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
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
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.
151 * Running Protoize:: Automatically adding or removing function prototypes.
157 @section Option Summary
159 Here is a summary of all the options, grouped by type. Explanations are
160 in the following sections.
163 @item Overall Options
164 @xref{Overall Options,,Options Controlling the Kind of Output}.
165 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{]} --target-help @gol
167 --version -wrapper@@@var{file}}
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 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
194 -fno-default-inline -fvisibility-inlines-hidden @gol
195 -fvisibility-ms-compat @gol
196 -Wabi -Wctor-dtor-privacy @gol
197 -Wnon-virtual-dtor -Wreorder @gol
198 -Weffc++ -Wstrict-null-sentinel @gol
199 -Wno-non-template-friend -Wold-style-cast @gol
200 -Woverloaded-virtual -Wno-pmf-conversions @gol
203 @item Objective-C and Objective-C++ Language Options
204 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
205 Objective-C and Objective-C++ Dialects}.
206 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
207 -fgnu-runtime -fnext-runtime @gol
208 -fno-nil-receivers @gol
209 -fobjc-call-cxx-cdtors @gol
210 -fobjc-direct-dispatch @gol
211 -fobjc-exceptions @gol
213 -freplace-objc-classes @gol
216 -Wassign-intercept @gol
217 -Wno-protocol -Wselector @gol
218 -Wstrict-selector-match @gol
219 -Wundeclared-selector}
221 @item Language Independent Options
222 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
223 @gccoptlist{-fmessage-length=@var{n} @gol
224 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
225 -fdiagnostics-show-option}
227 @item Warning Options
228 @xref{Warning Options,,Options to Request or Suppress Warnings}.
229 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
230 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
231 -Wno-attributes -Wno-builtin-macro-redefined @gol
232 -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
233 -Wchar-subscripts -Wclobbered -Wcomment @gol
234 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
235 -Wno-deprecated-declarations -Wdisabled-optimization @gol
236 -Wdisallowed-function-list=@var{sym},@var{sym},@dots{} @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} -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 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
264 -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 @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-phiopt@r{[}-@var{n}@r{]} @gol
295 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-nrv -fdump-tree-vect @gol
298 -fdump-tree-sink @gol
299 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
300 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
301 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
302 -ftree-vectorizer-verbose=@var{n} @gol
303 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
304 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
305 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
306 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
307 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
308 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
309 -ftest-coverage -ftime-report -fvar-tracking @gol
310 -g -g@var{level} -gcoff -gdwarf-2 @gol
311 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
312 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
313 -fdebug-prefix-map=@var{old}=@var{new} @gol
314 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
315 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
316 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
317 -print-multi-directory -print-multi-lib @gol
318 -print-prog-name=@var{program} -print-search-dirs -Q @gol
319 -print-sysroot -print-sysroot-headers-suffix @gol
322 @item Optimization Options
323 @xref{Optimize Options,,Options that Control Optimization}.
325 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
326 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
327 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
328 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
329 -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping @gol
330 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
331 -fdata-sections -fdce -fdce @gol
332 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
333 -fearly-inlining -fexpensive-optimizations -ffast-math @gol
334 -ffinite-math-only -ffloat-store -fforward-propagate @gol
335 -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
336 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
337 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
338 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta @gol
339 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
340 -fipa-type-escape -fira -fira-algorithm=@var{algorithm} @gol
341 -fira-region=@var{region} -fira-coalesce -fno-ira-share-save-slots @gol
342 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
343 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
344 -floop-block -floop-interchange -floop-strip-mine @gol
345 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
346 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
347 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
348 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
349 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
350 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
351 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
352 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
353 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
354 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
355 -fprofile-generate=@var{path} @gol
356 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
357 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
358 -freorder-blocks-and-partition -freorder-functions @gol
359 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
360 -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks @gol
361 -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
362 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
363 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
364 -fselective-scheduling -fselective-scheduling2 @gol
365 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
366 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
367 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
368 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
369 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
370 -ftree-copyrename -ftree-dce @gol
371 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
372 -ftree-loop-distribution @gol
373 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
374 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-reassoc @gol
375 -ftree-sink -ftree-sra -ftree-switch-conversion @gol
376 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
377 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
378 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
379 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
381 --param @var{name}=@var{value}
382 -O -O0 -O1 -O2 -O3 -Os}
384 @item Preprocessor Options
385 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
386 @gccoptlist{-A@var{question}=@var{answer} @gol
387 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
388 -C -dD -dI -dM -dN @gol
389 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
390 -idirafter @var{dir} @gol
391 -include @var{file} -imacros @var{file} @gol
392 -iprefix @var{file} -iwithprefix @var{dir} @gol
393 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
394 -imultilib @var{dir} -isysroot @var{dir} @gol
395 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
396 -P -fworking-directory -remap @gol
397 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
398 -Xpreprocessor @var{option}}
400 @item Assembler Option
401 @xref{Assembler Options,,Passing Options to the Assembler}.
402 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
405 @xref{Link Options,,Options for Linking}.
406 @gccoptlist{@var{object-file-name} -l@var{library} @gol
407 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
408 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
409 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
412 @item Directory Options
413 @xref{Directory Options,,Options for Directory Search}.
414 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
415 -specs=@var{file} -I- --sysroot=@var{dir}}
418 @c I wrote this xref this way to avoid overfull hbox. -- rms
419 @xref{Target Options}.
420 @gccoptlist{-V @var{version} -b @var{machine}}
422 @item Machine Dependent Options
423 @xref{Submodel Options,,Hardware Models and Configurations}.
424 @c This list is ordered alphanumerically by subsection name.
425 @c Try and put the significant identifier (CPU or system) first,
426 @c so users have a clue at guessing where the ones they want will be.
429 @gccoptlist{-EB -EL @gol
430 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
431 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
434 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
435 -mabi=@var{name} @gol
436 -mapcs-stack-check -mno-apcs-stack-check @gol
437 -mapcs-float -mno-apcs-float @gol
438 -mapcs-reentrant -mno-apcs-reentrant @gol
439 -msched-prolog -mno-sched-prolog @gol
440 -mlittle-endian -mbig-endian -mwords-little-endian @gol
441 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
442 -mthumb-interwork -mno-thumb-interwork @gol
443 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
444 -mstructure-size-boundary=@var{n} @gol
445 -mabort-on-noreturn @gol
446 -mlong-calls -mno-long-calls @gol
447 -msingle-pic-base -mno-single-pic-base @gol
448 -mpic-register=@var{reg} @gol
449 -mnop-fun-dllimport @gol
450 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
451 -mpoke-function-name @gol
453 -mtpcs-frame -mtpcs-leaf-frame @gol
454 -mcaller-super-interworking -mcallee-super-interworking @gol
456 -mword-relocations @gol
457 -mfix-cortex-m3-ldrd}
460 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
461 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
463 @emph{Blackfin Options}
464 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
465 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
466 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
467 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
468 -mno-id-shared-library -mshared-library-id=@var{n} @gol
469 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
470 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
471 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
475 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
476 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
477 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
478 -mstack-align -mdata-align -mconst-align @gol
479 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
480 -melf -maout -melinux -mlinux -sim -sim2 @gol
481 -mmul-bug-workaround -mno-mul-bug-workaround}
484 @gccoptlist{-mmac -mpush-args}
486 @emph{Darwin Options}
487 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
488 -arch_only -bind_at_load -bundle -bundle_loader @gol
489 -client_name -compatibility_version -current_version @gol
491 -dependency-file -dylib_file -dylinker_install_name @gol
492 -dynamic -dynamiclib -exported_symbols_list @gol
493 -filelist -flat_namespace -force_cpusubtype_ALL @gol
494 -force_flat_namespace -headerpad_max_install_names @gol
496 -image_base -init -install_name -keep_private_externs @gol
497 -multi_module -multiply_defined -multiply_defined_unused @gol
498 -noall_load -no_dead_strip_inits_and_terms @gol
499 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
500 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
501 -private_bundle -read_only_relocs -sectalign @gol
502 -sectobjectsymbols -whyload -seg1addr @gol
503 -sectcreate -sectobjectsymbols -sectorder @gol
504 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
505 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
506 -segprot -segs_read_only_addr -segs_read_write_addr @gol
507 -single_module -static -sub_library -sub_umbrella @gol
508 -twolevel_namespace -umbrella -undefined @gol
509 -unexported_symbols_list -weak_reference_mismatches @gol
510 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
511 -mkernel -mone-byte-bool}
513 @emph{DEC Alpha Options}
514 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
515 -mieee -mieee-with-inexact -mieee-conformant @gol
516 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
517 -mtrap-precision=@var{mode} -mbuild-constants @gol
518 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
519 -mbwx -mmax -mfix -mcix @gol
520 -mfloat-vax -mfloat-ieee @gol
521 -mexplicit-relocs -msmall-data -mlarge-data @gol
522 -msmall-text -mlarge-text @gol
523 -mmemory-latency=@var{time}}
525 @emph{DEC Alpha/VMS Options}
526 @gccoptlist{-mvms-return-codes}
529 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
530 -mhard-float -msoft-float @gol
531 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
532 -mdouble -mno-double @gol
533 -mmedia -mno-media -mmuladd -mno-muladd @gol
534 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
535 -mlinked-fp -mlong-calls -malign-labels @gol
536 -mlibrary-pic -macc-4 -macc-8 @gol
537 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
538 -moptimize-membar -mno-optimize-membar @gol
539 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
540 -mvliw-branch -mno-vliw-branch @gol
541 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
542 -mno-nested-cond-exec -mtomcat-stats @gol
546 @emph{GNU/Linux Options}
547 @gccoptlist{-muclibc}
549 @emph{H8/300 Options}
550 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
553 @gccoptlist{-march=@var{architecture-type} @gol
554 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
555 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
556 -mfixed-range=@var{register-range} @gol
557 -mjump-in-delay -mlinker-opt -mlong-calls @gol
558 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
559 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
560 -mno-jump-in-delay -mno-long-load-store @gol
561 -mno-portable-runtime -mno-soft-float @gol
562 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
563 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
564 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
565 -munix=@var{unix-std} -nolibdld -static -threads}
567 @emph{i386 and x86-64 Options}
568 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
569 -mfpmath=@var{unit} @gol
570 -masm=@var{dialect} -mno-fancy-math-387 @gol
571 -mno-fp-ret-in-387 -msoft-float @gol
572 -mno-wide-multiply -mrtd -malign-double @gol
573 -mpreferred-stack-boundary=@var{num}
574 -mincoming-stack-boundary=@var{num}
575 -mcld -mcx16 -msahf -mrecip @gol
576 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
578 -msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
579 -mthreads -mno-align-stringops -minline-all-stringops @gol
580 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
581 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
582 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
583 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
584 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
585 -mcmodel=@var{code-model} @gol
586 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
587 -mfused-madd -mno-fused-madd -msse2avx}
590 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
591 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
592 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
593 -minline-float-divide-max-throughput @gol
594 -minline-int-divide-min-latency @gol
595 -minline-int-divide-max-throughput @gol
596 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
597 -mno-dwarf2-asm -mearly-stop-bits @gol
598 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
599 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
600 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
601 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
602 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
603 -mno-sched-prefer-non-data-spec-insns @gol
604 -mno-sched-prefer-non-control-spec-insns @gol
605 -mno-sched-count-spec-in-critical-path}
607 @emph{M32R/D Options}
608 @gccoptlist{-m32r2 -m32rx -m32r @gol
610 -malign-loops -mno-align-loops @gol
611 -missue-rate=@var{number} @gol
612 -mbranch-cost=@var{number} @gol
613 -mmodel=@var{code-size-model-type} @gol
614 -msdata=@var{sdata-type} @gol
615 -mno-flush-func -mflush-func=@var{name} @gol
616 -mno-flush-trap -mflush-trap=@var{number} @gol
620 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
622 @emph{M680x0 Options}
623 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
624 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
625 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
626 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
627 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
628 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
629 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
630 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
633 @emph{M68hc1x Options}
634 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
635 -mauto-incdec -minmax -mlong-calls -mshort @gol
636 -msoft-reg-count=@var{count}}
639 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
640 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
641 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
642 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
643 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
646 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
647 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
648 -mips64 -mips64r2 @gol
649 -mips16 -mno-mips16 -mflip-mips16 @gol
650 -minterlink-mips16 -mno-interlink-mips16 @gol
651 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
652 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
653 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
654 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
655 -mfpu=@var{fpu-type} @gol
656 -msmartmips -mno-smartmips @gol
657 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
658 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
659 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
660 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
661 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
662 -membedded-data -mno-embedded-data @gol
663 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
664 -mcode-readable=@var{setting} @gol
665 -msplit-addresses -mno-split-addresses @gol
666 -mexplicit-relocs -mno-explicit-relocs @gol
667 -mcheck-zero-division -mno-check-zero-division @gol
668 -mdivide-traps -mdivide-breaks @gol
669 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
670 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
671 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
672 -mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol
673 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
674 -mflush-func=@var{func} -mno-flush-func @gol
675 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
676 -mfp-exceptions -mno-fp-exceptions @gol
677 -mvr4130-align -mno-vr4130-align}
680 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
681 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
682 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
683 -mno-base-addresses -msingle-exit -mno-single-exit}
685 @emph{MN10300 Options}
686 @gccoptlist{-mmult-bug -mno-mult-bug @gol
687 -mam33 -mno-am33 @gol
688 -mam33-2 -mno-am33-2 @gol
689 -mreturn-pointer-on-d0 @gol
692 @emph{PDP-11 Options}
693 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
694 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
695 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
696 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
697 -mbranch-expensive -mbranch-cheap @gol
698 -msplit -mno-split -munix-asm -mdec-asm}
700 @emph{picoChip Options}
701 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N}
702 -msymbol-as-address -mno-inefficient-warnings}
704 @emph{PowerPC Options}
705 See RS/6000 and PowerPC Options.
707 @emph{RS/6000 and PowerPC Options}
708 @gccoptlist{-mcpu=@var{cpu-type} @gol
709 -mtune=@var{cpu-type} @gol
710 -mpower -mno-power -mpower2 -mno-power2 @gol
711 -mpowerpc -mpowerpc64 -mno-powerpc @gol
712 -maltivec -mno-altivec @gol
713 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
714 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
715 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
716 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
717 -mnew-mnemonics -mold-mnemonics @gol
718 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
719 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
720 -malign-power -malign-natural @gol
721 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
722 -msingle-float -mdouble-float -msimple-fpu @gol
723 -mstring -mno-string -mupdate -mno-update @gol
724 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
725 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
726 -mstrict-align -mno-strict-align -mrelocatable @gol
727 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
728 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
729 -mdynamic-no-pic -maltivec -mswdiv @gol
730 -mprioritize-restricted-insns=@var{priority} @gol
731 -msched-costly-dep=@var{dependence_type} @gol
732 -minsert-sched-nops=@var{scheme} @gol
733 -mcall-sysv -mcall-netbsd @gol
734 -maix-struct-return -msvr4-struct-return @gol
735 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
736 -misel -mno-isel @gol
737 -misel=yes -misel=no @gol
739 -mspe=yes -mspe=no @gol
741 -mgen-cell-microcode -mwarn-cell-microcode @gol
742 -mvrsave -mno-vrsave @gol
743 -mmulhw -mno-mulhw @gol
744 -mdlmzb -mno-dlmzb @gol
745 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
746 -mprototype -mno-prototype @gol
747 -msim -mmvme -mads -myellowknife -memb -msdata @gol
748 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
750 @emph{S/390 and zSeries Options}
751 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
752 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
753 -mlong-double-64 -mlong-double-128 @gol
754 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
755 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
756 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
757 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
758 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
761 @gccoptlist{-meb -mel @gol
765 -mscore5 -mscore5u -mscore7 -mscore7d}
768 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
769 -m4-nofpu -m4-single-only -m4-single -m4 @gol
770 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
771 -m5-64media -m5-64media-nofpu @gol
772 -m5-32media -m5-32media-nofpu @gol
773 -m5-compact -m5-compact-nofpu @gol
774 -mb -ml -mdalign -mrelax @gol
775 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
776 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
777 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
778 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
779 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
783 @gccoptlist{-mcpu=@var{cpu-type} @gol
784 -mtune=@var{cpu-type} @gol
785 -mcmodel=@var{code-model} @gol
786 -m32 -m64 -mapp-regs -mno-app-regs @gol
787 -mfaster-structs -mno-faster-structs @gol
788 -mfpu -mno-fpu -mhard-float -msoft-float @gol
789 -mhard-quad-float -msoft-quad-float @gol
790 -mimpure-text -mno-impure-text -mlittle-endian @gol
791 -mstack-bias -mno-stack-bias @gol
792 -munaligned-doubles -mno-unaligned-doubles @gol
793 -mv8plus -mno-v8plus -mvis -mno-vis
794 -threads -pthreads -pthread}
797 @gccoptlist{-mwarn-reloc -merror-reloc @gol
798 -msafe-dma -munsafe-dma @gol
800 -msmall-mem -mlarge-mem -mstdmain @gol
801 -mfixed-range=@var{register-range}}
803 @emph{System V Options}
804 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
807 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
808 -mprolog-function -mno-prolog-function -mspace @gol
809 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
810 -mapp-regs -mno-app-regs @gol
811 -mdisable-callt -mno-disable-callt @gol
817 @gccoptlist{-mg -mgnu -munix}
819 @emph{VxWorks Options}
820 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
821 -Xbind-lazy -Xbind-now}
823 @emph{x86-64 Options}
824 See i386 and x86-64 Options.
826 @emph{Xstormy16 Options}
829 @emph{Xtensa Options}
830 @gccoptlist{-mconst16 -mno-const16 @gol
831 -mfused-madd -mno-fused-madd @gol
832 -mserialize-volatile -mno-serialize-volatile @gol
833 -mtext-section-literals -mno-text-section-literals @gol
834 -mtarget-align -mno-target-align @gol
835 -mlongcalls -mno-longcalls}
837 @emph{zSeries Options}
838 See S/390 and zSeries Options.
840 @item Code Generation Options
841 @xref{Code Gen Options,,Options for Code Generation Conventions}.
842 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
843 -ffixed-@var{reg} -fexceptions @gol
844 -fnon-call-exceptions -funwind-tables @gol
845 -fasynchronous-unwind-tables @gol
846 -finhibit-size-directive -finstrument-functions @gol
847 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
848 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
849 -fno-common -fno-ident @gol
850 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
851 -fno-jump-tables @gol
852 -frecord-gcc-switches @gol
853 -freg-struct-return -fshort-enums @gol
854 -fshort-double -fshort-wchar @gol
855 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
856 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
857 -fno-stack-limit -fargument-alias -fargument-noalias @gol
858 -fargument-noalias-global -fargument-noalias-anything @gol
859 -fleading-underscore -ftls-model=@var{model} @gol
860 -ftrapv -fwrapv -fbounds-check @gol
865 * Overall Options:: Controlling the kind of output:
866 an executable, object files, assembler files,
867 or preprocessed source.
868 * C Dialect Options:: Controlling the variant of C language compiled.
869 * C++ Dialect Options:: Variations on C++.
870 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
872 * Language Independent Options:: Controlling how diagnostics should be
874 * Warning Options:: How picky should the compiler be?
875 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
876 * Optimize Options:: How much optimization?
877 * Preprocessor Options:: Controlling header files and macro definitions.
878 Also, getting dependency information for Make.
879 * Assembler Options:: Passing options to the assembler.
880 * Link Options:: Specifying libraries and so on.
881 * Directory Options:: Where to find header files and libraries.
882 Where to find the compiler executable files.
883 * Spec Files:: How to pass switches to sub-processes.
884 * Target Options:: Running a cross-compiler, or an old version of GCC.
887 @node Overall Options
888 @section Options Controlling the Kind of Output
890 Compilation can involve up to four stages: preprocessing, compilation
891 proper, assembly and linking, always in that order. GCC is capable of
892 preprocessing and compiling several files either into several
893 assembler input files, or into one assembler input file; then each
894 assembler input file produces an object file, and linking combines all
895 the object files (those newly compiled, and those specified as input)
896 into an executable file.
898 @cindex file name suffix
899 For any given input file, the file name suffix determines what kind of
904 C source code which must be preprocessed.
907 C source code which should not be preprocessed.
910 C++ source code which should not be preprocessed.
913 Objective-C source code. Note that you must link with the @file{libobjc}
914 library to make an Objective-C program work.
917 Objective-C source code which should not be preprocessed.
921 Objective-C++ source code. Note that you must link with the @file{libobjc}
922 library to make an Objective-C++ program work. Note that @samp{.M} refers
923 to a literal capital M@.
926 Objective-C++ source code which should not be preprocessed.
929 C, C++, Objective-C or Objective-C++ header file to be turned into a
934 @itemx @var{file}.cxx
935 @itemx @var{file}.cpp
936 @itemx @var{file}.CPP
937 @itemx @var{file}.c++
939 C++ source code which must be preprocessed. Note that in @samp{.cxx},
940 the last two letters must both be literally @samp{x}. Likewise,
941 @samp{.C} refers to a literal capital C@.
945 Objective-C++ source code which must be preprocessed.
948 Objective-C++ source code which should not be preprocessed.
953 @itemx @var{file}.hxx
954 @itemx @var{file}.hpp
955 @itemx @var{file}.HPP
956 @itemx @var{file}.h++
957 @itemx @var{file}.tcc
958 C++ header file to be turned into a precompiled header.
961 @itemx @var{file}.for
962 @itemx @var{file}.ftn
963 Fixed form Fortran source code which should not be preprocessed.
966 @itemx @var{file}.FOR
967 @itemx @var{file}.fpp
968 @itemx @var{file}.FPP
969 @itemx @var{file}.FTN
970 Fixed form Fortran source code which must be preprocessed (with the traditional
974 @itemx @var{file}.f95
975 @itemx @var{file}.f03
976 @itemx @var{file}.f08
977 Free form Fortran source code which should not be preprocessed.
980 @itemx @var{file}.F95
981 @itemx @var{file}.F03
982 @itemx @var{file}.F08
983 Free form Fortran source code which must be preprocessed (with the
984 traditional preprocessor).
986 @c FIXME: Descriptions of Java file types.
993 Ada source code file which contains a library unit declaration (a
994 declaration of a package, subprogram, or generic, or a generic
995 instantiation), or a library unit renaming declaration (a package,
996 generic, or subprogram renaming declaration). Such files are also
1000 Ada source code file containing a library unit body (a subprogram or
1001 package body). Such files are also called @dfn{bodies}.
1003 @c GCC also knows about some suffixes for languages not yet included:
1014 @itemx @var{file}.sx
1015 Assembler code which must be preprocessed.
1018 An object file to be fed straight into linking.
1019 Any file name with no recognized suffix is treated this way.
1023 You can specify the input language explicitly with the @option{-x} option:
1026 @item -x @var{language}
1027 Specify explicitly the @var{language} for the following input files
1028 (rather than letting the compiler choose a default based on the file
1029 name suffix). This option applies to all following input files until
1030 the next @option{-x} option. Possible values for @var{language} are:
1032 c c-header c-cpp-output
1033 c++ c++-header c++-cpp-output
1034 objective-c objective-c-header objective-c-cpp-output
1035 objective-c++ objective-c++-header objective-c++-cpp-output
1036 assembler assembler-with-cpp
1038 f77 f77-cpp-input f95 f95-cpp-input
1043 Turn off any specification of a language, so that subsequent files are
1044 handled according to their file name suffixes (as they are if @option{-x}
1045 has not been used at all).
1047 @item -pass-exit-codes
1048 @opindex pass-exit-codes
1049 Normally the @command{gcc} program will exit with the code of 1 if any
1050 phase of the compiler returns a non-success return code. If you specify
1051 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1052 numerically highest error produced by any phase that returned an error
1053 indication. The C, C++, and Fortran frontends return 4, if an internal
1054 compiler error is encountered.
1057 If you only want some of the stages of compilation, you can use
1058 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1059 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1060 @command{gcc} is to stop. Note that some combinations (for example,
1061 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1066 Compile or assemble the source files, but do not link. The linking
1067 stage simply is not done. The ultimate output is in the form of an
1068 object file for each source file.
1070 By default, the object file name for a source file is made by replacing
1071 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1073 Unrecognized input files, not requiring compilation or assembly, are
1078 Stop after the stage of compilation proper; do not assemble. The output
1079 is in the form of an assembler code file for each non-assembler input
1082 By default, the assembler file name for a source file is made by
1083 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1085 Input files that don't require compilation are ignored.
1089 Stop after the preprocessing stage; do not run the compiler proper. The
1090 output is in the form of preprocessed source code, which is sent to the
1093 Input files which don't require preprocessing are ignored.
1095 @cindex output file option
1098 Place output in file @var{file}. This applies regardless to whatever
1099 sort of output is being produced, whether it be an executable file,
1100 an object file, an assembler file or preprocessed C code.
1102 If @option{-o} is not specified, the default is to put an executable
1103 file in @file{a.out}, the object file for
1104 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1105 assembler file in @file{@var{source}.s}, a precompiled header file in
1106 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1111 Print (on standard error output) the commands executed to run the stages
1112 of compilation. Also print the version number of the compiler driver
1113 program and of the preprocessor and the compiler proper.
1117 Like @option{-v} except the commands are not executed and all command
1118 arguments are quoted. This is useful for shell scripts to capture the
1119 driver-generated command lines.
1123 Use pipes rather than temporary files for communication between the
1124 various stages of compilation. This fails to work on some systems where
1125 the assembler is unable to read from a pipe; but the GNU assembler has
1130 If you are compiling multiple source files, this option tells the driver
1131 to pass all the source files to the compiler at once (for those
1132 languages for which the compiler can handle this). This will allow
1133 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1134 language for which this is supported is C@. If you pass source files for
1135 multiple languages to the driver, using this option, the driver will invoke
1136 the compiler(s) that support IMA once each, passing each compiler all the
1137 source files appropriate for it. For those languages that do not support
1138 IMA this option will be ignored, and the compiler will be invoked once for
1139 each source file in that language. If you use this option in conjunction
1140 with @option{-save-temps}, the compiler will generate multiple
1142 (one for each source file), but only one (combined) @file{.o} or
1147 Print (on the standard output) a description of the command line options
1148 understood by @command{gcc}. If the @option{-v} option is also specified
1149 then @option{--help} will also be passed on to the various processes
1150 invoked by @command{gcc}, so that they can display the command line options
1151 they accept. If the @option{-Wextra} option has also been specified
1152 (prior to the @option{--help} option), then command line options which
1153 have no documentation associated with them will also be displayed.
1156 @opindex target-help
1157 Print (on the standard output) a description of target-specific command
1158 line options for each tool. For some targets extra target-specific
1159 information may also be printed.
1161 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1162 Print (on the standard output) a description of the command line
1163 options understood by the compiler that fit into a specific class.
1164 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1165 @samp{params}, or @var{language}:
1168 @item @samp{optimizers}
1169 This will display all of the optimization options supported by the
1172 @item @samp{warnings}
1173 This will display all of the options controlling warning messages
1174 produced by the compiler.
1177 This will display target-specific options. Unlike the
1178 @option{--target-help} option however, target-specific options of the
1179 linker and assembler will not be displayed. This is because those
1180 tools do not currently support the extended @option{--help=} syntax.
1183 This will display the values recognized by the @option{--param}
1186 @item @var{language}
1187 This will display the options supported for @var{language}, where
1188 @var{language} is the name of one of the languages supported in this
1192 This will display the options that are common to all languages.
1195 It is possible to further refine the output of the @option{--help=}
1196 option by adding a comma separated list of qualifiers after the
1197 class. These can be any from the following list:
1200 @item @samp{undocumented}
1201 Display only those options which are undocumented.
1204 Display options which take an argument that appears after an equal
1205 sign in the same continuous piece of text, such as:
1206 @samp{--help=target}.
1208 @item @samp{separate}
1209 Display options which take an argument that appears as a separate word
1210 following the original option, such as: @samp{-o output-file}.
1213 Thus for example to display all the undocumented target-specific
1214 switches supported by the compiler the following can be used:
1217 --help=target,undocumented
1220 The sense of a qualifier can be inverted by prefixing it with the
1221 @var{^} character, so for example to display all binary warning
1222 options (i.e., ones that are either on or off and that do not take an
1223 argument), which have a description the following can be used:
1226 --help=warnings,^joined,^undocumented
1229 A class can also be used as a qualifier, although this usually
1230 restricts the output by so much that there is nothing to display. One
1231 case where it does work however is when one of the classes is
1232 @var{target}. So for example to display all the target-specific
1233 optimization options the following can be used:
1236 --help=target,optimizers
1239 The @option{--help=} option can be repeated on the command line. Each
1240 successive use will display its requested class of options, skipping
1241 those that have already been displayed.
1243 If the @option{-Q} option appears on the command line before the
1244 @option{--help=} option, then the descriptive text displayed by
1245 @option{--help=} is changed. Instead of describing the displayed
1246 options, an indication is given as to whether the option is enabled,
1247 disabled or set to a specific value (assuming that the compiler
1248 knows this at the point where the @option{--help=} option is used).
1250 Here is a truncated example from the ARM port of @command{gcc}:
1253 % gcc -Q -mabi=2 --help=target -c
1254 The following options are target specific:
1256 -mabort-on-noreturn [disabled]
1260 The output is sensitive to the effects of previous command line
1261 options, so for example it is possible to find out which optimizations
1262 are enabled at @option{-O2} by using:
1265 -O2 --help=optimizers
1268 Alternatively you can discover which binary optimizations are enabled
1269 by @option{-O3} by using:
1272 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1273 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1274 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1279 Display the version number and copyrights of the invoked GCC@.
1283 Invoke all subcommands under a wrapper program. It takes a single
1284 comma separated list as an argument, which will be used to invoke
1288 gcc -c t.c -wrapper gdb,--args
1291 This will invoke all subprograms of gcc under "gdb --args",
1292 thus cc1 invocation will be "gdb --args cc1 ...".
1294 @include @value{srcdir}/../libiberty/at-file.texi
1298 @section Compiling C++ Programs
1300 @cindex suffixes for C++ source
1301 @cindex C++ source file suffixes
1302 C++ source files conventionally use one of the suffixes @samp{.C},
1303 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1304 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1305 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1306 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1307 files with these names and compiles them as C++ programs even if you
1308 call the compiler the same way as for compiling C programs (usually
1309 with the name @command{gcc}).
1313 However, the use of @command{gcc} does not add the C++ library.
1314 @command{g++} is a program that calls GCC and treats @samp{.c},
1315 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1316 files unless @option{-x} is used, and automatically specifies linking
1317 against the C++ library. This program is also useful when
1318 precompiling a C header file with a @samp{.h} extension for use in C++
1319 compilations. On many systems, @command{g++} is also installed with
1320 the name @command{c++}.
1322 @cindex invoking @command{g++}
1323 When you compile C++ programs, you may specify many of the same
1324 command-line options that you use for compiling programs in any
1325 language; or command-line options meaningful for C and related
1326 languages; or options that are meaningful only for C++ programs.
1327 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1328 explanations of options for languages related to C@.
1329 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1330 explanations of options that are meaningful only for C++ programs.
1332 @node C Dialect Options
1333 @section Options Controlling C Dialect
1334 @cindex dialect options
1335 @cindex language dialect options
1336 @cindex options, dialect
1338 The following options control the dialect of C (or languages derived
1339 from C, such as C++, Objective-C and Objective-C++) that the compiler
1343 @cindex ANSI support
1347 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1348 equivalent to @samp{-std=c++98}.
1350 This turns off certain features of GCC that are incompatible with ISO
1351 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1352 such as the @code{asm} and @code{typeof} keywords, and
1353 predefined macros such as @code{unix} and @code{vax} that identify the
1354 type of system you are using. It also enables the undesirable and
1355 rarely used ISO trigraph feature. For the C compiler,
1356 it disables recognition of C++ style @samp{//} comments as well as
1357 the @code{inline} keyword.
1359 The alternate keywords @code{__asm__}, @code{__extension__},
1360 @code{__inline__} and @code{__typeof__} continue to work despite
1361 @option{-ansi}. You would not want to use them in an ISO C program, of
1362 course, but it is useful to put them in header files that might be included
1363 in compilations done with @option{-ansi}. Alternate predefined macros
1364 such as @code{__unix__} and @code{__vax__} are also available, with or
1365 without @option{-ansi}.
