which is not
3507 actually a problem. To help focus on important issues, several
3508 warning levels are defined. No warnings are issued for the use of
3509 undefined signed overflow when estimating how many iterations a loop
3510 will require, in particular when determining whether a loop will be
3514 @item -Wstrict-overflow=1
3515 Warn about cases which are both questionable and easy to avoid. For
3516 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3517 compiler will simplify this to @code{1}. This level of
3518 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3519 are not, and must be explicitly requested.
3521 @item -Wstrict-overflow=2
3522 Also warn about other cases where a comparison is simplified to a
3523 constant. For example: @code{abs (x) >= 0}. This can only be
3524 simplified when @option{-fstrict-overflow} is in effect, because
3525 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3526 zero. @option{-Wstrict-overflow} (with no level) is the same as
3527 @option{-Wstrict-overflow=2}.
3529 @item -Wstrict-overflow=3
3530 Also warn about other cases where a comparison is simplified. For
3531 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3533 @item -Wstrict-overflow=4
3534 Also warn about other simplifications not covered by the above cases.
3535 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3537 @item -Wstrict-overflow=5
3538 Also warn about cases where the compiler reduces the magnitude of a
3539 constant involved in a comparison. For example: @code{x + 2 > y} will
3540 be simplified to @code{x + 1 >= y}. This is reported only at the
3541 highest warning level because this simplification applies to many
3542 comparisons, so this warning level will give a very large number of
3546 @item -Warray-bounds
3547 @opindex Wno-array-bounds
3548 @opindex Warray-bounds
3549 This option is only active when @option{-ftree-vrp} is active
3550 (default for -O2 and above). It warns about subscripts to arrays
3551 that are always out of bounds. This warning is enabled by @option{-Wall}.
3553 @item -Wno-div-by-zero
3554 @opindex Wno-div-by-zero
3555 @opindex Wdiv-by-zero
3556 Do not warn about compile-time integer division by zero. Floating point
3557 division by zero is not warned about, as it can be a legitimate way of
3558 obtaining infinities and NaNs.
3560 @item -Wsystem-headers
3561 @opindex Wsystem-headers
3562 @opindex Wno-system-headers
3563 @cindex warnings from system headers
3564 @cindex system headers, warnings from
3565 Print warning messages for constructs found in system header files.
3566 Warnings from system headers are normally suppressed, on the assumption
3567 that they usually do not indicate real problems and would only make the
3568 compiler output harder to read. Using this command line option tells
3569 GCC to emit warnings from system headers as if they occurred in user
3570 code. However, note that using @option{-Wall} in conjunction with this
3571 option will @emph{not} warn about unknown pragmas in system
3572 headers---for that, @option{-Wunknown-pragmas} must also be used.
3575 @opindex Wfloat-equal
3576 @opindex Wno-float-equal
3577 Warn if floating point values are used in equality comparisons.
3579 The idea behind this is that sometimes it is convenient (for the
3580 programmer) to consider floating-point values as approximations to
3581 infinitely precise real numbers. If you are doing this, then you need
3582 to compute (by analyzing the code, or in some other way) the maximum or
3583 likely maximum error that the computation introduces, and allow for it
3584 when performing comparisons (and when producing output, but that's a
3585 different problem). In particular, instead of testing for equality, you
3586 would check to see whether the two values have ranges that overlap; and
3587 this is done with the relational operators, so equality comparisons are
3590 @item -Wtraditional @r{(C and Objective-C only)}
3591 @opindex Wtraditional
3592 @opindex Wno-traditional
3593 Warn about certain constructs that behave differently in traditional and
3594 ISO C@. Also warn about ISO C constructs that have no traditional C
3595 equivalent, and/or problematic constructs which should be avoided.
3599 Macro parameters that appear within string literals in the macro body.
3600 In traditional C macro replacement takes place within string literals,
3601 but does not in ISO C@.
3604 In traditional C, some preprocessor directives did not exist.
3605 Traditional preprocessors would only consider a line to be a directive
3606 if the @samp{#} appeared in column 1 on the line. Therefore
3607 @option{-Wtraditional} warns about directives that traditional C
3608 understands but would ignore because the @samp{#} does not appear as the
3609 first character on the line. It also suggests you hide directives like
3610 @samp{#pragma} not understood by traditional C by indenting them. Some
3611 traditional implementations would not recognize @samp{#elif}, so it
3612 suggests avoiding it altogether.
3615 A function-like macro that appears without arguments.
3618 The unary plus operator.
3621 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3622 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3623 constants.) Note, these suffixes appear in macros defined in the system
3624 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3625 Use of these macros in user code might normally lead to spurious
3626 warnings, however GCC's integrated preprocessor has enough context to
3627 avoid warning in these cases.
3630 A function declared external in one block and then used after the end of
3634 A @code{switch} statement has an operand of type @code{long}.
3637 A non-@code{static} function declaration follows a @code{static} one.
3638 This construct is not accepted by some traditional C compilers.
3641 The ISO type of an integer constant has a different width or
3642 signedness from its traditional type. This warning is only issued if
3643 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3644 typically represent bit patterns, are not warned about.
3647 Usage of ISO string concatenation is detected.
3650 Initialization of automatic aggregates.
3653 Identifier conflicts with labels. Traditional C lacks a separate
3654 namespace for labels.
3657 Initialization of unions. If the initializer is zero, the warning is
3658 omitted. This is done under the assumption that the zero initializer in
3659 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3660 initializer warnings and relies on default initialization to zero in the
3664 Conversions by prototypes between fixed/floating point values and vice
3665 versa. The absence of these prototypes when compiling with traditional
3666 C would cause serious problems. This is a subset of the possible
3667 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3670 Use of ISO C style function definitions. This warning intentionally is
3671 @emph{not} issued for prototype declarations or variadic functions
3672 because these ISO C features will appear in your code when using
3673 libiberty's traditional C compatibility macros, @code{PARAMS} and
3674 @code{VPARAMS}. This warning is also bypassed for nested functions
3675 because that feature is already a GCC extension and thus not relevant to
3676 traditional C compatibility.
3679 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3680 @opindex Wtraditional-conversion
3681 @opindex Wno-traditional-conversion
3682 Warn if a prototype causes a type conversion that is different from what
3683 would happen to the same argument in the absence of a prototype. This
3684 includes conversions of fixed point to floating and vice versa, and
3685 conversions changing the width or signedness of a fixed point argument
3686 except when the same as the default promotion.
3688 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3689 @opindex Wdeclaration-after-statement
3690 @opindex Wno-declaration-after-statement
3691 Warn when a declaration is found after a statement in a block. This
3692 construct, known from C++, was introduced with ISO C99 and is by default
3693 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3694 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3699 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3701 @item -Wno-endif-labels
3702 @opindex Wno-endif-labels
3703 @opindex Wendif-labels
3704 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3709 Warn whenever a local variable shadows another local variable, parameter or
3710 global variable or whenever a built-in function is shadowed.
3712 @item -Wlarger-than=@var{len}
3713 @opindex Wlarger-than=@var{len}
3714 @opindex Wlarger-than-@var{len}
3715 Warn whenever an object of larger than @var{len} bytes is defined.
3717 @item -Wframe-larger-than=@var{len}
3718 @opindex Wframe-larger-than
3719 Warn if the size of a function frame is larger than @var{len} bytes.
3720 The computation done to determine the stack frame size is approximate
3721 and not conservative.
3722 The actual requirements may be somewhat greater than @var{len}
3723 even if you do not get a warning. In addition, any space allocated
3724 via @code{alloca}, variable-length arrays, or related constructs
3725 is not included by the compiler when determining
3726 whether or not to issue a warning.
3728 @item -Wunsafe-loop-optimizations
3729 @opindex Wunsafe-loop-optimizations
3730 @opindex Wno-unsafe-loop-optimizations
3731 Warn if the loop cannot be optimized because the compiler could not
3732 assume anything on the bounds of the loop indices. With
3733 @option{-funsafe-loop-optimizations} warn if the compiler made
3736 @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
3737 @opindex Wno-pedantic-ms-format
3738 @opindex Wpedantic-ms-format
3739 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3740 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3741 depending on the MS runtime, when you are using the options @option{-Wformat}
3742 and @option{-pedantic} without gnu-extensions.
3744 @item -Wpointer-arith
3745 @opindex Wpointer-arith
3746 @opindex Wno-pointer-arith
3747 Warn about anything that depends on the ``size of'' a function type or
3748 of @code{void}. GNU C assigns these types a size of 1, for
3749 convenience in calculations with @code{void *} pointers and pointers
3750 to functions. In C++, warn also when an arithmetic operation involves
3751 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3754 @opindex Wtype-limits
3755 @opindex Wno-type-limits
3756 Warn if a comparison is always true or always false due to the limited
3757 range of the data type, but do not warn for constant expressions. For
3758 example, warn if an unsigned variable is compared against zero with
3759 @samp{<} or @samp{>=}. This warning is also enabled by
3762 @item -Wbad-function-cast @r{(C and Objective-C only)}
3763 @opindex Wbad-function-cast
3764 @opindex Wno-bad-function-cast
3765 Warn whenever a function call is cast to a non-matching type.
3766 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3768 @item -Wc++-compat @r{(C and Objective-C only)}
3769 Warn about ISO C constructs that are outside of the common subset of
3770 ISO C and ISO C++, e.g.@: request for implicit conversion from
3771 @code{void *} to a pointer to non-@code{void} type.
3773 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3774 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3775 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3776 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3780 @opindex Wno-cast-qual
3781 Warn whenever a pointer is cast so as to remove a type qualifier from
3782 the target type. For example, warn if a @code{const char *} is cast
3783 to an ordinary @code{char *}.
3785 Also warn when making a cast which introduces a type qualifier in an
3786 unsafe way. For example, casting @code{char **} to @code{const char **}
3787 is unsafe, as in this example:
3790 /* p is char ** value. */
3791 const char **q = (const char **) p;
3792 /* Assignment of readonly string to const char * is OK. */
3794 /* Now char** pointer points to read-only memory. */
3799 @opindex Wcast-align
3800 @opindex Wno-cast-align
3801 Warn whenever a pointer is cast such that the required alignment of the
3802 target is increased. For example, warn if a @code{char *} is cast to
3803 an @code{int *} on machines where integers can only be accessed at
3804 two- or four-byte boundaries.
3806 @item -Wwrite-strings
3807 @opindex Wwrite-strings
3808 @opindex Wno-write-strings
3809 When compiling C, give string constants the type @code{const
3810 char[@var{length}]} so that copying the address of one into a
3811 non-@code{const} @code{char *} pointer will get a warning. These
3812 warnings will help you find at compile time code that can try to write
3813 into a string constant, but only if you have been very careful about
3814 using @code{const} in declarations and prototypes. Otherwise, it will
3815 just be a nuisance. This is why we did not make @option{-Wall} request
3818 When compiling C++, warn about the deprecated conversion from string
3819 literals to @code{char *}. This warning is enabled by default for C++
3824 @opindex Wno-clobbered
3825 Warn for variables that might be changed by @samp{longjmp} or
3826 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3829 @opindex Wconversion
3830 @opindex Wno-conversion
3831 Warn for implicit conversions that may alter a value. This includes
3832 conversions between real and integer, like @code{abs (x)} when
3833 @code{x} is @code{double}; conversions between signed and unsigned,
3834 like @code{unsigned ui = -1}; and conversions to smaller types, like
3835 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3836 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3837 changed by the conversion like in @code{abs (2.0)}. Warnings about
3838 conversions between signed and unsigned integers can be disabled by
3839 using @option{-Wno-sign-conversion}.
3841 For C++, also warn for conversions between @code{NULL} and non-pointer
3842 types; confusing overload resolution for user-defined conversions; and
3843 conversions that will never use a type conversion operator:
3844 conversions to @code{void}, the same type, a base class or a reference
3845 to them. Warnings about conversions between signed and unsigned
3846 integers are disabled by default in C++ unless
3847 @option{-Wsign-conversion} is explicitly enabled.
3850 @opindex Wempty-body
3851 @opindex Wno-empty-body
3852 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3853 while} statement. This warning is also enabled by @option{-Wextra}.
3855 @item -Wenum-compare
3856 @opindex Wenum-compare
3857 @opindex Wno-enum-compare
3858 Warn about a comparison between values of different enum types. In C++
3859 this warning is enabled by default. In C this warning is enabled by
3862 @item -Wjump-misses-init @r{(C, Objective-C only)}
3863 @opindex Wjump-misses-init
3864 @opindex Wno-jump-misses-init
3865 Warn if a @code{goto} statement or a @code{switch} statement jumps
3866 forward across the initialization of a variable, or jumps backward to a
3867 label after the variable has been initialized. This only warns about
3868 variables which are initialized when they are declared. This warning is
3869 only supported for C and Objective C; in C++ this sort of branch is an
3872 @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
3873 can be disabled with the @option{-Wno-jump-misses-init} option.
3875 @item -Wsign-compare
3876 @opindex Wsign-compare
3877 @opindex Wno-sign-compare
3878 @cindex warning for comparison of signed and unsigned values
3879 @cindex comparison of signed and unsigned values, warning
3880 @cindex signed and unsigned values, comparison warning
3881 Warn when a comparison between signed and unsigned values could produce
3882 an incorrect result when the signed value is converted to unsigned.
3883 This warning is also enabled by @option{-Wextra}; to get the other warnings
3884 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3886 @item -Wsign-conversion
3887 @opindex Wsign-conversion
3888 @opindex Wno-sign-conversion
3889 Warn for implicit conversions that may change the sign of an integer
3890 value, like assigning a signed integer expression to an unsigned
3891 integer variable. An explicit cast silences the warning. In C, this
3892 option is enabled also by @option{-Wconversion}.
3896 @opindex Wno-address
3897 Warn about suspicious uses of memory addresses. These include using
3898 the address of a function in a conditional expression, such as
3899 @code{void func(void); if (func)}, and comparisons against the memory
3900 address of a string literal, such as @code{if (x == "abc")}. Such
3901 uses typically indicate a programmer error: the address of a function
3902 always evaluates to true, so their use in a conditional usually
3903 indicate that the programmer forgot the parentheses in a function
3904 call; and comparisons against string literals result in unspecified
3905 behavior and are not portable in C, so they usually indicate that the
3906 programmer intended to use @code{strcmp}. This warning is enabled by
3910 @opindex Wlogical-op
3911 @opindex Wno-logical-op
3912 Warn about suspicious uses of logical operators in expressions.
3913 This includes using logical operators in contexts where a
3914 bit-wise operator is likely to be expected.
3916 @item -Waggregate-return
3917 @opindex Waggregate-return
3918 @opindex Wno-aggregate-return
3919 Warn if any functions that return structures or unions are defined or
3920 called. (In languages where you can return an array, this also elicits
3923 @item -Wno-attributes
3924 @opindex Wno-attributes
3925 @opindex Wattributes
3926 Do not warn if an unexpected @code{__attribute__} is used, such as
3927 unrecognized attributes, function attributes applied to variables,
3928 etc. This will not stop errors for incorrect use of supported
3931 @item -Wno-builtin-macro-redefined
3932 @opindex Wno-builtin-macro-redefined
3933 @opindex Wbuiltin-macro-redefined
3934 Do not warn if certain built-in macros are redefined. This suppresses
3935 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
3936 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
3938 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3939 @opindex Wstrict-prototypes
3940 @opindex Wno-strict-prototypes
3941 Warn if a function is declared or defined without specifying the
3942 argument types. (An old-style function definition is permitted without
3943 a warning if preceded by a declaration which specifies the argument
3946 @item -Wold-style-declaration @r{(C and Objective-C only)}
3947 @opindex Wold-style-declaration
3948 @opindex Wno-old-style-declaration
3949 Warn for obsolescent usages, according to the C Standard, in a
3950 declaration. For example, warn if storage-class specifiers like
3951 @code{static} are not the first things in a declaration. This warning
3952 is also enabled by @option{-Wextra}.
3954 @item -Wold-style-definition @r{(C and Objective-C only)}
3955 @opindex Wold-style-definition
3956 @opindex Wno-old-style-definition
3957 Warn if an old-style function definition is used. A warning is given
3958 even if there is a previous prototype.
3960 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3961 @opindex Wmissing-parameter-type
3962 @opindex Wno-missing-parameter-type
3963 A function parameter is declared without a type specifier in K&R-style
3970 This warning is also enabled by @option{-Wextra}.
3972 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3973 @opindex Wmissing-prototypes
3974 @opindex Wno-missing-prototypes
3975 Warn if a global function is defined without a previous prototype
3976 declaration. This warning is issued even if the definition itself
3977 provides a prototype. The aim is to detect global functions that fail
3978 to be declared in header files.
3980 @item -Wmissing-declarations
3981 @opindex Wmissing-declarations
3982 @opindex Wno-missing-declarations
3983 Warn if a global function is defined without a previous declaration.
3984 Do so even if the definition itself provides a prototype.
3985 Use this option to detect global functions that are not declared in
3986 header files. In C++, no warnings are issued for function templates,
3987 or for inline functions, or for functions in anonymous namespaces.
3989 @item -Wmissing-field-initializers
3990 @opindex Wmissing-field-initializers
3991 @opindex Wno-missing-field-initializers
3995 Warn if a structure's initializer has some fields missing. For
3996 example, the following code would cause such a warning, because
3997 @code{x.h} is implicitly zero:
4000 struct s @{ int f, g, h; @};
4001 struct s x = @{ 3, 4 @};
4004 This option does not warn about designated initializers, so the following
4005 modification would not trigger a warning:
4008 struct s @{ int f, g, h; @};
4009 struct s x = @{ .f = 3, .g = 4 @};
4012 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
4013 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
4015 @item -Wmissing-noreturn
4016 @opindex Wmissing-noreturn
4017 @opindex Wno-missing-noreturn
4018 Warn about functions which might be candidates for attribute @code{noreturn}.
4019 Note these are only possible candidates, not absolute ones. Care should
4020 be taken to manually verify functions actually do not ever return before
4021 adding the @code{noreturn} attribute, otherwise subtle code generation
4022 bugs could be introduced. You will not get a warning for @code{main} in
4023 hosted C environments.
4025 @item -Wmissing-format-attribute
4026 @opindex Wmissing-format-attribute
4027 @opindex Wno-missing-format-attribute
4030 Warn about function pointers which might be candidates for @code{format}
4031 attributes. Note these are only possible candidates, not absolute ones.
4032 GCC will guess that function pointers with @code{format} attributes that
4033 are used in assignment, initialization, parameter passing or return
4034 statements should have a corresponding @code{format} attribute in the
4035 resulting type. I.e.@: the left-hand side of the assignment or
4036 initialization, the type of the parameter variable, or the return type
4037 of the containing function respectively should also have a @code{format}
4038 attribute to avoid the warning.
4040 GCC will also warn about function definitions which might be
4041 candidates for @code{format} attributes. Again, these are only
4042 possible candidates. GCC will guess that @code{format} attributes
4043 might be appropriate for any function that calls a function like
4044 @code{vprintf} or @code{vscanf}, but this might not always be the
4045 case, and some functions for which @code{format} attributes are
4046 appropriate may not be detected.
4048 @item -Wno-multichar
4049 @opindex Wno-multichar
4051 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
4052 Usually they indicate a typo in the user's code, as they have
4053 implementation-defined values, and should not be used in portable code.
4055 @item -Wnormalized=<none|id|nfc|nfkc>
4056 @opindex Wnormalized=
4059 @cindex character set, input normalization
4060 In ISO C and ISO C++, two identifiers are different if they are
4061 different sequences of characters. However, sometimes when characters
4062 outside the basic ASCII character set are used, you can have two
4063 different character sequences that look the same. To avoid confusion,
4064 the ISO 10646 standard sets out some @dfn{normalization rules} which
4065 when applied ensure that two sequences that look the same are turned into
4066 the same sequence. GCC can warn you if you are using identifiers which
4067 have not been normalized; this option controls that warning.
4069 There are four levels of warning that GCC supports. The default is
4070 @option{-Wnormalized=nfc}, which warns about any identifier which is
4071 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
4072 recommended form for most uses.
4074 Unfortunately, there are some characters which ISO C and ISO C++ allow
4075 in identifiers that when turned into NFC aren't allowable as
4076 identifiers. That is, there's no way to use these symbols in portable
4077 ISO C or C++ and have all your identifiers in NFC@.
4078 @option{-Wnormalized=id} suppresses the warning for these characters.
4079 It is hoped that future versions of the standards involved will correct
4080 this, which is why this option is not the default.
4082 You can switch the warning off for all characters by writing
4083 @option{-Wnormalized=none}. You would only want to do this if you
4084 were using some other normalization scheme (like ``D''), because
4085 otherwise you can easily create bugs that are literally impossible to see.
4087 Some characters in ISO 10646 have distinct meanings but look identical
4088 in some fonts or display methodologies, especially once formatting has
4089 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
4090 LETTER N'', will display just like a regular @code{n} which has been
4091 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
4092 normalization scheme to convert all these into a standard form as
4093 well, and GCC will warn if your code is not in NFKC if you use
4094 @option{-Wnormalized=nfkc}. This warning is comparable to warning
4095 about every identifier that contains the letter O because it might be
4096 confused with the digit 0, and so is not the default, but may be
4097 useful as a local coding convention if the programming environment is
4098 unable to be fixed to display these characters distinctly.
4100 @item -Wno-deprecated
4101 @opindex Wno-deprecated
4102 @opindex Wdeprecated
4103 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
4105 @item -Wno-deprecated-declarations
4106 @opindex Wno-deprecated-declarations
4107 @opindex Wdeprecated-declarations
4108 Do not warn about uses of functions (@pxref{Function Attributes}),
4109 variables (@pxref{Variable Attributes}), and types (@pxref{Type
4110 Attributes}) marked as deprecated by using the @code{deprecated}
4114 @opindex Wno-overflow
4116 Do not warn about compile-time overflow in constant expressions.
4118 @item -Woverride-init @r{(C and Objective-C only)}
4119 @opindex Woverride-init
4120 @opindex Wno-override-init
4124 Warn if an initialized field without side effects is overridden when
4125 using designated initializers (@pxref{Designated Inits, , Designated
4128 This warning is included in @option{-Wextra}. To get other
4129 @option{-Wextra} warnings without this one, use @samp{-Wextra
4130 -Wno-override-init}.
4135 Warn if a structure is given the packed attribute, but the packed
4136 attribute has no effect on the layout or size of the structure.
4137 Such structures may be mis-aligned for little benefit. For
4138 instance, in this code, the variable @code{f.x} in @code{struct bar}
4139 will be misaligned even though @code{struct bar} does not itself
4140 have the packed attribute:
4147 @} __attribute__((packed));
4155 @item -Wpacked-bitfield-compat
4156 @opindex Wpacked-bitfield-compat
4157 @opindex Wno-packed-bitfield-compat
4158 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
4159 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
4160 the change can lead to differences in the structure layout. GCC
4161 informs you when the offset of such a field has changed in GCC 4.4.
4162 For example there is no longer a 4-bit padding between field @code{a}
4163 and @code{b} in this structure:
4170 @} __attribute__ ((packed));
4173 This warning is enabled by default. Use
4174 @option{-Wno-packed-bitfield-compat} to disable this warning.
4179 Warn if padding is included in a structure, either to align an element
4180 of the structure or to align the whole structure. Sometimes when this
4181 happens it is possible to rearrange the fields of the structure to
4182 reduce the padding and so make the structure smaller.
4184 @item -Wredundant-decls
4185 @opindex Wredundant-decls
4186 @opindex Wno-redundant-decls
4187 Warn if anything is declared more than once in the same scope, even in
4188 cases where multiple declaration is valid and changes nothing.
4190 @item -Wnested-externs @r{(C and Objective-C only)}
4191 @opindex Wnested-externs
4192 @opindex Wno-nested-externs
4193 Warn if an @code{extern} declaration is encountered within a function.
4195 @item -Wunreachable-code
4196 @opindex Wunreachable-code
4197 @opindex Wno-unreachable-code
4198 Warn if the compiler detects that code will never be executed.
4200 This option is intended to warn when the compiler detects that at
4201 least a whole line of source code will never be executed, because
4202 some condition is never satisfied or because it is after a
4203 procedure that never returns.
4205 It is possible for this option to produce a warning even though there
4206 are circumstances under which part of the affected line can be executed,
4207 so care should be taken when removing apparently-unreachable code.
4209 For instance, when a function is inlined, a warning may mean that the
4210 line is unreachable in only one inlined copy of the function.
4212 This option is not made part of @option{-Wall} because in a debugging
4213 version of a program there is often substantial code which checks
4214 correct functioning of the program and is, hopefully, unreachable
4215 because the program does work. Another common use of unreachable
4216 code is to provide behavior which is selectable at compile-time.
4221 Warn if a function can not be inlined and it was declared as inline.
4222 Even with this option, the compiler will not warn about failures to
4223 inline functions declared in system headers.
4225 The compiler uses a variety of heuristics to determine whether or not
4226 to inline a function. For example, the compiler takes into account
4227 the size of the function being inlined and the amount of inlining
4228 that has already been done in the current function. Therefore,
4229 seemingly insignificant changes in the source program can cause the
4230 warnings produced by @option{-Winline} to appear or disappear.
4232 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4233 @opindex Wno-invalid-offsetof
4234 @opindex Winvalid-offsetof
4235 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4236 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4237 to a non-POD type is undefined. In existing C++ implementations,
4238 however, @samp{offsetof} typically gives meaningful results even when
4239 applied to certain kinds of non-POD types. (Such as a simple
4240 @samp{struct} that fails to be a POD type only by virtue of having a
4241 constructor.) This flag is for users who are aware that they are
4242 writing nonportable code and who have deliberately chosen to ignore the
4245 The restrictions on @samp{offsetof} may be relaxed in a future version
4246 of the C++ standard.
4248 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4249 @opindex Wno-int-to-pointer-cast
4250 @opindex Wint-to-pointer-cast
4251 Suppress warnings from casts to pointer type of an integer of a
4254 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4255 @opindex Wno-pointer-to-int-cast
4256 @opindex Wpointer-to-int-cast
4257 Suppress warnings from casts from a pointer to an integer type of a
4261 @opindex Winvalid-pch
4262 @opindex Wno-invalid-pch
4263 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4264 the search path but can't be used.
4268 @opindex Wno-long-long
4269 Warn if @samp{long long} type is used. This is enabled by either
4270 @option{-pedantic} or @option{-Wtraditional} in ISO C90 and C++98
4271 modes. To inhibit the warning messages, use @option{-Wno-long-long}.
4273 @item -Wvariadic-macros
4274 @opindex Wvariadic-macros
4275 @opindex Wno-variadic-macros
4276 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4277 alternate syntax when in pedantic ISO C99 mode. This is default.
4278 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4283 Warn if variable length array is used in the code.
4284 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4285 the variable length array.
4287 @item -Wvolatile-register-var
4288 @opindex Wvolatile-register-var
4289 @opindex Wno-volatile-register-var
4290 Warn if a register variable is declared volatile. The volatile
4291 modifier does not inhibit all optimizations that may eliminate reads
4292 and/or writes to register variables. This warning is enabled by
4295 @item -Wdisabled-optimization
4296 @opindex Wdisabled-optimization
4297 @opindex Wno-disabled-optimization
4298 Warn if a requested optimization pass is disabled. This warning does
4299 not generally indicate that there is anything wrong with your code; it
4300 merely indicates that GCC's optimizers were unable to handle the code
4301 effectively. Often, the problem is that your code is too big or too
4302 complex; GCC will refuse to optimize programs when the optimization
4303 itself is likely to take inordinate amounts of time.
4305 @item -Wpointer-sign @r{(C and Objective-C only)}
4306 @opindex Wpointer-sign
4307 @opindex Wno-pointer-sign
4308 Warn for pointer argument passing or assignment with different signedness.
4309 This option is only supported for C and Objective-C@. It is implied by
4310 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4311 @option{-Wno-pointer-sign}.
4313 @item -Wstack-protector
4314 @opindex Wstack-protector
4315 @opindex Wno-stack-protector
4316 This option is only active when @option{-fstack-protector} is active. It
4317 warns about functions that will not be protected against stack smashing.
4320 @opindex Wno-mudflap
4321 Suppress warnings about constructs that cannot be instrumented by
4324 @item -Woverlength-strings
4325 @opindex Woverlength-strings
4326 @opindex Wno-overlength-strings
4327 Warn about string constants which are longer than the ``minimum
4328 maximum'' length specified in the C standard. Modern compilers
4329 generally allow string constants which are much longer than the
4330 standard's minimum limit, but very portable programs should avoid
4331 using longer strings.
4333 The limit applies @emph{after} string constant concatenation, and does
4334 not count the trailing NUL@. In C89, the limit was 509 characters; in
4335 C99, it was raised to 4095. C++98 does not specify a normative
4336 minimum maximum, so we do not diagnose overlength strings in C++@.
4338 This option is implied by @option{-pedantic}, and can be disabled with
4339 @option{-Wno-overlength-strings}.
4341 @item -Wunsuffixed-float-constants @r{(C and Objective-C only)}
4342 @opindex Wunsuffixed-float-constants
4344 GCC will issue a warning for any floating constant that does not have
4345 a suffix. When used together with @option{-Wsystem-headers} it will
4346 warn about such constants in system header files. This can be useful
4347 when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
4348 from the decimal floating-point extension to C99.
4351 @node Debugging Options
4352 @section Options for Debugging Your Program or GCC
4353 @cindex options, debugging
4354 @cindex debugging information options
4356 GCC has various special options that are used for debugging
4357 either your program or GCC:
4362 Produce debugging information in the operating system's native format
4363 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4366 On most systems that use stabs format, @option{-g} enables use of extra
4367 debugging information that only GDB can use; this extra information
4368 makes debugging work better in GDB but will probably make other debuggers
4370 refuse to read the program. If you want to control for certain whether
4371 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4372 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4374 GCC allows you to use @option{-g} with
4375 @option{-O}. The shortcuts taken by optimized code may occasionally
4376 produce surprising results: some variables you declared may not exist
4377 at all; flow of control may briefly move where you did not expect it;
4378 some statements may not be executed because they compute constant
4379 results or their values were already at hand; some statements may
4380 execute in different places because they were moved out of loops.
4382 Nevertheless it proves possible to debug optimized output. This makes
4383 it reasonable to use the optimizer for programs that might have bugs.
4385 The following options are useful when GCC is generated with the
4386 capability for more than one debugging format.
4390 Produce debugging information for use by GDB@. This means to use the
4391 most expressive format available (DWARF 2, stabs, or the native format
4392 if neither of those are supported), including GDB extensions if at all
4397 Produce debugging information in stabs format (if that is supported),
4398 without GDB extensions. This is the format used by DBX on most BSD
4399 systems. On MIPS, Alpha and System V Release 4 systems this option
4400 produces stabs debugging output which is not understood by DBX or SDB@.
4401 On System V Release 4 systems this option requires the GNU assembler.
4403 @item -feliminate-unused-debug-symbols
4404 @opindex feliminate-unused-debug-symbols
4405 Produce debugging information in stabs format (if that is supported),
4406 for only symbols that are actually used.
4408 @item -femit-class-debug-always
4409 Instead of emitting debugging information for a C++ class in only one
4410 object file, emit it in all object files using the class. This option
4411 should be used only with debuggers that are unable to handle the way GCC
4412 normally emits debugging information for classes because using this
4413 option will increase the size of debugging information by as much as a
4418 Produce debugging information in stabs format (if that is supported),
4419 using GNU extensions understood only by the GNU debugger (GDB)@. The
4420 use of these extensions is likely to make other debuggers crash or
4421 refuse to read the program.
4425 Produce debugging information in COFF format (if that is supported).
4426 This is the format used by SDB on most System V systems prior to
4431 Produce debugging information in XCOFF format (if that is supported).
4432 This is the format used by the DBX debugger on IBM RS/6000 systems.
4436 Produce debugging information in XCOFF format (if that is supported),
4437 using GNU extensions understood only by the GNU debugger (GDB)@. The
4438 use of these extensions is likely to make other debuggers crash or
4439 refuse to read the program, and may cause assemblers other than the GNU
4440 assembler (GAS) to fail with an error.
4442 @item -gdwarf-@var{version}
4443 @opindex gdwarf-@var{version}
4444 Produce debugging information in DWARF format (if that is
4445 supported). This is the format used by DBX on IRIX 6. The value
4446 of @var{version} may be either 2, 3 or 4; the default version is 2.
4448 Note that with DWARF version 2 some ports require, and will always
4449 use, some non-conflicting DWARF 3 extensions in the unwind tables.
4451 Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
4452 for maximum benefit.
4454 @item -gstrict-dwarf
4455 @opindex gstrict-dwarf
4456 Disallow using extensions of later DWARF standard version than selected
4457 with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
4458 DWARF extensions from later standard versions is allowed.
4460 @item -gno-strict-dwarf
4461 @opindex gno-strict-dwarf
4462 Allow using extensions of later DWARF standard version than selected with
4463 @option{-gdwarf-@var{version}}.
4467 Produce debugging information in VMS debug format (if that is
4468 supported). This is the format used by DEBUG on VMS systems.
4471 @itemx -ggdb@var{level}
4472 @itemx -gstabs@var{level}
4473 @itemx -gcoff@var{level}
4474 @itemx -gxcoff@var{level}
4475 @itemx -gvms@var{level}
4476 Request debugging information and also use @var{level} to specify how
4477 much information. The default level is 2.
4479 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4482 Level 1 produces minimal information, enough for making backtraces in
4483 parts of the program that you don't plan to debug. This includes
4484 descriptions of functions and external variables, but no information
4485 about local variables and no line numbers.
4487 Level 3 includes extra information, such as all the macro definitions
4488 present in the program. Some debuggers support macro expansion when
4489 you use @option{-g3}.
4491 @option{-gdwarf-2} does not accept a concatenated debug level, because
4492 GCC used to support an option @option{-gdwarf} that meant to generate
4493 debug information in version 1 of the DWARF format (which is very
4494 different from version 2), and it would have been too confusing. That
4495 debug format is long obsolete, but the option cannot be changed now.
4496 Instead use an additional @option{-g@var{level}} option to change the
4497 debug level for DWARF.
4501 Turn off generation of debug info, if leaving out this option would have
4502 generated it, or turn it on at level 2 otherwise. The position of this
4503 argument in the command line does not matter, it takes effect after all
4504 other options are processed, and it does so only once, no matter how
4505 many times it is given. This is mainly intended to be used with
4506 @option{-fcompare-debug}.
4508 @item -fdump-final-insns@r{[}=@var{file}@r{]}
4509 @opindex fdump-final-insns
4510 Dump the final internal representation (RTL) to @var{file}. If the
4511 optional argument is omitted (or if @var{file} is @code{.}), the name
4512 of the dump file will be determined by appending @code{.gkd} to the
4513 compilation output file name.
4515 @item -fcompare-debug@r{[}=@var{opts}@r{]}
4516 @opindex fcompare-debug
4517 @opindex fno-compare-debug
4518 If no error occurs during compilation, run the compiler a second time,
4519 adding @var{opts} and @option{-fcompare-debug-second} to the arguments
4520 passed to the second compilation. Dump the final internal
4521 representation in both compilations, and print an error if they differ.
4523 If the equal sign is omitted, the default @option{-gtoggle} is used.
4525 The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
4526 and nonzero, implicitly enables @option{-fcompare-debug}. If
4527 @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
4528 then it is used for @var{opts}, otherwise the default @option{-gtoggle}
4531 @option{-fcompare-debug=}, with the equal sign but without @var{opts},
4532 is equivalent to @option{-fno-compare-debug}, which disables the dumping
4533 of the final representation and the second compilation, preventing even
4534 @env{GCC_COMPARE_DEBUG} from taking effect.
4536 To verify full coverage during @option{-fcompare-debug} testing, set
4537 @env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden},
4538 which GCC will reject as an invalid option in any actual compilation
4539 (rather than preprocessing, assembly or linking). To get just a
4540 warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
4541 not overridden} will do.
4543 @item -fcompare-debug-second
4544 @opindex fcompare-debug-second
4545 This option is implicitly passed to the compiler for the second
4546 compilation requested by @option{-fcompare-debug}, along with options to
4547 silence warnings, and omitting other options that would cause
4548 side-effect compiler outputs to files or to the standard output. Dump
4549 files and preserved temporary files are renamed so as to contain the
4550 @code{.gk} additional extension during the second compilation, to avoid
4551 overwriting those generated by the first.
4553 When this option is passed to the compiler driver, it causes the
4554 @emph{first} compilation to be skipped, which makes it useful for little
4555 other than debugging the compiler proper.
4557 @item -feliminate-dwarf2-dups
4558 @opindex feliminate-dwarf2-dups
4559 Compress DWARF2 debugging information by eliminating duplicated
4560 information about each symbol. This option only makes sense when
4561 generating DWARF2 debugging information with @option{-gdwarf-2}.
4563 @item -femit-struct-debug-baseonly
4564 Emit debug information for struct-like types
4565 only when the base name of the compilation source file
4566 matches the base name of file in which the struct was defined.
4568 This option substantially reduces the size of debugging information,
4569 but at significant potential loss in type information to the debugger.
4570 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4571 See @option{-femit-struct-debug-detailed} for more detailed control.
4573 This option works only with DWARF 2.
4575 @item -femit-struct-debug-reduced
4576 Emit debug information for struct-like types
4577 only when the base name of the compilation source file
4578 matches the base name of file in which the type was defined,
4579 unless the struct is a template or defined in a system header.
4581 This option significantly reduces the size of debugging information,
4582 with some potential loss in type information to the debugger.
4583 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4584 See @option{-femit-struct-debug-detailed} for more detailed control.
4586 This option works only with DWARF 2.
4588 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4589 Specify the struct-like types
4590 for which the compiler will generate debug information.
4591 The intent is to reduce duplicate struct debug information
4592 between different object files within the same program.
4594 This option is a detailed version of
4595 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4596 which will serve for most needs.
4598 A specification has the syntax
4599 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4601 The optional first word limits the specification to
4602 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4603 A struct type is used directly when it is the type of a variable, member.
4604 Indirect uses arise through pointers to structs.
4605 That is, when use of an incomplete struct would be legal, the use is indirect.
4607 @samp{struct one direct; struct two * indirect;}.
4609 The optional second word limits the specification to
4610 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4611 Generic structs are a bit complicated to explain.
4612 For C++, these are non-explicit specializations of template classes,
4613 or non-template classes within the above.
4614 Other programming languages have generics,
4615 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4617 The third word specifies the source files for those
4618 structs for which the compiler will emit debug information.
4619 The values @samp{none} and @samp{any} have the normal meaning.
4620 The value @samp{base} means that
4621 the base of name of the file in which the type declaration appears
4622 must match the base of the name of the main compilation file.
4623 In practice, this means that
4624 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4625 but types declared in other header will not.
4626 The value @samp{sys} means those types satisfying @samp{base}
4627 or declared in system or compiler headers.
4629 You may need to experiment to determine the best settings for your application.
4631 The default is @samp{-femit-struct-debug-detailed=all}.
4633 This option works only with DWARF 2.
4635 @item -fenable-icf-debug
4636 @opindex fenable-icf-debug
4637 Generate additional debug information to support identical code folding (ICF).
4638 This option only works with DWARF version 2 or higher.
4640 @item -fno-merge-debug-strings
4641 @opindex fmerge-debug-strings
4642 @opindex fno-merge-debug-strings
4643 Direct the linker to not merge together strings in the debugging
4644 information which are identical in different object files. Merging is
4645 not supported by all assemblers or linkers. Merging decreases the size
4646 of the debug information in the output file at the cost of increasing
4647 link processing time. Merging is enabled by default.
4649 @item -fdebug-prefix-map=@var{old}=@var{new}
4650 @opindex fdebug-prefix-map
4651 When compiling files in directory @file{@var{old}}, record debugging
4652 information describing them as in @file{@var{new}} instead.
4654 @item -fno-dwarf2-cfi-asm
4655 @opindex fdwarf2-cfi-asm
4656 @opindex fno-dwarf2-cfi-asm
4657 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4658 instead of using GAS @code{.cfi_*} directives.
4660 @cindex @command{prof}
4663 Generate extra code to write profile information suitable for the
4664 analysis program @command{prof}. You must use this option when compiling
4665 the source files you want data about, and you must also use it when
4668 @cindex @command{gprof}
4671 Generate extra code to write profile information suitable for the
4672 analysis program @command{gprof}. You must use this option when compiling
4673 the source files you want data about, and you must also use it when
4678 Makes the compiler print out each function name as it is compiled, and
4679 print some statistics about each pass when it finishes.
4682 @opindex ftime-report
4683 Makes the compiler print some statistics about the time consumed by each
4684 pass when it finishes.
4687 @opindex fmem-report
4688 Makes the compiler print some statistics about permanent memory
4689 allocation when it finishes.
4691 @item -fpre-ipa-mem-report
4692 @opindex fpre-ipa-mem-report
4693 @item -fpost-ipa-mem-report
4694 @opindex fpost-ipa-mem-report
4695 Makes the compiler print some statistics about permanent memory
4696 allocation before or after interprocedural optimization.
4698 @item -fprofile-arcs
4699 @opindex fprofile-arcs
4700 Add code so that program flow @dfn{arcs} are instrumented. During
4701 execution the program records how many times each branch and call is
4702 executed and how many times it is taken or returns. When the compiled
4703 program exits it saves this data to a file called
4704 @file{@var{auxname}.gcda} for each source file. The data may be used for
4705 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4706 test coverage analysis (@option{-ftest-coverage}). Each object file's
4707 @var{auxname} is generated from the name of the output file, if
4708 explicitly specified and it is not the final executable, otherwise it is
4709 the basename of the source file. In both cases any suffix is removed
4710 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4711 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4712 @xref{Cross-profiling}.
4714 @cindex @command{gcov}
4718 This option is used to compile and link code instrumented for coverage
4719 analysis. The option is a synonym for @option{-fprofile-arcs}
4720 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4721 linking). See the documentation for those options for more details.
4726 Compile the source files with @option{-fprofile-arcs} plus optimization
4727 and code generation options. For test coverage analysis, use the
4728 additional @option{-ftest-coverage} option. You do not need to profile
4729 every source file in a program.
4732 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4733 (the latter implies the former).
4736 Run the program on a representative workload to generate the arc profile
4737 information. This may be repeated any number of times. You can run
4738 concurrent instances of your program, and provided that the file system
4739 supports locking, the data files will be correctly updated. Also
4740 @code{fork} calls are detected and correctly handled (double counting
4744 For profile-directed optimizations, compile the source files again with
4745 the same optimization and code generation options plus
4746 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4747 Control Optimization}).
4750 For test coverage analysis, use @command{gcov} to produce human readable
4751 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4752 @command{gcov} documentation for further information.
4756 With @option{-fprofile-arcs}, for each function of your program GCC
4757 creates a program flow graph, then finds a spanning tree for the graph.
4758 Only arcs that are not on the spanning tree have to be instrumented: the
4759 compiler adds code to count the number of times that these arcs are
4760 executed. When an arc is the only exit or only entrance to a block, the
4761 instrumentation code can be added to the block; otherwise, a new basic
4762 block must be created to hold the instrumentation code.
4765 @item -ftest-coverage
4766 @opindex ftest-coverage
4767 Produce a notes file that the @command{gcov} code-coverage utility
4768 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4769 show program coverage. Each source file's note file is called
4770 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4771 above for a description of @var{auxname} and instructions on how to
4772 generate test coverage data. Coverage data will match the source files
4773 more closely, if you do not optimize.
4775 @item -fdbg-cnt-list
4776 @opindex fdbg-cnt-list
4777 Print the name and the counter upperbound for all debug counters.
4779 @item -fdbg-cnt=@var{counter-value-list}
4781 Set the internal debug counter upperbound. @var{counter-value-list}
4782 is a comma-separated list of @var{name}:@var{value} pairs
4783 which sets the upperbound of each debug counter @var{name} to @var{value}.
4784 All debug counters have the initial upperbound of @var{UINT_MAX},
4785 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4786 e.g. With -fdbg-cnt=dce:10,tail_call:0
4787 dbg_cnt(dce) will return true only for first 10 invocations
4788 and dbg_cnt(tail_call) will return false always.
4790 @item -d@var{letters}
4791 @itemx -fdump-rtl-@var{pass}
4793 Says to make debugging dumps during compilation at times specified by
4794 @var{letters}. This is used for debugging the RTL-based passes of the
4795 compiler. The file names for most of the dumps are made by appending
4796 a pass number and a word to the @var{dumpname}, and the files are
4797 created in the directory of the output file. @var{dumpname} is
4798 generated from the name of the output file, if explicitly specified
4799 and it is not an executable, otherwise it is the basename of the
4800 source file. These switches may have different effects when
4801 @option{-E} is used for preprocessing.
4803 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
4804 @option{-d} option @var{letters}. Here are the possible
4805 letters for use in @var{pass} and @var{letters}, and their meanings:
4809 @item -fdump-rtl-alignments
4810 @opindex fdump-rtl-alignments
4811 Dump after branch alignments have been computed.
4813 @item -fdump-rtl-asmcons
4814 @opindex fdump-rtl-asmcons
4815 Dump after fixing rtl statements that have unsatisfied in/out constraints.
4817 @item -fdump-rtl-auto_inc_dec
4818 @opindex fdump-rtl-auto_inc_dec
4819 Dump after auto-inc-dec discovery. This pass is only run on
4820 architectures that have auto inc or auto dec instructions.
4822 @item -fdump-rtl-barriers
4823 @opindex fdump-rtl-barriers
4824 Dump after cleaning up the barrier instructions.
4826 @item -fdump-rtl-bbpart
4827 @opindex fdump-rtl-bbpart
4828 Dump after partitioning hot and cold basic blocks.
4830 @item -fdump-rtl-bbro
4831 @opindex fdump-rtl-bbro
4832 Dump after block reordering.
4834 @item -fdump-rtl-btl1
4835 @itemx -fdump-rtl-btl2
4836 @opindex fdump-rtl-btl2
4837 @opindex fdump-rtl-btl2
4838 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
4839 after the two branch
4840 target load optimization passes.
4842 @item -fdump-rtl-bypass
4843 @opindex fdump-rtl-bypass
4844 Dump after jump bypassing and control flow optimizations.
4846 @item -fdump-rtl-combine
4847 @opindex fdump-rtl-combine
4848 Dump after the RTL instruction combination pass.
4850 @item -fdump-rtl-compgotos
4851 @opindex fdump-rtl-compgotos
4852 Dump after duplicating the computed gotos.
4854 @item -fdump-rtl-ce1
4855 @itemx -fdump-rtl-ce2
4856 @itemx -fdump-rtl-ce3
4857 @opindex fdump-rtl-ce1
4858 @opindex fdump-rtl-ce2
4859 @opindex fdump-rtl-ce3
4860 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
4861 @option{-fdump-rtl-ce3} enable dumping after the three
4862 if conversion passes.
4864 @itemx -fdump-rtl-cprop_hardreg
4865 @opindex fdump-rtl-cprop_hardreg
4866 Dump after hard register copy propagation.
4868 @itemx -fdump-rtl-csa
4869 @opindex fdump-rtl-csa
4870 Dump after combining stack adjustments.
4872 @item -fdump-rtl-cse1
4873 @itemx -fdump-rtl-cse2
4874 @opindex fdump-rtl-cse1
4875 @opindex fdump-rtl-cse2
4876 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
4877 the two common sub-expression elimination passes.
4879 @itemx -fdump-rtl-dce
4880 @opindex fdump-rtl-dce
4881 Dump after the standalone dead code elimination passes.
4883 @itemx -fdump-rtl-dbr
4884 @opindex fdump-rtl-dbr
4885 Dump after delayed branch scheduling.
4887 @item -fdump-rtl-dce1
4888 @itemx -fdump-rtl-dce2
4889 @opindex fdump-rtl-dce1
4890 @opindex fdump-rtl-dce2
4891 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
4892 the two dead store elimination passes.
4895 @opindex fdump-rtl-eh
4896 Dump after finalization of EH handling code.
4898 @item -fdump-rtl-eh_ranges
4899 @opindex fdump-rtl-eh_ranges
4900 Dump after conversion of EH handling range regions.
4902 @item -fdump-rtl-expand
4903 @opindex fdump-rtl-expand
4904 Dump after RTL generation.
4906 @item -fdump-rtl-fwprop1
4907 @itemx -fdump-rtl-fwprop2
4908 @opindex fdump-rtl-fwprop1
4909 @opindex fdump-rtl-fwprop2
4910 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
4911 dumping after the two forward propagation passes.
4913 @item -fdump-rtl-gcse1
4914 @itemx -fdump-rtl-gcse2
4915 @opindex fdump-rtl-gcse1
4916 @opindex fdump-rtl-gcse2
4917 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
4918 after global common subexpression elimination.
4920 @item -fdump-rtl-init-regs
4921 @opindex fdump-rtl-init-regs
4922 Dump after the initialization of the registers.
4924 @item -fdump-rtl-initvals
4925 @opindex fdump-rtl-initvals
4926 Dump after the computation of the initial value sets.
4928 @itemx -fdump-rtl-into_cfglayout
4929 @opindex fdump-rtl-into_cfglayout
4930 Dump after converting to cfglayout mode.
4932 @item -fdump-rtl-ira
4933 @opindex fdump-rtl-ira
4934 Dump after iterated register allocation.
4936 @item -fdump-rtl-jump
4937 @opindex fdump-rtl-jump
4938 Dump after the second jump optimization.
4940 @item -fdump-rtl-loop2
4941 @opindex fdump-rtl-loop2
4942 @option{-fdump-rtl-loop2} enables dumping after the rtl
4943 loop optimization passes.
4945 @item -fdump-rtl-mach
4946 @opindex fdump-rtl-mach
4947 Dump after performing the machine dependent reorganization pass, if that
4950 @item -fdump-rtl-mode_sw
4951 @opindex fdump-rtl-mode_sw
4952 Dump after removing redundant mode switches.
4954 @item -fdump-rtl-rnreg
4955 @opindex fdump-rtl-rnreg
4956 Dump after register renumbering.
4958 @itemx -fdump-rtl-outof_cfglayout
4959 @opindex fdump-rtl-outof_cfglayout
4960 Dump after converting from cfglayout mode.
4962 @item -fdump-rtl-peephole2
4963 @opindex fdump-rtl-peephole2
4964 Dump after the peephole pass.
4966 @item -fdump-rtl-postreload
4967 @opindex fdump-rtl-postreload
4968 Dump after post-reload optimizations.
4970 @itemx -fdump-rtl-pro_and_epilogue
4971 @opindex fdump-rtl-pro_and_epilogue
4972 Dump after generating the function pro and epilogues.
4974 @item -fdump-rtl-regmove
4975 @opindex fdump-rtl-regmove
4976 Dump after the register move pass.
4978 @item -fdump-rtl-sched1
4979 @itemx -fdump-rtl-sched2
4980 @opindex fdump-rtl-sched1
4981 @opindex fdump-rtl-sched2
4982 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
4983 after the basic block scheduling passes.
4985 @item -fdump-rtl-see
4986 @opindex fdump-rtl-see
4987 Dump after sign extension elimination.
4989 @item -fdump-rtl-seqabstr
4990 @opindex fdump-rtl-seqabstr
4991 Dump after common sequence discovery.
4993 @item -fdump-rtl-shorten
4994 @opindex fdump-rtl-shorten
4995 Dump after shortening branches.
4997 @item -fdump-rtl-sibling
4998 @opindex fdump-rtl-sibling
4999 Dump after sibling call optimizations.
5001 @item -fdump-rtl-split1
5002 @itemx -fdump-rtl-split2
5003 @itemx -fdump-rtl-split3
5004 @itemx -fdump-rtl-split4
5005 @itemx -fdump-rtl-split5
5006 @opindex fdump-rtl-split1
5007 @opindex fdump-rtl-split2
5008 @opindex fdump-rtl-split3
5009 @opindex fdump-rtl-split4
5010 @opindex fdump-rtl-split5
5011 @option{-fdump-rtl-split1}, @option{-fdump-rtl-split2},
5012 @option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and
5013 @option{-fdump-rtl-split5} enable dumping after five rounds of
5014 instruction splitting.
5016 @item -fdump-rtl-sms
5017 @opindex fdump-rtl-sms
5018 Dump after modulo scheduling. This pass is only run on some
5021 @item -fdump-rtl-stack
5022 @opindex fdump-rtl-stack
5023 Dump after conversion from GCC's "flat register file" registers to the
5024 x87's stack-like registers. This pass is only run on x86 variants.
5026 @item -fdump-rtl-subreg1
5027 @itemx -fdump-rtl-subreg2
5028 @opindex fdump-rtl-subreg1
5029 @opindex fdump-rtl-subreg2
5030 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
5031 the two subreg expansion passes.
5033 @item -fdump-rtl-unshare
5034 @opindex fdump-rtl-unshare
5035 Dump after all rtl has been unshared.
5037 @item -fdump-rtl-vartrack
5038 @opindex fdump-rtl-vartrack
5039 Dump after variable tracking.
5041 @item -fdump-rtl-vregs
5042 @opindex fdump-rtl-vregs
5043 Dump after converting virtual registers to hard registers.
5045 @item -fdump-rtl-web
5046 @opindex fdump-rtl-web
5047 Dump after live range splitting.
5049 @item -fdump-rtl-regclass
5050 @itemx -fdump-rtl-subregs_of_mode_init
5051 @itemx -fdump-rtl-subregs_of_mode_finish
5052 @itemx -fdump-rtl-dfinit
5053 @itemx -fdump-rtl-dfinish
5054 @opindex fdump-rtl-regclass
5055 @opindex fdump-rtl-subregs_of_mode_init
5056 @opindex fdump-rtl-subregs_of_mode_finish
5057 @opindex fdump-rtl-dfinit
5058 @opindex fdump-rtl-dfinish
5059 These dumps are defined but always produce empty files.
5061 @item -fdump-rtl-all
5062 @opindex fdump-rtl-all
5063 Produce all the dumps listed above.
5067 Annotate the assembler output with miscellaneous debugging information.
5071 Dump all macro definitions, at the end of preprocessing, in addition to
5076 Produce a core dump whenever an error occurs.
5080 Print statistics on memory usage, at the end of the run, to
5085 Annotate the assembler output with a comment indicating which
5086 pattern and alternative was used. The length of each instruction is
5091 Dump the RTL in the assembler output as a comment before each instruction.
5092 Also turns on @option{-dp} annotation.
5096 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
5097 dump a representation of the control flow graph suitable for viewing with VCG
5098 to @file{@var{file}.@var{pass}.vcg}.
5102 Just generate RTL for a function instead of compiling it. Usually used
5103 with @option{-fdump-rtl-expand}.
5107 Dump debugging information during parsing, to standard error.
5111 @opindex fdump-noaddr
5112 When doing debugging dumps, suppress address output. This makes it more
5113 feasible to use diff on debugging dumps for compiler invocations with
5114 different compiler binaries and/or different
5115 text / bss / data / heap / stack / dso start locations.
5117 @item -fdump-unnumbered
5118 @opindex fdump-unnumbered
5119 When doing debugging dumps, suppress instruction numbers and address output.
5120 This makes it more feasible to use diff on debugging dumps for compiler
5121 invocations with different options, in particular with and without
5124 @item -fdump-unnumbered-links
5125 @opindex fdump-unnumbered-links
5126 When doing debugging dumps (see @option{-d} option above), suppress
5127 instruction numbers for the links to the previous and next instructions
5130 @item -fdump-translation-unit @r{(C++ only)}
5131 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
5132 @opindex fdump-translation-unit
5133 Dump a representation of the tree structure for the entire translation
5134 unit to a file. The file name is made by appending @file{.tu} to the
5135 source file name, and the file is created in the same directory as the
5136 output file. If the @samp{-@var{options}} form is used, @var{options}
5137 controls the details of the dump as described for the
5138 @option{-fdump-tree} options.
5140 @item -fdump-class-hierarchy @r{(C++ only)}
5141 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
5142 @opindex fdump-class-hierarchy
5143 Dump a representation of each class's hierarchy and virtual function
5144 table layout to a file. The file name is made by appending
5145 @file{.class} to the source file name, and the file is created in the
5146 same directory as the output file. If the @samp{-@var{options}} form
5147 is used, @var{options} controls the details of the dump as described
5148 for the @option{-fdump-tree} options.
5150 @item -fdump-ipa-@var{switch}
5152 Control the dumping at various stages of inter-procedural analysis
5153 language tree to a file. The file name is generated by appending a
5154 switch specific suffix to the source file name, and the file is created
5155 in the same directory as the output file. The following dumps are
5160 Enables all inter-procedural analysis dumps.
5163 Dumps information about call-graph optimization, unused function removal,
5164 and inlining decisions.
5167 Dump after function inlining.
5171 @item -fdump-statistics-@var{option}
5172 @opindex fdump-statistics
5173 Enable and control dumping of pass statistics in a separate file. The
5174 file name is generated by appending a suffix ending in
5175 @samp{.statistics} to the source file name, and the file is created in
5176 the same directory as the output file. If the @samp{-@var{option}}
5177 form is used, @samp{-stats} will cause counters to be summed over the
5178 whole compilation unit while @samp{-details} will dump every event as
5179 the passes generate them. The default with no option is to sum
5180 counters for each function compiled.