1367 The @option{-ansi} option does not cause non-ISO programs to be
1368 rejected gratuitously. For that, @option{-pedantic} is required in
1369 addition to @option{-ansi}. @xref{Warning Options}.
1371 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1372 option is used. Some header files may notice this macro and refrain
1373 from declaring certain functions or defining certain macros that the
1374 ISO standard doesn't call for; this is to avoid interfering with any
1375 programs that might use these names for other things.
1377 Functions that would normally be built in but do not have semantics
1378 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1379 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1380 built-in functions provided by GCC}, for details of the functions
1385 Determine the language standard. @xref{Standards,,Language Standards
1386 Supported by GCC}, for details of these standard versions. This option
1387 is currently only supported when compiling C or C++.
1389 The compiler can accept several base standards, such as @samp{c89} or
1390 @samp{c++98}, and GNU dialects of those standards, such as
1391 @samp{gnu89} or @samp{gnu++98}. By specifying a base standard, the
1392 compiler will accept all programs following that standard and those
1393 using GNU extensions that do not contradict it. For example,
1394 @samp{-std=c89} turns off certain features of GCC that are
1395 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1396 keywords, but not other GNU extensions that do not have a meaning in
1397 ISO C90, such as omitting the middle term of a @code{?:}
1398 expression. On the other hand, by specifying a GNU dialect of a
1399 standard, all features the compiler support are enabled, even when
1400 those features change the meaning of the base standard and some
1401 strict-conforming programs may be rejected. The particular standard
1402 is used by @option{-pedantic} to identify which features are GNU
1403 extensions given that version of the standard. For example
1404 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1405 comments, while @samp{-std=gnu99 -pedantic} would not.
1407 A value for this option must be provided; possible values are
1412 Support all ISO C90 programs (certain GNU extensions that conflict
1413 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1415 @item iso9899:199409
1416 ISO C90 as modified in amendment 1.
1422 ISO C99. Note that this standard is not yet fully supported; see
1423 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1424 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1427 GNU dialect of ISO C90 (including some C99 features). This
1428 is the default for C code.
1432 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1433 this will become the default. The name @samp{gnu9x} is deprecated.
1436 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1440 GNU dialect of @option{-std=c++98}. This is the default for
1444 The working draft of the upcoming ISO C++0x standard. This option
1445 enables experimental features that are likely to be included in
1446 C++0x. The working draft is constantly changing, and any feature that is
1447 enabled by this flag may be removed from future versions of GCC if it is
1448 not part of the C++0x standard.
1451 GNU dialect of @option{-std=c++0x}. This option enables
1452 experimental features that may be removed in future versions of GCC.
1455 @item -fgnu89-inline
1456 @opindex fgnu89-inline
1457 The option @option{-fgnu89-inline} tells GCC to use the traditional
1458 GNU semantics for @code{inline} functions when in C99 mode.
1459 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1460 is accepted and ignored by GCC versions 4.1.3 up to but not including
1461 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1462 C99 mode. Using this option is roughly equivalent to adding the
1463 @code{gnu_inline} function attribute to all inline functions
1464 (@pxref{Function Attributes}).
1466 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1467 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1468 specifies the default behavior). This option was first supported in
1469 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1471 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1472 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1473 in effect for @code{inline} functions. @xref{Common Predefined
1474 Macros,,,cpp,The C Preprocessor}.
1476 @item -aux-info @var{filename}
1478 Output to the given filename prototyped declarations for all functions
1479 declared and/or defined in a translation unit, including those in header
1480 files. This option is silently ignored in any language other than C@.
1482 Besides declarations, the file indicates, in comments, the origin of
1483 each declaration (source file and line), whether the declaration was
1484 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1485 @samp{O} for old, respectively, in the first character after the line
1486 number and the colon), and whether it came from a declaration or a
1487 definition (@samp{C} or @samp{F}, respectively, in the following
1488 character). In the case of function definitions, a K&R-style list of
1489 arguments followed by their declarations is also provided, inside
1490 comments, after the declaration.
1494 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1495 keyword, so that code can use these words as identifiers. You can use
1496 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1497 instead. @option{-ansi} implies @option{-fno-asm}.
1499 In C++, this switch only affects the @code{typeof} keyword, since
1500 @code{asm} and @code{inline} are standard keywords. You may want to
1501 use the @option{-fno-gnu-keywords} flag instead, which has the same
1502 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1503 switch only affects the @code{asm} and @code{typeof} keywords, since
1504 @code{inline} is a standard keyword in ISO C99.
1507 @itemx -fno-builtin-@var{function}
1508 @opindex fno-builtin
1509 @cindex built-in functions
1510 Don't recognize built-in functions that do not begin with
1511 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1512 functions provided by GCC}, for details of the functions affected,
1513 including those which are not built-in functions when @option{-ansi} or
1514 @option{-std} options for strict ISO C conformance are used because they
1515 do not have an ISO standard meaning.
1517 GCC normally generates special code to handle certain built-in functions
1518 more efficiently; for instance, calls to @code{alloca} may become single
1519 instructions that adjust the stack directly, and calls to @code{memcpy}
1520 may become inline copy loops. The resulting code is often both smaller
1521 and faster, but since the function calls no longer appear as such, you
1522 cannot set a breakpoint on those calls, nor can you change the behavior
1523 of the functions by linking with a different library. In addition,
1524 when a function is recognized as a built-in function, GCC may use
1525 information about that function to warn about problems with calls to
1526 that function, or to generate more efficient code, even if the
1527 resulting code still contains calls to that function. For example,
1528 warnings are given with @option{-Wformat} for bad calls to
1529 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1530 known not to modify global memory.
1532 With the @option{-fno-builtin-@var{function}} option
1533 only the built-in function @var{function} is
1534 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1535 function is named that is not built-in in this version of GCC, this
1536 option is ignored. There is no corresponding
1537 @option{-fbuiltin-@var{function}} option; if you wish to enable
1538 built-in functions selectively when using @option{-fno-builtin} or
1539 @option{-ffreestanding}, you may define macros such as:
1542 #define abs(n) __builtin_abs ((n))
1543 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1548 @cindex hosted environment
1550 Assert that compilation takes place in a hosted environment. This implies
1551 @option{-fbuiltin}. A hosted environment is one in which the
1552 entire standard library is available, and in which @code{main} has a return
1553 type of @code{int}. Examples are nearly everything except a kernel.
1554 This is equivalent to @option{-fno-freestanding}.
1556 @item -ffreestanding
1557 @opindex ffreestanding
1558 @cindex hosted environment
1560 Assert that compilation takes place in a freestanding environment. This
1561 implies @option{-fno-builtin}. A freestanding environment
1562 is one in which the standard library may not exist, and program startup may
1563 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1564 This is equivalent to @option{-fno-hosted}.
1566 @xref{Standards,,Language Standards Supported by GCC}, for details of
1567 freestanding and hosted environments.
1571 @cindex openmp parallel
1572 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1573 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1574 compiler generates parallel code according to the OpenMP Application
1575 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1576 implies @option{-pthread}, and thus is only supported on targets that
1577 have support for @option{-pthread}.
1579 @item -fms-extensions
1580 @opindex fms-extensions
1581 Accept some non-standard constructs used in Microsoft header files.
1583 Some cases of unnamed fields in structures and unions are only
1584 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1585 fields within structs/unions}, for details.
1589 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1590 options for strict ISO C conformance) implies @option{-trigraphs}.
1592 @item -no-integrated-cpp
1593 @opindex no-integrated-cpp
1594 Performs a compilation in two passes: preprocessing and compiling. This
1595 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1596 @option{-B} option. The user supplied compilation step can then add in
1597 an additional preprocessing step after normal preprocessing but before
1598 compiling. The default is to use the integrated cpp (internal cpp)
1600 The semantics of this option will change if "cc1", "cc1plus", and
1601 "cc1obj" are merged.
1603 @cindex traditional C language
1604 @cindex C language, traditional
1606 @itemx -traditional-cpp
1607 @opindex traditional-cpp
1608 @opindex traditional
1609 Formerly, these options caused GCC to attempt to emulate a pre-standard
1610 C compiler. They are now only supported with the @option{-E} switch.
1611 The preprocessor continues to support a pre-standard mode. See the GNU
1612 CPP manual for details.
1614 @item -fcond-mismatch
1615 @opindex fcond-mismatch
1616 Allow conditional expressions with mismatched types in the second and
1617 third arguments. The value of such an expression is void. This option
1618 is not supported for C++.
1620 @item -flax-vector-conversions
1621 @opindex flax-vector-conversions
1622 Allow implicit conversions between vectors with differing numbers of
1623 elements and/or incompatible element types. This option should not be
1626 @item -funsigned-char
1627 @opindex funsigned-char
1628 Let the type @code{char} be unsigned, like @code{unsigned char}.
1630 Each kind of machine has a default for what @code{char} should
1631 be. It is either like @code{unsigned char} by default or like
1632 @code{signed char} by default.
1634 Ideally, a portable program should always use @code{signed char} or
1635 @code{unsigned char} when it depends on the signedness of an object.
1636 But many programs have been written to use plain @code{char} and
1637 expect it to be signed, or expect it to be unsigned, depending on the
1638 machines they were written for. This option, and its inverse, let you
1639 make such a program work with the opposite default.
1641 The type @code{char} is always a distinct type from each of
1642 @code{signed char} or @code{unsigned char}, even though its behavior
1643 is always just like one of those two.
1646 @opindex fsigned-char
1647 Let the type @code{char} be signed, like @code{signed char}.
1649 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1650 the negative form of @option{-funsigned-char}. Likewise, the option
1651 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1653 @item -fsigned-bitfields
1654 @itemx -funsigned-bitfields
1655 @itemx -fno-signed-bitfields
1656 @itemx -fno-unsigned-bitfields
1657 @opindex fsigned-bitfields
1658 @opindex funsigned-bitfields
1659 @opindex fno-signed-bitfields
1660 @opindex fno-unsigned-bitfields
1661 These options control whether a bit-field is signed or unsigned, when the
1662 declaration does not use either @code{signed} or @code{unsigned}. By
1663 default, such a bit-field is signed, because this is consistent: the
1664 basic integer types such as @code{int} are signed types.
1667 @node C++ Dialect Options
1668 @section Options Controlling C++ Dialect
1670 @cindex compiler options, C++
1671 @cindex C++ options, command line
1672 @cindex options, C++
1673 This section describes the command-line options that are only meaningful
1674 for C++ programs; but you can also use most of the GNU compiler options
1675 regardless of what language your program is in. For example, you
1676 might compile a file @code{firstClass.C} like this:
1679 g++ -g -frepo -O -c firstClass.C
1683 In this example, only @option{-frepo} is an option meant
1684 only for C++ programs; you can use the other options with any
1685 language supported by GCC@.
1687 Here is a list of options that are @emph{only} for compiling C++ programs:
1691 @item -fabi-version=@var{n}
1692 @opindex fabi-version
1693 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1694 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1695 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1696 the version that conforms most closely to the C++ ABI specification.
1697 Therefore, the ABI obtained using version 0 will change as ABI bugs
1700 The default is version 2.
1702 @item -fno-access-control
1703 @opindex fno-access-control
1704 Turn off all access checking. This switch is mainly useful for working
1705 around bugs in the access control code.
1709 Check that the pointer returned by @code{operator new} is non-null
1710 before attempting to modify the storage allocated. This check is
1711 normally unnecessary because the C++ standard specifies that
1712 @code{operator new} will only return @code{0} if it is declared
1713 @samp{throw()}, in which case the compiler will always check the
1714 return value even without this option. In all other cases, when
1715 @code{operator new} has a non-empty exception specification, memory
1716 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1717 @samp{new (nothrow)}.
1719 @item -fconserve-space
1720 @opindex fconserve-space
1721 Put uninitialized or runtime-initialized global variables into the
1722 common segment, as C does. This saves space in the executable at the
1723 cost of not diagnosing duplicate definitions. If you compile with this
1724 flag and your program mysteriously crashes after @code{main()} has
1725 completed, you may have an object that is being destroyed twice because
1726 two definitions were merged.
1728 This option is no longer useful on most targets, now that support has
1729 been added for putting variables into BSS without making them common.
1731 @item -ffriend-injection
1732 @opindex ffriend-injection
1733 Inject friend functions into the enclosing namespace, so that they are
1734 visible outside the scope of the class in which they are declared.
1735 Friend functions were documented to work this way in the old Annotated
1736 C++ Reference Manual, and versions of G++ before 4.1 always worked
1737 that way. However, in ISO C++ a friend function which is not declared
1738 in an enclosing scope can only be found using argument dependent
1739 lookup. This option causes friends to be injected as they were in
1742 This option is for compatibility, and may be removed in a future
1745 @item -fno-elide-constructors
1746 @opindex fno-elide-constructors
1747 The C++ standard allows an implementation to omit creating a temporary
1748 which is only used to initialize another object of the same type.
1749 Specifying this option disables that optimization, and forces G++ to
1750 call the copy constructor in all cases.
1752 @item -fno-enforce-eh-specs
1753 @opindex fno-enforce-eh-specs
1754 Don't generate code to check for violation of exception specifications
1755 at runtime. This option violates the C++ standard, but may be useful
1756 for reducing code size in production builds, much like defining
1757 @samp{NDEBUG}. This does not give user code permission to throw
1758 exceptions in violation of the exception specifications; the compiler
1759 will still optimize based on the specifications, so throwing an
1760 unexpected exception will result in undefined behavior.
1763 @itemx -fno-for-scope
1765 @opindex fno-for-scope
1766 If @option{-ffor-scope} is specified, the scope of variables declared in
1767 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1768 as specified by the C++ standard.
1769 If @option{-fno-for-scope} is specified, the scope of variables declared in
1770 a @i{for-init-statement} extends to the end of the enclosing scope,
1771 as was the case in old versions of G++, and other (traditional)
1772 implementations of C++.
1774 The default if neither flag is given to follow the standard,
1775 but to allow and give a warning for old-style code that would
1776 otherwise be invalid, or have different behavior.
1778 @item -fno-gnu-keywords
1779 @opindex fno-gnu-keywords
1780 Do not recognize @code{typeof} as a keyword, so that code can use this
1781 word as an identifier. You can use the keyword @code{__typeof__} instead.
1782 @option{-ansi} implies @option{-fno-gnu-keywords}.
1784 @item -fno-implicit-templates
1785 @opindex fno-implicit-templates
1786 Never emit code for non-inline templates which are instantiated
1787 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1788 @xref{Template Instantiation}, for more information.
1790 @item -fno-implicit-inline-templates
1791 @opindex fno-implicit-inline-templates
1792 Don't emit code for implicit instantiations of inline templates, either.
1793 The default is to handle inlines differently so that compiles with and
1794 without optimization will need the same set of explicit instantiations.
1796 @item -fno-implement-inlines
1797 @opindex fno-implement-inlines
1798 To save space, do not emit out-of-line copies of inline functions
1799 controlled by @samp{#pragma implementation}. This will cause linker
1800 errors if these functions are not inlined everywhere they are called.
1802 @item -fms-extensions
1803 @opindex fms-extensions
1804 Disable pedantic warnings about constructs used in MFC, such as implicit
1805 int and getting a pointer to member function via non-standard syntax.
1807 @item -fno-nonansi-builtins
1808 @opindex fno-nonansi-builtins
1809 Disable built-in declarations of functions that are not mandated by
1810 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1811 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1813 @item -fno-operator-names
1814 @opindex fno-operator-names
1815 Do not treat the operator name keywords @code{and}, @code{bitand},
1816 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1817 synonyms as keywords.
1819 @item -fno-optional-diags
1820 @opindex fno-optional-diags
1821 Disable diagnostics that the standard says a compiler does not need to
1822 issue. Currently, the only such diagnostic issued by G++ is the one for
1823 a name having multiple meanings within a class.
1826 @opindex fpermissive
1827 Downgrade some diagnostics about nonconformant code from errors to
1828 warnings. Thus, using @option{-fpermissive} will allow some
1829 nonconforming code to compile.
1833 Enable automatic template instantiation at link time. This option also
1834 implies @option{-fno-implicit-templates}. @xref{Template
1835 Instantiation}, for more information.
1839 Disable generation of information about every class with virtual
1840 functions for use by the C++ runtime type identification features
1841 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1842 of the language, you can save some space by using this flag. Note that
1843 exception handling uses the same information, but it will generate it as
1844 needed. The @samp{dynamic_cast} operator can still be used for casts that
1845 do not require runtime type information, i.e.@: casts to @code{void *} or to
1846 unambiguous base classes.
1850 Emit statistics about front-end processing at the end of the compilation.
1851 This information is generally only useful to the G++ development team.
1853 @item -ftemplate-depth-@var{n}
1854 @opindex ftemplate-depth
1855 Set the maximum instantiation depth for template classes to @var{n}.
1856 A limit on the template instantiation depth is needed to detect
1857 endless recursions during template class instantiation. ANSI/ISO C++
1858 conforming programs must not rely on a maximum depth greater than 17.
1860 @item -fno-threadsafe-statics
1861 @opindex fno-threadsafe-statics
1862 Do not emit the extra code to use the routines specified in the C++
1863 ABI for thread-safe initialization of local statics. You can use this
1864 option to reduce code size slightly in code that doesn't need to be
1867 @item -fuse-cxa-atexit
1868 @opindex fuse-cxa-atexit
1869 Register destructors for objects with static storage duration with the
1870 @code{__cxa_atexit} function rather than the @code{atexit} function.
1871 This option is required for fully standards-compliant handling of static
1872 destructors, but will only work if your C library supports
1873 @code{__cxa_atexit}.
1875 @item -fno-use-cxa-get-exception-ptr
1876 @opindex fno-use-cxa-get-exception-ptr
1877 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1878 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1879 if the runtime routine is not available.
1881 @item -fvisibility-inlines-hidden
1882 @opindex fvisibility-inlines-hidden
1883 This switch declares that the user does not attempt to compare
1884 pointers to inline methods where the addresses of the two functions
1885 were taken in different shared objects.
1887 The effect of this is that GCC may, effectively, mark inline methods with
1888 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1889 appear in the export table of a DSO and do not require a PLT indirection
1890 when used within the DSO@. Enabling this option can have a dramatic effect
1891 on load and link times of a DSO as it massively reduces the size of the
1892 dynamic export table when the library makes heavy use of templates.
1894 The behavior of this switch is not quite the same as marking the
1895 methods as hidden directly, because it does not affect static variables
1896 local to the function or cause the compiler to deduce that
1897 the function is defined in only one shared object.
1899 You may mark a method as having a visibility explicitly to negate the
1900 effect of the switch for that method. For example, if you do want to
1901 compare pointers to a particular inline method, you might mark it as
1902 having default visibility. Marking the enclosing class with explicit
1903 visibility will have no effect.
1905 Explicitly instantiated inline methods are unaffected by this option
1906 as their linkage might otherwise cross a shared library boundary.
1907 @xref{Template Instantiation}.
1909 @item -fvisibility-ms-compat
1910 @opindex fvisibility-ms-compat
1911 This flag attempts to use visibility settings to make GCC's C++
1912 linkage model compatible with that of Microsoft Visual Studio.
1914 The flag makes these changes to GCC's linkage model:
1918 It sets the default visibility to @code{hidden}, like
1919 @option{-fvisibility=hidden}.
1922 Types, but not their members, are not hidden by default.
1925 The One Definition Rule is relaxed for types without explicit
1926 visibility specifications which are defined in more than one different
1927 shared object: those declarations are permitted if they would have
1928 been permitted when this option was not used.
1931 In new code it is better to use @option{-fvisibility=hidden} and
1932 export those classes which are intended to be externally visible.
1933 Unfortunately it is possible for code to rely, perhaps accidentally,
1934 on the Visual Studio behavior.
1936 Among the consequences of these changes are that static data members
1937 of the same type with the same name but defined in different shared
1938 objects will be different, so changing one will not change the other;
1939 and that pointers to function members defined in different shared
1940 objects may not compare equal. When this flag is given, it is a
1941 violation of the ODR to define types with the same name differently.
1945 Do not use weak symbol support, even if it is provided by the linker.
1946 By default, G++ will use weak symbols if they are available. This
1947 option exists only for testing, and should not be used by end-users;
1948 it will result in inferior code and has no benefits. This option may
1949 be removed in a future release of G++.
1953 Do not search for header files in the standard directories specific to
1954 C++, but do still search the other standard directories. (This option
1955 is used when building the C++ library.)
1958 In addition, these optimization, warning, and code generation options
1959 have meanings only for C++ programs:
1962 @item -fno-default-inline
1963 @opindex fno-default-inline
1964 Do not assume @samp{inline} for functions defined inside a class scope.
1965 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1966 functions will have linkage like inline functions; they just won't be
1969 @item -Wabi @r{(C++ and Objective-C++ only)}
1972 Warn when G++ generates code that is probably not compatible with the
1973 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1974 all such cases, there are probably some cases that are not warned about,
1975 even though G++ is generating incompatible code. There may also be
1976 cases where warnings are emitted even though the code that is generated
1979 You should rewrite your code to avoid these warnings if you are
1980 concerned about the fact that code generated by G++ may not be binary
1981 compatible with code generated by other compilers.
1983 The known incompatibilities at this point include:
1988 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1989 pack data into the same byte as a base class. For example:
1992 struct A @{ virtual void f(); int f1 : 1; @};
1993 struct B : public A @{ int f2 : 1; @};
1997 In this case, G++ will place @code{B::f2} into the same byte
1998 as@code{A::f1}; other compilers will not. You can avoid this problem
1999 by explicitly padding @code{A} so that its size is a multiple of the
2000 byte size on your platform; that will cause G++ and other compilers to
2001 layout @code{B} identically.
2004 Incorrect handling of tail-padding for virtual bases. G++ does not use
2005 tail padding when laying out virtual bases. For example:
2008 struct A @{ virtual void f(); char c1; @};
2009 struct B @{ B(); char c2; @};
2010 struct C : public A, public virtual B @{@};
2014 In this case, G++ will not place @code{B} into the tail-padding for
2015 @code{A}; other compilers will. You can avoid this problem by
2016 explicitly padding @code{A} so that its size is a multiple of its
2017 alignment (ignoring virtual base classes); that will cause G++ and other
2018 compilers to layout @code{C} identically.
2021 Incorrect handling of bit-fields with declared widths greater than that
2022 of their underlying types, when the bit-fields appear in a union. For
2026 union U @{ int i : 4096; @};
2030 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2031 union too small by the number of bits in an @code{int}.
2034 Empty classes can be placed at incorrect offsets. For example:
2044 struct C : public B, public A @{@};
2048 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2049 it should be placed at offset zero. G++ mistakenly believes that the
2050 @code{A} data member of @code{B} is already at offset zero.
2053 Names of template functions whose types involve @code{typename} or
2054 template template parameters can be mangled incorrectly.
2057 template <typename Q>
2058 void f(typename Q::X) @{@}
2060 template <template <typename> class Q>
2061 void f(typename Q<int>::X) @{@}
2065 Instantiations of these templates may be mangled incorrectly.
2069 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2070 @opindex Wctor-dtor-privacy
2071 @opindex Wno-ctor-dtor-privacy
2072 Warn when a class seems unusable because all the constructors or
2073 destructors in that class are private, and it has neither friends nor
2074 public static member functions.
2076 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2077 @opindex Wnon-virtual-dtor
2078 @opindex Wno-non-virtual-dtor
2079 Warn when a class has virtual functions and accessible non-virtual
2080 destructor, in which case it would be possible but unsafe to delete
2081 an instance of a derived class through a pointer to the base class.
2082 This warning is also enabled if -Weffc++ is specified.
2084 @item -Wreorder @r{(C++ and Objective-C++ only)}
2086 @opindex Wno-reorder
2087 @cindex reordering, warning
2088 @cindex warning for reordering of member initializers
2089 Warn when the order of member initializers given in the code does not
2090 match the order in which they must be executed. For instance:
2096 A(): j (0), i (1) @{ @}
2100 The compiler will rearrange the member initializers for @samp{i}
2101 and @samp{j} to match the declaration order of the members, emitting
2102 a warning to that effect. This warning is enabled by @option{-Wall}.
2105 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2108 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2111 Warn about violations of the following style guidelines from Scott Meyers'
2112 @cite{Effective C++} book:
2116 Item 11: Define a copy constructor and an assignment operator for classes
2117 with dynamically allocated memory.
2120 Item 12: Prefer initialization to assignment in constructors.
2123 Item 14: Make destructors virtual in base classes.
2126 Item 15: Have @code{operator=} return a reference to @code{*this}.
2129 Item 23: Don't try to return a reference when you must return an object.
2133 Also warn about violations of the following style guidelines from
2134 Scott Meyers' @cite{More Effective C++} book:
2138 Item 6: Distinguish between prefix and postfix forms of increment and
2139 decrement operators.
2142 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2146 When selecting this option, be aware that the standard library
2147 headers do not obey all of these guidelines; use @samp{grep -v}
2148 to filter out those warnings.
2150 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2151 @opindex Wstrict-null-sentinel
2152 @opindex Wno-strict-null-sentinel
2153 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2154 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2155 to @code{__null}. Although it is a null pointer constant not a null pointer,
2156 it is guaranteed to be of the same size as a pointer. But this use is
2157 not portable across different compilers.
2159 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2160 @opindex Wno-non-template-friend
2161 @opindex Wnon-template-friend
2162 Disable warnings when non-templatized friend functions are declared
2163 within a template. Since the advent of explicit template specification
2164 support in G++, if the name of the friend is an unqualified-id (i.e.,
2165 @samp{friend foo(int)}), the C++ language specification demands that the
2166 friend declare or define an ordinary, nontemplate function. (Section
2167 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2168 could be interpreted as a particular specialization of a templatized
2169 function. Because this non-conforming behavior is no longer the default
2170 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2171 check existing code for potential trouble spots and is on by default.
2172 This new compiler behavior can be turned off with
2173 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2174 but disables the helpful warning.
2176 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2177 @opindex Wold-style-cast
2178 @opindex Wno-old-style-cast
2179 Warn if an old-style (C-style) cast to a non-void type is used within
2180 a C++ program. The new-style casts (@samp{dynamic_cast},
2181 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2182 less vulnerable to unintended effects and much easier to search for.
2184 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2185 @opindex Woverloaded-virtual
2186 @opindex Wno-overloaded-virtual
2187 @cindex overloaded virtual fn, warning
2188 @cindex warning for overloaded virtual fn
2189 Warn when a function declaration hides virtual functions from a
2190 base class. For example, in:
2197 struct B: public A @{
2202 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2210 will fail to compile.
2212 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2213 @opindex Wno-pmf-conversions
2214 @opindex Wpmf-conversions
2215 Disable the diagnostic for converting a bound pointer to member function
2218 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2219 @opindex Wsign-promo
2220 @opindex Wno-sign-promo
2221 Warn when overload resolution chooses a promotion from unsigned or
2222 enumerated type to a signed type, over a conversion to an unsigned type of
2223 the same size. Previous versions of G++ would try to preserve
2224 unsignedness, but the standard mandates the current behavior.
2229 A& operator = (int);
2239 In this example, G++ will synthesize a default @samp{A& operator =
2240 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2243 @node Objective-C and Objective-C++ Dialect Options
2244 @section Options Controlling Objective-C and Objective-C++ Dialects
2246 @cindex compiler options, Objective-C and Objective-C++
2247 @cindex Objective-C and Objective-C++ options, command line
2248 @cindex options, Objective-C and Objective-C++
2249 (NOTE: This manual does not describe the Objective-C and Objective-C++
2250 languages themselves. See @xref{Standards,,Language Standards
2251 Supported by GCC}, for references.)
2253 This section describes the command-line options that are only meaningful
2254 for Objective-C and Objective-C++ programs, but you can also use most of
2255 the language-independent GNU compiler options.
2256 For example, you might compile a file @code{some_class.m} like this:
2259 gcc -g -fgnu-runtime -O -c some_class.m
2263 In this example, @option{-fgnu-runtime} is an option meant only for
2264 Objective-C and Objective-C++ programs; you can use the other options with
2265 any language supported by GCC@.
2267 Note that since Objective-C is an extension of the C language, Objective-C
2268 compilations may also use options specific to the C front-end (e.g.,
2269 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2270 C++-specific options (e.g., @option{-Wabi}).
2272 Here is a list of options that are @emph{only} for compiling Objective-C
2273 and Objective-C++ programs:
2276 @item -fconstant-string-class=@var{class-name}
2277 @opindex fconstant-string-class
2278 Use @var{class-name} as the name of the class to instantiate for each
2279 literal string specified with the syntax @code{@@"@dots{}"}. The default
2280 class name is @code{NXConstantString} if the GNU runtime is being used, and
2281 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2282 @option{-fconstant-cfstrings} option, if also present, will override the
2283 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2284 to be laid out as constant CoreFoundation strings.
2287 @opindex fgnu-runtime
2288 Generate object code compatible with the standard GNU Objective-C
2289 runtime. This is the default for most types of systems.
2291 @item -fnext-runtime
2292 @opindex fnext-runtime
2293 Generate output compatible with the NeXT runtime. This is the default
2294 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2295 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2298 @item -fno-nil-receivers
2299 @opindex fno-nil-receivers
2300 Assume that all Objective-C message dispatches (e.g.,
2301 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2302 is not @code{nil}. This allows for more efficient entry points in the runtime
2303 to be used. Currently, this option is only available in conjunction with
2304 the NeXT runtime on Mac OS X 10.3 and later.
2306 @item -fobjc-call-cxx-cdtors
2307 @opindex fobjc-call-cxx-cdtors
2308 For each Objective-C class, check if any of its instance variables is a
2309 C++ object with a non-trivial default constructor. If so, synthesize a
2310 special @code{- (id) .cxx_construct} instance method that will run
2311 non-trivial default constructors on any such instance variables, in order,
2312 and then return @code{self}. Similarly, check if any instance variable
2313 is a C++ object with a non-trivial destructor, and if so, synthesize a
2314 special @code{- (void) .cxx_destruct} method that will run
2315 all such default destructors, in reverse order.
2317 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2318 thusly generated will only operate on instance variables declared in the
2319 current Objective-C class, and not those inherited from superclasses. It
2320 is the responsibility of the Objective-C runtime to invoke all such methods
2321 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2322 will be invoked by the runtime immediately after a new object
2323 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2324 be invoked immediately before the runtime deallocates an object instance.
2326 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2327 support for invoking the @code{- (id) .cxx_construct} and
2328 @code{- (void) .cxx_destruct} methods.
2330 @item -fobjc-direct-dispatch
2331 @opindex fobjc-direct-dispatch
2332 Allow fast jumps to the message dispatcher. On Darwin this is
2333 accomplished via the comm page.
2335 @item -fobjc-exceptions
2336 @opindex fobjc-exceptions
2337 Enable syntactic support for structured exception handling in Objective-C,
2338 similar to what is offered by C++ and Java. This option is
2339 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2348 @@catch (AnObjCClass *exc) @{
2355 @@catch (AnotherClass *exc) @{
2358 @@catch (id allOthers) @{
2368 The @code{@@throw} statement may appear anywhere in an Objective-C or
2369 Objective-C++ program; when used inside of a @code{@@catch} block, the
2370 @code{@@throw} may appear without an argument (as shown above), in which case
2371 the object caught by the @code{@@catch} will be rethrown.
2373 Note that only (pointers to) Objective-C objects may be thrown and
2374 caught using this scheme. When an object is thrown, it will be caught
2375 by the nearest @code{@@catch} clause capable of handling objects of that type,
2376 analogously to how @code{catch} blocks work in C++ and Java. A
2377 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2378 any and all Objective-C exceptions not caught by previous @code{@@catch}
2381 The @code{@@finally} clause, if present, will be executed upon exit from the
2382 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2383 regardless of whether any exceptions are thrown, caught or rethrown
2384 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2385 of the @code{finally} clause in Java.