5182 @item -fdump-tree-@var{switch}
5183 @itemx -fdump-tree-@var{switch}-@var{options}
5185 Control the dumping at various stages of processing the intermediate
5186 language tree to a file. The file name is generated by appending a
5187 switch specific suffix to the source file name, and the file is
5188 created in the same directory as the output file. If the
5189 @samp{-@var{options}} form is used, @var{options} is a list of
5190 @samp{-} separated options that control the details of the dump. Not
5191 all options are applicable to all dumps, those which are not
5192 meaningful will be ignored. The following options are available
5196 Print the address of each node. Usually this is not meaningful as it
5197 changes according to the environment and source file. Its primary use
5198 is for tying up a dump file with a debug environment.
5200 If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
5201 in the dump instead of @code{DECL_NAME}. Its primary use is ease of
5202 use working backward from mangled names in the assembly file.
5204 Inhibit dumping of members of a scope or body of a function merely
5205 because that scope has been reached. Only dump such items when they
5206 are directly reachable by some other path. When dumping pretty-printed
5207 trees, this option inhibits dumping the bodies of control structures.
5209 Print a raw representation of the tree. By default, trees are
5210 pretty-printed into a C-like representation.
5212 Enable more detailed dumps (not honored by every dump option).
5214 Enable dumping various statistics about the pass (not honored by every dump
5217 Enable showing basic block boundaries (disabled in raw dumps).
5219 Enable showing virtual operands for every statement.
5221 Enable showing line numbers for statements.
5223 Enable showing the unique ID (@code{DECL_UID}) for each variable.
5225 Enable showing the tree dump for each statement.
5227 Enable showing the EH region number holding each statement.
5229 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
5230 and @option{lineno}.
5233 The following tree dumps are possible:
5237 @opindex fdump-tree-original
5238 Dump before any tree based optimization, to @file{@var{file}.original}.
5241 @opindex fdump-tree-optimized
5242 Dump after all tree based optimization, to @file{@var{file}.optimized}.
5245 @opindex fdump-tree-gimple
5246 Dump each function before and after the gimplification pass to a file. The
5247 file name is made by appending @file{.gimple} to the source file name.
5250 @opindex fdump-tree-cfg
5251 Dump the control flow graph of each function to a file. The file name is
5252 made by appending @file{.cfg} to the source file name.
5255 @opindex fdump-tree-vcg
5256 Dump the control flow graph of each function to a file in VCG format. The
5257 file name is made by appending @file{.vcg} to the source file name. Note
5258 that if the file contains more than one function, the generated file cannot
5259 be used directly by VCG@. You will need to cut and paste each function's
5260 graph into its own separate file first.
5263 @opindex fdump-tree-ch
5264 Dump each function after copying loop headers. The file name is made by
5265 appending @file{.ch} to the source file name.
5268 @opindex fdump-tree-ssa
5269 Dump SSA related information to a file. The file name is made by appending
5270 @file{.ssa} to the source file name.
5273 @opindex fdump-tree-alias
5274 Dump aliasing information for each function. The file name is made by
5275 appending @file{.alias} to the source file name.
5278 @opindex fdump-tree-ccp
5279 Dump each function after CCP@. The file name is made by appending
5280 @file{.ccp} to the source file name.
5283 @opindex fdump-tree-storeccp
5284 Dump each function after STORE-CCP@. The file name is made by appending
5285 @file{.storeccp} to the source file name.
5288 @opindex fdump-tree-pre
5289 Dump trees after partial redundancy elimination. The file name is made
5290 by appending @file{.pre} to the source file name.
5293 @opindex fdump-tree-fre
5294 Dump trees after full redundancy elimination. The file name is made
5295 by appending @file{.fre} to the source file name.
5298 @opindex fdump-tree-copyprop
5299 Dump trees after copy propagation. The file name is made
5300 by appending @file{.copyprop} to the source file name.
5302 @item store_copyprop
5303 @opindex fdump-tree-store_copyprop
5304 Dump trees after store copy-propagation. The file name is made
5305 by appending @file{.store_copyprop} to the source file name.
5308 @opindex fdump-tree-dce
5309 Dump each function after dead code elimination. The file name is made by
5310 appending @file{.dce} to the source file name.
5313 @opindex fdump-tree-mudflap
5314 Dump each function after adding mudflap instrumentation. The file name is
5315 made by appending @file{.mudflap} to the source file name.
5318 @opindex fdump-tree-sra
5319 Dump each function after performing scalar replacement of aggregates. The
5320 file name is made by appending @file{.sra} to the source file name.
5323 @opindex fdump-tree-sink
5324 Dump each function after performing code sinking. The file name is made
5325 by appending @file{.sink} to the source file name.
5328 @opindex fdump-tree-dom
5329 Dump each function after applying dominator tree optimizations. The file
5330 name is made by appending @file{.dom} to the source file name.
5333 @opindex fdump-tree-dse
5334 Dump each function after applying dead store elimination. The file
5335 name is made by appending @file{.dse} to the source file name.
5338 @opindex fdump-tree-phiopt
5339 Dump each function after optimizing PHI nodes into straightline code. The file
5340 name is made by appending @file{.phiopt} to the source file name.
5343 @opindex fdump-tree-forwprop
5344 Dump each function after forward propagating single use variables. The file
5345 name is made by appending @file{.forwprop} to the source file name.
5348 @opindex fdump-tree-copyrename
5349 Dump each function after applying the copy rename optimization. The file
5350 name is made by appending @file{.copyrename} to the source file name.
5353 @opindex fdump-tree-nrv
5354 Dump each function after applying the named return value optimization on
5355 generic trees. The file name is made by appending @file{.nrv} to the source
5359 @opindex fdump-tree-vect
5360 Dump each function after applying vectorization of loops. The file name is
5361 made by appending @file{.vect} to the source file name.
5364 @opindex fdump-tree-slp
5365 Dump each function after applying vectorization of basic blocks. The file name
5366 is made by appending @file{.slp} to the source file name.
5369 @opindex fdump-tree-vrp
5370 Dump each function after Value Range Propagation (VRP). The file name
5371 is made by appending @file{.vrp} to the source file name.
5374 @opindex fdump-tree-all
5375 Enable all the available tree dumps with the flags provided in this option.
5378 @item -ftree-vectorizer-verbose=@var{n}
5379 @opindex ftree-vectorizer-verbose
5380 This option controls the amount of debugging output the vectorizer prints.
5381 This information is written to standard error, unless
5382 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
5383 in which case it is output to the usual dump listing file, @file{.vect}.
5384 For @var{n}=0 no diagnostic information is reported.
5385 If @var{n}=1 the vectorizer reports each loop that got vectorized,
5386 and the total number of loops that got vectorized.
5387 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
5388 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
5389 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
5390 level that @option{-fdump-tree-vect-stats} uses.
5391 Higher verbosity levels mean either more information dumped for each
5392 reported loop, or same amount of information reported for more loops:
5393 if @var{n}=3, vectorizer cost model information is reported.
5394 If @var{n}=4, alignment related information is added to the reports.
5395 If @var{n}=5, data-references related information (e.g.@: memory dependences,
5396 memory access-patterns) is added to the reports.
5397 If @var{n}=6, the vectorizer reports also non-vectorized inner-most loops
5398 that did not pass the first analysis phase (i.e., may not be countable, or
5399 may have complicated control-flow).
5400 If @var{n}=7, the vectorizer reports also non-vectorized nested loops.
5401 If @var{n}=8, SLP related information is added to the reports.
5402 For @var{n}=9, all the information the vectorizer generates during its
5403 analysis and transformation is reported. This is the same verbosity level
5404 that @option{-fdump-tree-vect-details} uses.
5406 @item -frandom-seed=@var{string}
5407 @opindex frandom-seed
5408 This option provides a seed that GCC uses when it would otherwise use
5409 random numbers. It is used to generate certain symbol names
5410 that have to be different in every compiled file. It is also used to
5411 place unique stamps in coverage data files and the object files that
5412 produce them. You can use the @option{-frandom-seed} option to produce
5413 reproducibly identical object files.
5415 The @var{string} should be different for every file you compile.
5417 @item -fsched-verbose=@var{n}
5418 @opindex fsched-verbose
5419 On targets that use instruction scheduling, this option controls the
5420 amount of debugging output the scheduler prints. This information is
5421 written to standard error, unless @option{-fdump-rtl-sched1} or
5422 @option{-fdump-rtl-sched2} is specified, in which case it is output
5423 to the usual dump listing file, @file{.sched} or @file{.sched2}
5424 respectively. However for @var{n} greater than nine, the output is
5425 always printed to standard error.
5427 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5428 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5429 For @var{n} greater than one, it also output basic block probabilities,
5430 detailed ready list information and unit/insn info. For @var{n} greater
5431 than two, it includes RTL at abort point, control-flow and regions info.
5432 And for @var{n} over four, @option{-fsched-verbose} also includes
5436 @itemx -save-temps=cwd
5438 Store the usual ``temporary'' intermediate files permanently; place them
5439 in the current directory and name them based on the source file. Thus,
5440 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5441 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5442 preprocessed @file{foo.i} output file even though the compiler now
5443 normally uses an integrated preprocessor.
5445 When used in combination with the @option{-x} command line option,
5446 @option{-save-temps} is sensible enough to avoid over writing an
5447 input source file with the same extension as an intermediate file.
5448 The corresponding intermediate file may be obtained by renaming the
5449 source file before using @option{-save-temps}.
5451 If you invoke GCC in parallel, compiling several different source
5452 files that share a common base name in different subdirectories or the
5453 same source file compiled for multiple output destinations, it is
5454 likely that the different parallel compilers will interfere with each
5455 other, and overwrite the temporary files. For instance:
5458 gcc -save-temps -o outdir1/foo.o indir1/foo.c&
5459 gcc -save-temps -o outdir2/foo.o indir2/foo.c&
5462 may result in @file{foo.i} and @file{foo.o} being written to
5463 simultaneously by both compilers.
5465 @item -save-temps=obj
5466 @opindex save-temps=obj
5467 Store the usual ``temporary'' intermediate files permanently. If the
5468 @option{-o} option is used, the temporary files are based on the
5469 object file. If the @option{-o} option is not used, the
5470 @option{-save-temps=obj} switch behaves like @option{-save-temps}.
5475 gcc -save-temps=obj -c foo.c
5476 gcc -save-temps=obj -c bar.c -o dir/xbar.o
5477 gcc -save-temps=obj foobar.c -o dir2/yfoobar
5480 would create @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
5481 @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
5482 @file{dir2/yfoobar.o}.
5484 @item -time@r{[}=@var{file}@r{]}
5486 Report the CPU time taken by each subprocess in the compilation
5487 sequence. For C source files, this is the compiler proper and assembler
5488 (plus the linker if linking is done).
5490 Without the specification of an output file, the output looks like this:
5497 The first number on each line is the ``user time'', that is time spent
5498 executing the program itself. The second number is ``system time'',
5499 time spent executing operating system routines on behalf of the program.
5500 Both numbers are in seconds.
5502 With the specification of an output file, the output is appended to the
5503 named file, and it looks like this:
5506 0.12 0.01 cc1 @var{options}
5507 0.00 0.01 as @var{options}
5510 The ``user time'' and the ``system time'' are moved before the program
5511 name, and the options passed to the program are displayed, so that one
5512 can later tell what file was being compiled, and with which options.
5514 @item -fvar-tracking
5515 @opindex fvar-tracking
5516 Run variable tracking pass. It computes where variables are stored at each
5517 position in code. Better debugging information is then generated
5518 (if the debugging information format supports this information).
5520 It is enabled by default when compiling with optimization (@option{-Os},
5521 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5522 the debug info format supports it.
5524 @item -fvar-tracking-assignments
5525 @opindex fvar-tracking-assignments
5526 @opindex fno-var-tracking-assignments
5527 Annotate assignments to user variables early in the compilation and
5528 attempt to carry the annotations over throughout the compilation all the
5529 way to the end, in an attempt to improve debug information while
5530 optimizing. Use of @option{-gdwarf-4} is recommended along with it.
5532 It can be enabled even if var-tracking is disabled, in which case
5533 annotations will be created and maintained, but discarded at the end.
5535 @item -fvar-tracking-assignments-toggle
5536 @opindex fvar-tracking-assignments-toggle
5537 @opindex fno-var-tracking-assignments-toggle
5538 Toggle @option{-fvar-tracking-assignments}, in the same way that
5539 @option{-gtoggle} toggles @option{-g}.
5541 @item -print-file-name=@var{library}
5542 @opindex print-file-name
5543 Print the full absolute name of the library file @var{library} that
5544 would be used when linking---and don't do anything else. With this
5545 option, GCC does not compile or link anything; it just prints the
5548 @item -print-multi-directory
5549 @opindex print-multi-directory
5550 Print the directory name corresponding to the multilib selected by any
5551 other switches present in the command line. This directory is supposed
5552 to exist in @env{GCC_EXEC_PREFIX}.
5554 @item -print-multi-lib
5555 @opindex print-multi-lib
5556 Print the mapping from multilib directory names to compiler switches
5557 that enable them. The directory name is separated from the switches by
5558 @samp{;}, and each switch starts with an @samp{@@} instead of the
5559 @samp{-}, without spaces between multiple switches. This is supposed to
5560 ease shell-processing.
5562 @item -print-multi-os-directory
5563 @opindex print-multi-os-directory
5564 Print the path to OS libraries for the selected
5565 multilib, relative to some @file{lib} subdirectory. If OS libraries are
5566 present in the @file{lib} subdirectory and no multilibs are used, this is
5567 usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
5568 sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
5569 @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
5570 subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
5572 @item -print-prog-name=@var{program}
5573 @opindex print-prog-name
5574 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5576 @item -print-libgcc-file-name
5577 @opindex print-libgcc-file-name
5578 Same as @option{-print-file-name=libgcc.a}.
5580 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5581 but you do want to link with @file{libgcc.a}. You can do
5584 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5587 @item -print-search-dirs
5588 @opindex print-search-dirs
5589 Print the name of the configured installation directory and a list of
5590 program and library directories @command{gcc} will search---and don't do anything else.
5592 This is useful when @command{gcc} prints the error message
5593 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5594 To resolve this you either need to put @file{cpp0} and the other compiler
5595 components where @command{gcc} expects to find them, or you can set the environment
5596 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5597 Don't forget the trailing @samp{/}.
5598 @xref{Environment Variables}.
5600 @item -print-sysroot
5601 @opindex print-sysroot
5602 Print the target sysroot directory that will be used during
5603 compilation. This is the target sysroot specified either at configure
5604 time or using the @option{--sysroot} option, possibly with an extra
5605 suffix that depends on compilation options. If no target sysroot is
5606 specified, the option prints nothing.
5608 @item -print-sysroot-headers-suffix
5609 @opindex print-sysroot-headers-suffix
5610 Print the suffix added to the target sysroot when searching for
5611 headers, or give an error if the compiler is not configured with such
5612 a suffix---and don't do anything else.
5615 @opindex dumpmachine
5616 Print the compiler's target machine (for example,
5617 @samp{i686-pc-linux-gnu})---and don't do anything else.
5620 @opindex dumpversion
5621 Print the compiler version (for example, @samp{3.0})---and don't do
5626 Print the compiler's built-in specs---and don't do anything else. (This
5627 is used when GCC itself is being built.) @xref{Spec Files}.
5629 @item -feliminate-unused-debug-types
5630 @opindex feliminate-unused-debug-types
5631 Normally, when producing DWARF2 output, GCC will emit debugging
5632 information for all types declared in a compilation
5633 unit, regardless of whether or not they are actually used
5634 in that compilation unit. Sometimes this is useful, such as
5635 if, in the debugger, you want to cast a value to a type that is
5636 not actually used in your program (but is declared). More often,
5637 however, this results in a significant amount of wasted space.
5638 With this option, GCC will avoid producing debug symbol output
5639 for types that are nowhere used in the source file being compiled.
5642 @node Optimize Options
5643 @section Options That Control Optimization
5644 @cindex optimize options
5645 @cindex options, optimization
5647 These options control various sorts of optimizations.
5649 Without any optimization option, the compiler's goal is to reduce the
5650 cost of compilation and to make debugging produce the expected
5651 results. Statements are independent: if you stop the program with a
5652 breakpoint between statements, you can then assign a new value to any
5653 variable or change the program counter to any other statement in the
5654 function and get exactly the results you would expect from the source
5657 Turning on optimization flags makes the compiler attempt to improve
5658 the performance and/or code size at the expense of compilation time
5659 and possibly the ability to debug the program.
5661 The compiler performs optimization based on the knowledge it has of the
5662 program. Compiling multiple files at once to a single output file mode allows
5663 the compiler to use information gained from all of the files when compiling
5666 Not all optimizations are controlled directly by a flag. Only
5667 optimizations that have a flag are listed in this section.
5669 Most of the optimizations are not enabled if a @option{-O} level is not set on
5670 the command line, even if individual optimization flags are specified.
5672 Depending on the target and how GCC was configured, a slightly different
5673 set of optimizations may be enabled at each @option{-O} level than
5674 those listed here. You can invoke GCC with @samp{-Q --help=optimizers}
5675 to find out the exact set of optimizations that are enabled at each level.
5676 @xref{Overall Options}, for examples.
5683 Optimize. Optimizing compilation takes somewhat more time, and a lot
5684 more memory for a large function.
5686 With @option{-O}, the compiler tries to reduce code size and execution
5687 time, without performing any optimizations that take a great deal of
5690 @option{-O} turns on the following optimization flags:
5693 -fcprop-registers @gol
5696 -fdelayed-branch @gol
5698 -fguess-branch-probability @gol
5699 -fif-conversion2 @gol
5700 -fif-conversion @gol
5701 -fipa-pure-const @gol
5702 -fipa-reference @gol
5704 -fsplit-wide-types @gol
5705 -ftree-builtin-call-dce @gol
5708 -ftree-copyrename @gol
5710 -ftree-dominator-opts @gol
5712 -ftree-forwprop @gol
5720 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5721 where doing so does not interfere with debugging.
5725 Optimize even more. GCC performs nearly all supported optimizations
5726 that do not involve a space-speed tradeoff.
5727 As compared to @option{-O}, this option increases both compilation time
5728 and the performance of the generated code.
5730 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5731 also turns on the following optimization flags:
5732 @gccoptlist{-fthread-jumps @gol
5733 -falign-functions -falign-jumps @gol
5734 -falign-loops -falign-labels @gol
5737 -fcse-follow-jumps -fcse-skip-blocks @gol
5738 -fdelete-null-pointer-checks @gol
5739 -fexpensive-optimizations @gol
5740 -fgcse -fgcse-lm @gol
5741 -finline-small-functions @gol
5742 -findirect-inlining @gol
5744 -foptimize-sibling-calls @gol
5747 -freorder-blocks -freorder-functions @gol
5748 -frerun-cse-after-loop @gol
5749 -fsched-interblock -fsched-spec @gol
5750 -fschedule-insns -fschedule-insns2 @gol
5751 -fstrict-aliasing -fstrict-overflow @gol
5752 -ftree-switch-conversion @gol
5756 Please note the warning under @option{-fgcse} about
5757 invoking @option{-O2} on programs that use computed gotos.
5761 Optimize yet more. @option{-O3} turns on all optimizations specified
5762 by @option{-O2} and also turns on the @option{-finline-functions},
5763 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5764 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5768 Reduce compilation time and make debugging produce the expected
5769 results. This is the default.
5773 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5774 do not typically increase code size. It also performs further
5775 optimizations designed to reduce code size.
5777 @option{-Os} disables the following optimization flags:
5778 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5779 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5780 -fprefetch-loop-arrays -ftree-vect-loop-version}
5782 If you use multiple @option{-O} options, with or without level numbers,
5783 the last such option is the one that is effective.
5786 Options of the form @option{-f@var{flag}} specify machine-independent
5787 flags. Most flags have both positive and negative forms; the negative
5788 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5789 below, only one of the forms is listed---the one you typically will
5790 use. You can figure out the other form by either removing @samp{no-}
5793 The following options control specific optimizations. They are either
5794 activated by @option{-O} options or are related to ones that are. You
5795 can use the following flags in the rare cases when ``fine-tuning'' of
5796 optimizations to be performed is desired.
5799 @item -fno-default-inline
5800 @opindex fno-default-inline
5801 Do not make member functions inline by default merely because they are
5802 defined inside the class scope (C++ only). Otherwise, when you specify
5803 @w{@option{-O}}, member functions defined inside class scope are compiled
5804 inline by default; i.e., you don't need to add @samp{inline} in front of
5805 the member function name.
5807 @item -fno-defer-pop
5808 @opindex fno-defer-pop
5809 Always pop the arguments to each function call as soon as that function
5810 returns. For machines which must pop arguments after a function call,
5811 the compiler normally lets arguments accumulate on the stack for several
5812 function calls and pops them all at once.
5814 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5816 @item -fforward-propagate
5817 @opindex fforward-propagate
5818 Perform a forward propagation pass on RTL@. The pass tries to combine two
5819 instructions and checks if the result can be simplified. If loop unrolling
5820 is active, two passes are performed and the second is scheduled after
5823 This option is enabled by default at optimization levels @option{-O},
5824 @option{-O2}, @option{-O3}, @option{-Os}.
5826 @item -fomit-frame-pointer
5827 @opindex fomit-frame-pointer
5828 Don't keep the frame pointer in a register for functions that
5829 don't need one. This avoids the instructions to save, set up and
5830 restore frame pointers; it also makes an extra register available
5831 in many functions. @strong{It also makes debugging impossible on
5834 On some machines, such as the VAX, this flag has no effect, because
5835 the standard calling sequence automatically handles the frame pointer
5836 and nothing is saved by pretending it doesn't exist. The
5837 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5838 whether a target machine supports this flag. @xref{Registers,,Register
5839 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5841 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5843 @item -foptimize-sibling-calls
5844 @opindex foptimize-sibling-calls
5845 Optimize sibling and tail recursive calls.
5847 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5851 Don't pay attention to the @code{inline} keyword. Normally this option
5852 is used to keep the compiler from expanding any functions inline.
5853 Note that if you are not optimizing, no functions can be expanded inline.
5855 @item -finline-small-functions
5856 @opindex finline-small-functions
5857 Integrate functions into their callers when their body is smaller than expected
5858 function call code (so overall size of program gets smaller). The compiler
5859 heuristically decides which functions are simple enough to be worth integrating
5862 Enabled at level @option{-O2}.
5864 @item -findirect-inlining
5865 @opindex findirect-inlining
5866 Inline also indirect calls that are discovered to be known at compile
5867 time thanks to previous inlining. This option has any effect only
5868 when inlining itself is turned on by the @option{-finline-functions}
5869 or @option{-finline-small-functions} options.
5871 Enabled at level @option{-O2}.
5873 @item -finline-functions
5874 @opindex finline-functions
5875 Integrate all simple functions into their callers. The compiler
5876 heuristically decides which functions are simple enough to be worth
5877 integrating in this way.
5879 If all calls to a given function are integrated, and the function is
5880 declared @code{static}, then the function is normally not output as
5881 assembler code in its own right.
5883 Enabled at level @option{-O3}.
5885 @item -finline-functions-called-once
5886 @opindex finline-functions-called-once
5887 Consider all @code{static} functions called once for inlining into their
5888 caller even if they are not marked @code{inline}. If a call to a given
5889 function is integrated, then the function is not output as assembler code
5892 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5894 @item -fearly-inlining
5895 @opindex fearly-inlining
5896 Inline functions marked by @code{always_inline} and functions whose body seems
5897 smaller than the function call overhead early before doing
5898 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5899 makes profiling significantly cheaper and usually inlining faster on programs
5900 having large chains of nested wrapper functions.
5906 Perform interprocedural scalar replacement of aggregates, removal of
5907 unused parameters and replacement of parameters passed by reference
5908 by parameters passed by value.
5910 Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
5912 @item -finline-limit=@var{n}
5913 @opindex finline-limit
5914 By default, GCC limits the size of functions that can be inlined. This flag
5915 allows coarse control of this limit. @var{n} is the size of functions that
5916 can be inlined in number of pseudo instructions.
5918 Inlining is actually controlled by a number of parameters, which may be
5919 specified individually by using @option{--param @var{name}=@var{value}}.
5920 The @option{-finline-limit=@var{n}} option sets some of these parameters
5924 @item max-inline-insns-single
5925 is set to @var{n}/2.
5926 @item max-inline-insns-auto
5927 is set to @var{n}/2.
5930 See below for a documentation of the individual
5931 parameters controlling inlining and for the defaults of these parameters.
5933 @emph{Note:} there may be no value to @option{-finline-limit} that results
5934 in default behavior.
5936 @emph{Note:} pseudo instruction represents, in this particular context, an
5937 abstract measurement of function's size. In no way does it represent a count
5938 of assembly instructions and as such its exact meaning might change from one
5939 release to an another.
5941 @item -fkeep-inline-functions
5942 @opindex fkeep-inline-functions
5943 In C, emit @code{static} functions that are declared @code{inline}
5944 into the object file, even if the function has been inlined into all
5945 of its callers. This switch does not affect functions using the
5946 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5947 inline functions into the object file.
5949 @item -fkeep-static-consts
5950 @opindex fkeep-static-consts
5951 Emit variables declared @code{static const} when optimization isn't turned
5952 on, even if the variables aren't referenced.
5954 GCC enables this option by default. If you want to force the compiler to
5955 check if the variable was referenced, regardless of whether or not
5956 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5958 @item -fmerge-constants
5959 @opindex fmerge-constants
5960 Attempt to merge identical constants (string constants and floating point
5961 constants) across compilation units.
5963 This option is the default for optimized compilation if the assembler and
5964 linker support it. Use @option{-fno-merge-constants} to inhibit this
5967 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5969 @item -fmerge-all-constants
5970 @opindex fmerge-all-constants
5971 Attempt to merge identical constants and identical variables.
5973 This option implies @option{-fmerge-constants}. In addition to
5974 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5975 arrays or initialized constant variables with integral or floating point
5976 types. Languages like C or C++ require each variable, including multiple
5977 instances of the same variable in recursive calls, to have distinct locations,
5978 so using this option will result in non-conforming
5981 @item -fmodulo-sched
5982 @opindex fmodulo-sched
5983 Perform swing modulo scheduling immediately before the first scheduling
5984 pass. This pass looks at innermost loops and reorders their
5985 instructions by overlapping different iterations.
5987 @item -fmodulo-sched-allow-regmoves
5988 @opindex fmodulo-sched-allow-regmoves
5989 Perform more aggressive SMS based modulo scheduling with register moves
5990 allowed. By setting this flag certain anti-dependences edges will be
5991 deleted which will trigger the generation of reg-moves based on the
5992 life-range analysis. This option is effective only with
5993 @option{-fmodulo-sched} enabled.
5995 @item -fno-branch-count-reg
5996 @opindex fno-branch-count-reg
5997 Do not use ``decrement and branch'' instructions on a count register,
5998 but instead generate a sequence of instructions that decrement a
5999 register, compare it against zero, then branch based upon the result.
6000 This option is only meaningful on architectures that support such
6001 instructions, which include x86, PowerPC, IA-64 and S/390.
6003 The default is @option{-fbranch-count-reg}.
6005 @item -fno-function-cse
6006 @opindex fno-function-cse
6007 Do not put function addresses in registers; make each instruction that
6008 calls a constant function contain the function's address explicitly.
6010 This option results in less efficient code, but some strange hacks
6011 that alter the assembler output may be confused by the optimizations
6012 performed when this option is not used.
6014 The default is @option{-ffunction-cse}
6016 @item -fno-zero-initialized-in-bss
6017 @opindex fno-zero-initialized-in-bss
6018 If the target supports a BSS section, GCC by default puts variables that
6019 are initialized to zero into BSS@. This can save space in the resulting
6022 This option turns off this behavior because some programs explicitly
6023 rely on variables going to the data section. E.g., so that the
6024 resulting executable can find the beginning of that section and/or make
6025 assumptions based on that.
6027 The default is @option{-fzero-initialized-in-bss}.
6029 @item -fmudflap -fmudflapth -fmudflapir
6033 @cindex bounds checking
6035 For front-ends that support it (C and C++), instrument all risky
6036 pointer/array dereferencing operations, some standard library
6037 string/heap functions, and some other associated constructs with
6038 range/validity tests. Modules so instrumented should be immune to
6039 buffer overflows, invalid heap use, and some other classes of C/C++
6040 programming errors. The instrumentation relies on a separate runtime
6041 library (@file{libmudflap}), which will be linked into a program if
6042 @option{-fmudflap} is given at link time. Run-time behavior of the
6043 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
6044 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
6047 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
6048 link if your program is multi-threaded. Use @option{-fmudflapir}, in
6049 addition to @option{-fmudflap} or @option{-fmudflapth}, if
6050 instrumentation should ignore pointer reads. This produces less
6051 instrumentation (and therefore faster execution) and still provides
6052 some protection against outright memory corrupting writes, but allows
6053 erroneously read data to propagate within a program.
6055 @item -fthread-jumps
6056 @opindex fthread-jumps
6057 Perform optimizations where we check to see if a jump branches to a
6058 location where another comparison subsumed by the first is found. If
6059 so, the first branch is redirected to either the destination of the
6060 second branch or a point immediately following it, depending on whether
6061 the condition is known to be true or false.
6063 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6065 @item -fsplit-wide-types
6066 @opindex fsplit-wide-types
6067 When using a type that occupies multiple registers, such as @code{long
6068 long} on a 32-bit system, split the registers apart and allocate them
6069 independently. This normally generates better code for those types,
6070 but may make debugging more difficult.
6072 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
6075 @item -fcse-follow-jumps
6076 @opindex fcse-follow-jumps
6077 In common subexpression elimination (CSE), scan through jump instructions
6078 when the target of the jump is not reached by any other path. For
6079 example, when CSE encounters an @code{if} statement with an
6080 @code{else} clause, CSE will follow the jump when the condition
6083 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6085 @item -fcse-skip-blocks
6086 @opindex fcse-skip-blocks
6087 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
6088 follow jumps which conditionally skip over blocks. When CSE
6089 encounters a simple @code{if} statement with no else clause,
6090 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
6091 body of the @code{if}.
6093 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6095 @item -frerun-cse-after-loop
6096 @opindex frerun-cse-after-loop
6097 Re-run common subexpression elimination after loop optimizations has been
6100 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6104 Perform a global common subexpression elimination pass.
6105 This pass also performs global constant and copy propagation.
6107 @emph{Note:} When compiling a program using computed gotos, a GCC
6108 extension, you may get better runtime performance if you disable
6109 the global common subexpression elimination pass by adding
6110 @option{-fno-gcse} to the command line.
6112 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6116 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
6117 attempt to move loads which are only killed by stores into themselves. This
6118 allows a loop containing a load/store sequence to be changed to a load outside
6119 the loop, and a copy/store within the loop.
6121 Enabled by default when gcse is enabled.
6125 When @option{-fgcse-sm} is enabled, a store motion pass is run after
6126 global common subexpression elimination. This pass will attempt to move
6127 stores out of loops. When used in conjunction with @option{-fgcse-lm},
6128 loops containing a load/store sequence can be changed to a load before
6129 the loop and a store after the loop.
6131 Not enabled at any optimization level.
6135 When @option{-fgcse-las} is enabled, the global common subexpression
6136 elimination pass eliminates redundant loads that come after stores to the
6137 same memory location (both partial and full redundancies).
6139 Not enabled at any optimization level.
6141 @item -fgcse-after-reload
6142 @opindex fgcse-after-reload
6143 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
6144 pass is performed after reload. The purpose of this pass is to cleanup
6147 @item -funsafe-loop-optimizations
6148 @opindex funsafe-loop-optimizations
6149 If given, the loop optimizer will assume that loop indices do not
6150 overflow, and that the loops with nontrivial exit condition are not
6151 infinite. This enables a wider range of loop optimizations even if
6152 the loop optimizer itself cannot prove that these assumptions are valid.
6153 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
6154 if it finds this kind of loop.
6156 @item -fcrossjumping
6157 @opindex fcrossjumping
6158 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
6159 resulting code may or may not perform better than without cross-jumping.
6161 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6163 @item -fauto-inc-dec
6164 @opindex fauto-inc-dec
6165 Combine increments or decrements of addresses with memory accesses.
6166 This pass is always skipped on architectures that do not have
6167 instructions to support this. Enabled by default at @option{-O} and
6168 higher on architectures that support this.
6172 Perform dead code elimination (DCE) on RTL@.
6173 Enabled by default at @option{-O} and higher.
6177 Perform dead store elimination (DSE) on RTL@.
6178 Enabled by default at @option{-O} and higher.
6180 @item -fif-conversion
6181 @opindex fif-conversion
6182 Attempt to transform conditional jumps into branch-less equivalents. This
6183 include use of conditional moves, min, max, set flags and abs instructions, and
6184 some tricks doable by standard arithmetics. The use of conditional execution
6185 on chips where it is available is controlled by @code{if-conversion2}.
6187 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6189 @item -fif-conversion2
6190 @opindex fif-conversion2
6191 Use conditional execution (where available) to transform conditional jumps into
6192 branch-less equivalents.
6194 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6196 @item -fdelete-null-pointer-checks
6197 @opindex fdelete-null-pointer-checks
6198 Assume that programs cannot safely dereference null pointers, and that
6199 no code or data element resides there. This enables simple constant
6200 folding optimizations at all optimization levels. In addition, other
6201 optimization passes in GCC use this flag to control global dataflow
6202 analyses that eliminate useless checks for null pointers; these assume
6203 that if a pointer is checked after it has already been dereferenced,
6206 Note however that in some environments this assumption is not true.
6207 Use @option{-fno-delete-null-pointer-checks} to disable this optimization
6208 for programs which depend on that behavior.
6210 Some targets, especially embedded ones, disable this option at all levels.
6211 Otherwise it is enabled at all levels: @option{-O0}, @option{-O1},
6212 @option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information
6213 are enabled independently at different optimization levels.
6215 @item -fexpensive-optimizations
6216 @opindex fexpensive-optimizations
6217 Perform a number of minor optimizations that are relatively expensive.
6219 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6221 @item -foptimize-register-move
6223 @opindex foptimize-register-move
6225 Attempt to reassign register numbers in move instructions and as
6226 operands of other simple instructions in order to maximize the amount of
6227 register tying. This is especially helpful on machines with two-operand
6230 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
6233 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6235 @item -fira-algorithm=@var{algorithm}
6236 Use specified coloring algorithm for the integrated register
6237 allocator. The @var{algorithm} argument should be @code{priority} or
6238 @code{CB}. The first algorithm specifies Chow's priority coloring,
6239 the second one specifies Chaitin-Briggs coloring. The second
6240 algorithm can be unimplemented for some architectures. If it is
6241 implemented, it is the default because Chaitin-Briggs coloring as a
6242 rule generates a better code.
6244 @item -fira-region=@var{region}
6245 Use specified regions for the integrated register allocator. The
6246 @var{region} argument should be one of @code{all}, @code{mixed}, or
6247 @code{one}. The first value means using all loops as register
6248 allocation regions, the second value which is the default means using
6249 all loops except for loops with small register pressure as the
6250 regions, and third one means using all function as a single region.
6251 The first value can give best result for machines with small size and
6252 irregular register set, the third one results in faster and generates
6253 decent code and the smallest size code, and the default value usually
6254 give the best results in most cases and for most architectures.
6256 @item -fira-coalesce
6257 @opindex fira-coalesce
6258 Do optimistic register coalescing. This option might be profitable for
6259 architectures with big regular register files.
6261 @item -fira-loop-pressure
6262 @opindex fira-loop-pressure
6263 Use IRA to evaluate register pressure in loops for decision to move
6264 loop invariants. Usage of this option usually results in generation
6265 of faster and smaller code on machines with big register files (>= 32
6266 registers) but it can slow compiler down.
6268 This option is enabled at level @option{-O3} for some targets.
6270 @item -fno-ira-share-save-slots
6271 @opindex fno-ira-share-save-slots
6272 Switch off sharing stack slots used for saving call used hard
6273 registers living through a call. Each hard register will get a
6274 separate stack slot and as a result function stack frame will be
6277 @item -fno-ira-share-spill-slots
6278 @opindex fno-ira-share-spill-slots
6279 Switch off sharing stack slots allocated for pseudo-registers. Each
6280 pseudo-register which did not get a hard register will get a separate
6281 stack slot and as a result function stack frame will be bigger.
6283 @item -fira-verbose=@var{n}
6284 @opindex fira-verbose
6285 Set up how verbose dump file for the integrated register allocator
6286 will be. Default value is 5. If the value is greater or equal to 10,
6287 the dump file will be stderr as if the value were @var{n} minus 10.
6289 @item -fdelayed-branch
6290 @opindex fdelayed-branch
6291 If supported for the target machine, attempt to reorder instructions
6292 to exploit instruction slots available after delayed branch
6295 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6297 @item -fschedule-insns
6298 @opindex fschedule-insns
6299 If supported for the target machine, attempt to reorder instructions to
6300 eliminate execution stalls due to required data being unavailable. This
6301 helps machines that have slow floating point or memory load instructions
6302 by allowing other instructions to be issued until the result of the load
6303 or floating point instruction is required.
6305 Enabled at levels @option{-O2}, @option{-O3}.
6307 @item -fschedule-insns2
6308 @opindex fschedule-insns2
6309 Similar to @option{-fschedule-insns}, but requests an additional pass of
6310 instruction scheduling after register allocation has been done. This is
6311 especially useful on machines with a relatively small number of
6312 registers and where memory load instructions take more than one cycle.
6314 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6316 @item -fno-sched-interblock
6317 @opindex fno-sched-interblock
6318 Don't schedule instructions across basic blocks. This is normally
6319 enabled by default when scheduling before register allocation, i.e.@:
6320 with @option{-fschedule-insns} or at @option{-O2} or higher.
6322 @item -fno-sched-spec
6323 @opindex fno-sched-spec
6324 Don't allow speculative motion of non-load instructions. This is normally
6325 enabled by default when scheduling before register allocation, i.e.@:
6326 with @option{-fschedule-insns} or at @option{-O2} or higher.
6328 @item -fsched-pressure
6329 @opindex fsched-pressure
6330 Enable register pressure sensitive insn scheduling before the register
6331 allocation. This only makes sense when scheduling before register
6332 allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
6333 @option{-O2} or higher. Usage of this option can improve the
6334 generated code and decrease its size by preventing register pressure
6335 increase above the number of available hard registers and as a
6336 consequence register spills in the register allocation.
6338 @item -fsched-spec-load
6339 @opindex fsched-spec-load
6340 Allow speculative motion of some load instructions. This only makes
6341 sense when scheduling before register allocation, i.e.@: with
6342 @option{-fschedule-insns} or at @option{-O2} or higher.
6344 @item -fsched-spec-load-dangerous
6345 @opindex fsched-spec-load-dangerous
6346 Allow speculative motion of more load instructions. This only makes
6347 sense when scheduling before register allocation, i.e.@: with
6348 @option{-fschedule-insns} or at @option{-O2} or higher.
6350 @item -fsched-stalled-insns
6351 @itemx -fsched-stalled-insns=@var{n}
6352 @opindex fsched-stalled-insns
6353 Define how many insns (if any) can be moved prematurely from the queue
6354 of stalled insns into the ready list, during the second scheduling pass.
6355 @option{-fno-sched-stalled-insns} means that no insns will be moved
6356 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
6357 on how many queued insns can be moved prematurely.
6358 @option{-fsched-stalled-insns} without a value is equivalent to
6359 @option{-fsched-stalled-insns=1}.
6361 @item -fsched-stalled-insns-dep
6362 @itemx -fsched-stalled-insns-dep=@var{n}
6363 @opindex fsched-stalled-insns-dep
6364 Define how many insn groups (cycles) will be examined for a dependency
6365 on a stalled insn that is candidate for premature removal from the queue
6366 of stalled insns. This has an effect only during the second scheduling pass,
6367 and only if @option{-fsched-stalled-insns} is used.
6368 @option{-fno-sched-stalled-insns-dep} is equivalent to
6369 @option{-fsched-stalled-insns-dep=0}.
6370 @option{-fsched-stalled-insns-dep} without a value is equivalent to
6371 @option{-fsched-stalled-insns-dep=1}.
6373 @item -fsched2-use-superblocks
6374 @opindex fsched2-use-superblocks
6375 When scheduling after register allocation, do use superblock scheduling
6376 algorithm. Superblock scheduling allows motion across basic block boundaries
6377 resulting on faster schedules. This option is experimental, as not all machine
6378 descriptions used by GCC model the CPU closely enough to avoid unreliable
6379 results from the algorithm.
6381 This only makes sense when scheduling after register allocation, i.e.@: with
6382 @option{-fschedule-insns2} or at @option{-O2} or higher.
6384 @item -fsched-group-heuristic
6385 @opindex fsched-group-heuristic
6386 Enable the group heuristic in the scheduler. This heuristic favors
6387 the instruction that belongs to a schedule group. This is enabled
6388 by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
6389 or @option{-fschedule-insns2} or at @option{-O2} or higher.
6391 @item -fsched-critical-path-heuristic
6392 @opindex fsched-critical-path-heuristic
6393 Enable the critical-path heuristic in the scheduler. This heuristic favors
6394 instructions on the critical path. This is enabled by default when
6395 scheduling is enabled, i.e.@: with @option{-fschedule-insns}
6396 or @option{-fschedule-insns2} or at @option{-O2} or higher.
6398 @item -fsched-spec-insn-heuristic
6399 @opindex fsched-spec-insn-heuristic
6400 Enable the speculative instruction heuristic in the scheduler. This
6401 heuristic favors speculative instructions with greater dependency weakness.
6402 This is enabled by default when scheduling is enabled, i.e.@:
6403 with @option{-fschedule-insns} or @option{-fschedule-insns2}
6404 or at @option{-O2} or higher.
6406 @item -fsched-rank-heuristic
6407 @opindex fsched-rank-heuristic
6408 Enable the rank heuristic in the scheduler. This heuristic favors
6409 the instruction belonging to a basic block with greater size or frequency.
6410 This is enabled by default when scheduling is enabled, i.e.@:
6411 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6412 at @option{-O2} or higher.
6414 @item -fsched-last-insn-heuristic
6415 @opindex fsched-last-insn-heuristic
6416 Enable the last-instruction heuristic in the scheduler. This heuristic
6417 favors the instruction that is less dependent on the last instruction
6418 scheduled. This is enabled by default when scheduling is enabled,
6419 i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6420 at @option{-O2} or higher.
6422 @item -fsched-dep-count-heuristic
6423 @opindex fsched-dep-count-heuristic
6424 Enable the dependent-count heuristic in the scheduler. This heuristic
6425 favors the instruction that has more instructions depending on it.
6426 This is enabled by default when scheduling is enabled, i.e.@:
6427 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6428 at @option{-O2} or higher.
6430 @item -fsched2-use-traces
6431 @opindex fsched2-use-traces
6432 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
6433 allocation and additionally perform code duplication in order to increase the
6434 size of superblocks using tracer pass. See @option{-ftracer} for details on
6437 This mode should produce faster but significantly longer programs. Also
6438 without @option{-fbranch-probabilities} the traces constructed may not
6439 match the reality and hurt the performance. This only makes
6440 sense when scheduling after register allocation, i.e.@: with
6441 @option{-fschedule-insns2} or at @option{-O2} or higher.
6443 @item -freschedule-modulo-scheduled-loops
6444 @opindex freschedule-modulo-scheduled-loops
6445 The modulo scheduling comes before the traditional scheduling, if a loop
6446 was modulo scheduled we may want to prevent the later scheduling passes
6447 from changing its schedule, we use this option to control that.
6449 @item -fselective-scheduling
6450 @opindex fselective-scheduling
6451 Schedule instructions using selective scheduling algorithm. Selective
6452 scheduling runs instead of the first scheduler pass.
6454 @item -fselective-scheduling2
6455 @opindex fselective-scheduling2
6456 Schedule instructions using selective scheduling algorithm. Selective
6457 scheduling runs instead of the second scheduler pass.
6459 @item -fsel-sched-pipelining
6460 @opindex fsel-sched-pipelining
6461 Enable software pipelining of innermost loops during selective scheduling.
6462 This option has no effect until one of @option{-fselective-scheduling} or
6463 @option{-fselective-scheduling2} is turned on.
6465 @item -fsel-sched-pipelining-outer-loops
6466 @opindex fsel-sched-pipelining-outer-loops
6467 When pipelining loops during selective scheduling, also pipeline outer loops.
6468 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
6470 @item -fcaller-saves
6471 @opindex fcaller-saves
6472 Enable values to be allocated in registers that will be clobbered by
6473 function calls, by emitting extra instructions to save and restore the
6474 registers around such calls. Such allocation is done only when it
6475 seems to result in better code than would otherwise be produced.
6477 This option is always enabled by default on certain machines, usually
6478 those which have no call-preserved registers to use instead.
6480 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6482 @item -fconserve-stack
6483 @opindex fconserve-stack
6484 Attempt to minimize stack usage. The compiler will attempt to use less
6485 stack space, even if that makes the program slower. This option
6486 implies setting the @option{large-stack-frame} parameter to 100
6487 and the @option{large-stack-frame-growth} parameter to 400.
6489 @item -ftree-reassoc
6490 @opindex ftree-reassoc
6491 Perform reassociation on trees. This flag is enabled by default
6492 at @option{-O} and higher.
6496 Perform partial redundancy elimination (PRE) on trees. This flag is
6497 enabled by default at @option{-O2} and @option{-O3}.
6499 @item -ftree-forwprop
6500 @opindex ftree-forwprop
6501 Perform forward propagation on trees. This flag is enabled by default
6502 at @option{-O} and higher.
6506 Perform full redundancy elimination (FRE) on trees. The difference
6507 between FRE and PRE is that FRE only considers expressions
6508 that are computed on all paths leading to the redundant computation.
6509 This analysis is faster than PRE, though it exposes fewer redundancies.
6510 This flag is enabled by default at @option{-O} and higher.
6512 @item -ftree-phiprop
6513 @opindex ftree-phiprop
6514 Perform hoisting of loads from conditional pointers on trees. This
6515 pass is enabled by default at @option{-O} and higher.
6517 @item -ftree-copy-prop
6518 @opindex ftree-copy-prop
6519 Perform copy propagation on trees. This pass eliminates unnecessary
6520 copy operations. This flag is enabled by default at @option{-O} and
6523 @item -fipa-pure-const
6524 @opindex fipa-pure-const
6525 Discover which functions are pure or constant.
6526 Enabled by default at @option{-O} and higher.
6528 @item -fipa-reference
6529 @opindex fipa-reference
6530 Discover which static variables do not escape cannot escape the
6532 Enabled by default at @option{-O} and higher.
6534 @item -fipa-struct-reorg
6535 @opindex fipa-struct-reorg
6536 Perform structure reorganization optimization, that change C-like structures
6537 layout in order to better utilize spatial locality. This transformation is
6538 affective for programs containing arrays of structures. Available in two
6539 compilation modes: profile-based (enabled with @option{-fprofile-generate})
6540 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
6541 to provide the safety of this transformation. It works only in whole program
6542 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
6543 enabled. Structures considered @samp{cold} by this transformation are not
6544 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
6546 With this flag, the program debug info reflects a new structure layout.
6550 Perform interprocedural pointer analysis. This option is experimental
6551 and does not affect generated code.
6555 Perform interprocedural constant propagation.
6556 This optimization analyzes the program to determine when values passed
6557 to functions are constants and then optimizes accordingly.
6558 This optimization can substantially increase performance
6559 if the application has constants passed to functions.
6560 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
6562 @item -fipa-cp-clone
6563 @opindex fipa-cp-clone
6564 Perform function cloning to make interprocedural constant propagation stronger.
6565 When enabled, interprocedural constant propagation will perform function cloning
6566 when externally visible function can be called with constant arguments.
6567 Because this optimization can create multiple copies of functions,
6568 it may significantly increase code size
6569 (see @option{--param ipcp-unit-growth=@var{value}}).
6570 This flag is enabled by default at @option{-O3}.
6572 @item -fipa-matrix-reorg
6573 @opindex fipa-matrix-reorg
6574 Perform matrix flattening and transposing.
6575 Matrix flattening tries to replace an @math{m}-dimensional matrix
6576 with its equivalent @math{n}-dimensional matrix, where @math{n < m}.
6577 This reduces the level of indirection needed for accessing the elements
6578 of the matrix. The second optimization is matrix transposing that
6579 attempts to change the order of the matrix's dimensions in order to
6580 improve cache locality.
6581 Both optimizations need the @option{-fwhole-program} flag.
6582 Transposing is enabled only if profiling information is available.
6586 Perform forward store motion on trees. This flag is
6587 enabled by default at @option{-O} and higher.
6591 Perform sparse conditional constant propagation (CCP) on trees. This
6592 pass only operates on local scalar variables and is enabled by default
6593 at @option{-O} and higher.
6595 @item -ftree-switch-conversion
6596 Perform conversion of simple initializations in a switch to
6597 initializations from a scalar array. This flag is enabled by default
6598 at @option{-O2} and higher.
6602 Perform dead code elimination (DCE) on trees. This flag is enabled by
6603 default at @option{-O} and higher.
6605 @item -ftree-builtin-call-dce
6606 @opindex ftree-builtin-call-dce
6607 Perform conditional dead code elimination (DCE) for calls to builtin functions
6608 that may set @code{errno} but are otherwise side-effect free. This flag is
6609 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6612 @item -ftree-dominator-opts
6613 @opindex ftree-dominator-opts
6614 Perform a variety of simple scalar cleanups (constant/copy
6615 propagation, redundancy elimination, range propagation and expression
6616 simplification) based on a dominator tree traversal. This also
6617 performs jump threading (to reduce jumps to jumps). This flag is
6618 enabled by default at @option{-O} and higher.
6622 Perform dead store elimination (DSE) on trees. A dead store is a store into
6623 a memory location which will later be overwritten by another store without
6624 any intervening loads. In this case the earlier store can be deleted. This
6625 flag is enabled by default at @option{-O} and higher.
6629 Perform loop header copying on trees. This is beneficial since it increases
6630 effectiveness of code motion optimizations. It also saves one jump. This flag
6631 is enabled by default at @option{-O} and higher. It is not enabled
6632 for @option{-Os}, since it usually increases code size.
6634 @item -ftree-loop-optimize
6635 @opindex ftree-loop-optimize
6636 Perform loop optimizations on trees. This flag is enabled by default
6637 at @option{-O} and higher.
6639 @item -ftree-loop-linear
6640 @opindex ftree-loop-linear
6641 Perform linear loop transformations on tree. This flag can improve cache
6642 performance and allow further loop optimizations to take place.
6644 @item -floop-interchange
6645 Perform loop interchange transformations on loops. Interchanging two
6646 nested loops switches the inner and outer loops. For example, given a
6651 A(J, I) = A(J, I) * C
6655 loop interchange will transform the loop as if the user had written:
6659 A(J, I) = A(J, I) * C
6663 which can be beneficial when @code{N} is larger than the caches,
6664 because in Fortran, the elements of an array are stored in memory
6665 contiguously by column, and the original loop iterates over rows,
6666 potentially creating at each access a cache miss. This optimization
6667 applies to all the languages supported by GCC and is not limited to
6668 Fortran. To use this code transformation, GCC has to be configured
6669 with @option{--with-ppl} and @option{--with-cloog} to enable the
6670 Graphite loop transformation infrastructure.
6672 @item -floop-strip-mine
6673 Perform loop strip mining transformations on loops. Strip mining
6674 splits a loop into two nested loops. The outer loop has strides
6675 equal to the strip size and the inner loop has strides of the
6676 original loop within a strip. For example, given a loop like:
6682 loop strip mining will transform the loop as if the user had written:
6685 DO I = II, min (II + 3, N)
6690 This optimization applies to all the languages supported by GCC and is
6691 not limited to Fortran. To use this code transformation, GCC has to
6692 be configured with @option{--with-ppl} and @option{--with-cloog} to
6693 enable the Graphite loop transformation infrastructure.
6696 Perform loop blocking transformations on loops. Blocking strip mines
6697 each loop in the loop nest such that the memory accesses of the
6698 element loops fit inside caches. For example, given a loop like:
6702 A(J, I) = B(I) + C(J)
6706 loop blocking will transform the loop as if the user had written:
6710 DO I = II, min (II + 63, N)
6711 DO J = JJ, min (JJ + 63, M)
6712 A(J, I) = B(I) + C(J)
6718 which can be beneficial when @code{M} is larger than the caches,
6719 because the innermost loop will iterate over a smaller amount of data
6720 that can be kept in the caches. This optimization applies to all the
6721 languages supported by GCC and is not limited to Fortran. To use this
6722 code transformation, GCC has to be configured with @option{--with-ppl}
6723 and @option{--with-cloog} to enable the Graphite loop transformation
6726 @item -fgraphite-identity
6727 @opindex fgraphite-identity
6728 Enable the identity transformation for graphite. For every SCoP we generate
6729 the polyhedral representation and transform it back to gimple. Using
6730 @option{-fgraphite-identity} we can check the costs or benefits of the
6731 GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
6732 are also performed by the code generator CLooG, like index splitting and
6733 dead code elimination in loops.
6735 @item -floop-parallelize-all
6736 Use the Graphite data dependence analysis to identify loops that can
6737 be parallelized. Parallelize all the loops that can be analyzed to
6738 not contain loop carried dependences without checking that it is
6739 profitable to parallelize the loops.
6741 @item -fcheck-data-deps
6742 @opindex fcheck-data-deps
6743 Compare the results of several data dependence analyzers. This option
6744 is used for debugging the data dependence analyzers.
6746 @item -ftree-loop-distribution
6747 Perform loop distribution. This flag can improve cache performance on
6748 big loop bodies and allow further loop optimizations, like
6749 parallelization or vectorization, to take place. For example, the loop
6766 @item -ftree-loop-im
6767 @opindex ftree-loop-im
6768 Perform loop invariant motion on trees. This pass moves only invariants that
6769 would be hard to handle at RTL level (function calls, operations that expand to
6770 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
6771 operands of conditions that are invariant out of the loop, so that we can use
6772 just trivial invariantness analysis in loop unswitching. The pass also includes
6775 @item -ftree-loop-ivcanon
6776 @opindex ftree-loop-ivcanon
6777 Create a canonical counter for number of iterations in the loop for that
6778 determining number of iterations requires complicated analysis. Later
6779 optimizations then may determine the number easily. Useful especially
6780 in connection with unrolling.
6784 Perform induction variable optimizations (strength reduction, induction
6785 variable merging and induction variable elimination) on trees.
6787 @item -ftree-parallelize-loops=n
6788 @opindex ftree-parallelize-loops
6789 Parallelize loops, i.e., split their iteration space to run in n threads.
6790 This is only possible for loops whose iterations are independent
6791 and can be arbitrarily reordered. The optimization is only
6792 profitable on multiprocessor machines, for loops that are CPU-intensive,
6793 rather than constrained e.g.@: by memory bandwidth. This option
6794 implies @option{-pthread}, and thus is only supported on targets
6795 that have support for @option{-pthread}.
6799 Perform function-local points-to analysis on trees. This flag is
6800 enabled by default at @option{-O} and higher.
6804 Perform scalar replacement of aggregates. This pass replaces structure
6805 references with scalars to prevent committing structures to memory too
6806 early. This flag is enabled by default at @option{-O} and higher.
6808 @item -ftree-copyrename
6809 @opindex ftree-copyrename
6810 Perform copy renaming on trees. This pass attempts to rename compiler
6811 temporaries to other variables at copy locations, usually resulting in
6812 variable names which more closely resemble the original variables. This flag
6813 is enabled by default at @option{-O} and higher.
6817 Perform temporary expression replacement during the SSA->normal phase. Single
6818 use/single def temporaries are replaced at their use location with their
6819 defining expression. This results in non-GIMPLE code, but gives the expanders
6820 much more complex trees to work on resulting in better RTL generation. This is
6821 enabled by default at @option{-O} and higher.
6823 @item -ftree-vectorize
6824 @opindex ftree-vectorize
6825 Perform loop vectorization on trees. This flag is enabled by default at
6828 @item -ftree-slp-vectorize
6829 @opindex ftree-slp-vectorize
6830 Perform basic block vectorization on trees. This flag is enabled by default at
6831 @option{-O3} and when @option{-ftree-vectorize} is enabled.
6833 @item -ftree-vect-loop-version
6834 @opindex ftree-vect-loop-version
6835 Perform loop versioning when doing loop vectorization on trees. When a loop
6836 appears to be vectorizable except that data alignment or data dependence cannot
6837 be determined at compile time then vectorized and non-vectorized versions of
6838 the loop are generated along with runtime checks for alignment or dependence
6839 to control which version is executed. This option is enabled by default
6840 except at level @option{-Os} where it is disabled.
6842 @item -fvect-cost-model
6843 @opindex fvect-cost-model
6844 Enable cost model for vectorization.
6848 Perform Value Range Propagation on trees. This is similar to the
6849 constant propagation pass, but instead of values, ranges of values are
6850 propagated. This allows the optimizers to remove unnecessary range
6851 checks like array bound checks and null pointer checks. This is
6852 enabled by default at @option{-O2} and higher. Null pointer check
6853 elimination is only done if @option{-fdelete-null-pointer-checks} is
6858 Perform tail duplication to enlarge superblock size. This transformation
6859 simplifies the control flow of the function allowing other optimizations to do
6862 @item -funroll-loops
6863 @opindex funroll-loops
6864 Unroll loops whose number of iterations can be determined at compile
6865 time or upon entry to the loop. @option{-funroll-loops} implies
6866 @option{-frerun-cse-after-loop}. This option makes code larger,
6867 and may or may not make it run faster.