2387 There are several caveats to using the new exception mechanism:
2391 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2392 idioms provided by the @code{NSException} class, the new
2393 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2394 systems, due to additional functionality needed in the (NeXT) Objective-C
2398 As mentioned above, the new exceptions do not support handling
2399 types other than Objective-C objects. Furthermore, when used from
2400 Objective-C++, the Objective-C exception model does not interoperate with C++
2401 exceptions at this time. This means you cannot @code{@@throw} an exception
2402 from Objective-C and @code{catch} it in C++, or vice versa
2403 (i.e., @code{throw @dots{} @@catch}).
2406 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2407 blocks for thread-safe execution:
2410 @@synchronized (ObjCClass *guard) @{
2415 Upon entering the @code{@@synchronized} block, a thread of execution shall
2416 first check whether a lock has been placed on the corresponding @code{guard}
2417 object by another thread. If it has, the current thread shall wait until
2418 the other thread relinquishes its lock. Once @code{guard} becomes available,
2419 the current thread will place its own lock on it, execute the code contained in
2420 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2421 making @code{guard} available to other threads).
2423 Unlike Java, Objective-C does not allow for entire methods to be marked
2424 @code{@@synchronized}. Note that throwing exceptions out of
2425 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2426 to be unlocked properly.
2430 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2432 @item -freplace-objc-classes
2433 @opindex freplace-objc-classes
2434 Emit a special marker instructing @command{ld(1)} not to statically link in
2435 the resulting object file, and allow @command{dyld(1)} to load it in at
2436 run time instead. This is used in conjunction with the Fix-and-Continue
2437 debugging mode, where the object file in question may be recompiled and
2438 dynamically reloaded in the course of program execution, without the need
2439 to restart the program itself. Currently, Fix-and-Continue functionality
2440 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2445 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2446 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2447 compile time) with static class references that get initialized at load time,
2448 which improves run-time performance. Specifying the @option{-fzero-link} flag
2449 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2450 to be retained. This is useful in Zero-Link debugging mode, since it allows
2451 for individual class implementations to be modified during program execution.
2455 Dump interface declarations for all classes seen in the source file to a
2456 file named @file{@var{sourcename}.decl}.
2458 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2459 @opindex Wassign-intercept
2460 @opindex Wno-assign-intercept
2461 Warn whenever an Objective-C assignment is being intercepted by the
2464 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2465 @opindex Wno-protocol
2467 If a class is declared to implement a protocol, a warning is issued for
2468 every method in the protocol that is not implemented by the class. The
2469 default behavior is to issue a warning for every method not explicitly
2470 implemented in the class, even if a method implementation is inherited
2471 from the superclass. If you use the @option{-Wno-protocol} option, then
2472 methods inherited from the superclass are considered to be implemented,
2473 and no warning is issued for them.
2475 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2477 @opindex Wno-selector
2478 Warn if multiple methods of different types for the same selector are
2479 found during compilation. The check is performed on the list of methods
2480 in the final stage of compilation. Additionally, a check is performed
2481 for each selector appearing in a @code{@@selector(@dots{})}
2482 expression, and a corresponding method for that selector has been found
2483 during compilation. Because these checks scan the method table only at
2484 the end of compilation, these warnings are not produced if the final
2485 stage of compilation is not reached, for example because an error is
2486 found during compilation, or because the @option{-fsyntax-only} option is
2489 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2490 @opindex Wstrict-selector-match
2491 @opindex Wno-strict-selector-match
2492 Warn if multiple methods with differing argument and/or return types are
2493 found for a given selector when attempting to send a message using this
2494 selector to a receiver of type @code{id} or @code{Class}. When this flag
2495 is off (which is the default behavior), the compiler will omit such warnings
2496 if any differences found are confined to types which share the same size
2499 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2500 @opindex Wundeclared-selector
2501 @opindex Wno-undeclared-selector
2502 Warn if a @code{@@selector(@dots{})} expression referring to an
2503 undeclared selector is found. A selector is considered undeclared if no
2504 method with that name has been declared before the
2505 @code{@@selector(@dots{})} expression, either explicitly in an
2506 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2507 an @code{@@implementation} section. This option always performs its
2508 checks as soon as a @code{@@selector(@dots{})} expression is found,
2509 while @option{-Wselector} only performs its checks in the final stage of
2510 compilation. This also enforces the coding style convention
2511 that methods and selectors must be declared before being used.
2513 @item -print-objc-runtime-info
2514 @opindex print-objc-runtime-info
2515 Generate C header describing the largest structure that is passed by
2520 @node Language Independent Options
2521 @section Options to Control Diagnostic Messages Formatting
2522 @cindex options to control diagnostics formatting
2523 @cindex diagnostic messages
2524 @cindex message formatting
2526 Traditionally, diagnostic messages have been formatted irrespective of
2527 the output device's aspect (e.g.@: its width, @dots{}). The options described
2528 below can be used to control the diagnostic messages formatting
2529 algorithm, e.g.@: how many characters per line, how often source location
2530 information should be reported. Right now, only the C++ front end can
2531 honor these options. However it is expected, in the near future, that
2532 the remaining front ends would be able to digest them correctly.
2535 @item -fmessage-length=@var{n}
2536 @opindex fmessage-length
2537 Try to format error messages so that they fit on lines of about @var{n}
2538 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2539 the front ends supported by GCC@. If @var{n} is zero, then no
2540 line-wrapping will be done; each error message will appear on a single
2543 @opindex fdiagnostics-show-location
2544 @item -fdiagnostics-show-location=once
2545 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2546 reporter to emit @emph{once} source location information; that is, in
2547 case the message is too long to fit on a single physical line and has to
2548 be wrapped, the source location won't be emitted (as prefix) again,
2549 over and over, in subsequent continuation lines. This is the default
2552 @item -fdiagnostics-show-location=every-line
2553 Only meaningful in line-wrapping mode. Instructs the diagnostic
2554 messages reporter to emit the same source location information (as
2555 prefix) for physical lines that result from the process of breaking
2556 a message which is too long to fit on a single line.
2558 @item -fdiagnostics-show-option
2559 @opindex fdiagnostics-show-option
2560 This option instructs the diagnostic machinery to add text to each
2561 diagnostic emitted, which indicates which command line option directly
2562 controls that diagnostic, when such an option is known to the
2563 diagnostic machinery.
2565 @item -Wcoverage-mismatch
2566 @opindex Wcoverage-mismatch
2567 Warn if feedback profiles do not match when using the
2568 @option{-fprofile-use} option.
2569 If a source file was changed between @option{-fprofile-gen} and
2570 @option{-fprofile-use}, the files with the profile feedback can fail
2571 to match the source file and GCC can not use the profile feedback
2572 information. By default, GCC emits an error message in this case.
2573 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2574 error. GCC does not use appropriate feedback profiles, so using this
2575 option can result in poorly optimized code. This option is useful
2576 only in the case of very minor changes such as bug fixes to an
2581 @node Warning Options
2582 @section Options to Request or Suppress Warnings
2583 @cindex options to control warnings
2584 @cindex warning messages
2585 @cindex messages, warning
2586 @cindex suppressing warnings
2588 Warnings are diagnostic messages that report constructions which
2589 are not inherently erroneous but which are risky or suggest there
2590 may have been an error.
2592 The following language-independent options do not enable specific
2593 warnings but control the kinds of diagnostics produced by GCC.
2596 @cindex syntax checking
2598 @opindex fsyntax-only
2599 Check the code for syntax errors, but don't do anything beyond that.
2603 Inhibit all warning messages.
2608 Make all warnings into errors.
2613 Make the specified warning into an error. The specifier for a warning
2614 is appended, for example @option{-Werror=switch} turns the warnings
2615 controlled by @option{-Wswitch} into errors. This switch takes a
2616 negative form, to be used to negate @option{-Werror} for specific
2617 warnings, for example @option{-Wno-error=switch} makes
2618 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2619 is in effect. You can use the @option{-fdiagnostics-show-option}
2620 option to have each controllable warning amended with the option which
2621 controls it, to determine what to use with this option.
2623 Note that specifying @option{-Werror=}@var{foo} automatically implies
2624 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2627 @item -Wfatal-errors
2628 @opindex Wfatal-errors
2629 @opindex Wno-fatal-errors
2630 This option causes the compiler to abort compilation on the first error
2631 occurred rather than trying to keep going and printing further error
2636 You can request many specific warnings with options beginning
2637 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2638 implicit declarations. Each of these specific warning options also
2639 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2640 example, @option{-Wno-implicit}. This manual lists only one of the
2641 two forms, whichever is not the default. For further,
2642 language-specific options also refer to @ref{C++ Dialect Options} and
2643 @ref{Objective-C and Objective-C++ Dialect Options}.
2648 Issue all the warnings demanded by strict ISO C and ISO C++;
2649 reject all programs that use forbidden extensions, and some other
2650 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2651 version of the ISO C standard specified by any @option{-std} option used.
2653 Valid ISO C and ISO C++ programs should compile properly with or without
2654 this option (though a rare few will require @option{-ansi} or a
2655 @option{-std} option specifying the required version of ISO C)@. However,
2656 without this option, certain GNU extensions and traditional C and C++
2657 features are supported as well. With this option, they are rejected.
2659 @option{-pedantic} does not cause warning messages for use of the
2660 alternate keywords whose names begin and end with @samp{__}. Pedantic
2661 warnings are also disabled in the expression that follows
2662 @code{__extension__}. However, only system header files should use
2663 these escape routes; application programs should avoid them.
2664 @xref{Alternate Keywords}.
2666 Some users try to use @option{-pedantic} to check programs for strict ISO
2667 C conformance. They soon find that it does not do quite what they want:
2668 it finds some non-ISO practices, but not all---only those for which
2669 ISO C @emph{requires} a diagnostic, and some others for which
2670 diagnostics have been added.
2672 A feature to report any failure to conform to ISO C might be useful in
2673 some instances, but would require considerable additional work and would
2674 be quite different from @option{-pedantic}. We don't have plans to
2675 support such a feature in the near future.
2677 Where the standard specified with @option{-std} represents a GNU
2678 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2679 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2680 extended dialect is based. Warnings from @option{-pedantic} are given
2681 where they are required by the base standard. (It would not make sense
2682 for such warnings to be given only for features not in the specified GNU
2683 C dialect, since by definition the GNU dialects of C include all
2684 features the compiler supports with the given option, and there would be
2685 nothing to warn about.)
2687 @item -pedantic-errors
2688 @opindex pedantic-errors
2689 Like @option{-pedantic}, except that errors are produced rather than
2695 This enables all the warnings about constructions that some users
2696 consider questionable, and that are easy to avoid (or modify to
2697 prevent the warning), even in conjunction with macros. This also
2698 enables some language-specific warnings described in @ref{C++ Dialect
2699 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2701 @option{-Wall} turns on the following warning flags:
2703 @gccoptlist{-Waddress @gol
2704 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2706 -Wchar-subscripts @gol
2708 -Wimplicit-function-declaration @gol
2711 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2712 -Wmissing-braces @gol
2718 -Wsequence-point @gol
2719 -Wsign-compare @r{(only in C++)} @gol
2720 -Wstrict-aliasing @gol
2721 -Wstrict-overflow=1 @gol
2724 -Wuninitialized @gol
2725 -Wunknown-pragmas @gol
2726 -Wunused-function @gol
2729 -Wunused-variable @gol
2730 -Wvolatile-register-var @gol
2733 Note that some warning flags are not implied by @option{-Wall}. Some of
2734 them warn about constructions that users generally do not consider
2735 questionable, but which occasionally you might wish to check for;
2736 others warn about constructions that are necessary or hard to avoid in
2737 some cases, and there is no simple way to modify the code to suppress
2738 the warning. Some of them are enabled by @option{-Wextra} but many of
2739 them must be enabled individually.
2745 This enables some extra warning flags that are not enabled by
2746 @option{-Wall}. (This option used to be called @option{-W}. The older
2747 name is still supported, but the newer name is more descriptive.)
2749 @gccoptlist{-Wclobbered @gol
2751 -Wignored-qualifiers @gol
2752 -Wmissing-field-initializers @gol
2753 -Wmissing-parameter-type @r{(C only)} @gol
2754 -Wold-style-declaration @r{(C only)} @gol
2755 -Woverride-init @gol
2758 -Wuninitialized @gol
2759 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2762 The option @option{-Wextra} also prints warning messages for the
2768 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2769 @samp{>}, or @samp{>=}.
2772 (C++ only) An enumerator and a non-enumerator both appear in a
2773 conditional expression.
2776 (C++ only) Ambiguous virtual bases.
2779 (C++ only) Subscripting an array which has been declared @samp{register}.
2782 (C++ only) Taking the address of a variable which has been declared
2786 (C++ only) A base class is not initialized in a derived class' copy
2791 @item -Wchar-subscripts
2792 @opindex Wchar-subscripts
2793 @opindex Wno-char-subscripts
2794 Warn if an array subscript has type @code{char}. This is a common cause
2795 of error, as programmers often forget that this type is signed on some
2797 This warning is enabled by @option{-Wall}.
2801 @opindex Wno-comment
2802 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2803 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2804 This warning is enabled by @option{-Wall}.
2809 @opindex ffreestanding
2810 @opindex fno-builtin
2811 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2812 the arguments supplied have types appropriate to the format string
2813 specified, and that the conversions specified in the format string make
2814 sense. This includes standard functions, and others specified by format
2815 attributes (@pxref{Function Attributes}), in the @code{printf},
2816 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2817 not in the C standard) families (or other target-specific families).
2818 Which functions are checked without format attributes having been
2819 specified depends on the standard version selected, and such checks of
2820 functions without the attribute specified are disabled by
2821 @option{-ffreestanding} or @option{-fno-builtin}.
2823 The formats are checked against the format features supported by GNU
2824 libc version 2.2. These include all ISO C90 and C99 features, as well
2825 as features from the Single Unix Specification and some BSD and GNU
2826 extensions. Other library implementations may not support all these
2827 features; GCC does not support warning about features that go beyond a
2828 particular library's limitations. However, if @option{-pedantic} is used
2829 with @option{-Wformat}, warnings will be given about format features not
2830 in the selected standard version (but not for @code{strfmon} formats,
2831 since those are not in any version of the C standard). @xref{C Dialect
2832 Options,,Options Controlling C Dialect}.
2834 Since @option{-Wformat} also checks for null format arguments for
2835 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2837 @option{-Wformat} is included in @option{-Wall}. For more control over some
2838 aspects of format checking, the options @option{-Wformat-y2k},
2839 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2840 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2841 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2844 @opindex Wformat-y2k
2845 @opindex Wno-format-y2k
2846 If @option{-Wformat} is specified, also warn about @code{strftime}
2847 formats which may yield only a two-digit year.
2849 @item -Wno-format-contains-nul
2850 @opindex Wno-format-contains-nul
2851 @opindex Wformat-contains-nul
2852 If @option{-Wformat} is specified, do not warn about format strings that
2855 @item -Wno-format-extra-args
2856 @opindex Wno-format-extra-args
2857 @opindex Wformat-extra-args
2858 If @option{-Wformat} is specified, do not warn about excess arguments to a
2859 @code{printf} or @code{scanf} format function. The C standard specifies
2860 that such arguments are ignored.
2862 Where the unused arguments lie between used arguments that are
2863 specified with @samp{$} operand number specifications, normally
2864 warnings are still given, since the implementation could not know what
2865 type to pass to @code{va_arg} to skip the unused arguments. However,
2866 in the case of @code{scanf} formats, this option will suppress the
2867 warning if the unused arguments are all pointers, since the Single
2868 Unix Specification says that such unused arguments are allowed.
2870 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2871 @opindex Wno-format-zero-length
2872 @opindex Wformat-zero-length
2873 If @option{-Wformat} is specified, do not warn about zero-length formats.
2874 The C standard specifies that zero-length formats are allowed.
2876 @item -Wformat-nonliteral
2877 @opindex Wformat-nonliteral
2878 @opindex Wno-format-nonliteral
2879 If @option{-Wformat} is specified, also warn if the format string is not a
2880 string literal and so cannot be checked, unless the format function
2881 takes its format arguments as a @code{va_list}.
2883 @item -Wformat-security
2884 @opindex Wformat-security
2885 @opindex Wno-format-security
2886 If @option{-Wformat} is specified, also warn about uses of format
2887 functions that represent possible security problems. At present, this
2888 warns about calls to @code{printf} and @code{scanf} functions where the
2889 format string is not a string literal and there are no format arguments,
2890 as in @code{printf (foo);}. This may be a security hole if the format
2891 string came from untrusted input and contains @samp{%n}. (This is
2892 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2893 in future warnings may be added to @option{-Wformat-security} that are not
2894 included in @option{-Wformat-nonliteral}.)
2898 @opindex Wno-format=2
2899 Enable @option{-Wformat} plus format checks not included in
2900 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2901 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2903 @item -Wnonnull @r{(C and Objective-C only)}
2905 @opindex Wno-nonnull
2906 Warn about passing a null pointer for arguments marked as
2907 requiring a non-null value by the @code{nonnull} function attribute.
2909 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2910 can be disabled with the @option{-Wno-nonnull} option.
2912 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2914 @opindex Wno-init-self
2915 Warn about uninitialized variables which are initialized with themselves.
2916 Note this option can only be used with the @option{-Wuninitialized} option.
2918 For example, GCC will warn about @code{i} being uninitialized in the
2919 following snippet only when @option{-Winit-self} has been specified:
2930 @item -Wimplicit-int @r{(C and Objective-C only)}
2931 @opindex Wimplicit-int
2932 @opindex Wno-implicit-int
2933 Warn when a declaration does not specify a type.
2934 This warning is enabled by @option{-Wall}.
2936 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2937 @opindex Wimplicit-function-declaration
2938 @opindex Wno-implicit-function-declaration
2939 Give a warning whenever a function is used before being declared. In
2940 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2941 enabled by default and it is made into an error by
2942 @option{-pedantic-errors}. This warning is also enabled by
2947 @opindex Wno-implicit
2948 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2949 This warning is enabled by @option{-Wall}.
2951 @item -Wignored-qualifiers @r{(C and C++ only)}
2952 @opindex Wignored-qualifiers
2953 @opindex Wno-ignored-qualifiers
2954 Warn if the return type of a function has a type qualifier
2955 such as @code{const}. For ISO C such a type qualifier has no effect,
2956 since the value returned by a function is not an lvalue.
2957 For C++, the warning is only emitted for scalar types or @code{void}.
2958 ISO C prohibits qualified @code{void} return types on function
2959 definitions, so such return types always receive a warning
2960 even without this option.
2962 This warning is also enabled by @option{-Wextra}.
2967 Warn if the type of @samp{main} is suspicious. @samp{main} should be
2968 a function with external linkage, returning int, taking either zero
2969 arguments, two, or three arguments of appropriate types. This warning
2970 is enabled by default in C++ and is enabled by either @option{-Wall}
2971 or @option{-pedantic}.
2973 @item -Wmissing-braces
2974 @opindex Wmissing-braces
2975 @opindex Wno-missing-braces
2976 Warn if an aggregate or union initializer is not fully bracketed. In
2977 the following example, the initializer for @samp{a} is not fully
2978 bracketed, but that for @samp{b} is fully bracketed.
2981 int a[2][2] = @{ 0, 1, 2, 3 @};
2982 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2985 This warning is enabled by @option{-Wall}.
2987 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2988 @opindex Wmissing-include-dirs
2989 @opindex Wno-missing-include-dirs
2990 Warn if a user-supplied include directory does not exist.
2993 @opindex Wparentheses
2994 @opindex Wno-parentheses
2995 Warn if parentheses are omitted in certain contexts, such
2996 as when there is an assignment in a context where a truth value
2997 is expected, or when operators are nested whose precedence people
2998 often get confused about.
3000 Also warn if a comparison like @samp{x<=y<=z} appears; this is
3001 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
3002 interpretation from that of ordinary mathematical notation.
3004 Also warn about constructions where there may be confusion to which
3005 @code{if} statement an @code{else} branch belongs. Here is an example of
3020 In C/C++, every @code{else} branch belongs to the innermost possible
3021 @code{if} statement, which in this example is @code{if (b)}. This is
3022 often not what the programmer expected, as illustrated in the above
3023 example by indentation the programmer chose. When there is the
3024 potential for this confusion, GCC will issue a warning when this flag
3025 is specified. To eliminate the warning, add explicit braces around
3026 the innermost @code{if} statement so there is no way the @code{else}
3027 could belong to the enclosing @code{if}. The resulting code would
3044 This warning is enabled by @option{-Wall}.
3046 @item -Wsequence-point
3047 @opindex Wsequence-point
3048 @opindex Wno-sequence-point
3049 Warn about code that may have undefined semantics because of violations
3050 of sequence point rules in the C and C++ standards.
3052 The C and C++ standards defines the order in which expressions in a C/C++
3053 program are evaluated in terms of @dfn{sequence points}, which represent
3054 a partial ordering between the execution of parts of the program: those
3055 executed before the sequence point, and those executed after it. These
3056 occur after the evaluation of a full expression (one which is not part
3057 of a larger expression), after the evaluation of the first operand of a
3058 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3059 function is called (but after the evaluation of its arguments and the
3060 expression denoting the called function), and in certain other places.
3061 Other than as expressed by the sequence point rules, the order of
3062 evaluation of subexpressions of an expression is not specified. All
3063 these rules describe only a partial order rather than a total order,
3064 since, for example, if two functions are called within one expression
3065 with no sequence point between them, the order in which the functions
3066 are called is not specified. However, the standards committee have
3067 ruled that function calls do not overlap.
3069 It is not specified when between sequence points modifications to the
3070 values of objects take effect. Programs whose behavior depends on this
3071 have undefined behavior; the C and C++ standards specify that ``Between
3072 the previous and next sequence point an object shall have its stored
3073 value modified at most once by the evaluation of an expression.
3074 Furthermore, the prior value shall be read only to determine the value
3075 to be stored.''. If a program breaks these rules, the results on any
3076 particular implementation are entirely unpredictable.
3078 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3079 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3080 diagnosed by this option, and it may give an occasional false positive
3081 result, but in general it has been found fairly effective at detecting
3082 this sort of problem in programs.
3084 The standard is worded confusingly, therefore there is some debate
3085 over the precise meaning of the sequence point rules in subtle cases.
3086 Links to discussions of the problem, including proposed formal
3087 definitions, may be found on the GCC readings page, at
3088 @w{@uref{http://gcc.gnu.org/readings.html}}.
3090 This warning is enabled by @option{-Wall} for C and C++.
3093 @opindex Wreturn-type
3094 @opindex Wno-return-type
3095 Warn whenever a function is defined with a return-type that defaults
3096 to @code{int}. Also warn about any @code{return} statement with no
3097 return-value in a function whose return-type is not @code{void}
3098 (falling off the end of the function body is considered returning
3099 without a value), and about a @code{return} statement with a
3100 expression in a function whose return-type is @code{void}.
3102 For C++, a function without return type always produces a diagnostic
3103 message, even when @option{-Wno-return-type} is specified. The only
3104 exceptions are @samp{main} and functions defined in system headers.
3106 This warning is enabled by @option{-Wall}.
3111 Warn whenever a @code{switch} statement has an index of enumerated type
3112 and lacks a @code{case} for one or more of the named codes of that
3113 enumeration. (The presence of a @code{default} label prevents this
3114 warning.) @code{case} labels outside the enumeration range also
3115 provoke warnings when this option is used.
3116 This warning is enabled by @option{-Wall}.
3118 @item -Wswitch-default
3119 @opindex Wswitch-default
3120 @opindex Wno-switch-default
3121 Warn whenever a @code{switch} statement does not have a @code{default}
3125 @opindex Wswitch-enum
3126 @opindex Wno-switch-enum
3127 Warn whenever a @code{switch} statement has an index of enumerated type
3128 and lacks a @code{case} for one or more of the named codes of that
3129 enumeration. @code{case} labels outside the enumeration range also
3130 provoke warnings when this option is used.
3134 @opindex Wno-sync-nand
3135 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
3136 built-in functions are used. These functions changed semantics in GCC 4.4.
3140 @opindex Wno-trigraphs
3141 Warn if any trigraphs are encountered that might change the meaning of
3142 the program (trigraphs within comments are not warned about).
3143 This warning is enabled by @option{-Wall}.
3145 @item -Wunused-function
3146 @opindex Wunused-function
3147 @opindex Wno-unused-function
3148 Warn whenever a static function is declared but not defined or a
3149 non-inline static function is unused.
3150 This warning is enabled by @option{-Wall}.
3152 @item -Wunused-label
3153 @opindex Wunused-label
3154 @opindex Wno-unused-label
3155 Warn whenever a label is declared but not used.
3156 This warning is enabled by @option{-Wall}.
3158 To suppress this warning use the @samp{unused} attribute
3159 (@pxref{Variable Attributes}).
3161 @item -Wunused-parameter
3162 @opindex Wunused-parameter
3163 @opindex Wno-unused-parameter
3164 Warn whenever a function parameter is unused aside from its declaration.
3166 To suppress this warning use the @samp{unused} attribute
3167 (@pxref{Variable Attributes}).
3169 @item -Wunused-variable
3170 @opindex Wunused-variable
3171 @opindex Wno-unused-variable
3172 Warn whenever a local variable or non-constant static variable is unused
3173 aside from its declaration.
3174 This warning is enabled by @option{-Wall}.
3176 To suppress this warning use the @samp{unused} attribute
3177 (@pxref{Variable Attributes}).
3179 @item -Wunused-value
3180 @opindex Wunused-value
3181 @opindex Wno-unused-value
3182 Warn whenever a statement computes a result that is explicitly not
3183 used. To suppress this warning cast the unused expression to
3184 @samp{void}. This includes an expression-statement or the left-hand
3185 side of a comma expression that contains no side effects. For example,
3186 an expression such as @samp{x[i,j]} will cause a warning, while
3187 @samp{x[(void)i,j]} will not.
3189 This warning is enabled by @option{-Wall}.
3194 All the above @option{-Wunused} options combined.
3196 In order to get a warning about an unused function parameter, you must
3197 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3198 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3200 @item -Wuninitialized
3201 @opindex Wuninitialized
3202 @opindex Wno-uninitialized
3203 Warn if an automatic variable is used without first being initialized
3204 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3205 warn if a non-static reference or non-static @samp{const} member
3206 appears in a class without constructors.
3208 If you want to warn about code which uses the uninitialized value of the
3209 variable in its own initializer, use the @option{-Winit-self} option.
3211 These warnings occur for individual uninitialized or clobbered
3212 elements of structure, union or array variables as well as for
3213 variables which are uninitialized or clobbered as a whole. They do
3214 not occur for variables or elements declared @code{volatile}. Because
3215 these warnings depend on optimization, the exact variables or elements
3216 for which there are warnings will depend on the precise optimization
3217 options and version of GCC used.
3219 Note that there may be no warning about a variable that is used only
3220 to compute a value that itself is never used, because such
3221 computations may be deleted by data flow analysis before the warnings
3224 These warnings are made optional because GCC is not smart
3225 enough to see all the reasons why the code might be correct
3226 despite appearing to have an error. Here is one example of how
3247 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3248 always initialized, but GCC doesn't know this. Here is
3249 another common case:
3254 if (change_y) save_y = y, y = new_y;
3256 if (change_y) y = save_y;
3261 This has no bug because @code{save_y} is used only if it is set.
3263 @cindex @code{longjmp} warnings
3264 This option also warns when a non-volatile automatic variable might be
3265 changed by a call to @code{longjmp}. These warnings as well are possible
3266 only in optimizing compilation.
3268 The compiler sees only the calls to @code{setjmp}. It cannot know
3269 where @code{longjmp} will be called; in fact, a signal handler could
3270 call it at any point in the code. As a result, you may get a warning
3271 even when there is in fact no problem because @code{longjmp} cannot
3272 in fact be called at the place which would cause a problem.
3274 Some spurious warnings can be avoided if you declare all the functions
3275 you use that never return as @code{noreturn}. @xref{Function
3278 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3280 @item -Wunknown-pragmas
3281 @opindex Wunknown-pragmas
3282 @opindex Wno-unknown-pragmas
3283 @cindex warning for unknown pragmas
3284 @cindex unknown pragmas, warning
3285 @cindex pragmas, warning of unknown
3286 Warn when a #pragma directive is encountered which is not understood by
3287 GCC@. If this command line option is used, warnings will even be issued
3288 for unknown pragmas in system header files. This is not the case if
3289 the warnings were only enabled by the @option{-Wall} command line option.
3292 @opindex Wno-pragmas
3294 Do not warn about misuses of pragmas, such as incorrect parameters,
3295 invalid syntax, or conflicts between pragmas. See also
3296 @samp{-Wunknown-pragmas}.
3298 @item -Wstrict-aliasing
3299 @opindex Wstrict-aliasing
3300 @opindex Wno-strict-aliasing
3301 This option is only active when @option{-fstrict-aliasing} is active.
3302 It warns about code which might break the strict aliasing rules that the
3303 compiler is using for optimization. The warning does not catch all
3304 cases, but does attempt to catch the more common pitfalls. It is
3305 included in @option{-Wall}.
3306 It is equivalent to @option{-Wstrict-aliasing=3}
3308 @item -Wstrict-aliasing=n
3309 @opindex Wstrict-aliasing=n
3310 @opindex Wno-strict-aliasing=n
3311 This option is only active when @option{-fstrict-aliasing} is active.
3312 It warns about code which might break the strict aliasing rules that the
3313 compiler is using for optimization.
3314 Higher levels correspond to higher accuracy (fewer false positives).
3315 Higher levels also correspond to more effort, similar to the way -O works.
3316 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3319 Level 1: Most aggressive, quick, least accurate.
3320 Possibly useful when higher levels
3321 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3322 false negatives. However, it has many false positives.
3323 Warns for all pointer conversions between possibly incompatible types,
3324 even if never dereferenced. Runs in the frontend only.
3326 Level 2: Aggressive, quick, not too precise.
3327 May still have many false positives (not as many as level 1 though),
3328 and few false negatives (but possibly more than level 1).
3329 Unlike level 1, it only warns when an address is taken. Warns about
3330 incomplete types. Runs in the frontend only.
3332 Level 3 (default for @option{-Wstrict-aliasing}):
3333 Should have very few false positives and few false
3334 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3335 Takes care of the common punn+dereference pattern in the frontend:
3336 @code{*(int*)&some_float}.
3337 If optimization is enabled, it also runs in the backend, where it deals
3338 with multiple statement cases using flow-sensitive points-to information.
3339 Only warns when the converted pointer is dereferenced.
3340 Does not warn about incomplete types.
3342 @item -Wstrict-overflow
3343 @itemx -Wstrict-overflow=@var{n}
3344 @opindex Wstrict-overflow
3345 @opindex Wno-strict-overflow
3346 This option is only active when @option{-fstrict-overflow} is active.
3347 It warns about cases where the compiler optimizes based on the
3348 assumption that signed overflow does not occur. Note that it does not
3349 warn about all cases where the code might overflow: it only warns
3350 about cases where the compiler implements some optimization. Thus
3351 this warning depends on the optimization level.
3353 An optimization which assumes that signed overflow does not occur is
3354 perfectly safe if the values of the variables involved are such that
3355 overflow never does, in fact, occur. Therefore this warning can
3356 easily give a false positive: a warning about code which is not
3357 actually a problem. To help focus on important issues, several
3358 warning levels are defined. No warnings are issued for the use of
3359 undefined signed overflow when estimating how many iterations a loop
3360 will require, in particular when determining whether a loop will be
3364 @item -Wstrict-overflow=1
3365 Warn about cases which are both questionable and easy to avoid. For
3366 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3367 compiler will simplify this to @code{1}. This level of
3368 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3369 are not, and must be explicitly requested.
3371 @item -Wstrict-overflow=2
3372 Also warn about other cases where a comparison is simplified to a
3373 constant. For example: @code{abs (x) >= 0}. This can only be
3374 simplified when @option{-fstrict-overflow} is in effect, because
3375 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3376 zero. @option{-Wstrict-overflow} (with no level) is the same as
3377 @option{-Wstrict-overflow=2}.