6869 @item -funroll-all-loops
6870 @opindex funroll-all-loops
6871 Unroll all loops, even if their number of iterations is uncertain when
6872 the loop is entered. This usually makes programs run more slowly.
6873 @option{-funroll-all-loops} implies the same options as
6874 @option{-funroll-loops},
6876 @item -fsplit-ivs-in-unroller
6877 @opindex fsplit-ivs-in-unroller
6878 Enables expressing of values of induction variables in later iterations
6879 of the unrolled loop using the value in the first iteration. This breaks
6880 long dependency chains, thus improving efficiency of the scheduling passes.
6882 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6883 same effect. However in cases the loop body is more complicated than
6884 a single basic block, this is not reliable. It also does not work at all
6885 on some of the architectures due to restrictions in the CSE pass.
6887 This optimization is enabled by default.
6889 @item -fvariable-expansion-in-unroller
6890 @opindex fvariable-expansion-in-unroller
6891 With this option, the compiler will create multiple copies of some
6892 local variables when unrolling a loop which can result in superior code.
6894 @item -fpredictive-commoning
6895 @opindex fpredictive-commoning
6896 Perform predictive commoning optimization, i.e., reusing computations
6897 (especially memory loads and stores) performed in previous
6898 iterations of loops.
6900 This option is enabled at level @option{-O3}.
6902 @item -fprefetch-loop-arrays
6903 @opindex fprefetch-loop-arrays
6904 If supported by the target machine, generate instructions to prefetch
6905 memory to improve the performance of loops that access large arrays.
6907 This option may generate better or worse code; results are highly
6908 dependent on the structure of loops within the source code.
6910 Disabled at level @option{-Os}.
6913 @itemx -fno-peephole2
6914 @opindex fno-peephole
6915 @opindex fno-peephole2
6916 Disable any machine-specific peephole optimizations. The difference
6917 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6918 are implemented in the compiler; some targets use one, some use the
6919 other, a few use both.
6921 @option{-fpeephole} is enabled by default.
6922 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6924 @item -fno-guess-branch-probability
6925 @opindex fno-guess-branch-probability
6926 Do not guess branch probabilities using heuristics.
6928 GCC will use heuristics to guess branch probabilities if they are
6929 not provided by profiling feedback (@option{-fprofile-arcs}). These
6930 heuristics are based on the control flow graph. If some branch probabilities
6931 are specified by @samp{__builtin_expect}, then the heuristics will be
6932 used to guess branch probabilities for the rest of the control flow graph,
6933 taking the @samp{__builtin_expect} info into account. The interactions
6934 between the heuristics and @samp{__builtin_expect} can be complex, and in
6935 some cases, it may be useful to disable the heuristics so that the effects
6936 of @samp{__builtin_expect} are easier to understand.
6938 The default is @option{-fguess-branch-probability} at levels
6939 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6941 @item -freorder-blocks
6942 @opindex freorder-blocks
6943 Reorder basic blocks in the compiled function in order to reduce number of
6944 taken branches and improve code locality.
6946 Enabled at levels @option{-O2}, @option{-O3}.
6948 @item -freorder-blocks-and-partition
6949 @opindex freorder-blocks-and-partition
6950 In addition to reordering basic blocks in the compiled function, in order
6951 to reduce number of taken branches, partitions hot and cold basic blocks
6952 into separate sections of the assembly and .o files, to improve
6953 paging and cache locality performance.
6955 This optimization is automatically turned off in the presence of
6956 exception handling, for linkonce sections, for functions with a user-defined
6957 section attribute and on any architecture that does not support named
6960 @item -freorder-functions
6961 @opindex freorder-functions
6962 Reorder functions in the object file in order to
6963 improve code locality. This is implemented by using special
6964 subsections @code{.text.hot} for most frequently executed functions and
6965 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6966 the linker so object file format must support named sections and linker must
6967 place them in a reasonable way.
6969 Also profile feedback must be available in to make this option effective. See
6970 @option{-fprofile-arcs} for details.
6972 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6974 @item -fstrict-aliasing
6975 @opindex fstrict-aliasing
6976 Allow the compiler to assume the strictest aliasing rules applicable to
6977 the language being compiled. For C (and C++), this activates
6978 optimizations based on the type of expressions. In particular, an
6979 object of one type is assumed never to reside at the same address as an
6980 object of a different type, unless the types are almost the same. For
6981 example, an @code{unsigned int} can alias an @code{int}, but not a
6982 @code{void*} or a @code{double}. A character type may alias any other
6985 @anchor{Type-punning}Pay special attention to code like this:
6998 The practice of reading from a different union member than the one most
6999 recently written to (called ``type-punning'') is common. Even with
7000 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
7001 is accessed through the union type. So, the code above will work as
7002 expected. @xref{Structures unions enumerations and bit-fields
7003 implementation}. However, this code might not:
7014 Similarly, access by taking the address, casting the resulting pointer
7015 and dereferencing the result has undefined behavior, even if the cast
7016 uses a union type, e.g.:
7020 return ((union a_union *) &d)->i;
7024 The @option{-fstrict-aliasing} option is enabled at levels
7025 @option{-O2}, @option{-O3}, @option{-Os}.
7027 @item -fstrict-overflow
7028 @opindex fstrict-overflow
7029 Allow the compiler to assume strict signed overflow rules, depending
7030 on the language being compiled. For C (and C++) this means that
7031 overflow when doing arithmetic with signed numbers is undefined, which
7032 means that the compiler may assume that it will not happen. This
7033 permits various optimizations. For example, the compiler will assume
7034 that an expression like @code{i + 10 > i} will always be true for
7035 signed @code{i}. This assumption is only valid if signed overflow is
7036 undefined, as the expression is false if @code{i + 10} overflows when
7037 using twos complement arithmetic. When this option is in effect any
7038 attempt to determine whether an operation on signed numbers will
7039 overflow must be written carefully to not actually involve overflow.
7041 This option also allows the compiler to assume strict pointer
7042 semantics: given a pointer to an object, if adding an offset to that
7043 pointer does not produce a pointer to the same object, the addition is
7044 undefined. This permits the compiler to conclude that @code{p + u >
7045 p} is always true for a pointer @code{p} and unsigned integer
7046 @code{u}. This assumption is only valid because pointer wraparound is
7047 undefined, as the expression is false if @code{p + u} overflows using
7048 twos complement arithmetic.
7050 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
7051 that integer signed overflow is fully defined: it wraps. When
7052 @option{-fwrapv} is used, there is no difference between
7053 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
7054 integers. With @option{-fwrapv} certain types of overflow are
7055 permitted. For example, if the compiler gets an overflow when doing
7056 arithmetic on constants, the overflowed value can still be used with
7057 @option{-fwrapv}, but not otherwise.
7059 The @option{-fstrict-overflow} option is enabled at levels
7060 @option{-O2}, @option{-O3}, @option{-Os}.
7062 @item -falign-functions
7063 @itemx -falign-functions=@var{n}
7064 @opindex falign-functions
7065 Align the start of functions to the next power-of-two greater than
7066 @var{n}, skipping up to @var{n} bytes. For instance,
7067 @option{-falign-functions=32} aligns functions to the next 32-byte
7068 boundary, but @option{-falign-functions=24} would align to the next
7069 32-byte boundary only if this can be done by skipping 23 bytes or less.
7071 @option{-fno-align-functions} and @option{-falign-functions=1} are
7072 equivalent and mean that functions will not be aligned.
7074 Some assemblers only support this flag when @var{n} is a power of two;
7075 in that case, it is rounded up.
7077 If @var{n} is not specified or is zero, use a machine-dependent default.
7079 Enabled at levels @option{-O2}, @option{-O3}.
7081 @item -falign-labels
7082 @itemx -falign-labels=@var{n}
7083 @opindex falign-labels
7084 Align all branch targets to a power-of-two boundary, skipping up to
7085 @var{n} bytes like @option{-falign-functions}. This option can easily
7086 make code slower, because it must insert dummy operations for when the
7087 branch target is reached in the usual flow of the code.
7089 @option{-fno-align-labels} and @option{-falign-labels=1} are
7090 equivalent and mean that labels will not be aligned.
7092 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
7093 are greater than this value, then their values are used instead.
7095 If @var{n} is not specified or is zero, use a machine-dependent default
7096 which is very likely to be @samp{1}, meaning no alignment.
7098 Enabled at levels @option{-O2}, @option{-O3}.
7101 @itemx -falign-loops=@var{n}
7102 @opindex falign-loops
7103 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
7104 like @option{-falign-functions}. The hope is that the loop will be
7105 executed many times, which will make up for any execution of the dummy
7108 @option{-fno-align-loops} and @option{-falign-loops=1} are
7109 equivalent and mean that loops will not be aligned.
7111 If @var{n} is not specified or is zero, use a machine-dependent default.
7113 Enabled at levels @option{-O2}, @option{-O3}.
7116 @itemx -falign-jumps=@var{n}
7117 @opindex falign-jumps
7118 Align branch targets to a power-of-two boundary, for branch targets
7119 where the targets can only be reached by jumping, skipping up to @var{n}
7120 bytes like @option{-falign-functions}. In this case, no dummy operations
7123 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
7124 equivalent and mean that loops will not be aligned.
7126 If @var{n} is not specified or is zero, use a machine-dependent default.
7128 Enabled at levels @option{-O2}, @option{-O3}.
7130 @item -funit-at-a-time
7131 @opindex funit-at-a-time
7132 This option is left for compatibility reasons. @option{-funit-at-a-time}
7133 has no effect, while @option{-fno-unit-at-a-time} implies
7134 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
7138 @item -fno-toplevel-reorder
7139 @opindex fno-toplevel-reorder
7140 Do not reorder top-level functions, variables, and @code{asm}
7141 statements. Output them in the same order that they appear in the
7142 input file. When this option is used, unreferenced static variables
7143 will not be removed. This option is intended to support existing code
7144 which relies on a particular ordering. For new code, it is better to
7147 Enabled at level @option{-O0}. When disabled explicitly, it also imply
7148 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
7153 Constructs webs as commonly used for register allocation purposes and assign
7154 each web individual pseudo register. This allows the register allocation pass
7155 to operate on pseudos directly, but also strengthens several other optimization
7156 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
7157 however, make debugging impossible, since variables will no longer stay in a
7160 Enabled by default with @option{-funroll-loops}.
7162 @item -fwhole-program
7163 @opindex fwhole-program
7164 Assume that the current compilation unit represents the whole program being
7165 compiled. All public functions and variables with the exception of @code{main}
7166 and those merged by attribute @code{externally_visible} become static functions
7167 and in effect are optimized more aggressively by interprocedural optimizers.
7168 While this option is equivalent to proper use of the @code{static} keyword for
7169 programs consisting of a single file, in combination with option
7170 @option{-combine}, @option{-flto} or @option{-fwhopr} this flag can be used to
7171 compile many smaller scale programs since the functions and variables become
7172 local for the whole combined compilation unit, not for the single source file
7175 This option implies @option{-fwhole-file} for Fortran programs.
7179 This option runs the standard link-time optimizer. When invoked
7180 with source code, it generates GIMPLE (one of GCC's internal
7181 representations) and writes it to special ELF sections in the object
7182 file. When the object files are linked together, all the function
7183 bodies are read from these ELF sections and instantiated as if they
7184 had been part of the same translation unit.
7186 To use the link-timer optimizer, @option{-flto} needs to be specified at
7187 compile time and during the final link. For example,
7190 gcc -c -O2 -flto foo.c
7191 gcc -c -O2 -flto bar.c
7192 gcc -o myprog -flto -O2 foo.o bar.o
7195 The first two invocations to GCC will save a bytecode representation
7196 of GIMPLE into special ELF sections inside @file{foo.o} and
7197 @file{bar.o}. The final invocation will read the GIMPLE bytecode from
7198 @file{foo.o} and @file{bar.o}, merge the two files into a single
7199 internal image, and compile the result as usual. Since both
7200 @file{foo.o} and @file{bar.o} are merged into a single image, this
7201 causes all the inter-procedural analyses and optimizations in GCC to
7202 work across the two files as if they were a single one. This means,
7203 for example, that the inliner will be able to inline functions in
7204 @file{bar.o} into functions in @file{foo.o} and vice-versa.
7206 Another (simpler) way to enable link-time optimization is,
7209 gcc -o myprog -flto -O2 foo.c bar.c
7212 The above will generate bytecode for @file{foo.c} and @file{bar.c},
7213 merge them together into a single GIMPLE representation and optimize
7214 them as usual to produce @file{myprog}.
7216 The only important thing to keep in mind is that to enable link-time
7217 optimizations the @option{-flto} flag needs to be passed to both the
7218 compile and the link commands.
7220 Note that when a file is compiled with @option{-flto}, the generated
7221 object file will be larger than a regular object file because it will
7222 contain GIMPLE bytecodes and the usual final code. This means that
7223 object files with LTO information can be linked as a normal object
7224 file. So, in the previous example, if the final link is done with
7227 gcc -o myprog foo.o bar.o
7230 The only difference will be that no inter-procedural optimizations
7231 will be applied to produce @file{myprog}. The two object files
7232 @file{foo.o} and @file{bar.o} will be simply sent to the regular
7235 Additionally, the optimization flags used to compile individual files
7236 are not necessarily related to those used at link-time. For instance,
7239 gcc -c -O0 -flto foo.c
7240 gcc -c -O0 -flto bar.c
7241 gcc -o myprog -flto -O3 foo.o bar.o
7244 This will produce individual object files with unoptimized assembler
7245 code, but the resulting binary @file{myprog} will be optimized at
7246 @option{-O3}. Now, if the final binary is generated without
7247 @option{-flto}, then @file{myprog} will not be optimized.
7249 When producing the final binary with @option{-flto}, GCC will only
7250 apply link-time optimizations to those files that contain bytecode.
7251 Therefore, you can mix and match object files and libraries with
7252 GIMPLE bytecodes and final object code. GCC will automatically select
7253 which files to optimize in LTO mode and which files to link without
7256 There are some code generation flags that GCC will preserve when
7257 generating bytecodes, as they need to be used during the final link
7258 stage. Currently, the following options are saved into the GIMPLE
7259 bytecode files: @option{-fPIC}, @option{-fcommon} and all the
7260 @option{-m} target flags.
7262 At link time, these options are read-in and reapplied. Note that the
7263 current implementation makes no attempt at recognizing conflicting
7264 values for these options. If two or more files have a conflicting
7265 value (e.g., one file is compiled with @option{-fPIC} and another
7266 isn't), the compiler will simply use the last value read from the
7267 bytecode files. It is recommended, then, that all the files
7268 participating in the same link be compiled with the same options.
7270 Another feature of LTO is that it is possible to apply interprocedural
7271 optimizations on files written in different languages. This requires
7272 some support in the language front end. Currently, the C, C++ and
7273 Fortran front ends are capable of emitting GIMPLE bytecodes, so
7274 something like this should work
7279 gfortran -c -flto baz.f90
7280 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
7283 Notice that the final link is done with @command{g++} to get the C++
7284 runtime libraries and @option{-lgfortran} is added to get the Fortran
7285 runtime libraries. In general, when mixing languages in LTO mode, you
7286 should use the same link command used when mixing languages in a
7287 regular (non-LTO) compilation. This means that if your build process
7288 was mixing languages before, all you need to add is @option{-flto} to
7289 all the compile and link commands.
7291 If object files containing GIMPLE bytecode are stored in a library
7292 archive, say @file{libfoo.a}, it is possible to extract and use them
7293 in an LTO link if you are using @command{gold} as the linker (which,
7294 in turn requires GCC to be configured with @option{--enable-gold}).
7295 To enable this feature, use the flag @option{-fuse-linker-plugin} at
7299 gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
7302 With the linker plugin enabled, @command{gold} will extract the needed
7303 GIMPLE files from @file{libfoo.a} and pass them on to the running GCC
7304 to make them part of the aggregated GIMPLE image to be optimized.
7306 If you are not using @command{gold} and/or do not specify
7307 @option{-fuse-linker-plugin} then the objects inside @file{libfoo.a}
7308 will be extracted and linked as usual, but they will not participate
7309 in the LTO optimization process.
7311 Link time optimizations do not require the presence of the whole
7312 program to operate. If the program does not require any symbols to
7313 be exported, it is possible to combine @option{-flto} and
7314 @option{-fwhopr} with @option{-fwhole-program} to allow the
7315 interprocedural optimizers to use more aggressive assumptions which
7316 may lead to improved optimization opportunities.
7318 Regarding portability: the current implementation of LTO makes no
7319 attempt at generating bytecode that can be ported between different
7320 types of hosts. The bytecode files are versioned and there is a
7321 strict version check, so bytecode files generated in one version of
7322 GCC will not work with an older/newer version of GCC.
7324 Link time optimization does not play well with generating debugging
7325 information. Combining @option{-flto} or @option{-fwhopr} with
7326 @option{-g} is experimental.
7328 This option is disabled by default.
7332 This option is identical in functionality to @option{-flto} but it
7333 differs in how the final link stage is executed. Instead of loading
7334 all the function bodies in memory, the callgraph is analyzed and
7335 optimization decisions are made (whole program analysis or WPA). Once
7336 optimization decisions are made, the callgraph is partitioned and the
7337 different sections are compiled separately (local transformations or
7338 LTRANS)@. This process allows optimizations on very large programs
7339 that otherwise would not fit in memory. This option enables
7340 @option{-fwpa} and @option{-fltrans} automatically.
7342 Disabled by default.
7344 This option is experimental.
7348 This is an internal option used by GCC when compiling with
7349 @option{-fwhopr}. You should never need to use it.
7351 This option runs the link-time optimizer in the whole-program-analysis
7352 (WPA) mode, which reads in summary information from all inputs and
7353 performs a whole-program analysis based on summary information only.
7354 It generates object files for subsequent runs of the link-time
7355 optimizer where individual object files are optimized using both
7356 summary information from the WPA mode and the actual function bodies.
7357 It then drives the LTRANS phase.
7359 Disabled by default.
7363 This is an internal option used by GCC when compiling with
7364 @option{-fwhopr}. You should never need to use it.
7366 This option runs the link-time optimizer in the local-transformation (LTRANS)
7367 mode, which reads in output from a previous run of the LTO in WPA mode.
7368 In the LTRANS mode, LTO optimizes an object and produces the final assembly.
7370 Disabled by default.
7372 @item -fltrans-output-list=@var{file}
7373 @opindex fltrans-output-list
7374 This is an internal option used by GCC when compiling with
7375 @option{-fwhopr}. You should never need to use it.
7377 This option specifies a file to which the names of LTRANS output files are
7378 written. This option is only meaningful in conjunction with @option{-fwpa}.
7380 Disabled by default.
7382 @item -flto-compression-level=@var{n}
7383 This option specifies the level of compression used for intermediate
7384 language written to LTO object files, and is only meaningful in
7385 conjunction with LTO mode (@option{-fwhopr}, @option{-flto}). Valid
7386 values are 0 (no compression) to 9 (maximum compression). Values
7387 outside this range are clamped to either 0 or 9. If the option is not
7388 given, a default balanced compression setting is used.
7391 Prints a report with internal details on the workings of the link-time
7392 optimizer. The contents of this report vary from version to version,
7393 it is meant to be useful to GCC developers when processing object
7394 files in LTO mode (via @option{-fwhopr} or @option{-flto}).
7396 Disabled by default.
7398 @item -fuse-linker-plugin
7399 Enables the extraction of objects with GIMPLE bytecode information
7400 from library archives. This option relies on features available only
7401 in @command{gold}, so to use this you must configure GCC with
7402 @option{--enable-gold}. See @option{-flto} for a description on the
7403 effect of this flag and how to use it.
7405 Disabled by default.
7407 @item -fcprop-registers
7408 @opindex fcprop-registers
7409 After register allocation and post-register allocation instruction splitting,
7410 we perform a copy-propagation pass to try to reduce scheduling dependencies
7411 and occasionally eliminate the copy.
7413 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7415 @item -fprofile-correction
7416 @opindex fprofile-correction
7417 Profiles collected using an instrumented binary for multi-threaded programs may
7418 be inconsistent due to missed counter updates. When this option is specified,
7419 GCC will use heuristics to correct or smooth out such inconsistencies. By
7420 default, GCC will emit an error message when an inconsistent profile is detected.
7422 @item -fprofile-dir=@var{path}
7423 @opindex fprofile-dir
7425 Set the directory to search the profile data files in to @var{path}.
7426 This option affects only the profile data generated by
7427 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
7428 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
7429 and its related options.
7430 By default, GCC will use the current directory as @var{path}
7431 thus the profile data file will appear in the same directory as the object file.
7433 @item -fprofile-generate
7434 @itemx -fprofile-generate=@var{path}
7435 @opindex fprofile-generate
7437 Enable options usually used for instrumenting application to produce
7438 profile useful for later recompilation with profile feedback based
7439 optimization. You must use @option{-fprofile-generate} both when
7440 compiling and when linking your program.
7442 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
7444 If @var{path} is specified, GCC will look at the @var{path} to find
7445 the profile feedback data files. See @option{-fprofile-dir}.
7448 @itemx -fprofile-use=@var{path}
7449 @opindex fprofile-use
7450 Enable profile feedback directed optimizations, and optimizations
7451 generally profitable only with profile feedback available.
7453 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
7454 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
7456 By default, GCC emits an error message if the feedback profiles do not
7457 match the source code. This error can be turned into a warning by using
7458 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
7461 If @var{path} is specified, GCC will look at the @var{path} to find
7462 the profile feedback data files. See @option{-fprofile-dir}.
7465 The following options control compiler behavior regarding floating
7466 point arithmetic. These options trade off between speed and
7467 correctness. All must be specifically enabled.
7471 @opindex ffloat-store
7472 Do not store floating point variables in registers, and inhibit other
7473 options that might change whether a floating point value is taken from a
7476 @cindex floating point precision
7477 This option prevents undesirable excess precision on machines such as
7478 the 68000 where the floating registers (of the 68881) keep more
7479 precision than a @code{double} is supposed to have. Similarly for the
7480 x86 architecture. For most programs, the excess precision does only
7481 good, but a few programs rely on the precise definition of IEEE floating
7482 point. Use @option{-ffloat-store} for such programs, after modifying
7483 them to store all pertinent intermediate computations into variables.
7485 @item -fexcess-precision=@var{style}
7486 @opindex fexcess-precision
7487 This option allows further control over excess precision on machines
7488 where floating-point registers have more precision than the IEEE
7489 @code{float} and @code{double} types and the processor does not
7490 support operations rounding to those types. By default,
7491 @option{-fexcess-precision=fast} is in effect; this means that
7492 operations are carried out in the precision of the registers and that
7493 it is unpredictable when rounding to the types specified in the source
7494 code takes place. When compiling C, if
7495 @option{-fexcess-precision=standard} is specified then excess
7496 precision will follow the rules specified in ISO C99; in particular,
7497 both casts and assignments cause values to be rounded to their
7498 semantic types (whereas @option{-ffloat-store} only affects
7499 assignments). This option is enabled by default for C if a strict
7500 conformance option such as @option{-std=c99} is used.
7503 @option{-fexcess-precision=standard} is not implemented for languages
7504 other than C, and has no effect if
7505 @option{-funsafe-math-optimizations} or @option{-ffast-math} is
7506 specified. On the x86, it also has no effect if @option{-mfpmath=sse}
7507 or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
7508 semantics apply without excess precision, and in the latter, rounding
7513 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
7514 @option{-ffinite-math-only}, @option{-fno-rounding-math},
7515 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
7517 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
7519 This option is not turned on by any @option{-O} option since
7520 it can result in incorrect output for programs which depend on
7521 an exact implementation of IEEE or ISO rules/specifications for
7522 math functions. It may, however, yield faster code for programs
7523 that do not require the guarantees of these specifications.
7525 @item -fno-math-errno
7526 @opindex fno-math-errno
7527 Do not set ERRNO after calling math functions that are executed
7528 with a single instruction, e.g., sqrt. A program that relies on
7529 IEEE exceptions for math error handling may want to use this flag
7530 for speed while maintaining IEEE arithmetic compatibility.
7532 This option is not turned on by any @option{-O} option since
7533 it can result in incorrect output for programs which depend on
7534 an exact implementation of IEEE or ISO rules/specifications for
7535 math functions. It may, however, yield faster code for programs
7536 that do not require the guarantees of these specifications.
7538 The default is @option{-fmath-errno}.
7540 On Darwin systems, the math library never sets @code{errno}. There is
7541 therefore no reason for the compiler to consider the possibility that
7542 it might, and @option{-fno-math-errno} is the default.
7544 @item -funsafe-math-optimizations
7545 @opindex funsafe-math-optimizations
7547 Allow optimizations for floating-point arithmetic that (a) assume
7548 that arguments and results are valid and (b) may violate IEEE or
7549 ANSI standards. When used at link-time, it may include libraries
7550 or startup files that change the default FPU control word or other
7551 similar optimizations.
7553 This option is not turned on by any @option{-O} option since
7554 it can result in incorrect output for programs which depend on
7555 an exact implementation of IEEE or ISO rules/specifications for
7556 math functions. It may, however, yield faster code for programs
7557 that do not require the guarantees of these specifications.
7558 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
7559 @option{-fassociative-math} and @option{-freciprocal-math}.
7561 The default is @option{-fno-unsafe-math-optimizations}.
7563 @item -fassociative-math
7564 @opindex fassociative-math
7566 Allow re-association of operands in series of floating-point operations.
7567 This violates the ISO C and C++ language standard by possibly changing
7568 computation result. NOTE: re-ordering may change the sign of zero as
7569 well as ignore NaNs and inhibit or create underflow or overflow (and
7570 thus cannot be used on a code which relies on rounding behavior like
7571 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
7572 and thus may not be used when ordered comparisons are required.
7573 This option requires that both @option{-fno-signed-zeros} and
7574 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
7575 much sense with @option{-frounding-math}.
7577 The default is @option{-fno-associative-math}.
7579 @item -freciprocal-math
7580 @opindex freciprocal-math
7582 Allow the reciprocal of a value to be used instead of dividing by
7583 the value if this enables optimizations. For example @code{x / y}
7584 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
7585 is subject to common subexpression elimination. Note that this loses
7586 precision and increases the number of flops operating on the value.
7588 The default is @option{-fno-reciprocal-math}.
7590 @item -ffinite-math-only
7591 @opindex ffinite-math-only
7592 Allow optimizations for floating-point arithmetic that assume
7593 that arguments and results are not NaNs or +-Infs.
7595 This option is not turned on by any @option{-O} option since
7596 it can result in incorrect output for programs which depend on
7597 an exact implementation of IEEE or ISO rules/specifications for
7598 math functions. It may, however, yield faster code for programs
7599 that do not require the guarantees of these specifications.
7601 The default is @option{-fno-finite-math-only}.
7603 @item -fno-signed-zeros
7604 @opindex fno-signed-zeros
7605 Allow optimizations for floating point arithmetic that ignore the
7606 signedness of zero. IEEE arithmetic specifies the behavior of
7607 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
7608 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
7609 This option implies that the sign of a zero result isn't significant.
7611 The default is @option{-fsigned-zeros}.
7613 @item -fno-trapping-math
7614 @opindex fno-trapping-math
7615 Compile code assuming that floating-point operations cannot generate
7616 user-visible traps. These traps include division by zero, overflow,
7617 underflow, inexact result and invalid operation. This option requires
7618 that @option{-fno-signaling-nans} be in effect. Setting this option may
7619 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
7621 This option should never be turned on by any @option{-O} option since
7622 it can result in incorrect output for programs which depend on
7623 an exact implementation of IEEE or ISO rules/specifications for
7626 The default is @option{-ftrapping-math}.
7628 @item -frounding-math
7629 @opindex frounding-math
7630 Disable transformations and optimizations that assume default floating
7631 point rounding behavior. This is round-to-zero for all floating point
7632 to integer conversions, and round-to-nearest for all other arithmetic
7633 truncations. This option should be specified for programs that change
7634 the FP rounding mode dynamically, or that may be executed with a
7635 non-default rounding mode. This option disables constant folding of
7636 floating point expressions at compile-time (which may be affected by
7637 rounding mode) and arithmetic transformations that are unsafe in the
7638 presence of sign-dependent rounding modes.
7640 The default is @option{-fno-rounding-math}.
7642 This option is experimental and does not currently guarantee to
7643 disable all GCC optimizations that are affected by rounding mode.
7644 Future versions of GCC may provide finer control of this setting
7645 using C99's @code{FENV_ACCESS} pragma. This command line option
7646 will be used to specify the default state for @code{FENV_ACCESS}.
7648 @item -fsignaling-nans
7649 @opindex fsignaling-nans
7650 Compile code assuming that IEEE signaling NaNs may generate user-visible
7651 traps during floating-point operations. Setting this option disables
7652 optimizations that may change the number of exceptions visible with
7653 signaling NaNs. This option implies @option{-ftrapping-math}.
7655 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
7658 The default is @option{-fno-signaling-nans}.
7660 This option is experimental and does not currently guarantee to
7661 disable all GCC optimizations that affect signaling NaN behavior.
7663 @item -fsingle-precision-constant
7664 @opindex fsingle-precision-constant
7665 Treat floating point constant as single precision constant instead of
7666 implicitly converting it to double precision constant.
7668 @item -fcx-limited-range
7669 @opindex fcx-limited-range
7670 When enabled, this option states that a range reduction step is not
7671 needed when performing complex division. Also, there is no checking
7672 whether the result of a complex multiplication or division is @code{NaN
7673 + I*NaN}, with an attempt to rescue the situation in that case. The
7674 default is @option{-fno-cx-limited-range}, but is enabled by
7675 @option{-ffast-math}.
7677 This option controls the default setting of the ISO C99
7678 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
7681 @item -fcx-fortran-rules
7682 @opindex fcx-fortran-rules
7683 Complex multiplication and division follow Fortran rules. Range
7684 reduction is done as part of complex division, but there is no checking
7685 whether the result of a complex multiplication or division is @code{NaN
7686 + I*NaN}, with an attempt to rescue the situation in that case.
7688 The default is @option{-fno-cx-fortran-rules}.
7692 The following options control optimizations that may improve
7693 performance, but are not enabled by any @option{-O} options. This
7694 section includes experimental options that may produce broken code.
7697 @item -fbranch-probabilities
7698 @opindex fbranch-probabilities
7699 After running a program compiled with @option{-fprofile-arcs}
7700 (@pxref{Debugging Options,, Options for Debugging Your Program or
7701 @command{gcc}}), you can compile it a second time using
7702 @option{-fbranch-probabilities}, to improve optimizations based on
7703 the number of times each branch was taken. When the program
7704 compiled with @option{-fprofile-arcs} exits it saves arc execution
7705 counts to a file called @file{@var{sourcename}.gcda} for each source
7706 file. The information in this data file is very dependent on the
7707 structure of the generated code, so you must use the same source code
7708 and the same optimization options for both compilations.
7710 With @option{-fbranch-probabilities}, GCC puts a
7711 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
7712 These can be used to improve optimization. Currently, they are only
7713 used in one place: in @file{reorg.c}, instead of guessing which path a
7714 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
7715 exactly determine which path is taken more often.
7717 @item -fprofile-values
7718 @opindex fprofile-values
7719 If combined with @option{-fprofile-arcs}, it adds code so that some
7720 data about values of expressions in the program is gathered.
7722 With @option{-fbranch-probabilities}, it reads back the data gathered
7723 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
7724 notes to instructions for their later usage in optimizations.
7726 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
7730 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
7731 a code to gather information about values of expressions.
7733 With @option{-fbranch-probabilities}, it reads back the data gathered
7734 and actually performs the optimizations based on them.
7735 Currently the optimizations include specialization of division operation
7736 using the knowledge about the value of the denominator.
7738 @item -frename-registers
7739 @opindex frename-registers
7740 Attempt to avoid false dependencies in scheduled code by making use
7741 of registers left over after register allocation. This optimization
7742 will most benefit processors with lots of registers. Depending on the
7743 debug information format adopted by the target, however, it can
7744 make debugging impossible, since variables will no longer stay in
7745 a ``home register''.
7747 Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}.
7751 Perform tail duplication to enlarge superblock size. This transformation
7752 simplifies the control flow of the function allowing other optimizations to do
7755 Enabled with @option{-fprofile-use}.
7757 @item -funroll-loops
7758 @opindex funroll-loops
7759 Unroll loops whose number of iterations can be determined at compile time or
7760 upon entry to the loop. @option{-funroll-loops} implies
7761 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
7762 It also turns on complete loop peeling (i.e.@: complete removal of loops with
7763 small constant number of iterations). This option makes code larger, and may
7764 or may not make it run faster.
7766 Enabled with @option{-fprofile-use}.
7768 @item -funroll-all-loops
7769 @opindex funroll-all-loops
7770 Unroll all loops, even if their number of iterations is uncertain when
7771 the loop is entered. This usually makes programs run more slowly.
7772 @option{-funroll-all-loops} implies the same options as
7773 @option{-funroll-loops}.
7776 @opindex fpeel-loops
7777 Peels the loops for that there is enough information that they do not
7778 roll much (from profile feedback). It also turns on complete loop peeling
7779 (i.e.@: complete removal of loops with small constant number of iterations).
7781 Enabled with @option{-fprofile-use}.
7783 @item -fmove-loop-invariants
7784 @opindex fmove-loop-invariants
7785 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
7786 at level @option{-O1}
7788 @item -funswitch-loops
7789 @opindex funswitch-loops
7790 Move branches with loop invariant conditions out of the loop, with duplicates
7791 of the loop on both branches (modified according to result of the condition).
7793 @item -ffunction-sections
7794 @itemx -fdata-sections
7795 @opindex ffunction-sections
7796 @opindex fdata-sections
7797 Place each function or data item into its own section in the output
7798 file if the target supports arbitrary sections. The name of the
7799 function or the name of the data item determines the section's name
7802 Use these options on systems where the linker can perform optimizations
7803 to improve locality of reference in the instruction space. Most systems
7804 using the ELF object format and SPARC processors running Solaris 2 have
7805 linkers with such optimizations. AIX may have these optimizations in
7808 Only use these options when there are significant benefits from doing
7809 so. When you specify these options, the assembler and linker will
7810 create larger object and executable files and will also be slower.
7811 You will not be able to use @code{gprof} on all systems if you
7812 specify this option and you may have problems with debugging if
7813 you specify both this option and @option{-g}.
7815 @item -fbranch-target-load-optimize
7816 @opindex fbranch-target-load-optimize
7817 Perform branch target register load optimization before prologue / epilogue
7819 The use of target registers can typically be exposed only during reload,
7820 thus hoisting loads out of loops and doing inter-block scheduling needs
7821 a separate optimization pass.
7823 @item -fbranch-target-load-optimize2
7824 @opindex fbranch-target-load-optimize2
7825 Perform branch target register load optimization after prologue / epilogue
7828 @item -fbtr-bb-exclusive
7829 @opindex fbtr-bb-exclusive
7830 When performing branch target register load optimization, don't reuse
7831 branch target registers in within any basic block.
7833 @item -fstack-protector
7834 @opindex fstack-protector
7835 Emit extra code to check for buffer overflows, such as stack smashing
7836 attacks. This is done by adding a guard variable to functions with
7837 vulnerable objects. This includes functions that call alloca, and
7838 functions with buffers larger than 8 bytes. The guards are initialized
7839 when a function is entered and then checked when the function exits.
7840 If a guard check fails, an error message is printed and the program exits.
7842 @item -fstack-protector-all
7843 @opindex fstack-protector-all
7844 Like @option{-fstack-protector} except that all functions are protected.
7846 @item -fsection-anchors
7847 @opindex fsection-anchors
7848 Try to reduce the number of symbolic address calculations by using
7849 shared ``anchor'' symbols to address nearby objects. This transformation
7850 can help to reduce the number of GOT entries and GOT accesses on some
7853 For example, the implementation of the following function @code{foo}:
7857 int foo (void) @{ return a + b + c; @}
7860 would usually calculate the addresses of all three variables, but if you
7861 compile it with @option{-fsection-anchors}, it will access the variables
7862 from a common anchor point instead. The effect is similar to the
7863 following pseudocode (which isn't valid C):
7868 register int *xr = &x;
7869 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
7873 Not all targets support this option.
7875 @item --param @var{name}=@var{value}
7877 In some places, GCC uses various constants to control the amount of
7878 optimization that is done. For example, GCC will not inline functions
7879 that contain more that a certain number of instructions. You can
7880 control some of these constants on the command-line using the
7881 @option{--param} option.
7883 The names of specific parameters, and the meaning of the values, are
7884 tied to the internals of the compiler, and are subject to change
7885 without notice in future releases.
7887 In each case, the @var{value} is an integer. The allowable choices for
7888 @var{name} are given in the following table:
7891 @item struct-reorg-cold-struct-ratio
7892 The threshold ratio (as a percentage) between a structure frequency
7893 and the frequency of the hottest structure in the program. This parameter
7894 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
7895 We say that if the ratio of a structure frequency, calculated by profiling,
7896 to the hottest structure frequency in the program is less than this
7897 parameter, then structure reorganization is not applied to this structure.
7900 @item predictable-branch-cost-outcome
7901 When branch is predicted to be taken with probability lower than this threshold
7902 (in percent), then it is considered well predictable. The default is 10.
7904 @item max-crossjump-edges
7905 The maximum number of incoming edges to consider for crossjumping.
7906 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
7907 the number of edges incoming to each block. Increasing values mean
7908 more aggressive optimization, making the compile time increase with
7909 probably small improvement in executable size.
7911 @item min-crossjump-insns
7912 The minimum number of instructions which must be matched at the end
7913 of two blocks before crossjumping will be performed on them. This
7914 value is ignored in the case where all instructions in the block being
7915 crossjumped from are matched. The default value is 5.
7917 @item max-grow-copy-bb-insns
7918 The maximum code size expansion factor when copying basic blocks
7919 instead of jumping. The expansion is relative to a jump instruction.
7920 The default value is 8.
7922 @item max-goto-duplication-insns
7923 The maximum number of instructions to duplicate to a block that jumps
7924 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
7925 passes, GCC factors computed gotos early in the compilation process,
7926 and unfactors them as late as possible. Only computed jumps at the
7927 end of a basic blocks with no more than max-goto-duplication-insns are
7928 unfactored. The default value is 8.
7930 @item max-delay-slot-insn-search
7931 The maximum number of instructions to consider when looking for an
7932 instruction to fill a delay slot. If more than this arbitrary number of
7933 instructions is searched, the time savings from filling the delay slot
7934 will be minimal so stop searching. Increasing values mean more
7935 aggressive optimization, making the compile time increase with probably
7936 small improvement in executable run time.
7938 @item max-delay-slot-live-search
7939 When trying to fill delay slots, the maximum number of instructions to
7940 consider when searching for a block with valid live register
7941 information. Increasing this arbitrarily chosen value means more
7942 aggressive optimization, increasing the compile time. This parameter
7943 should be removed when the delay slot code is rewritten to maintain the
7946 @item max-gcse-memory
7947 The approximate maximum amount of memory that will be allocated in
7948 order to perform the global common subexpression elimination
7949 optimization. If more memory than specified is required, the
7950 optimization will not be done.
7952 @item max-pending-list-length
7953 The maximum number of pending dependencies scheduling will allow
7954 before flushing the current state and starting over. Large functions
7955 with few branches or calls can create excessively large lists which
7956 needlessly consume memory and resources.
7958 @item max-inline-insns-single
7959 Several parameters control the tree inliner used in gcc.
7960 This number sets the maximum number of instructions (counted in GCC's
7961 internal representation) in a single function that the tree inliner
7962 will consider for inlining. This only affects functions declared
7963 inline and methods implemented in a class declaration (C++).
7964 The default value is 300.
7966 @item max-inline-insns-auto
7967 When you use @option{-finline-functions} (included in @option{-O3}),
7968 a lot of functions that would otherwise not be considered for inlining
7969 by the compiler will be investigated. To those functions, a different
7970 (more restrictive) limit compared to functions declared inline can
7972 The default value is 50.
7974 @item large-function-insns
7975 The limit specifying really large functions. For functions larger than this
7976 limit after inlining, inlining is constrained by
7977 @option{--param large-function-growth}. This parameter is useful primarily
7978 to avoid extreme compilation time caused by non-linear algorithms used by the
7980 The default value is 2700.
7982 @item large-function-growth
7983 Specifies maximal growth of large function caused by inlining in percents.
7984 The default value is 100 which limits large function growth to 2.0 times
7987 @item large-unit-insns
7988 The limit specifying large translation unit. Growth caused by inlining of
7989 units larger than this limit is limited by @option{--param inline-unit-growth}.
7990 For small units this might be too tight (consider unit consisting of function A
7991 that is inline and B that just calls A three time. If B is small relative to
7992 A, the growth of unit is 300\% and yet such inlining is very sane. For very
7993 large units consisting of small inlineable functions however the overall unit
7994 growth limit is needed to avoid exponential explosion of code size. Thus for
7995 smaller units, the size is increased to @option{--param large-unit-insns}
7996 before applying @option{--param inline-unit-growth}. The default is 10000
7998 @item inline-unit-growth
7999 Specifies maximal overall growth of the compilation unit caused by inlining.
8000 The default value is 30 which limits unit growth to 1.3 times the original
8003 @item ipcp-unit-growth
8004 Specifies maximal overall growth of the compilation unit caused by
8005 interprocedural constant propagation. The default value is 10 which limits
8006 unit growth to 1.1 times the original size.
8008 @item large-stack-frame
8009 The limit specifying large stack frames. While inlining the algorithm is trying
8010 to not grow past this limit too much. Default value is 256 bytes.
8012 @item large-stack-frame-growth
8013 Specifies maximal growth of large stack frames caused by inlining in percents.
8014 The default value is 1000 which limits large stack frame growth to 11 times
8017 @item max-inline-insns-recursive
8018 @itemx max-inline-insns-recursive-auto
8019 Specifies maximum number of instructions out-of-line copy of self recursive inline
8020 function can grow into by performing recursive inlining.
8022 For functions declared inline @option{--param max-inline-insns-recursive} is
8023 taken into account. For function not declared inline, recursive inlining
8024 happens only when @option{-finline-functions} (included in @option{-O3}) is
8025 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
8026 default value is 450.
8028 @item max-inline-recursive-depth
8029 @itemx max-inline-recursive-depth-auto
8030 Specifies maximum recursion depth used by the recursive inlining.
8032 For functions declared inline @option{--param max-inline-recursive-depth} is
8033 taken into account. For function not declared inline, recursive inlining
8034 happens only when @option{-finline-functions} (included in @option{-O3}) is
8035 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
8038 @item min-inline-recursive-probability
8039 Recursive inlining is profitable only for function having deep recursion
8040 in average and can hurt for function having little recursion depth by
8041 increasing the prologue size or complexity of function body to other
8044 When profile feedback is available (see @option{-fprofile-generate}) the actual
8045 recursion depth can be guessed from probability that function will recurse via
8046 given call expression. This parameter limits inlining only to call expression
8047 whose probability exceeds given threshold (in percents). The default value is
8050 @item early-inlining-insns
8051 Specify growth that early inliner can make. In effect it increases amount of
8052 inlining for code having large abstraction penalty. The default value is 8.
8054 @item max-early-inliner-iterations
8055 @itemx max-early-inliner-iterations
8056 Limit of iterations of early inliner. This basically bounds number of nested
8057 indirect calls early inliner can resolve. Deeper chains are still handled by
8060 @item min-vect-loop-bound
8061 The minimum number of iterations under which a loop will not get vectorized
8062 when @option{-ftree-vectorize} is used. The number of iterations after
8063 vectorization needs to be greater than the value specified by this option
8064 to allow vectorization. The default value is 0.
8066 @item max-unrolled-insns
8067 The maximum number of instructions that a loop should have if that loop
8068 is unrolled, and if the loop is unrolled, it determines how many times
8069 the loop code is unrolled.
8071 @item max-average-unrolled-insns
8072 The maximum number of instructions biased by probabilities of their execution
8073 that a loop should have if that loop is unrolled, and if the loop is unrolled,
8074 it determines how many times the loop code is unrolled.
8076 @item max-unroll-times
8077 The maximum number of unrollings of a single loop.
8079 @item max-peeled-insns
8080 The maximum number of instructions that a loop should have if that loop
8081 is peeled, and if the loop is peeled, it determines how many times
8082 the loop code is peeled.
8084 @item max-peel-times
8085 The maximum number of peelings of a single loop.
8087 @item max-completely-peeled-insns
8088 The maximum number of insns of a completely peeled loop.
8090 @item max-completely-peel-times
8091 The maximum number of iterations of a loop to be suitable for complete peeling.
8093 @item max-unswitch-insns
8094 The maximum number of insns of an unswitched loop.
8096 @item max-unswitch-level
8097 The maximum number of branches unswitched in a single loop.
8100 The minimum cost of an expensive expression in the loop invariant motion.
8102 @item iv-consider-all-candidates-bound
8103 Bound on number of candidates for induction variables below that
8104 all candidates are considered for each use in induction variable
8105 optimizations. Only the most relevant candidates are considered
8106 if there are more candidates, to avoid quadratic time complexity.
8108 @item iv-max-considered-uses
8109 The induction variable optimizations give up on loops that contain more
8110 induction variable uses.
8112 @item iv-always-prune-cand-set-bound
8113 If number of candidates in the set is smaller than this value,
8114 we always try to remove unnecessary ivs from the set during its
8115 optimization when a new iv is added to the set.
8117 @item scev-max-expr-size
8118 Bound on size of expressions used in the scalar evolutions analyzer.
8119 Large expressions slow the analyzer.
8121 @item omega-max-vars
8122 The maximum number of variables in an Omega constraint system.
8123 The default value is 128.
8125 @item omega-max-geqs
8126 The maximum number of inequalities in an Omega constraint system.
8127 The default value is 256.
8130 The maximum number of equalities in an Omega constraint system.
8131 The default value is 128.
8133 @item omega-max-wild-cards
8134 The maximum number of wildcard variables that the Omega solver will
8135 be able to insert. The default value is 18.
8137 @item omega-hash-table-size
8138 The size of the hash table in the Omega solver. The default value is
8141 @item omega-max-keys
8142 The maximal number of keys used by the Omega solver. The default
8145 @item omega-eliminate-redundant-constraints
8146 When set to 1, use expensive methods to eliminate all redundant
8147 constraints. The default value is 0.
8149 @item vect-max-version-for-alignment-checks
8150 The maximum number of runtime checks that can be performed when
8151 doing loop versioning for alignment in the vectorizer. See option
8152 ftree-vect-loop-version for more information.
8154 @item vect-max-version-for-alias-checks
8155 The maximum number of runtime checks that can be performed when
8156 doing loop versioning for alias in the vectorizer. See option
8157 ftree-vect-loop-version for more information.
8159 @item max-iterations-to-track
8161 The maximum number of iterations of a loop the brute force algorithm
8162 for analysis of # of iterations of the loop tries to evaluate.
8164 @item hot-bb-count-fraction
8165 Select fraction of the maximal count of repetitions of basic block in program
8166 given basic block needs to have to be considered hot.
8168 @item hot-bb-frequency-fraction
8169 Select fraction of the maximal frequency of executions of basic block in
8170 function given basic block needs to have to be considered hot
8172 @item max-predicted-iterations
8173 The maximum number of loop iterations we predict statically. This is useful
8174 in cases where function contain single loop with known bound and other loop
8175 with unknown. We predict the known number of iterations correctly, while
8176 the unknown number of iterations average to roughly 10. This means that the
8177 loop without bounds would appear artificially cold relative to the other one.
8179 @item align-threshold
8181 Select fraction of the maximal frequency of executions of basic block in
8182 function given basic block will get aligned.
8184 @item align-loop-iterations
8186 A loop expected to iterate at lest the selected number of iterations will get
8189 @item tracer-dynamic-coverage
8190 @itemx tracer-dynamic-coverage-feedback
8192 This value is used to limit superblock formation once the given percentage of
8193 executed instructions is covered. This limits unnecessary code size
8196 The @option{tracer-dynamic-coverage-feedback} is used only when profile
8197 feedback is available. The real profiles (as opposed to statically estimated
8198 ones) are much less balanced allowing the threshold to be larger value.
8200 @item tracer-max-code-growth
8201 Stop tail duplication once code growth has reached given percentage. This is
8202 rather hokey argument, as most of the duplicates will be eliminated later in
8203 cross jumping, so it may be set to much higher values than is the desired code
8206 @item tracer-min-branch-ratio
8208 Stop reverse growth when the reverse probability of best edge is less than this
8209 threshold (in percent).
8211 @item tracer-min-branch-ratio
8212 @itemx tracer-min-branch-ratio-feedback
8214 Stop forward growth if the best edge do have probability lower than this
8217 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
8218 compilation for profile feedback and one for compilation without. The value
8219 for compilation with profile feedback needs to be more conservative (higher) in
8220 order to make tracer effective.
8222 @item max-cse-path-length
8224 Maximum number of basic blocks on path that cse considers. The default is 10.
8227 The maximum instructions CSE process before flushing. The default is 1000.
8229 @item ggc-min-expand
8231 GCC uses a garbage collector to manage its own memory allocation. This
8232 parameter specifies the minimum percentage by which the garbage
8233 collector's heap should be allowed to expand between collections.
8234 Tuning this may improve compilation speed; it has no effect on code
8237 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
8238 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
8239 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
8240 GCC is not able to calculate RAM on a particular platform, the lower
8241 bound of 30% is used. Setting this parameter and
8242 @option{ggc-min-heapsize} to zero causes a full collection to occur at
8243 every opportunity. This is extremely slow, but can be useful for
8246 @item ggc-min-heapsize
8248 Minimum size of the garbage collector's heap before it begins bothering
8249 to collect garbage. The first collection occurs after the heap expands
8250 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
8251 tuning this may improve compilation speed, and has no effect on code
8254 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
8255 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
8256 with a lower bound of 4096 (four megabytes) and an upper bound of
8257 131072 (128 megabytes). If GCC is not able to calculate RAM on a
8258 particular platform, the lower bound is used. Setting this parameter
8259 very large effectively disables garbage collection. Setting this
8260 parameter and @option{ggc-min-expand} to zero causes a full collection
8261 to occur at every opportunity.
8263 @item max-reload-search-insns
8264 The maximum number of instruction reload should look backward for equivalent
8265 register. Increasing values mean more aggressive optimization, making the
8266 compile time increase with probably slightly better performance. The default
8269 @item max-cselib-memory-locations
8270 The maximum number of memory locations cselib should take into account.
8271 Increasing values mean more aggressive optimization, making the compile time
8272 increase with probably slightly better performance. The default value is 500.
8274 @item reorder-blocks-duplicate
8275 @itemx reorder-blocks-duplicate-feedback
8277 Used by basic block reordering pass to decide whether to use unconditional
8278 branch or duplicate the code on its destination. Code is duplicated when its
8279 estimated size is smaller than this value multiplied by the estimated size of
8280 unconditional jump in the hot spots of the program.
8282 The @option{reorder-block-duplicate-feedback} is used only when profile
8283 feedback is available and may be set to higher values than
8284 @option{reorder-block-duplicate} since information about the hot spots is more
8287 @item max-sched-ready-insns
8288 The maximum number of instructions ready to be issued the scheduler should
8289 consider at any given time during the first scheduling pass. Increasing
8290 values mean more thorough searches, making the compilation time increase
8291 with probably little benefit. The default value is 100.
8293 @item max-sched-region-blocks
8294 The maximum number of blocks in a region to be considered for
8295 interblock scheduling. The default value is 10.
8297 @item max-pipeline-region-blocks
8298 The maximum number of blocks in a region to be considered for
8299 pipelining in the selective scheduler. The default value is 15.
8301 @item max-sched-region-insns
8302 The maximum number of insns in a region to be considered for
8303 interblock scheduling. The default value is 100.
8305 @item max-pipeline-region-insns
8306 The maximum number of insns in a region to be considered for
8307 pipelining in the selective scheduler. The default value is 200.
8310 The minimum probability (in percents) of reaching a source block
8311 for interblock speculative scheduling. The default value is 40.
8313 @item max-sched-extend-regions-iters
8314 The maximum number of iterations through CFG to extend regions.
8315 0 - disable region extension,
8316 N - do at most N iterations.
8317 The default value is 0.
8319 @item max-sched-insn-conflict-delay
8320 The maximum conflict delay for an insn to be considered for speculative motion.
8321 The default value is 3.
8323 @item sched-spec-prob-cutoff
8324 The minimal probability of speculation success (in percents), so that
8325 speculative insn will be scheduled.
8326 The default value is 40.
8328 @item sched-mem-true-dep-cost
8329 Minimal distance (in CPU cycles) between store and load targeting same
8330 memory locations. The default value is 1.
8332 @item selsched-max-lookahead
8333 The maximum size of the lookahead window of selective scheduling. It is a
8334 depth of search for available instructions.
8335 The default value is 50.
8337 @item selsched-max-sched-times
8338 The maximum number of times that an instruction will be scheduled during
8339 selective scheduling. This is the limit on the number of iterations
8340 through which the instruction may be pipelined. The default value is 2.
8342 @item selsched-max-insns-to-rename
8343 The maximum number of best instructions in the ready list that are considered
8344 for renaming in the selective scheduler. The default value is 2.
8346 @item max-last-value-rtl
8347 The maximum size measured as number of RTLs that can be recorded in an expression
8348 in combiner for a pseudo register as last known value of that register. The default
8351 @item integer-share-limit
8352 Small integer constants can use a shared data structure, reducing the
8353 compiler's memory usage and increasing its speed. This sets the maximum
8354 value of a shared integer constant. The default value is 256.
8356 @item min-virtual-mappings
8357 Specifies the minimum number of virtual mappings in the incremental
8358 SSA updater that should be registered to trigger the virtual mappings
8359 heuristic defined by virtual-mappings-ratio. The default value is
8362 @item virtual-mappings-ratio
8363 If the number of virtual mappings is virtual-mappings-ratio bigger
8364 than the number of virtual symbols to be updated, then the incremental
8365 SSA updater switches to a full update for those symbols. The default
8368 @item ssp-buffer-size
8369 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
8370 protection when @option{-fstack-protection} is used.
8372 @item max-jump-thread-duplication-stmts
8373 Maximum number of statements allowed in a block that needs to be
8374 duplicated when threading jumps.
8376 @item max-fields-for-field-sensitive
8377 Maximum number of fields in a structure we will treat in
8378 a field sensitive manner during pointer analysis. The default is zero
8379 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
8381 @item prefetch-latency
8382 Estimate on average number of instructions that are executed before
8383 prefetch finishes. The distance we prefetch ahead is proportional
8384 to this constant. Increasing this number may also lead to less
8385 streams being prefetched (see @option{simultaneous-prefetches}).
8387 @item simultaneous-prefetches
8388 Maximum number of prefetches that can run at the same time.
8390 @item l1-cache-line-size
8391 The size of cache line in L1 cache, in bytes.
8394 The size of L1 cache, in kilobytes.
8397 The size of L2 cache, in kilobytes.
8399 @item min-insn-to-prefetch-ratio
8400 The minimum ratio between the number of instructions and the
8401 number of prefetches to enable prefetching in a loop with an
8404 @item prefetch-min-insn-to-mem-ratio
8405 The minimum ratio between the number of instructions and the
8406 number of memory references to enable prefetching in a loop.
8408 @item use-canonical-types
8409 Whether the compiler should use the ``canonical'' type system. By
8410 default, this should always be 1, which uses a more efficient internal
8411 mechanism for comparing types in C++ and Objective-C++. However, if
8412 bugs in the canonical type system are causing compilation failures,
8413 set this value to 0 to disable canonical types.
8415 @item switch-conversion-max-branch-ratio
8416 Switch initialization conversion will refuse to create arrays that are
8417 bigger than @option{switch-conversion-max-branch-ratio} times the number of
8418 branches in the switch.
8420 @item max-partial-antic-length
8421 Maximum length of the partial antic set computed during the tree
8422 partial redundancy elimination optimization (@option{-ftree-pre}) when
8423 optimizing at @option{-O3} and above. For some sorts of source code
8424 the enhanced partial redundancy elimination optimization can run away,
8425 consuming all of the memory available on the host machine. This
8426 parameter sets a limit on the length of the sets that are computed,
8427 which prevents the runaway behavior. Setting a value of 0 for
8428 this parameter will allow an unlimited set length.
8430 @item sccvn-max-scc-size
8431 Maximum size of a strongly connected component (SCC) during SCCVN
8432 processing. If this limit is hit, SCCVN processing for the whole
8433 function will not be done and optimizations depending on it will
8434 be disabled. The default maximum SCC size is 10000.
8436 @item ira-max-loops-num
8437 IRA uses a regional register allocation by default. If a function
8438 contains loops more than number given by the parameter, only at most
8439 given number of the most frequently executed loops will form regions
8440 for the regional register allocation. The default value of the
8443 @item ira-max-conflict-table-size
8444 Although IRA uses a sophisticated algorithm of compression conflict
8445 table, the table can be still big for huge functions. If the conflict
8446 table for a function could be more than size in MB given by the
8447 parameter, the conflict table is not built and faster, simpler, and
8448 lower quality register allocation algorithm will be used. The
8449 algorithm do not use pseudo-register conflicts. The default value of
8450 the parameter is 2000.