3379 @item -Wstrict-overflow=3
3380 Also warn about other cases where a comparison is simplified. For
3381 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3383 @item -Wstrict-overflow=4
3384 Also warn about other simplifications not covered by the above cases.
3385 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3387 @item -Wstrict-overflow=5
3388 Also warn about cases where the compiler reduces the magnitude of a
3389 constant involved in a comparison. For example: @code{x + 2 > y} will
3390 be simplified to @code{x + 1 >= y}. This is reported only at the
3391 highest warning level because this simplification applies to many
3392 comparisons, so this warning level will give a very large number of
3396 @item -Warray-bounds
3397 @opindex Wno-array-bounds
3398 @opindex Warray-bounds
3399 This option is only active when @option{-ftree-vrp} is active
3400 (default for -O2 and above). It warns about subscripts to arrays
3401 that are always out of bounds. This warning is enabled by @option{-Wall}.
3403 @item -Wno-div-by-zero
3404 @opindex Wno-div-by-zero
3405 @opindex Wdiv-by-zero
3406 Do not warn about compile-time integer division by zero. Floating point
3407 division by zero is not warned about, as it can be a legitimate way of
3408 obtaining infinities and NaNs.
3410 @item -Wsystem-headers
3411 @opindex Wsystem-headers
3412 @opindex Wno-system-headers
3413 @cindex warnings from system headers
3414 @cindex system headers, warnings from
3415 Print warning messages for constructs found in system header files.
3416 Warnings from system headers are normally suppressed, on the assumption
3417 that they usually do not indicate real problems and would only make the
3418 compiler output harder to read. Using this command line option tells
3419 GCC to emit warnings from system headers as if they occurred in user
3420 code. However, note that using @option{-Wall} in conjunction with this
3421 option will @emph{not} warn about unknown pragmas in system
3422 headers---for that, @option{-Wunknown-pragmas} must also be used.
3425 @opindex Wfloat-equal
3426 @opindex Wno-float-equal
3427 Warn if floating point values are used in equality comparisons.
3429 The idea behind this is that sometimes it is convenient (for the
3430 programmer) to consider floating-point values as approximations to
3431 infinitely precise real numbers. If you are doing this, then you need
3432 to compute (by analyzing the code, or in some other way) the maximum or
3433 likely maximum error that the computation introduces, and allow for it
3434 when performing comparisons (and when producing output, but that's a
3435 different problem). In particular, instead of testing for equality, you
3436 would check to see whether the two values have ranges that overlap; and
3437 this is done with the relational operators, so equality comparisons are
3440 @item -Wtraditional @r{(C and Objective-C only)}
3441 @opindex Wtraditional
3442 @opindex Wno-traditional
3443 Warn about certain constructs that behave differently in traditional and
3444 ISO C@. Also warn about ISO C constructs that have no traditional C
3445 equivalent, and/or problematic constructs which should be avoided.
3449 Macro parameters that appear within string literals in the macro body.
3450 In traditional C macro replacement takes place within string literals,
3451 but does not in ISO C@.
3454 In traditional C, some preprocessor directives did not exist.
3455 Traditional preprocessors would only consider a line to be a directive
3456 if the @samp{#} appeared in column 1 on the line. Therefore
3457 @option{-Wtraditional} warns about directives that traditional C
3458 understands but would ignore because the @samp{#} does not appear as the
3459 first character on the line. It also suggests you hide directives like
3460 @samp{#pragma} not understood by traditional C by indenting them. Some
3461 traditional implementations would not recognize @samp{#elif}, so it
3462 suggests avoiding it altogether.
3465 A function-like macro that appears without arguments.
3468 The unary plus operator.
3471 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3472 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3473 constants.) Note, these suffixes appear in macros defined in the system
3474 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3475 Use of these macros in user code might normally lead to spurious
3476 warnings, however GCC's integrated preprocessor has enough context to
3477 avoid warning in these cases.
3480 A function declared external in one block and then used after the end of
3484 A @code{switch} statement has an operand of type @code{long}.
3487 A non-@code{static} function declaration follows a @code{static} one.
3488 This construct is not accepted by some traditional C compilers.
3491 The ISO type of an integer constant has a different width or
3492 signedness from its traditional type. This warning is only issued if
3493 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3494 typically represent bit patterns, are not warned about.
3497 Usage of ISO string concatenation is detected.
3500 Initialization of automatic aggregates.
3503 Identifier conflicts with labels. Traditional C lacks a separate
3504 namespace for labels.
3507 Initialization of unions. If the initializer is zero, the warning is
3508 omitted. This is done under the assumption that the zero initializer in
3509 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3510 initializer warnings and relies on default initialization to zero in the
3514 Conversions by prototypes between fixed/floating point values and vice
3515 versa. The absence of these prototypes when compiling with traditional
3516 C would cause serious problems. This is a subset of the possible
3517 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3520 Use of ISO C style function definitions. This warning intentionally is
3521 @emph{not} issued for prototype declarations or variadic functions
3522 because these ISO C features will appear in your code when using
3523 libiberty's traditional C compatibility macros, @code{PARAMS} and
3524 @code{VPARAMS}. This warning is also bypassed for nested functions
3525 because that feature is already a GCC extension and thus not relevant to
3526 traditional C compatibility.
3529 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3530 @opindex Wtraditional-conversion
3531 @opindex Wno-traditional-conversion
3532 Warn if a prototype causes a type conversion that is different from what
3533 would happen to the same argument in the absence of a prototype. This
3534 includes conversions of fixed point to floating and vice versa, and
3535 conversions changing the width or signedness of a fixed point argument
3536 except when the same as the default promotion.
3538 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3539 @opindex Wdeclaration-after-statement
3540 @opindex Wno-declaration-after-statement
3541 Warn when a declaration is found after a statement in a block. This
3542 construct, known from C++, was introduced with ISO C99 and is by default
3543 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3544 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3549 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3551 @item -Wno-endif-labels
3552 @opindex Wno-endif-labels
3553 @opindex Wendif-labels
3554 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3559 Warn whenever a local variable shadows another local variable, parameter or
3560 global variable or whenever a built-in function is shadowed.
3562 @item -Wlarger-than=@var{len}
3563 @opindex Wlarger-than=@var{len}
3564 @opindex Wlarger-than-@var{len}
3565 Warn whenever an object of larger than @var{len} bytes is defined.
3567 @item -Wframe-larger-than=@var{len}
3568 @opindex Wframe-larger-than
3569 Warn if the size of a function frame is larger than @var{len} bytes.
3570 The computation done to determine the stack frame size is approximate
3571 and not conservative.
3572 The actual requirements may be somewhat greater than @var{len}
3573 even if you do not get a warning. In addition, any space allocated
3574 via @code{alloca}, variable-length arrays, or related constructs
3575 is not included by the compiler when determining
3576 whether or not to issue a warning.
3578 @item -Wunsafe-loop-optimizations
3579 @opindex Wunsafe-loop-optimizations
3580 @opindex Wno-unsafe-loop-optimizations
3581 Warn if the loop cannot be optimized because the compiler could not
3582 assume anything on the bounds of the loop indices. With
3583 @option{-funsafe-loop-optimizations} warn if the compiler made
3586 @item -Wno-pedantic-ms-format
3587 @opindex Wno-pedantic-ms-format
3588 @opindex Wpedantic-ms-format
3589 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3590 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3591 depending on the MS runtime, when you are using the options @option{-Wformat}
3592 and @option{-pedantic} without gnu-extensions.
3594 @item -Wpointer-arith
3595 @opindex Wpointer-arith
3596 @opindex Wno-pointer-arith
3597 Warn about anything that depends on the ``size of'' a function type or
3598 of @code{void}. GNU C assigns these types a size of 1, for
3599 convenience in calculations with @code{void *} pointers and pointers
3600 to functions. In C++, warn also when an arithmetic operation involves
3601 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3604 @opindex Wtype-limits
3605 @opindex Wno-type-limits
3606 Warn if a comparison is always true or always false due to the limited
3607 range of the data type, but do not warn for constant expressions. For
3608 example, warn if an unsigned variable is compared against zero with
3609 @samp{<} or @samp{>=}. This warning is also enabled by
3612 @item -Wbad-function-cast @r{(C and Objective-C only)}
3613 @opindex Wbad-function-cast
3614 @opindex Wno-bad-function-cast
3615 Warn whenever a function call is cast to a non-matching type.
3616 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3618 @item -Wc++-compat @r{(C and Objective-C only)}
3619 Warn about ISO C constructs that are outside of the common subset of
3620 ISO C and ISO C++, e.g.@: request for implicit conversion from
3621 @code{void *} to a pointer to non-@code{void} type.
3623 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3624 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3625 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3626 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3630 @opindex Wno-cast-qual
3631 Warn whenever a pointer is cast so as to remove a type qualifier from
3632 the target type. For example, warn if a @code{const char *} is cast
3633 to an ordinary @code{char *}.
3636 @opindex Wcast-align
3637 @opindex Wno-cast-align
3638 Warn whenever a pointer is cast such that the required alignment of the
3639 target is increased. For example, warn if a @code{char *} is cast to
3640 an @code{int *} on machines where integers can only be accessed at
3641 two- or four-byte boundaries.
3643 @item -Wwrite-strings
3644 @opindex Wwrite-strings
3645 @opindex Wno-write-strings
3646 When compiling C, give string constants the type @code{const
3647 char[@var{length}]} so that copying the address of one into a
3648 non-@code{const} @code{char *} pointer will get a warning. These
3649 warnings will help you find at compile time code that can try to write
3650 into a string constant, but only if you have been very careful about
3651 using @code{const} in declarations and prototypes. Otherwise, it will
3652 just be a nuisance. This is why we did not make @option{-Wall} request
3655 When compiling C++, warn about the deprecated conversion from string
3656 literals to @code{char *}. This warning is enabled by default for C++
3661 @opindex Wno-clobbered
3662 Warn for variables that might be changed by @samp{longjmp} or
3663 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3666 @opindex Wconversion
3667 @opindex Wno-conversion
3668 Warn for implicit conversions that may alter a value. This includes
3669 conversions between real and integer, like @code{abs (x)} when
3670 @code{x} is @code{double}; conversions between signed and unsigned,
3671 like @code{unsigned ui = -1}; and conversions to smaller types, like
3672 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3673 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3674 changed by the conversion like in @code{abs (2.0)}. Warnings about
3675 conversions between signed and unsigned integers can be disabled by
3676 using @option{-Wno-sign-conversion}.
3678 For C++, also warn for conversions between @code{NULL} and non-pointer
3679 types; confusing overload resolution for user-defined conversions; and
3680 conversions that will never use a type conversion operator:
3681 conversions to @code{void}, the same type, a base class or a reference
3682 to them. Warnings about conversions between signed and unsigned
3683 integers are disabled by default in C++ unless
3684 @option{-Wsign-conversion} is explicitly enabled.
3687 @opindex Wempty-body
3688 @opindex Wno-empty-body
3689 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3690 while} statement. This warning is also enabled by @option{-Wextra}.
3692 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3693 @opindex Wenum-compare
3694 @opindex Wno-enum-compare
3695 Warn about a comparison between values of different enum types. This
3696 warning is enabled by default.
3698 @item -Wsign-compare
3699 @opindex Wsign-compare
3700 @opindex Wno-sign-compare
3701 @cindex warning for comparison of signed and unsigned values
3702 @cindex comparison of signed and unsigned values, warning
3703 @cindex signed and unsigned values, comparison warning
3704 Warn when a comparison between signed and unsigned values could produce
3705 an incorrect result when the signed value is converted to unsigned.
3706 This warning is also enabled by @option{-Wextra}; to get the other warnings
3707 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3709 @item -Wsign-conversion
3710 @opindex Wsign-conversion
3711 @opindex Wno-sign-conversion
3712 Warn for implicit conversions that may change the sign of an integer
3713 value, like assigning a signed integer expression to an unsigned
3714 integer variable. An explicit cast silences the warning. In C, this
3715 option is enabled also by @option{-Wconversion}.
3719 @opindex Wno-address
3720 Warn about suspicious uses of memory addresses. These include using
3721 the address of a function in a conditional expression, such as
3722 @code{void func(void); if (func)}, and comparisons against the memory
3723 address of a string literal, such as @code{if (x == "abc")}. Such
3724 uses typically indicate a programmer error: the address of a function
3725 always evaluates to true, so their use in a conditional usually
3726 indicate that the programmer forgot the parentheses in a function
3727 call; and comparisons against string literals result in unspecified
3728 behavior and are not portable in C, so they usually indicate that the
3729 programmer intended to use @code{strcmp}. This warning is enabled by
3733 @opindex Wlogical-op
3734 @opindex Wno-logical-op
3735 Warn about suspicious uses of logical operators in expressions.
3736 This includes using logical operators in contexts where a
3737 bit-wise operator is likely to be expected.
3739 @item -Waggregate-return
3740 @opindex Waggregate-return
3741 @opindex Wno-aggregate-return
3742 Warn if any functions that return structures or unions are defined or
3743 called. (In languages where you can return an array, this also elicits
3746 @item -Wno-attributes
3747 @opindex Wno-attributes
3748 @opindex Wattributes
3749 Do not warn if an unexpected @code{__attribute__} is used, such as
3750 unrecognized attributes, function attributes applied to variables,
3751 etc. This will not stop errors for incorrect use of supported
3754 @item -Wno-builtin-macro-redefined
3755 @opindex Wno-builtin-macro-redefined
3756 @opindex Wbuiltin-macro-redefined
3757 Do not warn if certain built-in macros are redefined. This suppresses
3758 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
3759 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
3761 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3762 @opindex Wstrict-prototypes
3763 @opindex Wno-strict-prototypes
3764 Warn if a function is declared or defined without specifying the
3765 argument types. (An old-style function definition is permitted without
3766 a warning if preceded by a declaration which specifies the argument
3769 @item -Wold-style-declaration @r{(C and Objective-C only)}
3770 @opindex Wold-style-declaration
3771 @opindex Wno-old-style-declaration
3772 Warn for obsolescent usages, according to the C Standard, in a
3773 declaration. For example, warn if storage-class specifiers like
3774 @code{static} are not the first things in a declaration. This warning
3775 is also enabled by @option{-Wextra}.
3777 @item -Wold-style-definition @r{(C and Objective-C only)}
3778 @opindex Wold-style-definition
3779 @opindex Wno-old-style-definition
3780 Warn if an old-style function definition is used. A warning is given
3781 even if there is a previous prototype.
3783 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3784 @opindex Wmissing-parameter-type
3785 @opindex Wno-missing-parameter-type
3786 A function parameter is declared without a type specifier in K&R-style
3793 This warning is also enabled by @option{-Wextra}.
3795 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3796 @opindex Wmissing-prototypes
3797 @opindex Wno-missing-prototypes
3798 Warn if a global function is defined without a previous prototype
3799 declaration. This warning is issued even if the definition itself
3800 provides a prototype. The aim is to detect global functions that fail
3801 to be declared in header files.
3803 @item -Wmissing-declarations
3804 @opindex Wmissing-declarations
3805 @opindex Wno-missing-declarations
3806 Warn if a global function is defined without a previous declaration.
3807 Do so even if the definition itself provides a prototype.
3808 Use this option to detect global functions that are not declared in
3809 header files. In C++, no warnings are issued for function templates,
3810 or for inline functions, or for functions in anonymous namespaces.
3812 @item -Wmissing-field-initializers
3813 @opindex Wmissing-field-initializers
3814 @opindex Wno-missing-field-initializers
3818 Warn if a structure's initializer has some fields missing. For
3819 example, the following code would cause such a warning, because
3820 @code{x.h} is implicitly zero:
3823 struct s @{ int f, g, h; @};
3824 struct s x = @{ 3, 4 @};
3827 This option does not warn about designated initializers, so the following
3828 modification would not trigger a warning:
3831 struct s @{ int f, g, h; @};
3832 struct s x = @{ .f = 3, .g = 4 @};
3835 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3836 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3838 @item -Wmissing-noreturn
3839 @opindex Wmissing-noreturn
3840 @opindex Wno-missing-noreturn
3841 Warn about functions which might be candidates for attribute @code{noreturn}.
3842 Note these are only possible candidates, not absolute ones. Care should
3843 be taken to manually verify functions actually do not ever return before
3844 adding the @code{noreturn} attribute, otherwise subtle code generation
3845 bugs could be introduced. You will not get a warning for @code{main} in
3846 hosted C environments.
3848 @item -Wmissing-format-attribute
3849 @opindex Wmissing-format-attribute
3850 @opindex Wno-missing-format-attribute
3853 Warn about function pointers which might be candidates for @code{format}
3854 attributes. Note these are only possible candidates, not absolute ones.
3855 GCC will guess that function pointers with @code{format} attributes that
3856 are used in assignment, initialization, parameter passing or return
3857 statements should have a corresponding @code{format} attribute in the
3858 resulting type. I.e.@: the left-hand side of the assignment or
3859 initialization, the type of the parameter variable, or the return type
3860 of the containing function respectively should also have a @code{format}
3861 attribute to avoid the warning.
3863 GCC will also warn about function definitions which might be
3864 candidates for @code{format} attributes. Again, these are only
3865 possible candidates. GCC will guess that @code{format} attributes
3866 might be appropriate for any function that calls a function like
3867 @code{vprintf} or @code{vscanf}, but this might not always be the
3868 case, and some functions for which @code{format} attributes are
3869 appropriate may not be detected.
3871 @item -Wno-multichar
3872 @opindex Wno-multichar
3874 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3875 Usually they indicate a typo in the user's code, as they have
3876 implementation-defined values, and should not be used in portable code.
3878 @item -Wnormalized=<none|id|nfc|nfkc>
3879 @opindex Wnormalized=
3882 @cindex character set, input normalization
3883 In ISO C and ISO C++, two identifiers are different if they are
3884 different sequences of characters. However, sometimes when characters
3885 outside the basic ASCII character set are used, you can have two
3886 different character sequences that look the same. To avoid confusion,
3887 the ISO 10646 standard sets out some @dfn{normalization rules} which
3888 when applied ensure that two sequences that look the same are turned into
3889 the same sequence. GCC can warn you if you are using identifiers which
3890 have not been normalized; this option controls that warning.
3892 There are four levels of warning that GCC supports. The default is
3893 @option{-Wnormalized=nfc}, which warns about any identifier which is
3894 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3895 recommended form for most uses.
3897 Unfortunately, there are some characters which ISO C and ISO C++ allow
3898 in identifiers that when turned into NFC aren't allowable as
3899 identifiers. That is, there's no way to use these symbols in portable
3900 ISO C or C++ and have all your identifiers in NFC@.
3901 @option{-Wnormalized=id} suppresses the warning for these characters.
3902 It is hoped that future versions of the standards involved will correct
3903 this, which is why this option is not the default.
3905 You can switch the warning off for all characters by writing
3906 @option{-Wnormalized=none}. You would only want to do this if you
3907 were using some other normalization scheme (like ``D''), because
3908 otherwise you can easily create bugs that are literally impossible to see.
3910 Some characters in ISO 10646 have distinct meanings but look identical
3911 in some fonts or display methodologies, especially once formatting has
3912 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3913 LETTER N'', will display just like a regular @code{n} which has been
3914 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3915 normalization scheme to convert all these into a standard form as
3916 well, and GCC will warn if your code is not in NFKC if you use
3917 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3918 about every identifier that contains the letter O because it might be
3919 confused with the digit 0, and so is not the default, but may be
3920 useful as a local coding convention if the programming environment is
3921 unable to be fixed to display these characters distinctly.
3923 @item -Wno-deprecated
3924 @opindex Wno-deprecated
3925 @opindex Wdeprecated
3926 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3928 @item -Wno-deprecated-declarations
3929 @opindex Wno-deprecated-declarations
3930 @opindex Wdeprecated-declarations
3931 Do not warn about uses of functions (@pxref{Function Attributes}),
3932 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3933 Attributes}) marked as deprecated by using the @code{deprecated}
3937 @opindex Wno-overflow
3939 Do not warn about compile-time overflow in constant expressions.
3941 @item -Woverride-init @r{(C and Objective-C only)}
3942 @opindex Woverride-init
3943 @opindex Wno-override-init
3947 Warn if an initialized field without side effects is overridden when
3948 using designated initializers (@pxref{Designated Inits, , Designated
3951 This warning is included in @option{-Wextra}. To get other
3952 @option{-Wextra} warnings without this one, use @samp{-Wextra
3953 -Wno-override-init}.
3958 Warn if a structure is given the packed attribute, but the packed
3959 attribute has no effect on the layout or size of the structure.
3960 Such structures may be mis-aligned for little benefit. For
3961 instance, in this code, the variable @code{f.x} in @code{struct bar}
3962 will be misaligned even though @code{struct bar} does not itself
3963 have the packed attribute:
3970 @} __attribute__((packed));
3978 @item -Wpacked-bitfield-compat
3979 @opindex Wpacked-bitfield-compat
3980 @opindex Wno-packed-bitfield-compat
3981 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
3982 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
3983 the change can lead to differences in the structure layout. GCC
3984 informs you when the offset of such a field has changed in GCC 4.4.
3985 For example there is no longer a 4-bit padding between field @code{a}
3986 and @code{b} in this structure:
3993 @} __attribute__ ((packed));
3996 This warning is enabled by default. Use
3997 @option{-Wno-packed-bitfield-compat} to disable this warning.
4002 Warn if padding is included in a structure, either to align an element
4003 of the structure or to align the whole structure. Sometimes when this
4004 happens it is possible to rearrange the fields of the structure to
4005 reduce the padding and so make the structure smaller.
4007 @item -Wredundant-decls
4008 @opindex Wredundant-decls
4009 @opindex Wno-redundant-decls
4010 Warn if anything is declared more than once in the same scope, even in
4011 cases where multiple declaration is valid and changes nothing.
4013 @item -Wnested-externs @r{(C and Objective-C only)}
4014 @opindex Wnested-externs
4015 @opindex Wno-nested-externs
4016 Warn if an @code{extern} declaration is encountered within a function.
4018 @item -Wunreachable-code
4019 @opindex Wunreachable-code
4020 @opindex Wno-unreachable-code
4021 Warn if the compiler detects that code will never be executed.
4023 This option is intended to warn when the compiler detects that at
4024 least a whole line of source code will never be executed, because
4025 some condition is never satisfied or because it is after a
4026 procedure that never returns.
4028 It is possible for this option to produce a warning even though there
4029 are circumstances under which part of the affected line can be executed,
4030 so care should be taken when removing apparently-unreachable code.
4032 For instance, when a function is inlined, a warning may mean that the
4033 line is unreachable in only one inlined copy of the function.
4035 This option is not made part of @option{-Wall} because in a debugging
4036 version of a program there is often substantial code which checks
4037 correct functioning of the program and is, hopefully, unreachable
4038 because the program does work. Another common use of unreachable
4039 code is to provide behavior which is selectable at compile-time.
4044 Warn if a function can not be inlined and it was declared as inline.
4045 Even with this option, the compiler will not warn about failures to
4046 inline functions declared in system headers.
4048 The compiler uses a variety of heuristics to determine whether or not
4049 to inline a function. For example, the compiler takes into account
4050 the size of the function being inlined and the amount of inlining
4051 that has already been done in the current function. Therefore,
4052 seemingly insignificant changes in the source program can cause the
4053 warnings produced by @option{-Winline} to appear or disappear.
4055 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4056 @opindex Wno-invalid-offsetof
4057 @opindex Winvalid-offsetof
4058 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4059 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4060 to a non-POD type is undefined. In existing C++ implementations,
4061 however, @samp{offsetof} typically gives meaningful results even when
4062 applied to certain kinds of non-POD types. (Such as a simple
4063 @samp{struct} that fails to be a POD type only by virtue of having a
4064 constructor.) This flag is for users who are aware that they are
4065 writing nonportable code and who have deliberately chosen to ignore the
4068 The restrictions on @samp{offsetof} may be relaxed in a future version
4069 of the C++ standard.
4071 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4072 @opindex Wno-int-to-pointer-cast
4073 @opindex Wint-to-pointer-cast
4074 Suppress warnings from casts to pointer type of an integer of a
4077 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4078 @opindex Wno-pointer-to-int-cast
4079 @opindex Wpointer-to-int-cast
4080 Suppress warnings from casts from a pointer to an integer type of a
4084 @opindex Winvalid-pch
4085 @opindex Wno-invalid-pch
4086 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4087 the search path but can't be used.
4091 @opindex Wno-long-long
4092 Warn if @samp{long long} type is used. This is default. To inhibit
4093 the warning messages, use @option{-Wno-long-long}. Flags
4094 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4095 only when @option{-pedantic} flag is used.
4097 @item -Wvariadic-macros
4098 @opindex Wvariadic-macros
4099 @opindex Wno-variadic-macros
4100 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4101 alternate syntax when in pedantic ISO C99 mode. This is default.
4102 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4107 Warn if variable length array is used in the code.
4108 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4109 the variable length array.
4111 @item -Wvolatile-register-var
4112 @opindex Wvolatile-register-var
4113 @opindex Wno-volatile-register-var
4114 Warn if a register variable is declared volatile. The volatile
4115 modifier does not inhibit all optimizations that may eliminate reads
4116 and/or writes to register variables. This warning is enabled by
4119 @item -Wdisabled-optimization
4120 @opindex Wdisabled-optimization
4121 @opindex Wno-disabled-optimization
4122 Warn if a requested optimization pass is disabled. This warning does
4123 not generally indicate that there is anything wrong with your code; it
4124 merely indicates that GCC's optimizers were unable to handle the code
4125 effectively. Often, the problem is that your code is too big or too
4126 complex; GCC will refuse to optimize programs when the optimization
4127 itself is likely to take inordinate amounts of time.
4129 @item -Wpointer-sign @r{(C and Objective-C only)}
4130 @opindex Wpointer-sign
4131 @opindex Wno-pointer-sign
4132 Warn for pointer argument passing or assignment with different signedness.
4133 This option is only supported for C and Objective-C@. It is implied by
4134 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4135 @option{-Wno-pointer-sign}.
4137 @item -Wstack-protector
4138 @opindex Wstack-protector
4139 @opindex Wno-stack-protector
4140 This option is only active when @option{-fstack-protector} is active. It
4141 warns about functions that will not be protected against stack smashing.
4144 @opindex Wno-mudflap
4145 Suppress warnings about constructs that cannot be instrumented by
4148 @item -Woverlength-strings
4149 @opindex Woverlength-strings
4150 @opindex Wno-overlength-strings
4151 Warn about string constants which are longer than the ``minimum
4152 maximum'' length specified in the C standard. Modern compilers
4153 generally allow string constants which are much longer than the
4154 standard's minimum limit, but very portable programs should avoid
4155 using longer strings.
4157 The limit applies @emph{after} string constant concatenation, and does
4158 not count the trailing NUL@. In C89, the limit was 509 characters; in
4159 C99, it was raised to 4095. C++98 does not specify a normative
4160 minimum maximum, so we do not diagnose overlength strings in C++@.
4162 This option is implied by @option{-pedantic}, and can be disabled with
4163 @option{-Wno-overlength-strings}.
4165 @item -Wdisallowed-function-list=@var{sym},@var{sym},@dots{}
4166 @opindex Wdisallowed-function-list
4168 If any of @var{sym} is called, GCC will issue a warning. This can be useful
4169 in enforcing coding conventions that ban calls to certain functions, for
4170 example, @code{alloca}, @code{malloc}, etc.
4173 @node Debugging Options
4174 @section Options for Debugging Your Program or GCC
4175 @cindex options, debugging
4176 @cindex debugging information options
4178 GCC has various special options that are used for debugging
4179 either your program or GCC:
4184 Produce debugging information in the operating system's native format
4185 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4188 On most systems that use stabs format, @option{-g} enables use of extra
4189 debugging information that only GDB can use; this extra information
4190 makes debugging work better in GDB but will probably make other debuggers
4192 refuse to read the program. If you want to control for certain whether
4193 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4194 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4196 GCC allows you to use @option{-g} with
4197 @option{-O}. The shortcuts taken by optimized code may occasionally
4198 produce surprising results: some variables you declared may not exist
4199 at all; flow of control may briefly move where you did not expect it;
4200 some statements may not be executed because they compute constant
4201 results or their values were already at hand; some statements may
4202 execute in different places because they were moved out of loops.
4204 Nevertheless it proves possible to debug optimized output. This makes
4205 it reasonable to use the optimizer for programs that might have bugs.
4207 The following options are useful when GCC is generated with the
4208 capability for more than one debugging format.
4212 Produce debugging information for use by GDB@. This means to use the
4213 most expressive format available (DWARF 2, stabs, or the native format
4214 if neither of those are supported), including GDB extensions if at all
4219 Produce debugging information in stabs format (if that is supported),
4220 without GDB extensions. This is the format used by DBX on most BSD
4221 systems. On MIPS, Alpha and System V Release 4 systems this option
4222 produces stabs debugging output which is not understood by DBX or SDB@.
4223 On System V Release 4 systems this option requires the GNU assembler.
4225 @item -feliminate-unused-debug-symbols
4226 @opindex feliminate-unused-debug-symbols
4227 Produce debugging information in stabs format (if that is supported),
4228 for only symbols that are actually used.
4230 @item -femit-class-debug-always
4231 Instead of emitting debugging information for a C++ class in only one
4232 object file, emit it in all object files using the class. This option
4233 should be used only with debuggers that are unable to handle the way GCC
4234 normally emits debugging information for classes because using this
4235 option will increase the size of debugging information by as much as a
4240 Produce debugging information in stabs format (if that is supported),
4241 using GNU extensions understood only by the GNU debugger (GDB)@. The
4242 use of these extensions is likely to make other debuggers crash or
4243 refuse to read the program.
4247 Produce debugging information in COFF format (if that is supported).
4248 This is the format used by SDB on most System V systems prior to
4253 Produce debugging information in XCOFF format (if that is supported).
4254 This is the format used by the DBX debugger on IBM RS/6000 systems.
4258 Produce debugging information in XCOFF format (if that is supported),
4259 using GNU extensions understood only by the GNU debugger (GDB)@. The
4260 use of these extensions is likely to make other debuggers crash or
4261 refuse to read the program, and may cause assemblers other than the GNU
4262 assembler (GAS) to fail with an error.
4266 Produce debugging information in DWARF version 2 format (if that is
4267 supported). This is the format used by DBX on IRIX 6. With this
4268 option, GCC uses features of DWARF version 3 when they are useful;
4269 version 3 is upward compatible with version 2, but may still cause
4270 problems for older debuggers.
4274 Produce debugging information in VMS debug format (if that is
4275 supported). This is the format used by DEBUG on VMS systems.
4278 @itemx -ggdb@var{level}
4279 @itemx -gstabs@var{level}
4280 @itemx -gcoff@var{level}
4281 @itemx -gxcoff@var{level}
4282 @itemx -gvms@var{level}
4283 Request debugging information and also use @var{level} to specify how
4284 much information. The default level is 2.
4286 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4289 Level 1 produces minimal information, enough for making backtraces in
4290 parts of the program that you don't plan to debug. This includes
4291 descriptions of functions and external variables, but no information
4292 about local variables and no line numbers.
4294 Level 3 includes extra information, such as all the macro definitions
4295 present in the program. Some debuggers support macro expansion when
4296 you use @option{-g3}.
4298 @option{-gdwarf-2} does not accept a concatenated debug level, because
4299 GCC used to support an option @option{-gdwarf} that meant to generate
4300 debug information in version 1 of the DWARF format (which is very
4301 different from version 2), and it would have been too confusing. That
4302 debug format is long obsolete, but the option cannot be changed now.
4303 Instead use an additional @option{-g@var{level}} option to change the
4304 debug level for DWARF2.
4306 @item -feliminate-dwarf2-dups
4307 @opindex feliminate-dwarf2-dups
4308 Compress DWARF2 debugging information by eliminating duplicated
4309 information about each symbol. This option only makes sense when
4310 generating DWARF2 debugging information with @option{-gdwarf-2}.
4312 @item -femit-struct-debug-baseonly
4313 Emit debug information for struct-like types
4314 only when the base name of the compilation source file
4315 matches the base name of file in which the struct was defined.
4317 This option substantially reduces the size of debugging information,
4318 but at significant potential loss in type information to the debugger.
4319 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4320 See @option{-femit-struct-debug-detailed} for more detailed control.
4322 This option works only with DWARF 2.
4324 @item -femit-struct-debug-reduced
4325 Emit debug information for struct-like types
4326 only when the base name of the compilation source file
4327 matches the base name of file in which the type was defined,
4328 unless the struct is a template or defined in a system header.