8452 @item ira-loop-reserved-regs
8453 IRA can be used to evaluate more accurate register pressure in loops
8454 for decision to move loop invariants (see @option{-O3}). The number
8455 of available registers reserved for some other purposes is described
8456 by this parameter. The default value of the parameter is 2 which is
8457 minimal number of registers needed for execution of typical
8458 instruction. This value is the best found from numerous experiments.
8460 @item loop-invariant-max-bbs-in-loop
8461 Loop invariant motion can be very expensive, both in compile time and
8462 in amount of needed compile time memory, with very large loops. Loops
8463 with more basic blocks than this parameter won't have loop invariant
8464 motion optimization performed on them. The default value of the
8465 parameter is 1000 for -O1 and 10000 for -O2 and above.
8467 @item min-nondebug-insn-uid
8468 Use uids starting at this parameter for nondebug insns. The range below
8469 the parameter is reserved exclusively for debug insns created by
8470 @option{-fvar-tracking-assignments}, but debug insns may get
8471 (non-overlapping) uids above it if the reserved range is exhausted.
8473 @item ipa-sra-ptr-growth-factor
8474 IPA-SRA will replace a pointer to an aggregate with one or more new
8475 parameters only when their cumulative size is less or equal to
8476 @option{ipa-sra-ptr-growth-factor} times the size of the original
8482 @node Preprocessor Options
8483 @section Options Controlling the Preprocessor
8484 @cindex preprocessor options
8485 @cindex options, preprocessor
8487 These options control the C preprocessor, which is run on each C source
8488 file before actual compilation.
8490 If you use the @option{-E} option, nothing is done except preprocessing.
8491 Some of these options make sense only together with @option{-E} because
8492 they cause the preprocessor output to be unsuitable for actual
8496 @item -Wp,@var{option}
8498 You can use @option{-Wp,@var{option}} to bypass the compiler driver
8499 and pass @var{option} directly through to the preprocessor. If
8500 @var{option} contains commas, it is split into multiple options at the
8501 commas. However, many options are modified, translated or interpreted
8502 by the compiler driver before being passed to the preprocessor, and
8503 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
8504 interface is undocumented and subject to change, so whenever possible
8505 you should avoid using @option{-Wp} and let the driver handle the
8508 @item -Xpreprocessor @var{option}
8509 @opindex Xpreprocessor
8510 Pass @var{option} as an option to the preprocessor. You can use this to
8511 supply system-specific preprocessor options which GCC does not know how to
8514 If you want to pass an option that takes an argument, you must use
8515 @option{-Xpreprocessor} twice, once for the option and once for the argument.
8518 @include cppopts.texi
8520 @node Assembler Options
8521 @section Passing Options to the Assembler
8523 @c prevent bad page break with this line
8524 You can pass options to the assembler.
8527 @item -Wa,@var{option}
8529 Pass @var{option} as an option to the assembler. If @var{option}
8530 contains commas, it is split into multiple options at the commas.
8532 @item -Xassembler @var{option}
8534 Pass @var{option} as an option to the assembler. You can use this to
8535 supply system-specific assembler options which GCC does not know how to
8538 If you want to pass an option that takes an argument, you must use
8539 @option{-Xassembler} twice, once for the option and once for the argument.
8544 @section Options for Linking
8545 @cindex link options
8546 @cindex options, linking
8548 These options come into play when the compiler links object files into
8549 an executable output file. They are meaningless if the compiler is
8550 not doing a link step.
8554 @item @var{object-file-name}
8555 A file name that does not end in a special recognized suffix is
8556 considered to name an object file or library. (Object files are
8557 distinguished from libraries by the linker according to the file
8558 contents.) If linking is done, these object files are used as input
8567 If any of these options is used, then the linker is not run, and
8568 object file names should not be used as arguments. @xref{Overall
8572 @item -l@var{library}
8573 @itemx -l @var{library}
8575 Search the library named @var{library} when linking. (The second
8576 alternative with the library as a separate argument is only for
8577 POSIX compliance and is not recommended.)
8579 It makes a difference where in the command you write this option; the
8580 linker searches and processes libraries and object files in the order they
8581 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
8582 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
8583 to functions in @samp{z}, those functions may not be loaded.
8585 The linker searches a standard list of directories for the library,
8586 which is actually a file named @file{lib@var{library}.a}. The linker
8587 then uses this file as if it had been specified precisely by name.
8589 The directories searched include several standard system directories
8590 plus any that you specify with @option{-L}.
8592 Normally the files found this way are library files---archive files
8593 whose members are object files. The linker handles an archive file by
8594 scanning through it for members which define symbols that have so far
8595 been referenced but not defined. But if the file that is found is an
8596 ordinary object file, it is linked in the usual fashion. The only
8597 difference between using an @option{-l} option and specifying a file name
8598 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
8599 and searches several directories.
8603 You need this special case of the @option{-l} option in order to
8604 link an Objective-C or Objective-C++ program.
8607 @opindex nostartfiles
8608 Do not use the standard system startup files when linking.
8609 The standard system libraries are used normally, unless @option{-nostdlib}
8610 or @option{-nodefaultlibs} is used.
8612 @item -nodefaultlibs
8613 @opindex nodefaultlibs
8614 Do not use the standard system libraries when linking.
8615 Only the libraries you specify will be passed to the linker, options
8616 specifying linkage of the system libraries, such as @code{-static-libgcc}
8617 or @code{-shared-libgcc}, will be ignored.
8618 The standard startup files are used normally, unless @option{-nostartfiles}
8619 is used. The compiler may generate calls to @code{memcmp},
8620 @code{memset}, @code{memcpy} and @code{memmove}.
8621 These entries are usually resolved by entries in
8622 libc. These entry points should be supplied through some other
8623 mechanism when this option is specified.
8627 Do not use the standard system startup files or libraries when linking.
8628 No startup files and only the libraries you specify will be passed to
8629 the linker, options specifying linkage of the system libraries, such as
8630 @code{-static-libgcc} or @code{-shared-libgcc}, will be ignored.
8631 The compiler may generate calls to @code{memcmp}, @code{memset},
8632 @code{memcpy} and @code{memmove}.
8633 These entries are usually resolved by entries in
8634 libc. These entry points should be supplied through some other
8635 mechanism when this option is specified.
8637 @cindex @option{-lgcc}, use with @option{-nostdlib}
8638 @cindex @option{-nostdlib} and unresolved references
8639 @cindex unresolved references and @option{-nostdlib}
8640 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
8641 @cindex @option{-nodefaultlibs} and unresolved references
8642 @cindex unresolved references and @option{-nodefaultlibs}
8643 One of the standard libraries bypassed by @option{-nostdlib} and
8644 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
8645 that GCC uses to overcome shortcomings of particular machines, or special
8646 needs for some languages.
8647 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
8648 Collection (GCC) Internals},
8649 for more discussion of @file{libgcc.a}.)
8650 In most cases, you need @file{libgcc.a} even when you want to avoid
8651 other standard libraries. In other words, when you specify @option{-nostdlib}
8652 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
8653 This ensures that you have no unresolved references to internal GCC
8654 library subroutines. (For example, @samp{__main}, used to ensure C++
8655 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
8656 GNU Compiler Collection (GCC) Internals}.)
8660 Produce a position independent executable on targets which support it.
8661 For predictable results, you must also specify the same set of options
8662 that were used to generate code (@option{-fpie}, @option{-fPIE},
8663 or model suboptions) when you specify this option.
8667 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
8668 that support it. This instructs the linker to add all symbols, not
8669 only used ones, to the dynamic symbol table. This option is needed
8670 for some uses of @code{dlopen} or to allow obtaining backtraces
8671 from within a program.
8675 Remove all symbol table and relocation information from the executable.
8679 On systems that support dynamic linking, this prevents linking with the shared
8680 libraries. On other systems, this option has no effect.
8684 Produce a shared object which can then be linked with other objects to
8685 form an executable. Not all systems support this option. For predictable
8686 results, you must also specify the same set of options that were used to
8687 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
8688 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
8689 needs to build supplementary stub code for constructors to work. On
8690 multi-libbed systems, @samp{gcc -shared} must select the correct support
8691 libraries to link against. Failing to supply the correct flags may lead
8692 to subtle defects. Supplying them in cases where they are not necessary
8695 @item -shared-libgcc
8696 @itemx -static-libgcc
8697 @opindex shared-libgcc
8698 @opindex static-libgcc
8699 On systems that provide @file{libgcc} as a shared library, these options
8700 force the use of either the shared or static version respectively.
8701 If no shared version of @file{libgcc} was built when the compiler was
8702 configured, these options have no effect.
8704 There are several situations in which an application should use the
8705 shared @file{libgcc} instead of the static version. The most common
8706 of these is when the application wishes to throw and catch exceptions
8707 across different shared libraries. In that case, each of the libraries
8708 as well as the application itself should use the shared @file{libgcc}.
8710 Therefore, the G++ and GCJ drivers automatically add
8711 @option{-shared-libgcc} whenever you build a shared library or a main
8712 executable, because C++ and Java programs typically use exceptions, so
8713 this is the right thing to do.
8715 If, instead, you use the GCC driver to create shared libraries, you may
8716 find that they will not always be linked with the shared @file{libgcc}.
8717 If GCC finds, at its configuration time, that you have a non-GNU linker
8718 or a GNU linker that does not support option @option{--eh-frame-hdr},
8719 it will link the shared version of @file{libgcc} into shared libraries
8720 by default. Otherwise, it will take advantage of the linker and optimize
8721 away the linking with the shared version of @file{libgcc}, linking with
8722 the static version of libgcc by default. This allows exceptions to
8723 propagate through such shared libraries, without incurring relocation
8724 costs at library load time.
8726 However, if a library or main executable is supposed to throw or catch
8727 exceptions, you must link it using the G++ or GCJ driver, as appropriate
8728 for the languages used in the program, or using the option
8729 @option{-shared-libgcc}, such that it is linked with the shared
8732 @item -static-libstdc++
8733 When the @command{g++} program is used to link a C++ program, it will
8734 normally automatically link against @option{libstdc++}. If
8735 @file{libstdc++} is available as a shared library, and the
8736 @option{-static} option is not used, then this will link against the
8737 shared version of @file{libstdc++}. That is normally fine. However, it
8738 is sometimes useful to freeze the version of @file{libstdc++} used by
8739 the program without going all the way to a fully static link. The
8740 @option{-static-libstdc++} option directs the @command{g++} driver to
8741 link @file{libstdc++} statically, without necessarily linking other
8742 libraries statically.
8746 Bind references to global symbols when building a shared object. Warn
8747 about any unresolved references (unless overridden by the link editor
8748 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
8751 @item -T @var{script}
8753 @cindex linker script
8754 Use @var{script} as the linker script. This option is supported by most
8755 systems using the GNU linker. On some targets, such as bare-board
8756 targets without an operating system, the @option{-T} option may be required
8757 when linking to avoid references to undefined symbols.
8759 @item -Xlinker @var{option}
8761 Pass @var{option} as an option to the linker. You can use this to
8762 supply system-specific linker options which GCC does not know how to
8765 If you want to pass an option that takes a separate argument, you must use
8766 @option{-Xlinker} twice, once for the option and once for the argument.
8767 For example, to pass @option{-assert definitions}, you must write
8768 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
8769 @option{-Xlinker "-assert definitions"}, because this passes the entire
8770 string as a single argument, which is not what the linker expects.
8772 When using the GNU linker, it is usually more convenient to pass
8773 arguments to linker options using the @option{@var{option}=@var{value}}
8774 syntax than as separate arguments. For example, you can specify
8775 @samp{-Xlinker -Map=output.map} rather than
8776 @samp{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
8777 this syntax for command-line options.
8779 @item -Wl,@var{option}
8781 Pass @var{option} as an option to the linker. If @var{option} contains
8782 commas, it is split into multiple options at the commas. You can use this
8783 syntax to pass an argument to the option.
8784 For example, @samp{-Wl,-Map,output.map} passes @samp{-Map output.map} to the
8785 linker. When using the GNU linker, you can also get the same effect with
8786 @samp{-Wl,-Map=output.map}.
8788 @item -u @var{symbol}
8790 Pretend the symbol @var{symbol} is undefined, to force linking of
8791 library modules to define it. You can use @option{-u} multiple times with
8792 different symbols to force loading of additional library modules.
8795 @node Directory Options
8796 @section Options for Directory Search
8797 @cindex directory options
8798 @cindex options, directory search
8801 These options specify directories to search for header files, for
8802 libraries and for parts of the compiler:
8807 Add the directory @var{dir} to the head of the list of directories to be
8808 searched for header files. This can be used to override a system header
8809 file, substituting your own version, since these directories are
8810 searched before the system header file directories. However, you should
8811 not use this option to add directories that contain vendor-supplied
8812 system header files (use @option{-isystem} for that). If you use more than
8813 one @option{-I} option, the directories are scanned in left-to-right
8814 order; the standard system directories come after.
8816 If a standard system include directory, or a directory specified with
8817 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
8818 option will be ignored. The directory will still be searched but as a
8819 system directory at its normal position in the system include chain.
8820 This is to ensure that GCC's procedure to fix buggy system headers and
8821 the ordering for the include_next directive are not inadvertently changed.
8822 If you really need to change the search order for system directories,
8823 use the @option{-nostdinc} and/or @option{-isystem} options.
8825 @item -iquote@var{dir}
8827 Add the directory @var{dir} to the head of the list of directories to
8828 be searched for header files only for the case of @samp{#include
8829 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
8830 otherwise just like @option{-I}.
8834 Add directory @var{dir} to the list of directories to be searched
8837 @item -B@var{prefix}
8839 This option specifies where to find the executables, libraries,
8840 include files, and data files of the compiler itself.
8842 The compiler driver program runs one or more of the subprograms
8843 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
8844 @var{prefix} as a prefix for each program it tries to run, both with and
8845 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
8847 For each subprogram to be run, the compiler driver first tries the
8848 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
8849 was not specified, the driver tries two standard prefixes, which are
8850 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
8851 those results in a file name that is found, the unmodified program
8852 name is searched for using the directories specified in your
8853 @env{PATH} environment variable.
8855 The compiler will check to see if the path provided by the @option{-B}
8856 refers to a directory, and if necessary it will add a directory
8857 separator character at the end of the path.
8859 @option{-B} prefixes that effectively specify directory names also apply
8860 to libraries in the linker, because the compiler translates these
8861 options into @option{-L} options for the linker. They also apply to
8862 includes files in the preprocessor, because the compiler translates these
8863 options into @option{-isystem} options for the preprocessor. In this case,
8864 the compiler appends @samp{include} to the prefix.
8866 The run-time support file @file{libgcc.a} can also be searched for using
8867 the @option{-B} prefix, if needed. If it is not found there, the two
8868 standard prefixes above are tried, and that is all. The file is left
8869 out of the link if it is not found by those means.
8871 Another way to specify a prefix much like the @option{-B} prefix is to use
8872 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
8875 As a special kludge, if the path provided by @option{-B} is
8876 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
8877 9, then it will be replaced by @file{[dir/]include}. This is to help
8878 with boot-strapping the compiler.
8880 @item -specs=@var{file}
8882 Process @var{file} after the compiler reads in the standard @file{specs}
8883 file, in order to override the defaults that the @file{gcc} driver
8884 program uses when determining what switches to pass to @file{cc1},
8885 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
8886 @option{-specs=@var{file}} can be specified on the command line, and they
8887 are processed in order, from left to right.
8889 @item --sysroot=@var{dir}
8891 Use @var{dir} as the logical root directory for headers and libraries.
8892 For example, if the compiler would normally search for headers in
8893 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
8894 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
8896 If you use both this option and the @option{-isysroot} option, then
8897 the @option{--sysroot} option will apply to libraries, but the
8898 @option{-isysroot} option will apply to header files.
8900 The GNU linker (beginning with version 2.16) has the necessary support
8901 for this option. If your linker does not support this option, the
8902 header file aspect of @option{--sysroot} will still work, but the
8903 library aspect will not.
8907 This option has been deprecated. Please use @option{-iquote} instead for
8908 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
8909 Any directories you specify with @option{-I} options before the @option{-I-}
8910 option are searched only for the case of @samp{#include "@var{file}"};
8911 they are not searched for @samp{#include <@var{file}>}.
8913 If additional directories are specified with @option{-I} options after
8914 the @option{-I-}, these directories are searched for all @samp{#include}
8915 directives. (Ordinarily @emph{all} @option{-I} directories are used
8918 In addition, the @option{-I-} option inhibits the use of the current
8919 directory (where the current input file came from) as the first search
8920 directory for @samp{#include "@var{file}"}. There is no way to
8921 override this effect of @option{-I-}. With @option{-I.} you can specify
8922 searching the directory which was current when the compiler was
8923 invoked. That is not exactly the same as what the preprocessor does
8924 by default, but it is often satisfactory.
8926 @option{-I-} does not inhibit the use of the standard system directories
8927 for header files. Thus, @option{-I-} and @option{-nostdinc} are
8934 @section Specifying subprocesses and the switches to pass to them
8937 @command{gcc} is a driver program. It performs its job by invoking a
8938 sequence of other programs to do the work of compiling, assembling and
8939 linking. GCC interprets its command-line parameters and uses these to
8940 deduce which programs it should invoke, and which command-line options
8941 it ought to place on their command lines. This behavior is controlled
8942 by @dfn{spec strings}. In most cases there is one spec string for each
8943 program that GCC can invoke, but a few programs have multiple spec
8944 strings to control their behavior. The spec strings built into GCC can
8945 be overridden by using the @option{-specs=} command-line switch to specify
8948 @dfn{Spec files} are plaintext files that are used to construct spec
8949 strings. They consist of a sequence of directives separated by blank
8950 lines. The type of directive is determined by the first non-whitespace
8951 character on the line and it can be one of the following:
8954 @item %@var{command}
8955 Issues a @var{command} to the spec file processor. The commands that can
8959 @item %include <@var{file}>
8961 Search for @var{file} and insert its text at the current point in the
8964 @item %include_noerr <@var{file}>
8965 @cindex %include_noerr
8966 Just like @samp{%include}, but do not generate an error message if the include
8967 file cannot be found.
8969 @item %rename @var{old_name} @var{new_name}
8971 Rename the spec string @var{old_name} to @var{new_name}.
8975 @item *[@var{spec_name}]:
8976 This tells the compiler to create, override or delete the named spec
8977 string. All lines after this directive up to the next directive or
8978 blank line are considered to be the text for the spec string. If this
8979 results in an empty string then the spec will be deleted. (Or, if the
8980 spec did not exist, then nothing will happened.) Otherwise, if the spec
8981 does not currently exist a new spec will be created. If the spec does
8982 exist then its contents will be overridden by the text of this
8983 directive, unless the first character of that text is the @samp{+}
8984 character, in which case the text will be appended to the spec.
8986 @item [@var{suffix}]:
8987 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
8988 and up to the next directive or blank line are considered to make up the
8989 spec string for the indicated suffix. When the compiler encounters an
8990 input file with the named suffix, it will processes the spec string in
8991 order to work out how to compile that file. For example:
8998 This says that any input file whose name ends in @samp{.ZZ} should be
8999 passed to the program @samp{z-compile}, which should be invoked with the
9000 command-line switch @option{-input} and with the result of performing the
9001 @samp{%i} substitution. (See below.)
9003 As an alternative to providing a spec string, the text that follows a
9004 suffix directive can be one of the following:
9007 @item @@@var{language}
9008 This says that the suffix is an alias for a known @var{language}. This is
9009 similar to using the @option{-x} command-line switch to GCC to specify a
9010 language explicitly. For example:
9017 Says that .ZZ files are, in fact, C++ source files.
9020 This causes an error messages saying:
9023 @var{name} compiler not installed on this system.
9027 GCC already has an extensive list of suffixes built into it.
9028 This directive will add an entry to the end of the list of suffixes, but
9029 since the list is searched from the end backwards, it is effectively
9030 possible to override earlier entries using this technique.
9034 GCC has the following spec strings built into it. Spec files can
9035 override these strings or create their own. Note that individual
9036 targets can also add their own spec strings to this list.
9039 asm Options to pass to the assembler
9040 asm_final Options to pass to the assembler post-processor
9041 cpp Options to pass to the C preprocessor
9042 cc1 Options to pass to the C compiler
9043 cc1plus Options to pass to the C++ compiler
9044 endfile Object files to include at the end of the link
9045 link Options to pass to the linker
9046 lib Libraries to include on the command line to the linker
9047 libgcc Decides which GCC support library to pass to the linker
9048 linker Sets the name of the linker
9049 predefines Defines to be passed to the C preprocessor
9050 signed_char Defines to pass to CPP to say whether @code{char} is signed
9052 startfile Object files to include at the start of the link
9055 Here is a small example of a spec file:
9061 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
9064 This example renames the spec called @samp{lib} to @samp{old_lib} and
9065 then overrides the previous definition of @samp{lib} with a new one.
9066 The new definition adds in some extra command-line options before
9067 including the text of the old definition.
9069 @dfn{Spec strings} are a list of command-line options to be passed to their
9070 corresponding program. In addition, the spec strings can contain
9071 @samp{%}-prefixed sequences to substitute variable text or to
9072 conditionally insert text into the command line. Using these constructs
9073 it is possible to generate quite complex command lines.
9075 Here is a table of all defined @samp{%}-sequences for spec
9076 strings. Note that spaces are not generated automatically around the
9077 results of expanding these sequences. Therefore you can concatenate them
9078 together or combine them with constant text in a single argument.
9082 Substitute one @samp{%} into the program name or argument.
9085 Substitute the name of the input file being processed.
9088 Substitute the basename of the input file being processed.
9089 This is the substring up to (and not including) the last period
9090 and not including the directory.
9093 This is the same as @samp{%b}, but include the file suffix (text after
9097 Marks the argument containing or following the @samp{%d} as a
9098 temporary file name, so that that file will be deleted if GCC exits
9099 successfully. Unlike @samp{%g}, this contributes no text to the
9102 @item %g@var{suffix}
9103 Substitute a file name that has suffix @var{suffix} and is chosen
9104 once per compilation, and mark the argument in the same way as
9105 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
9106 name is now chosen in a way that is hard to predict even when previously
9107 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
9108 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
9109 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
9110 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
9111 was simply substituted with a file name chosen once per compilation,
9112 without regard to any appended suffix (which was therefore treated
9113 just like ordinary text), making such attacks more likely to succeed.
9115 @item %u@var{suffix}
9116 Like @samp{%g}, but generates a new temporary file name even if
9117 @samp{%u@var{suffix}} was already seen.
9119 @item %U@var{suffix}
9120 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
9121 new one if there is no such last file name. In the absence of any
9122 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
9123 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
9124 would involve the generation of two distinct file names, one
9125 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
9126 simply substituted with a file name chosen for the previous @samp{%u},
9127 without regard to any appended suffix.
9129 @item %j@var{suffix}
9130 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
9131 writable, and if save-temps is off; otherwise, substitute the name
9132 of a temporary file, just like @samp{%u}. This temporary file is not
9133 meant for communication between processes, but rather as a junk
9136 @item %|@var{suffix}
9137 @itemx %m@var{suffix}
9138 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
9139 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
9140 all. These are the two most common ways to instruct a program that it
9141 should read from standard input or write to standard output. If you
9142 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
9143 construct: see for example @file{f/lang-specs.h}.
9145 @item %.@var{SUFFIX}
9146 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
9147 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
9148 terminated by the next space or %.
9151 Marks the argument containing or following the @samp{%w} as the
9152 designated output file of this compilation. This puts the argument
9153 into the sequence of arguments that @samp{%o} will substitute later.
9156 Substitutes the names of all the output files, with spaces
9157 automatically placed around them. You should write spaces
9158 around the @samp{%o} as well or the results are undefined.
9159 @samp{%o} is for use in the specs for running the linker.
9160 Input files whose names have no recognized suffix are not compiled
9161 at all, but they are included among the output files, so they will
9165 Substitutes the suffix for object files. Note that this is
9166 handled specially when it immediately follows @samp{%g, %u, or %U},
9167 because of the need for those to form complete file names. The
9168 handling is such that @samp{%O} is treated exactly as if it had already
9169 been substituted, except that @samp{%g, %u, and %U} do not currently
9170 support additional @var{suffix} characters following @samp{%O} as they would
9171 following, for example, @samp{.o}.
9174 Substitutes the standard macro predefinitions for the
9175 current target machine. Use this when running @code{cpp}.
9178 Like @samp{%p}, but puts @samp{__} before and after the name of each
9179 predefined macro, except for macros that start with @samp{__} or with
9180 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
9184 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
9185 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
9186 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
9187 and @option{-imultilib} as necessary.
9190 Current argument is the name of a library or startup file of some sort.
9191 Search for that file in a standard list of directories and substitute
9192 the full name found. The current working directory is included in the
9193 list of directories scanned.
9196 Current argument is the name of a linker script. Search for that file
9197 in the current list of directories to scan for libraries. If the file
9198 is located insert a @option{--script} option into the command line
9199 followed by the full path name found. If the file is not found then
9200 generate an error message. Note: the current working directory is not
9204 Print @var{str} as an error message. @var{str} is terminated by a newline.
9205 Use this when inconsistent options are detected.
9208 Substitute the contents of spec string @var{name} at this point.
9211 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
9213 @item %x@{@var{option}@}
9214 Accumulate an option for @samp{%X}.
9217 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
9221 Output the accumulated assembler options specified by @option{-Wa}.
9224 Output the accumulated preprocessor options specified by @option{-Wp}.
9227 Process the @code{asm} spec. This is used to compute the
9228 switches to be passed to the assembler.
9231 Process the @code{asm_final} spec. This is a spec string for
9232 passing switches to an assembler post-processor, if such a program is
9236 Process the @code{link} spec. This is the spec for computing the
9237 command line passed to the linker. Typically it will make use of the
9238 @samp{%L %G %S %D and %E} sequences.
9241 Dump out a @option{-L} option for each directory that GCC believes might
9242 contain startup files. If the target supports multilibs then the
9243 current multilib directory will be prepended to each of these paths.
9246 Process the @code{lib} spec. This is a spec string for deciding which
9247 libraries should be included on the command line to the linker.
9250 Process the @code{libgcc} spec. This is a spec string for deciding
9251 which GCC support library should be included on the command line to the linker.
9254 Process the @code{startfile} spec. This is a spec for deciding which
9255 object files should be the first ones passed to the linker. Typically
9256 this might be a file named @file{crt0.o}.
9259 Process the @code{endfile} spec. This is a spec string that specifies
9260 the last object files that will be passed to the linker.
9263 Process the @code{cpp} spec. This is used to construct the arguments
9264 to be passed to the C preprocessor.
9267 Process the @code{cc1} spec. This is used to construct the options to be
9268 passed to the actual C compiler (@samp{cc1}).
9271 Process the @code{cc1plus} spec. This is used to construct the options to be
9272 passed to the actual C++ compiler (@samp{cc1plus}).
9275 Substitute the variable part of a matched option. See below.
9276 Note that each comma in the substituted string is replaced by
9280 Remove all occurrences of @code{-S} from the command line. Note---this
9281 command is position dependent. @samp{%} commands in the spec string
9282 before this one will see @code{-S}, @samp{%} commands in the spec string
9283 after this one will not.
9285 @item %:@var{function}(@var{args})
9286 Call the named function @var{function}, passing it @var{args}.
9287 @var{args} is first processed as a nested spec string, then split
9288 into an argument vector in the usual fashion. The function returns
9289 a string which is processed as if it had appeared literally as part
9290 of the current spec.
9292 The following built-in spec functions are provided:
9296 The @code{getenv} spec function takes two arguments: an environment
9297 variable name and a string. If the environment variable is not
9298 defined, a fatal error is issued. Otherwise, the return value is the
9299 value of the environment variable concatenated with the string. For
9300 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
9303 %:getenv(TOPDIR /include)
9306 expands to @file{/path/to/top/include}.
9308 @item @code{if-exists}
9309 The @code{if-exists} spec function takes one argument, an absolute
9310 pathname to a file. If the file exists, @code{if-exists} returns the
9311 pathname. Here is a small example of its usage:
9315 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
9318 @item @code{if-exists-else}
9319 The @code{if-exists-else} spec function is similar to the @code{if-exists}
9320 spec function, except that it takes two arguments. The first argument is
9321 an absolute pathname to a file. If the file exists, @code{if-exists-else}
9322 returns the pathname. If it does not exist, it returns the second argument.
9323 This way, @code{if-exists-else} can be used to select one file or another,
9324 based on the existence of the first. Here is a small example of its usage:
9328 crt0%O%s %:if-exists(crti%O%s) \
9329 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
9332 @item @code{replace-outfile}
9333 The @code{replace-outfile} spec function takes two arguments. It looks for the
9334 first argument in the outfiles array and replaces it with the second argument. Here
9335 is a small example of its usage:
9338 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
9341 @item @code{print-asm-header}
9342 The @code{print-asm-header} function takes no arguments and simply
9343 prints a banner like:
9349 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
9352 It is used to separate compiler options from assembler options
9353 in the @option{--target-help} output.
9357 Substitutes the @code{-S} switch, if that switch was given to GCC@.
9358 If that switch was not specified, this substitutes nothing. Note that
9359 the leading dash is omitted when specifying this option, and it is
9360 automatically inserted if the substitution is performed. Thus the spec
9361 string @samp{%@{foo@}} would match the command-line option @option{-foo}
9362 and would output the command line option @option{-foo}.
9364 @item %W@{@code{S}@}
9365 Like %@{@code{S}@} but mark last argument supplied within as a file to be
9368 @item %@{@code{S}*@}
9369 Substitutes all the switches specified to GCC whose names start
9370 with @code{-S}, but which also take an argument. This is used for
9371 switches like @option{-o}, @option{-D}, @option{-I}, etc.
9372 GCC considers @option{-o foo} as being
9373 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
9374 text, including the space. Thus two arguments would be generated.
9376 @item %@{@code{S}*&@code{T}*@}
9377 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
9378 (the order of @code{S} and @code{T} in the spec is not significant).
9379 There can be any number of ampersand-separated variables; for each the
9380 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
9382 @item %@{@code{S}:@code{X}@}
9383 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
9385 @item %@{!@code{S}:@code{X}@}
9386 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
9388 @item %@{@code{S}*:@code{X}@}
9389 Substitutes @code{X} if one or more switches whose names start with
9390 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
9391 once, no matter how many such switches appeared. However, if @code{%*}
9392 appears somewhere in @code{X}, then @code{X} will be substituted once
9393 for each matching switch, with the @code{%*} replaced by the part of
9394 that switch that matched the @code{*}.
9396 @item %@{.@code{S}:@code{X}@}
9397 Substitutes @code{X}, if processing a file with suffix @code{S}.
9399 @item %@{!.@code{S}:@code{X}@}
9400 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
9402 @item %@{,@code{S}:@code{X}@}
9403 Substitutes @code{X}, if processing a file for language @code{S}.
9405 @item %@{!,@code{S}:@code{X}@}
9406 Substitutes @code{X}, if not processing a file for language @code{S}.
9408 @item %@{@code{S}|@code{P}:@code{X}@}
9409 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
9410 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
9411 @code{*} sequences as well, although they have a stronger binding than
9412 the @samp{|}. If @code{%*} appears in @code{X}, all of the
9413 alternatives must be starred, and only the first matching alternative
9416 For example, a spec string like this:
9419 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
9422 will output the following command-line options from the following input
9423 command-line options:
9428 -d fred.c -foo -baz -boggle
9429 -d jim.d -bar -baz -boggle
9432 @item %@{S:X; T:Y; :D@}
9434 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
9435 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
9436 be as many clauses as you need. This may be combined with @code{.},
9437 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
9442 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
9443 construct may contain other nested @samp{%} constructs or spaces, or
9444 even newlines. They are processed as usual, as described above.
9445 Trailing white space in @code{X} is ignored. White space may also
9446 appear anywhere on the left side of the colon in these constructs,
9447 except between @code{.} or @code{*} and the corresponding word.
9449 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
9450 handled specifically in these constructs. If another value of
9451 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
9452 @option{-W} switch is found later in the command line, the earlier
9453 switch value is ignored, except with @{@code{S}*@} where @code{S} is
9454 just one letter, which passes all matching options.
9456 The character @samp{|} at the beginning of the predicate text is used to
9457 indicate that a command should be piped to the following command, but
9458 only if @option{-pipe} is specified.
9460 It is built into GCC which switches take arguments and which do not.
9461 (You might think it would be useful to generalize this to allow each
9462 compiler's spec to say which switches take arguments. But this cannot
9463 be done in a consistent fashion. GCC cannot even decide which input
9464 files have been specified without knowing which switches take arguments,
9465 and it must know which input files to compile in order to tell which
9468 GCC also knows implicitly that arguments starting in @option{-l} are to be
9469 treated as compiler output files, and passed to the linker in their
9470 proper position among the other output files.
9472 @c man begin OPTIONS
9474 @node Target Options
9475 @section Specifying Target Machine and Compiler Version
9476 @cindex target options
9477 @cindex cross compiling
9478 @cindex specifying machine version
9479 @cindex specifying compiler version and target machine
9480 @cindex compiler version, specifying
9481 @cindex target machine, specifying
9483 The usual way to run GCC is to run the executable called @file{gcc}, or
9484 @file{<machine>-gcc} when cross-compiling, or
9485 @file{<machine>-gcc-<version>} to run a version other than the one that
9486 was installed last. Sometimes this is inconvenient, so GCC provides
9487 options that will switch to another cross-compiler or version.
9490 @item -b @var{machine}
9492 The argument @var{machine} specifies the target machine for compilation.
9494 The value to use for @var{machine} is the same as was specified as the
9495 machine type when configuring GCC as a cross-compiler. For
9496 example, if a cross-compiler was configured with @samp{configure
9497 arm-elf}, meaning to compile for an arm processor with elf binaries,
9498 then you would specify @option{-b arm-elf} to run that cross compiler.
9499 Because there are other options beginning with @option{-b}, the
9500 configuration must contain a hyphen, or @option{-b} alone should be one
9501 argument followed by the configuration in the next argument.
9503 @item -V @var{version}
9505 The argument @var{version} specifies which version of GCC to run.
9506 This is useful when multiple versions are installed. For example,
9507 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
9510 The @option{-V} and @option{-b} options work by running the
9511 @file{<machine>-gcc-<version>} executable, so there's no real reason to
9512 use them if you can just run that directly.
9514 @node Submodel Options
9515 @section Hardware Models and Configurations
9516 @cindex submodel options
9517 @cindex specifying hardware config
9518 @cindex hardware models and configurations, specifying
9519 @cindex machine dependent options
9521 Earlier we discussed the standard option @option{-b} which chooses among
9522 different installed compilers for completely different target
9523 machines, such as VAX vs.@: 68000 vs.@: 80386.
9525 In addition, each of these target machine types can have its own
9526 special options, starting with @samp{-m}, to choose among various
9527 hardware models or configurations---for example, 68010 vs 68020,
9528 floating coprocessor or none. A single installed version of the
9529 compiler can compile for any model or configuration, according to the
9532 Some configurations of the compiler also support additional special
9533 options, usually for compatibility with other compilers on the same
9536 @c This list is ordered alphanumerically by subsection name.
9537 @c It should be the same order and spelling as these options are listed
9538 @c in Machine Dependent Options
9544 * Blackfin Options::
9548 * DEC Alpha Options::
9549 * DEC Alpha/VMS Options::
9552 * GNU/Linux Options::
9555 * i386 and x86-64 Options::
9556 * i386 and x86-64 Windows Options::
9558 * IA-64/VMS Options::
9570 * picoChip Options::
9572 * RS/6000 and PowerPC Options::
9574 * S/390 and zSeries Options::
9579 * System V Options::
9584 * Xstormy16 Options::
9590 @subsection ARC Options
9593 These options are defined for ARC implementations:
9598 Compile code for little endian mode. This is the default.
9602 Compile code for big endian mode.
9605 @opindex mmangle-cpu
9606 Prepend the name of the cpu to all public symbol names.
9607 In multiple-processor systems, there are many ARC variants with different
9608 instruction and register set characteristics. This flag prevents code
9609 compiled for one cpu to be linked with code compiled for another.
9610 No facility exists for handling variants that are ``almost identical''.
9611 This is an all or nothing option.
9613 @item -mcpu=@var{cpu}
9615 Compile code for ARC variant @var{cpu}.
9616 Which variants are supported depend on the configuration.
9617 All variants support @option{-mcpu=base}, this is the default.
9619 @item -mtext=@var{text-section}
9620 @itemx -mdata=@var{data-section}
9621 @itemx -mrodata=@var{readonly-data-section}
9625 Put functions, data, and readonly data in @var{text-section},
9626 @var{data-section}, and @var{readonly-data-section} respectively
9627 by default. This can be overridden with the @code{section} attribute.
9628 @xref{Variable Attributes}.
9630 @item -mfix-cortex-m3-ldrd
9631 @opindex mfix-cortex-m3-ldrd
9632 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
9633 with overlapping destination and base registers are used. This option avoids
9634 generating these instructions. This option is enabled by default when
9635 @option{-mcpu=cortex-m3} is specified.
9640 @subsection ARM Options
9643 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
9647 @item -mabi=@var{name}
9649 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
9650 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
9653 @opindex mapcs-frame
9654 Generate a stack frame that is compliant with the ARM Procedure Call
9655 Standard for all functions, even if this is not strictly necessary for
9656 correct execution of the code. Specifying @option{-fomit-frame-pointer}
9657 with this option will cause the stack frames not to be generated for
9658 leaf functions. The default is @option{-mno-apcs-frame}.
9662 This is a synonym for @option{-mapcs-frame}.
9665 @c not currently implemented
9666 @item -mapcs-stack-check
9667 @opindex mapcs-stack-check
9668 Generate code to check the amount of stack space available upon entry to
9669 every function (that actually uses some stack space). If there is
9670 insufficient space available then either the function
9671 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
9672 called, depending upon the amount of stack space required. The run time
9673 system is required to provide these functions. The default is
9674 @option{-mno-apcs-stack-check}, since this produces smaller code.
9676 @c not currently implemented
9678 @opindex mapcs-float
9679 Pass floating point arguments using the float point registers. This is
9680 one of the variants of the APCS@. This option is recommended if the
9681 target hardware has a floating point unit or if a lot of floating point
9682 arithmetic is going to be performed by the code. The default is
9683 @option{-mno-apcs-float}, since integer only code is slightly increased in
9684 size if @option{-mapcs-float} is used.
9686 @c not currently implemented
9687 @item -mapcs-reentrant
9688 @opindex mapcs-reentrant
9689 Generate reentrant, position independent code. The default is
9690 @option{-mno-apcs-reentrant}.
9693 @item -mthumb-interwork
9694 @opindex mthumb-interwork
9695 Generate code which supports calling between the ARM and Thumb
9696 instruction sets. Without this option the two instruction sets cannot
9697 be reliably used inside one program. The default is
9698 @option{-mno-thumb-interwork}, since slightly larger code is generated
9699 when @option{-mthumb-interwork} is specified.
9701 @item -mno-sched-prolog
9702 @opindex mno-sched-prolog
9703 Prevent the reordering of instructions in the function prolog, or the
9704 merging of those instruction with the instructions in the function's
9705 body. This means that all functions will start with a recognizable set
9706 of instructions (or in fact one of a choice from a small set of
9707 different function prologues), and this information can be used to
9708 locate the start if functions inside an executable piece of code. The
9709 default is @option{-msched-prolog}.
9711 @item -mfloat-abi=@var{name}
9713 Specifies which floating-point ABI to use. Permissible values
9714 are: @samp{soft}, @samp{softfp} and @samp{hard}.
9716 Specifying @samp{soft} causes GCC to generate output containing
9717 library calls for floating-point operations.
9718 @samp{softfp} allows the generation of code using hardware floating-point
9719 instructions, but still uses the soft-float calling conventions.
9720 @samp{hard} allows generation of floating-point instructions
9721 and uses FPU-specific calling conventions.
9723 The default depends on the specific target configuration. Note that
9724 the hard-float and soft-float ABIs are not link-compatible; you must
9725 compile your entire program with the same ABI, and link with a
9726 compatible set of libraries.
9729 @opindex mhard-float
9730 Equivalent to @option{-mfloat-abi=hard}.
9733 @opindex msoft-float
9734 Equivalent to @option{-mfloat-abi=soft}.
9736 @item -mlittle-endian
9737 @opindex mlittle-endian
9738 Generate code for a processor running in little-endian mode. This is
9739 the default for all standard configurations.
9742 @opindex mbig-endian
9743 Generate code for a processor running in big-endian mode; the default is
9744 to compile code for a little-endian processor.
9746 @item -mwords-little-endian
9747 @opindex mwords-little-endian
9748 This option only applies when generating code for big-endian processors.
9749 Generate code for a little-endian word order but a big-endian byte
9750 order. That is, a byte order of the form @samp{32107654}. Note: this
9751 option should only be used if you require compatibility with code for
9752 big-endian ARM processors generated by versions of the compiler prior to
9755 @item -mcpu=@var{name}
9757 This specifies the name of the target ARM processor. GCC uses this name
9758 to determine what kind of instructions it can emit when generating
9759 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
9760 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
9761 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
9762 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
9763 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
9765 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
9766 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
9767 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
9768 @samp{strongarm1110},
9769 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
9770 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
9771 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
9772 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
9773 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
9774 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
9775 @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
9776 @samp{cortex-a5}, @samp{cortex-a8}, @samp{cortex-a9},
9777 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
9780 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
9782 @item -mtune=@var{name}
9784 This option is very similar to the @option{-mcpu=} option, except that
9785 instead of specifying the actual target processor type, and hence
9786 restricting which instructions can be used, it specifies that GCC should
9787 tune the performance of the code as if the target were of the type
9788 specified in this option, but still choosing the instructions that it
9789 will generate based on the cpu specified by a @option{-mcpu=} option.
9790 For some ARM implementations better performance can be obtained by using
9793 @item -march=@var{name}
9795 This specifies the name of the target ARM architecture. GCC uses this
9796 name to determine what kind of instructions it can emit when generating
9797 assembly code. This option can be used in conjunction with or instead
9798 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
9799 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
9800 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
9801 @samp{armv6}, @samp{armv6j},
9802 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
9803 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
9804 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
9806 @item -mfpu=@var{name}
9807 @itemx -mfpe=@var{number}
9808 @itemx -mfp=@var{number}
9812 This specifies what floating point hardware (or hardware emulation) is
9813 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
9814 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-fp16},
9815 @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, @samp{vfpv3xd-fp16},
9816 @samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, @samp{vfpv4-d16},
9817 @samp{fpv4-sp-d16} and @samp{neon-vfpv4}.
9818 @option{-mfp} and @option{-mfpe} are synonyms for
9819 @option{-mfpu}=@samp{fpe}@var{number}, for compatibility with older versions
9822 If @option{-msoft-float} is specified this specifies the format of
9823 floating point values.
9825 @item -mfp16-format=@var{name}
9826 @opindex mfp16-format
9827 Specify the format of the @code{__fp16} half-precision floating-point type.
9828 Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
9829 the default is @samp{none}, in which case the @code{__fp16} type is not
9830 defined. @xref{Half-Precision}, for more information.
9832 @item -mstructure-size-boundary=@var{n}
9833 @opindex mstructure-size-boundary
9834 The size of all structures and unions will be rounded up to a multiple
9835 of the number of bits set by this option. Permissible values are 8, 32
9836 and 64. The default value varies for different toolchains. For the COFF
9837 targeted toolchain the default value is 8. A value of 64 is only allowed
9838 if the underlying ABI supports it.
9840 Specifying the larger number can produce faster, more efficient code, but
9841 can also increase the size of the program. Different values are potentially
9842 incompatible. Code compiled with one value cannot necessarily expect to
9843 work with code or libraries compiled with another value, if they exchange
9844 information using structures or unions.
9846 @item -mabort-on-noreturn
9847 @opindex mabort-on-noreturn
9848 Generate a call to the function @code{abort} at the end of a
9849 @code{noreturn} function. It will be executed if the function tries to
9853 @itemx -mno-long-calls
9854 @opindex mlong-calls
9855 @opindex mno-long-calls
9856 Tells the compiler to perform function calls by first loading the
9857 address of the function into a register and then performing a subroutine
9858 call on this register. This switch is needed if the target function
9859 will lie outside of the 64 megabyte addressing range of the offset based
9860 version of subroutine call instruction.
9862 Even if this switch is enabled, not all function calls will be turned
9863 into long calls. The heuristic is that static functions, functions
9864 which have the @samp{short-call} attribute, functions that are inside
9865 the scope of a @samp{#pragma no_long_calls} directive and functions whose
9866 definitions have already been compiled within the current compilation
9867 unit, will not be turned into long calls. The exception to this rule is
9868 that weak function definitions, functions with the @samp{long-call}
9869 attribute or the @samp{section} attribute, and functions that are within
9870 the scope of a @samp{#pragma long_calls} directive, will always be
9871 turned into long calls.
9873 This feature is not enabled by default. Specifying
9874 @option{-mno-long-calls} will restore the default behavior, as will
9875 placing the function calls within the scope of a @samp{#pragma
9876 long_calls_off} directive. Note these switches have no effect on how
9877 the compiler generates code to handle function calls via function
9880 @item -msingle-pic-base
9881 @opindex msingle-pic-base
9882 Treat the register used for PIC addressing as read-only, rather than
9883 loading it in the prologue for each function. The run-time system is
9884 responsible for initializing this register with an appropriate value
9885 before execution begins.
9887 @item -mpic-register=@var{reg}
9888 @opindex mpic-register
9889 Specify the register to be used for PIC addressing. The default is R10
9890 unless stack-checking is enabled, when R9 is used.
9892 @item -mcirrus-fix-invalid-insns
9893 @opindex mcirrus-fix-invalid-insns
9894 @opindex mno-cirrus-fix-invalid-insns
9895 Insert NOPs into the instruction stream to in order to work around
9896 problems with invalid Maverick instruction combinations. This option
9897 is only valid if the @option{-mcpu=ep9312} option has been used to
9898 enable generation of instructions for the Cirrus Maverick floating
9899 point co-processor. This option is not enabled by default, since the
9900 problem is only present in older Maverick implementations. The default
9901 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
9904 @item -mpoke-function-name
9905 @opindex mpoke-function-name
9906 Write the name of each function into the text section, directly
9907 preceding the function prologue. The generated code is similar to this:
9911 .ascii "arm_poke_function_name", 0
9914 .word 0xff000000 + (t1 - t0)
9915 arm_poke_function_name
9917 stmfd sp!, @{fp, ip, lr, pc@}
9921 When performing a stack backtrace, code can inspect the value of
9922 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
9923 location @code{pc - 12} and the top 8 bits are set, then we know that
9924 there is a function name embedded immediately preceding this location
9925 and has length @code{((pc[-3]) & 0xff000000)}.
9929 Generate code for the Thumb instruction set. The default is to
9930 use the 32-bit ARM instruction set.
9931 This option automatically enables either 16-bit Thumb-1 or
9932 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
9933 and @option{-march=@var{name}} options. This option is not passed to the
9934 assembler. If you want to force assembler files to be interpreted as Thumb code,
9935 either add a @samp{.thumb} directive to the source or pass the @option{-mthumb}
9936 option directly to the assembler by prefixing it with @option{-Wa}.
9939 @opindex mtpcs-frame
9940 Generate a stack frame that is compliant with the Thumb Procedure Call
9941 Standard for all non-leaf functions. (A leaf function is one that does
9942 not call any other functions.) The default is @option{-mno-tpcs-frame}.
9944 @item -mtpcs-leaf-frame
9945 @opindex mtpcs-leaf-frame
9946 Generate a stack frame that is compliant with the Thumb Procedure Call
9947 Standard for all leaf functions. (A leaf function is one that does
9948 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
9950 @item -mcallee-super-interworking
9951 @opindex mcallee-super-interworking
9952 Gives all externally visible functions in the file being compiled an ARM
9953 instruction set header which switches to Thumb mode before executing the
9954 rest of the function. This allows these functions to be called from
9955 non-interworking code. This option is not valid in AAPCS configurations
9956 because interworking is enabled by default.
9958 @item -mcaller-super-interworking
9959 @opindex mcaller-super-interworking
9960 Allows calls via function pointers (including virtual functions) to
9961 execute correctly regardless of whether the target code has been
9962 compiled for interworking or not. There is a small overhead in the cost
9963 of executing a function pointer if this option is enabled. This option
9964 is not valid in AAPCS configurations because interworking is enabled
9967 @item -mtp=@var{name}
9969 Specify the access model for the thread local storage pointer. The valid
9970 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
9971 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
9972 (supported in the arm6k architecture), and @option{auto}, which uses the
9973 best available method for the selected processor. The default setting is
9976 @item -mword-relocations
9977 @opindex mword-relocations
9978 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
9979 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
9980 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
9986 @subsection AVR Options
9989 These options are defined for AVR implementations:
9992 @item -mmcu=@var{mcu}
9994 Specify ATMEL AVR instruction set or MCU type.
9996 Instruction set avr1 is for the minimal AVR core, not supported by the C
9997 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9998 attiny11, attiny12, attiny15, attiny28).
10000 Instruction set avr2 (default) is for the classic AVR core with up to
10001 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
10002 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
10003 at90c8534, at90s8535).
10005 Instruction set avr3 is for the classic AVR core with up to 128K program
10006 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
10008 Instruction set avr4 is for the enhanced AVR core with up to 8K program
10009 memory space (MCU types: atmega8, atmega83, atmega85).
10011 Instruction set avr5 is for the enhanced AVR core with up to 128K program
10012 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
10013 atmega64, atmega128, at43usb355, at94k).
10015 @item -mno-interrupts
10016 @opindex mno-interrupts
10017 Generated code is not compatible with hardware interrupts.
10018 Code size will be smaller.
10020 @item -mcall-prologues
10021 @opindex mcall-prologues
10022 Functions prologues/epilogues expanded as call to appropriate
10023 subroutines. Code size will be smaller.
10026 @opindex mtiny-stack
10027 Change only the low 8 bits of the stack pointer.
10031 Assume int to be 8 bit integer. This affects the sizes of all types: A
10032 char will be 1 byte, an int will be 1 byte, a long will be 2 bytes
10033 and long long will be 4 bytes. Please note that this option does not
10034 comply to the C standards, but it will provide you with smaller code
10038 @node Blackfin Options
10039 @subsection Blackfin Options
10040 @cindex Blackfin Options
10043 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
10045 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
10046 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
10047 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
10048 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
10049 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
10050 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
10051 @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
10053 The optional @var{sirevision} specifies the silicon revision of the target
10054 Blackfin processor. Any workarounds available for the targeted silicon revision
10055 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
10056 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
10057 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
10058 hexadecimal digits representing the major and minor numbers in the silicon
10059 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
10060 is not defined. If @var{sirevision} is @samp{any}, the
10061 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
10062 If this optional @var{sirevision} is not used, GCC assumes the latest known
10063 silicon revision of the targeted Blackfin processor.
10065 Support for @samp{bf561} is incomplete. For @samp{bf561},
10066 Only the processor macro is defined.
10067 Without this option, @samp{bf532} is used as the processor by default.
10068 The corresponding predefined processor macros for @var{cpu} is to
10069 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
10070 provided by libgloss to be linked in if @option{-msim} is not given.
10074 Specifies that the program will be run on the simulator. This causes
10075 the simulator BSP provided by libgloss to be linked in. This option
10076 has effect only for @samp{bfin-elf} toolchain.
10077 Certain other options, such as @option{-mid-shared-library} and
10078 @option{-mfdpic}, imply @option{-msim}.
10080 @item -momit-leaf-frame-pointer
10081 @opindex momit-leaf-frame-pointer
10082 Don't keep the frame pointer in a register for leaf functions. This
10083 avoids the instructions to save, set up and restore frame pointers and
10084 makes an extra register available in leaf functions. The option
10085 @option{-fomit-frame-pointer} removes the frame pointer for all functions
10086 which might make debugging harder.
10088 @item -mspecld-anomaly
10089 @opindex mspecld-anomaly
10090 When enabled, the compiler will ensure that the generated code does not
10091 contain speculative loads after jump instructions. If this option is used,
10092 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
10094 @item -mno-specld-anomaly
10095 @opindex mno-specld-anomaly
10096 Don't generate extra code to prevent speculative loads from occurring.
10098 @item -mcsync-anomaly
10099 @opindex mcsync-anomaly
10100 When enabled, the compiler will ensure that the generated code does not
10101 contain CSYNC or SSYNC instructions too soon after conditional branches.
10102 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
10104 @item -mno-csync-anomaly
10105 @opindex mno-csync-anomaly
10106 Don't generate extra code to prevent CSYNC or SSYNC instructions from
10107 occurring too soon after a conditional branch.
10111 When enabled, the compiler is free to take advantage of the knowledge that
10112 the entire program fits into the low 64k of memory.
10115 @opindex mno-low-64k
10116 Assume that the program is arbitrarily large. This is the default.
10118 @item -mstack-check-l1
10119 @opindex mstack-check-l1
10120 Do stack checking using information placed into L1 scratchpad memory by the
10123 @item -mid-shared-library
10124 @opindex mid-shared-library
10125 Generate code that supports shared libraries via the library ID method.
10126 This allows for execute in place and shared libraries in an environment
10127 without virtual memory management. This option implies @option{-fPIC}.
10128 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10130 @item -mno-id-shared-library
10131 @opindex mno-id-shared-library
10132 Generate code that doesn't assume ID based shared libraries are being used.
10133 This is the default.
10135 @item -mleaf-id-shared-library
10136 @opindex mleaf-id-shared-library
10137 Generate code that supports shared libraries via the library ID method,
10138 but assumes that this library or executable won't link against any other
10139 ID shared libraries. That allows the compiler to use faster code for jumps
10142 @item -mno-leaf-id-shared-library
10143 @opindex mno-leaf-id-shared-library
10144 Do not assume that the code being compiled won't link against any ID shared
10145 libraries. Slower code will be generated for jump and call insns.
10147 @item -mshared-library-id=n
10148 @opindex mshared-library-id
10149 Specified the identification number of the ID based shared library being
10150 compiled. Specifying a value of 0 will generate more compact code, specifying
10151 other values will force the allocation of that number to the current
10152 library but is no more space or time efficient than omitting this option.
10156 Generate code that allows the data segment to be located in a different
10157 area of memory from the text segment. This allows for execute in place in
10158 an environment without virtual memory management by eliminating relocations
10159 against the text section.
10161 @item -mno-sep-data
10162 @opindex mno-sep-data
10163 Generate code that assumes that the data segment follows the text segment.
10164 This is the default.
10167 @itemx -mno-long-calls
10168 @opindex mlong-calls
10169 @opindex mno-long-calls
10170 Tells the compiler to perform function calls by first loading the
10171 address of the function into a register and then performing a subroutine
10172 call on this register. This switch is needed if the target function
10173 will lie outside of the 24 bit addressing range of the offset based
10174 version of subroutine call instruction.
10176 This feature is not enabled by default. Specifying
10177 @option{-mno-long-calls} will restore the default behavior. Note these
10178 switches have no effect on how the compiler generates code to handle
10179 function calls via function pointers.
10183 Link with the fast floating-point library. This library relaxes some of
10184 the IEEE floating-point standard's rules for checking inputs against
10185 Not-a-Number (NAN), in the interest of performance.
10188 @opindex minline-plt
10189 Enable inlining of PLT entries in function calls to functions that are
10190 not known to bind locally. It has no effect without @option{-mfdpic}.
10193 @opindex mmulticore
10194 Build standalone application for multicore Blackfin processor. Proper
10195 start files and link scripts will be used to support multicore.
10196 This option defines @code{__BFIN_MULTICORE}. It can only be used with
10197 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
10198 @option{-mcorea} or @option{-mcoreb}. If it's used without
10199 @option{-mcorea} or @option{-mcoreb}, single application/dual core
10200 programming model is used. In this model, the main function of Core B
10201 should be named as coreb_main. If it's used with @option{-mcorea} or
10202 @option{-mcoreb}, one application per core programming model is used.
10203 If this option is not used, single core application programming
10208 Build standalone application for Core A of BF561 when using
10209 one application per core programming model. Proper start files
10210 and link scripts will be used to support Core A. This option
10211 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
10215 Build standalone application for Core B of BF561 when using
10216 one application per core programming model. Proper start files
10217 and link scripts will be used to support Core B. This option
10218 defines @code{__BFIN_COREB}. When this option is used, coreb_main
10219 should be used instead of main. It must be used with
10220 @option{-mmulticore}.
10224 Build standalone application for SDRAM. Proper start files and
10225 link scripts will be used to put the application into SDRAM.
10226 Loader should initialize SDRAM before loading the application
10227 into SDRAM. This option defines @code{__BFIN_SDRAM}.
10231 Assume that ICPLBs are enabled at runtime. This has an effect on certain
10232 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
10233 are enabled; for standalone applications the default is off.
10237 @subsection CRIS Options
10238 @cindex CRIS Options
10240 These options are defined specifically for the CRIS ports.
10243 @item -march=@var{architecture-type}
10244 @itemx -mcpu=@var{architecture-type}
10247 Generate code for the specified architecture. The choices for
10248 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
10249 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
10250 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
10253 @item -mtune=@var{architecture-type}
10255 Tune to @var{architecture-type} everything applicable about the generated
10256 code, except for the ABI and the set of available instructions. The
10257 choices for @var{architecture-type} are the same as for
10258 @option{-march=@var{architecture-type}}.