4330 This option significantly reduces the size of debugging information,
4331 with some potential loss in type information to the debugger.
4332 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4333 See @option{-femit-struct-debug-detailed} for more detailed control.
4335 This option works only with DWARF 2.
4337 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4338 Specify the struct-like types
4339 for which the compiler will generate debug information.
4340 The intent is to reduce duplicate struct debug information
4341 between different object files within the same program.
4343 This option is a detailed version of
4344 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4345 which will serve for most needs.
4347 A specification has the syntax
4348 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4350 The optional first word limits the specification to
4351 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4352 A struct type is used directly when it is the type of a variable, member.
4353 Indirect uses arise through pointers to structs.
4354 That is, when use of an incomplete struct would be legal, the use is indirect.
4356 @samp{struct one direct; struct two * indirect;}.
4358 The optional second word limits the specification to
4359 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4360 Generic structs are a bit complicated to explain.
4361 For C++, these are non-explicit specializations of template classes,
4362 or non-template classes within the above.
4363 Other programming languages have generics,
4364 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4366 The third word specifies the source files for those
4367 structs for which the compiler will emit debug information.
4368 The values @samp{none} and @samp{any} have the normal meaning.
4369 The value @samp{base} means that
4370 the base of name of the file in which the type declaration appears
4371 must match the base of the name of the main compilation file.
4372 In practice, this means that
4373 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4374 but types declared in other header will not.
4375 The value @samp{sys} means those types satisfying @samp{base}
4376 or declared in system or compiler headers.
4378 You may need to experiment to determine the best settings for your application.
4380 The default is @samp{-femit-struct-debug-detailed=all}.
4382 This option works only with DWARF 2.
4384 @item -fno-merge-debug-strings
4385 @opindex fmerge-debug-strings
4386 @opindex fno-merge-debug-strings
4387 Direct the linker to merge together strings which are identical in
4388 different object files. This is not supported by all assemblers or
4389 linker. This decreases the size of the debug information in the
4390 output file at the cost of increasing link processing time. This is
4393 @item -fdebug-prefix-map=@var{old}=@var{new}
4394 @opindex fdebug-prefix-map
4395 When compiling files in directory @file{@var{old}}, record debugging
4396 information describing them as in @file{@var{new}} instead.
4398 @item -fno-dwarf2-cfi-asm
4399 @opindex fdwarf2-cfi-asm
4400 @opindex fno-dwarf2-cfi-asm
4401 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4402 instead of using GAS @code{.cfi_*} directives.
4404 @cindex @command{prof}
4407 Generate extra code to write profile information suitable for the
4408 analysis program @command{prof}. You must use this option when compiling
4409 the source files you want data about, and you must also use it when
4412 @cindex @command{gprof}
4415 Generate extra code to write profile information suitable for the
4416 analysis program @command{gprof}. You must use this option when compiling
4417 the source files you want data about, and you must also use it when
4422 Makes the compiler print out each function name as it is compiled, and
4423 print some statistics about each pass when it finishes.
4426 @opindex ftime-report
4427 Makes the compiler print some statistics about the time consumed by each
4428 pass when it finishes.
4431 @opindex fmem-report
4432 Makes the compiler print some statistics about permanent memory
4433 allocation when it finishes.
4435 @item -fpre-ipa-mem-report
4436 @opindex fpre-ipa-mem-report
4437 @item -fpost-ipa-mem-report
4438 @opindex fpost-ipa-mem-report
4439 Makes the compiler print some statistics about permanent memory
4440 allocation before or after interprocedural optimization.
4442 @item -fprofile-arcs
4443 @opindex fprofile-arcs
4444 Add code so that program flow @dfn{arcs} are instrumented. During
4445 execution the program records how many times each branch and call is
4446 executed and how many times it is taken or returns. When the compiled
4447 program exits it saves this data to a file called
4448 @file{@var{auxname}.gcda} for each source file. The data may be used for
4449 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4450 test coverage analysis (@option{-ftest-coverage}). Each object file's
4451 @var{auxname} is generated from the name of the output file, if
4452 explicitly specified and it is not the final executable, otherwise it is
4453 the basename of the source file. In both cases any suffix is removed
4454 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4455 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4456 @xref{Cross-profiling}.
4458 @cindex @command{gcov}
4462 This option is used to compile and link code instrumented for coverage
4463 analysis. The option is a synonym for @option{-fprofile-arcs}
4464 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4465 linking). See the documentation for those options for more details.
4470 Compile the source files with @option{-fprofile-arcs} plus optimization
4471 and code generation options. For test coverage analysis, use the
4472 additional @option{-ftest-coverage} option. You do not need to profile
4473 every source file in a program.
4476 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4477 (the latter implies the former).
4480 Run the program on a representative workload to generate the arc profile
4481 information. This may be repeated any number of times. You can run
4482 concurrent instances of your program, and provided that the file system
4483 supports locking, the data files will be correctly updated. Also
4484 @code{fork} calls are detected and correctly handled (double counting
4488 For profile-directed optimizations, compile the source files again with
4489 the same optimization and code generation options plus
4490 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4491 Control Optimization}).
4494 For test coverage analysis, use @command{gcov} to produce human readable
4495 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4496 @command{gcov} documentation for further information.
4500 With @option{-fprofile-arcs}, for each function of your program GCC
4501 creates a program flow graph, then finds a spanning tree for the graph.
4502 Only arcs that are not on the spanning tree have to be instrumented: the
4503 compiler adds code to count the number of times that these arcs are
4504 executed. When an arc is the only exit or only entrance to a block, the
4505 instrumentation code can be added to the block; otherwise, a new basic
4506 block must be created to hold the instrumentation code.
4509 @item -ftest-coverage
4510 @opindex ftest-coverage
4511 Produce a notes file that the @command{gcov} code-coverage utility
4512 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4513 show program coverage. Each source file's note file is called
4514 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4515 above for a description of @var{auxname} and instructions on how to
4516 generate test coverage data. Coverage data will match the source files
4517 more closely, if you do not optimize.
4519 @item -fdbg-cnt-list
4520 @opindex fdbg-cnt-list
4521 Print the name and the counter upperbound for all debug counters.
4523 @item -fdbg-cnt=@var{counter-value-list}
4525 Set the internal debug counter upperbound. @var{counter-value-list}
4526 is a comma-separated list of @var{name}:@var{value} pairs
4527 which sets the upperbound of each debug counter @var{name} to @var{value}.
4528 All debug counters have the initial upperbound of @var{UINT_MAX},
4529 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4530 e.g. With -fdbg-cnt=dce:10,tail_call:0
4531 dbg_cnt(dce) will return true only for first 10 invocations
4532 and dbg_cnt(tail_call) will return false always.
4534 @item -d@var{letters}
4535 @itemx -fdump-rtl-@var{pass}
4537 Says to make debugging dumps during compilation at times specified by
4538 @var{letters}. This is used for debugging the RTL-based passes of the
4539 compiler. The file names for most of the dumps are made by appending a
4540 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4541 from the name of the output file, if explicitly specified and it is not
4542 an executable, otherwise it is the basename of the source file. These
4543 switches may have different effects when @option{-E} is used for
4546 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
4547 @option{-d} option @var{letters}. Here are the possible
4548 letters for use in @var{letters} and @var{pass}, and their meanings:
4553 Annotate the assembler output with miscellaneous debugging information.
4555 @item -fdump-rtl-bbro
4556 @opindex fdump-rtl-bbro
4557 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4559 @item -fdump-rtl-combine
4560 @opindex fdump-rtl-combine
4561 Dump after the RTL instruction combination pass, to the file
4562 @file{@var{file}.129r.combine}.
4564 @item -fdump-rtl-ce1
4565 @itemx -fdump-rtl-ce2
4566 @opindex fdump-rtl-ce1
4567 @opindex fdump-rtl-ce2
4568 @option{-fdump-rtl-ce1} enable dumping after the
4569 first if conversion, to the file @file{@var{file}.117r.ce1}.
4570 @option{-fdump-rtl-ce2} enable dumping after the second if
4571 conversion, to the file @file{@var{file}.130r.ce2}.
4573 @item -fdump-rtl-btl
4574 @itemx -fdump-rtl-dbr
4575 @opindex fdump-rtl-btl
4576 @opindex fdump-rtl-dbr
4577 @option{-fdump-rtl-btl} enable dumping after branch
4578 target load optimization, to @file{@var{file}.31.btl}.
4579 @option{-fdump-rtl-dbr} enable dumping after delayed branch
4580 scheduling, to @file{@var{file}.36.dbr}.
4584 Dump all macro definitions, at the end of preprocessing, in addition to
4587 @item -fdump-rtl-ce3
4588 @opindex fdump-rtl-ce3
4589 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4591 @item -fdump-rtl-cfg
4592 @itemx -fdump-rtl-life
4593 @opindex fdump-rtl-cfg
4594 @opindex fdump-rtl-life
4595 @option{-fdump-rtl-cfg} enable dumping after control
4596 and data flow analysis, to @file{@var{file}.116r.cfg}.
4597 @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4598 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4600 @item -fdump-rtl-greg
4601 @opindex fdump-rtl-greg
4602 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4604 @item -fdump-rtl-gcse
4605 @itemx -fdump-rtl-bypass
4606 @opindex fdump-rtl-gcse
4607 @opindex fdump-rtl-bypass
4608 @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4609 @file{@var{file}.114r.gcse}. @option{-fdump-rtl-bypass}
4610 enable dumping after jump bypassing and control flow optimizations, to
4611 @file{@var{file}.115r.bypass}.
4614 @opindex fdump-rtl-eh
4615 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4617 @item -fdump-rtl-sibling
4618 @opindex fdump-rtl-sibling
4619 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4621 @item -fdump-rtl-jump
4622 @opindex fdump-rtl-jump
4623 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4625 @item -fdump-rtl-stack
4626 @opindex fdump-rtl-stack
4627 Dump after conversion from GCC's "flat register file" registers to the
4628 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4630 @item -fdump-rtl-lreg
4631 @opindex fdump-rtl-lreg
4632 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4634 @item -fdump-rtl-loop2
4635 @opindex fdump-rtl-loop2
4636 @option{-fdump-rtl-loop2} enables dumping after the
4637 loop optimization pass, to @file{@var{file}.119r.loop2},
4638 @file{@var{file}.120r.loop2_init},
4639 @file{@var{file}.121r.loop2_invariant}, and
4640 @file{@var{file}.125r.loop2_done}.
4642 @item -fdump-rtl-sms
4643 @opindex fdump-rtl-sms
4644 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4646 @item -fdump-rtl-mach
4647 @opindex fdump-rtl-mach
4648 Dump after performing the machine dependent reorganization pass, to
4649 @file{@var{file}.155r.mach} if that pass exists.
4651 @item -fdump-rtl-rnreg
4652 @opindex fdump-rtl-rnreg
4653 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4655 @item -fdump-rtl-regmove
4656 @opindex fdump-rtl-regmove
4657 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4659 @item -fdump-rtl-postreload
4660 @opindex fdump-rtl-postreload
4661 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4663 @item -fdump-rtl-expand
4664 @opindex fdump-rtl-expand
4665 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4667 @item -fdump-rtl-sched2
4668 @opindex fdump-rtl-sched2
4669 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4671 @item -fdump-rtl-cse
4672 @opindex fdump-rtl-cse
4673 Dump after CSE (including the jump optimization that sometimes follows
4674 CSE), to @file{@var{file}.113r.cse}.
4676 @item -fdump-rtl-sched1
4677 @opindex fdump-rtl-sched1
4678 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4680 @item -fdump-rtl-cse2
4681 @opindex fdump-rtl-cse2
4682 Dump after the second CSE pass (including the jump optimization that
4683 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4685 @item -fdump-rtl-tracer
4686 @opindex fdump-rtl-tracer
4687 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4689 @item -fdump-rtl-vpt
4690 @itemx -fdump-rtl-vartrack
4691 @opindex fdump-rtl-vpt
4692 @opindex fdump-rtl-vartrack
4693 @option{-fdump-rtl-vpt} enable dumping after the value
4694 profile transformations, to @file{@var{file}.10.vpt}.
4695 @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4696 to @file{@var{file}.154r.vartrack}.
4698 @item -fdump-rtl-flow2
4699 @opindex fdump-rtl-flow2
4700 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4702 @item -fdump-rtl-peephole2
4703 @opindex fdump-rtl-peephole2
4704 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4706 @item -fdump-rtl-web
4707 @opindex fdump-rtl-web
4708 Dump after live range splitting, to @file{@var{file}.126r.web}.
4710 @item -fdump-rtl-all
4711 @opindex fdump-rtl-all
4712 Produce all the dumps listed above.
4716 Produce a core dump whenever an error occurs.
4720 Print statistics on memory usage, at the end of the run, to
4725 Annotate the assembler output with a comment indicating which
4726 pattern and alternative was used. The length of each instruction is
4731 Dump the RTL in the assembler output as a comment before each instruction.
4732 Also turns on @option{-dp} annotation.
4736 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
4737 dump a representation of the control flow graph suitable for viewing with VCG
4738 to @file{@var{file}.@var{pass}.vcg}.
4742 Just generate RTL for a function instead of compiling it. Usually used
4743 with @option{-fdump-rtl-expand}.
4747 Dump debugging information during parsing, to standard error.
4751 @opindex fdump-noaddr
4752 When doing debugging dumps, suppress address output. This makes it more
4753 feasible to use diff on debugging dumps for compiler invocations with
4754 different compiler binaries and/or different
4755 text / bss / data / heap / stack / dso start locations.
4757 @item -fdump-unnumbered
4758 @opindex fdump-unnumbered
4759 When doing debugging dumps, suppress instruction numbers and address output.
4760 This makes it more feasible to use diff on debugging dumps for compiler
4761 invocations with different options, in particular with and without
4764 @item -fdump-translation-unit @r{(C++ only)}
4765 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4766 @opindex fdump-translation-unit
4767 Dump a representation of the tree structure for the entire translation
4768 unit to a file. The file name is made by appending @file{.tu} to the
4769 source file name. If the @samp{-@var{options}} form is used, @var{options}
4770 controls the details of the dump as described for the
4771 @option{-fdump-tree} options.
4773 @item -fdump-class-hierarchy @r{(C++ only)}
4774 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4775 @opindex fdump-class-hierarchy
4776 Dump a representation of each class's hierarchy and virtual function
4777 table layout to a file. The file name is made by appending @file{.class}
4778 to the source file name. If the @samp{-@var{options}} form is used,
4779 @var{options} controls the details of the dump as described for the
4780 @option{-fdump-tree} options.
4782 @item -fdump-ipa-@var{switch}
4784 Control the dumping at various stages of inter-procedural analysis
4785 language tree to a file. The file name is generated by appending a switch
4786 specific suffix to the source file name. The following dumps are possible:
4790 Enables all inter-procedural analysis dumps.
4793 Dumps information about call-graph optimization, unused function removal,
4794 and inlining decisions.
4797 Dump after function inlining.
4801 @item -fdump-statistics-@var{option}
4802 @opindex -fdump-statistics
4803 Enable and control dumping of pass statistics in a separate file. The
4804 file name is generated by appending a suffix ending in @samp{.statistics}
4805 to the source file name. If the @samp{-@var{option}} form is used,
4806 @samp{-stats} will cause counters to be summed over the whole compilation unit
4807 while @samp{-details} will dump every event as the passes generate them.
4808 The default with no option is to sum counters for each function compiled.
4810 @item -fdump-tree-@var{switch}
4811 @itemx -fdump-tree-@var{switch}-@var{options}
4813 Control the dumping at various stages of processing the intermediate
4814 language tree to a file. The file name is generated by appending a switch
4815 specific suffix to the source file name. If the @samp{-@var{options}}
4816 form is used, @var{options} is a list of @samp{-} separated options that
4817 control the details of the dump. Not all options are applicable to all
4818 dumps, those which are not meaningful will be ignored. The following
4819 options are available
4823 Print the address of each node. Usually this is not meaningful as it
4824 changes according to the environment and source file. Its primary use
4825 is for tying up a dump file with a debug environment.
4827 Inhibit dumping of members of a scope or body of a function merely
4828 because that scope has been reached. Only dump such items when they
4829 are directly reachable by some other path. When dumping pretty-printed
4830 trees, this option inhibits dumping the bodies of control structures.
4832 Print a raw representation of the tree. By default, trees are
4833 pretty-printed into a C-like representation.
4835 Enable more detailed dumps (not honored by every dump option).
4837 Enable dumping various statistics about the pass (not honored by every dump
4840 Enable showing basic block boundaries (disabled in raw dumps).
4842 Enable showing virtual operands for every statement.
4844 Enable showing line numbers for statements.
4846 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4848 Enable showing the tree dump for each statement.
4850 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4851 and @option{lineno}.
4854 The following tree dumps are possible:
4858 Dump before any tree based optimization, to @file{@var{file}.original}.
4861 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4864 @opindex fdump-tree-gimple
4865 Dump each function before and after the gimplification pass to a file. The
4866 file name is made by appending @file{.gimple} to the source file name.
4869 @opindex fdump-tree-cfg
4870 Dump the control flow graph of each function to a file. The file name is
4871 made by appending @file{.cfg} to the source file name.
4874 @opindex fdump-tree-vcg
4875 Dump the control flow graph of each function to a file in VCG format. The
4876 file name is made by appending @file{.vcg} to the source file name. Note
4877 that if the file contains more than one function, the generated file cannot
4878 be used directly by VCG@. You will need to cut and paste each function's
4879 graph into its own separate file first.
4882 @opindex fdump-tree-ch
4883 Dump each function after copying loop headers. The file name is made by
4884 appending @file{.ch} to the source file name.
4887 @opindex fdump-tree-ssa
4888 Dump SSA related information to a file. The file name is made by appending
4889 @file{.ssa} to the source file name.
4892 @opindex fdump-tree-alias
4893 Dump aliasing information for each function. The file name is made by
4894 appending @file{.alias} to the source file name.
4897 @opindex fdump-tree-ccp
4898 Dump each function after CCP@. The file name is made by appending
4899 @file{.ccp} to the source file name.
4902 @opindex fdump-tree-storeccp
4903 Dump each function after STORE-CCP@. The file name is made by appending
4904 @file{.storeccp} to the source file name.
4907 @opindex fdump-tree-pre
4908 Dump trees after partial redundancy elimination. The file name is made
4909 by appending @file{.pre} to the source file name.
4912 @opindex fdump-tree-fre
4913 Dump trees after full redundancy elimination. The file name is made
4914 by appending @file{.fre} to the source file name.
4917 @opindex fdump-tree-copyprop
4918 Dump trees after copy propagation. The file name is made
4919 by appending @file{.copyprop} to the source file name.
4921 @item store_copyprop
4922 @opindex fdump-tree-store_copyprop
4923 Dump trees after store copy-propagation. The file name is made
4924 by appending @file{.store_copyprop} to the source file name.
4927 @opindex fdump-tree-dce
4928 Dump each function after dead code elimination. The file name is made by
4929 appending @file{.dce} to the source file name.
4932 @opindex fdump-tree-mudflap
4933 Dump each function after adding mudflap instrumentation. The file name is
4934 made by appending @file{.mudflap} to the source file name.
4937 @opindex fdump-tree-sra
4938 Dump each function after performing scalar replacement of aggregates. The
4939 file name is made by appending @file{.sra} to the source file name.
4942 @opindex fdump-tree-sink
4943 Dump each function after performing code sinking. The file name is made
4944 by appending @file{.sink} to the source file name.
4947 @opindex fdump-tree-dom
4948 Dump each function after applying dominator tree optimizations. The file
4949 name is made by appending @file{.dom} to the source file name.
4952 @opindex fdump-tree-dse
4953 Dump each function after applying dead store elimination. The file
4954 name is made by appending @file{.dse} to the source file name.
4957 @opindex fdump-tree-phiopt
4958 Dump each function after optimizing PHI nodes into straightline code. The file
4959 name is made by appending @file{.phiopt} to the source file name.
4962 @opindex fdump-tree-forwprop
4963 Dump each function after forward propagating single use variables. The file
4964 name is made by appending @file{.forwprop} to the source file name.
4967 @opindex fdump-tree-copyrename
4968 Dump each function after applying the copy rename optimization. The file
4969 name is made by appending @file{.copyrename} to the source file name.
4972 @opindex fdump-tree-nrv
4973 Dump each function after applying the named return value optimization on
4974 generic trees. The file name is made by appending @file{.nrv} to the source
4978 @opindex fdump-tree-vect
4979 Dump each function after applying vectorization of loops. The file name is
4980 made by appending @file{.vect} to the source file name.
4983 @opindex fdump-tree-vrp
4984 Dump each function after Value Range Propagation (VRP). The file name
4985 is made by appending @file{.vrp} to the source file name.
4988 @opindex fdump-tree-all
4989 Enable all the available tree dumps with the flags provided in this option.
4992 @item -ftree-vectorizer-verbose=@var{n}
4993 @opindex ftree-vectorizer-verbose
4994 This option controls the amount of debugging output the vectorizer prints.
4995 This information is written to standard error, unless
4996 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4997 in which case it is output to the usual dump listing file, @file{.vect}.
4998 For @var{n}=0 no diagnostic information is reported.
4999 If @var{n}=1 the vectorizer reports each loop that got vectorized,
5000 and the total number of loops that got vectorized.
5001 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
5002 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
5003 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
5004 level that @option{-fdump-tree-vect-stats} uses.
5005 Higher verbosity levels mean either more information dumped for each
5006 reported loop, or same amount of information reported for more loops:
5007 If @var{n}=3, alignment related information is added to the reports.
5008 If @var{n}=4, data-references related information (e.g.@: memory dependences,
5009 memory access-patterns) is added to the reports.
5010 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
5011 that did not pass the first analysis phase (i.e., may not be countable, or
5012 may have complicated control-flow).
5013 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
5014 For @var{n}=7, all the information the vectorizer generates during its
5015 analysis and transformation is reported. This is the same verbosity level
5016 that @option{-fdump-tree-vect-details} uses.
5018 @item -frandom-seed=@var{string}
5019 @opindex frandom-string
5020 This option provides a seed that GCC uses when it would otherwise use
5021 random numbers. It is used to generate certain symbol names
5022 that have to be different in every compiled file. It is also used to
5023 place unique stamps in coverage data files and the object files that
5024 produce them. You can use the @option{-frandom-seed} option to produce
5025 reproducibly identical object files.
5027 The @var{string} should be different for every file you compile.
5029 @item -fsched-verbose=@var{n}
5030 @opindex fsched-verbose
5031 On targets that use instruction scheduling, this option controls the
5032 amount of debugging output the scheduler prints. This information is
5033 written to standard error, unless @option{-fdump-rtl-sched1} or
5034 @option{-fdump-rtl-sched2} is specified, in which case it is output
5035 to the usual dump listing file, @file{.sched} or @file{.sched2}
5036 respectively. However for @var{n} greater than nine, the output is
5037 always printed to standard error.
5039 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5040 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5041 For @var{n} greater than one, it also output basic block probabilities,
5042 detailed ready list information and unit/insn info. For @var{n} greater
5043 than two, it includes RTL at abort point, control-flow and regions info.
5044 And for @var{n} over four, @option{-fsched-verbose} also includes
5049 Store the usual ``temporary'' intermediate files permanently; place them
5050 in the current directory and name them based on the source file. Thus,
5051 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5052 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5053 preprocessed @file{foo.i} output file even though the compiler now
5054 normally uses an integrated preprocessor.
5056 When used in combination with the @option{-x} command line option,
5057 @option{-save-temps} is sensible enough to avoid over writing an
5058 input source file with the same extension as an intermediate file.
5059 The corresponding intermediate file may be obtained by renaming the
5060 source file before using @option{-save-temps}.
5064 Report the CPU time taken by each subprocess in the compilation
5065 sequence. For C source files, this is the compiler proper and assembler
5066 (plus the linker if linking is done). The output looks like this:
5073 The first number on each line is the ``user time'', that is time spent
5074 executing the program itself. The second number is ``system time'',
5075 time spent executing operating system routines on behalf of the program.
5076 Both numbers are in seconds.
5078 @item -fvar-tracking
5079 @opindex fvar-tracking
5080 Run variable tracking pass. It computes where variables are stored at each
5081 position in code. Better debugging information is then generated
5082 (if the debugging information format supports this information).
5084 It is enabled by default when compiling with optimization (@option{-Os},
5085 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5086 the debug info format supports it.
5088 @item -print-file-name=@var{library}
5089 @opindex print-file-name
5090 Print the full absolute name of the library file @var{library} that
5091 would be used when linking---and don't do anything else. With this
5092 option, GCC does not compile or link anything; it just prints the
5095 @item -print-multi-directory
5096 @opindex print-multi-directory
5097 Print the directory name corresponding to the multilib selected by any
5098 other switches present in the command line. This directory is supposed
5099 to exist in @env{GCC_EXEC_PREFIX}.
5101 @item -print-multi-lib
5102 @opindex print-multi-lib
5103 Print the mapping from multilib directory names to compiler switches
5104 that enable them. The directory name is separated from the switches by
5105 @samp{;}, and each switch starts with an @samp{@@} instead of the
5106 @samp{-}, without spaces between multiple switches. This is supposed to
5107 ease shell-processing.
5109 @item -print-prog-name=@var{program}
5110 @opindex print-prog-name
5111 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5113 @item -print-libgcc-file-name
5114 @opindex print-libgcc-file-name
5115 Same as @option{-print-file-name=libgcc.a}.
5117 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5118 but you do want to link with @file{libgcc.a}. You can do
5121 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5124 @item -print-search-dirs
5125 @opindex print-search-dirs
5126 Print the name of the configured installation directory and a list of
5127 program and library directories @command{gcc} will search---and don't do anything else.
5129 This is useful when @command{gcc} prints the error message
5130 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5131 To resolve this you either need to put @file{cpp0} and the other compiler
5132 components where @command{gcc} expects to find them, or you can set the environment
5133 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5134 Don't forget the trailing @samp{/}.
5135 @xref{Environment Variables}.
5137 @item -print-sysroot
5138 @opindex print-sysroot
5139 Print the target sysroot directory that will be used during
5140 compilation. This is the target sysroot specified either at configure
5141 time or using the @option{--sysroot} option, possibly with an extra
5142 suffix that depends on compilation options. If no target sysroot is
5143 specified, the option prints nothing.
5145 @item -print-sysroot-headers-suffix
5146 @opindex print-sysroot-headers-suffix
5147 Print the suffix added to the target sysroot when searching for
5148 headers, or give an error if the compiler is not configured with such
5149 a suffix---and don't do anything else.
5152 @opindex dumpmachine
5153 Print the compiler's target machine (for example,
5154 @samp{i686-pc-linux-gnu})---and don't do anything else.
5157 @opindex dumpversion
5158 Print the compiler version (for example, @samp{3.0})---and don't do
5163 Print the compiler's built-in specs---and don't do anything else. (This
5164 is used when GCC itself is being built.) @xref{Spec Files}.
5166 @item -feliminate-unused-debug-types
5167 @opindex feliminate-unused-debug-types
5168 Normally, when producing DWARF2 output, GCC will emit debugging
5169 information for all types declared in a compilation
5170 unit, regardless of whether or not they are actually used
5171 in that compilation unit. Sometimes this is useful, such as
5172 if, in the debugger, you want to cast a value to a type that is
5173 not actually used in your program (but is declared). More often,
5174 however, this results in a significant amount of wasted space.
5175 With this option, GCC will avoid producing debug symbol output
5176 for types that are nowhere used in the source file being compiled.
5179 @node Optimize Options
5180 @section Options That Control Optimization
5181 @cindex optimize options
5182 @cindex options, optimization
5184 These options control various sorts of optimizations.
5186 Without any optimization option, the compiler's goal is to reduce the
5187 cost of compilation and to make debugging produce the expected
5188 results. Statements are independent: if you stop the program with a
5189 breakpoint between statements, you can then assign a new value to any
5190 variable or change the program counter to any other statement in the
5191 function and get exactly the results you would expect from the source
5194 Turning on optimization flags makes the compiler attempt to improve
5195 the performance and/or code size at the expense of compilation time
5196 and possibly the ability to debug the program.
5198 The compiler performs optimization based on the knowledge it has of the
5199 program. Compiling multiple files at once to a single output file mode allows
5200 the compiler to use information gained from all of the files when compiling
5203 Not all optimizations are controlled directly by a flag. Only
5204 optimizations that have a flag are listed.
5211 Optimize. Optimizing compilation takes somewhat more time, and a lot
5212 more memory for a large function.
5214 With @option{-O}, the compiler tries to reduce code size and execution
5215 time, without performing any optimizations that take a great deal of
5218 @option{-O} turns on the following optimization flags:
5221 -fcprop-registers @gol
5224 -fdelayed-branch @gol
5226 -fguess-branch-probability @gol
5227 -fif-conversion2 @gol
5228 -fif-conversion @gol
5229 -finline-small-functions @gol
5230 -fipa-pure-const @gol
5231 -fipa-reference @gol
5233 -fsplit-wide-types @gol
5234 -ftree-builtin-call-dce @gol
5237 -ftree-copyrename @gol
5239 -ftree-dominator-opts @gol
5246 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5247 where doing so does not interfere with debugging.
5251 Optimize even more. GCC performs nearly all supported optimizations
5252 that do not involve a space-speed tradeoff. The compiler does not
5253 perform loop unrolling or function inlining when you specify @option{-O2}.
5254 As compared to @option{-O}, this option increases both compilation time
5255 and the performance of the generated code.
5257 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5258 also turns on the following optimization flags:
5259 @gccoptlist{-fthread-jumps @gol
5260 -falign-functions -falign-jumps @gol
5261 -falign-loops -falign-labels @gol
5264 -fcse-follow-jumps -fcse-skip-blocks @gol
5265 -fdelete-null-pointer-checks @gol
5266 -fexpensive-optimizations @gol
5267 -fgcse -fgcse-lm @gol
5268 -findirect-inlining @gol
5269 -foptimize-sibling-calls @gol
5272 -freorder-blocks -freorder-functions @gol
5273 -frerun-cse-after-loop @gol
5274 -fsched-interblock -fsched-spec @gol
5275 -fschedule-insns -fschedule-insns2 @gol
5276 -fstrict-aliasing -fstrict-overflow @gol
5277 -ftree-switch-conversion @gol
5281 Please note the warning under @option{-fgcse} about
5282 invoking @option{-O2} on programs that use computed gotos.
5286 Optimize yet more. @option{-O3} turns on all optimizations specified
5287 by @option{-O2} and also turns on the @option{-finline-functions},
5288 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5289 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5293 Reduce compilation time and make debugging produce the expected
5294 results. This is the default.
5298 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5299 do not typically increase code size. It also performs further
5300 optimizations designed to reduce code size.
5302 @option{-Os} disables the following optimization flags:
5303 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5304 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5305 -fprefetch-loop-arrays -ftree-vect-loop-version}
5307 If you use multiple @option{-O} options, with or without level numbers,
5308 the last such option is the one that is effective.
5311 Options of the form @option{-f@var{flag}} specify machine-independent
5312 flags. Most flags have both positive and negative forms; the negative
5313 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5314 below, only one of the forms is listed---the one you typically will
5315 use. You can figure out the other form by either removing @samp{no-}
5318 The following options control specific optimizations. They are either
5319 activated by @option{-O} options or are related to ones that are. You
5320 can use the following flags in the rare cases when ``fine-tuning'' of
5321 optimizations to be performed is desired.
5324 @item -fno-default-inline
5325 @opindex fno-default-inline
5326 Do not make member functions inline by default merely because they are
5327 defined inside the class scope (C++ only). Otherwise, when you specify
5328 @w{@option{-O}}, member functions defined inside class scope are compiled
5329 inline by default; i.e., you don't need to add @samp{inline} in front of
5330 the member function name.
5332 @item -fno-defer-pop
5333 @opindex fno-defer-pop
5334 Always pop the arguments to each function call as soon as that function
5335 returns. For machines which must pop arguments after a function call,
5336 the compiler normally lets arguments accumulate on the stack for several
5337 function calls and pops them all at once.