10260 @item -mmax-stack-frame=@var{n}
10261 @opindex mmax-stack-frame
10262 Warn when the stack frame of a function exceeds @var{n} bytes.
10268 The options @option{-metrax4} and @option{-metrax100} are synonyms for
10269 @option{-march=v3} and @option{-march=v8} respectively.
10271 @item -mmul-bug-workaround
10272 @itemx -mno-mul-bug-workaround
10273 @opindex mmul-bug-workaround
10274 @opindex mno-mul-bug-workaround
10275 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
10276 models where it applies. This option is active by default.
10280 Enable CRIS-specific verbose debug-related information in the assembly
10281 code. This option also has the effect to turn off the @samp{#NO_APP}
10282 formatted-code indicator to the assembler at the beginning of the
10287 Do not use condition-code results from previous instruction; always emit
10288 compare and test instructions before use of condition codes.
10290 @item -mno-side-effects
10291 @opindex mno-side-effects
10292 Do not emit instructions with side-effects in addressing modes other than
10295 @item -mstack-align
10296 @itemx -mno-stack-align
10297 @itemx -mdata-align
10298 @itemx -mno-data-align
10299 @itemx -mconst-align
10300 @itemx -mno-const-align
10301 @opindex mstack-align
10302 @opindex mno-stack-align
10303 @opindex mdata-align
10304 @opindex mno-data-align
10305 @opindex mconst-align
10306 @opindex mno-const-align
10307 These options (no-options) arranges (eliminate arrangements) for the
10308 stack-frame, individual data and constants to be aligned for the maximum
10309 single data access size for the chosen CPU model. The default is to
10310 arrange for 32-bit alignment. ABI details such as structure layout are
10311 not affected by these options.
10319 Similar to the stack- data- and const-align options above, these options
10320 arrange for stack-frame, writable data and constants to all be 32-bit,
10321 16-bit or 8-bit aligned. The default is 32-bit alignment.
10323 @item -mno-prologue-epilogue
10324 @itemx -mprologue-epilogue
10325 @opindex mno-prologue-epilogue
10326 @opindex mprologue-epilogue
10327 With @option{-mno-prologue-epilogue}, the normal function prologue and
10328 epilogue that sets up the stack-frame are omitted and no return
10329 instructions or return sequences are generated in the code. Use this
10330 option only together with visual inspection of the compiled code: no
10331 warnings or errors are generated when call-saved registers must be saved,
10332 or storage for local variable needs to be allocated.
10336 @opindex mno-gotplt
10338 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10339 instruction sequences that load addresses for functions from the PLT part
10340 of the GOT rather than (traditional on other architectures) calls to the
10341 PLT@. The default is @option{-mgotplt}.
10345 Legacy no-op option only recognized with the cris-axis-elf and
10346 cris-axis-linux-gnu targets.
10350 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10354 This option, recognized for the cris-axis-elf arranges
10355 to link with input-output functions from a simulator library. Code,
10356 initialized data and zero-initialized data are allocated consecutively.
10360 Like @option{-sim}, but pass linker options to locate initialized data at
10361 0x40000000 and zero-initialized data at 0x80000000.
10365 @subsection CRX Options
10366 @cindex CRX Options
10368 These options are defined specifically for the CRX ports.
10374 Enable the use of multiply-accumulate instructions. Disabled by default.
10377 @opindex mpush-args
10378 Push instructions will be used to pass outgoing arguments when functions
10379 are called. Enabled by default.
10382 @node Darwin Options
10383 @subsection Darwin Options
10384 @cindex Darwin options
10386 These options are defined for all architectures running the Darwin operating
10389 FSF GCC on Darwin does not create ``fat'' object files; it will create
10390 an object file for the single architecture that it was built to
10391 target. Apple's GCC on Darwin does create ``fat'' files if multiple
10392 @option{-arch} options are used; it does so by running the compiler or
10393 linker multiple times and joining the results together with
10396 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
10397 @samp{i686}) is determined by the flags that specify the ISA
10398 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
10399 @option{-force_cpusubtype_ALL} option can be used to override this.
10401 The Darwin tools vary in their behavior when presented with an ISA
10402 mismatch. The assembler, @file{as}, will only permit instructions to
10403 be used that are valid for the subtype of the file it is generating,
10404 so you cannot put 64-bit instructions in a @samp{ppc750} object file.
10405 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
10406 and print an error if asked to create a shared library with a less
10407 restrictive subtype than its input files (for instance, trying to put
10408 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
10409 for executables, @file{ld}, will quietly give the executable the most
10410 restrictive subtype of any of its input files.
10415 Add the framework directory @var{dir} to the head of the list of
10416 directories to be searched for header files. These directories are
10417 interleaved with those specified by @option{-I} options and are
10418 scanned in a left-to-right order.
10420 A framework directory is a directory with frameworks in it. A
10421 framework is a directory with a @samp{"Headers"} and/or
10422 @samp{"PrivateHeaders"} directory contained directly in it that ends
10423 in @samp{".framework"}. The name of a framework is the name of this
10424 directory excluding the @samp{".framework"}. Headers associated with
10425 the framework are found in one of those two directories, with
10426 @samp{"Headers"} being searched first. A subframework is a framework
10427 directory that is in a framework's @samp{"Frameworks"} directory.
10428 Includes of subframework headers can only appear in a header of a
10429 framework that contains the subframework, or in a sibling subframework
10430 header. Two subframeworks are siblings if they occur in the same
10431 framework. A subframework should not have the same name as a
10432 framework, a warning will be issued if this is violated. Currently a
10433 subframework cannot have subframeworks, in the future, the mechanism
10434 may be extended to support this. The standard frameworks can be found
10435 in @samp{"/System/Library/Frameworks"} and
10436 @samp{"/Library/Frameworks"}. An example include looks like
10437 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
10438 the name of the framework and header.h is found in the
10439 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
10441 @item -iframework@var{dir}
10442 @opindex iframework
10443 Like @option{-F} except the directory is a treated as a system
10444 directory. The main difference between this @option{-iframework} and
10445 @option{-F} is that with @option{-iframework} the compiler does not
10446 warn about constructs contained within header files found via
10447 @var{dir}. This option is valid only for the C family of languages.
10451 Emit debugging information for symbols that are used. For STABS
10452 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
10453 This is by default ON@.
10457 Emit debugging information for all symbols and types.
10459 @item -mmacosx-version-min=@var{version}
10460 The earliest version of MacOS X that this executable will run on
10461 is @var{version}. Typical values of @var{version} include @code{10.1},
10462 @code{10.2}, and @code{10.3.9}.
10464 If the compiler was built to use the system's headers by default,
10465 then the default for this option is the system version on which the
10466 compiler is running, otherwise the default is to make choices which
10467 are compatible with as many systems and code bases as possible.
10471 Enable kernel development mode. The @option{-mkernel} option sets
10472 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
10473 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
10474 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
10475 applicable. This mode also sets @option{-mno-altivec},
10476 @option{-msoft-float}, @option{-fno-builtin} and
10477 @option{-mlong-branch} for PowerPC targets.
10479 @item -mone-byte-bool
10480 @opindex mone-byte-bool
10481 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
10482 By default @samp{sizeof(bool)} is @samp{4} when compiling for
10483 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
10484 option has no effect on x86.
10486 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
10487 to generate code that is not binary compatible with code generated
10488 without that switch. Using this switch may require recompiling all
10489 other modules in a program, including system libraries. Use this
10490 switch to conform to a non-default data model.
10492 @item -mfix-and-continue
10493 @itemx -ffix-and-continue
10494 @itemx -findirect-data
10495 @opindex mfix-and-continue
10496 @opindex ffix-and-continue
10497 @opindex findirect-data
10498 Generate code suitable for fast turn around development. Needed to
10499 enable gdb to dynamically load @code{.o} files into already running
10500 programs. @option{-findirect-data} and @option{-ffix-and-continue}
10501 are provided for backwards compatibility.
10505 Loads all members of static archive libraries.
10506 See man ld(1) for more information.
10508 @item -arch_errors_fatal
10509 @opindex arch_errors_fatal
10510 Cause the errors having to do with files that have the wrong architecture
10513 @item -bind_at_load
10514 @opindex bind_at_load
10515 Causes the output file to be marked such that the dynamic linker will
10516 bind all undefined references when the file is loaded or launched.
10520 Produce a Mach-o bundle format file.
10521 See man ld(1) for more information.
10523 @item -bundle_loader @var{executable}
10524 @opindex bundle_loader
10525 This option specifies the @var{executable} that will be loading the build
10526 output file being linked. See man ld(1) for more information.
10529 @opindex dynamiclib
10530 When passed this option, GCC will produce a dynamic library instead of
10531 an executable when linking, using the Darwin @file{libtool} command.
10533 @item -force_cpusubtype_ALL
10534 @opindex force_cpusubtype_ALL
10535 This causes GCC's output file to have the @var{ALL} subtype, instead of
10536 one controlled by the @option{-mcpu} or @option{-march} option.
10538 @item -allowable_client @var{client_name}
10539 @itemx -client_name
10540 @itemx -compatibility_version
10541 @itemx -current_version
10543 @itemx -dependency-file
10545 @itemx -dylinker_install_name
10547 @itemx -exported_symbols_list
10549 @itemx -flat_namespace
10550 @itemx -force_flat_namespace
10551 @itemx -headerpad_max_install_names
10554 @itemx -install_name
10555 @itemx -keep_private_externs
10556 @itemx -multi_module
10557 @itemx -multiply_defined
10558 @itemx -multiply_defined_unused
10560 @itemx -no_dead_strip_inits_and_terms
10561 @itemx -nofixprebinding
10562 @itemx -nomultidefs
10564 @itemx -noseglinkedit
10565 @itemx -pagezero_size
10567 @itemx -prebind_all_twolevel_modules
10568 @itemx -private_bundle
10569 @itemx -read_only_relocs
10571 @itemx -sectobjectsymbols
10575 @itemx -sectobjectsymbols
10578 @itemx -segs_read_only_addr
10579 @itemx -segs_read_write_addr
10580 @itemx -seg_addr_table
10581 @itemx -seg_addr_table_filename
10582 @itemx -seglinkedit
10584 @itemx -segs_read_only_addr
10585 @itemx -segs_read_write_addr
10586 @itemx -single_module
10588 @itemx -sub_library
10589 @itemx -sub_umbrella
10590 @itemx -twolevel_namespace
10593 @itemx -unexported_symbols_list
10594 @itemx -weak_reference_mismatches
10595 @itemx -whatsloaded
10596 @opindex allowable_client
10597 @opindex client_name
10598 @opindex compatibility_version
10599 @opindex current_version
10600 @opindex dead_strip
10601 @opindex dependency-file
10602 @opindex dylib_file
10603 @opindex dylinker_install_name
10605 @opindex exported_symbols_list
10607 @opindex flat_namespace
10608 @opindex force_flat_namespace
10609 @opindex headerpad_max_install_names
10610 @opindex image_base
10612 @opindex install_name
10613 @opindex keep_private_externs
10614 @opindex multi_module
10615 @opindex multiply_defined
10616 @opindex multiply_defined_unused
10617 @opindex noall_load
10618 @opindex no_dead_strip_inits_and_terms
10619 @opindex nofixprebinding
10620 @opindex nomultidefs
10622 @opindex noseglinkedit
10623 @opindex pagezero_size
10625 @opindex prebind_all_twolevel_modules
10626 @opindex private_bundle
10627 @opindex read_only_relocs
10629 @opindex sectobjectsymbols
10632 @opindex sectcreate
10633 @opindex sectobjectsymbols
10636 @opindex segs_read_only_addr
10637 @opindex segs_read_write_addr
10638 @opindex seg_addr_table
10639 @opindex seg_addr_table_filename
10640 @opindex seglinkedit
10642 @opindex segs_read_only_addr
10643 @opindex segs_read_write_addr
10644 @opindex single_module
10646 @opindex sub_library
10647 @opindex sub_umbrella
10648 @opindex twolevel_namespace
10651 @opindex unexported_symbols_list
10652 @opindex weak_reference_mismatches
10653 @opindex whatsloaded
10654 These options are passed to the Darwin linker. The Darwin linker man page
10655 describes them in detail.
10658 @node DEC Alpha Options
10659 @subsection DEC Alpha Options
10661 These @samp{-m} options are defined for the DEC Alpha implementations:
10664 @item -mno-soft-float
10665 @itemx -msoft-float
10666 @opindex mno-soft-float
10667 @opindex msoft-float
10668 Use (do not use) the hardware floating-point instructions for
10669 floating-point operations. When @option{-msoft-float} is specified,
10670 functions in @file{libgcc.a} will be used to perform floating-point
10671 operations. Unless they are replaced by routines that emulate the
10672 floating-point operations, or compiled in such a way as to call such
10673 emulations routines, these routines will issue floating-point
10674 operations. If you are compiling for an Alpha without floating-point
10675 operations, you must ensure that the library is built so as not to call
10678 Note that Alpha implementations without floating-point operations are
10679 required to have floating-point registers.
10682 @itemx -mno-fp-regs
10684 @opindex mno-fp-regs
10685 Generate code that uses (does not use) the floating-point register set.
10686 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
10687 register set is not used, floating point operands are passed in integer
10688 registers as if they were integers and floating-point results are passed
10689 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
10690 so any function with a floating-point argument or return value called by code
10691 compiled with @option{-mno-fp-regs} must also be compiled with that
10694 A typical use of this option is building a kernel that does not use,
10695 and hence need not save and restore, any floating-point registers.
10699 The Alpha architecture implements floating-point hardware optimized for
10700 maximum performance. It is mostly compliant with the IEEE floating
10701 point standard. However, for full compliance, software assistance is
10702 required. This option generates code fully IEEE compliant code
10703 @emph{except} that the @var{inexact-flag} is not maintained (see below).
10704 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
10705 defined during compilation. The resulting code is less efficient but is
10706 able to correctly support denormalized numbers and exceptional IEEE
10707 values such as not-a-number and plus/minus infinity. Other Alpha
10708 compilers call this option @option{-ieee_with_no_inexact}.
10710 @item -mieee-with-inexact
10711 @opindex mieee-with-inexact
10712 This is like @option{-mieee} except the generated code also maintains
10713 the IEEE @var{inexact-flag}. Turning on this option causes the
10714 generated code to implement fully-compliant IEEE math. In addition to
10715 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
10716 macro. On some Alpha implementations the resulting code may execute
10717 significantly slower than the code generated by default. Since there is
10718 very little code that depends on the @var{inexact-flag}, you should
10719 normally not specify this option. Other Alpha compilers call this
10720 option @option{-ieee_with_inexact}.
10722 @item -mfp-trap-mode=@var{trap-mode}
10723 @opindex mfp-trap-mode
10724 This option controls what floating-point related traps are enabled.
10725 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
10726 The trap mode can be set to one of four values:
10730 This is the default (normal) setting. The only traps that are enabled
10731 are the ones that cannot be disabled in software (e.g., division by zero
10735 In addition to the traps enabled by @samp{n}, underflow traps are enabled
10739 Like @samp{u}, but the instructions are marked to be safe for software
10740 completion (see Alpha architecture manual for details).
10743 Like @samp{su}, but inexact traps are enabled as well.
10746 @item -mfp-rounding-mode=@var{rounding-mode}
10747 @opindex mfp-rounding-mode
10748 Selects the IEEE rounding mode. Other Alpha compilers call this option
10749 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
10754 Normal IEEE rounding mode. Floating point numbers are rounded towards
10755 the nearest machine number or towards the even machine number in case
10759 Round towards minus infinity.
10762 Chopped rounding mode. Floating point numbers are rounded towards zero.
10765 Dynamic rounding mode. A field in the floating point control register
10766 (@var{fpcr}, see Alpha architecture reference manual) controls the
10767 rounding mode in effect. The C library initializes this register for
10768 rounding towards plus infinity. Thus, unless your program modifies the
10769 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
10772 @item -mtrap-precision=@var{trap-precision}
10773 @opindex mtrap-precision
10774 In the Alpha architecture, floating point traps are imprecise. This
10775 means without software assistance it is impossible to recover from a
10776 floating trap and program execution normally needs to be terminated.
10777 GCC can generate code that can assist operating system trap handlers
10778 in determining the exact location that caused a floating point trap.
10779 Depending on the requirements of an application, different levels of
10780 precisions can be selected:
10784 Program precision. This option is the default and means a trap handler
10785 can only identify which program caused a floating point exception.
10788 Function precision. The trap handler can determine the function that
10789 caused a floating point exception.
10792 Instruction precision. The trap handler can determine the exact
10793 instruction that caused a floating point exception.
10796 Other Alpha compilers provide the equivalent options called
10797 @option{-scope_safe} and @option{-resumption_safe}.
10799 @item -mieee-conformant
10800 @opindex mieee-conformant
10801 This option marks the generated code as IEEE conformant. You must not
10802 use this option unless you also specify @option{-mtrap-precision=i} and either
10803 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
10804 is to emit the line @samp{.eflag 48} in the function prologue of the
10805 generated assembly file. Under DEC Unix, this has the effect that
10806 IEEE-conformant math library routines will be linked in.
10808 @item -mbuild-constants
10809 @opindex mbuild-constants
10810 Normally GCC examines a 32- or 64-bit integer constant to
10811 see if it can construct it from smaller constants in two or three
10812 instructions. If it cannot, it will output the constant as a literal and
10813 generate code to load it from the data segment at runtime.
10815 Use this option to require GCC to construct @emph{all} integer constants
10816 using code, even if it takes more instructions (the maximum is six).
10818 You would typically use this option to build a shared library dynamic
10819 loader. Itself a shared library, it must relocate itself in memory
10820 before it can find the variables and constants in its own data segment.
10826 Select whether to generate code to be assembled by the vendor-supplied
10827 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
10845 Indicate whether GCC should generate code to use the optional BWX,
10846 CIX, FIX and MAX instruction sets. The default is to use the instruction
10847 sets supported by the CPU type specified via @option{-mcpu=} option or that
10848 of the CPU on which GCC was built if none was specified.
10851 @itemx -mfloat-ieee
10852 @opindex mfloat-vax
10853 @opindex mfloat-ieee
10854 Generate code that uses (does not use) VAX F and G floating point
10855 arithmetic instead of IEEE single and double precision.
10857 @item -mexplicit-relocs
10858 @itemx -mno-explicit-relocs
10859 @opindex mexplicit-relocs
10860 @opindex mno-explicit-relocs
10861 Older Alpha assemblers provided no way to generate symbol relocations
10862 except via assembler macros. Use of these macros does not allow
10863 optimal instruction scheduling. GNU binutils as of version 2.12
10864 supports a new syntax that allows the compiler to explicitly mark
10865 which relocations should apply to which instructions. This option
10866 is mostly useful for debugging, as GCC detects the capabilities of
10867 the assembler when it is built and sets the default accordingly.
10870 @itemx -mlarge-data
10871 @opindex msmall-data
10872 @opindex mlarge-data
10873 When @option{-mexplicit-relocs} is in effect, static data is
10874 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
10875 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
10876 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
10877 16-bit relocations off of the @code{$gp} register. This limits the
10878 size of the small data area to 64KB, but allows the variables to be
10879 directly accessed via a single instruction.
10881 The default is @option{-mlarge-data}. With this option the data area
10882 is limited to just below 2GB@. Programs that require more than 2GB of
10883 data must use @code{malloc} or @code{mmap} to allocate the data in the
10884 heap instead of in the program's data segment.
10886 When generating code for shared libraries, @option{-fpic} implies
10887 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
10890 @itemx -mlarge-text
10891 @opindex msmall-text
10892 @opindex mlarge-text
10893 When @option{-msmall-text} is used, the compiler assumes that the
10894 code of the entire program (or shared library) fits in 4MB, and is
10895 thus reachable with a branch instruction. When @option{-msmall-data}
10896 is used, the compiler can assume that all local symbols share the
10897 same @code{$gp} value, and thus reduce the number of instructions
10898 required for a function call from 4 to 1.
10900 The default is @option{-mlarge-text}.
10902 @item -mcpu=@var{cpu_type}
10904 Set the instruction set and instruction scheduling parameters for
10905 machine type @var{cpu_type}. You can specify either the @samp{EV}
10906 style name or the corresponding chip number. GCC supports scheduling
10907 parameters for the EV4, EV5 and EV6 family of processors and will
10908 choose the default values for the instruction set from the processor
10909 you specify. If you do not specify a processor type, GCC will default
10910 to the processor on which the compiler was built.
10912 Supported values for @var{cpu_type} are
10918 Schedules as an EV4 and has no instruction set extensions.
10922 Schedules as an EV5 and has no instruction set extensions.
10926 Schedules as an EV5 and supports the BWX extension.
10931 Schedules as an EV5 and supports the BWX and MAX extensions.
10935 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
10939 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
10942 Native Linux/GNU toolchains also support the value @samp{native},
10943 which selects the best architecture option for the host processor.
10944 @option{-mcpu=native} has no effect if GCC does not recognize
10947 @item -mtune=@var{cpu_type}
10949 Set only the instruction scheduling parameters for machine type
10950 @var{cpu_type}. The instruction set is not changed.
10952 Native Linux/GNU toolchains also support the value @samp{native},
10953 which selects the best architecture option for the host processor.
10954 @option{-mtune=native} has no effect if GCC does not recognize
10957 @item -mmemory-latency=@var{time}
10958 @opindex mmemory-latency
10959 Sets the latency the scheduler should assume for typical memory
10960 references as seen by the application. This number is highly
10961 dependent on the memory access patterns used by the application
10962 and the size of the external cache on the machine.
10964 Valid options for @var{time} are
10968 A decimal number representing clock cycles.
10974 The compiler contains estimates of the number of clock cycles for
10975 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
10976 (also called Dcache, Scache, and Bcache), as well as to main memory.
10977 Note that L3 is only valid for EV5.
10982 @node DEC Alpha/VMS Options
10983 @subsection DEC Alpha/VMS Options
10985 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
10988 @item -mvms-return-codes
10989 @opindex mvms-return-codes
10990 Return VMS condition codes from main. The default is to return POSIX
10991 style condition (e.g.@: error) codes.
10993 @item -mdebug-main=@var{prefix}
10994 @opindex mdebug-main=@var{prefix}
10995 Flag the first routine whose name starts with @var{prefix} as the main
10996 routine for the debugger.
11000 Default to 64bit memory allocation routines.
11004 @subsection FR30 Options
11005 @cindex FR30 Options
11007 These options are defined specifically for the FR30 port.
11011 @item -msmall-model
11012 @opindex msmall-model
11013 Use the small address space model. This can produce smaller code, but
11014 it does assume that all symbolic values and addresses will fit into a
11019 Assume that run-time support has been provided and so there is no need
11020 to include the simulator library (@file{libsim.a}) on the linker
11026 @subsection FRV Options
11027 @cindex FRV Options
11033 Only use the first 32 general purpose registers.
11038 Use all 64 general purpose registers.
11043 Use only the first 32 floating point registers.
11048 Use all 64 floating point registers
11051 @opindex mhard-float
11053 Use hardware instructions for floating point operations.
11056 @opindex msoft-float
11058 Use library routines for floating point operations.
11063 Dynamically allocate condition code registers.
11068 Do not try to dynamically allocate condition code registers, only
11069 use @code{icc0} and @code{fcc0}.
11074 Change ABI to use double word insns.
11079 Do not use double word instructions.
11084 Use floating point double instructions.
11087 @opindex mno-double
11089 Do not use floating point double instructions.
11094 Use media instructions.
11099 Do not use media instructions.
11104 Use multiply and add/subtract instructions.
11107 @opindex mno-muladd
11109 Do not use multiply and add/subtract instructions.
11114 Select the FDPIC ABI, that uses function descriptors to represent
11115 pointers to functions. Without any PIC/PIE-related options, it
11116 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
11117 assumes GOT entries and small data are within a 12-bit range from the
11118 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
11119 are computed with 32 bits.
11120 With a @samp{bfin-elf} target, this option implies @option{-msim}.
11123 @opindex minline-plt
11125 Enable inlining of PLT entries in function calls to functions that are
11126 not known to bind locally. It has no effect without @option{-mfdpic}.
11127 It's enabled by default if optimizing for speed and compiling for
11128 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
11129 optimization option such as @option{-O3} or above is present in the
11135 Assume a large TLS segment when generating thread-local code.
11140 Do not assume a large TLS segment when generating thread-local code.
11145 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
11146 that is known to be in read-only sections. It's enabled by default,
11147 except for @option{-fpic} or @option{-fpie}: even though it may help
11148 make the global offset table smaller, it trades 1 instruction for 4.
11149 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
11150 one of which may be shared by multiple symbols, and it avoids the need
11151 for a GOT entry for the referenced symbol, so it's more likely to be a
11152 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
11154 @item -multilib-library-pic
11155 @opindex multilib-library-pic
11157 Link with the (library, not FD) pic libraries. It's implied by
11158 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
11159 @option{-fpic} without @option{-mfdpic}. You should never have to use
11163 @opindex mlinked-fp
11165 Follow the EABI requirement of always creating a frame pointer whenever
11166 a stack frame is allocated. This option is enabled by default and can
11167 be disabled with @option{-mno-linked-fp}.
11170 @opindex mlong-calls
11172 Use indirect addressing to call functions outside the current
11173 compilation unit. This allows the functions to be placed anywhere
11174 within the 32-bit address space.
11176 @item -malign-labels
11177 @opindex malign-labels
11179 Try to align labels to an 8-byte boundary by inserting nops into the
11180 previous packet. This option only has an effect when VLIW packing
11181 is enabled. It doesn't create new packets; it merely adds nops to
11184 @item -mlibrary-pic
11185 @opindex mlibrary-pic
11187 Generate position-independent EABI code.
11192 Use only the first four media accumulator registers.
11197 Use all eight media accumulator registers.
11202 Pack VLIW instructions.
11207 Do not pack VLIW instructions.
11210 @opindex mno-eflags
11212 Do not mark ABI switches in e_flags.
11215 @opindex mcond-move
11217 Enable the use of conditional-move instructions (default).
11219 This switch is mainly for debugging the compiler and will likely be removed
11220 in a future version.
11222 @item -mno-cond-move
11223 @opindex mno-cond-move
11225 Disable the use of conditional-move instructions.
11227 This switch is mainly for debugging the compiler and will likely be removed
11228 in a future version.
11233 Enable the use of conditional set instructions (default).
11235 This switch is mainly for debugging the compiler and will likely be removed
11236 in a future version.
11241 Disable the use of conditional set instructions.
11243 This switch is mainly for debugging the compiler and will likely be removed
11244 in a future version.
11247 @opindex mcond-exec
11249 Enable the use of conditional execution (default).
11251 This switch is mainly for debugging the compiler and will likely be removed
11252 in a future version.
11254 @item -mno-cond-exec
11255 @opindex mno-cond-exec
11257 Disable the use of conditional execution.
11259 This switch is mainly for debugging the compiler and will likely be removed
11260 in a future version.
11262 @item -mvliw-branch
11263 @opindex mvliw-branch
11265 Run a pass to pack branches into VLIW instructions (default).
11267 This switch is mainly for debugging the compiler and will likely be removed
11268 in a future version.
11270 @item -mno-vliw-branch
11271 @opindex mno-vliw-branch
11273 Do not run a pass to pack branches into VLIW instructions.
11275 This switch is mainly for debugging the compiler and will likely be removed
11276 in a future version.
11278 @item -mmulti-cond-exec
11279 @opindex mmulti-cond-exec
11281 Enable optimization of @code{&&} and @code{||} in conditional execution
11284 This switch is mainly for debugging the compiler and will likely be removed
11285 in a future version.
11287 @item -mno-multi-cond-exec
11288 @opindex mno-multi-cond-exec
11290 Disable optimization of @code{&&} and @code{||} in conditional execution.
11292 This switch is mainly for debugging the compiler and will likely be removed
11293 in a future version.
11295 @item -mnested-cond-exec
11296 @opindex mnested-cond-exec
11298 Enable nested conditional execution optimizations (default).
11300 This switch is mainly for debugging the compiler and will likely be removed
11301 in a future version.
11303 @item -mno-nested-cond-exec
11304 @opindex mno-nested-cond-exec
11306 Disable nested conditional execution optimizations.
11308 This switch is mainly for debugging the compiler and will likely be removed
11309 in a future version.
11311 @item -moptimize-membar
11312 @opindex moptimize-membar
11314 This switch removes redundant @code{membar} instructions from the
11315 compiler generated code. It is enabled by default.
11317 @item -mno-optimize-membar
11318 @opindex mno-optimize-membar
11320 This switch disables the automatic removal of redundant @code{membar}
11321 instructions from the generated code.
11323 @item -mtomcat-stats
11324 @opindex mtomcat-stats
11326 Cause gas to print out tomcat statistics.
11328 @item -mcpu=@var{cpu}
11331 Select the processor type for which to generate code. Possible values are
11332 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
11333 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
11337 @node GNU/Linux Options
11338 @subsection GNU/Linux Options
11340 These @samp{-m} options are defined for GNU/Linux targets:
11345 Use the GNU C library instead of uClibc. This is the default except
11346 on @samp{*-*-linux-*uclibc*} targets.
11350 Use uClibc instead of the GNU C library. This is the default on
11351 @samp{*-*-linux-*uclibc*} targets.
11354 @node H8/300 Options
11355 @subsection H8/300 Options
11357 These @samp{-m} options are defined for the H8/300 implementations:
11362 Shorten some address references at link time, when possible; uses the
11363 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
11364 ld, Using ld}, for a fuller description.
11368 Generate code for the H8/300H@.
11372 Generate code for the H8S@.
11376 Generate code for the H8S and H8/300H in the normal mode. This switch
11377 must be used either with @option{-mh} or @option{-ms}.
11381 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
11385 Make @code{int} data 32 bits by default.
11388 @opindex malign-300
11389 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
11390 The default for the H8/300H and H8S is to align longs and floats on 4
11392 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
11393 This option has no effect on the H8/300.
11397 @subsection HPPA Options
11398 @cindex HPPA Options
11400 These @samp{-m} options are defined for the HPPA family of computers:
11403 @item -march=@var{architecture-type}
11405 Generate code for the specified architecture. The choices for
11406 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
11407 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
11408 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
11409 architecture option for your machine. Code compiled for lower numbered
11410 architectures will run on higher numbered architectures, but not the
11413 @item -mpa-risc-1-0
11414 @itemx -mpa-risc-1-1
11415 @itemx -mpa-risc-2-0
11416 @opindex mpa-risc-1-0
11417 @opindex mpa-risc-1-1
11418 @opindex mpa-risc-2-0
11419 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
11422 @opindex mbig-switch
11423 Generate code suitable for big switch tables. Use this option only if
11424 the assembler/linker complain about out of range branches within a switch
11427 @item -mjump-in-delay
11428 @opindex mjump-in-delay
11429 Fill delay slots of function calls with unconditional jump instructions
11430 by modifying the return pointer for the function call to be the target
11431 of the conditional jump.
11433 @item -mdisable-fpregs
11434 @opindex mdisable-fpregs
11435 Prevent floating point registers from being used in any manner. This is
11436 necessary for compiling kernels which perform lazy context switching of
11437 floating point registers. If you use this option and attempt to perform
11438 floating point operations, the compiler will abort.
11440 @item -mdisable-indexing
11441 @opindex mdisable-indexing
11442 Prevent the compiler from using indexing address modes. This avoids some
11443 rather obscure problems when compiling MIG generated code under MACH@.
11445 @item -mno-space-regs
11446 @opindex mno-space-regs
11447 Generate code that assumes the target has no space registers. This allows
11448 GCC to generate faster indirect calls and use unscaled index address modes.
11450 Such code is suitable for level 0 PA systems and kernels.
11452 @item -mfast-indirect-calls
11453 @opindex mfast-indirect-calls
11454 Generate code that assumes calls never cross space boundaries. This
11455 allows GCC to emit code which performs faster indirect calls.
11457 This option will not work in the presence of shared libraries or nested
11460 @item -mfixed-range=@var{register-range}
11461 @opindex mfixed-range
11462 Generate code treating the given register range as fixed registers.
11463 A fixed register is one that the register allocator can not use. This is
11464 useful when compiling kernel code. A register range is specified as
11465 two registers separated by a dash. Multiple register ranges can be
11466 specified separated by a comma.
11468 @item -mlong-load-store
11469 @opindex mlong-load-store
11470 Generate 3-instruction load and store sequences as sometimes required by
11471 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
11474 @item -mportable-runtime
11475 @opindex mportable-runtime
11476 Use the portable calling conventions proposed by HP for ELF systems.
11480 Enable the use of assembler directives only GAS understands.
11482 @item -mschedule=@var{cpu-type}
11484 Schedule code according to the constraints for the machine type
11485 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
11486 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
11487 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
11488 proper scheduling option for your machine. The default scheduling is
11492 @opindex mlinker-opt
11493 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
11494 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
11495 linkers in which they give bogus error messages when linking some programs.
11498 @opindex msoft-float
11499 Generate output containing library calls for floating point.
11500 @strong{Warning:} the requisite libraries are not available for all HPPA
11501 targets. Normally the facilities of the machine's usual C compiler are
11502 used, but this cannot be done directly in cross-compilation. You must make
11503 your own arrangements to provide suitable library functions for
11506 @option{-msoft-float} changes the calling convention in the output file;
11507 therefore, it is only useful if you compile @emph{all} of a program with
11508 this option. In particular, you need to compile @file{libgcc.a}, the
11509 library that comes with GCC, with @option{-msoft-float} in order for
11514 Generate the predefine, @code{_SIO}, for server IO@. The default is
11515 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
11516 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
11517 options are available under HP-UX and HI-UX@.
11521 Use GNU ld specific options. This passes @option{-shared} to ld when
11522 building a shared library. It is the default when GCC is configured,
11523 explicitly or implicitly, with the GNU linker. This option does not
11524 have any affect on which ld is called, it only changes what parameters
11525 are passed to that ld. The ld that is called is determined by the
11526 @option{--with-ld} configure option, GCC's program search path, and
11527 finally by the user's @env{PATH}. The linker used by GCC can be printed
11528 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
11529 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
11533 Use HP ld specific options. This passes @option{-b} to ld when building
11534 a shared library and passes @option{+Accept TypeMismatch} to ld on all
11535 links. It is the default when GCC is configured, explicitly or
11536 implicitly, with the HP linker. This option does not have any affect on
11537 which ld is called, it only changes what parameters are passed to that
11538 ld. The ld that is called is determined by the @option{--with-ld}
11539 configure option, GCC's program search path, and finally by the user's
11540 @env{PATH}. The linker used by GCC can be printed using @samp{which
11541 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
11542 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
11545 @opindex mno-long-calls
11546 Generate code that uses long call sequences. This ensures that a call
11547 is always able to reach linker generated stubs. The default is to generate
11548 long calls only when the distance from the call site to the beginning
11549 of the function or translation unit, as the case may be, exceeds a
11550 predefined limit set by the branch type being used. The limits for
11551 normal calls are 7,600,000 and 240,000 bytes, respectively for the
11552 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
11555 Distances are measured from the beginning of functions when using the
11556 @option{-ffunction-sections} option, or when using the @option{-mgas}
11557 and @option{-mno-portable-runtime} options together under HP-UX with
11560 It is normally not desirable to use this option as it will degrade
11561 performance. However, it may be useful in large applications,
11562 particularly when partial linking is used to build the application.
11564 The types of long calls used depends on the capabilities of the
11565 assembler and linker, and the type of code being generated. The
11566 impact on systems that support long absolute calls, and long pic
11567 symbol-difference or pc-relative calls should be relatively small.
11568 However, an indirect call is used on 32-bit ELF systems in pic code
11569 and it is quite long.
11571 @item -munix=@var{unix-std}
11573 Generate compiler predefines and select a startfile for the specified
11574 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
11575 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
11576 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
11577 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
11578 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
11581 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
11582 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
11583 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
11584 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
11585 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
11586 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
11588 It is @emph{important} to note that this option changes the interfaces
11589 for various library routines. It also affects the operational behavior
11590 of the C library. Thus, @emph{extreme} care is needed in using this
11593 Library code that is intended to operate with more than one UNIX
11594 standard must test, set and restore the variable @var{__xpg4_extended_mask}
11595 as appropriate. Most GNU software doesn't provide this capability.
11599 Suppress the generation of link options to search libdld.sl when the
11600 @option{-static} option is specified on HP-UX 10 and later.
11604 The HP-UX implementation of setlocale in libc has a dependency on
11605 libdld.sl. There isn't an archive version of libdld.sl. Thus,
11606 when the @option{-static} option is specified, special link options
11607 are needed to resolve this dependency.
11609 On HP-UX 10 and later, the GCC driver adds the necessary options to
11610 link with libdld.sl when the @option{-static} option is specified.
11611 This causes the resulting binary to be dynamic. On the 64-bit port,
11612 the linkers generate dynamic binaries by default in any case. The
11613 @option{-nolibdld} option can be used to prevent the GCC driver from
11614 adding these link options.
11618 Add support for multithreading with the @dfn{dce thread} library
11619 under HP-UX@. This option sets flags for both the preprocessor and
11623 @node i386 and x86-64 Options
11624 @subsection Intel 386 and AMD x86-64 Options
11625 @cindex i386 Options
11626 @cindex x86-64 Options
11627 @cindex Intel 386 Options
11628 @cindex AMD x86-64 Options
11630 These @samp{-m} options are defined for the i386 and x86-64 family of
11634 @item -mtune=@var{cpu-type}
11636 Tune to @var{cpu-type} everything applicable about the generated code, except
11637 for the ABI and the set of available instructions. The choices for
11638 @var{cpu-type} are:
11641 Produce code optimized for the most common IA32/AMD64/EM64T processors.
11642 If you know the CPU on which your code will run, then you should use
11643 the corresponding @option{-mtune} option instead of
11644 @option{-mtune=generic}. But, if you do not know exactly what CPU users
11645 of your application will have, then you should use this option.
11647 As new processors are deployed in the marketplace, the behavior of this
11648 option will change. Therefore, if you upgrade to a newer version of
11649 GCC, the code generated option will change to reflect the processors
11650 that were most common when that version of GCC was released.
11652 There is no @option{-march=generic} option because @option{-march}
11653 indicates the instruction set the compiler can use, and there is no
11654 generic instruction set applicable to all processors. In contrast,
11655 @option{-mtune} indicates the processor (or, in this case, collection of
11656 processors) for which the code is optimized.
11658 This selects the CPU to tune for at compilation time by determining
11659 the processor type of the compiling machine. Using @option{-mtune=native}
11660 will produce code optimized for the local machine under the constraints
11661 of the selected instruction set. Using @option{-march=native} will
11662 enable all instruction subsets supported by the local machine (hence
11663 the result might not run on different machines).
11665 Original Intel's i386 CPU@.
11667 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
11668 @item i586, pentium
11669 Intel Pentium CPU with no MMX support.
11671 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
11673 Intel PentiumPro CPU@.
11675 Same as @code{generic}, but when used as @code{march} option, PentiumPro
11676 instruction set will be used, so the code will run on all i686 family chips.
11678 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
11679 @item pentium3, pentium3m
11680 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
11683 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
11684 support. Used by Centrino notebooks.
11685 @item pentium4, pentium4m
11686 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
11688 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
11691 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
11692 SSE2 and SSE3 instruction set support.
11694 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
11695 instruction set support.
11697 Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
11698 instruction set support.
11700 AMD K6 CPU with MMX instruction set support.
11702 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
11703 @item athlon, athlon-tbird
11704 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
11706 @item athlon-4, athlon-xp, athlon-mp
11707 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
11708 instruction set support.
11709 @item k8, opteron, athlon64, athlon-fx
11710 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
11711 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
11712 @item k8-sse3, opteron-sse3, athlon64-sse3
11713 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
11714 @item amdfam10, barcelona
11715 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
11716 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
11717 instruction set extensions.)
11719 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
11722 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
11723 instruction set support.
11725 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
11726 implemented for this chip.)
11728 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
11729 implemented for this chip.)
11731 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
11734 While picking a specific @var{cpu-type} will schedule things appropriately
11735 for that particular chip, the compiler will not generate any code that
11736 does not run on the i386 without the @option{-march=@var{cpu-type}} option
11739 @item -march=@var{cpu-type}
11741 Generate instructions for the machine type @var{cpu-type}. The choices
11742 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
11743 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
11745 @item -mcpu=@var{cpu-type}
11747 A deprecated synonym for @option{-mtune}.
11749 @item -mfpmath=@var{unit}
11751 Generate floating point arithmetics for selected unit @var{unit}. The choices
11752 for @var{unit} are:
11756 Use the standard 387 floating point coprocessor present majority of chips and
11757 emulated otherwise. Code compiled with this option will run almost everywhere.
11758 The temporary results are computed in 80bit precision instead of precision
11759 specified by the type resulting in slightly different results compared to most
11760 of other chips. See @option{-ffloat-store} for more detailed description.
11762 This is the default choice for i386 compiler.
11765 Use scalar floating point instructions present in the SSE instruction set.
11766 This instruction set is supported by Pentium3 and newer chips, in the AMD line
11767 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
11768 instruction set supports only single precision arithmetics, thus the double and
11769 extended precision arithmetics is still done using 387. Later version, present
11770 only in Pentium4 and the future AMD x86-64 chips supports double precision
11773 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
11774 or @option{-msse2} switches to enable SSE extensions and make this option
11775 effective. For the x86-64 compiler, these extensions are enabled by default.
11777 The resulting code should be considerably faster in the majority of cases and avoid
11778 the numerical instability problems of 387 code, but may break some existing
11779 code that expects temporaries to be 80bit.
11781 This is the default choice for the x86-64 compiler.
11786 Attempt to utilize both instruction sets at once. This effectively double the
11787 amount of available registers and on chips with separate execution units for
11788 387 and SSE the execution resources too. Use this option with care, as it is
11789 still experimental, because the GCC register allocator does not model separate
11790 functional units well resulting in instable performance.
11793 @item -masm=@var{dialect}
11794 @opindex masm=@var{dialect}
11795 Output asm instructions using selected @var{dialect}. Supported
11796 choices are @samp{intel} or @samp{att} (the default one). Darwin does
11797 not support @samp{intel}.
11800 @itemx -mno-ieee-fp
11802 @opindex mno-ieee-fp
11803 Control whether or not the compiler uses IEEE floating point
11804 comparisons. These handle correctly the case where the result of a
11805 comparison is unordered.
11808 @opindex msoft-float
11809 Generate output containing library calls for floating point.
11810 @strong{Warning:} the requisite libraries are not part of GCC@.
11811 Normally the facilities of the machine's usual C compiler are used, but
11812 this can't be done directly in cross-compilation. You must make your
11813 own arrangements to provide suitable library functions for
11816 On machines where a function returns floating point results in the 80387
11817 register stack, some floating point opcodes may be emitted even if
11818 @option{-msoft-float} is used.
11820 @item -mno-fp-ret-in-387
11821 @opindex mno-fp-ret-in-387
11822 Do not use the FPU registers for return values of functions.
11824 The usual calling convention has functions return values of types
11825 @code{float} and @code{double} in an FPU register, even if there
11826 is no FPU@. The idea is that the operating system should emulate
11829 The option @option{-mno-fp-ret-in-387} causes such values to be returned
11830 in ordinary CPU registers instead.
11832 @item -mno-fancy-math-387
11833 @opindex mno-fancy-math-387
11834 Some 387 emulators do not support the @code{sin}, @code{cos} and
11835 @code{sqrt} instructions for the 387. Specify this option to avoid
11836 generating those instructions. This option is the default on FreeBSD,
11837 OpenBSD and NetBSD@. This option is overridden when @option{-march}
11838 indicates that the target cpu will always have an FPU and so the
11839 instruction will not need emulation. As of revision 2.6.1, these
11840 instructions are not generated unless you also use the
11841 @option{-funsafe-math-optimizations} switch.
11843 @item -malign-double
11844 @itemx -mno-align-double
11845 @opindex malign-double
11846 @opindex mno-align-double
11847 Control whether GCC aligns @code{double}, @code{long double}, and
11848 @code{long long} variables on a two word boundary or a one word
11849 boundary. Aligning @code{double} variables on a two word boundary will
11850 produce code that runs somewhat faster on a @samp{Pentium} at the
11851 expense of more memory.
11853 On x86-64, @option{-malign-double} is enabled by default.
11855 @strong{Warning:} if you use the @option{-malign-double} switch,
11856 structures containing the above types will be aligned differently than
11857 the published application binary interface specifications for the 386
11858 and will not be binary compatible with structures in code compiled
11859 without that switch.
11861 @item -m96bit-long-double
11862 @itemx -m128bit-long-double
11863 @opindex m96bit-long-double
11864 @opindex m128bit-long-double
11865 These switches control the size of @code{long double} type. The i386
11866 application binary interface specifies the size to be 96 bits,
11867 so @option{-m96bit-long-double} is the default in 32 bit mode.
11869 Modern architectures (Pentium and newer) would prefer @code{long double}
11870 to be aligned to an 8 or 16 byte boundary. In arrays or structures
11871 conforming to the ABI, this would not be possible. So specifying a
11872 @option{-m128bit-long-double} will align @code{long double}
11873 to a 16 byte boundary by padding the @code{long double} with an additional
11876 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
11877 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
11879 Notice that neither of these options enable any extra precision over the x87
11880 standard of 80 bits for a @code{long double}.
11882 @strong{Warning:} if you override the default value for your target ABI, the
11883 structures and arrays containing @code{long double} variables will change
11884 their size as well as function calling convention for function taking
11885 @code{long double} will be modified. Hence they will not be binary
11886 compatible with arrays or structures in code compiled without that switch.
11888 @item -mlarge-data-threshold=@var{number}
11889 @opindex mlarge-data-threshold=@var{number}
11890 When @option{-mcmodel=medium} is specified, the data greater than
11891 @var{threshold} are placed in large data section. This value must be the
11892 same across all object linked into the binary and defaults to 65535.
11896 Use a different function-calling convention, in which functions that
11897 take a fixed number of arguments return with the @code{ret} @var{num}
11898 instruction, which pops their arguments while returning. This saves one
11899 instruction in the caller since there is no need to pop the arguments
11902 You can specify that an individual function is called with this calling
11903 sequence with the function attribute @samp{stdcall}. You can also
11904 override the @option{-mrtd} option by using the function attribute
11905 @samp{cdecl}. @xref{Function Attributes}.
11907 @strong{Warning:} this calling convention is incompatible with the one
11908 normally used on Unix, so you cannot use it if you need to call
11909 libraries compiled with the Unix compiler.
11911 Also, you must provide function prototypes for all functions that
11912 take variable numbers of arguments (including @code{printf});
11913 otherwise incorrect code will be generated for calls to those
11916 In addition, seriously incorrect code will result if you call a
11917 function with too many arguments. (Normally, extra arguments are
11918 harmlessly ignored.)
11920 @item -mregparm=@var{num}
11922 Control how many registers are used to pass integer arguments. By
11923 default, no registers are used to pass arguments, and at most 3
11924 registers can be used. You can control this behavior for a specific
11925 function by using the function attribute @samp{regparm}.
11926 @xref{Function Attributes}.
11928 @strong{Warning:} if you use this switch, and
11929 @var{num} is nonzero, then you must build all modules with the same
11930 value, including any libraries. This includes the system libraries and
11934 @opindex msseregparm
11935 Use SSE register passing conventions for float and double arguments
11936 and return values. You can control this behavior for a specific
11937 function by using the function attribute @samp{sseregparm}.
11938 @xref{Function Attributes}.
11940 @strong{Warning:} if you use this switch then you must build all
11941 modules with the same value, including any libraries. This includes
11942 the system libraries and startup modules.
11951 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
11952 is specified, the significands of results of floating-point operations are
11953 rounded to 24 bits (single precision); @option{-mpc64} rounds the
11954 significands of results of floating-point operations to 53 bits (double
11955 precision) and @option{-mpc80} rounds the significands of results of
11956 floating-point operations to 64 bits (extended double precision), which is
11957 the default. When this option is used, floating-point operations in higher
11958 precisions are not available to the programmer without setting the FPU
11959 control word explicitly.
11961 Setting the rounding of floating-point operations to less than the default
11962 80 bits can speed some programs by 2% or more. Note that some mathematical
11963 libraries assume that extended precision (80 bit) floating-point operations
11964 are enabled by default; routines in such libraries could suffer significant
11965 loss of accuracy, typically through so-called "catastrophic cancellation",
11966 when this option is used to set the precision to less than extended precision.
11968 @item -mstackrealign
11969 @opindex mstackrealign
11970 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
11971 option will generate an alternate prologue and epilogue that realigns the
11972 runtime stack if necessary. This supports mixing legacy codes that keep
11973 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
11974 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
11975 applicable to individual functions.
11977 @item -mpreferred-stack-boundary=@var{num}
11978 @opindex mpreferred-stack-boundary
11979 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
11980 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
11981 the default is 4 (16 bytes or 128 bits).
11983 @item -mincoming-stack-boundary=@var{num}
11984 @opindex mincoming-stack-boundary
11985 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
11986 boundary. If @option{-mincoming-stack-boundary} is not specified,
11987 the one specified by @option{-mpreferred-stack-boundary} will be used.
11989 On Pentium and PentiumPro, @code{double} and @code{long double} values
11990 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
11991 suffer significant run time performance penalties. On Pentium III, the
11992 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
11993 properly if it is not 16 byte aligned.
11995 To ensure proper alignment of this values on the stack, the stack boundary
11996 must be as aligned as that required by any value stored on the stack.
11997 Further, every function must be generated such that it keeps the stack
11998 aligned. Thus calling a function compiled with a higher preferred
11999 stack boundary from a function compiled with a lower preferred stack
12000 boundary will most likely misalign the stack. It is recommended that
12001 libraries that use callbacks always use the default setting.
12003 This extra alignment does consume extra stack space, and generally
12004 increases code size. Code that is sensitive to stack space usage, such
12005 as embedded systems and operating system kernels, may want to reduce the
12006 preferred alignment to @option{-mpreferred-stack-boundary=2}.
12050 These switches enable or disable the use of instructions in the MMX,
12051 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, FMA4, XOP,
12052 LWP, ABM or 3DNow!@: extended instruction sets.
12053 These extensions are also available as built-in functions: see
12054 @ref{X86 Built-in Functions}, for details of the functions enabled and
12055 disabled by these switches.
12057 To have SSE/SSE2 instructions generated automatically from floating-point
12058 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
12060 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
12061 generates new AVX instructions or AVX equivalence for all SSEx instructions
12064 These options will enable GCC to use these extended instructions in
12065 generated code, even without @option{-mfpmath=sse}. Applications which
12066 perform runtime CPU detection must compile separate files for each
12067 supported architecture, using the appropriate flags. In particular,
12068 the file containing the CPU detection code should be compiled without
12072 @itemx -mno-fused-madd
12073 @opindex mfused-madd
12074 @opindex mno-fused-madd
12075 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
12076 instructions. The default is to use these instructions.
12080 This option instructs GCC to emit a @code{cld} instruction in the prologue
12081 of functions that use string instructions. String instructions depend on
12082 the DF flag to select between autoincrement or autodecrement mode. While the
12083 ABI specifies the DF flag to be cleared on function entry, some operating
12084 systems violate this specification by not clearing the DF flag in their
12085 exception dispatchers. The exception handler can be invoked with the DF flag
12086 set which leads to wrong direction mode, when string instructions are used.
12087 This option can be enabled by default on 32-bit x86 targets by configuring
12088 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
12089 instructions can be suppressed with the @option{-mno-cld} compiler option
12094 This option will enable GCC to use CMPXCHG16B instruction in generated code.
12095 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
12096 data types. This is useful for high resolution counters that could be updated
12097 by multiple processors (or cores). This instruction is generated as part of
12098 atomic built-in functions: see @ref{Atomic Builtins} for details.
12102 This option will enable GCC to use SAHF instruction in generated 64-bit code.
12103 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
12104 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
12105 SAHF are load and store instructions, respectively, for certain status flags.
12106 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
12107 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
12111 This option will enable GCC to use movbe instruction to implement
12112 @code{__builtin_bswap32} and @code{__builtin_bswap64}.
12116 This option will enable built-in functions, @code{__builtin_ia32_crc32qi},
12117 @code{__builtin_ia32_crc32hi}. @code{__builtin_ia32_crc32si} and
12118 @code{__builtin_ia32_crc32di} to generate the crc32 machine instruction.
12122 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
12123 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Raphson step
12124 to increase precision instead of DIVSS and SQRTSS (and their vectorized
12125 variants) for single precision floating point arguments. These instructions
12126 are generated only when @option{-funsafe-math-optimizations} is enabled
12127 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
12128 Note that while the throughput of the sequence is higher than the throughput
12129 of the non-reciprocal instruction, the precision of the sequence can be
12130 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
12132 Note that GCC implements 1.0f/sqrtf(x) in terms of RSQRTSS (or RSQRTPS)
12133 already with @option{-ffast-math} (or the above option combination), and
12134 doesn't need @option{-mrecip}.
12136 @item -mveclibabi=@var{type}
12137 @opindex mveclibabi
12138 Specifies the ABI type to use for vectorizing intrinsics using an
12139 external library. Supported types are @code{svml} for the Intel short
12140 vector math library and @code{acml} for the AMD math core library style
12141 of interfacing. GCC will currently emit calls to @code{vmldExp2},
12142 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
12143 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
12144 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
12145 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
12146 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
12147 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
12148 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
12149 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
12150 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
12151 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
12152 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
12153 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
12154 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
12155 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
12156 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
12157 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
12158 compatible library will have to be specified at link time.
12160 @item -mabi=@var{name}
12162 Generate code for the specified calling convention. Permissible values
12163 are: @samp{sysv} for the ABI used on GNU/Linux and other systems and
12164 @samp{ms} for the Microsoft ABI. The default is to use the Microsoft
12165 ABI when targeting Windows. On all other systems, the default is the
12166 SYSV ABI. You can control this behavior for a specific function by
12167 using the function attribute @samp{ms_abi}/@samp{sysv_abi}.
12168 @xref{Function Attributes}.
12171 @itemx -mno-push-args
12172 @opindex mpush-args
12173 @opindex mno-push-args
12174 Use PUSH operations to store outgoing parameters. This method is shorter
12175 and usually equally fast as method using SUB/MOV operations and is enabled
12176 by default. In some cases disabling it may improve performance because of
12177 improved scheduling and reduced dependencies.
12179 @item -maccumulate-outgoing-args
12180 @opindex maccumulate-outgoing-args
12181 If enabled, the maximum amount of space required for outgoing arguments will be
12182 computed in the function prologue. This is faster on most modern CPUs
12183 because of reduced dependencies, improved scheduling and reduced stack usage
12184 when preferred stack boundary is not equal to 2. The drawback is a notable
12185 increase in code size. This switch implies @option{-mno-push-args}.
12189 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
12190 on thread-safe exception handling must compile and link all code with the
12191 @option{-mthreads} option. When compiling, @option{-mthreads} defines
12192 @option{-D_MT}; when linking, it links in a special thread helper library
12193 @option{-lmingwthrd} which cleans up per thread exception handling data.
12195 @item -mno-align-stringops
12196 @opindex mno-align-stringops
12197 Do not align destination of inlined string operations. This switch reduces
12198 code size and improves performance in case the destination is already aligned,
12199 but GCC doesn't know about it.
12201 @item -minline-all-stringops
12202 @opindex minline-all-stringops
12203 By default GCC inlines string operations only when destination is known to be
12204 aligned at least to 4 byte boundary. This enables more inlining, increase code
12205 size, but may improve performance of code that depends on fast memcpy, strlen
12206 and memset for short lengths.
12208 @item -minline-stringops-dynamically
12209 @opindex minline-stringops-dynamically
12210 For string operation of unknown size, inline runtime checks so for small
12211 blocks inline code is used, while for large blocks library call is used.
12213 @item -mstringop-strategy=@var{alg}
12214 @opindex mstringop-strategy=@var{alg}
12215 Overwrite internal decision heuristic about particular algorithm to inline
12216 string operation with. The allowed values are @code{rep_byte},
12217 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
12218 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
12219 expanding inline loop, @code{libcall} for always expanding library call.
12221 @item -momit-leaf-frame-pointer
12222 @opindex momit-leaf-frame-pointer
12223 Don't keep the frame pointer in a register for leaf functions. This
12224 avoids the instructions to save, set up and restore frame pointers and
12225 makes an extra register available in leaf functions. The option
12226 @option{-fomit-frame-pointer} removes the frame pointer for all functions
12227 which might make debugging harder.
12229 @item -mtls-direct-seg-refs
12230 @itemx -mno-tls-direct-seg-refs
12231 @opindex mtls-direct-seg-refs
12232 Controls whether TLS variables may be accessed with offsets from the
12233 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
12234 or whether the thread base pointer must be added. Whether or not this
12235 is legal depends on the operating system, and whether it maps the
12236 segment to cover the entire TLS area.
12238 For systems that use GNU libc, the default is on.
12241 @itemx -mno-sse2avx
12243 Specify that the assembler should encode SSE instructions with VEX
12244 prefix. The option @option{-mavx} turns this on by default.
12247 These @samp{-m} switches are supported in addition to the above
12248 on AMD x86-64 processors in 64-bit environments.
12255 Generate code for a 32-bit or 64-bit environment.
12256 The 32-bit environment sets int, long and pointer to 32 bits and
12257 generates code that runs on any i386 system.