5339 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5341 @item -fforward-propagate
5342 @opindex fforward-propagate
5343 Perform a forward propagation pass on RTL@. The pass tries to combine two
5344 instructions and checks if the result can be simplified. If loop unrolling
5345 is active, two passes are performed and the second is scheduled after
5348 This option is enabled by default at optimization levels @option{-O2},
5349 @option{-O3}, @option{-Os}.
5351 @item -fomit-frame-pointer
5352 @opindex fomit-frame-pointer
5353 Don't keep the frame pointer in a register for functions that
5354 don't need one. This avoids the instructions to save, set up and
5355 restore frame pointers; it also makes an extra register available
5356 in many functions. @strong{It also makes debugging impossible on
5359 On some machines, such as the VAX, this flag has no effect, because
5360 the standard calling sequence automatically handles the frame pointer
5361 and nothing is saved by pretending it doesn't exist. The
5362 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5363 whether a target machine supports this flag. @xref{Registers,,Register
5364 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5366 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5368 @item -foptimize-sibling-calls
5369 @opindex foptimize-sibling-calls
5370 Optimize sibling and tail recursive calls.
5372 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5376 Don't pay attention to the @code{inline} keyword. Normally this option
5377 is used to keep the compiler from expanding any functions inline.
5378 Note that if you are not optimizing, no functions can be expanded inline.
5380 @item -finline-small-functions
5381 @opindex finline-small-functions
5382 Integrate functions into their callers when their body is smaller than expected
5383 function call code (so overall size of program gets smaller). The compiler
5384 heuristically decides which functions are simple enough to be worth integrating
5387 Enabled at level @option{-O2}.
5389 @item -findirect-inlining
5390 @opindex findirect-inlining
5391 Inline also indirect calls that are discovered to be known at compile
5392 time thanks to previous inlining. This option has any effect only
5393 when inlining itself is turned on by the @option{-finline-functions}
5394 or @option{-finline-small-functions} options.
5396 Enabled at level @option{-O2}.
5398 @item -finline-functions
5399 @opindex finline-functions
5400 Integrate all simple functions into their callers. The compiler
5401 heuristically decides which functions are simple enough to be worth
5402 integrating in this way.
5404 If all calls to a given function are integrated, and the function is
5405 declared @code{static}, then the function is normally not output as
5406 assembler code in its own right.
5408 Enabled at level @option{-O3}.
5410 @item -finline-functions-called-once
5411 @opindex finline-functions-called-once
5412 Consider all @code{static} functions called once for inlining into their
5413 caller even if they are not marked @code{inline}. If a call to a given
5414 function is integrated, then the function is not output as assembler code
5417 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5419 @item -fearly-inlining
5420 @opindex fearly-inlining
5421 Inline functions marked by @code{always_inline} and functions whose body seems
5422 smaller than the function call overhead early before doing
5423 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5424 makes profiling significantly cheaper and usually inlining faster on programs
5425 having large chains of nested wrapper functions.
5429 @item -finline-limit=@var{n}
5430 @opindex finline-limit
5431 By default, GCC limits the size of functions that can be inlined. This flag
5432 allows coarse control of this limit. @var{n} is the size of functions that
5433 can be inlined in number of pseudo instructions.
5435 Inlining is actually controlled by a number of parameters, which may be
5436 specified individually by using @option{--param @var{name}=@var{value}}.
5437 The @option{-finline-limit=@var{n}} option sets some of these parameters
5441 @item max-inline-insns-single
5442 is set to @var{n}/2.
5443 @item max-inline-insns-auto
5444 is set to @var{n}/2.
5447 See below for a documentation of the individual
5448 parameters controlling inlining and for the defaults of these parameters.
5450 @emph{Note:} there may be no value to @option{-finline-limit} that results
5451 in default behavior.
5453 @emph{Note:} pseudo instruction represents, in this particular context, an
5454 abstract measurement of function's size. In no way does it represent a count
5455 of assembly instructions and as such its exact meaning might change from one
5456 release to an another.
5458 @item -fkeep-inline-functions
5459 @opindex fkeep-inline-functions
5460 In C, emit @code{static} functions that are declared @code{inline}
5461 into the object file, even if the function has been inlined into all
5462 of its callers. This switch does not affect functions using the
5463 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5464 inline functions into the object file.
5466 @item -fkeep-static-consts
5467 @opindex fkeep-static-consts
5468 Emit variables declared @code{static const} when optimization isn't turned
5469 on, even if the variables aren't referenced.
5471 GCC enables this option by default. If you want to force the compiler to
5472 check if the variable was referenced, regardless of whether or not
5473 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5475 @item -fmerge-constants
5476 @opindex fmerge-constants
5477 Attempt to merge identical constants (string constants and floating point
5478 constants) across compilation units.
5480 This option is the default for optimized compilation if the assembler and
5481 linker support it. Use @option{-fno-merge-constants} to inhibit this
5484 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5486 @item -fmerge-all-constants
5487 @opindex fmerge-all-constants
5488 Attempt to merge identical constants and identical variables.
5490 This option implies @option{-fmerge-constants}. In addition to
5491 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5492 arrays or initialized constant variables with integral or floating point
5493 types. Languages like C or C++ require each variable, including multiple
5494 instances of the same variable in recursive calls, to have distinct locations,
5495 so using this option will result in non-conforming
5498 @item -fmodulo-sched
5499 @opindex fmodulo-sched
5500 Perform swing modulo scheduling immediately before the first scheduling
5501 pass. This pass looks at innermost loops and reorders their
5502 instructions by overlapping different iterations.
5504 @item -fmodulo-sched-allow-regmoves
5505 @opindex fmodulo-sched-allow-regmoves
5506 Perform more aggressive SMS based modulo scheduling with register moves
5507 allowed. By setting this flag certain anti-dependences edges will be
5508 deleted which will trigger the generation of reg-moves based on the
5509 life-range analysis. This option is effective only with
5510 @option{-fmodulo-sched} enabled.
5512 @item -fno-branch-count-reg
5513 @opindex fno-branch-count-reg
5514 Do not use ``decrement and branch'' instructions on a count register,
5515 but instead generate a sequence of instructions that decrement a
5516 register, compare it against zero, then branch based upon the result.
5517 This option is only meaningful on architectures that support such
5518 instructions, which include x86, PowerPC, IA-64 and S/390.
5520 The default is @option{-fbranch-count-reg}.
5522 @item -fno-function-cse
5523 @opindex fno-function-cse
5524 Do not put function addresses in registers; make each instruction that
5525 calls a constant function contain the function's address explicitly.
5527 This option results in less efficient code, but some strange hacks
5528 that alter the assembler output may be confused by the optimizations
5529 performed when this option is not used.
5531 The default is @option{-ffunction-cse}
5533 @item -fno-zero-initialized-in-bss
5534 @opindex fno-zero-initialized-in-bss
5535 If the target supports a BSS section, GCC by default puts variables that
5536 are initialized to zero into BSS@. This can save space in the resulting
5539 This option turns off this behavior because some programs explicitly
5540 rely on variables going to the data section. E.g., so that the
5541 resulting executable can find the beginning of that section and/or make
5542 assumptions based on that.
5544 The default is @option{-fzero-initialized-in-bss}.
5546 @item -fmudflap -fmudflapth -fmudflapir
5550 @cindex bounds checking
5552 For front-ends that support it (C and C++), instrument all risky
5553 pointer/array dereferencing operations, some standard library
5554 string/heap functions, and some other associated constructs with
5555 range/validity tests. Modules so instrumented should be immune to
5556 buffer overflows, invalid heap use, and some other classes of C/C++
5557 programming errors. The instrumentation relies on a separate runtime
5558 library (@file{libmudflap}), which will be linked into a program if
5559 @option{-fmudflap} is given at link time. Run-time behavior of the
5560 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5561 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5564 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5565 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5566 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5567 instrumentation should ignore pointer reads. This produces less
5568 instrumentation (and therefore faster execution) and still provides
5569 some protection against outright memory corrupting writes, but allows
5570 erroneously read data to propagate within a program.
5572 @item -fthread-jumps
5573 @opindex fthread-jumps
5574 Perform optimizations where we check to see if a jump branches to a
5575 location where another comparison subsumed by the first is found. If
5576 so, the first branch is redirected to either the destination of the
5577 second branch or a point immediately following it, depending on whether
5578 the condition is known to be true or false.
5580 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5582 @item -fsplit-wide-types
5583 @opindex fsplit-wide-types
5584 When using a type that occupies multiple registers, such as @code{long
5585 long} on a 32-bit system, split the registers apart and allocate them
5586 independently. This normally generates better code for those types,
5587 but may make debugging more difficult.
5589 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5592 @item -fcse-follow-jumps
5593 @opindex fcse-follow-jumps
5594 In common subexpression elimination (CSE), scan through jump instructions
5595 when the target of the jump is not reached by any other path. For
5596 example, when CSE encounters an @code{if} statement with an
5597 @code{else} clause, CSE will follow the jump when the condition
5600 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5602 @item -fcse-skip-blocks
5603 @opindex fcse-skip-blocks
5604 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5605 follow jumps which conditionally skip over blocks. When CSE
5606 encounters a simple @code{if} statement with no else clause,
5607 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5608 body of the @code{if}.
5610 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5612 @item -frerun-cse-after-loop
5613 @opindex frerun-cse-after-loop
5614 Re-run common subexpression elimination after loop optimizations has been
5617 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5621 Perform a global common subexpression elimination pass.
5622 This pass also performs global constant and copy propagation.
5624 @emph{Note:} When compiling a program using computed gotos, a GCC
5625 extension, you may get better runtime performance if you disable
5626 the global common subexpression elimination pass by adding
5627 @option{-fno-gcse} to the command line.
5629 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5633 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5634 attempt to move loads which are only killed by stores into themselves. This
5635 allows a loop containing a load/store sequence to be changed to a load outside
5636 the loop, and a copy/store within the loop.
5638 Enabled by default when gcse is enabled.
5642 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5643 global common subexpression elimination. This pass will attempt to move
5644 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5645 loops containing a load/store sequence can be changed to a load before
5646 the loop and a store after the loop.
5648 Not enabled at any optimization level.
5652 When @option{-fgcse-las} is enabled, the global common subexpression
5653 elimination pass eliminates redundant loads that come after stores to the
5654 same memory location (both partial and full redundancies).
5656 Not enabled at any optimization level.
5658 @item -fgcse-after-reload
5659 @opindex fgcse-after-reload
5660 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5661 pass is performed after reload. The purpose of this pass is to cleanup
5664 @item -funsafe-loop-optimizations
5665 @opindex funsafe-loop-optimizations
5666 If given, the loop optimizer will assume that loop indices do not
5667 overflow, and that the loops with nontrivial exit condition are not
5668 infinite. This enables a wider range of loop optimizations even if
5669 the loop optimizer itself cannot prove that these assumptions are valid.
5670 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5671 if it finds this kind of loop.
5673 @item -fcrossjumping
5674 @opindex fcrossjumping
5675 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5676 resulting code may or may not perform better than without cross-jumping.
5678 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5680 @item -fauto-inc-dec
5681 @opindex fauto-inc-dec
5682 Combine increments or decrements of addresses with memory accesses.
5683 This pass is always skipped on architectures that do not have
5684 instructions to support this. Enabled by default at @option{-O} and
5685 higher on architectures that support this.
5689 Perform dead code elimination (DCE) on RTL@.
5690 Enabled by default at @option{-O} and higher.
5694 Perform dead store elimination (DSE) on RTL@.
5695 Enabled by default at @option{-O} and higher.
5697 @item -fif-conversion
5698 @opindex fif-conversion
5699 Attempt to transform conditional jumps into branch-less equivalents. This
5700 include use of conditional moves, min, max, set flags and abs instructions, and
5701 some tricks doable by standard arithmetics. The use of conditional execution
5702 on chips where it is available is controlled by @code{if-conversion2}.
5704 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5706 @item -fif-conversion2
5707 @opindex fif-conversion2
5708 Use conditional execution (where available) to transform conditional jumps into
5709 branch-less equivalents.
5711 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5713 @item -fdelete-null-pointer-checks
5714 @opindex fdelete-null-pointer-checks
5715 Use global dataflow analysis to identify and eliminate useless checks
5716 for null pointers. The compiler assumes that dereferencing a null
5717 pointer would have halted the program. If a pointer is checked after
5718 it has already been dereferenced, it cannot be null.
5720 In some environments, this assumption is not true, and programs can
5721 safely dereference null pointers. Use
5722 @option{-fno-delete-null-pointer-checks} to disable this optimization
5723 for programs which depend on that behavior.
5725 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5727 @item -fexpensive-optimizations
5728 @opindex fexpensive-optimizations
5729 Perform a number of minor optimizations that are relatively expensive.
5731 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5733 @item -foptimize-register-move
5735 @opindex foptimize-register-move
5737 Attempt to reassign register numbers in move instructions and as
5738 operands of other simple instructions in order to maximize the amount of
5739 register tying. This is especially helpful on machines with two-operand
5742 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5745 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5749 Use the integrated register allocator (@acronym{IRA}) for register
5750 allocation. It is a default if @acronym{IRA} has been ported for the
5753 @item -fira-algorithm=@var{algorithm}
5754 Use specified coloring algorithm for the integrated register
5755 allocator. The @var{algorithm} argument should be @code{priority} or
5756 @code{CB}. The first algorithm specifies Chow's priority coloring,
5757 the second one specifies Chaitin-Briggs coloring. The second
5758 algorithm can be unimplemented for some architectures. If it is
5759 implemented, it is the default because Chaitin-Briggs coloring as a
5760 rule generates a better code.
5762 @item -fira-region=@var{region}
5763 Use specified regions for the integrated register allocator. The
5764 @var{region} argument should be one of @code{all}, @code{mixed}, or
5765 @code{one}. The first value means using all loops as register
5766 allocation regions, the second value which is the default means using
5767 all loops except for loops with small register pressure as the
5768 regions, and third one means using all function as a single region.
5769 The first value can give best result for machines with small size and
5770 irregular register set, the third one results in faster and generates
5771 decent code and the smallest size code, and the default value usually
5772 give the best results in most cases and for most architectures.
5774 @item -fira-coalesce
5775 @opindex fira-coalesce
5776 Do optimistic register coalescing. This option might be profitable for
5777 architectures with big regular register files.
5779 @item -fno-ira-share-save-slots
5780 @opindex fno-ira-share-save-slots
5781 Switch off sharing stack slots used for saving call used hard
5782 registers living through a call. Each hard register will get a
5783 separate stack slot and as a result function stack frame will be
5786 @item -fno-ira-share-spill-slots
5787 @opindex fno-ira-share-spill-slots
5788 Switch off sharing stack slots allocated for pseudo-registers. Each
5789 pseudo-register which did not get a hard register will get a separate
5790 stack slot and as a result function stack frame will be bigger.
5792 @item -fira-verbose=@var{n}
5793 @opindex fira-verbose
5794 Set up how verbose dump file for the integrated register allocator
5795 will be. Default value is 5. If the value is greater or equal to 10,
5796 the dump file will be stderr as if the value were @var{n} minus 10.
5798 @item -fdelayed-branch
5799 @opindex fdelayed-branch
5800 If supported for the target machine, attempt to reorder instructions
5801 to exploit instruction slots available after delayed branch
5804 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5806 @item -fschedule-insns
5807 @opindex fschedule-insns
5808 If supported for the target machine, attempt to reorder instructions to
5809 eliminate execution stalls due to required data being unavailable. This
5810 helps machines that have slow floating point or memory load instructions
5811 by allowing other instructions to be issued until the result of the load
5812 or floating point instruction is required.
5814 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5816 @item -fschedule-insns2
5817 @opindex fschedule-insns2
5818 Similar to @option{-fschedule-insns}, but requests an additional pass of
5819 instruction scheduling after register allocation has been done. This is
5820 especially useful on machines with a relatively small number of
5821 registers and where memory load instructions take more than one cycle.
5823 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5825 @item -fno-sched-interblock
5826 @opindex fno-sched-interblock
5827 Don't schedule instructions across basic blocks. This is normally
5828 enabled by default when scheduling before register allocation, i.e.@:
5829 with @option{-fschedule-insns} or at @option{-O2} or higher.
5831 @item -fno-sched-spec
5832 @opindex fno-sched-spec
5833 Don't allow speculative motion of non-load instructions. This is normally
5834 enabled by default when scheduling before register allocation, i.e.@:
5835 with @option{-fschedule-insns} or at @option{-O2} or higher.
5837 @item -fsched-spec-load
5838 @opindex fsched-spec-load
5839 Allow speculative motion of some load instructions. This only makes
5840 sense when scheduling before register allocation, i.e.@: with
5841 @option{-fschedule-insns} or at @option{-O2} or higher.
5843 @item -fsched-spec-load-dangerous
5844 @opindex fsched-spec-load-dangerous
5845 Allow speculative motion of more load instructions. This only makes
5846 sense when scheduling before register allocation, i.e.@: with
5847 @option{-fschedule-insns} or at @option{-O2} or higher.
5849 @item -fsched-stalled-insns
5850 @itemx -fsched-stalled-insns=@var{n}
5851 @opindex fsched-stalled-insns
5852 Define how many insns (if any) can be moved prematurely from the queue
5853 of stalled insns into the ready list, during the second scheduling pass.
5854 @option{-fno-sched-stalled-insns} means that no insns will be moved
5855 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5856 on how many queued insns can be moved prematurely.
5857 @option{-fsched-stalled-insns} without a value is equivalent to
5858 @option{-fsched-stalled-insns=1}.
5860 @item -fsched-stalled-insns-dep
5861 @itemx -fsched-stalled-insns-dep=@var{n}
5862 @opindex fsched-stalled-insns-dep
5863 Define how many insn groups (cycles) will be examined for a dependency
5864 on a stalled insn that is candidate for premature removal from the queue
5865 of stalled insns. This has an effect only during the second scheduling pass,
5866 and only if @option{-fsched-stalled-insns} is used.
5867 @option{-fno-sched-stalled-insns-dep} is equivalent to
5868 @option{-fsched-stalled-insns-dep=0}.
5869 @option{-fsched-stalled-insns-dep} without a value is equivalent to
5870 @option{-fsched-stalled-insns-dep=1}.
5872 @item -fsched2-use-superblocks
5873 @opindex fsched2-use-superblocks
5874 When scheduling after register allocation, do use superblock scheduling
5875 algorithm. Superblock scheduling allows motion across basic block boundaries
5876 resulting on faster schedules. This option is experimental, as not all machine
5877 descriptions used by GCC model the CPU closely enough to avoid unreliable
5878 results from the algorithm.
5880 This only makes sense when scheduling after register allocation, i.e.@: with
5881 @option{-fschedule-insns2} or at @option{-O2} or higher.
5883 @item -fsched2-use-traces
5884 @opindex fsched2-use-traces
5885 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5886 allocation and additionally perform code duplication in order to increase the
5887 size of superblocks using tracer pass. See @option{-ftracer} for details on
5890 This mode should produce faster but significantly longer programs. Also
5891 without @option{-fbranch-probabilities} the traces constructed may not
5892 match the reality and hurt the performance. This only makes
5893 sense when scheduling after register allocation, i.e.@: with
5894 @option{-fschedule-insns2} or at @option{-O2} or higher.
5898 Eliminate redundant sign extension instructions and move the non-redundant
5899 ones to optimal placement using lazy code motion (LCM).
5901 @item -freschedule-modulo-scheduled-loops
5902 @opindex freschedule-modulo-scheduled-loops
5903 The modulo scheduling comes before the traditional scheduling, if a loop
5904 was modulo scheduled we may want to prevent the later scheduling passes
5905 from changing its schedule, we use this option to control that.
5907 @item -fselective-scheduling
5908 @opindex fselective-scheduling
5909 Schedule instructions using selective scheduling algorithm. Selective
5910 scheduling runs instead of the first scheduler pass.
5912 @item -fselective-scheduling2
5913 @opindex fselective-scheduling2
5914 Schedule instructions using selective scheduling algorithm. Selective
5915 scheduling runs instead of the second scheduler pass.
5917 @item -fsel-sched-pipelining
5918 @opindex fsel-sched-pipelining
5919 Enable software pipelining of innermost loops during selective scheduling.
5920 This option has no effect until one of @option{-fselective-scheduling} or
5921 @option{-fselective-scheduling2} is turned on.
5923 @item -fsel-sched-pipelining-outer-loops
5924 @opindex fsel-sched-pipelining-outer-loops
5925 When pipelining loops during selective scheduling, also pipeline outer loops.
5926 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
5928 @item -fcaller-saves
5929 @opindex fcaller-saves
5930 Enable values to be allocated in registers that will be clobbered by
5931 function calls, by emitting extra instructions to save and restore the
5932 registers around such calls. Such allocation is done only when it
5933 seems to result in better code than would otherwise be produced.
5935 This option is always enabled by default on certain machines, usually
5936 those which have no call-preserved registers to use instead.
5938 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5940 @item -fconserve-stack
5941 @opindex fconserve-stack
5942 Attempt to minimize stack usage. The compiler will attempt to use less
5943 stack space, even if that makes the program slower. This option
5944 implies setting the @option{large-stack-frame} parameter to 100
5945 and the @option{large-stack-frame-growth} parameter to 400.
5947 @item -ftree-reassoc
5948 @opindex ftree-reassoc
5949 Perform reassociation on trees. This flag is enabled by default
5950 at @option{-O} and higher.
5954 Perform partial redundancy elimination (PRE) on trees. This flag is
5955 enabled by default at @option{-O2} and @option{-O3}.
5959 Perform full redundancy elimination (FRE) on trees. The difference
5960 between FRE and PRE is that FRE only considers expressions
5961 that are computed on all paths leading to the redundant computation.
5962 This analysis is faster than PRE, though it exposes fewer redundancies.
5963 This flag is enabled by default at @option{-O} and higher.
5965 @item -ftree-copy-prop
5966 @opindex ftree-copy-prop
5967 Perform copy propagation on trees. This pass eliminates unnecessary
5968 copy operations. This flag is enabled by default at @option{-O} and
5971 @item -fipa-pure-const
5972 @opindex fipa-pure-const
5973 Discover which functions are pure or constant.
5974 Enabled by default at @option{-O} and higher.
5976 @item -fipa-reference
5977 @opindex fipa-reference
5978 Discover which static variables do not escape cannot escape the
5980 Enabled by default at @option{-O} and higher.
5982 @item -fipa-struct-reorg
5983 @opindex fipa-struct-reorg
5984 Perform structure reorganization optimization, that change C-like structures
5985 layout in order to better utilize spatial locality. This transformation is
5986 affective for programs containing arrays of structures. Available in two
5987 compilation modes: profile-based (enabled with @option{-fprofile-generate})
5988 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
5989 to provide the safety of this transformation. It works only in whole program
5990 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
5991 enabled. Structures considered @samp{cold} by this transformation are not
5992 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
5994 With this flag, the program debug info reflects a new structure layout.
5998 Perform interprocedural pointer analysis. This option is experimental
5999 and does not affect generated code.
6003 Perform interprocedural constant propagation.
6004 This optimization analyzes the program to determine when values passed
6005 to functions are constants and then optimizes accordingly.
6006 This optimization can substantially increase performance
6007 if the application has constants passed to functions.
6008 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
6010 @item -fipa-cp-clone
6011 @opindex fipa-cp-clone
6012 Perform function cloning to make interprocedural constant propagation stronger.
6013 When enabled, interprocedural constant propagation will perform function cloning
6014 when externally visible function can be called with constant arguments.
6015 Because this optimization can create multiple copies of functions,
6016 it may significantly increase code size
6017 (see @option{--param ipcp-unit-growth=@var{value}}).
6018 This flag is enabled by default at @option{-O3}.
6020 @item -fipa-matrix-reorg
6021 @opindex fipa-matrix-reorg
6022 Perform matrix flattening and transposing.
6023 Matrix flattening tries to replace a m-dimensional matrix
6024 with its equivalent n-dimensional matrix, where n < m.
6025 This reduces the level of indirection needed for accessing the elements
6026 of the matrix. The second optimization is matrix transposing that
6027 attemps to change the order of the matrix's dimensions in order to
6028 improve cache locality.
6029 Both optimizations need the @option{-fwhole-program} flag.
6030 Transposing is enabled only if profiling information is available.
6035 Perform forward store motion on trees. This flag is
6036 enabled by default at @option{-O} and higher.
6040 Perform sparse conditional constant propagation (CCP) on trees. This
6041 pass only operates on local scalar variables and is enabled by default
6042 at @option{-O} and higher.
6044 @item -ftree-switch-conversion
6045 Perform conversion of simple initializations in a switch to
6046 initializations from a scalar array. This flag is enabled by default
6047 at @option{-O2} and higher.
6051 Perform dead code elimination (DCE) on trees. This flag is enabled by
6052 default at @option{-O} and higher.
6054 @item -ftree-builtin-call-dce
6055 @opindex ftree-builtin-call-dce
6056 Perform conditional dead code elimination (DCE) for calls to builtin functions
6057 that may set @code{errno} but are otherwise side-effect free. This flag is
6058 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6061 @item -ftree-dominator-opts
6062 @opindex ftree-dominator-opts
6063 Perform a variety of simple scalar cleanups (constant/copy
6064 propagation, redundancy elimination, range propagation and expression
6065 simplification) based on a dominator tree traversal. This also
6066 performs jump threading (to reduce jumps to jumps). This flag is
6067 enabled by default at @option{-O} and higher.
6071 Perform dead store elimination (DSE) on trees. A dead store is a store into
6072 a memory location which will later be overwritten by another store without
6073 any intervening loads. In this case the earlier store can be deleted. This
6074 flag is enabled by default at @option{-O} and higher.
6078 Perform loop header copying on trees. This is beneficial since it increases
6079 effectiveness of code motion optimizations. It also saves one jump. This flag
6080 is enabled by default at @option{-O} and higher. It is not enabled
6081 for @option{-Os}, since it usually increases code size.
6083 @item -ftree-loop-optimize
6084 @opindex ftree-loop-optimize
6085 Perform loop optimizations on trees. This flag is enabled by default
6086 at @option{-O} and higher.
6088 @item -ftree-loop-linear
6089 @opindex ftree-loop-linear
6090 Perform linear loop transformations on tree. This flag can improve cache
6091 performance and allow further loop optimizations to take place.
6093 @item -floop-interchange
6094 Perform loop interchange transformations on loops. Interchanging two
6095 nested loops switches the inner and outer loops. For example, given a
6100 A(J, I) = A(J, I) * C
6104 loop interchange will transform the loop as if the user had written:
6108 A(J, I) = A(J, I) * C
6112 which can be beneficial when @code{N} is larger than the caches,
6113 because in Fortran, the elements of an array are stored in memory
6114 contiguously by column, and the original loop iterates over rows,
6115 potentially creating at each access a cache miss. This optimization
6116 applies to all the languages supported by GCC and is not limited to
6119 @item -floop-strip-mine
6120 Perform loop strip mining transformations on loops. Strip mining
6121 splits a loop into two nested loops. The outer loop has strides
6122 equal to the strip size and the inner loop has strides of the
6123 original loop within a strip. For example, given a loop like:
6129 loop strip mining will transform the loop as if the user had written:
6132 DO I = II, min (II + 3, N)
6137 This optimization applies to all the languages supported by GCC and is
6138 not limited to Fortran.
6141 Perform loop blocking transformations on loops. Blocking strip mines
6142 each loop in the loop nest such that the memory accesses of the
6143 element loops fit inside caches. For example, given a loop like:
6147 A(J, I) = B(I) + C(J)
6151 loop blocking will transform the loop as if the user had written:
6155 DO I = II, min (II + 63, N)
6156 DO J = JJ, min (JJ + 63, M)
6157 A(J, I) = B(I) + C(J)
6163 which can be beneficial when @code{M} is larger than the caches,
6164 because the innermost loop will iterate over a smaller amount of data
6165 that can be kept in the caches. This optimization applies to all the
6166 languages supported by GCC and is not limited to Fortran.
6168 @item -fcheck-data-deps
6169 @opindex fcheck-data-deps
6170 Compare the results of several data dependence analyzers. This option
6171 is used for debugging the data dependence analyzers.
6173 @item -ftree-loop-distribution
6174 Perform loop distribution. This flag can improve cache performance on
6175 big loop bodies and allow further loop optimizations, like
6176 parallelization or vectorization, to take place. For example, the loop
6193 @item -ftree-loop-im
6194 @opindex ftree-loop-im
6195 Perform loop invariant motion on trees. This pass moves only invariants that
6196 would be hard to handle at RTL level (function calls, operations that expand to
6197 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
6198 operands of conditions that are invariant out of the loop, so that we can use
6199 just trivial invariantness analysis in loop unswitching. The pass also includes
6202 @item -ftree-loop-ivcanon
6203 @opindex ftree-loop-ivcanon
6204 Create a canonical counter for number of iterations in the loop for that
6205 determining number of iterations requires complicated analysis. Later
6206 optimizations then may determine the number easily. Useful especially
6207 in connection with unrolling.
6211 Perform induction variable optimizations (strength reduction, induction
6212 variable merging and induction variable elimination) on trees.
6214 @item -ftree-parallelize-loops=n
6215 @opindex ftree-parallelize-loops
6216 Parallelize loops, i.e., split their iteration space to run in n threads.
6217 This is only possible for loops whose iterations are independent
6218 and can be arbitrarily reordered. The optimization is only
6219 profitable on multiprocessor machines, for loops that are CPU-intensive,
6220 rather than constrained e.g.@: by memory bandwidth. This option
6221 implies @option{-pthread}, and thus is only supported on targets
6222 that have support for @option{-pthread}.
6226 Perform scalar replacement of aggregates. This pass replaces structure
6227 references with scalars to prevent committing structures to memory too
6228 early. This flag is enabled by default at @option{-O} and higher.
6230 @item -ftree-copyrename
6231 @opindex ftree-copyrename
6232 Perform copy renaming on trees. This pass attempts to rename compiler
6233 temporaries to other variables at copy locations, usually resulting in
6234 variable names which more closely resemble the original variables. This flag
6235 is enabled by default at @option{-O} and higher.
6239 Perform temporary expression replacement during the SSA->normal phase. Single
6240 use/single def temporaries are replaced at their use location with their
6241 defining expression. This results in non-GIMPLE code, but gives the expanders
6242 much more complex trees to work on resulting in better RTL generation. This is
6243 enabled by default at @option{-O} and higher.
6245 @item -ftree-vectorize
6246 @opindex ftree-vectorize
6247 Perform loop vectorization on trees. This flag is enabled by default at
6250 @item -ftree-vect-loop-version
6251 @opindex ftree-vect-loop-version
6252 Perform loop versioning when doing loop vectorization on trees. When a loop
6253 appears to be vectorizable except that data alignment or data dependence cannot
6254 be determined at compile time then vectorized and non-vectorized versions of
6255 the loop are generated along with runtime checks for alignment or dependence
6256 to control which version is executed. This option is enabled by default
6257 except at level @option{-Os} where it is disabled.
6259 @item -fvect-cost-model
6260 @opindex fvect-cost-model
6261 Enable cost model for vectorization.
6265 Perform Value Range Propagation on trees. This is similar to the
6266 constant propagation pass, but instead of values, ranges of values are
6267 propagated. This allows the optimizers to remove unnecessary range
6268 checks like array bound checks and null pointer checks. This is
6269 enabled by default at @option{-O2} and higher. Null pointer check
6270 elimination is only done if @option{-fdelete-null-pointer-checks} is
6275 Perform tail duplication to enlarge superblock size. This transformation
6276 simplifies the control flow of the function allowing other optimizations to do
6279 @item -funroll-loops
6280 @opindex funroll-loops
6281 Unroll loops whose number of iterations can be determined at compile
6282 time or upon entry to the loop. @option{-funroll-loops} implies
6283 @option{-frerun-cse-after-loop}. This option makes code larger,
6284 and may or may not make it run faster.
6286 @item -funroll-all-loops
6287 @opindex funroll-all-loops
6288 Unroll all loops, even if their number of iterations is uncertain when
6289 the loop is entered. This usually makes programs run more slowly.
6290 @option{-funroll-all-loops} implies the same options as
6291 @option{-funroll-loops},
6293 @item -fsplit-ivs-in-unroller
6294 @opindex fsplit-ivs-in-unroller
6295 Enables expressing of values of induction variables in later iterations
6296 of the unrolled loop using the value in the first iteration. This breaks
6297 long dependency chains, thus improving efficiency of the scheduling passes.