12258 The 64-bit environment sets int to 32 bits and long and pointer
12259 to 64 bits and generates code for AMD's x86-64 architecture. For
12260 darwin only the -m64 option turns off the @option{-fno-pic} and
12261 @option{-mdynamic-no-pic} options.
12263 @item -mno-red-zone
12264 @opindex mno-red-zone
12265 Do not use a so called red zone for x86-64 code. The red zone is mandated
12266 by the x86-64 ABI, it is a 128-byte area beyond the location of the
12267 stack pointer that will not be modified by signal or interrupt handlers
12268 and therefore can be used for temporary data without adjusting the stack
12269 pointer. The flag @option{-mno-red-zone} disables this red zone.
12271 @item -mcmodel=small
12272 @opindex mcmodel=small
12273 Generate code for the small code model: the program and its symbols must
12274 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
12275 Programs can be statically or dynamically linked. This is the default
12278 @item -mcmodel=kernel
12279 @opindex mcmodel=kernel
12280 Generate code for the kernel code model. The kernel runs in the
12281 negative 2 GB of the address space.
12282 This model has to be used for Linux kernel code.
12284 @item -mcmodel=medium
12285 @opindex mcmodel=medium
12286 Generate code for the medium model: The program is linked in the lower 2
12287 GB of the address space. Small symbols are also placed there. Symbols
12288 with sizes larger than @option{-mlarge-data-threshold} are put into
12289 large data or bss sections and can be located above 2GB. Programs can
12290 be statically or dynamically linked.
12292 @item -mcmodel=large
12293 @opindex mcmodel=large
12294 Generate code for the large model: This model makes no assumptions
12295 about addresses and sizes of sections.
12298 @node IA-64 Options
12299 @subsection IA-64 Options
12300 @cindex IA-64 Options
12302 These are the @samp{-m} options defined for the Intel IA-64 architecture.
12306 @opindex mbig-endian
12307 Generate code for a big endian target. This is the default for HP-UX@.
12309 @item -mlittle-endian
12310 @opindex mlittle-endian
12311 Generate code for a little endian target. This is the default for AIX5
12317 @opindex mno-gnu-as
12318 Generate (or don't) code for the GNU assembler. This is the default.
12319 @c Also, this is the default if the configure option @option{--with-gnu-as}
12325 @opindex mno-gnu-ld
12326 Generate (or don't) code for the GNU linker. This is the default.
12327 @c Also, this is the default if the configure option @option{--with-gnu-ld}
12332 Generate code that does not use a global pointer register. The result
12333 is not position independent code, and violates the IA-64 ABI@.
12335 @item -mvolatile-asm-stop
12336 @itemx -mno-volatile-asm-stop
12337 @opindex mvolatile-asm-stop
12338 @opindex mno-volatile-asm-stop
12339 Generate (or don't) a stop bit immediately before and after volatile asm
12342 @item -mregister-names
12343 @itemx -mno-register-names
12344 @opindex mregister-names
12345 @opindex mno-register-names
12346 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
12347 the stacked registers. This may make assembler output more readable.
12353 Disable (or enable) optimizations that use the small data section. This may
12354 be useful for working around optimizer bugs.
12356 @item -mconstant-gp
12357 @opindex mconstant-gp
12358 Generate code that uses a single constant global pointer value. This is
12359 useful when compiling kernel code.
12363 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
12364 This is useful when compiling firmware code.
12366 @item -minline-float-divide-min-latency
12367 @opindex minline-float-divide-min-latency
12368 Generate code for inline divides of floating point values
12369 using the minimum latency algorithm.
12371 @item -minline-float-divide-max-throughput
12372 @opindex minline-float-divide-max-throughput
12373 Generate code for inline divides of floating point values
12374 using the maximum throughput algorithm.
12376 @item -mno-inline-float-divide
12377 @opindex mno-inline-float-divide
12378 Do not generate inline code for divides of floating point values.
12380 @item -minline-int-divide-min-latency
12381 @opindex minline-int-divide-min-latency
12382 Generate code for inline divides of integer values
12383 using the minimum latency algorithm.
12385 @item -minline-int-divide-max-throughput
12386 @opindex minline-int-divide-max-throughput
12387 Generate code for inline divides of integer values
12388 using the maximum throughput algorithm.
12390 @item -mno-inline-int-divide
12391 @opindex mno-inline-int-divide
12392 Do not generate inline code for divides of integer values.
12394 @item -minline-sqrt-min-latency
12395 @opindex minline-sqrt-min-latency
12396 Generate code for inline square roots
12397 using the minimum latency algorithm.
12399 @item -minline-sqrt-max-throughput
12400 @opindex minline-sqrt-max-throughput
12401 Generate code for inline square roots
12402 using the maximum throughput algorithm.
12404 @item -mno-inline-sqrt
12405 @opindex mno-inline-sqrt
12406 Do not generate inline code for sqrt.
12409 @itemx -mno-fused-madd
12410 @opindex mfused-madd
12411 @opindex mno-fused-madd
12412 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
12413 instructions. The default is to use these instructions.
12415 @item -mno-dwarf2-asm
12416 @itemx -mdwarf2-asm
12417 @opindex mno-dwarf2-asm
12418 @opindex mdwarf2-asm
12419 Don't (or do) generate assembler code for the DWARF2 line number debugging
12420 info. This may be useful when not using the GNU assembler.
12422 @item -mearly-stop-bits
12423 @itemx -mno-early-stop-bits
12424 @opindex mearly-stop-bits
12425 @opindex mno-early-stop-bits
12426 Allow stop bits to be placed earlier than immediately preceding the
12427 instruction that triggered the stop bit. This can improve instruction
12428 scheduling, but does not always do so.
12430 @item -mfixed-range=@var{register-range}
12431 @opindex mfixed-range
12432 Generate code treating the given register range as fixed registers.
12433 A fixed register is one that the register allocator can not use. This is
12434 useful when compiling kernel code. A register range is specified as
12435 two registers separated by a dash. Multiple register ranges can be
12436 specified separated by a comma.
12438 @item -mtls-size=@var{tls-size}
12440 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
12443 @item -mtune=@var{cpu-type}
12445 Tune the instruction scheduling for a particular CPU, Valid values are
12446 itanium, itanium1, merced, itanium2, and mckinley.
12452 Generate code for a 32-bit or 64-bit environment.
12453 The 32-bit environment sets int, long and pointer to 32 bits.
12454 The 64-bit environment sets int to 32 bits and long and pointer
12455 to 64 bits. These are HP-UX specific flags.
12457 @item -mno-sched-br-data-spec
12458 @itemx -msched-br-data-spec
12459 @opindex mno-sched-br-data-spec
12460 @opindex msched-br-data-spec
12461 (Dis/En)able data speculative scheduling before reload.
12462 This will result in generation of the ld.a instructions and
12463 the corresponding check instructions (ld.c / chk.a).
12464 The default is 'disable'.
12466 @item -msched-ar-data-spec
12467 @itemx -mno-sched-ar-data-spec
12468 @opindex msched-ar-data-spec
12469 @opindex mno-sched-ar-data-spec
12470 (En/Dis)able data speculative scheduling after reload.
12471 This will result in generation of the ld.a instructions and
12472 the corresponding check instructions (ld.c / chk.a).
12473 The default is 'enable'.
12475 @item -mno-sched-control-spec
12476 @itemx -msched-control-spec
12477 @opindex mno-sched-control-spec
12478 @opindex msched-control-spec
12479 (Dis/En)able control speculative scheduling. This feature is
12480 available only during region scheduling (i.e.@: before reload).
12481 This will result in generation of the ld.s instructions and
12482 the corresponding check instructions chk.s .
12483 The default is 'disable'.
12485 @item -msched-br-in-data-spec
12486 @itemx -mno-sched-br-in-data-spec
12487 @opindex msched-br-in-data-spec
12488 @opindex mno-sched-br-in-data-spec
12489 (En/Dis)able speculative scheduling of the instructions that
12490 are dependent on the data speculative loads before reload.
12491 This is effective only with @option{-msched-br-data-spec} enabled.
12492 The default is 'enable'.
12494 @item -msched-ar-in-data-spec
12495 @itemx -mno-sched-ar-in-data-spec
12496 @opindex msched-ar-in-data-spec
12497 @opindex mno-sched-ar-in-data-spec
12498 (En/Dis)able speculative scheduling of the instructions that
12499 are dependent on the data speculative loads after reload.
12500 This is effective only with @option{-msched-ar-data-spec} enabled.
12501 The default is 'enable'.
12503 @item -msched-in-control-spec
12504 @itemx -mno-sched-in-control-spec
12505 @opindex msched-in-control-spec
12506 @opindex mno-sched-in-control-spec
12507 (En/Dis)able speculative scheduling of the instructions that
12508 are dependent on the control speculative loads.
12509 This is effective only with @option{-msched-control-spec} enabled.
12510 The default is 'enable'.
12512 @item -mno-sched-prefer-non-data-spec-insns
12513 @itemx -msched-prefer-non-data-spec-insns
12514 @opindex mno-sched-prefer-non-data-spec-insns
12515 @opindex msched-prefer-non-data-spec-insns
12516 If enabled, data speculative instructions will be chosen for schedule
12517 only if there are no other choices at the moment. This will make
12518 the use of the data speculation much more conservative.
12519 The default is 'disable'.
12521 @item -mno-sched-prefer-non-control-spec-insns
12522 @itemx -msched-prefer-non-control-spec-insns
12523 @opindex mno-sched-prefer-non-control-spec-insns
12524 @opindex msched-prefer-non-control-spec-insns
12525 If enabled, control speculative instructions will be chosen for schedule
12526 only if there are no other choices at the moment. This will make
12527 the use of the control speculation much more conservative.
12528 The default is 'disable'.
12530 @item -mno-sched-count-spec-in-critical-path
12531 @itemx -msched-count-spec-in-critical-path
12532 @opindex mno-sched-count-spec-in-critical-path
12533 @opindex msched-count-spec-in-critical-path
12534 If enabled, speculative dependencies will be considered during
12535 computation of the instructions priorities. This will make the use of the
12536 speculation a bit more conservative.
12537 The default is 'disable'.
12539 @item -msched-spec-ldc
12540 @opindex msched-spec-ldc
12541 Use a simple data speculation check. This option is on by default.
12543 @item -msched-control-spec-ldc
12544 @opindex msched-spec-ldc
12545 Use a simple check for control speculation. This option is on by default.
12547 @item -msched-stop-bits-after-every-cycle
12548 @opindex msched-stop-bits-after-every-cycle
12549 Place a stop bit after every cycle when scheduling. This option is on
12552 @item -msched-fp-mem-deps-zero-cost
12553 @opindex msched-fp-mem-deps-zero-cost
12554 Assume that floating-point stores and loads are not likely to cause a conflict
12555 when placed into the same instruction group. This option is disabled by
12558 @item -msel-sched-dont-check-control-spec
12559 @opindex msel-sched-dont-check-control-spec
12560 Generate checks for control speculation in selective scheduling.
12561 This flag is disabled by default.
12563 @item -msched-max-memory-insns=@var{max-insns}
12564 @opindex msched-max-memory-insns
12565 Limit on the number of memory insns per instruction group, giving lower
12566 priority to subsequent memory insns attempting to schedule in the same
12567 instruction group. Frequently useful to prevent cache bank conflicts.
12568 The default value is 1.
12570 @item -msched-max-memory-insns-hard-limit
12571 @opindex msched-max-memory-insns-hard-limit
12572 Disallow more than `msched-max-memory-insns' in instruction group.
12573 Otherwise, limit is `soft' meaning that we would prefer non-memory operations
12574 when limit is reached but may still schedule memory operations.
12578 @node IA-64/VMS Options
12579 @subsection IA-64/VMS Options
12581 These @samp{-m} options are defined for the IA-64/VMS implementations:
12584 @item -mvms-return-codes
12585 @opindex mvms-return-codes
12586 Return VMS condition codes from main. The default is to return POSIX
12587 style condition (e.g.@ error) codes.
12589 @item -mdebug-main=@var{prefix}
12590 @opindex mdebug-main=@var{prefix}
12591 Flag the first routine whose name starts with @var{prefix} as the main
12592 routine for the debugger.
12596 Default to 64bit memory allocation routines.
12600 @subsection LM32 Options
12601 @cindex LM32 options
12603 These @option{-m} options are defined for the Lattice Mico32 architecture:
12606 @item -mbarrel-shift-enabled
12607 @opindex mbarrel-shift-enabled
12608 Enable barrel-shift instructions.
12610 @item -mdivide-enabled
12611 @opindex mdivide-enabled
12612 Enable divide and modulus instructions.
12614 @item -mmultiply-enabled
12615 @opindex multiply-enabled
12616 Enable multiply instructions.
12618 @item -msign-extend-enabled
12619 @opindex msign-extend-enabled
12620 Enable sign extend instructions.
12622 @item -muser-enabled
12623 @opindex muser-enabled
12624 Enable user-defined instructions.
12629 @subsection M32C Options
12630 @cindex M32C options
12633 @item -mcpu=@var{name}
12635 Select the CPU for which code is generated. @var{name} may be one of
12636 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
12637 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
12638 the M32C/80 series.
12642 Specifies that the program will be run on the simulator. This causes
12643 an alternate runtime library to be linked in which supports, for
12644 example, file I/O@. You must not use this option when generating
12645 programs that will run on real hardware; you must provide your own
12646 runtime library for whatever I/O functions are needed.
12648 @item -memregs=@var{number}
12650 Specifies the number of memory-based pseudo-registers GCC will use
12651 during code generation. These pseudo-registers will be used like real
12652 registers, so there is a tradeoff between GCC's ability to fit the
12653 code into available registers, and the performance penalty of using
12654 memory instead of registers. Note that all modules in a program must
12655 be compiled with the same value for this option. Because of that, you
12656 must not use this option with the default runtime libraries gcc
12661 @node M32R/D Options
12662 @subsection M32R/D Options
12663 @cindex M32R/D options
12665 These @option{-m} options are defined for Renesas M32R/D architectures:
12670 Generate code for the M32R/2@.
12674 Generate code for the M32R/X@.
12678 Generate code for the M32R@. This is the default.
12680 @item -mmodel=small
12681 @opindex mmodel=small
12682 Assume all objects live in the lower 16MB of memory (so that their addresses
12683 can be loaded with the @code{ld24} instruction), and assume all subroutines
12684 are reachable with the @code{bl} instruction.
12685 This is the default.
12687 The addressability of a particular object can be set with the
12688 @code{model} attribute.
12690 @item -mmodel=medium
12691 @opindex mmodel=medium
12692 Assume objects may be anywhere in the 32-bit address space (the compiler
12693 will generate @code{seth/add3} instructions to load their addresses), and
12694 assume all subroutines are reachable with the @code{bl} instruction.
12696 @item -mmodel=large
12697 @opindex mmodel=large
12698 Assume objects may be anywhere in the 32-bit address space (the compiler
12699 will generate @code{seth/add3} instructions to load their addresses), and
12700 assume subroutines may not be reachable with the @code{bl} instruction
12701 (the compiler will generate the much slower @code{seth/add3/jl}
12702 instruction sequence).
12705 @opindex msdata=none
12706 Disable use of the small data area. Variables will be put into
12707 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
12708 @code{section} attribute has been specified).
12709 This is the default.
12711 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
12712 Objects may be explicitly put in the small data area with the
12713 @code{section} attribute using one of these sections.
12715 @item -msdata=sdata
12716 @opindex msdata=sdata
12717 Put small global and static data in the small data area, but do not
12718 generate special code to reference them.
12721 @opindex msdata=use
12722 Put small global and static data in the small data area, and generate
12723 special instructions to reference them.
12727 @cindex smaller data references
12728 Put global and static objects less than or equal to @var{num} bytes
12729 into the small data or bss sections instead of the normal data or bss
12730 sections. The default value of @var{num} is 8.
12731 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
12732 for this option to have any effect.
12734 All modules should be compiled with the same @option{-G @var{num}} value.
12735 Compiling with different values of @var{num} may or may not work; if it
12736 doesn't the linker will give an error message---incorrect code will not be
12741 Makes the M32R specific code in the compiler display some statistics
12742 that might help in debugging programs.
12744 @item -malign-loops
12745 @opindex malign-loops
12746 Align all loops to a 32-byte boundary.
12748 @item -mno-align-loops
12749 @opindex mno-align-loops
12750 Do not enforce a 32-byte alignment for loops. This is the default.
12752 @item -missue-rate=@var{number}
12753 @opindex missue-rate=@var{number}
12754 Issue @var{number} instructions per cycle. @var{number} can only be 1
12757 @item -mbranch-cost=@var{number}
12758 @opindex mbranch-cost=@var{number}
12759 @var{number} can only be 1 or 2. If it is 1 then branches will be
12760 preferred over conditional code, if it is 2, then the opposite will
12763 @item -mflush-trap=@var{number}
12764 @opindex mflush-trap=@var{number}
12765 Specifies the trap number to use to flush the cache. The default is
12766 12. Valid numbers are between 0 and 15 inclusive.
12768 @item -mno-flush-trap
12769 @opindex mno-flush-trap
12770 Specifies that the cache cannot be flushed by using a trap.
12772 @item -mflush-func=@var{name}
12773 @opindex mflush-func=@var{name}
12774 Specifies the name of the operating system function to call to flush
12775 the cache. The default is @emph{_flush_cache}, but a function call
12776 will only be used if a trap is not available.
12778 @item -mno-flush-func
12779 @opindex mno-flush-func
12780 Indicates that there is no OS function for flushing the cache.
12784 @node M680x0 Options
12785 @subsection M680x0 Options
12786 @cindex M680x0 options
12788 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
12789 The default settings depend on which architecture was selected when
12790 the compiler was configured; the defaults for the most common choices
12794 @item -march=@var{arch}
12796 Generate code for a specific M680x0 or ColdFire instruction set
12797 architecture. Permissible values of @var{arch} for M680x0
12798 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
12799 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
12800 architectures are selected according to Freescale's ISA classification
12801 and the permissible values are: @samp{isaa}, @samp{isaaplus},
12802 @samp{isab} and @samp{isac}.
12804 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
12805 code for a ColdFire target. The @var{arch} in this macro is one of the
12806 @option{-march} arguments given above.
12808 When used together, @option{-march} and @option{-mtune} select code
12809 that runs on a family of similar processors but that is optimized
12810 for a particular microarchitecture.
12812 @item -mcpu=@var{cpu}
12814 Generate code for a specific M680x0 or ColdFire processor.
12815 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
12816 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
12817 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
12818 below, which also classifies the CPUs into families:
12820 @multitable @columnfractions 0.20 0.80
12821 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
12822 @item @samp{51} @tab @samp{51} @samp{51ac} @samp{51cn} @samp{51em} @samp{51qe}
12823 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
12824 @item @samp{5206e} @tab @samp{5206e}
12825 @item @samp{5208} @tab @samp{5207} @samp{5208}
12826 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
12827 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
12828 @item @samp{5216} @tab @samp{5214} @samp{5216}
12829 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
12830 @item @samp{5225} @tab @samp{5224} @samp{5225}
12831 @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259}
12832 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
12833 @item @samp{5249} @tab @samp{5249}
12834 @item @samp{5250} @tab @samp{5250}
12835 @item @samp{5271} @tab @samp{5270} @samp{5271}
12836 @item @samp{5272} @tab @samp{5272}
12837 @item @samp{5275} @tab @samp{5274} @samp{5275}
12838 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
12839 @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017}
12840 @item @samp{5307} @tab @samp{5307}
12841 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
12842 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
12843 @item @samp{5407} @tab @samp{5407}
12844 @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
12847 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
12848 @var{arch} is compatible with @var{cpu}. Other combinations of
12849 @option{-mcpu} and @option{-march} are rejected.
12851 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
12852 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
12853 where the value of @var{family} is given by the table above.
12855 @item -mtune=@var{tune}
12857 Tune the code for a particular microarchitecture, within the
12858 constraints set by @option{-march} and @option{-mcpu}.
12859 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
12860 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
12861 and @samp{cpu32}. The ColdFire microarchitectures
12862 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
12864 You can also use @option{-mtune=68020-40} for code that needs
12865 to run relatively well on 68020, 68030 and 68040 targets.
12866 @option{-mtune=68020-60} is similar but includes 68060 targets
12867 as well. These two options select the same tuning decisions as
12868 @option{-m68020-40} and @option{-m68020-60} respectively.
12870 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
12871 when tuning for 680x0 architecture @var{arch}. It also defines
12872 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
12873 option is used. If gcc is tuning for a range of architectures,
12874 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
12875 it defines the macros for every architecture in the range.
12877 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
12878 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
12879 of the arguments given above.
12885 Generate output for a 68000. This is the default
12886 when the compiler is configured for 68000-based systems.
12887 It is equivalent to @option{-march=68000}.
12889 Use this option for microcontrollers with a 68000 or EC000 core,
12890 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
12894 Generate output for a 68010. This is the default
12895 when the compiler is configured for 68010-based systems.
12896 It is equivalent to @option{-march=68010}.
12902 Generate output for a 68020. This is the default
12903 when the compiler is configured for 68020-based systems.
12904 It is equivalent to @option{-march=68020}.
12908 Generate output for a 68030. This is the default when the compiler is
12909 configured for 68030-based systems. It is equivalent to
12910 @option{-march=68030}.
12914 Generate output for a 68040. This is the default when the compiler is
12915 configured for 68040-based systems. It is equivalent to
12916 @option{-march=68040}.
12918 This option inhibits the use of 68881/68882 instructions that have to be
12919 emulated by software on the 68040. Use this option if your 68040 does not
12920 have code to emulate those instructions.
12924 Generate output for a 68060. This is the default when the compiler is
12925 configured for 68060-based systems. It is equivalent to
12926 @option{-march=68060}.
12928 This option inhibits the use of 68020 and 68881/68882 instructions that
12929 have to be emulated by software on the 68060. Use this option if your 68060
12930 does not have code to emulate those instructions.
12934 Generate output for a CPU32. This is the default
12935 when the compiler is configured for CPU32-based systems.
12936 It is equivalent to @option{-march=cpu32}.
12938 Use this option for microcontrollers with a
12939 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
12940 68336, 68340, 68341, 68349 and 68360.
12944 Generate output for a 520X ColdFire CPU@. This is the default
12945 when the compiler is configured for 520X-based systems.
12946 It is equivalent to @option{-mcpu=5206}, and is now deprecated
12947 in favor of that option.
12949 Use this option for microcontroller with a 5200 core, including
12950 the MCF5202, MCF5203, MCF5204 and MCF5206.
12954 Generate output for a 5206e ColdFire CPU@. The option is now
12955 deprecated in favor of the equivalent @option{-mcpu=5206e}.
12959 Generate output for a member of the ColdFire 528X family.
12960 The option is now deprecated in favor of the equivalent
12961 @option{-mcpu=528x}.
12965 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
12966 in favor of the equivalent @option{-mcpu=5307}.
12970 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
12971 in favor of the equivalent @option{-mcpu=5407}.
12975 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
12976 This includes use of hardware floating point instructions.
12977 The option is equivalent to @option{-mcpu=547x}, and is now
12978 deprecated in favor of that option.
12982 Generate output for a 68040, without using any of the new instructions.
12983 This results in code which can run relatively efficiently on either a
12984 68020/68881 or a 68030 or a 68040. The generated code does use the
12985 68881 instructions that are emulated on the 68040.
12987 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
12991 Generate output for a 68060, without using any of the new instructions.
12992 This results in code which can run relatively efficiently on either a
12993 68020/68881 or a 68030 or a 68040. The generated code does use the
12994 68881 instructions that are emulated on the 68060.
12996 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
13000 @opindex mhard-float
13002 Generate floating-point instructions. This is the default for 68020
13003 and above, and for ColdFire devices that have an FPU@. It defines the
13004 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
13005 on ColdFire targets.
13008 @opindex msoft-float
13009 Do not generate floating-point instructions; use library calls instead.
13010 This is the default for 68000, 68010, and 68832 targets. It is also
13011 the default for ColdFire devices that have no FPU.
13017 Generate (do not generate) ColdFire hardware divide and remainder
13018 instructions. If @option{-march} is used without @option{-mcpu},
13019 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
13020 architectures. Otherwise, the default is taken from the target CPU
13021 (either the default CPU, or the one specified by @option{-mcpu}). For
13022 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
13023 @option{-mcpu=5206e}.
13025 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
13029 Consider type @code{int} to be 16 bits wide, like @code{short int}.
13030 Additionally, parameters passed on the stack are also aligned to a
13031 16-bit boundary even on targets whose API mandates promotion to 32-bit.
13035 Do not consider type @code{int} to be 16 bits wide. This is the default.
13038 @itemx -mno-bitfield
13039 @opindex mnobitfield
13040 @opindex mno-bitfield
13041 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
13042 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
13046 Do use the bit-field instructions. The @option{-m68020} option implies
13047 @option{-mbitfield}. This is the default if you use a configuration
13048 designed for a 68020.
13052 Use a different function-calling convention, in which functions
13053 that take a fixed number of arguments return with the @code{rtd}
13054 instruction, which pops their arguments while returning. This
13055 saves one instruction in the caller since there is no need to pop
13056 the arguments there.
13058 This calling convention is incompatible with the one normally
13059 used on Unix, so you cannot use it if you need to call libraries
13060 compiled with the Unix compiler.
13062 Also, you must provide function prototypes for all functions that
13063 take variable numbers of arguments (including @code{printf});
13064 otherwise incorrect code will be generated for calls to those
13067 In addition, seriously incorrect code will result if you call a
13068 function with too many arguments. (Normally, extra arguments are
13069 harmlessly ignored.)
13071 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
13072 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
13076 Do not use the calling conventions selected by @option{-mrtd}.
13077 This is the default.
13080 @itemx -mno-align-int
13081 @opindex malign-int
13082 @opindex mno-align-int
13083 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
13084 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
13085 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
13086 Aligning variables on 32-bit boundaries produces code that runs somewhat
13087 faster on processors with 32-bit busses at the expense of more memory.
13089 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
13090 align structures containing the above types differently than
13091 most published application binary interface specifications for the m68k.
13095 Use the pc-relative addressing mode of the 68000 directly, instead of
13096 using a global offset table. At present, this option implies @option{-fpic},
13097 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
13098 not presently supported with @option{-mpcrel}, though this could be supported for
13099 68020 and higher processors.
13101 @item -mno-strict-align
13102 @itemx -mstrict-align
13103 @opindex mno-strict-align
13104 @opindex mstrict-align
13105 Do not (do) assume that unaligned memory references will be handled by
13109 Generate code that allows the data segment to be located in a different
13110 area of memory from the text segment. This allows for execute in place in
13111 an environment without virtual memory management. This option implies
13114 @item -mno-sep-data
13115 Generate code that assumes that the data segment follows the text segment.
13116 This is the default.
13118 @item -mid-shared-library
13119 Generate code that supports shared libraries via the library ID method.
13120 This allows for execute in place and shared libraries in an environment
13121 without virtual memory management. This option implies @option{-fPIC}.
13123 @item -mno-id-shared-library
13124 Generate code that doesn't assume ID based shared libraries are being used.
13125 This is the default.
13127 @item -mshared-library-id=n
13128 Specified the identification number of the ID based shared library being
13129 compiled. Specifying a value of 0 will generate more compact code, specifying
13130 other values will force the allocation of that number to the current
13131 library but is no more space or time efficient than omitting this option.
13137 When generating position-independent code for ColdFire, generate code
13138 that works if the GOT has more than 8192 entries. This code is
13139 larger and slower than code generated without this option. On M680x0
13140 processors, this option is not needed; @option{-fPIC} suffices.
13142 GCC normally uses a single instruction to load values from the GOT@.
13143 While this is relatively efficient, it only works if the GOT
13144 is smaller than about 64k. Anything larger causes the linker
13145 to report an error such as:
13147 @cindex relocation truncated to fit (ColdFire)
13149 relocation truncated to fit: R_68K_GOT16O foobar
13152 If this happens, you should recompile your code with @option{-mxgot}.
13153 It should then work with very large GOTs. However, code generated with
13154 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
13155 the value of a global symbol.
13157 Note that some linkers, including newer versions of the GNU linker,
13158 can create multiple GOTs and sort GOT entries. If you have such a linker,
13159 you should only need to use @option{-mxgot} when compiling a single
13160 object file that accesses more than 8192 GOT entries. Very few do.
13162 These options have no effect unless GCC is generating
13163 position-independent code.
13167 @node M68hc1x Options
13168 @subsection M68hc1x Options
13169 @cindex M68hc1x options
13171 These are the @samp{-m} options defined for the 68hc11 and 68hc12
13172 microcontrollers. The default values for these options depends on
13173 which style of microcontroller was selected when the compiler was configured;
13174 the defaults for the most common choices are given below.
13181 Generate output for a 68HC11. This is the default
13182 when the compiler is configured for 68HC11-based systems.
13188 Generate output for a 68HC12. This is the default
13189 when the compiler is configured for 68HC12-based systems.
13195 Generate output for a 68HCS12.
13197 @item -mauto-incdec
13198 @opindex mauto-incdec
13199 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
13206 Enable the use of 68HC12 min and max instructions.
13209 @itemx -mno-long-calls
13210 @opindex mlong-calls
13211 @opindex mno-long-calls
13212 Treat all calls as being far away (near). If calls are assumed to be
13213 far away, the compiler will use the @code{call} instruction to
13214 call a function and the @code{rtc} instruction for returning.
13218 Consider type @code{int} to be 16 bits wide, like @code{short int}.
13220 @item -msoft-reg-count=@var{count}
13221 @opindex msoft-reg-count
13222 Specify the number of pseudo-soft registers which are used for the
13223 code generation. The maximum number is 32. Using more pseudo-soft
13224 register may or may not result in better code depending on the program.
13225 The default is 4 for 68HC11 and 2 for 68HC12.
13229 @node MCore Options
13230 @subsection MCore Options
13231 @cindex MCore options
13233 These are the @samp{-m} options defined for the Motorola M*Core
13239 @itemx -mno-hardlit
13241 @opindex mno-hardlit
13242 Inline constants into the code stream if it can be done in two
13243 instructions or less.
13249 Use the divide instruction. (Enabled by default).
13251 @item -mrelax-immediate
13252 @itemx -mno-relax-immediate
13253 @opindex mrelax-immediate
13254 @opindex mno-relax-immediate
13255 Allow arbitrary sized immediates in bit operations.
13257 @item -mwide-bitfields
13258 @itemx -mno-wide-bitfields
13259 @opindex mwide-bitfields
13260 @opindex mno-wide-bitfields
13261 Always treat bit-fields as int-sized.
13263 @item -m4byte-functions
13264 @itemx -mno-4byte-functions
13265 @opindex m4byte-functions
13266 @opindex mno-4byte-functions
13267 Force all functions to be aligned to a four byte boundary.
13269 @item -mcallgraph-data
13270 @itemx -mno-callgraph-data
13271 @opindex mcallgraph-data
13272 @opindex mno-callgraph-data
13273 Emit callgraph information.
13276 @itemx -mno-slow-bytes
13277 @opindex mslow-bytes
13278 @opindex mno-slow-bytes
13279 Prefer word access when reading byte quantities.
13281 @item -mlittle-endian
13282 @itemx -mbig-endian
13283 @opindex mlittle-endian
13284 @opindex mbig-endian
13285 Generate code for a little endian target.
13291 Generate code for the 210 processor.
13295 Assume that run-time support has been provided and so omit the
13296 simulator library (@file{libsim.a)} from the linker command line.
13298 @item -mstack-increment=@var{size}
13299 @opindex mstack-increment
13300 Set the maximum amount for a single stack increment operation. Large
13301 values can increase the speed of programs which contain functions
13302 that need a large amount of stack space, but they can also trigger a
13303 segmentation fault if the stack is extended too much. The default
13309 @subsection MeP Options
13310 @cindex MeP options
13316 Enables the @code{abs} instruction, which is the absolute difference
13317 between two registers.
13321 Enables all the optional instructions - average, multiply, divide, bit
13322 operations, leading zero, absolute difference, min/max, clip, and
13328 Enables the @code{ave} instruction, which computes the average of two
13331 @item -mbased=@var{n}
13333 Variables of size @var{n} bytes or smaller will be placed in the
13334 @code{.based} section by default. Based variables use the @code{$tp}
13335 register as a base register, and there is a 128 byte limit to the
13336 @code{.based} section.
13340 Enables the bit operation instructions - bit test (@code{btstm}), set
13341 (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
13342 test-and-set (@code{tas}).
13344 @item -mc=@var{name}
13346 Selects which section constant data will be placed in. @var{name} may
13347 be @code{tiny}, @code{near}, or @code{far}.
13351 Enables the @code{clip} instruction. Note that @code{-mclip} is not
13352 useful unless you also provide @code{-mminmax}.
13354 @item -mconfig=@var{name}
13356 Selects one of the build-in core configurations. Each MeP chip has
13357 one or more modules in it; each module has a core CPU and a variety of
13358 coprocessors, optional instructions, and peripherals. The
13359 @code{MeP-Integrator} tool, not part of GCC, provides these
13360 configurations through this option; using this option is the same as
13361 using all the corresponding command line options. The default
13362 configuration is @code{default}.
13366 Enables the coprocessor instructions. By default, this is a 32-bit
13367 coprocessor. Note that the coprocessor is normally enabled via the
13368 @code{-mconfig=} option.
13372 Enables the 32-bit coprocessor's instructions.
13376 Enables the 64-bit coprocessor's instructions.
13380 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
13384 Causes constant variables to be placed in the @code{.near} section.
13388 Enables the @code{div} and @code{divu} instructions.
13392 Generate big-endian code.
13396 Generate little-endian code.
13398 @item -mio-volatile
13399 @opindex mio-volatile
13400 Tells the compiler that any variable marked with the @code{io}
13401 attribute is to be considered volatile.
13405 Causes variables to be assigned to the @code{.far} section by default.
13409 Enables the @code{leadz} (leading zero) instruction.
13413 Causes variables to be assigned to the @code{.near} section by default.
13417 Enables the @code{min} and @code{max} instructions.
13421 Enables the multiplication and multiply-accumulate instructions.
13425 Disables all the optional instructions enabled by @code{-mall-opts}.
13429 Enables the @code{repeat} and @code{erepeat} instructions, used for
13430 low-overhead looping.
13434 Causes all variables to default to the @code{.tiny} section. Note
13435 that there is a 65536 byte limit to this section. Accesses to these
13436 variables use the @code{%gp} base register.
13440 Enables the saturation instructions. Note that the compiler does not
13441 currently generate these itself, but this option is included for
13442 compatibility with other tools, like @code{as}.
13446 Link the SDRAM-based runtime instead of the default ROM-based runtime.
13450 Link the simulator runtime libraries.
13454 Link the simulator runtime libraries, excluding built-in support
13455 for reset and exception vectors and tables.
13459 Causes all functions to default to the @code{.far} section. Without
13460 this option, functions default to the @code{.near} section.
13462 @item -mtiny=@var{n}
13464 Variables that are @var{n} bytes or smaller will be allocated to the
13465 @code{.tiny} section. These variables use the @code{$gp} base
13466 register. The default for this option is 4, but note that there's a
13467 65536 byte limit to the @code{.tiny} section.
13472 @subsection MIPS Options
13473 @cindex MIPS options
13479 Generate big-endian code.
13483 Generate little-endian code. This is the default for @samp{mips*el-*-*}
13486 @item -march=@var{arch}
13488 Generate code that will run on @var{arch}, which can be the name of a
13489 generic MIPS ISA, or the name of a particular processor.
13491 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
13492 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
13493 The processor names are:
13494 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
13495 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
13496 @samp{5kc}, @samp{5kf},
13498 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
13499 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
13500 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
13501 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
13502 @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
13503 @samp{loongson2e}, @samp{loongson2f},
13507 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
13508 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
13509 @samp{rm7000}, @samp{rm9000},
13510 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
13513 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
13514 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
13516 The special value @samp{from-abi} selects the
13517 most compatible architecture for the selected ABI (that is,
13518 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
13520 Native Linux/GNU toolchains also support the value @samp{native},
13521 which selects the best architecture option for the host processor.
13522 @option{-march=native} has no effect if GCC does not recognize
13525 In processor names, a final @samp{000} can be abbreviated as @samp{k}
13526 (for example, @samp{-march=r2k}). Prefixes are optional, and
13527 @samp{vr} may be written @samp{r}.
13529 Names of the form @samp{@var{n}f2_1} refer to processors with
13530 FPUs clocked at half the rate of the core, names of the form
13531 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
13532 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
13533 processors with FPUs clocked a ratio of 3:2 with respect to the core.
13534 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
13535 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
13536 accepted as synonyms for @samp{@var{n}f1_1}.
13538 GCC defines two macros based on the value of this option. The first
13539 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
13540 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
13541 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
13542 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
13543 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
13545 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
13546 above. In other words, it will have the full prefix and will not
13547 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
13548 the macro names the resolved architecture (either @samp{"mips1"} or
13549 @samp{"mips3"}). It names the default architecture when no
13550 @option{-march} option is given.
13552 @item -mtune=@var{arch}
13554 Optimize for @var{arch}. Among other things, this option controls
13555 the way instructions are scheduled, and the perceived cost of arithmetic
13556 operations. The list of @var{arch} values is the same as for
13559 When this option is not used, GCC will optimize for the processor
13560 specified by @option{-march}. By using @option{-march} and
13561 @option{-mtune} together, it is possible to generate code that will
13562 run on a family of processors, but optimize the code for one
13563 particular member of that family.
13565 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
13566 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
13567 @samp{-march} ones described above.
13571 Equivalent to @samp{-march=mips1}.
13575 Equivalent to @samp{-march=mips2}.
13579 Equivalent to @samp{-march=mips3}.
13583 Equivalent to @samp{-march=mips4}.
13587 Equivalent to @samp{-march=mips32}.
13591 Equivalent to @samp{-march=mips32r2}.
13595 Equivalent to @samp{-march=mips64}.
13599 Equivalent to @samp{-march=mips64r2}.
13604 @opindex mno-mips16
13605 Generate (do not generate) MIPS16 code. If GCC is targetting a
13606 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
13608 MIPS16 code generation can also be controlled on a per-function basis
13609 by means of @code{mips16} and @code{nomips16} attributes.
13610 @xref{Function Attributes}, for more information.
13612 @item -mflip-mips16
13613 @opindex mflip-mips16
13614 Generate MIPS16 code on alternating functions. This option is provided
13615 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
13616 not intended for ordinary use in compiling user code.
13618 @item -minterlink-mips16
13619 @itemx -mno-interlink-mips16
13620 @opindex minterlink-mips16
13621 @opindex mno-interlink-mips16
13622 Require (do not require) that non-MIPS16 code be link-compatible with
13625 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
13626 it must either use a call or an indirect jump. @option{-minterlink-mips16}
13627 therefore disables direct jumps unless GCC knows that the target of the
13628 jump is not MIPS16.
13640 Generate code for the given ABI@.
13642 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
13643 generates 64-bit code when you select a 64-bit architecture, but you
13644 can use @option{-mgp32} to get 32-bit code instead.
13646 For information about the O64 ABI, see
13647 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
13649 GCC supports a variant of the o32 ABI in which floating-point registers
13650 are 64 rather than 32 bits wide. You can select this combination with
13651 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
13652 and @samp{mfhc1} instructions and is therefore only supported for
13653 MIPS32R2 processors.
13655 The register assignments for arguments and return values remain the
13656 same, but each scalar value is passed in a single 64-bit register
13657 rather than a pair of 32-bit registers. For example, scalar
13658 floating-point values are returned in @samp{$f0} only, not a
13659 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
13660 remains the same, but all 64 bits are saved.
13663 @itemx -mno-abicalls
13665 @opindex mno-abicalls
13666 Generate (do not generate) code that is suitable for SVR4-style
13667 dynamic objects. @option{-mabicalls} is the default for SVR4-based
13672 Generate (do not generate) code that is fully position-independent,
13673 and that can therefore be linked into shared libraries. This option
13674 only affects @option{-mabicalls}.
13676 All @option{-mabicalls} code has traditionally been position-independent,
13677 regardless of options like @option{-fPIC} and @option{-fpic}. However,
13678 as an extension, the GNU toolchain allows executables to use absolute
13679 accesses for locally-binding symbols. It can also use shorter GP
13680 initialization sequences and generate direct calls to locally-defined
13681 functions. This mode is selected by @option{-mno-shared}.
13683 @option{-mno-shared} depends on binutils 2.16 or higher and generates
13684 objects that can only be linked by the GNU linker. However, the option
13685 does not affect the ABI of the final executable; it only affects the ABI
13686 of relocatable objects. Using @option{-mno-shared} will generally make
13687 executables both smaller and quicker.
13689 @option{-mshared} is the default.
13695 Assume (do not assume) that the static and dynamic linkers
13696 support PLTs and copy relocations. This option only affects
13697 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
13698 has no effect without @samp{-msym32}.
13700 You can make @option{-mplt} the default by configuring
13701 GCC with @option{--with-mips-plt}. The default is
13702 @option{-mno-plt} otherwise.
13708 Lift (do not lift) the usual restrictions on the size of the global
13711 GCC normally uses a single instruction to load values from the GOT@.
13712 While this is relatively efficient, it will only work if the GOT
13713 is smaller than about 64k. Anything larger will cause the linker
13714 to report an error such as:
13716 @cindex relocation truncated to fit (MIPS)
13718 relocation truncated to fit: R_MIPS_GOT16 foobar
13721 If this happens, you should recompile your code with @option{-mxgot}.
13722 It should then work with very large GOTs, although it will also be
13723 less efficient, since it will take three instructions to fetch the
13724 value of a global symbol.
13726 Note that some linkers can create multiple GOTs. If you have such a
13727 linker, you should only need to use @option{-mxgot} when a single object
13728 file accesses more than 64k's worth of GOT entries. Very few do.
13730 These options have no effect unless GCC is generating position
13735 Assume that general-purpose registers are 32 bits wide.
13739 Assume that general-purpose registers are 64 bits wide.
13743 Assume that floating-point registers are 32 bits wide.
13747 Assume that floating-point registers are 64 bits wide.
13750 @opindex mhard-float
13751 Use floating-point coprocessor instructions.
13754 @opindex msoft-float
13755 Do not use floating-point coprocessor instructions. Implement
13756 floating-point calculations using library calls instead.
13758 @item -msingle-float
13759 @opindex msingle-float
13760 Assume that the floating-point coprocessor only supports single-precision
13763 @item -mdouble-float
13764 @opindex mdouble-float
13765 Assume that the floating-point coprocessor supports double-precision
13766 operations. This is the default.
13772 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
13773 implement atomic memory built-in functions. When neither option is
13774 specified, GCC will use the instructions if the target architecture
13777 @option{-mllsc} is useful if the runtime environment can emulate the
13778 instructions and @option{-mno-llsc} can be useful when compiling for
13779 nonstandard ISAs. You can make either option the default by
13780 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
13781 respectively. @option{--with-llsc} is the default for some
13782 configurations; see the installation documentation for details.
13788 Use (do not use) revision 1 of the MIPS DSP ASE@.
13789 @xref{MIPS DSP Built-in Functions}. This option defines the
13790 preprocessor macro @samp{__mips_dsp}. It also defines
13791 @samp{__mips_dsp_rev} to 1.
13797 Use (do not use) revision 2 of the MIPS DSP ASE@.
13798 @xref{MIPS DSP Built-in Functions}. This option defines the
13799 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
13800 It also defines @samp{__mips_dsp_rev} to 2.
13803 @itemx -mno-smartmips
13804 @opindex msmartmips
13805 @opindex mno-smartmips
13806 Use (do not use) the MIPS SmartMIPS ASE.
13808 @item -mpaired-single
13809 @itemx -mno-paired-single
13810 @opindex mpaired-single
13811 @opindex mno-paired-single
13812 Use (do not use) paired-single floating-point instructions.
13813 @xref{MIPS Paired-Single Support}. This option requires
13814 hardware floating-point support to be enabled.
13820 Use (do not use) MIPS Digital Media Extension instructions.
13821 This option can only be used when generating 64-bit code and requires
13822 hardware floating-point support to be enabled.
13827 @opindex mno-mips3d
13828 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
13829 The option @option{-mips3d} implies @option{-mpaired-single}.
13835 Use (do not use) MT Multithreading instructions.
13839 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
13840 an explanation of the default and the way that the pointer size is
13845 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
13847 The default size of @code{int}s, @code{long}s and pointers depends on
13848 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
13849 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
13850 32-bit @code{long}s. Pointers are the same size as @code{long}s,
13851 or the same size as integer registers, whichever is smaller.
13857 Assume (do not assume) that all symbols have 32-bit values, regardless
13858 of the selected ABI@. This option is useful in combination with
13859 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
13860 to generate shorter and faster references to symbolic addresses.
13864 Put definitions of externally-visible data in a small data section
13865 if that data is no bigger than @var{num} bytes. GCC can then access
13866 the data more efficiently; see @option{-mgpopt} for details.
13868 The default @option{-G} option depends on the configuration.
13870 @item -mlocal-sdata
13871 @itemx -mno-local-sdata
13872 @opindex mlocal-sdata
13873 @opindex mno-local-sdata
13874 Extend (do not extend) the @option{-G} behavior to local data too,
13875 such as to static variables in C@. @option{-mlocal-sdata} is the
13876 default for all configurations.
13878 If the linker complains that an application is using too much small data,
13879 you might want to try rebuilding the less performance-critical parts with
13880 @option{-mno-local-sdata}. You might also want to build large
13881 libraries with @option{-mno-local-sdata}, so that the libraries leave
13882 more room for the main program.
13884 @item -mextern-sdata
13885 @itemx -mno-extern-sdata
13886 @opindex mextern-sdata
13887 @opindex mno-extern-sdata
13888 Assume (do not assume) that externally-defined data will be in
13889 a small data section if that data is within the @option{-G} limit.
13890 @option{-mextern-sdata} is the default for all configurations.
13892 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
13893 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
13894 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
13895 is placed in a small data section. If @var{Var} is defined by another
13896 module, you must either compile that module with a high-enough
13897 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
13898 definition. If @var{Var} is common, you must link the application
13899 with a high-enough @option{-G} setting.
13901 The easiest way of satisfying these restrictions is to compile
13902 and link every module with the same @option{-G} option. However,
13903 you may wish to build a library that supports several different
13904 small data limits. You can do this by compiling the library with
13905 the highest supported @option{-G} setting and additionally using
13906 @option{-mno-extern-sdata} to stop the library from making assumptions
13907 about externally-defined data.
13913 Use (do not use) GP-relative accesses for symbols that are known to be
13914 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
13915 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
13918 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
13919 might not hold the value of @code{_gp}. For example, if the code is
13920 part of a library that might be used in a boot monitor, programs that
13921 call boot monitor routines will pass an unknown value in @code{$gp}.
13922 (In such situations, the boot monitor itself would usually be compiled
13923 with @option{-G0}.)
13925 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
13926 @option{-mno-extern-sdata}.
13928 @item -membedded-data
13929 @itemx -mno-embedded-data
13930 @opindex membedded-data
13931 @opindex mno-embedded-data
13932 Allocate variables to the read-only data section first if possible, then
13933 next in the small data section if possible, otherwise in data. This gives
13934 slightly slower code than the default, but reduces the amount of RAM required
13935 when executing, and thus may be preferred for some embedded systems.
13937 @item -muninit-const-in-rodata
13938 @itemx -mno-uninit-const-in-rodata
13939 @opindex muninit-const-in-rodata
13940 @opindex mno-uninit-const-in-rodata
13941 Put uninitialized @code{const} variables in the read-only data section.
13942 This option is only meaningful in conjunction with @option{-membedded-data}.
13944 @item -mcode-readable=@var{setting}
13945 @opindex mcode-readable
13946 Specify whether GCC may generate code that reads from executable sections.
13947 There are three possible settings:
13950 @item -mcode-readable=yes
13951 Instructions may freely access executable sections. This is the
13954 @item -mcode-readable=pcrel
13955 MIPS16 PC-relative load instructions can access executable sections,
13956 but other instructions must not do so. This option is useful on 4KSc
13957 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
13958 It is also useful on processors that can be configured to have a dual
13959 instruction/data SRAM interface and that, like the M4K, automatically
13960 redirect PC-relative loads to the instruction RAM.
13962 @item -mcode-readable=no
13963 Instructions must not access executable sections. This option can be
13964 useful on targets that are configured to have a dual instruction/data
13965 SRAM interface but that (unlike the M4K) do not automatically redirect
13966 PC-relative loads to the instruction RAM.
13969 @item -msplit-addresses
13970 @itemx -mno-split-addresses
13971 @opindex msplit-addresses
13972 @opindex mno-split-addresses
13973 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
13974 relocation operators. This option has been superseded by
13975 @option{-mexplicit-relocs} but is retained for backwards compatibility.
13977 @item -mexplicit-relocs
13978 @itemx -mno-explicit-relocs
13979 @opindex mexplicit-relocs
13980 @opindex mno-explicit-relocs
13981 Use (do not use) assembler relocation operators when dealing with symbolic
13982 addresses. The alternative, selected by @option{-mno-explicit-relocs},
13983 is to use assembler macros instead.
13985 @option{-mexplicit-relocs} is the default if GCC was configured
13986 to use an assembler that supports relocation operators.
13988 @item -mcheck-zero-division
13989 @itemx -mno-check-zero-division
13990 @opindex mcheck-zero-division
13991 @opindex mno-check-zero-division
13992 Trap (do not trap) on integer division by zero.
13994 The default is @option{-mcheck-zero-division}.
13996 @item -mdivide-traps
13997 @itemx -mdivide-breaks
13998 @opindex mdivide-traps
13999 @opindex mdivide-breaks
14000 MIPS systems check for division by zero by generating either a
14001 conditional trap or a break instruction. Using traps results in
14002 smaller code, but is only supported on MIPS II and later. Also, some
14003 versions of the Linux kernel have a bug that prevents trap from
14004 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
14005 allow conditional traps on architectures that support them and
14006 @option{-mdivide-breaks} to force the use of breaks.
14008 The default is usually @option{-mdivide-traps}, but this can be
14009 overridden at configure time using @option{--with-divide=breaks}.
14010 Divide-by-zero checks can be completely disabled using
14011 @option{-mno-check-zero-division}.
14016 @opindex mno-memcpy
14017 Force (do not force) the use of @code{memcpy()} for non-trivial block
14018 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
14019 most constant-sized copies.
14022 @itemx -mno-long-calls
14023 @opindex mlong-calls
14024 @opindex mno-long-calls
14025 Disable (do not disable) use of the @code{jal} instruction. Calling
14026 functions using @code{jal} is more efficient but requires the caller
14027 and callee to be in the same 256 megabyte segment.
14029 This option has no effect on abicalls code. The default is
14030 @option{-mno-long-calls}.
14036 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
14037 instructions, as provided by the R4650 ISA@.
14040 @itemx -mno-fused-madd
14041 @opindex mfused-madd
14042 @opindex mno-fused-madd
14043 Enable (disable) use of the floating point multiply-accumulate
14044 instructions, when they are available. The default is
14045 @option{-mfused-madd}.
14047 When multiply-accumulate instructions are used, the intermediate
14048 product is calculated to infinite precision and is not subject to
14049 the FCSR Flush to Zero bit. This may be undesirable in some
14054 Tell the MIPS assembler to not run its preprocessor over user
14055 assembler files (with a @samp{.s} suffix) when assembling them.
14058 @itemx -mno-fix-r4000
14059 @opindex mfix-r4000
14060 @opindex mno-fix-r4000
14061 Work around certain R4000 CPU errata:
14064 A double-word or a variable shift may give an incorrect result if executed
14065 immediately after starting an integer division.
14067 A double-word or a variable shift may give an incorrect result if executed
14068 while an integer multiplication is in progress.
14070 An integer division may give an incorrect result if started in a delay slot
14071 of a taken branch or a jump.
14075 @itemx -mno-fix-r4400
14076 @opindex mfix-r4400
14077 @opindex mno-fix-r4400
14078 Work around certain R4400 CPU errata:
14081 A double-word or a variable shift may give an incorrect result if executed
14082 immediately after starting an integer division.
14086 @itemx -mno-fix-r10000
14087 @opindex mfix-r10000
14088 @opindex mno-fix-r10000
14089 Work around certain R10000 errata:
14092 @code{ll}/@code{sc} sequences may not behave atomically on revisions
14093 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
14096 This option can only be used if the target architecture supports
14097 branch-likely instructions. @option{-mfix-r10000} is the default when
14098 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
14102 @itemx -mno-fix-vr4120
14103 @opindex mfix-vr4120
14104 Work around certain VR4120 errata:
14107 @code{dmultu} does not always produce the correct result.
14109 @code{div} and @code{ddiv} do not always produce the correct result if one
14110 of the operands is negative.
14112 The workarounds for the division errata rely on special functions in
14113 @file{libgcc.a}. At present, these functions are only provided by
14114 the @code{mips64vr*-elf} configurations.
14116 Other VR4120 errata require a nop to be inserted between certain pairs of
14117 instructions. These errata are handled by the assembler, not by GCC itself.
14120 @opindex mfix-vr4130
14121 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
14122 workarounds are implemented by the assembler rather than by GCC,
14123 although GCC will avoid using @code{mflo} and @code{mfhi} if the
14124 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
14125 instructions are available instead.
14128 @itemx -mno-fix-sb1
14130 Work around certain SB-1 CPU core errata.
14131 (This flag currently works around the SB-1 revision 2
14132 ``F1'' and ``F2'' floating point errata.)
14134 @item -mr10k-cache-barrier=@var{setting}
14135 @opindex mr10k-cache-barrier
14136 Specify whether GCC should insert cache barriers to avoid the
14137 side-effects of speculation on R10K processors.
14139 In common with many processors, the R10K tries to predict the outcome
14140 of a conditional branch and speculatively executes instructions from
14141 the ``taken'' branch. It later aborts these instructions if the
14142 predicted outcome was wrong. However, on the R10K, even aborted
14143 instructions can have side effects.
14145 This problem only affects kernel stores and, depending on the system,
14146 kernel loads. As an example, a speculatively-executed store may load
14147 the target memory into cache and mark the cache line as dirty, even if
14148 the store itself is later aborted. If a DMA operation writes to the
14149 same area of memory before the ``dirty'' line is flushed, the cached
14150 data will overwrite the DMA-ed data. See the R10K processor manual
14151 for a full description, including other potential problems.
14153 One workaround is to insert cache barrier instructions before every memory
14154 access that might be speculatively executed and that might have side
14155 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
14156 controls GCC's implementation of this workaround. It assumes that
14157 aborted accesses to any byte in the following regions will not have
14162 the memory occupied by the current function's stack frame;
14165 the memory occupied by an incoming stack argument;
14168 the memory occupied by an object with a link-time-constant address.
14171 It is the kernel's responsibility to ensure that speculative
14172 accesses to these regions are indeed safe.
14174 If the input program contains a function declaration such as:
14180 then the implementation of @code{foo} must allow @code{j foo} and
14181 @code{jal foo} to be executed speculatively. GCC honors this
14182 restriction for functions it compiles itself. It expects non-GCC
14183 functions (such as hand-written assembly code) to do the same.
14185 The option has three forms:
14188 @item -mr10k-cache-barrier=load-store
14189 Insert a cache barrier before a load or store that might be
14190 speculatively executed and that might have side effects even
14193 @item -mr10k-cache-barrier=store
14194 Insert a cache barrier before a store that might be speculatively
14195 executed and that might have side effects even if aborted.
14197 @item -mr10k-cache-barrier=none
14198 Disable the insertion of cache barriers. This is the default setting.
14201 @item -mflush-func=@var{func}
14202 @itemx -mno-flush-func
14203 @opindex mflush-func
14204 Specifies the function to call to flush the I and D caches, or to not
14205 call any such function. If called, the function must take the same
14206 arguments as the common @code{_flush_func()}, that is, the address of the
14207 memory range for which the cache is being flushed, the size of the
14208 memory range, and the number 3 (to flush both caches). The default
14209 depends on the target GCC was configured for, but commonly is either
14210 @samp{_flush_func} or @samp{__cpu_flush}.
14212 @item mbranch-cost=@var{num}
14213 @opindex mbranch-cost
14214 Set the cost of branches to roughly @var{num} ``simple'' instructions.
14215 This cost is only a heuristic and is not guaranteed to produce
14216 consistent results across releases. A zero cost redundantly selects
14217 the default, which is based on the @option{-mtune} setting.
14219 @item -mbranch-likely
14220 @itemx -mno-branch-likely
14221 @opindex mbranch-likely
14222 @opindex mno-branch-likely
14223 Enable or disable use of Branch Likely instructions, regardless of the
14224 default for the selected architecture. By default, Branch Likely
14225 instructions may be generated if they are supported by the selected
14226 architecture. An exception is for the MIPS32 and MIPS64 architectures
14227 and processors which implement those architectures; for those, Branch
14228 Likely instructions will not be generated by default because the MIPS32
14229 and MIPS64 architectures specifically deprecate their use.
14231 @item -mfp-exceptions
14232 @itemx -mno-fp-exceptions
14233 @opindex mfp-exceptions
14234 Specifies whether FP exceptions are enabled. This affects how we schedule
14235 FP instructions for some processors. The default is that FP exceptions are
14238 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
14239 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
14242 @item -mvr4130-align
14243 @itemx -mno-vr4130-align
14244 @opindex mvr4130-align
14245 The VR4130 pipeline is two-way superscalar, but can only issue two
14246 instructions together if the first one is 8-byte aligned. When this
14247 option is enabled, GCC will align pairs of instructions that it
14248 thinks should execute in parallel.
14250 This option only has an effect when optimizing for the VR4130.
14251 It normally makes code faster, but at the expense of making it bigger.
14252 It is enabled by default at optimization level @option{-O3}.
14257 Enable (disable) generation of @code{synci} instructions on
14258 architectures that support it. The @code{synci} instructions (if
14259 enabled) will be generated when @code{__builtin___clear_cache()} is
14262 This option defaults to @code{-mno-synci}, but the default can be
14263 overridden by configuring with @code{--with-synci}.
14265 When compiling code for single processor systems, it is generally safe
14266 to use @code{synci}. However, on many multi-core (SMP) systems, it
14267 will not invalidate the instruction caches on all cores and may lead
14268 to undefined behavior.
14270 @item -mrelax-pic-calls
14271 @itemx -mno-relax-pic-calls
14272 @opindex mrelax-pic-calls
14273 Try to turn PIC calls that are normally dispatched via register
14274 @code{$25} into direct calls. This is only possible if the linker can
14275 resolve the destination at link-time and if the destination is within
14276 range for a direct call.
14278 @option{-mrelax-pic-calls} is the default if GCC was configured to use
14279 an assembler and a linker that supports the @code{.reloc} assembly
14280 directive and @code{-mexplicit-relocs} is in effect. With
14281 @code{-mno-explicit-relocs}, this optimization can be performed by the
14282 assembler and the linker alone without help from the compiler.
14284 @item -mmcount-ra-address
14285 @itemx -mno-mcount-ra-address
14286 @opindex mmcount-ra-address
14287 @opindex mno-mcount-ra-address
14288 Emit (do not emit) code that allows @code{_mcount} to modify the
14289 calling function's return address. When enabled, this option extends
14290 the usual @code{_mcount} interface with a new @var{ra-address}
14291 parameter, which has type @code{intptr_t *} and is passed in register
14292 @code{$12}. @code{_mcount} can then modify the return address by
14293 doing both of the following:
14296 Returning the new address in register @code{$31}.
14298 Storing the new address in @code{*@var{ra-address}},
14299 if @var{ra-address} is nonnull.
14302 The default is @option{-mno-mcount-ra-address}.
14307 @subsection MMIX Options
14308 @cindex MMIX Options
14310 These options are defined for the MMIX:
14314 @itemx -mno-libfuncs
14316 @opindex mno-libfuncs
14317 Specify that intrinsic library functions are being compiled, passing all
14318 values in registers, no matter the size.
14321 @itemx -mno-epsilon
14323 @opindex mno-epsilon
14324 Generate floating-point comparison instructions that compare with respect
14325 to the @code{rE} epsilon register.
14327 @item -mabi=mmixware
14329 @opindex mabi=mmixware
14331 Generate code that passes function parameters and return values that (in
14332 the called function) are seen as registers @code{$0} and up, as opposed to
14333 the GNU ABI which uses global registers @code{$231} and up.
14335 @item -mzero-extend
14336 @itemx -mno-zero-extend
14337 @opindex mzero-extend
14338 @opindex mno-zero-extend
14339 When reading data from memory in sizes shorter than 64 bits, use (do not
14340 use) zero-extending load instructions by default, rather than
14341 sign-extending ones.
14344 @itemx -mno-knuthdiv
14346 @opindex mno-knuthdiv
14347 Make the result of a division yielding a remainder have the same sign as
14348 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
14349 remainder follows the sign of the dividend. Both methods are
14350 arithmetically valid, the latter being almost exclusively used.
14352 @item -mtoplevel-symbols
14353 @itemx -mno-toplevel-symbols
14354 @opindex mtoplevel-symbols
14355 @opindex mno-toplevel-symbols
14356 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
14357 code can be used with the @code{PREFIX} assembly directive.
14361 Generate an executable in the ELF format, rather than the default
14362 @samp{mmo} format used by the @command{mmix} simulator.
14364 @item -mbranch-predict
14365 @itemx -mno-branch-predict
14366 @opindex mbranch-predict
14367 @opindex mno-branch-predict
14368 Use (do not use) the probable-branch instructions, when static branch
14369 prediction indicates a probable branch.
14371 @item -mbase-addresses
14372 @itemx -mno-base-addresses
14373 @opindex mbase-addresses
14374 @opindex mno-base-addresses
14375 Generate (do not generate) code that uses @emph{base addresses}. Using a
14376 base address automatically generates a request (handled by the assembler
14377 and the linker) for a constant to be set up in a global register. The
14378 register is used for one or more base address requests within the range 0
14379 to 255 from the value held in the register. The generally leads to short
14380 and fast code, but the number of different data items that can be
14381 addressed is limited. This means that a program that uses lots of static
14382 data may require @option{-mno-base-addresses}.
14384 @item -msingle-exit
14385 @itemx -mno-single-exit
14386 @opindex msingle-exit
14387 @opindex mno-single-exit
14388 Force (do not force) generated code to have a single exit point in each
14392 @node MN10300 Options
14393 @subsection MN10300 Options
14394 @cindex MN10300 options
14396 These @option{-m} options are defined for Matsushita MN10300 architectures:
14401 Generate code to avoid bugs in the multiply instructions for the MN10300
14402 processors. This is the default.
14404 @item -mno-mult-bug
14405 @opindex mno-mult-bug
14406 Do not generate code to avoid bugs in the multiply instructions for the
14407 MN10300 processors.
14411 Generate code which uses features specific to the AM33 processor.
14415 Do not generate code which uses features specific to the AM33 processor. This
14418 @item -mreturn-pointer-on-d0
14419 @opindex mreturn-pointer-on-d0
14420 When generating a function which returns a pointer, return the pointer
14421 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
14422 only in a0, and attempts to call such functions without a prototype
14423 would result in errors. Note that this option is on by default; use
14424 @option{-mno-return-pointer-on-d0} to disable it.
14428 Do not link in the C run-time initialization object file.
14432 Indicate to the linker that it should perform a relaxation optimization pass
14433 to shorten branches, calls and absolute memory addresses. This option only
14434 has an effect when used on the command line for the final link step.
14436 This option makes symbolic debugging impossible.
14439 @node PDP-11 Options
14440 @subsection PDP-11 Options
14441 @cindex PDP-11 Options
14443 These options are defined for the PDP-11:
14448 Use hardware FPP floating point. This is the default. (FIS floating
14449 point on the PDP-11/40 is not supported.)
14452 @opindex msoft-float
14453 Do not use hardware floating point.
14457 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
14461 Return floating-point results in memory. This is the default.
14465 Generate code for a PDP-11/40.
14469 Generate code for a PDP-11/45. This is the default.
14473 Generate code for a PDP-11/10.
14475 @item -mbcopy-builtin
14476 @opindex mbcopy-builtin
14477 Use inline @code{movmemhi} patterns for copying memory. This is the
14482 Do not use inline @code{movmemhi} patterns for copying memory.
14488 Use 16-bit @code{int}. This is the default.
14494 Use 32-bit @code{int}.
14497 @itemx -mno-float32
14499 @opindex mno-float32
14500 Use 64-bit @code{float}. This is the default.
14503 @itemx -mno-float64
14505 @opindex mno-float64
14506 Use 32-bit @code{float}.
14510 Use @code{abshi2} pattern. This is the default.
14514 Do not use @code{abshi2} pattern.
14516 @item -mbranch-expensive
14517 @opindex mbranch-expensive
14518 Pretend that branches are expensive. This is for experimenting with
14519 code generation only.
14521 @item -mbranch-cheap
14522 @opindex mbranch-cheap
14523 Do not pretend that branches are expensive. This is the default.
14527 Generate code for a system with split I&D@.
14531 Generate code for a system without split I&D@. This is the default.
14535 Use Unix assembler syntax. This is the default when configured for
14536 @samp{pdp11-*-bsd}.
14540 Use DEC assembler syntax. This is the default when configured for any
14541 PDP-11 target other than @samp{pdp11-*-bsd}.
14544 @node picoChip Options
14545 @subsection picoChip Options
14546 @cindex picoChip options
14548 These @samp{-m} options are defined for picoChip implementations:
14552 @item -mae=@var{ae_type}
14554 Set the instruction set, register set, and instruction scheduling
14555 parameters for array element type @var{ae_type}. Supported values
14556 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
14558 @option{-mae=ANY} selects a completely generic AE type. Code
14559 generated with this option will run on any of the other AE types. The
14560 code will not be as efficient as it would be if compiled for a specific
14561 AE type, and some types of operation (e.g., multiplication) will not
14562 work properly on all types of AE.
14564 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
14565 for compiled code, and is the default.
14567 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
14568 option may suffer from poor performance of byte (char) manipulation,
14569 since the DSP AE does not provide hardware support for byte load/stores.
14571 @item -msymbol-as-address
14572 Enable the compiler to directly use a symbol name as an address in a
14573 load/store instruction, without first loading it into a
14574 register. Typically, the use of this option will generate larger
14575 programs, which run faster than when the option isn't used. However, the
14576 results vary from program to program, so it is left as a user option,
14577 rather than being permanently enabled.
14579 @item -mno-inefficient-warnings
14580 Disables warnings about the generation of inefficient code. These
14581 warnings can be generated, for example, when compiling code which
14582 performs byte-level memory operations on the MAC AE type. The MAC AE has
14583 no hardware support for byte-level memory operations, so all byte
14584 load/stores must be synthesized from word load/store operations. This is
14585 inefficient and a warning will be generated indicating to the programmer
14586 that they should rewrite the code to avoid byte operations, or to target
14587 an AE type which has the necessary hardware support. This option enables
14588 the warning to be turned off.
14592 @node PowerPC Options
14593 @subsection PowerPC Options
14594 @cindex PowerPC options
14596 These are listed under @xref{RS/6000 and PowerPC Options}.
14598 @node RS/6000 and PowerPC Options
14599 @subsection IBM RS/6000 and PowerPC Options
14600 @cindex RS/6000 and PowerPC Options
14601 @cindex IBM RS/6000 and PowerPC Options
14603 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
14610 @itemx -mno-powerpc
14611 @itemx -mpowerpc-gpopt
14612 @itemx -mno-powerpc-gpopt
14613 @itemx -mpowerpc-gfxopt
14614 @itemx -mno-powerpc-gfxopt
14616 @itemx -mno-powerpc64
14620 @itemx -mno-popcntb
14622 @itemx -mno-popcntd
14630 @itemx -mno-hard-dfp
14634 @opindex mno-power2
14636 @opindex mno-powerpc
14637 @opindex mpowerpc-gpopt
14638 @opindex mno-powerpc-gpopt
14639 @opindex mpowerpc-gfxopt
14640 @opindex mno-powerpc-gfxopt
14641 @opindex mpowerpc64
14642 @opindex mno-powerpc64
14646 @opindex mno-popcntb
14648 @opindex mno-popcntd
14654 @opindex mno-mfpgpr
14656 @opindex mno-hard-dfp
14657 GCC supports two related instruction set architectures for the
14658 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
14659 instructions supported by the @samp{rios} chip set used in the original
14660 RS/6000 systems and the @dfn{PowerPC} instruction set is the
14661 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
14662 the IBM 4xx, 6xx, and follow-on microprocessors.
14664 Neither architecture is a subset of the other. However there is a
14665 large common subset of instructions supported by both. An MQ
14666 register is included in processors supporting the POWER architecture.
14668 You use these options to specify which instructions are available on the
14669 processor you are using. The default value of these options is
14670 determined when configuring GCC@. Specifying the
14671 @option{-mcpu=@var{cpu_type}} overrides the specification of these
14672 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
14673 rather than the options listed above.
14675 The @option{-mpower} option allows GCC to generate instructions that
14676 are found only in the POWER architecture and to use the MQ register.
14677 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
14678 to generate instructions that are present in the POWER2 architecture but
14679 not the original POWER architecture.
14681 The @option{-mpowerpc} option allows GCC to generate instructions that
14682 are found only in the 32-bit subset of the PowerPC architecture.
14683 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
14684 GCC to use the optional PowerPC architecture instructions in the
14685 General Purpose group, including floating-point square root. Specifying
14686 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
14687 use the optional PowerPC architecture instructions in the Graphics
14688 group, including floating-point select.
14690 The @option{-mmfcrf} option allows GCC to generate the move from
14691 condition register field instruction implemented on the POWER4
14692 processor and other processors that support the PowerPC V2.01
14694 The @option{-mpopcntb} option allows GCC to generate the popcount and
14695 double precision FP reciprocal estimate instruction implemented on the
14696 POWER5 processor and other processors that support the PowerPC V2.02
14698 The @option{-mpopcntd} option allows GCC to generate the popcount
14699 instruction implemented on the POWER7 processor and other processors
14700 that support the PowerPC V2.06 architecture.
14701 The @option{-mfprnd} option allows GCC to generate the FP round to
14702 integer instructions implemented on the POWER5+ processor and other
14703 processors that support the PowerPC V2.03 architecture.
14704 The @option{-mcmpb} option allows GCC to generate the compare bytes
14705 instruction implemented on the POWER6 processor and other processors
14706 that support the PowerPC V2.05 architecture.
14707 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
14708 general purpose register instructions implemented on the POWER6X
14709 processor and other processors that support the extended PowerPC V2.05
14711 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
14712 point instructions implemented on some POWER processors.
14714 The @option{-mpowerpc64} option allows GCC to generate the additional
14715 64-bit instructions that are found in the full PowerPC64 architecture
14716 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
14717 @option{-mno-powerpc64}.
14719 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
14720 will use only the instructions in the common subset of both
14721 architectures plus some special AIX common-mode calls, and will not use
14722 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
14723 permits GCC to use any instruction from either architecture and to
14724 allow use of the MQ register; specify this for the Motorola MPC601.
14726 @item -mnew-mnemonics
14727 @itemx -mold-mnemonics
14728 @opindex mnew-mnemonics
14729 @opindex mold-mnemonics
14730 Select which mnemonics to use in the generated assembler code. With
14731 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
14732 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
14733 assembler mnemonics defined for the POWER architecture. Instructions
14734 defined in only one architecture have only one mnemonic; GCC uses that
14735 mnemonic irrespective of which of these options is specified.
14737 GCC defaults to the mnemonics appropriate for the architecture in
14738 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
14739 value of these option. Unless you are building a cross-compiler, you
14740 should normally not specify either @option{-mnew-mnemonics} or
14741 @option{-mold-mnemonics}, but should instead accept the default.
14743 @item -mcpu=@var{cpu_type}
14745 Set architecture type, register usage, choice of mnemonics, and
14746 instruction scheduling parameters for machine type @var{cpu_type}.
14747 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
14748 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
14749 @samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603},
14750 @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740},
14751 @samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
14752 @samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2},
14753 @samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{ec603e}, @samp{G3},
14754 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
14755 @samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x},
14756 @samp{power7}, @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
14757 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
14759 @option{-mcpu=common} selects a completely generic processor. Code
14760 generated under this option will run on any POWER or PowerPC processor.
14761 GCC will use only the instructions in the common subset of both
14762 architectures, and will not use the MQ register. GCC assumes a generic
14763 processor model for scheduling purposes.
14765 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
14766 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
14767 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
14768 types, with an appropriate, generic processor model assumed for
14769 scheduling purposes.
14771 The other options specify a specific processor. Code generated under
14772 those options will run best on that processor, and may not run at all on
14775 The @option{-mcpu} options automatically enable or disable the
14778 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
14779 -mnew-mnemonics -mpopcntb -mpopcntd -mpower -mpower2 -mpowerpc64 @gol
14780 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
14781 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx}
14783 The particular options set for any particular CPU will vary between
14784 compiler versions, depending on what setting seems to produce optimal
14785 code for that CPU; it doesn't necessarily reflect the actual hardware's
14786 capabilities. If you wish to set an individual option to a particular
14787 value, you may specify it after the @option{-mcpu} option, like
14788 @samp{-mcpu=970 -mno-altivec}.
14790 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
14791 not enabled or disabled by the @option{-mcpu} option at present because
14792 AIX does not have full support for these options. You may still
14793 enable or disable them individually if you're sure it'll work in your
14796 @item -mtune=@var{cpu_type}
14798 Set the instruction scheduling parameters for machine type
14799 @var{cpu_type}, but do not set the architecture type, register usage, or
14800 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
14801 values for @var{cpu_type} are used for @option{-mtune} as for
14802 @option{-mcpu}. If both are specified, the code generated will use the
14803 architecture, registers, and mnemonics set by @option{-mcpu}, but the
14804 scheduling parameters set by @option{-mtune}.
14810 Generate code to compute division as reciprocal estimate and iterative
14811 refinement, creating opportunities for increased throughput. This
14812 feature requires: optional PowerPC Graphics instruction set for single
14813 precision and FRE instruction for double precision, assuming divides
14814 cannot generate user-visible traps, and the domain values not include
14815 Infinities, denormals or zero denominator.
14818 @itemx -mno-altivec
14820 @opindex mno-altivec
14821 Generate code that uses (does not use) AltiVec instructions, and also
14822 enable the use of built-in functions that allow more direct access to
14823 the AltiVec instruction set. You may also need to set
14824 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
14830 @opindex mno-vrsave
14831 Generate VRSAVE instructions when generating AltiVec code.
14833 @item -mgen-cell-microcode
14834 @opindex mgen-cell-microcode
14835 Generate Cell microcode instructions
14837 @item -mwarn-cell-microcode
14838 @opindex mwarn-cell-microcode
14839 Warning when a Cell microcode instruction is going to emitted. An example
14840 of a Cell microcode instruction is a variable shift.
14843 @opindex msecure-plt
14844 Generate code that allows ld and ld.so to build executables and shared
14845 libraries with non-exec .plt and .got sections. This is a PowerPC
14846 32-bit SYSV ABI option.
14850 Generate code that uses a BSS .plt section that ld.so fills in, and
14851 requires .plt and .got sections that are both writable and executable.
14852 This is a PowerPC 32-bit SYSV ABI option.
14858 This switch enables or disables the generation of ISEL instructions.
14860 @item -misel=@var{yes/no}
14861 This switch has been deprecated. Use @option{-misel} and
14862 @option{-mno-isel} instead.
14868 This switch enables or disables the generation of SPE simd
14874 @opindex mno-paired
14875 This switch enables or disables the generation of PAIRED simd
14878 @item -mspe=@var{yes/no}
14879 This option has been deprecated. Use @option{-mspe} and
14880 @option{-mno-spe} instead.
14886 Generate code that uses (does not use) vector/scalar (VSX)
14887 instructions, and also enable the use of built-in functions that allow
14888 more direct access to the VSX instruction set.
14890 @item -mfloat-gprs=@var{yes/single/double/no}
14891 @itemx -mfloat-gprs
14892 @opindex mfloat-gprs
14893 This switch enables or disables the generation of floating point
14894 operations on the general purpose registers for architectures that
14897 The argument @var{yes} or @var{single} enables the use of
14898 single-precision floating point operations.
14900 The argument @var{double} enables the use of single and
14901 double-precision floating point operations.
14903 The argument @var{no} disables floating point operations on the
14904 general purpose registers.
14906 This option is currently only available on the MPC854x.
14912 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
14913 targets (including GNU/Linux). The 32-bit environment sets int, long
14914 and pointer to 32 bits and generates code that runs on any PowerPC
14915 variant. The 64-bit environment sets int to 32 bits and long and
14916 pointer to 64 bits, and generates code for PowerPC64, as for
14917 @option{-mpowerpc64}.
14920 @itemx -mno-fp-in-toc
14921 @itemx -mno-sum-in-toc
14922 @itemx -mminimal-toc
14924 @opindex mno-fp-in-toc
14925 @opindex mno-sum-in-toc
14926 @opindex mminimal-toc
14927 Modify generation of the TOC (Table Of Contents), which is created for
14928 every executable file. The @option{-mfull-toc} option is selected by
14929 default. In that case, GCC will allocate at least one TOC entry for
14930 each unique non-automatic variable reference in your program. GCC
14931 will also place floating-point constants in the TOC@. However, only
14932 16,384 entries are available in the TOC@.
14934 If you receive a linker error message that saying you have overflowed
14935 the available TOC space, you can reduce the amount of TOC space used
14936 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
14937 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
14938 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
14939 generate code to calculate the sum of an address and a constant at
14940 run-time instead of putting that sum into the TOC@. You may specify one
14941 or both of these options. Each causes GCC to produce very slightly
14942 slower and larger code at the expense of conserving TOC space.
14944 If you still run out of space in the TOC even when you specify both of
14945 these options, specify @option{-mminimal-toc} instead. This option causes
14946 GCC to make only one TOC entry for every file. When you specify this
14947 option, GCC will produce code that is slower and larger but which
14948 uses extremely little TOC space. You may wish to use this option
14949 only on files that contain less frequently executed code.
14955 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
14956 @code{long} type, and the infrastructure needed to support them.
14957 Specifying @option{-maix64} implies @option{-mpowerpc64} and
14958 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
14959 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
14962 @itemx -mno-xl-compat
14963 @opindex mxl-compat
14964 @opindex mno-xl-compat
14965 Produce code that conforms more closely to IBM XL compiler semantics
14966 when using AIX-compatible ABI@. Pass floating-point arguments to
14967 prototyped functions beyond the register save area (RSA) on the stack
14968 in addition to argument FPRs. Do not assume that most significant
14969 double in 128-bit long double value is properly rounded when comparing
14970 values and converting to double. Use XL symbol names for long double
14973 The AIX calling convention was extended but not initially documented to
14974 handle an obscure K&R C case of calling a function that takes the
14975 address of its arguments with fewer arguments than declared. IBM XL
14976 compilers access floating point arguments which do not fit in the
14977 RSA from the stack when a subroutine is compiled without
14978 optimization. Because always storing floating-point arguments on the
14979 stack is inefficient and rarely needed, this option is not enabled by
14980 default and only is necessary when calling subroutines compiled by IBM
14981 XL compilers without optimization.
14985 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
14986 application written to use message passing with special startup code to
14987 enable the application to run. The system must have PE installed in the
14988 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
14989 must be overridden with the @option{-specs=} option to specify the
14990 appropriate directory location. The Parallel Environment does not
14991 support threads, so the @option{-mpe} option and the @option{-pthread}
14992 option are incompatible.
14994 @item -malign-natural
14995 @itemx -malign-power
14996 @opindex malign-natural
14997 @opindex malign-power
14998 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
14999 @option{-malign-natural} overrides the ABI-defined alignment of larger
15000 types, such as floating-point doubles, on their natural size-based boundary.
15001 The option @option{-malign-power} instructs GCC to follow the ABI-specified
15002 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
15004 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
15008 @itemx -mhard-float
15009 @opindex msoft-float
15010 @opindex mhard-float
15011 Generate code that does not use (uses) the floating-point register set.
15012 Software floating point emulation is provided if you use the
15013 @option{-msoft-float} option, and pass the option to GCC when linking.
15015 @item -msingle-float
15016 @itemx -mdouble-float
15017 @opindex msingle-float
15018 @opindex mdouble-float
15019 Generate code for single or double-precision floating point operations.
15020 @option{-mdouble-float} implies @option{-msingle-float}.
15023 @opindex msimple-fpu
15024 Do not generate sqrt and div instructions for hardware floating point unit.
15028 Specify type of floating point unit. Valid values are @var{sp_lite}
15029 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
15030 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
15031 and @var{dp_full} (equivalent to -mdouble-float).
15034 @opindex mxilinx-fpu
15035 Perform optimizations for floating point unit on Xilinx PPC 405/440.
15038 @itemx -mno-multiple
15040 @opindex mno-multiple
15041 Generate code that uses (does not use) the load multiple word
15042 instructions and the store multiple word instructions. These
15043 instructions are generated by default on POWER systems, and not
15044 generated on PowerPC systems. Do not use @option{-mmultiple} on little
15045 endian PowerPC systems, since those instructions do not work when the
15046 processor is in little endian mode. The exceptions are PPC740 and
15047 PPC750 which permit the instructions usage in little endian mode.
15052 @opindex mno-string
15053 Generate code that uses (does not use) the load string instructions
15054 and the store string word instructions to save multiple registers and
15055 do small block moves. These instructions are generated by default on
15056 POWER systems, and not generated on PowerPC systems. Do not use
15057 @option{-mstring} on little endian PowerPC systems, since those
15058 instructions do not work when the processor is in little endian mode.
15059 The exceptions are PPC740 and PPC750 which permit the instructions
15060 usage in little endian mode.
15065 @opindex mno-update
15066 Generate code that uses (does not use) the load or store instructions
15067 that update the base register to the address of the calculated memory
15068 location. These instructions are generated by default. If you use
15069 @option{-mno-update}, there is a small window between the time that the
15070 stack pointer is updated and the address of the previous frame is
15071 stored, which means code that walks the stack frame across interrupts or
15072 signals may get corrupted data.
15074 @item -mavoid-indexed-addresses
15075 @item -mno-avoid-indexed-addresses
15076 @opindex mavoid-indexed-addresses
15077 @opindex mno-avoid-indexed-addresses
15078 Generate code that tries to avoid (not avoid) the use of indexed load
15079 or store instructions. These instructions can incur a performance
15080 penalty on Power6 processors in certain situations, such as when
15081 stepping through large arrays that cross a 16M boundary. This option
15082 is enabled by default when targetting Power6 and disabled otherwise.
15085 @itemx -mno-fused-madd
15086 @opindex mfused-madd
15087 @opindex mno-fused-madd
15088 Generate code that uses (does not use) the floating point multiply and
15089 accumulate instructions. These instructions are generated by default if
15090 hardware floating is used.
15096 Generate code that uses (does not use) the half-word multiply and
15097 multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
15098 These instructions are generated by default when targetting those
15105 Generate code that uses (does not use) the string-search @samp{dlmzb}
15106 instruction on the IBM 405, 440, 464 and 476 processors. This instruction is
15107 generated by default when targetting those processors.
15109 @item -mno-bit-align
15111 @opindex mno-bit-align
15112 @opindex mbit-align
15113 On System V.4 and embedded PowerPC systems do not (do) force structures
15114 and unions that contain bit-fields to be aligned to the base type of the
15117 For example, by default a structure containing nothing but 8
15118 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
15119 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
15120 the structure would be aligned to a 1 byte boundary and be one byte in
15123 @item -mno-strict-align
15124 @itemx -mstrict-align
15125 @opindex mno-strict-align
15126 @opindex mstrict-align
15127 On System V.4 and embedded PowerPC systems do not (do) assume that
15128 unaligned memory references will be handled by the system.
15130 @item -mrelocatable
15131 @itemx -mno-relocatable
15132 @opindex mrelocatable
15133 @opindex mno-relocatable
15134 On embedded PowerPC systems generate code that allows (does not allow)
15135 the program to be relocated to a different address at runtime. If you
15136 use @option{-mrelocatable} on any module, all objects linked together must
15137 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
15139 @item -mrelocatable-lib
15140 @itemx -mno-relocatable-lib
15141 @opindex mrelocatable-lib
15142 @opindex mno-relocatable-lib
15143 On embedded PowerPC systems generate code that allows (does not allow)
15144 the program to be relocated to a different address at runtime. Modules
15145 compiled with @option{-mrelocatable-lib} can be linked with either modules
15146 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
15147 with modules compiled with the @option{-mrelocatable} options.
15153 On System V.4 and embedded PowerPC systems do not (do) assume that
15154 register 2 contains a pointer to a global area pointing to the addresses
15155 used in the program.
15158 @itemx -mlittle-endian
15160 @opindex mlittle-endian
15161 On System V.4 and embedded PowerPC systems compile code for the
15162 processor in little endian mode. The @option{-mlittle-endian} option is
15163 the same as @option{-mlittle}.
15166 @itemx -mbig-endian
15168 @opindex mbig-endian
15169 On System V.4 and embedded PowerPC systems compile code for the
15170 processor in big endian mode. The @option{-mbig-endian} option is
15171 the same as @option{-mbig}.
15173 @item -mdynamic-no-pic
15174 @opindex mdynamic-no-pic
15175 On Darwin and Mac OS X systems, compile code so that it is not
15176 relocatable, but that its external references are relocatable. The
15177 resulting code is suitable for applications, but not shared
15180 @item -mprioritize-restricted-insns=@var{priority}
15181 @opindex mprioritize-restricted-insns
15182 This option controls the priority that is assigned to
15183 dispatch-slot restricted instructions during the second scheduling
15184 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
15185 @var{no/highest/second-highest} priority to dispatch slot restricted
15188 @item -msched-costly-dep=@var{dependence_type}
15189 @opindex msched-costly-dep
15190 This option controls which dependences are considered costly
15191 by the target during instruction scheduling. The argument
15192 @var{dependence_type} takes one of the following values:
15193 @var{no}: no dependence is costly,
15194 @var{all}: all dependences are costly,
15195 @var{true_store_to_load}: a true dependence from store to load is costly,
15196 @var{store_to_load}: any dependence from store to load is costly,
15197 @var{number}: any dependence which latency >= @var{number} is costly.
15199 @item -minsert-sched-nops=@var{scheme}
15200 @opindex minsert-sched-nops
15201 This option controls which nop insertion scheme will be used during
15202 the second scheduling pass. The argument @var{scheme} takes one of the
15204 @var{no}: Don't insert nops.
15205 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
15206 according to the scheduler's grouping.
15207 @var{regroup_exact}: Insert nops to force costly dependent insns into
15208 separate groups. Insert exactly as many nops as needed to force an insn
15209 to a new group, according to the estimated processor grouping.
15210 @var{number}: Insert nops to force costly dependent insns into
15211 separate groups. Insert @var{number} nops to force an insn to a new group.
15214 @opindex mcall-sysv
15215 On System V.4 and embedded PowerPC systems compile code using calling
15216 conventions that adheres to the March 1995 draft of the System V
15217 Application Binary Interface, PowerPC processor supplement. This is the
15218 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
15220 @item -mcall-sysv-eabi
15222 @opindex mcall-sysv-eabi
15223 @opindex mcall-eabi
15224 Specify both @option{-mcall-sysv} and @option{-meabi} options.
15226 @item -mcall-sysv-noeabi
15227 @opindex mcall-sysv-noeabi
15228 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
15230 @item -mcall-aixdesc
15232 On System V.4 and embedded PowerPC systems compile code for the AIX
15236 @opindex mcall-linux
15237 On System V.4 and embedded PowerPC systems compile code for the
15238 Linux-based GNU system.
15242 On System V.4 and embedded PowerPC systems compile code for the
15243 Hurd-based GNU system.
15245 @item -mcall-freebsd
15246 @opindex mcall-freebsd
15247 On System V.4 and embedded PowerPC systems compile code for the
15248 FreeBSD operating system.
15250 @item -mcall-netbsd
15251 @opindex mcall-netbsd
15252 On System V.4 and embedded PowerPC systems compile code for the
15253 NetBSD operating system.
15255 @item -mcall-openbsd
15256 @opindex mcall-netbsd
15257 On System V.4 and embedded PowerPC systems compile code for the
15258 OpenBSD operating system.
15260 @item -maix-struct-return
15261 @opindex maix-struct-return
15262 Return all structures in memory (as specified by the AIX ABI)@.
15264 @item -msvr4-struct-return
15265 @opindex msvr4-struct-return
15266 Return structures smaller than 8 bytes in registers (as specified by the
15269 @item -mabi=@var{abi-type}
15271 Extend the current ABI with a particular extension, or remove such extension.
15272 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
15273 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
15277 Extend the current ABI with SPE ABI extensions. This does not change
15278 the default ABI, instead it adds the SPE ABI extensions to the current
15282 @opindex mabi=no-spe
15283 Disable Booke SPE ABI extensions for the current ABI@.
15285 @item -mabi=ibmlongdouble
15286 @opindex mabi=ibmlongdouble
15287 Change the current ABI to use IBM extended precision long double.
15288 This is a PowerPC 32-bit SYSV ABI option.
15290 @item -mabi=ieeelongdouble
15291 @opindex mabi=ieeelongdouble
15292 Change the current ABI to use IEEE extended precision long double.
15293 This is a PowerPC 32-bit Linux ABI option.
15296 @itemx -mno-prototype
15297 @opindex mprototype
15298 @opindex mno-prototype
15299 On System V.4 and embedded PowerPC systems assume that all calls to
15300 variable argument functions are properly prototyped. Otherwise, the
15301 compiler must insert an instruction before every non prototyped call to
15302 set or clear bit 6 of the condition code register (@var{CR}) to
15303 indicate whether floating point values were passed in the floating point
15304 registers in case the function takes a variable arguments. With
15305 @option{-mprototype}, only calls to prototyped variable argument functions
15306 will set or clear the bit.
15310 On embedded PowerPC systems, assume that the startup module is called
15311 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
15312 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
15317 On embedded PowerPC systems, assume that the startup module is called
15318 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
15323 On embedded PowerPC systems, assume that the startup module is called
15324 @file{crt0.o} and the standard C libraries are @file{libads.a} and
15327 @item -myellowknife
15328 @opindex myellowknife
15329 On embedded PowerPC systems, assume that the startup module is called
15330 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
15335 On System V.4 and embedded PowerPC systems, specify that you are
15336 compiling for a VxWorks system.
15340 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
15341 header to indicate that @samp{eabi} extended relocations are used.
15347 On System V.4 and embedded PowerPC systems do (do not) adhere to the
15348 Embedded Applications Binary Interface (eabi) which is a set of
15349 modifications to the System V.4 specifications. Selecting @option{-meabi}
15350 means that the stack is aligned to an 8 byte boundary, a function
15351 @code{__eabi} is called to from @code{main} to set up the eabi
15352 environment, and the @option{-msdata} option can use both @code{r2} and
15353 @code{r13} to point to two separate small data areas. Selecting
15354 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
15355 do not call an initialization function from @code{main}, and the
15356 @option{-msdata} option will only use @code{r13} to point to a single
15357 small data area. The @option{-meabi} option is on by default if you
15358 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
15361 @opindex msdata=eabi
15362 On System V.4 and embedded PowerPC systems, put small initialized
15363 @code{const} global and static data in the @samp{.sdata2} section, which
15364 is pointed to by register @code{r2}. Put small initialized
15365 non-@code{const} global and static data in the @samp{.sdata} section,
15366 which is pointed to by register @code{r13}. Put small uninitialized
15367 global and static data in the @samp{.sbss} section, which is adjacent to
15368 the @samp{.sdata} section. The @option{-msdata=eabi} option is
15369 incompatible with the @option{-mrelocatable} option. The
15370 @option{-msdata=eabi} option also sets the @option{-memb} option.
15373 @opindex msdata=sysv
15374 On System V.4 and embedded PowerPC systems, put small global and static
15375 data in the @samp{.sdata} section, which is pointed to by register
15376 @code{r13}. Put small uninitialized global and static data in the
15377 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
15378 The @option{-msdata=sysv} option is incompatible with the
15379 @option{-mrelocatable} option.
15381 @item -msdata=default
15383 @opindex msdata=default
15385 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
15386 compile code the same as @option{-msdata=eabi}, otherwise compile code the
15387 same as @option{-msdata=sysv}.
15390 @opindex msdata=data
15391 On System V.4 and embedded PowerPC systems, put small global
15392 data in the @samp{.sdata} section. Put small uninitialized global
15393 data in the @samp{.sbss} section. Do not use register @code{r13}
15394 to address small data however. This is the default behavior unless
15395 other @option{-msdata} options are used.
15399 @opindex msdata=none
15401 On embedded PowerPC systems, put all initialized global and static data
15402 in the @samp{.data} section, and all uninitialized data in the
15403 @samp{.bss} section.
15407 @cindex smaller data references (PowerPC)
15408 @cindex .sdata/.sdata2 references (PowerPC)
15409 On embedded PowerPC systems, put global and static items less than or
15410 equal to @var{num} bytes into the small data or bss sections instead of
15411 the normal data or bss section. By default, @var{num} is 8. The
15412 @option{-G @var{num}} switch is also passed to the linker.
15413 All modules should be compiled with the same @option{-G @var{num}} value.
15416 @itemx -mno-regnames
15418 @opindex mno-regnames
15419 On System V.4 and embedded PowerPC systems do (do not) emit register
15420 names in the assembly language output using symbolic forms.
15423 @itemx -mno-longcall
15425 @opindex mno-longcall
15426 By default assume that all calls are far away so that a longer more
15427 expensive calling sequence is required. This is required for calls
15428 further than 32 megabytes (33,554,432 bytes) from the current location.
15429 A short call will be generated if the compiler knows
15430 the call cannot be that far away. This setting can be overridden by
15431 the @code{shortcall} function attribute, or by @code{#pragma
15434 Some linkers are capable of detecting out-of-range calls and generating
15435 glue code on the fly. On these systems, long calls are unnecessary and
15436 generate slower code. As of this writing, the AIX linker can do this,
15437 as can the GNU linker for PowerPC/64. It is planned to add this feature
15438 to the GNU linker for 32-bit PowerPC systems as well.
15440 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
15441 callee, L42'', plus a ``branch island'' (glue code). The two target
15442 addresses represent the callee and the ``branch island''. The
15443 Darwin/PPC linker will prefer the first address and generate a ``bl
15444 callee'' if the PPC ``bl'' instruction will reach the callee directly;
15445 otherwise, the linker will generate ``bl L42'' to call the ``branch
15446 island''. The ``branch island'' is appended to the body of the
15447 calling function; it computes the full 32-bit address of the callee
15450 On Mach-O (Darwin) systems, this option directs the compiler emit to
15451 the glue for every direct call, and the Darwin linker decides whether
15452 to use or discard it.
15454 In the future, we may cause GCC to ignore all longcall specifications
15455 when the linker is known to generate glue.
15457 @item -mtls-markers
15458 @itemx -mno-tls-markers
15459 @opindex mtls-markers
15460 @opindex mno-tls-markers
15461 Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
15462 specifying the function argument. The relocation allows ld to
15463 reliably associate function call with argument setup instructions for
15464 TLS optimization, which in turn allows gcc to better schedule the
15469 Adds support for multithreading with the @dfn{pthreads} library.
15470 This option sets flags for both the preprocessor and linker.
15475 @subsection RX Options
15478 These @option{-m} options are defined for RX implementations:
15481 @item -m64bit-doubles
15482 @itemx -m32bit-doubles
15485 @opindex m64bit-doubles
15486 @opindex m32bit-doubles
15489 Make the @code{double} data type be 64-bits (@option{-m64bit-doubles})
15490 or 32-bits (@option{-m32bit-doubles}) in size. The default is
15491 @option{-m64bit-doubles}. @emph{Note} the RX's hardware floating
15492 point instructions are only used for 32-bit floating point values, and
15493 then only if @option{-ffast-math} has been specified on the command
15494 line. This is because the RX FPU instructions do not properly support
15495 denormal (or sub-normal) values.
15497 The options @option{-fpu} and @option{-nofpu} have been provided at
15498 the request of Rensas for compatibility with their toolchain. The
15499 @option{-mfpu} option enables the use of RX FPU instructions by
15500 selecting 32-bit doubles and enabling unsafe math optimizations. The
15501 @option{-mnofpu} option disables the use of RX FPU instructions, even
15502 if @option{-m32bit-doubles} is active and unsafe math optimizations
15505 @item -mcpu=@var{name}
15506 @itemx -patch=@var{name}
15509 Selects the type of RX CPU to be targeted. Currently on two types are
15510 supported, the generic @var{RX600} and the specific @var{RX610}. The
15511 only difference between them is that the @var{RX610} does not support
15512 the @code{MVTIPL} instruction.
15514 @item -mbig-endian-data
15515 @itemx -mlittle-endian-data
15516 @opindex mbig-endian-data
15517 @opindex mlittle-endian-data
15518 Store data (but not code) in the big-endian format. The default is
15519 @option{-mlittle-endian-data}, ie to store data in the little endian
15522 @item -msmall-data-limit=@var{N}
15523 @opindex msmall-data-limit
15524 Specifies the maximum size in bytes of global and static variables
15525 which can be placed into the small data area. Using the small data
15526 area can lead to smaller and faster code, but the size of area is
15527 limited and it is up to the programmer to ensure that the area does
15528 not overflow. Also when the small data area is used one of the RX's
15529 registers (@code{r13}) is reserved for use pointing to this area, so
15530 it is no longer available for use by the compiler. This could result
15531 in slower and/or larger code if variables which once could have been
15532 held in @code{r13} are now pushed onto the stack.
15534 Note, common variables (variables which have not been initialised) and
15535 constants are not placed into the small data area as they are assigned
15536 to other sections in the output executeable.
15538 The default value is zero, which disables this feature. Note, this
15539 feature is not enabled by default with higher optimization levels
15540 (@option{-O2} etc) because of the potentially deterimental effects of
15541 reserving register @code{r13}. It is up to the programmer to
15542 experiment and discover whether this feature is of benefit to their
15549 Use the simulator runtime. The default is to use the libgloss board
15552 @item -mas100-syntax
15553 @item -mno-as100-syntax
15554 @opindex mas100-syntax
15555 @opindex mno-as100-syntax
15556 When generating assembler output use a syntax that is compatible with
15557 Renesas's AS100 assembler. This syntax can also be handled by the GAS
15558 assembler but it has some restrictions so generating it is not the
15561 @item -mmax-constant-size=@var{N}
15562 @opindex mmax-constant-size
15563 Specifies the maxium size, in bytes, of a constant that can be used as
15564 an operand in a RX instruction. Although the RX instruction set does
15565 allow consants of up to 4 bytes in length to be used in instructions,
15566 a longer value equates to a longer instruction. Thus in some
15567 circumstances it can be beneficial to restrict the size of constants
15568 that are used in instructions. Constants that are too big are instead
15569 placed into a constant pool and referenced via register indirection.
15571 The value @var{N} can be between 0 and 3. A value of 0, the default,
15572 means that constants of any size are allowed.
15576 Enable linker relaxation. Linker relaxation is a process whereby the
15577 linker will attempt to reduce the size of a program by finding shorter
15578 versions of various instructions. Disabled by default.
15580 @item -mint-register=@var{N}
15581 @opindex mint-register
15582 Specify the number of registers to reserve for fast interrupt handler
15583 functions. The value @var{N} can be between 0 and 4. A value of 1
15584 means that register @code{r13} will be reserved for ther exclusive use
15585 of fast interrupt handlers. A value of 2 reserves @code{r13} and
15586 @code{r12}. A value of 3 reserves @code{r13}, @code{r12} and
15587 @code{r11}, and a value of 4 reserves @code{r13} through @code{r10}.
15588 A value of 0, the default, does not reserve any registers.
15590 @item -msave-acc-in-interrupts
15591 @opindex msave-acc-in-interrupts
15592 Specifies that interrupt handler functions should preserve the
15593 accumulator register. This is only necessary if normal code might use
15594 the accumulator register, for example because it performs 64-bit
15595 multiplications. The default is to ignore the accumulator as this
15596 makes the interrupt handlers faster.
15600 @emph{Note:} The generic GCC command line @option{-ffixed-@var{reg}}
15601 has special significance to the RX port when used with the
15602 @code{interrupt} function attribute. This attribute indicates a
15603 function intended to process fast interrupts. GCC will will ensure
15604 that it only uses the registers @code{r10}, @code{r11}, @code{r12}
15605 and/or @code{r13} and only provided that the normal use of the
15606 corresponding registers have been restricted via the
15607 @option{-ffixed-@var{reg}} or @option{-mint-register} command line
15610 @node S/390 and zSeries Options
15611 @subsection S/390 and zSeries Options
15612 @cindex S/390 and zSeries Options
15614 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
15618 @itemx -msoft-float
15619 @opindex mhard-float
15620 @opindex msoft-float
15621 Use (do not use) the hardware floating-point instructions and registers
15622 for floating-point operations. When @option{-msoft-float} is specified,
15623 functions in @file{libgcc.a} will be used to perform floating-point
15624 operations. When @option{-mhard-float} is specified, the compiler
15625 generates IEEE floating-point instructions. This is the default.
15628 @itemx -mno-hard-dfp
15630 @opindex mno-hard-dfp
15631 Use (do not use) the hardware decimal-floating-point instructions for
15632 decimal-floating-point operations. When @option{-mno-hard-dfp} is
15633 specified, functions in @file{libgcc.a} will be used to perform
15634 decimal-floating-point operations. When @option{-mhard-dfp} is
15635 specified, the compiler generates decimal-floating-point hardware
15636 instructions. This is the default for @option{-march=z9-ec} or higher.
15638 @item -mlong-double-64
15639 @itemx -mlong-double-128
15640 @opindex mlong-double-64
15641 @opindex mlong-double-128
15642 These switches control the size of @code{long double} type. A size
15643 of 64bit makes the @code{long double} type equivalent to the @code{double}
15644 type. This is the default.
15647 @itemx -mno-backchain
15648 @opindex mbackchain
15649 @opindex mno-backchain
15650 Store (do not store) the address of the caller's frame as backchain pointer
15651 into the callee's stack frame.
15652 A backchain may be needed to allow debugging using tools that do not understand
15653 DWARF-2 call frame information.
15654 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
15655 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
15656 the backchain is placed into the topmost word of the 96/160 byte register
15659 In general, code compiled with @option{-mbackchain} is call-compatible with
15660 code compiled with @option{-mmo-backchain}; however, use of the backchain
15661 for debugging purposes usually requires that the whole binary is built with
15662 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
15663 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
15664 to build a linux kernel use @option{-msoft-float}.
15666 The default is to not maintain the backchain.
15668 @item -mpacked-stack
15669 @itemx -mno-packed-stack
15670 @opindex mpacked-stack
15671 @opindex mno-packed-stack
15672 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
15673 specified, the compiler uses the all fields of the 96/160 byte register save
15674 area only for their default purpose; unused fields still take up stack space.
15675 When @option{-mpacked-stack} is specified, register save slots are densely
15676 packed at the top of the register save area; unused space is reused for other
15677 purposes, allowing for more efficient use of the available stack space.
15678 However, when @option{-mbackchain} is also in effect, the topmost word of
15679 the save area is always used to store the backchain, and the return address
15680 register is always saved two words below the backchain.
15682 As long as the stack frame backchain is not used, code generated with
15683 @option{-mpacked-stack} is call-compatible with code generated with
15684 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
15685 S/390 or zSeries generated code that uses the stack frame backchain at run
15686 time, not just for debugging purposes. Such code is not call-compatible
15687 with code compiled with @option{-mpacked-stack}. Also, note that the
15688 combination of @option{-mbackchain},
15689 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
15690 to build a linux kernel use @option{-msoft-float}.
15692 The default is to not use the packed stack layout.
15695 @itemx -mno-small-exec
15696 @opindex msmall-exec
15697 @opindex mno-small-exec
15698 Generate (or do not generate) code using the @code{bras} instruction
15699 to do subroutine calls.
15700 This only works reliably if the total executable size does not
15701 exceed 64k. The default is to use the @code{basr} instruction instead,
15702 which does not have this limitation.
15708 When @option{-m31} is specified, generate code compliant to the
15709 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
15710 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
15711 particular to generate 64-bit instructions. For the @samp{s390}
15712 targets, the default is @option{-m31}, while the @samp{s390x}
15713 targets default to @option{-m64}.
15719 When @option{-mzarch} is specified, generate code using the
15720 instructions available on z/Architecture.
15721 When @option{-mesa} is specified, generate code using the
15722 instructions available on ESA/390. Note that @option{-mesa} is
15723 not possible with @option{-m64}.
15724 When generating code compliant to the GNU/Linux for S/390 ABI,
15725 the default is @option{-mesa}. When generating code compliant
15726 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
15732 Generate (or do not generate) code using the @code{mvcle} instruction
15733 to perform block moves. When @option{-mno-mvcle} is specified,
15734 use a @code{mvc} loop instead. This is the default unless optimizing for
15741 Print (or do not print) additional debug information when compiling.
15742 The default is to not print debug information.
15744 @item -march=@var{cpu-type}
15746 Generate code that will run on @var{cpu-type}, which is the name of a system
15747 representing a certain processor type. Possible values for
15748 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
15749 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
15750 When generating code using the instructions available on z/Architecture,
15751 the default is @option{-march=z900}. Otherwise, the default is
15752 @option{-march=g5}.
15754 @item -mtune=@var{cpu-type}
15756 Tune to @var{cpu-type} everything applicable about the generated code,
15757 except for the ABI and the set of available instructions.
15758 The list of @var{cpu-type} values is the same as for @option{-march}.
15759 The default is the value used for @option{-march}.
15762 @itemx -mno-tpf-trace
15763 @opindex mtpf-trace
15764 @opindex mno-tpf-trace
15765 Generate code that adds (does not add) in TPF OS specific branches to trace
15766 routines in the operating system. This option is off by default, even
15767 when compiling for the TPF OS@.
15770 @itemx -mno-fused-madd
15771 @opindex mfused-madd
15772 @opindex mno-fused-madd
15773 Generate code that uses (does not use) the floating point multiply and
15774 accumulate instructions. These instructions are generated by default if
15775 hardware floating point is used.
15777 @item -mwarn-framesize=@var{framesize}
15778 @opindex mwarn-framesize
15779 Emit a warning if the current function exceeds the given frame size. Because
15780 this is a compile time check it doesn't need to be a real problem when the program
15781 runs. It is intended to identify functions which most probably cause
15782 a stack overflow. It is useful to be used in an environment with limited stack
15783 size e.g.@: the linux kernel.
15785 @item -mwarn-dynamicstack
15786 @opindex mwarn-dynamicstack
15787 Emit a warning if the function calls alloca or uses dynamically
15788 sized arrays. This is generally a bad idea with a limited stack size.
15790 @item -mstack-guard=@var{stack-guard}
15791 @itemx -mstack-size=@var{stack-size}
15792 @opindex mstack-guard
15793 @opindex mstack-size
15794 If these options are provided the s390 back end emits additional instructions in
15795 the function prologue which trigger a trap if the stack size is @var{stack-guard}
15796 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
15797 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
15798 the frame size of the compiled function is chosen.
15799 These options are intended to be used to help debugging stack overflow problems.
15800 The additionally emitted code causes only little overhead and hence can also be
15801 used in production like systems without greater performance degradation. The given
15802 values have to be exact powers of 2 and @var{stack-size} has to be greater than
15803 @var{stack-guard} without exceeding 64k.
15804 In order to be efficient the extra code makes the assumption that the stack starts
15805 at an address aligned to the value given by @var{stack-size}.
15806 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
15809 @node Score Options
15810 @subsection Score Options
15811 @cindex Score Options
15813 These options are defined for Score implementations:
15818 Compile code for big endian mode. This is the default.
15822 Compile code for little endian mode.
15826 Disable generate bcnz instruction.
15830 Enable generate unaligned load and store instruction.
15834 Enable the use of multiply-accumulate instructions. Disabled by default.
15838 Specify the SCORE5 as the target architecture.
15842 Specify the SCORE5U of the target architecture.
15846 Specify the SCORE7 as the target architecture. This is the default.
15850 Specify the SCORE7D as the target architecture.
15854 @subsection SH Options
15856 These @samp{-m} options are defined for the SH implementations:
15861 Generate code for the SH1.
15865 Generate code for the SH2.
15868 Generate code for the SH2e.
15872 Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
15873 that the floating-point unit is not used.
15875 @item -m2a-single-only
15876 @opindex m2a-single-only
15877 Generate code for the SH2a-FPU, in such a way that no double-precision
15878 floating point operations are used.
15881 @opindex m2a-single
15882 Generate code for the SH2a-FPU assuming the floating-point unit is in
15883 single-precision mode by default.
15887 Generate code for the SH2a-FPU assuming the floating-point unit is in
15888 double-precision mode by default.
15892 Generate code for the SH3.
15896 Generate code for the SH3e.
15900 Generate code for the SH4 without a floating-point unit.
15902 @item -m4-single-only
15903 @opindex m4-single-only
15904 Generate code for the SH4 with a floating-point unit that only
15905 supports single-precision arithmetic.
15909 Generate code for the SH4 assuming the floating-point unit is in
15910 single-precision mode by default.
15914 Generate code for the SH4.
15918 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
15919 floating-point unit is not used.
15921 @item -m4a-single-only
15922 @opindex m4a-single-only
15923 Generate code for the SH4a, in such a way that no double-precision
15924 floating point operations are used.
15927 @opindex m4a-single
15928 Generate code for the SH4a assuming the floating-point unit is in
15929 single-precision mode by default.
15933 Generate code for the SH4a.
15937 Same as @option{-m4a-nofpu}, except that it implicitly passes
15938 @option{-dsp} to the assembler. GCC doesn't generate any DSP
15939 instructions at the moment.
15943 Compile code for the processor in big endian mode.
15947 Compile code for the processor in little endian mode.
15951 Align doubles at 64-bit boundaries. Note that this changes the calling
15952 conventions, and thus some functions from the standard C library will
15953 not work unless you recompile it first with @option{-mdalign}.
15957 Shorten some address references at link time, when possible; uses the
15958 linker option @option{-relax}.
15962 Use 32-bit offsets in @code{switch} tables. The default is to use
15967 Enable the use of bit manipulation instructions on SH2A.
15971 Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
15972 alignment constraints.
15976 Comply with the calling conventions defined by Renesas.
15980 Comply with the calling conventions defined by Renesas.
15984 Comply with the calling conventions defined for GCC before the Renesas
15985 conventions were available. This option is the default for all
15986 targets of the SH toolchain except for @samp{sh-symbianelf}.
15989 @opindex mnomacsave
15990 Mark the @code{MAC} register as call-clobbered, even if
15991 @option{-mhitachi} is given.
15995 Increase IEEE-compliance of floating-point code.
15996 At the moment, this is equivalent to @option{-fno-finite-math-only}.
15997 When generating 16 bit SH opcodes, getting IEEE-conforming results for
15998 comparisons of NANs / infinities incurs extra overhead in every
15999 floating point comparison, therefore the default is set to
16000 @option{-ffinite-math-only}.
16002 @item -minline-ic_invalidate
16003 @opindex minline-ic_invalidate
16004 Inline code to invalidate instruction cache entries after setting up
16005 nested function trampolines.
16006 This option has no effect if -musermode is in effect and the selected
16007 code generation option (e.g. -m4) does not allow the use of the icbi
16009 If the selected code generation option does not allow the use of the icbi
16010 instruction, and -musermode is not in effect, the inlined code will
16011 manipulate the instruction cache address array directly with an associative
16012 write. This not only requires privileged mode, but it will also
16013 fail if the cache line had been mapped via the TLB and has become unmapped.
16017 Dump instruction size and location in the assembly code.
16020 @opindex mpadstruct
16021 This option is deprecated. It pads structures to multiple of 4 bytes,
16022 which is incompatible with the SH ABI@.
16026 Optimize for space instead of speed. Implied by @option{-Os}.
16029 @opindex mprefergot
16030 When generating position-independent code, emit function calls using
16031 the Global Offset Table instead of the Procedure Linkage Table.
16035 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
16036 if the inlined code would not work in user mode.
16037 This is the default when the target is @code{sh-*-linux*}.
16039 @item -multcost=@var{number}
16040 @opindex multcost=@var{number}
16041 Set the cost to assume for a multiply insn.
16043 @item -mdiv=@var{strategy}
16044 @opindex mdiv=@var{strategy}
16045 Set the division strategy to use for SHmedia code. @var{strategy} must be
16046 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
16047 inv:call2, inv:fp .
16048 "fp" performs the operation in floating point. This has a very high latency,
16049 but needs only a few instructions, so it might be a good choice if
16050 your code has enough easily exploitable ILP to allow the compiler to
16051 schedule the floating point instructions together with other instructions.
16052 Division by zero causes a floating point exception.
16053 "inv" uses integer operations to calculate the inverse of the divisor,
16054 and then multiplies the dividend with the inverse. This strategy allows
16055 cse and hoisting of the inverse calculation. Division by zero calculates
16056 an unspecified result, but does not trap.
16057 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
16058 have been found, or if the entire operation has been hoisted to the same
16059 place, the last stages of the inverse calculation are intertwined with the
16060 final multiply to reduce the overall latency, at the expense of using a few
16061 more instructions, and thus offering fewer scheduling opportunities with
16063 "call" calls a library function that usually implements the inv:minlat
16065 This gives high code density for m5-*media-nofpu compilations.
16066 "call2" uses a different entry point of the same library function, where it
16067 assumes that a pointer to a lookup table has already been set up, which
16068 exposes the pointer load to cse / code hoisting optimizations.
16069 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
16070 code generation, but if the code stays unoptimized, revert to the "call",
16071 "call2", or "fp" strategies, respectively. Note that the
16072 potentially-trapping side effect of division by zero is carried by a
16073 separate instruction, so it is possible that all the integer instructions
16074 are hoisted out, but the marker for the side effect stays where it is.
16075 A recombination to fp operations or a call is not possible in that case.
16076 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
16077 that the inverse calculation was nor separated from the multiply, they speed
16078 up division where the dividend fits into 20 bits (plus sign where applicable),
16079 by inserting a test to skip a number of operations in this case; this test
16080 slows down the case of larger dividends. inv20u assumes the case of a such
16081 a small dividend to be unlikely, and inv20l assumes it to be likely.
16083 @item -mdivsi3_libfunc=@var{name}
16084 @opindex mdivsi3_libfunc=@var{name}
16085 Set the name of the library function used for 32 bit signed division to
16086 @var{name}. This only affect the name used in the call and inv:call
16087 division strategies, and the compiler will still expect the same
16088 sets of input/output/clobbered registers as if this option was not present.