6299 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6300 same effect. However in cases the loop body is more complicated than
6301 a single basic block, this is not reliable. It also does not work at all
6302 on some of the architectures due to restrictions in the CSE pass.
6304 This optimization is enabled by default.
6306 @item -fvariable-expansion-in-unroller
6307 @opindex fvariable-expansion-in-unroller
6308 With this option, the compiler will create multiple copies of some
6309 local variables when unrolling a loop which can result in superior code.
6311 @item -fpredictive-commoning
6312 @opindex fpredictive-commoning
6313 Perform predictive commoning optimization, i.e., reusing computations
6314 (especially memory loads and stores) performed in previous
6315 iterations of loops.
6317 This option is enabled at level @option{-O3}.
6319 @item -fprefetch-loop-arrays
6320 @opindex fprefetch-loop-arrays
6321 If supported by the target machine, generate instructions to prefetch
6322 memory to improve the performance of loops that access large arrays.
6324 This option may generate better or worse code; results are highly
6325 dependent on the structure of loops within the source code.
6327 Disabled at level @option{-Os}.
6330 @itemx -fno-peephole2
6331 @opindex fno-peephole
6332 @opindex fno-peephole2
6333 Disable any machine-specific peephole optimizations. The difference
6334 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6335 are implemented in the compiler; some targets use one, some use the
6336 other, a few use both.
6338 @option{-fpeephole} is enabled by default.
6339 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6341 @item -fno-guess-branch-probability
6342 @opindex fno-guess-branch-probability
6343 Do not guess branch probabilities using heuristics.
6345 GCC will use heuristics to guess branch probabilities if they are
6346 not provided by profiling feedback (@option{-fprofile-arcs}). These
6347 heuristics are based on the control flow graph. If some branch probabilities
6348 are specified by @samp{__builtin_expect}, then the heuristics will be
6349 used to guess branch probabilities for the rest of the control flow graph,
6350 taking the @samp{__builtin_expect} info into account. The interactions
6351 between the heuristics and @samp{__builtin_expect} can be complex, and in
6352 some cases, it may be useful to disable the heuristics so that the effects
6353 of @samp{__builtin_expect} are easier to understand.
6355 The default is @option{-fguess-branch-probability} at levels
6356 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6358 @item -freorder-blocks
6359 @opindex freorder-blocks
6360 Reorder basic blocks in the compiled function in order to reduce number of
6361 taken branches and improve code locality.
6363 Enabled at levels @option{-O2}, @option{-O3}.
6365 @item -freorder-blocks-and-partition
6366 @opindex freorder-blocks-and-partition
6367 In addition to reordering basic blocks in the compiled function, in order
6368 to reduce number of taken branches, partitions hot and cold basic blocks
6369 into separate sections of the assembly and .o files, to improve
6370 paging and cache locality performance.
6372 This optimization is automatically turned off in the presence of
6373 exception handling, for linkonce sections, for functions with a user-defined
6374 section attribute and on any architecture that does not support named
6377 @item -freorder-functions
6378 @opindex freorder-functions
6379 Reorder functions in the object file in order to
6380 improve code locality. This is implemented by using special
6381 subsections @code{.text.hot} for most frequently executed functions and
6382 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6383 the linker so object file format must support named sections and linker must
6384 place them in a reasonable way.
6386 Also profile feedback must be available in to make this option effective. See
6387 @option{-fprofile-arcs} for details.
6389 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6391 @item -fstrict-aliasing
6392 @opindex fstrict-aliasing
6393 Allows the compiler to assume the strictest aliasing rules applicable to
6394 the language being compiled. For C (and C++), this activates
6395 optimizations based on the type of expressions. In particular, an
6396 object of one type is assumed never to reside at the same address as an
6397 object of a different type, unless the types are almost the same. For
6398 example, an @code{unsigned int} can alias an @code{int}, but not a
6399 @code{void*} or a @code{double}. A character type may alias any other
6402 @anchor{Type-punning}Pay special attention to code like this:
6415 The practice of reading from a different union member than the one most
6416 recently written to (called ``type-punning'') is common. Even with
6417 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6418 is accessed through the union type. So, the code above will work as
6419 expected. @xref{Structures unions enumerations and bit-fields
6420 implementation}. However, this code might not:
6431 Similarly, access by taking the address, casting the resulting pointer
6432 and dereferencing the result has undefined behavior, even if the cast
6433 uses a union type, e.g.:
6437 return ((union a_union *) &d)->i;
6441 The @option{-fstrict-aliasing} option is enabled at levels
6442 @option{-O2}, @option{-O3}, @option{-Os}.
6444 @item -fstrict-overflow
6445 @opindex fstrict-overflow
6446 Allow the compiler to assume strict signed overflow rules, depending
6447 on the language being compiled. For C (and C++) this means that
6448 overflow when doing arithmetic with signed numbers is undefined, which
6449 means that the compiler may assume that it will not happen. This
6450 permits various optimizations. For example, the compiler will assume
6451 that an expression like @code{i + 10 > i} will always be true for
6452 signed @code{i}. This assumption is only valid if signed overflow is
6453 undefined, as the expression is false if @code{i + 10} overflows when
6454 using twos complement arithmetic. When this option is in effect any
6455 attempt to determine whether an operation on signed numbers will
6456 overflow must be written carefully to not actually involve overflow.
6458 This option also allows the compiler to assume strict pointer
6459 semantics: given a pointer to an object, if adding an offset to that
6460 pointer does not produce a pointer to the same object, the addition is
6461 undefined. This permits the compiler to conclude that @code{p + u >
6462 p} is always true for a pointer @code{p} and unsigned integer
6463 @code{u}. This assumption is only valid because pointer wraparound is
6464 undefined, as the expression is false if @code{p + u} overflows using
6465 twos complement arithmetic.
6467 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6468 that integer signed overflow is fully defined: it wraps. When
6469 @option{-fwrapv} is used, there is no difference between
6470 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6471 integers. With @option{-fwrapv} certain types of overflow are
6472 permitted. For example, if the compiler gets an overflow when doing
6473 arithmetic on constants, the overflowed value can still be used with
6474 @option{-fwrapv}, but not otherwise.
6476 The @option{-fstrict-overflow} option is enabled at levels
6477 @option{-O2}, @option{-O3}, @option{-Os}.
6479 @item -falign-functions
6480 @itemx -falign-functions=@var{n}
6481 @opindex falign-functions
6482 Align the start of functions to the next power-of-two greater than
6483 @var{n}, skipping up to @var{n} bytes. For instance,
6484 @option{-falign-functions=32} aligns functions to the next 32-byte
6485 boundary, but @option{-falign-functions=24} would align to the next
6486 32-byte boundary only if this can be done by skipping 23 bytes or less.
6488 @option{-fno-align-functions} and @option{-falign-functions=1} are
6489 equivalent and mean that functions will not be aligned.
6491 Some assemblers only support this flag when @var{n} is a power of two;
6492 in that case, it is rounded up.
6494 If @var{n} is not specified or is zero, use a machine-dependent default.
6496 Enabled at levels @option{-O2}, @option{-O3}.
6498 @item -falign-labels
6499 @itemx -falign-labels=@var{n}
6500 @opindex falign-labels
6501 Align all branch targets to a power-of-two boundary, skipping up to
6502 @var{n} bytes like @option{-falign-functions}. This option can easily
6503 make code slower, because it must insert dummy operations for when the
6504 branch target is reached in the usual flow of the code.
6506 @option{-fno-align-labels} and @option{-falign-labels=1} are
6507 equivalent and mean that labels will not be aligned.
6509 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6510 are greater than this value, then their values are used instead.
6512 If @var{n} is not specified or is zero, use a machine-dependent default
6513 which is very likely to be @samp{1}, meaning no alignment.
6515 Enabled at levels @option{-O2}, @option{-O3}.
6518 @itemx -falign-loops=@var{n}
6519 @opindex falign-loops
6520 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6521 like @option{-falign-functions}. The hope is that the loop will be
6522 executed many times, which will make up for any execution of the dummy
6525 @option{-fno-align-loops} and @option{-falign-loops=1} are
6526 equivalent and mean that loops will not be aligned.
6528 If @var{n} is not specified or is zero, use a machine-dependent default.
6530 Enabled at levels @option{-O2}, @option{-O3}.
6533 @itemx -falign-jumps=@var{n}
6534 @opindex falign-jumps
6535 Align branch targets to a power-of-two boundary, for branch targets
6536 where the targets can only be reached by jumping, skipping up to @var{n}
6537 bytes like @option{-falign-functions}. In this case, no dummy operations
6540 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6541 equivalent and mean that loops will not be aligned.
6543 If @var{n} is not specified or is zero, use a machine-dependent default.
6545 Enabled at levels @option{-O2}, @option{-O3}.
6547 @item -funit-at-a-time
6548 @opindex funit-at-a-time
6549 This option is left for compatibility reasons. @option{-funit-at-a-time}
6550 has no effect, while @option{-fno-unit-at-a-time} implies
6551 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
6555 @item -fno-toplevel-reorder
6556 @opindex fno-toplevel-reorder
6557 Do not reorder top-level functions, variables, and @code{asm}
6558 statements. Output them in the same order that they appear in the
6559 input file. When this option is used, unreferenced static variables
6560 will not be removed. This option is intended to support existing code
6561 which relies on a particular ordering. For new code, it is better to
6564 Enabled at level @option{-O0}. When disabled explicitly, it also imply
6565 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
6570 Constructs webs as commonly used for register allocation purposes and assign
6571 each web individual pseudo register. This allows the register allocation pass
6572 to operate on pseudos directly, but also strengthens several other optimization
6573 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6574 however, make debugging impossible, since variables will no longer stay in a
6577 Enabled by default with @option{-funroll-loops}.
6579 @item -fwhole-program
6580 @opindex fwhole-program
6581 Assume that the current compilation unit represents whole program being
6582 compiled. All public functions and variables with the exception of @code{main}
6583 and those merged by attribute @code{externally_visible} become static functions
6584 and in a affect gets more aggressively optimized by interprocedural optimizers.
6585 While this option is equivalent to proper use of @code{static} keyword for
6586 programs consisting of single file, in combination with option
6587 @option{--combine} this flag can be used to compile most of smaller scale C
6588 programs since the functions and variables become local for the whole combined
6589 compilation unit, not for the single source file itself.
6591 This option is not supported for Fortran programs.
6593 @item -fcprop-registers
6594 @opindex fcprop-registers
6595 After register allocation and post-register allocation instruction splitting,
6596 we perform a copy-propagation pass to try to reduce scheduling dependencies
6597 and occasionally eliminate the copy.
6599 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6601 @item -fprofile-correction
6602 @opindex fprofile-correction
6603 Profiles collected using an instrumented binary for multi-threaded programs may
6604 be inconsistent due to missed counter updates. When this option is specified,
6605 GCC will use heuristics to correct or smooth out such inconsistencies. By
6606 default, GCC will emit an error message when an inconsistent profile is detected.
6608 @item -fprofile-dir=@var{path}
6609 @opindex fprofile-dir
6611 Set the directory to search the profile data files in to @var{path}.
6612 This option affects only the profile data generated by
6613 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6614 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6615 and its related options.
6616 By default, GCC will use the current directory as @var{path}
6617 thus the profile data file will appear in the same directory as the object file.
6619 @item -fprofile-generate
6620 @itemx -fprofile-generate=@var{path}
6621 @opindex fprofile-generate
6623 Enable options usually used for instrumenting application to produce
6624 profile useful for later recompilation with profile feedback based
6625 optimization. You must use @option{-fprofile-generate} both when
6626 compiling and when linking your program.
6628 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6630 If @var{path} is specified, GCC will look at the @var{path} to find
6631 the profile feedback data files. See @option{-fprofile-dir}.
6634 @itemx -fprofile-use=@var{path}
6635 @opindex fprofile-use
6636 Enable profile feedback directed optimizations, and optimizations
6637 generally profitable only with profile feedback available.
6639 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6640 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6642 By default, GCC emits an error message if the feedback profiles do not
6643 match the source code. This error can be turned into a warning by using
6644 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6647 If @var{path} is specified, GCC will look at the @var{path} to find
6648 the profile feedback data files. See @option{-fprofile-dir}.
6651 The following options control compiler behavior regarding floating
6652 point arithmetic. These options trade off between speed and
6653 correctness. All must be specifically enabled.
6657 @opindex ffloat-store
6658 Do not store floating point variables in registers, and inhibit other
6659 options that might change whether a floating point value is taken from a
6662 @cindex floating point precision
6663 This option prevents undesirable excess precision on machines such as
6664 the 68000 where the floating registers (of the 68881) keep more
6665 precision than a @code{double} is supposed to have. Similarly for the
6666 x86 architecture. For most programs, the excess precision does only
6667 good, but a few programs rely on the precise definition of IEEE floating
6668 point. Use @option{-ffloat-store} for such programs, after modifying
6669 them to store all pertinent intermediate computations into variables.
6673 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6674 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6675 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6677 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6679 This option is not turned on by any @option{-O} option since
6680 it can result in incorrect output for programs which depend on
6681 an exact implementation of IEEE or ISO rules/specifications for
6682 math functions. It may, however, yield faster code for programs
6683 that do not require the guarantees of these specifications.
6685 @item -fno-math-errno
6686 @opindex fno-math-errno
6687 Do not set ERRNO after calling math functions that are executed
6688 with a single instruction, e.g., sqrt. A program that relies on
6689 IEEE exceptions for math error handling may want to use this flag
6690 for speed while maintaining IEEE arithmetic compatibility.
6692 This option is not turned on by any @option{-O} option since
6693 it can result in incorrect output for programs which depend on
6694 an exact implementation of IEEE or ISO rules/specifications for
6695 math functions. It may, however, yield faster code for programs
6696 that do not require the guarantees of these specifications.
6698 The default is @option{-fmath-errno}.
6700 On Darwin systems, the math library never sets @code{errno}. There is
6701 therefore no reason for the compiler to consider the possibility that
6702 it might, and @option{-fno-math-errno} is the default.
6704 @item -funsafe-math-optimizations
6705 @opindex funsafe-math-optimizations
6707 Allow optimizations for floating-point arithmetic that (a) assume
6708 that arguments and results are valid and (b) may violate IEEE or
6709 ANSI standards. When used at link-time, it may include libraries
6710 or startup files that change the default FPU control word or other
6711 similar optimizations.
6713 This option is not turned on by any @option{-O} option since
6714 it can result in incorrect output for programs which depend on
6715 an exact implementation of IEEE or ISO rules/specifications for
6716 math functions. It may, however, yield faster code for programs
6717 that do not require the guarantees of these specifications.
6718 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6719 @option{-fassociative-math} and @option{-freciprocal-math}.
6721 The default is @option{-fno-unsafe-math-optimizations}.
6723 @item -fassociative-math
6724 @opindex fassociative-math
6726 Allow re-association of operands in series of floating-point operations.
6727 This violates the ISO C and C++ language standard by possibly changing
6728 computation result. NOTE: re-ordering may change the sign of zero as
6729 well as ignore NaNs and inhibit or create underflow or overflow (and
6730 thus cannot be used on a code which relies on rounding behavior like
6731 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6732 and thus may not be used when ordered comparisons are required.
6733 This option requires that both @option{-fno-signed-zeros} and
6734 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6735 much sense with @option{-frounding-math}.
6737 The default is @option{-fno-associative-math}.
6739 @item -freciprocal-math
6740 @opindex freciprocal-math
6742 Allow the reciprocal of a value to be used instead of dividing by
6743 the value if this enables optimizations. For example @code{x / y}
6744 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6745 is subject to common subexpression elimination. Note that this loses
6746 precision and increases the number of flops operating on the value.
6748 The default is @option{-fno-reciprocal-math}.
6750 @item -ffinite-math-only
6751 @opindex ffinite-math-only
6752 Allow optimizations for floating-point arithmetic that assume
6753 that arguments and results are not NaNs or +-Infs.
6755 This option is not turned on by any @option{-O} option since
6756 it can result in incorrect output for programs which depend on
6757 an exact implementation of IEEE or ISO rules/specifications for
6758 math functions. It may, however, yield faster code for programs
6759 that do not require the guarantees of these specifications.
6761 The default is @option{-fno-finite-math-only}.
6763 @item -fno-signed-zeros
6764 @opindex fno-signed-zeros
6765 Allow optimizations for floating point arithmetic that ignore the
6766 signedness of zero. IEEE arithmetic specifies the behavior of
6767 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6768 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6769 This option implies that the sign of a zero result isn't significant.
6771 The default is @option{-fsigned-zeros}.
6773 @item -fno-trapping-math
6774 @opindex fno-trapping-math
6775 Compile code assuming that floating-point operations cannot generate
6776 user-visible traps. These traps include division by zero, overflow,
6777 underflow, inexact result and invalid operation. This option requires
6778 that @option{-fno-signaling-nans} be in effect. Setting this option may
6779 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6781 This option should never be turned on by any @option{-O} option since
6782 it can result in incorrect output for programs which depend on
6783 an exact implementation of IEEE or ISO rules/specifications for
6786 The default is @option{-ftrapping-math}.
6788 @item -frounding-math
6789 @opindex frounding-math
6790 Disable transformations and optimizations that assume default floating
6791 point rounding behavior. This is round-to-zero for all floating point
6792 to integer conversions, and round-to-nearest for all other arithmetic
6793 truncations. This option should be specified for programs that change
6794 the FP rounding mode dynamically, or that may be executed with a
6795 non-default rounding mode. This option disables constant folding of
6796 floating point expressions at compile-time (which may be affected by
6797 rounding mode) and arithmetic transformations that are unsafe in the
6798 presence of sign-dependent rounding modes.
6800 The default is @option{-fno-rounding-math}.
6802 This option is experimental and does not currently guarantee to
6803 disable all GCC optimizations that are affected by rounding mode.
6804 Future versions of GCC may provide finer control of this setting
6805 using C99's @code{FENV_ACCESS} pragma. This command line option
6806 will be used to specify the default state for @code{FENV_ACCESS}.
6808 @item -frtl-abstract-sequences
6809 @opindex frtl-abstract-sequences
6810 It is a size optimization method. This option is to find identical
6811 sequences of code, which can be turned into pseudo-procedures and
6812 then replace all occurrences with calls to the newly created
6813 subroutine. It is kind of an opposite of @option{-finline-functions}.
6814 This optimization runs at RTL level.
6816 @item -fsignaling-nans
6817 @opindex fsignaling-nans
6818 Compile code assuming that IEEE signaling NaNs may generate user-visible
6819 traps during floating-point operations. Setting this option disables
6820 optimizations that may change the number of exceptions visible with
6821 signaling NaNs. This option implies @option{-ftrapping-math}.
6823 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6826 The default is @option{-fno-signaling-nans}.
6828 This option is experimental and does not currently guarantee to
6829 disable all GCC optimizations that affect signaling NaN behavior.
6831 @item -fsingle-precision-constant
6832 @opindex fsingle-precision-constant
6833 Treat floating point constant as single precision constant instead of
6834 implicitly converting it to double precision constant.
6836 @item -fcx-limited-range
6837 @opindex fcx-limited-range
6838 When enabled, this option states that a range reduction step is not
6839 needed when performing complex division. Also, there is no checking
6840 whether the result of a complex multiplication or division is @code{NaN
6841 + I*NaN}, with an attempt to rescue the situation in that case. The
6842 default is @option{-fno-cx-limited-range}, but is enabled by
6843 @option{-ffast-math}.
6845 This option controls the default setting of the ISO C99
6846 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6849 @item -fcx-fortran-rules
6850 @opindex fcx-fortran-rules
6851 Complex multiplication and division follow Fortran rules. Range
6852 reduction is done as part of complex division, but there is no checking
6853 whether the result of a complex multiplication or division is @code{NaN
6854 + I*NaN}, with an attempt to rescue the situation in that case.
6856 The default is @option{-fno-cx-fortran-rules}.
6860 The following options control optimizations that may improve
6861 performance, but are not enabled by any @option{-O} options. This
6862 section includes experimental options that may produce broken code.
6865 @item -fbranch-probabilities
6866 @opindex fbranch-probabilities
6867 After running a program compiled with @option{-fprofile-arcs}
6868 (@pxref{Debugging Options,, Options for Debugging Your Program or
6869 @command{gcc}}), you can compile it a second time using
6870 @option{-fbranch-probabilities}, to improve optimizations based on
6871 the number of times each branch was taken. When the program
6872 compiled with @option{-fprofile-arcs} exits it saves arc execution
6873 counts to a file called @file{@var{sourcename}.gcda} for each source
6874 file. The information in this data file is very dependent on the
6875 structure of the generated code, so you must use the same source code
6876 and the same optimization options for both compilations.
6878 With @option{-fbranch-probabilities}, GCC puts a
6879 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6880 These can be used to improve optimization. Currently, they are only
6881 used in one place: in @file{reorg.c}, instead of guessing which path a
6882 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6883 exactly determine which path is taken more often.
6885 @item -fprofile-values
6886 @opindex fprofile-values
6887 If combined with @option{-fprofile-arcs}, it adds code so that some
6888 data about values of expressions in the program is gathered.
6890 With @option{-fbranch-probabilities}, it reads back the data gathered
6891 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6892 notes to instructions for their later usage in optimizations.
6894 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6898 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6899 a code to gather information about values of expressions.
6901 With @option{-fbranch-probabilities}, it reads back the data gathered
6902 and actually performs the optimizations based on them.
6903 Currently the optimizations include specialization of division operation
6904 using the knowledge about the value of the denominator.
6906 @item -frename-registers
6907 @opindex frename-registers
6908 Attempt to avoid false dependencies in scheduled code by making use
6909 of registers left over after register allocation. This optimization
6910 will most benefit processors with lots of registers. Depending on the
6911 debug information format adopted by the target, however, it can
6912 make debugging impossible, since variables will no longer stay in
6913 a ``home register''.
6915 Enabled by default with @option{-funroll-loops}.
6919 Perform tail duplication to enlarge superblock size. This transformation
6920 simplifies the control flow of the function allowing other optimizations to do
6923 Enabled with @option{-fprofile-use}.
6925 @item -funroll-loops
6926 @opindex funroll-loops
6927 Unroll loops whose number of iterations can be determined at compile time or
6928 upon entry to the loop. @option{-funroll-loops} implies
6929 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6930 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6931 small constant number of iterations). This option makes code larger, and may
6932 or may not make it run faster.
6934 Enabled with @option{-fprofile-use}.
6936 @item -funroll-all-loops
6937 @opindex funroll-all-loops
6938 Unroll all loops, even if their number of iterations is uncertain when
6939 the loop is entered. This usually makes programs run more slowly.
6940 @option{-funroll-all-loops} implies the same options as
6941 @option{-funroll-loops}.
6944 @opindex fpeel-loops
6945 Peels the loops for that there is enough information that they do not
6946 roll much (from profile feedback). It also turns on complete loop peeling
6947 (i.e.@: complete removal of loops with small constant number of iterations).
6949 Enabled with @option{-fprofile-use}.
6951 @item -fmove-loop-invariants
6952 @opindex fmove-loop-invariants
6953 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6954 at level @option{-O1}
6956 @item -funswitch-loops
6957 @opindex funswitch-loops
6958 Move branches with loop invariant conditions out of the loop, with duplicates
6959 of the loop on both branches (modified according to result of the condition).
6961 @item -ffunction-sections
6962 @itemx -fdata-sections
6963 @opindex ffunction-sections
6964 @opindex fdata-sections
6965 Place each function or data item into its own section in the output
6966 file if the target supports arbitrary sections. The name of the
6967 function or the name of the data item determines the section's name
6970 Use these options on systems where the linker can perform optimizations
6971 to improve locality of reference in the instruction space. Most systems
6972 using the ELF object format and SPARC processors running Solaris 2 have
6973 linkers with such optimizations. AIX may have these optimizations in
6976 Only use these options when there are significant benefits from doing
6977 so. When you specify these options, the assembler and linker will
6978 create larger object and executable files and will also be slower.
6979 You will not be able to use @code{gprof} on all systems if you
6980 specify this option and you may have problems with debugging if
6981 you specify both this option and @option{-g}.
6983 @item -fbranch-target-load-optimize
6984 @opindex fbranch-target-load-optimize
6985 Perform branch target register load optimization before prologue / epilogue
6987 The use of target registers can typically be exposed only during reload,
6988 thus hoisting loads out of loops and doing inter-block scheduling needs
6989 a separate optimization pass.
6991 @item -fbranch-target-load-optimize2
6992 @opindex fbranch-target-load-optimize2
6993 Perform branch target register load optimization after prologue / epilogue
6996 @item -fbtr-bb-exclusive
6997 @opindex fbtr-bb-exclusive
6998 When performing branch target register load optimization, don't reuse
6999 branch target registers in within any basic block.
7001 @item -fstack-protector
7002 @opindex fstack-protector
7003 Emit extra code to check for buffer overflows, such as stack smashing
7004 attacks. This is done by adding a guard variable to functions with
7005 vulnerable objects. This includes functions that call alloca, and
7006 functions with buffers larger than 8 bytes. The guards are initialized
7007 when a function is entered and then checked when the function exits.
7008 If a guard check fails, an error message is printed and the program exits.
7010 @item -fstack-protector-all
7011 @opindex fstack-protector-all
7012 Like @option{-fstack-protector} except that all functions are protected.
7014 @item -fsection-anchors
7015 @opindex fsection-anchors
7016 Try to reduce the number of symbolic address calculations by using
7017 shared ``anchor'' symbols to address nearby objects. This transformation
7018 can help to reduce the number of GOT entries and GOT accesses on some
7021 For example, the implementation of the following function @code{foo}:
7025 int foo (void) @{ return a + b + c; @}
7028 would usually calculate the addresses of all three variables, but if you
7029 compile it with @option{-fsection-anchors}, it will access the variables
7030 from a common anchor point instead. The effect is similar to the
7031 following pseudocode (which isn't valid C):
7036 register int *xr = &x;
7037 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
7041 Not all targets support this option.
7043 @item --param @var{name}=@var{value}
7045 In some places, GCC uses various constants to control the amount of
7046 optimization that is done. For example, GCC will not inline functions
7047 that contain more that a certain number of instructions. You can
7048 control some of these constants on the command-line using the
7049 @option{--param} option.
7051 The names of specific parameters, and the meaning of the values, are
7052 tied to the internals of the compiler, and are subject to change
7053 without notice in future releases.
7055 In each case, the @var{value} is an integer. The allowable choices for
7056 @var{name} are given in the following table:
7059 @item sra-max-structure-size
7060 The maximum structure size, in bytes, at which the scalar replacement
7061 of aggregates (SRA) optimization will perform block copies. The
7062 default value, 0, implies that GCC will select the most appropriate
7065 @item sra-field-structure-ratio
7066 The threshold ratio (as a percentage) between instantiated fields and
7067 the complete structure size. We say that if the ratio of the number
7068 of bytes in instantiated fields to the number of bytes in the complete
7069 structure exceeds this parameter, then block copies are not used. The
7072 @item struct-reorg-cold-struct-ratio
7073 The threshold ratio (as a percentage) between a structure frequency
7074 and the frequency of the hottest structure in the program. This parameter
7075 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
7076 We say that if the ratio of a structure frequency, calculated by profiling,
7077 to the hottest structure frequency in the program is less than this
7078 parameter, then structure reorganization is not applied to this structure.
7081 @item predictable-branch-cost-outcome
7082 When branch is predicted to be taken with probability lower than this threshold
7083 (in percent), then it is considered well predictable. The default is 10.
7085 @item max-crossjump-edges
7086 The maximum number of incoming edges to consider for crossjumping.
7087 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
7088 the number of edges incoming to each block. Increasing values mean
7089 more aggressive optimization, making the compile time increase with
7090 probably small improvement in executable size.
7092 @item min-crossjump-insns
7093 The minimum number of instructions which must be matched at the end
7094 of two blocks before crossjumping will be performed on them. This
7095 value is ignored in the case where all instructions in the block being
7096 crossjumped from are matched. The default value is 5.
7098 @item max-grow-copy-bb-insns
7099 The maximum code size expansion factor when copying basic blocks
7100 instead of jumping. The expansion is relative to a jump instruction.
7101 The default value is 8.
7103 @item max-goto-duplication-insns
7104 The maximum number of instructions to duplicate to a block that jumps
7105 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
7106 passes, GCC factors computed gotos early in the compilation process,
7107 and unfactors them as late as possible. Only computed jumps at the
7108 end of a basic blocks with no more than max-goto-duplication-insns are
7109 unfactored. The default value is 8.
7111 @item max-delay-slot-insn-search
7112 The maximum number of instructions to consider when looking for an
7113 instruction to fill a delay slot. If more than this arbitrary number of
7114 instructions is searched, the time savings from filling the delay slot
7115 will be minimal so stop searching. Increasing values mean more
7116 aggressive optimization, making the compile time increase with probably
7117 small improvement in executable run time.
7119 @item max-delay-slot-live-search
7120 When trying to fill delay slots, the maximum number of instructions to
7121 consider when searching for a block with valid live register
7122 information. Increasing this arbitrarily chosen value means more
7123 aggressive optimization, increasing the compile time. This parameter
7124 should be removed when the delay slot code is rewritten to maintain the
7127 @item max-gcse-memory
7128 The approximate maximum amount of memory that will be allocated in
7129 order to perform the global common subexpression elimination
7130 optimization. If more memory than specified is required, the
7131 optimization will not be done.
7133 @item max-gcse-passes
7134 The maximum number of passes of GCSE to run. The default is 1.
7136 @item max-pending-list-length
7137 The maximum number of pending dependencies scheduling will allow
7138 before flushing the current state and starting over. Large functions
7139 with few branches or calls can create excessively large lists which
7140 needlessly consume memory and resources.
7142 @item max-inline-insns-single
7143 Several parameters control the tree inliner used in gcc.
7144 This number sets the maximum number of instructions (counted in GCC's
7145 internal representation) in a single function that the tree inliner
7146 will consider for inlining. This only affects functions declared
7147 inline and methods implemented in a class declaration (C++).
7148 The default value is 450.
7150 @item max-inline-insns-auto
7151 When you use @option{-finline-functions} (included in @option{-O3}),
7152 a lot of functions that would otherwise not be considered for inlining
7153 by the compiler will be investigated. To those functions, a different
7154 (more restrictive) limit compared to functions declared inline can
7156 The default value is 90.
7158 @item large-function-insns
7159 The limit specifying really large functions. For functions larger than this
7160 limit after inlining, inlining is constrained by
7161 @option{--param large-function-growth}. This parameter is useful primarily
7162 to avoid extreme compilation time caused by non-linear algorithms used by the
7164 The default value is 2700.
7166 @item large-function-growth
7167 Specifies maximal growth of large function caused by inlining in percents.
7168 The default value is 100 which limits large function growth to 2.0 times
7171 @item large-unit-insns
7172 The limit specifying large translation unit. Growth caused by inlining of
7173 units larger than this limit is limited by @option{--param inline-unit-growth}.
7174 For small units this might be too tight (consider unit consisting of function A
7175 that is inline and B that just calls A three time. If B is small relative to
7176 A, the growth of unit is 300\% and yet such inlining is very sane. For very
7177 large units consisting of small inlineable functions however the overall unit
7178 growth limit is needed to avoid exponential explosion of code size. Thus for
7179 smaller units, the size is increased to @option{--param large-unit-insns}
7180 before applying @option{--param inline-unit-growth}. The default is 10000
7182 @item inline-unit-growth
7183 Specifies maximal overall growth of the compilation unit caused by inlining.
7184 The default value is 30 which limits unit growth to 1.3 times the original
7187 @item ipcp-unit-growth
7188 Specifies maximal overall growth of the compilation unit caused by
7189 interprocedural constant propagation. The default value is 10 which limits
7190 unit growth to 1.1 times the original size.
7192 @item large-stack-frame
7193 The limit specifying large stack frames. While inlining the algorithm is trying
7194 to not grow past this limit too much. Default value is 256 bytes.