16090 @item -mfixed-range=@var{register-range}
16091 @opindex mfixed-range
16092 Generate code treating the given register range as fixed registers.
16093 A fixed register is one that the register allocator can not use. This is
16094 useful when compiling kernel code. A register range is specified as
16095 two registers separated by a dash. Multiple register ranges can be
16096 specified separated by a comma.
16098 @item -madjust-unroll
16099 @opindex madjust-unroll
16100 Throttle unrolling to avoid thrashing target registers.
16101 This option only has an effect if the gcc code base supports the
16102 TARGET_ADJUST_UNROLL_MAX target hook.
16104 @item -mindexed-addressing
16105 @opindex mindexed-addressing
16106 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
16107 This is only safe if the hardware and/or OS implement 32 bit wrap-around
16108 semantics for the indexed addressing mode. The architecture allows the
16109 implementation of processors with 64 bit MMU, which the OS could use to
16110 get 32 bit addressing, but since no current hardware implementation supports
16111 this or any other way to make the indexed addressing mode safe to use in
16112 the 32 bit ABI, the default is -mno-indexed-addressing.
16114 @item -mgettrcost=@var{number}
16115 @opindex mgettrcost=@var{number}
16116 Set the cost assumed for the gettr instruction to @var{number}.
16117 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
16121 Assume pt* instructions won't trap. This will generally generate better
16122 scheduled code, but is unsafe on current hardware. The current architecture
16123 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
16124 This has the unintentional effect of making it unsafe to schedule ptabs /
16125 ptrel before a branch, or hoist it out of a loop. For example,
16126 __do_global_ctors, a part of libgcc that runs constructors at program
16127 startup, calls functions in a list which is delimited by @minus{}1. With the
16128 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
16129 That means that all the constructors will be run a bit quicker, but when
16130 the loop comes to the end of the list, the program crashes because ptabs
16131 loads @minus{}1 into a target register. Since this option is unsafe for any
16132 hardware implementing the current architecture specification, the default
16133 is -mno-pt-fixed. Unless the user specifies a specific cost with
16134 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
16135 this deters register allocation using target registers for storing
16138 @item -minvalid-symbols
16139 @opindex minvalid-symbols
16140 Assume symbols might be invalid. Ordinary function symbols generated by
16141 the compiler will always be valid to load with movi/shori/ptabs or
16142 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
16143 to generate symbols that will cause ptabs / ptrel to trap.
16144 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
16145 It will then prevent cross-basic-block cse, hoisting and most scheduling
16146 of symbol loads. The default is @option{-mno-invalid-symbols}.
16149 @node SPARC Options
16150 @subsection SPARC Options
16151 @cindex SPARC options
16153 These @samp{-m} options are supported on the SPARC:
16156 @item -mno-app-regs
16158 @opindex mno-app-regs
16160 Specify @option{-mapp-regs} to generate output using the global registers
16161 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
16164 To be fully SVR4 ABI compliant at the cost of some performance loss,
16165 specify @option{-mno-app-regs}. You should compile libraries and system
16166 software with this option.
16169 @itemx -mhard-float
16171 @opindex mhard-float
16172 Generate output containing floating point instructions. This is the
16176 @itemx -msoft-float
16178 @opindex msoft-float
16179 Generate output containing library calls for floating point.
16180 @strong{Warning:} the requisite libraries are not available for all SPARC
16181 targets. Normally the facilities of the machine's usual C compiler are
16182 used, but this cannot be done directly in cross-compilation. You must make
16183 your own arrangements to provide suitable library functions for
16184 cross-compilation. The embedded targets @samp{sparc-*-aout} and
16185 @samp{sparclite-*-*} do provide software floating point support.
16187 @option{-msoft-float} changes the calling convention in the output file;
16188 therefore, it is only useful if you compile @emph{all} of a program with
16189 this option. In particular, you need to compile @file{libgcc.a}, the
16190 library that comes with GCC, with @option{-msoft-float} in order for
16193 @item -mhard-quad-float
16194 @opindex mhard-quad-float
16195 Generate output containing quad-word (long double) floating point
16198 @item -msoft-quad-float
16199 @opindex msoft-quad-float
16200 Generate output containing library calls for quad-word (long double)
16201 floating point instructions. The functions called are those specified
16202 in the SPARC ABI@. This is the default.
16204 As of this writing, there are no SPARC implementations that have hardware
16205 support for the quad-word floating point instructions. They all invoke
16206 a trap handler for one of these instructions, and then the trap handler
16207 emulates the effect of the instruction. Because of the trap handler overhead,
16208 this is much slower than calling the ABI library routines. Thus the
16209 @option{-msoft-quad-float} option is the default.
16211 @item -mno-unaligned-doubles
16212 @itemx -munaligned-doubles
16213 @opindex mno-unaligned-doubles
16214 @opindex munaligned-doubles
16215 Assume that doubles have 8 byte alignment. This is the default.
16217 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
16218 alignment only if they are contained in another type, or if they have an
16219 absolute address. Otherwise, it assumes they have 4 byte alignment.
16220 Specifying this option avoids some rare compatibility problems with code
16221 generated by other compilers. It is not the default because it results
16222 in a performance loss, especially for floating point code.
16224 @item -mno-faster-structs
16225 @itemx -mfaster-structs
16226 @opindex mno-faster-structs
16227 @opindex mfaster-structs
16228 With @option{-mfaster-structs}, the compiler assumes that structures
16229 should have 8 byte alignment. This enables the use of pairs of
16230 @code{ldd} and @code{std} instructions for copies in structure
16231 assignment, in place of twice as many @code{ld} and @code{st} pairs.
16232 However, the use of this changed alignment directly violates the SPARC
16233 ABI@. Thus, it's intended only for use on targets where the developer
16234 acknowledges that their resulting code will not be directly in line with
16235 the rules of the ABI@.
16237 @item -mimpure-text
16238 @opindex mimpure-text
16239 @option{-mimpure-text}, used in addition to @option{-shared}, tells
16240 the compiler to not pass @option{-z text} to the linker when linking a
16241 shared object. Using this option, you can link position-dependent
16242 code into a shared object.
16244 @option{-mimpure-text} suppresses the ``relocations remain against
16245 allocatable but non-writable sections'' linker error message.
16246 However, the necessary relocations will trigger copy-on-write, and the
16247 shared object is not actually shared across processes. Instead of
16248 using @option{-mimpure-text}, you should compile all source code with
16249 @option{-fpic} or @option{-fPIC}.
16251 This option is only available on SunOS and Solaris.
16253 @item -mcpu=@var{cpu_type}
16255 Set the instruction set, register set, and instruction scheduling parameters
16256 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
16257 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
16258 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
16259 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
16260 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
16262 Default instruction scheduling parameters are used for values that select
16263 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
16264 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
16266 Here is a list of each supported architecture and their supported
16271 v8: supersparc, hypersparc
16272 sparclite: f930, f934, sparclite86x
16274 v9: ultrasparc, ultrasparc3, niagara, niagara2
16277 By default (unless configured otherwise), GCC generates code for the V7
16278 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
16279 additionally optimizes it for the Cypress CY7C602 chip, as used in the
16280 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
16281 SPARCStation 1, 2, IPX etc.
16283 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
16284 architecture. The only difference from V7 code is that the compiler emits
16285 the integer multiply and integer divide instructions which exist in SPARC-V8
16286 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
16287 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
16290 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
16291 the SPARC architecture. This adds the integer multiply, integer divide step
16292 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
16293 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
16294 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
16295 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
16296 MB86934 chip, which is the more recent SPARClite with FPU@.
16298 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
16299 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
16300 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
16301 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
16302 optimizes it for the TEMIC SPARClet chip.
16304 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
16305 architecture. This adds 64-bit integer and floating-point move instructions,
16306 3 additional floating-point condition code registers and conditional move
16307 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
16308 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
16309 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
16310 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
16311 @option{-mcpu=niagara}, the compiler additionally optimizes it for
16312 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
16313 additionally optimizes it for Sun UltraSPARC T2 chips.
16315 @item -mtune=@var{cpu_type}
16317 Set the instruction scheduling parameters for machine type
16318 @var{cpu_type}, but do not set the instruction set or register set that the
16319 option @option{-mcpu=@var{cpu_type}} would.
16321 The same values for @option{-mcpu=@var{cpu_type}} can be used for
16322 @option{-mtune=@var{cpu_type}}, but the only useful values are those
16323 that select a particular cpu implementation. Those are @samp{cypress},
16324 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
16325 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
16326 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
16331 @opindex mno-v8plus
16332 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
16333 difference from the V8 ABI is that the global and out registers are
16334 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
16335 mode for all SPARC-V9 processors.
16341 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
16342 Visual Instruction Set extensions. The default is @option{-mno-vis}.
16345 These @samp{-m} options are supported in addition to the above
16346 on SPARC-V9 processors in 64-bit environments:
16349 @item -mlittle-endian
16350 @opindex mlittle-endian
16351 Generate code for a processor running in little-endian mode. It is only
16352 available for a few configurations and most notably not on Solaris and Linux.
16358 Generate code for a 32-bit or 64-bit environment.
16359 The 32-bit environment sets int, long and pointer to 32 bits.
16360 The 64-bit environment sets int to 32 bits and long and pointer
16363 @item -mcmodel=medlow
16364 @opindex mcmodel=medlow
16365 Generate code for the Medium/Low code model: 64-bit addresses, programs
16366 must be linked in the low 32 bits of memory. Programs can be statically
16367 or dynamically linked.
16369 @item -mcmodel=medmid
16370 @opindex mcmodel=medmid
16371 Generate code for the Medium/Middle code model: 64-bit addresses, programs
16372 must be linked in the low 44 bits of memory, the text and data segments must
16373 be less than 2GB in size and the data segment must be located within 2GB of
16376 @item -mcmodel=medany
16377 @opindex mcmodel=medany
16378 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
16379 may be linked anywhere in memory, the text and data segments must be less
16380 than 2GB in size and the data segment must be located within 2GB of the
16383 @item -mcmodel=embmedany
16384 @opindex mcmodel=embmedany
16385 Generate code for the Medium/Anywhere code model for embedded systems:
16386 64-bit addresses, the text and data segments must be less than 2GB in
16387 size, both starting anywhere in memory (determined at link time). The
16388 global register %g4 points to the base of the data segment. Programs
16389 are statically linked and PIC is not supported.
16392 @itemx -mno-stack-bias
16393 @opindex mstack-bias
16394 @opindex mno-stack-bias
16395 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
16396 frame pointer if present, are offset by @minus{}2047 which must be added back
16397 when making stack frame references. This is the default in 64-bit mode.
16398 Otherwise, assume no such offset is present.
16401 These switches are supported in addition to the above on Solaris:
16406 Add support for multithreading using the Solaris threads library. This
16407 option sets flags for both the preprocessor and linker. This option does
16408 not affect the thread safety of object code produced by the compiler or
16409 that of libraries supplied with it.
16413 Add support for multithreading using the POSIX threads library. This
16414 option sets flags for both the preprocessor and linker. This option does
16415 not affect the thread safety of object code produced by the compiler or
16416 that of libraries supplied with it.
16420 This is a synonym for @option{-pthreads}.
16424 @subsection SPU Options
16425 @cindex SPU options
16427 These @samp{-m} options are supported on the SPU:
16431 @itemx -merror-reloc
16432 @opindex mwarn-reloc
16433 @opindex merror-reloc
16435 The loader for SPU does not handle dynamic relocations. By default, GCC
16436 will give an error when it generates code that requires a dynamic
16437 relocation. @option{-mno-error-reloc} disables the error,
16438 @option{-mwarn-reloc} will generate a warning instead.
16441 @itemx -munsafe-dma
16443 @opindex munsafe-dma
16445 Instructions which initiate or test completion of DMA must not be
16446 reordered with respect to loads and stores of the memory which is being
16447 accessed. Users typically address this problem using the volatile
16448 keyword, but that can lead to inefficient code in places where the
16449 memory is known to not change. Rather than mark the memory as volatile
16450 we treat the DMA instructions as potentially effecting all memory. With
16451 @option{-munsafe-dma} users must use the volatile keyword to protect
16454 @item -mbranch-hints
16455 @opindex mbranch-hints
16457 By default, GCC will generate a branch hint instruction to avoid
16458 pipeline stalls for always taken or probably taken branches. A hint
16459 will not be generated closer than 8 instructions away from its branch.
16460 There is little reason to disable them, except for debugging purposes,
16461 or to make an object a little bit smaller.
16465 @opindex msmall-mem
16466 @opindex mlarge-mem
16468 By default, GCC generates code assuming that addresses are never larger
16469 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
16470 a full 32 bit address.
16475 By default, GCC links against startup code that assumes the SPU-style
16476 main function interface (which has an unconventional parameter list).
16477 With @option{-mstdmain}, GCC will link your program against startup
16478 code that assumes a C99-style interface to @code{main}, including a
16479 local copy of @code{argv} strings.
16481 @item -mfixed-range=@var{register-range}
16482 @opindex mfixed-range
16483 Generate code treating the given register range as fixed registers.
16484 A fixed register is one that the register allocator can not use. This is
16485 useful when compiling kernel code. A register range is specified as
16486 two registers separated by a dash. Multiple register ranges can be
16487 specified separated by a comma.
16493 Compile code assuming that pointers to the PPU address space accessed
16494 via the @code{__ea} named address space qualifier are either 32 or 64
16495 bits wide. The default is 32 bits. As this is an ABI changing option,
16496 all object code in an executable must be compiled with the same setting.
16498 @item -maddress-space-conversion
16499 @itemx -mno-address-space-conversion
16500 @opindex maddress-space-conversion
16501 @opindex mno-address-space-conversion
16502 Allow/disallow treating the @code{__ea} address space as superset
16503 of the generic address space. This enables explicit type casts
16504 between @code{__ea} and generic pointer as well as implicit
16505 conversions of generic pointers to @code{__ea} pointers. The
16506 default is to allow address space pointer conversions.
16508 @item -mcache-size=@var{cache-size}
16509 @opindex mcache-size
16510 This option controls the version of libgcc that the compiler links to an
16511 executable and selects a software-managed cache for accessing variables
16512 in the @code{__ea} address space with a particular cache size. Possible
16513 options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64}
16514 and @samp{128}. The default cache size is 64KB.
16516 @item -matomic-updates
16517 @itemx -mno-atomic-updates
16518 @opindex matomic-updates
16519 @opindex mno-atomic-updates
16520 This option controls the version of libgcc that the compiler links to an
16521 executable and selects whether atomic updates to the software-managed
16522 cache of PPU-side variables are used. If you use atomic updates, changes
16523 to a PPU variable from SPU code using the @code{__ea} named address space
16524 qualifier will not interfere with changes to other PPU variables residing
16525 in the same cache line from PPU code. If you do not use atomic updates,
16526 such interference may occur; however, writing back cache lines will be
16527 more efficient. The default behavior is to use atomic updates.
16530 @itemx -mdual-nops=@var{n}
16531 @opindex mdual-nops
16532 By default, GCC will insert nops to increase dual issue when it expects
16533 it to increase performance. @var{n} can be a value from 0 to 10. A
16534 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
16535 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
16537 @item -mhint-max-nops=@var{n}
16538 @opindex mhint-max-nops
16539 Maximum number of nops to insert for a branch hint. A branch hint must
16540 be at least 8 instructions away from the branch it is effecting. GCC
16541 will insert up to @var{n} nops to enforce this, otherwise it will not
16542 generate the branch hint.
16544 @item -mhint-max-distance=@var{n}
16545 @opindex mhint-max-distance
16546 The encoding of the branch hint instruction limits the hint to be within
16547 256 instructions of the branch it is effecting. By default, GCC makes
16548 sure it is within 125.
16551 @opindex msafe-hints
16552 Work around a hardware bug which causes the SPU to stall indefinitely.
16553 By default, GCC will insert the @code{hbrp} instruction to make sure
16554 this stall won't happen.
16558 @node System V Options
16559 @subsection Options for System V
16561 These additional options are available on System V Release 4 for
16562 compatibility with other compilers on those systems:
16567 Create a shared object.
16568 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
16572 Identify the versions of each tool used by the compiler, in a
16573 @code{.ident} assembler directive in the output.
16577 Refrain from adding @code{.ident} directives to the output file (this is
16580 @item -YP,@var{dirs}
16582 Search the directories @var{dirs}, and no others, for libraries
16583 specified with @option{-l}.
16585 @item -Ym,@var{dir}
16587 Look in the directory @var{dir} to find the M4 preprocessor.
16588 The assembler uses this option.
16589 @c This is supposed to go with a -Yd for predefined M4 macro files, but
16590 @c the generic assembler that comes with Solaris takes just -Ym.
16594 @subsection V850 Options
16595 @cindex V850 Options
16597 These @samp{-m} options are defined for V850 implementations:
16601 @itemx -mno-long-calls
16602 @opindex mlong-calls
16603 @opindex mno-long-calls
16604 Treat all calls as being far away (near). If calls are assumed to be
16605 far away, the compiler will always load the functions address up into a
16606 register, and call indirect through the pointer.
16612 Do not optimize (do optimize) basic blocks that use the same index
16613 pointer 4 or more times to copy pointer into the @code{ep} register, and
16614 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
16615 option is on by default if you optimize.
16617 @item -mno-prolog-function
16618 @itemx -mprolog-function
16619 @opindex mno-prolog-function
16620 @opindex mprolog-function
16621 Do not use (do use) external functions to save and restore registers
16622 at the prologue and epilogue of a function. The external functions
16623 are slower, but use less code space if more than one function saves
16624 the same number of registers. The @option{-mprolog-function} option
16625 is on by default if you optimize.
16629 Try to make the code as small as possible. At present, this just turns
16630 on the @option{-mep} and @option{-mprolog-function} options.
16632 @item -mtda=@var{n}
16634 Put static or global variables whose size is @var{n} bytes or less into
16635 the tiny data area that register @code{ep} points to. The tiny data
16636 area can hold up to 256 bytes in total (128 bytes for byte references).
16638 @item -msda=@var{n}
16640 Put static or global variables whose size is @var{n} bytes or less into
16641 the small data area that register @code{gp} points to. The small data
16642 area can hold up to 64 kilobytes.
16644 @item -mzda=@var{n}
16646 Put static or global variables whose size is @var{n} bytes or less into
16647 the first 32 kilobytes of memory.
16651 Specify that the target processor is the V850.
16654 @opindex mbig-switch
16655 Generate code suitable for big switch tables. Use this option only if
16656 the assembler/linker complain about out of range branches within a switch
16661 This option will cause r2 and r5 to be used in the code generated by
16662 the compiler. This setting is the default.
16664 @item -mno-app-regs
16665 @opindex mno-app-regs
16666 This option will cause r2 and r5 to be treated as fixed registers.
16670 Specify that the target processor is the V850E1. The preprocessor
16671 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
16672 this option is used.
16676 Specify that the target processor is the V850E@. The preprocessor
16677 constant @samp{__v850e__} will be defined if this option is used.
16679 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
16680 are defined then a default target processor will be chosen and the
16681 relevant @samp{__v850*__} preprocessor constant will be defined.
16683 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
16684 defined, regardless of which processor variant is the target.
16686 @item -mdisable-callt
16687 @opindex mdisable-callt
16688 This option will suppress generation of the CALLT instruction for the
16689 v850e and v850e1 flavors of the v850 architecture. The default is
16690 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
16695 @subsection VAX Options
16696 @cindex VAX options
16698 These @samp{-m} options are defined for the VAX:
16703 Do not output certain jump instructions (@code{aobleq} and so on)
16704 that the Unix assembler for the VAX cannot handle across long
16709 Do output those jump instructions, on the assumption that you
16710 will assemble with the GNU assembler.
16714 Output code for g-format floating point numbers instead of d-format.
16717 @node VxWorks Options
16718 @subsection VxWorks Options
16719 @cindex VxWorks Options
16721 The options in this section are defined for all VxWorks targets.
16722 Options specific to the target hardware are listed with the other
16723 options for that target.
16728 GCC can generate code for both VxWorks kernels and real time processes
16729 (RTPs). This option switches from the former to the latter. It also
16730 defines the preprocessor macro @code{__RTP__}.
16733 @opindex non-static
16734 Link an RTP executable against shared libraries rather than static
16735 libraries. The options @option{-static} and @option{-shared} can
16736 also be used for RTPs (@pxref{Link Options}); @option{-static}
16743 These options are passed down to the linker. They are defined for
16744 compatibility with Diab.
16747 @opindex Xbind-lazy
16748 Enable lazy binding of function calls. This option is equivalent to
16749 @option{-Wl,-z,now} and is defined for compatibility with Diab.
16753 Disable lazy binding of function calls. This option is the default and
16754 is defined for compatibility with Diab.
16757 @node x86-64 Options
16758 @subsection x86-64 Options
16759 @cindex x86-64 options
16761 These are listed under @xref{i386 and x86-64 Options}.
16763 @node i386 and x86-64 Windows Options
16764 @subsection i386 and x86-64 Windows Options
16765 @cindex i386 and x86-64 Windows Options
16767 These additional options are available for Windows targets:
16772 This option is available for Cygwin and MinGW targets. It
16773 specifies that a console application is to be generated, by
16774 instructing the linker to set the PE header subsystem type
16775 required for console applications.
16776 This is the default behavior for Cygwin and MinGW targets.
16780 This option is available for Cygwin targets. It specifies that
16781 the Cygwin internal interface is to be used for predefined
16782 preprocessor macros, C runtime libraries and related linker
16783 paths and options. For Cygwin targets this is the default behavior.
16784 This option is deprecated and will be removed in a future release.
16787 @opindex mno-cygwin
16788 This option is available for Cygwin targets. It specifies that
16789 the MinGW internal interface is to be used instead of Cygwin's, by
16790 setting MinGW-related predefined macros and linker paths and default
16792 This option is deprecated and will be removed in a future release.
16796 This option is available for Cygwin and MinGW targets. It
16797 specifies that a DLL - a dynamic link library - is to be
16798 generated, enabling the selection of the required runtime
16799 startup object and entry point.
16801 @item -mnop-fun-dllimport
16802 @opindex mnop-fun-dllimport
16803 This option is available for Cygwin and MinGW targets. It
16804 specifies that the dllimport attribute should be ignored.
16808 This option is available for MinGW targets. It specifies
16809 that MinGW-specific thread support is to be used.
16813 This option is available for mingw-w64 targets. It specifies
16814 that the UNICODE macro is getting pre-defined and that the
16815 unicode capable runtime startup code is choosen.
16819 This option is available for Cygwin and MinGW targets. It
16820 specifies that the typical Windows pre-defined macros are to
16821 be set in the pre-processor, but does not influence the choice
16822 of runtime library/startup code.
16826 This option is available for Cygwin and MinGW targets. It
16827 specifies that a GUI application is to be generated by
16828 instructing the linker to set the PE header subsystem type
16831 @item -fno-set-stack-executable
16832 @opindex fno-set-stack-executable
16833 This option is available for MinGW targets. It specifies that
16834 the executable flag for stack used by nested functions isn't
16835 set. This is necessary for binaries running in kernel mode of
16836 Windows, as there the user32 API, which is used to set executable
16837 privileges, isn't available.
16839 @item -mpe-aligned-commons
16840 @opindex mpe-aligned-commons
16841 This option is available for Cygwin and MinGW targets. It
16842 specifies that the GNU extension to the PE file format that
16843 permits the correct alignment of COMMON variables should be
16844 used when generating code. It will be enabled by default if
16845 GCC detects that the target assembler found during configuration
16846 supports the feature.
16849 See also under @ref{i386 and x86-64 Options} for standard options.
16851 @node Xstormy16 Options
16852 @subsection Xstormy16 Options
16853 @cindex Xstormy16 Options
16855 These options are defined for Xstormy16:
16860 Choose startup files and linker script suitable for the simulator.
16863 @node Xtensa Options
16864 @subsection Xtensa Options
16865 @cindex Xtensa Options
16867 These options are supported for Xtensa targets:
16871 @itemx -mno-const16
16873 @opindex mno-const16
16874 Enable or disable use of @code{CONST16} instructions for loading
16875 constant values. The @code{CONST16} instruction is currently not a
16876 standard option from Tensilica. When enabled, @code{CONST16}
16877 instructions are always used in place of the standard @code{L32R}
16878 instructions. The use of @code{CONST16} is enabled by default only if
16879 the @code{L32R} instruction is not available.
16882 @itemx -mno-fused-madd
16883 @opindex mfused-madd
16884 @opindex mno-fused-madd
16885 Enable or disable use of fused multiply/add and multiply/subtract
16886 instructions in the floating-point option. This has no effect if the
16887 floating-point option is not also enabled. Disabling fused multiply/add
16888 and multiply/subtract instructions forces the compiler to use separate
16889 instructions for the multiply and add/subtract operations. This may be
16890 desirable in some cases where strict IEEE 754-compliant results are
16891 required: the fused multiply add/subtract instructions do not round the
16892 intermediate result, thereby producing results with @emph{more} bits of
16893 precision than specified by the IEEE standard. Disabling fused multiply
16894 add/subtract instructions also ensures that the program output is not
16895 sensitive to the compiler's ability to combine multiply and add/subtract
16898 @item -mserialize-volatile
16899 @itemx -mno-serialize-volatile
16900 @opindex mserialize-volatile
16901 @opindex mno-serialize-volatile
16902 When this option is enabled, GCC inserts @code{MEMW} instructions before
16903 @code{volatile} memory references to guarantee sequential consistency.
16904 The default is @option{-mserialize-volatile}. Use
16905 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
16907 @item -mtext-section-literals
16908 @itemx -mno-text-section-literals
16909 @opindex mtext-section-literals
16910 @opindex mno-text-section-literals
16911 Control the treatment of literal pools. The default is
16912 @option{-mno-text-section-literals}, which places literals in a separate
16913 section in the output file. This allows the literal pool to be placed
16914 in a data RAM/ROM, and it also allows the linker to combine literal
16915 pools from separate object files to remove redundant literals and
16916 improve code size. With @option{-mtext-section-literals}, the literals
16917 are interspersed in the text section in order to keep them as close as
16918 possible to their references. This may be necessary for large assembly
16921 @item -mtarget-align
16922 @itemx -mno-target-align
16923 @opindex mtarget-align
16924 @opindex mno-target-align
16925 When this option is enabled, GCC instructs the assembler to
16926 automatically align instructions to reduce branch penalties at the
16927 expense of some code density. The assembler attempts to widen density
16928 instructions to align branch targets and the instructions following call
16929 instructions. If there are not enough preceding safe density
16930 instructions to align a target, no widening will be performed. The
16931 default is @option{-mtarget-align}. These options do not affect the
16932 treatment of auto-aligned instructions like @code{LOOP}, which the
16933 assembler will always align, either by widening density instructions or
16934 by inserting no-op instructions.
16937 @itemx -mno-longcalls
16938 @opindex mlongcalls
16939 @opindex mno-longcalls
16940 When this option is enabled, GCC instructs the assembler to translate
16941 direct calls to indirect calls unless it can determine that the target
16942 of a direct call is in the range allowed by the call instruction. This
16943 translation typically occurs for calls to functions in other source
16944 files. Specifically, the assembler translates a direct @code{CALL}
16945 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
16946 The default is @option{-mno-longcalls}. This option should be used in
16947 programs where the call target can potentially be out of range. This
16948 option is implemented in the assembler, not the compiler, so the
16949 assembly code generated by GCC will still show direct call
16950 instructions---look at the disassembled object code to see the actual
16951 instructions. Note that the assembler will use an indirect call for
16952 every cross-file call, not just those that really will be out of range.
16955 @node zSeries Options
16956 @subsection zSeries Options
16957 @cindex zSeries options
16959 These are listed under @xref{S/390 and zSeries Options}.
16961 @node Code Gen Options
16962 @section Options for Code Generation Conventions
16963 @cindex code generation conventions
16964 @cindex options, code generation
16965 @cindex run-time options
16967 These machine-independent options control the interface conventions
16968 used in code generation.
16970 Most of them have both positive and negative forms; the negative form
16971 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
16972 one of the forms is listed---the one which is not the default. You
16973 can figure out the other form by either removing @samp{no-} or adding
16977 @item -fbounds-check
16978 @opindex fbounds-check
16979 For front-ends that support it, generate additional code to check that
16980 indices used to access arrays are within the declared range. This is
16981 currently only supported by the Java and Fortran front-ends, where
16982 this option defaults to true and false respectively.
16986 This option generates traps for signed overflow on addition, subtraction,
16987 multiplication operations.
16991 This option instructs the compiler to assume that signed arithmetic
16992 overflow of addition, subtraction and multiplication wraps around
16993 using twos-complement representation. This flag enables some optimizations
16994 and disables others. This option is enabled by default for the Java
16995 front-end, as required by the Java language specification.
16998 @opindex fexceptions
16999 Enable exception handling. Generates extra code needed to propagate
17000 exceptions. For some targets, this implies GCC will generate frame
17001 unwind information for all functions, which can produce significant data
17002 size overhead, although it does not affect execution. If you do not
17003 specify this option, GCC will enable it by default for languages like
17004 C++ which normally require exception handling, and disable it for
17005 languages like C that do not normally require it. However, you may need
17006 to enable this option when compiling C code that needs to interoperate
17007 properly with exception handlers written in C++. You may also wish to
17008 disable this option if you are compiling older C++ programs that don't
17009 use exception handling.
17011 @item -fnon-call-exceptions
17012 @opindex fnon-call-exceptions
17013 Generate code that allows trapping instructions to throw exceptions.
17014 Note that this requires platform-specific runtime support that does
17015 not exist everywhere. Moreover, it only allows @emph{trapping}
17016 instructions to throw exceptions, i.e.@: memory references or floating
17017 point instructions. It does not allow exceptions to be thrown from
17018 arbitrary signal handlers such as @code{SIGALRM}.
17020 @item -funwind-tables
17021 @opindex funwind-tables
17022 Similar to @option{-fexceptions}, except that it will just generate any needed
17023 static data, but will not affect the generated code in any other way.
17024 You will normally not enable this option; instead, a language processor
17025 that needs this handling would enable it on your behalf.
17027 @item -fasynchronous-unwind-tables
17028 @opindex fasynchronous-unwind-tables
17029 Generate unwind table in dwarf2 format, if supported by target machine. The
17030 table is exact at each instruction boundary, so it can be used for stack
17031 unwinding from asynchronous events (such as debugger or garbage collector).
17033 @item -fpcc-struct-return
17034 @opindex fpcc-struct-return
17035 Return ``short'' @code{struct} and @code{union} values in memory like
17036 longer ones, rather than in registers. This convention is less
17037 efficient, but it has the advantage of allowing intercallability between
17038 GCC-compiled files and files compiled with other compilers, particularly
17039 the Portable C Compiler (pcc).
17041 The precise convention for returning structures in memory depends
17042 on the target configuration macros.
17044 Short structures and unions are those whose size and alignment match
17045 that of some integer type.
17047 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
17048 switch is not binary compatible with code compiled with the
17049 @option{-freg-struct-return} switch.
17050 Use it to conform to a non-default application binary interface.
17052 @item -freg-struct-return
17053 @opindex freg-struct-return
17054 Return @code{struct} and @code{union} values in registers when possible.
17055 This is more efficient for small structures than
17056 @option{-fpcc-struct-return}.
17058 If you specify neither @option{-fpcc-struct-return} nor
17059 @option{-freg-struct-return}, GCC defaults to whichever convention is
17060 standard for the target. If there is no standard convention, GCC
17061 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
17062 the principal compiler. In those cases, we can choose the standard, and
17063 we chose the more efficient register return alternative.
17065 @strong{Warning:} code compiled with the @option{-freg-struct-return}
17066 switch is not binary compatible with code compiled with the
17067 @option{-fpcc-struct-return} switch.
17068 Use it to conform to a non-default application binary interface.
17070 @item -fshort-enums
17071 @opindex fshort-enums
17072 Allocate to an @code{enum} type only as many bytes as it needs for the
17073 declared range of possible values. Specifically, the @code{enum} type
17074 will be equivalent to the smallest integer type which has enough room.
17076 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
17077 code that is not binary compatible with code generated without that switch.
17078 Use it to conform to a non-default application binary interface.
17080 @item -fshort-double
17081 @opindex fshort-double
17082 Use the same size for @code{double} as for @code{float}.
17084 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
17085 code that is not binary compatible with code generated without that switch.
17086 Use it to conform to a non-default application binary interface.
17088 @item -fshort-wchar
17089 @opindex fshort-wchar
17090 Override the underlying type for @samp{wchar_t} to be @samp{short
17091 unsigned int} instead of the default for the target. This option is
17092 useful for building programs to run under WINE@.
17094 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
17095 code that is not binary compatible with code generated without that switch.
17096 Use it to conform to a non-default application binary interface.
17099 @opindex fno-common
17100 In C code, controls the placement of uninitialized global variables.
17101 Unix C compilers have traditionally permitted multiple definitions of
17102 such variables in different compilation units by placing the variables
17104 This is the behavior specified by @option{-fcommon}, and is the default
17105 for GCC on most targets.
17106 On the other hand, this behavior is not required by ISO C, and on some
17107 targets may carry a speed or code size penalty on variable references.
17108 The @option{-fno-common} option specifies that the compiler should place
17109 uninitialized global variables in the data section of the object file,
17110 rather than generating them as common blocks.
17111 This has the effect that if the same variable is declared
17112 (without @code{extern}) in two different compilations,
17113 you will get a multiple-definition error when you link them.
17114 In this case, you must compile with @option{-fcommon} instead.
17115 Compiling with @option{-fno-common} is useful on targets for which
17116 it provides better performance, or if you wish to verify that the
17117 program will work on other systems which always treat uninitialized
17118 variable declarations this way.
17122 Ignore the @samp{#ident} directive.
17124 @item -finhibit-size-directive
17125 @opindex finhibit-size-directive
17126 Don't output a @code{.size} assembler directive, or anything else that
17127 would cause trouble if the function is split in the middle, and the
17128 two halves are placed at locations far apart in memory. This option is
17129 used when compiling @file{crtstuff.c}; you should not need to use it
17132 @item -fverbose-asm
17133 @opindex fverbose-asm
17134 Put extra commentary information in the generated assembly code to
17135 make it more readable. This option is generally only of use to those
17136 who actually need to read the generated assembly code (perhaps while
17137 debugging the compiler itself).
17139 @option{-fno-verbose-asm}, the default, causes the
17140 extra information to be omitted and is useful when comparing two assembler
17143 @item -frecord-gcc-switches
17144 @opindex frecord-gcc-switches
17145 This switch causes the command line that was used to invoke the
17146 compiler to be recorded into the object file that is being created.
17147 This switch is only implemented on some targets and the exact format
17148 of the recording is target and binary file format dependent, but it
17149 usually takes the form of a section containing ASCII text. This
17150 switch is related to the @option{-fverbose-asm} switch, but that
17151 switch only records information in the assembler output file as
17152 comments, so it never reaches the object file.
17156 @cindex global offset table
17158 Generate position-independent code (PIC) suitable for use in a shared
17159 library, if supported for the target machine. Such code accesses all
17160 constant addresses through a global offset table (GOT)@. The dynamic
17161 loader resolves the GOT entries when the program starts (the dynamic
17162 loader is not part of GCC; it is part of the operating system). If
17163 the GOT size for the linked executable exceeds a machine-specific
17164 maximum size, you get an error message from the linker indicating that
17165 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
17166 instead. (These maximums are 8k on the SPARC and 32k
17167 on the m68k and RS/6000. The 386 has no such limit.)
17169 Position-independent code requires special support, and therefore works
17170 only on certain machines. For the 386, GCC supports PIC for System V
17171 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
17172 position-independent.
17174 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
17179 If supported for the target machine, emit position-independent code,
17180 suitable for dynamic linking and avoiding any limit on the size of the
17181 global offset table. This option makes a difference on the m68k,
17182 PowerPC and SPARC@.
17184 Position-independent code requires special support, and therefore works
17185 only on certain machines.
17187 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
17194 These options are similar to @option{-fpic} and @option{-fPIC}, but
17195 generated position independent code can be only linked into executables.
17196 Usually these options are used when @option{-pie} GCC option will be
17197 used during linking.
17199 @option{-fpie} and @option{-fPIE} both define the macros
17200 @code{__pie__} and @code{__PIE__}. The macros have the value 1
17201 for @option{-fpie} and 2 for @option{-fPIE}.
17203 @item -fno-jump-tables
17204 @opindex fno-jump-tables
17205 Do not use jump tables for switch statements even where it would be
17206 more efficient than other code generation strategies. This option is
17207 of use in conjunction with @option{-fpic} or @option{-fPIC} for
17208 building code which forms part of a dynamic linker and cannot
17209 reference the address of a jump table. On some targets, jump tables
17210 do not require a GOT and this option is not needed.
17212 @item -ffixed-@var{reg}
17214 Treat the register named @var{reg} as a fixed register; generated code
17215 should never refer to it (except perhaps as a stack pointer, frame
17216 pointer or in some other fixed role).
17218 @var{reg} must be the name of a register. The register names accepted
17219 are machine-specific and are defined in the @code{REGISTER_NAMES}
17220 macro in the machine description macro file.
17222 This flag does not have a negative form, because it specifies a
17225 @item -fcall-used-@var{reg}
17226 @opindex fcall-used
17227 Treat the register named @var{reg} as an allocable register that is
17228 clobbered by function calls. It may be allocated for temporaries or
17229 variables that do not live across a call. Functions compiled this way
17230 will not save and restore the register @var{reg}.
17232 It is an error to used this flag with the frame pointer or stack pointer.
17233 Use of this flag for other registers that have fixed pervasive roles in
17234 the machine's execution model will produce disastrous results.
17236 This flag does not have a negative form, because it specifies a
17239 @item -fcall-saved-@var{reg}
17240 @opindex fcall-saved
17241 Treat the register named @var{reg} as an allocable register saved by
17242 functions. It may be allocated even for temporaries or variables that
17243 live across a call. Functions compiled this way will save and restore
17244 the register @var{reg} if they use it.
17246 It is an error to used this flag with the frame pointer or stack pointer.
17247 Use of this flag for other registers that have fixed pervasive roles in
17248 the machine's execution model will produce disastrous results.
17250 A different sort of disaster will result from the use of this flag for
17251 a register in which function values may be returned.
17253 This flag does not have a negative form, because it specifies a
17256 @item -fpack-struct[=@var{n}]
17257 @opindex fpack-struct
17258 Without a value specified, pack all structure members together without
17259 holes. When a value is specified (which must be a small power of two), pack
17260 structure members according to this value, representing the maximum
17261 alignment (that is, objects with default alignment requirements larger than
17262 this will be output potentially unaligned at the next fitting location.
17264 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
17265 code that is not binary compatible with code generated without that switch.
17266 Additionally, it makes the code suboptimal.
17267 Use it to conform to a non-default application binary interface.
17269 @item -finstrument-functions
17270 @opindex finstrument-functions
17271 Generate instrumentation calls for entry and exit to functions. Just
17272 after function entry and just before function exit, the following
17273 profiling functions will be called with the address of the current
17274 function and its call site. (On some platforms,
17275 @code{__builtin_return_address} does not work beyond the current
17276 function, so the call site information may not be available to the
17277 profiling functions otherwise.)
17280 void __cyg_profile_func_enter (void *this_fn,
17282 void __cyg_profile_func_exit (void *this_fn,
17286 The first argument is the address of the start of the current function,
17287 which may be looked up exactly in the symbol table.
17289 This instrumentation is also done for functions expanded inline in other
17290 functions. The profiling calls will indicate where, conceptually, the
17291 inline function is entered and exited. This means that addressable
17292 versions of such functions must be available. If all your uses of a
17293 function are expanded inline, this may mean an additional expansion of
17294 code size. If you use @samp{extern inline} in your C code, an
17295 addressable version of such functions must be provided. (This is
17296 normally the case anyways, but if you get lucky and the optimizer always
17297 expands the functions inline, you might have gotten away without
17298 providing static copies.)
17300 A function may be given the attribute @code{no_instrument_function}, in
17301 which case this instrumentation will not be done. This can be used, for
17302 example, for the profiling functions listed above, high-priority
17303 interrupt routines, and any functions from which the profiling functions
17304 cannot safely be called (perhaps signal handlers, if the profiling
17305 routines generate output or allocate memory).
17307 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
17308 @opindex finstrument-functions-exclude-file-list
17310 Set the list of functions that are excluded from instrumentation (see
17311 the description of @code{-finstrument-functions}). If the file that
17312 contains a function definition matches with one of @var{file}, then
17313 that function is not instrumented. The match is done on substrings:
17314 if the @var{file} parameter is a substring of the file name, it is
17315 considered to be a match.
17318 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
17319 will exclude any inline function defined in files whose pathnames
17320 contain @code{/bits/stl} or @code{include/sys}.
17322 If, for some reason, you want to include letter @code{','} in one of
17323 @var{sym}, write @code{'\,'}. For example,
17324 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
17325 (note the single quote surrounding the option).
17327 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
17328 @opindex finstrument-functions-exclude-function-list
17330 This is similar to @code{-finstrument-functions-exclude-file-list},
17331 but this option sets the list of function names to be excluded from
17332 instrumentation. The function name to be matched is its user-visible
17333 name, such as @code{vector<int> blah(const vector<int> &)}, not the
17334 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
17335 match is done on substrings: if the @var{sym} parameter is a substring
17336 of the function name, it is considered to be a match. For C99 and C++
17337 extended identifiers, the function name must be given in UTF-8, not
17338 using universal character names.
17340 @item -fstack-check
17341 @opindex fstack-check
17342 Generate code to verify that you do not go beyond the boundary of the
17343 stack. You should specify this flag if you are running in an
17344 environment with multiple threads, but only rarely need to specify it in
17345 a single-threaded environment since stack overflow is automatically
17346 detected on nearly all systems if there is only one stack.
17348 Note that this switch does not actually cause checking to be done; the
17349 operating system or the language runtime must do that. The switch causes
17350 generation of code to ensure that they see the stack being extended.
17352 You can additionally specify a string parameter: @code{no} means no
17353 checking, @code{generic} means force the use of old-style checking,
17354 @code{specific} means use the best checking method and is equivalent
17355 to bare @option{-fstack-check}.
17357 Old-style checking is a generic mechanism that requires no specific
17358 target support in the compiler but comes with the following drawbacks:
17362 Modified allocation strategy for large objects: they will always be
17363 allocated dynamically if their size exceeds a fixed threshold.
17366 Fixed limit on the size of the static frame of functions: when it is
17367 topped by a particular function, stack checking is not reliable and
17368 a warning is issued by the compiler.
17371 Inefficiency: because of both the modified allocation strategy and the
17372 generic implementation, the performances of the code are hampered.
17375 Note that old-style stack checking is also the fallback method for
17376 @code{specific} if no target support has been added in the compiler.
17378 @item -fstack-limit-register=@var{reg}
17379 @itemx -fstack-limit-symbol=@var{sym}
17380 @itemx -fno-stack-limit
17381 @opindex fstack-limit-register
17382 @opindex fstack-limit-symbol
17383 @opindex fno-stack-limit
17384 Generate code to ensure that the stack does not grow beyond a certain value,
17385 either the value of a register or the address of a symbol. If the stack
17386 would grow beyond the value, a signal is raised. For most targets,
17387 the signal is raised before the stack overruns the boundary, so
17388 it is possible to catch the signal without taking special precautions.
17390 For instance, if the stack starts at absolute address @samp{0x80000000}
17391 and grows downwards, you can use the flags
17392 @option{-fstack-limit-symbol=__stack_limit} and
17393 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
17394 of 128KB@. Note that this may only work with the GNU linker.
17396 @cindex aliasing of parameters
17397 @cindex parameters, aliased
17398 @item -fargument-alias
17399 @itemx -fargument-noalias
17400 @itemx -fargument-noalias-global
17401 @itemx -fargument-noalias-anything
17402 @opindex fargument-alias
17403 @opindex fargument-noalias
17404 @opindex fargument-noalias-global
17405 @opindex fargument-noalias-anything
17406 Specify the possible relationships among parameters and between
17407 parameters and global data.
17409 @option{-fargument-alias} specifies that arguments (parameters) may
17410 alias each other and may alias global storage.@*
17411 @option{-fargument-noalias} specifies that arguments do not alias
17412 each other, but may alias global storage.@*
17413 @option{-fargument-noalias-global} specifies that arguments do not
17414 alias each other and do not alias global storage.
17415 @option{-fargument-noalias-anything} specifies that arguments do not
17416 alias any other storage.
17418 Each language will automatically use whatever option is required by
17419 the language standard. You should not need to use these options yourself.
17421 @item -fleading-underscore
17422 @opindex fleading-underscore
17423 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
17424 change the way C symbols are represented in the object file. One use
17425 is to help link with legacy assembly code.
17427 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
17428 generate code that is not binary compatible with code generated without that
17429 switch. Use it to conform to a non-default application binary interface.
17430 Not all targets provide complete support for this switch.
17432 @item -ftls-model=@var{model}
17433 @opindex ftls-model
17434 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
17435 The @var{model} argument should be one of @code{global-dynamic},
17436 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
17438 The default without @option{-fpic} is @code{initial-exec}; with
17439 @option{-fpic} the default is @code{global-dynamic}.
17441 @item -fvisibility=@var{default|internal|hidden|protected}
17442 @opindex fvisibility
17443 Set the default ELF image symbol visibility to the specified option---all
17444 symbols will be marked with this unless overridden within the code.
17445 Using this feature can very substantially improve linking and
17446 load times of shared object libraries, produce more optimized
17447 code, provide near-perfect API export and prevent symbol clashes.
17448 It is @strong{strongly} recommended that you use this in any shared objects
17451 Despite the nomenclature, @code{default} always means public ie;
17452 available to be linked against from outside the shared object.
17453 @code{protected} and @code{internal} are pretty useless in real-world
17454 usage so the only other commonly used option will be @code{hidden}.
17455 The default if @option{-fvisibility} isn't specified is
17456 @code{default}, i.e., make every
17457 symbol public---this causes the same behavior as previous versions of
17460 A good explanation of the benefits offered by ensuring ELF
17461 symbols have the correct visibility is given by ``How To Write
17462 Shared Libraries'' by Ulrich Drepper (which can be found at
17463 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
17464 solution made possible by this option to marking things hidden when
17465 the default is public is to make the default hidden and mark things
17466 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
17467 and @code{__attribute__ ((visibility("default")))} instead of
17468 @code{__declspec(dllexport)} you get almost identical semantics with
17469 identical syntax. This is a great boon to those working with
17470 cross-platform projects.
17472 For those adding visibility support to existing code, you may find
17473 @samp{#pragma GCC visibility} of use. This works by you enclosing
17474 the declarations you wish to set visibility for with (for example)
17475 @samp{#pragma GCC visibility push(hidden)} and
17476 @samp{#pragma GCC visibility pop}.
17477 Bear in mind that symbol visibility should be viewed @strong{as
17478 part of the API interface contract} and thus all new code should
17479 always specify visibility when it is not the default ie; declarations
17480 only for use within the local DSO should @strong{always} be marked explicitly
17481 as hidden as so to avoid PLT indirection overheads---making this
17482 abundantly clear also aids readability and self-documentation of the code.
17483 Note that due to ISO C++ specification requirements, operator new and
17484 operator delete must always be of default visibility.
17486 Be aware that headers from outside your project, in particular system
17487 headers and headers from any other library you use, may not be
17488 expecting to be compiled with visibility other than the default. You
17489 may need to explicitly say @samp{#pragma GCC visibility push(default)}
17490 before including any such headers.
17492 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
17493 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
17494 no modifications. However, this means that calls to @samp{extern}
17495 functions with no explicit visibility will use the PLT, so it is more
17496 effective to use @samp{__attribute ((visibility))} and/or
17497 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
17498 declarations should be treated as hidden.
17500 Note that @samp{-fvisibility} does affect C++ vague linkage
17501 entities. This means that, for instance, an exception class that will
17502 be thrown between DSOs must be explicitly marked with default
17503 visibility so that the @samp{type_info} nodes will be unified between
17506 An overview of these techniques, their benefits and how to use them
17507 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
17513 @node Environment Variables
17514 @section Environment Variables Affecting GCC
17515 @cindex environment variables
17517 @c man begin ENVIRONMENT
17518 This section describes several environment variables that affect how GCC
17519 operates. Some of them work by specifying directories or prefixes to use
17520 when searching for various kinds of files. Some are used to specify other
17521 aspects of the compilation environment.
17523 Note that you can also specify places to search using options such as
17524 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
17525 take precedence over places specified using environment variables, which
17526 in turn take precedence over those specified by the configuration of GCC@.
17527 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
17528 GNU Compiler Collection (GCC) Internals}.
17533 @c @itemx LC_COLLATE
17535 @c @itemx LC_MONETARY
17536 @c @itemx LC_NUMERIC
17541 @c @findex LC_COLLATE
17542 @findex LC_MESSAGES
17543 @c @findex LC_MONETARY
17544 @c @findex LC_NUMERIC
17548 These environment variables control the way that GCC uses
17549 localization information that allow GCC to work with different
17550 national conventions. GCC inspects the locale categories
17551 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
17552 so. These locale categories can be set to any value supported by your
17553 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
17554 Kingdom encoded in UTF-8.
17556 The @env{LC_CTYPE} environment variable specifies character
17557 classification. GCC uses it to determine the character boundaries in
17558 a string; this is needed for some multibyte encodings that contain quote
17559 and escape characters that would otherwise be interpreted as a string
17562 The @env{LC_MESSAGES} environment variable specifies the language to
17563 use in diagnostic messages.
17565 If the @env{LC_ALL} environment variable is set, it overrides the value
17566 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
17567 and @env{LC_MESSAGES} default to the value of the @env{LANG}
17568 environment variable. If none of these variables are set, GCC
17569 defaults to traditional C English behavior.
17573 If @env{TMPDIR} is set, it specifies the directory to use for temporary
17574 files. GCC uses temporary files to hold the output of one stage of
17575 compilation which is to be used as input to the next stage: for example,
17576 the output of the preprocessor, which is the input to the compiler
17579 @item GCC_EXEC_PREFIX
17580 @findex GCC_EXEC_PREFIX
17581 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
17582 names of the subprograms executed by the compiler. No slash is added
17583 when this prefix is combined with the name of a subprogram, but you can
17584 specify a prefix that ends with a slash if you wish.
17586 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
17587 an appropriate prefix to use based on the pathname it was invoked with.
17589 If GCC cannot find the subprogram using the specified prefix, it
17590 tries looking in the usual places for the subprogram.
17592 The default value of @env{GCC_EXEC_PREFIX} is
17593 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
17594 the installed compiler. In many cases @var{prefix} is the value
17595 of @code{prefix} when you ran the @file{configure} script.
17597 Other prefixes specified with @option{-B} take precedence over this prefix.
17599 This prefix is also used for finding files such as @file{crt0.o} that are
17602 In addition, the prefix is used in an unusual way in finding the
17603 directories to search for header files. For each of the standard
17604 directories whose name normally begins with @samp{/usr/local/lib/gcc}
17605 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
17606 replacing that beginning with the specified prefix to produce an
17607 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
17608 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
17609 These alternate directories are searched first; the standard directories
17610 come next. If a standard directory begins with the configured
17611 @var{prefix} then the value of @var{prefix} is replaced by
17612 @env{GCC_EXEC_PREFIX} when looking for header files.
17614 @item COMPILER_PATH
17615 @findex COMPILER_PATH
17616 The value of @env{COMPILER_PATH} is a colon-separated list of
17617 directories, much like @env{PATH}. GCC tries the directories thus
17618 specified when searching for subprograms, if it can't find the
17619 subprograms using @env{GCC_EXEC_PREFIX}.
17622 @findex LIBRARY_PATH
17623 The value of @env{LIBRARY_PATH} is a colon-separated list of
17624 directories, much like @env{PATH}. When configured as a native compiler,
17625 GCC tries the directories thus specified when searching for special
17626 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
17627 using GCC also uses these directories when searching for ordinary
17628 libraries for the @option{-l} option (but directories specified with
17629 @option{-L} come first).
17633 @cindex locale definition
17634 This variable is used to pass locale information to the compiler. One way in
17635 which this information is used is to determine the character set to be used
17636 when character literals, string literals and comments are parsed in C and C++.
17637 When the compiler is configured to allow multibyte characters,
17638 the following values for @env{LANG} are recognized:
17642 Recognize JIS characters.
17644 Recognize SJIS characters.
17646 Recognize EUCJP characters.
17649 If @env{LANG} is not defined, or if it has some other value, then the
17650 compiler will use mblen and mbtowc as defined by the default locale to
17651 recognize and translate multibyte characters.
17655 Some additional environments variables affect the behavior of the
17658 @include cppenv.texi
17662 @node Precompiled Headers
17663 @section Using Precompiled Headers
17664 @cindex precompiled headers
17665 @cindex speed of compilation
17667 Often large projects have many header files that are included in every
17668 source file. The time the compiler takes to process these header files
17669 over and over again can account for nearly all of the time required to
17670 build the project. To make builds faster, GCC allows users to
17671 `precompile' a header file; then, if builds can use the precompiled
17672 header file they will be much faster.
17674 To create a precompiled header file, simply compile it as you would any
17675 other file, if necessary using the @option{-x} option to make the driver
17676 treat it as a C or C++ header file. You will probably want to use a
17677 tool like @command{make} to keep the precompiled header up-to-date when
17678 the headers it contains change.
17680 A precompiled header file will be searched for when @code{#include} is
17681 seen in the compilation. As it searches for the included file
17682 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
17683 compiler looks for a precompiled header in each directory just before it
17684 looks for the include file in that directory. The name searched for is
17685 the name specified in the @code{#include} with @samp{.gch} appended. If
17686 the precompiled header file can't be used, it is ignored.
17688 For instance, if you have @code{#include "all.h"}, and you have
17689 @file{all.h.gch} in the same directory as @file{all.h}, then the
17690 precompiled header file will be used if possible, and the original
17691 header will be used otherwise.
17693 Alternatively, you might decide to put the precompiled header file in a
17694 directory and use @option{-I} to ensure that directory is searched
17695 before (or instead of) the directory containing the original header.
17696 Then, if you want to check that the precompiled header file is always
17697 used, you can put a file of the same name as the original header in this
17698 directory containing an @code{#error} command.
17700 This also works with @option{-include}. So yet another way to use
17701 precompiled headers, good for projects not designed with precompiled
17702 header files in mind, is to simply take most of the header files used by
17703 a project, include them from another header file, precompile that header
17704 file, and @option{-include} the precompiled header. If the header files
17705 have guards against multiple inclusion, they will be skipped because
17706 they've already been included (in the precompiled header).
17708 If you need to precompile the same header file for different
17709 languages, targets, or compiler options, you can instead make a
17710 @emph{directory} named like @file{all.h.gch}, and put each precompiled
17711 header in the directory, perhaps using @option{-o}. It doesn't matter
17712 what you call the files in the directory, every precompiled header in
17713 the directory will be considered. The first precompiled header
17714 encountered in the directory that is valid for this compilation will
17715 be used; they're searched in no particular order.
17717 There are many other possibilities, limited only by your imagination,
17718 good sense, and the constraints of your build system.
17720 A precompiled header file can be used only when these conditions apply:
17724 Only one precompiled header can be used in a particular compilation.
17727 A precompiled header can't be used once the first C token is seen. You
17728 can have preprocessor directives before a precompiled header; you can
17729 even include a precompiled header from inside another header, so long as
17730 there are no C tokens before the @code{#include}.
17733 The precompiled header file must be produced for the same language as
17734 the current compilation. You can't use a C precompiled header for a C++
17738 The precompiled header file must have been produced by the same compiler
17739 binary as the current compilation is using.
17742 Any macros defined before the precompiled header is included must
17743 either be defined in the same way as when the precompiled header was
17744 generated, or must not affect the precompiled header, which usually
17745 means that they don't appear in the precompiled header at all.
17747 The @option{-D} option is one way to define a macro before a
17748 precompiled header is included; using a @code{#define} can also do it.
17749 There are also some options that define macros implicitly, like
17750 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
17753 @item If debugging information is output when using the precompiled
17754 header, using @option{-g} or similar, the same kind of debugging information
17755 must have been output when building the precompiled header. However,
17756 a precompiled header built using @option{-g} can be used in a compilation
17757 when no debugging information is being output.
17759 @item The same @option{-m} options must generally be used when building
17760 and using the precompiled header. @xref{Submodel Options},
17761 for any cases where this rule is relaxed.
17763 @item Each of the following options must be the same when building and using
17764 the precompiled header:
17766 @gccoptlist{-fexceptions}
17769 Some other command-line options starting with @option{-f},
17770 @option{-p}, or @option{-O} must be defined in the same way as when
17771 the precompiled header was generated. At present, it's not clear
17772 which options are safe to change and which are not; the safest choice
17773 is to use exactly the same options when generating and using the
17774 precompiled header. The following are known to be safe:
17776 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
17777 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
17778 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
17783 For all of these except the last, the compiler will automatically
17784 ignore the precompiled header if the conditions aren't met. If you
17785 find an option combination that doesn't work and doesn't cause the
17786 precompiled header to be ignored, please consider filing a bug report,
17789 If you do use differing options when generating and using the
17790 precompiled header, the actual behavior will be a mixture of the
17791 behavior for the options. For instance, if you use @option{-g} to
17792 generate the precompiled header but not when using it, you may or may
17793 not get debugging information for routines in the precompiled header.