7196 @item large-stack-frame-growth
7197 Specifies maximal growth of large stack frames caused by inlining in percents.
7198 The default value is 1000 which limits large stack frame growth to 11 times
7201 @item max-inline-insns-recursive
7202 @itemx max-inline-insns-recursive-auto
7203 Specifies maximum number of instructions out-of-line copy of self recursive inline
7204 function can grow into by performing recursive inlining.
7206 For functions declared inline @option{--param max-inline-insns-recursive} is
7207 taken into account. For function not declared inline, recursive inlining
7208 happens only when @option{-finline-functions} (included in @option{-O3}) is
7209 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
7210 default value is 450.
7212 @item max-inline-recursive-depth
7213 @itemx max-inline-recursive-depth-auto
7214 Specifies maximum recursion depth used by the recursive inlining.
7216 For functions declared inline @option{--param max-inline-recursive-depth} is
7217 taken into account. For function not declared inline, recursive inlining
7218 happens only when @option{-finline-functions} (included in @option{-O3}) is
7219 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
7222 @item min-inline-recursive-probability
7223 Recursive inlining is profitable only for function having deep recursion
7224 in average and can hurt for function having little recursion depth by
7225 increasing the prologue size or complexity of function body to other
7228 When profile feedback is available (see @option{-fprofile-generate}) the actual
7229 recursion depth can be guessed from probability that function will recurse via
7230 given call expression. This parameter limits inlining only to call expression
7231 whose probability exceeds given threshold (in percents). The default value is
7234 @item inline-call-cost
7235 Specify cost of call instruction relative to simple arithmetics operations
7236 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
7237 functions and at the same time increases size of leaf function that is believed to
7238 reduce function size by being inlined. In effect it increases amount of
7239 inlining for code having large abstraction penalty (many functions that just
7240 pass the arguments to other functions) and decrease inlining for code with low
7241 abstraction penalty. The default value is 12.
7243 @item min-vect-loop-bound
7244 The minimum number of iterations under which a loop will not get vectorized
7245 when @option{-ftree-vectorize} is used. The number of iterations after
7246 vectorization needs to be greater than the value specified by this option
7247 to allow vectorization. The default value is 0.
7249 @item max-unrolled-insns
7250 The maximum number of instructions that a loop should have if that loop
7251 is unrolled, and if the loop is unrolled, it determines how many times
7252 the loop code is unrolled.
7254 @item max-average-unrolled-insns
7255 The maximum number of instructions biased by probabilities of their execution
7256 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7257 it determines how many times the loop code is unrolled.
7259 @item max-unroll-times
7260 The maximum number of unrollings of a single loop.
7262 @item max-peeled-insns
7263 The maximum number of instructions that a loop should have if that loop
7264 is peeled, and if the loop is peeled, it determines how many times
7265 the loop code is peeled.
7267 @item max-peel-times
7268 The maximum number of peelings of a single loop.
7270 @item max-completely-peeled-insns
7271 The maximum number of insns of a completely peeled loop.
7273 @item max-completely-peel-times
7274 The maximum number of iterations of a loop to be suitable for complete peeling.
7276 @item max-unswitch-insns
7277 The maximum number of insns of an unswitched loop.
7279 @item max-unswitch-level
7280 The maximum number of branches unswitched in a single loop.
7283 The minimum cost of an expensive expression in the loop invariant motion.
7285 @item iv-consider-all-candidates-bound
7286 Bound on number of candidates for induction variables below that
7287 all candidates are considered for each use in induction variable
7288 optimizations. Only the most relevant candidates are considered
7289 if there are more candidates, to avoid quadratic time complexity.
7291 @item iv-max-considered-uses
7292 The induction variable optimizations give up on loops that contain more
7293 induction variable uses.
7295 @item iv-always-prune-cand-set-bound
7296 If number of candidates in the set is smaller than this value,
7297 we always try to remove unnecessary ivs from the set during its
7298 optimization when a new iv is added to the set.
7300 @item scev-max-expr-size
7301 Bound on size of expressions used in the scalar evolutions analyzer.
7302 Large expressions slow the analyzer.
7304 @item omega-max-vars
7305 The maximum number of variables in an Omega constraint system.
7306 The default value is 128.
7308 @item omega-max-geqs
7309 The maximum number of inequalities in an Omega constraint system.
7310 The default value is 256.
7313 The maximum number of equalities in an Omega constraint system.
7314 The default value is 128.
7316 @item omega-max-wild-cards
7317 The maximum number of wildcard variables that the Omega solver will
7318 be able to insert. The default value is 18.
7320 @item omega-hash-table-size
7321 The size of the hash table in the Omega solver. The default value is
7324 @item omega-max-keys
7325 The maximal number of keys used by the Omega solver. The default
7328 @item omega-eliminate-redundant-constraints
7329 When set to 1, use expensive methods to eliminate all redundant
7330 constraints. The default value is 0.
7332 @item vect-max-version-for-alignment-checks
7333 The maximum number of runtime checks that can be performed when
7334 doing loop versioning for alignment in the vectorizer. See option
7335 ftree-vect-loop-version for more information.
7337 @item vect-max-version-for-alias-checks
7338 The maximum number of runtime checks that can be performed when
7339 doing loop versioning for alias in the vectorizer. See option
7340 ftree-vect-loop-version for more information.
7342 @item max-iterations-to-track
7344 The maximum number of iterations of a loop the brute force algorithm
7345 for analysis of # of iterations of the loop tries to evaluate.
7347 @item hot-bb-count-fraction
7348 Select fraction of the maximal count of repetitions of basic block in program
7349 given basic block needs to have to be considered hot.
7351 @item hot-bb-frequency-fraction
7352 Select fraction of the maximal frequency of executions of basic block in
7353 function given basic block needs to have to be considered hot
7355 @item max-predicted-iterations
7356 The maximum number of loop iterations we predict statically. This is useful
7357 in cases where function contain single loop with known bound and other loop
7358 with unknown. We predict the known number of iterations correctly, while
7359 the unknown number of iterations average to roughly 10. This means that the
7360 loop without bounds would appear artificially cold relative to the other one.
7362 @item align-threshold
7364 Select fraction of the maximal frequency of executions of basic block in
7365 function given basic block will get aligned.
7367 @item align-loop-iterations
7369 A loop expected to iterate at lest the selected number of iterations will get
7372 @item tracer-dynamic-coverage
7373 @itemx tracer-dynamic-coverage-feedback
7375 This value is used to limit superblock formation once the given percentage of
7376 executed instructions is covered. This limits unnecessary code size
7379 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7380 feedback is available. The real profiles (as opposed to statically estimated
7381 ones) are much less balanced allowing the threshold to be larger value.
7383 @item tracer-max-code-growth
7384 Stop tail duplication once code growth has reached given percentage. This is
7385 rather hokey argument, as most of the duplicates will be eliminated later in
7386 cross jumping, so it may be set to much higher values than is the desired code
7389 @item tracer-min-branch-ratio
7391 Stop reverse growth when the reverse probability of best edge is less than this
7392 threshold (in percent).
7394 @item tracer-min-branch-ratio
7395 @itemx tracer-min-branch-ratio-feedback
7397 Stop forward growth if the best edge do have probability lower than this
7400 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7401 compilation for profile feedback and one for compilation without. The value
7402 for compilation with profile feedback needs to be more conservative (higher) in
7403 order to make tracer effective.
7405 @item max-cse-path-length
7407 Maximum number of basic blocks on path that cse considers. The default is 10.
7410 The maximum instructions CSE process before flushing. The default is 1000.
7412 @item max-aliased-vops
7414 Maximum number of virtual operands per function allowed to represent
7415 aliases before triggering the alias partitioning heuristic. Alias
7416 partitioning reduces compile times and memory consumption needed for
7417 aliasing at the expense of precision loss in alias information. The
7418 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7421 Notice that if a function contains more memory statements than the
7422 value of this parameter, it is not really possible to achieve this
7423 reduction. In this case, the compiler will use the number of memory
7424 statements as the value for @option{max-aliased-vops}.
7426 @item avg-aliased-vops
7428 Average number of virtual operands per statement allowed to represent
7429 aliases before triggering the alias partitioning heuristic. This
7430 works in conjunction with @option{max-aliased-vops}. If a function
7431 contains more than @option{max-aliased-vops} virtual operators, then
7432 memory symbols will be grouped into memory partitions until either the
7433 total number of virtual operators is below @option{max-aliased-vops}
7434 or the average number of virtual operators per memory statement is
7435 below @option{avg-aliased-vops}. The default value for this parameter
7436 is 1 for -O1 and -O2, and 3 for -O3.
7438 @item ggc-min-expand
7440 GCC uses a garbage collector to manage its own memory allocation. This
7441 parameter specifies the minimum percentage by which the garbage
7442 collector's heap should be allowed to expand between collections.
7443 Tuning this may improve compilation speed; it has no effect on code
7446 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7447 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7448 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7449 GCC is not able to calculate RAM on a particular platform, the lower
7450 bound of 30% is used. Setting this parameter and
7451 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7452 every opportunity. This is extremely slow, but can be useful for
7455 @item ggc-min-heapsize
7457 Minimum size of the garbage collector's heap before it begins bothering
7458 to collect garbage. The first collection occurs after the heap expands
7459 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7460 tuning this may improve compilation speed, and has no effect on code
7463 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7464 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7465 with a lower bound of 4096 (four megabytes) and an upper bound of
7466 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7467 particular platform, the lower bound is used. Setting this parameter
7468 very large effectively disables garbage collection. Setting this
7469 parameter and @option{ggc-min-expand} to zero causes a full collection
7470 to occur at every opportunity.
7472 @item max-reload-search-insns
7473 The maximum number of instruction reload should look backward for equivalent
7474 register. Increasing values mean more aggressive optimization, making the
7475 compile time increase with probably slightly better performance. The default
7478 @item max-cselib-memory-locations
7479 The maximum number of memory locations cselib should take into account.
7480 Increasing values mean more aggressive optimization, making the compile time
7481 increase with probably slightly better performance. The default value is 500.
7483 @item reorder-blocks-duplicate
7484 @itemx reorder-blocks-duplicate-feedback
7486 Used by basic block reordering pass to decide whether to use unconditional
7487 branch or duplicate the code on its destination. Code is duplicated when its
7488 estimated size is smaller than this value multiplied by the estimated size of
7489 unconditional jump in the hot spots of the program.
7491 The @option{reorder-block-duplicate-feedback} is used only when profile
7492 feedback is available and may be set to higher values than
7493 @option{reorder-block-duplicate} since information about the hot spots is more
7496 @item max-sched-ready-insns
7497 The maximum number of instructions ready to be issued the scheduler should
7498 consider at any given time during the first scheduling pass. Increasing
7499 values mean more thorough searches, making the compilation time increase
7500 with probably little benefit. The default value is 100.
7502 @item max-sched-region-blocks
7503 The maximum number of blocks in a region to be considered for
7504 interblock scheduling. The default value is 10.
7506 @item max-pipeline-region-blocks
7507 The maximum number of blocks in a region to be considered for
7508 pipelining in the selective scheduler. The default value is 15.
7510 @item max-sched-region-insns
7511 The maximum number of insns in a region to be considered for
7512 interblock scheduling. The default value is 100.
7514 @item max-pipeline-region-insns
7515 The maximum number of insns in a region to be considered for
7516 pipelining in the selective scheduler. The default value is 200.
7519 The minimum probability (in percents) of reaching a source block
7520 for interblock speculative scheduling. The default value is 40.
7522 @item max-sched-extend-regions-iters
7523 The maximum number of iterations through CFG to extend regions.
7524 0 - disable region extension,
7525 N - do at most N iterations.
7526 The default value is 0.
7528 @item max-sched-insn-conflict-delay
7529 The maximum conflict delay for an insn to be considered for speculative motion.
7530 The default value is 3.
7532 @item sched-spec-prob-cutoff
7533 The minimal probability of speculation success (in percents), so that
7534 speculative insn will be scheduled.
7535 The default value is 40.
7537 @item sched-mem-true-dep-cost
7538 Minimal distance (in CPU cycles) between store and load targeting same
7539 memory locations. The default value is 1.
7541 @item selsched-max-lookahead
7542 The maximum size of the lookahead window of selective scheduling. It is a
7543 depth of search for available instructions.
7544 The default value is 50.
7546 @item selsched-max-sched-times
7547 The maximum number of times that an instruction will be scheduled during
7548 selective scheduling. This is the limit on the number of iterations
7549 through which the instruction may be pipelined. The default value is 2.
7551 @item selsched-max-insns-to-rename
7552 The maximum number of best instructions in the ready list that are considered
7553 for renaming in the selective scheduler. The default value is 2.
7555 @item max-last-value-rtl
7556 The maximum size measured as number of RTLs that can be recorded in an expression
7557 in combiner for a pseudo register as last known value of that register. The default
7560 @item integer-share-limit
7561 Small integer constants can use a shared data structure, reducing the
7562 compiler's memory usage and increasing its speed. This sets the maximum
7563 value of a shared integer constant. The default value is 256.
7565 @item min-virtual-mappings
7566 Specifies the minimum number of virtual mappings in the incremental
7567 SSA updater that should be registered to trigger the virtual mappings
7568 heuristic defined by virtual-mappings-ratio. The default value is
7571 @item virtual-mappings-ratio
7572 If the number of virtual mappings is virtual-mappings-ratio bigger
7573 than the number of virtual symbols to be updated, then the incremental
7574 SSA updater switches to a full update for those symbols. The default
7577 @item ssp-buffer-size
7578 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7579 protection when @option{-fstack-protection} is used.
7581 @item max-jump-thread-duplication-stmts
7582 Maximum number of statements allowed in a block that needs to be
7583 duplicated when threading jumps.
7585 @item max-fields-for-field-sensitive
7586 Maximum number of fields in a structure we will treat in
7587 a field sensitive manner during pointer analysis. The default is zero
7588 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7590 @item prefetch-latency
7591 Estimate on average number of instructions that are executed before
7592 prefetch finishes. The distance we prefetch ahead is proportional
7593 to this constant. Increasing this number may also lead to less
7594 streams being prefetched (see @option{simultaneous-prefetches}).
7596 @item simultaneous-prefetches
7597 Maximum number of prefetches that can run at the same time.
7599 @item l1-cache-line-size
7600 The size of cache line in L1 cache, in bytes.
7603 The size of L1 cache, in kilobytes.
7606 The size of L2 cache, in kilobytes.
7608 @item use-canonical-types
7609 Whether the compiler should use the ``canonical'' type system. By
7610 default, this should always be 1, which uses a more efficient internal
7611 mechanism for comparing types in C++ and Objective-C++. However, if
7612 bugs in the canonical type system are causing compilation failures,
7613 set this value to 0 to disable canonical types.
7615 @item switch-conversion-max-branch-ratio
7616 Switch initialization conversion will refuse to create arrays that are
7617 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7618 branches in the switch.
7620 @item max-partial-antic-length
7621 Maximum length of the partial antic set computed during the tree
7622 partial redundancy elimination optimization (@option{-ftree-pre}) when
7623 optimizing at @option{-O3} and above. For some sorts of source code
7624 the enhanced partial redundancy elimination optimization can run away,
7625 consuming all of the memory available on the host machine. This
7626 parameter sets a limit on the length of the sets that are computed,
7627 which prevents the runaway behavior. Setting a value of 0 for
7628 this parameter will allow an unlimited set length.
7630 @item sccvn-max-scc-size
7631 Maximum size of a strongly connected component (SCC) during SCCVN
7632 processing. If this limit is hit, SCCVN processing for the whole
7633 function will not be done and optimizations depending on it will
7634 be disabled. The default maximum SCC size is 10000.
7636 @item ira-max-loops-num
7637 IRA uses a regional register allocation by default. If a function
7638 contains loops more than number given by the parameter, only at most
7639 given number of the most frequently executed loops will form regions
7640 for the regional register allocation. The default value of the
7643 @item ira-max-conflict-table-size
7644 Although IRA uses a sophisticated algorithm of compression conflict
7645 table, the table can be still big for huge functions. If the conflict
7646 table for a function could be more than size in MB given by the
7647 parameter, the conflict table is not built and faster, simpler, and
7648 lower quality register allocation algorithm will be used. The
7649 algorithm do not use pseudo-register conflicts. The default value of
7650 the parameter is 2000.
7655 @node Preprocessor Options
7656 @section Options Controlling the Preprocessor
7657 @cindex preprocessor options
7658 @cindex options, preprocessor
7660 These options control the C preprocessor, which is run on each C source
7661 file before actual compilation.
7663 If you use the @option{-E} option, nothing is done except preprocessing.
7664 Some of these options make sense only together with @option{-E} because
7665 they cause the preprocessor output to be unsuitable for actual
7670 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7671 and pass @var{option} directly through to the preprocessor. If
7672 @var{option} contains commas, it is split into multiple options at the
7673 commas. However, many options are modified, translated or interpreted
7674 by the compiler driver before being passed to the preprocessor, and
7675 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7676 interface is undocumented and subject to change, so whenever possible
7677 you should avoid using @option{-Wp} and let the driver handle the
7680 @item -Xpreprocessor @var{option}
7681 @opindex preprocessor
7682 Pass @var{option} as an option to the preprocessor. You can use this to
7683 supply system-specific preprocessor options which GCC does not know how to
7686 If you want to pass an option that takes an argument, you must use
7687 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7690 @include cppopts.texi
7692 @node Assembler Options
7693 @section Passing Options to the Assembler
7695 @c prevent bad page break with this line
7696 You can pass options to the assembler.
7699 @item -Wa,@var{option}
7701 Pass @var{option} as an option to the assembler. If @var{option}
7702 contains commas, it is split into multiple options at the commas.
7704 @item -Xassembler @var{option}
7706 Pass @var{option} as an option to the assembler. You can use this to
7707 supply system-specific assembler options which GCC does not know how to
7710 If you want to pass an option that takes an argument, you must use
7711 @option{-Xassembler} twice, once for the option and once for the argument.
7716 @section Options for Linking
7717 @cindex link options
7718 @cindex options, linking
7720 These options come into play when the compiler links object files into
7721 an executable output file. They are meaningless if the compiler is
7722 not doing a link step.
7726 @item @var{object-file-name}
7727 A file name that does not end in a special recognized suffix is
7728 considered to name an object file or library. (Object files are
7729 distinguished from libraries by the linker according to the file
7730 contents.) If linking is done, these object files are used as input
7739 If any of these options is used, then the linker is not run, and
7740 object file names should not be used as arguments. @xref{Overall
7744 @item -l@var{library}
7745 @itemx -l @var{library}
7747 Search the library named @var{library} when linking. (The second
7748 alternative with the library as a separate argument is only for
7749 POSIX compliance and is not recommended.)
7751 It makes a difference where in the command you write this option; the
7752 linker searches and processes libraries and object files in the order they
7753 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7754 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7755 to functions in @samp{z}, those functions may not be loaded.
7757 The linker searches a standard list of directories for the library,
7758 which is actually a file named @file{lib@var{library}.a}. The linker
7759 then uses this file as if it had been specified precisely by name.
7761 The directories searched include several standard system directories
7762 plus any that you specify with @option{-L}.
7764 Normally the files found this way are library files---archive files
7765 whose members are object files. The linker handles an archive file by
7766 scanning through it for members which define symbols that have so far
7767 been referenced but not defined. But if the file that is found is an
7768 ordinary object file, it is linked in the usual fashion. The only
7769 difference between using an @option{-l} option and specifying a file name
7770 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7771 and searches several directories.
7775 You need this special case of the @option{-l} option in order to
7776 link an Objective-C or Objective-C++ program.
7779 @opindex nostartfiles
7780 Do not use the standard system startup files when linking.
7781 The standard system libraries are used normally, unless @option{-nostdlib}
7782 or @option{-nodefaultlibs} is used.
7784 @item -nodefaultlibs
7785 @opindex nodefaultlibs
7786 Do not use the standard system libraries when linking.
7787 Only the libraries you specify will be passed to the linker.
7788 The standard startup files are used normally, unless @option{-nostartfiles}
7789 is used. The compiler may generate calls to @code{memcmp},
7790 @code{memset}, @code{memcpy} and @code{memmove}.
7791 These entries are usually resolved by entries in
7792 libc. These entry points should be supplied through some other
7793 mechanism when this option is specified.
7797 Do not use the standard system startup files or libraries when linking.
7798 No startup files and only the libraries you specify will be passed to
7799 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7800 @code{memcpy} and @code{memmove}.
7801 These entries are usually resolved by entries in
7802 libc. These entry points should be supplied through some other
7803 mechanism when this option is specified.
7805 @cindex @option{-lgcc}, use with @option{-nostdlib}
7806 @cindex @option{-nostdlib} and unresolved references
7807 @cindex unresolved references and @option{-nostdlib}
7808 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7809 @cindex @option{-nodefaultlibs} and unresolved references
7810 @cindex unresolved references and @option{-nodefaultlibs}
7811 One of the standard libraries bypassed by @option{-nostdlib} and
7812 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7813 that GCC uses to overcome shortcomings of particular machines, or special
7814 needs for some languages.
7815 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7816 Collection (GCC) Internals},
7817 for more discussion of @file{libgcc.a}.)
7818 In most cases, you need @file{libgcc.a} even when you want to avoid
7819 other standard libraries. In other words, when you specify @option{-nostdlib}
7820 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7821 This ensures that you have no unresolved references to internal GCC
7822 library subroutines. (For example, @samp{__main}, used to ensure C++
7823 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7824 GNU Compiler Collection (GCC) Internals}.)
7828 Produce a position independent executable on targets which support it.
7829 For predictable results, you must also specify the same set of options
7830 that were used to generate code (@option{-fpie}, @option{-fPIE},
7831 or model suboptions) when you specify this option.
7835 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7836 that support it. This instructs the linker to add all symbols, not
7837 only used ones, to the dynamic symbol table. This option is needed
7838 for some uses of @code{dlopen} or to allow obtaining backtraces
7839 from within a program.
7843 Remove all symbol table and relocation information from the executable.
7847 On systems that support dynamic linking, this prevents linking with the shared
7848 libraries. On other systems, this option has no effect.
7852 Produce a shared object which can then be linked with other objects to
7853 form an executable. Not all systems support this option. For predictable
7854 results, you must also specify the same set of options that were used to
7855 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7856 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7857 needs to build supplementary stub code for constructors to work. On
7858 multi-libbed systems, @samp{gcc -shared} must select the correct support
7859 libraries to link against. Failing to supply the correct flags may lead
7860 to subtle defects. Supplying them in cases where they are not necessary
7863 @item -shared-libgcc
7864 @itemx -static-libgcc
7865 @opindex shared-libgcc
7866 @opindex static-libgcc
7867 On systems that provide @file{libgcc} as a shared library, these options
7868 force the use of either the shared or static version respectively.
7869 If no shared version of @file{libgcc} was built when the compiler was
7870 configured, these options have no effect.
7872 There are several situations in which an application should use the
7873 shared @file{libgcc} instead of the static version. The most common
7874 of these is when the application wishes to throw and catch exceptions
7875 across different shared libraries. In that case, each of the libraries
7876 as well as the application itself should use the shared @file{libgcc}.
7878 Therefore, the G++ and GCJ drivers automatically add
7879 @option{-shared-libgcc} whenever you build a shared library or a main
7880 executable, because C++ and Java programs typically use exceptions, so
7881 this is the right thing to do.
7883 If, instead, you use the GCC driver to create shared libraries, you may
7884 find that they will not always be linked with the shared @file{libgcc}.
7885 If GCC finds, at its configuration time, that you have a non-GNU linker
7886 or a GNU linker that does not support option @option{--eh-frame-hdr},
7887 it will link the shared version of @file{libgcc} into shared libraries
7888 by default. Otherwise, it will take advantage of the linker and optimize
7889 away the linking with the shared version of @file{libgcc}, linking with
7890 the static version of libgcc by default. This allows exceptions to
7891 propagate through such shared libraries, without incurring relocation
7892 costs at library load time.
7894 However, if a library or main executable is supposed to throw or catch
7895 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7896 for the languages used in the program, or using the option
7897 @option{-shared-libgcc}, such that it is linked with the shared
7902 Bind references to global symbols when building a shared object. Warn
7903 about any unresolved references (unless overridden by the link editor
7904 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7907 @item -T @var{script}
7909 @cindex linker script
7910 Use @var{script} as the linker script. This option is supported by most
7911 systems using the GNU linker. On some targets, such as bare-board
7912 targets without an operating system, the @option{-T} option may be required
7913 when linking to avoid references to undefined symbols.
7915 @item -Xlinker @var{option}
7917 Pass @var{option} as an option to the linker. You can use this to
7918 supply system-specific linker options which GCC does not know how to
7921 If you want to pass an option that takes an argument, you must use
7922 @option{-Xlinker} twice, once for the option and once for the argument.
7923 For example, to pass @option{-assert definitions}, you must write
7924 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7925 @option{-Xlinker "-assert definitions"}, because this passes the entire
7926 string as a single argument, which is not what the linker expects.
7928 @item -Wl,@var{option}
7930 Pass @var{option} as an option to the linker. If @var{option} contains
7931 commas, it is split into multiple options at the commas.
7933 @item -u @var{symbol}
7935 Pretend the symbol @var{symbol} is undefined, to force linking of
7936 library modules to define it. You can use @option{-u} multiple times with
7937 different symbols to force loading of additional library modules.
7940 @node Directory Options
7941 @section Options for Directory Search
7942 @cindex directory options
7943 @cindex options, directory search
7946 These options specify directories to search for header files, for
7947 libraries and for parts of the compiler:
7952 Add the directory @var{dir} to the head of the list of directories to be
7953 searched for header files. This can be used to override a system header
7954 file, substituting your own version, since these directories are
7955 searched before the system header file directories. However, you should
7956 not use this option to add directories that contain vendor-supplied
7957 system header files (use @option{-isystem} for that). If you use more than
7958 one @option{-I} option, the directories are scanned in left-to-right
7959 order; the standard system directories come after.
7961 If a standard system include directory, or a directory specified with
7962 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7963 option will be ignored. The directory will still be searched but as a
7964 system directory at its normal position in the system include chain.
7965 This is to ensure that GCC's procedure to fix buggy system headers and
7966 the ordering for the include_next directive are not inadvertently changed.
7967 If you really need to change the search order for system directories,
7968 use the @option{-nostdinc} and/or @option{-isystem} options.
7970 @item -iquote@var{dir}
7972 Add the directory @var{dir} to the head of the list of directories to
7973 be searched for header files only for the case of @samp{#include
7974 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7975 otherwise just like @option{-I}.
7979 Add directory @var{dir} to the list of directories to be searched
7982 @item -B@var{prefix}
7984 This option specifies where to find the executables, libraries,
7985 include files, and data files of the compiler itself.
7987 The compiler driver program runs one or more of the subprograms
7988 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7989 @var{prefix} as a prefix for each program it tries to run, both with and
7990 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7992 For each subprogram to be run, the compiler driver first tries the
7993 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7994 was not specified, the driver tries two standard prefixes, which are
7995 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7996 those results in a file name that is found, the unmodified program
7997 name is searched for using the directories specified in your
7998 @env{PATH} environment variable.
8000 The compiler will check to see if the path provided by the @option{-B}
8001 refers to a directory, and if necessary it will add a directory
8002 separator character at the end of the path.
8004 @option{-B} prefixes that effectively specify directory names also apply
8005 to libraries in the linker, because the compiler translates these
8006 options into @option{-L} options for the linker. They also apply to
8007 includes files in the preprocessor, because the compiler translates these
8008 options into @option{-isystem} options for the preprocessor. In this case,
8009 the compiler appends @samp{include} to the prefix.
8011 The run-time support file @file{libgcc.a} can also be searched for using
8012 the @option{-B} prefix, if needed. If it is not found there, the two
8013 standard prefixes above are tried, and that is all. The file is left
8014 out of the link if it is not found by those means.
8016 Another way to specify a prefix much like the @option{-B} prefix is to use
8017 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
8020 As a special kludge, if the path provided by @option{-B} is
8021 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
8022 9, then it will be replaced by @file{[dir/]include}. This is to help
8023 with boot-strapping the compiler.
8025 @item -specs=@var{file}
8027 Process @var{file} after the compiler reads in the standard @file{specs}
8028 file, in order to override the defaults that the @file{gcc} driver
8029 program uses when determining what switches to pass to @file{cc1},
8030 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
8031 @option{-specs=@var{file}} can be specified on the command line, and they
8032 are processed in order, from left to right.
8034 @item --sysroot=@var{dir}
8036 Use @var{dir} as the logical root directory for headers and libraries.
8037 For example, if the compiler would normally search for headers in
8038 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
8039 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
8041 If you use both this option and the @option{-isysroot} option, then
8042 the @option{--sysroot} option will apply to libraries, but the
8043 @option{-isysroot} option will apply to header files.
8045 The GNU linker (beginning with version 2.16) has the necessary support
8046 for this option. If your linker does not support this option, the
8047 header file aspect of @option{--sysroot} will still work, but the
8048 library aspect will not.
8052 This option has been deprecated. Please use @option{-iquote} instead for
8053 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
8054 Any directories you specify with @option{-I} options before the @option{-I-}
8055 option are searched only for the case of @samp{#include "@var{file}"};
8056 they are not searched for @samp{#include <@var{file}>}.
8058 If additional directories are specified with @option{-I} options after
8059 the @option{-I-}, these directories are searched for all @samp{#include}
8060 directives. (Ordinarily @emph{all} @option{-I} directories are used
8063 In addition, the @option{-I-} option inhibits the use of the current
8064 directory (where the current input file came from) as the first search
8065 directory for @samp{#include "@var{file}"}. There is no way to
8066 override this effect of @option{-I-}. With @option{-I.} you can specify
8067 searching the directory which was current when the compiler was
8068 invoked. That is not exactly the same as what the preprocessor does
8069 by default, but it is often satisfactory.
8071 @option{-I-} does not inhibit the use of the standard system directories
8072 for header files. Thus, @option{-I-} and @option{-nostdinc} are
8079 @section Specifying subprocesses and the switches to pass to them
8082 @command{gcc} is a driver program. It performs its job by invoking a
8083 sequence of other programs to do the work of compiling, assembling and
8084 linking. GCC interprets its command-line parameters and uses these to
8085 deduce which programs it should invoke, and which command-line options
8086 it ought to place on their command lines. This behavior is controlled
8087 by @dfn{spec strings}. In most cases there is one spec string for each
8088 program that GCC can invoke, but a few programs have multiple spec
8089 strings to control their behavior. The spec strings built into GCC can
8090 be overridden by using the @option{-specs=} command-line switch to specify
8093 @dfn{Spec files} are plaintext files that are used to construct spec
8094 strings. They consist of a sequence of directives separated by blank
8095 lines. The type of directive is determined by the first non-whitespace
8096 character on the line and it can be one of the following:
8099 @item %@var{command}
8100 Issues a @var{command} to the spec file processor. The commands that can
8104 @item %include <@var{file}>
8106 Search for @var{file} and insert its text at the current point in the
8109 @item %include_noerr <@var{file}>
8110 @cindex %include_noerr
8111 Just like @samp{%include}, but do not generate an error message if the include
8112 file cannot be found.
8114 @item %rename @var{old_name} @var{new_name}
8116 Rename the spec string @var{old_name} to @var{new_name}.
8120 @item *[@var{spec_name}]:
8121 This tells the compiler to create, override or delete the named spec
8122 string. All lines after this directive up to the next directive or
8123 blank line are considered to be the text for the spec string. If this
8124 results in an empty string then the spec will be deleted. (Or, if the
8125 spec did not exist, then nothing will happened.) Otherwise, if the spec
8126 does not currently exist a new spec will be created. If the spec does
8127 exist then its contents will be overridden by the text of this
8128 directive, unless the first character of that text is the @samp{+}
8129 character, in which case the text will be appended to the spec.
8131 @item [@var{suffix}]:
8132 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
8133 and up to the next directive or blank line are considered to make up the
8134 spec string for the indicated suffix. When the compiler encounters an
8135 input file with the named suffix, it will processes the spec string in
8136 order to work out how to compile that file. For example:
8143 This says that any input file whose name ends in @samp{.ZZ} should be
8144 passed to the program @samp{z-compile}, which should be invoked with the
8145 command-line switch @option{-input} and with the result of performing the
8146 @samp{%i} substitution. (See below.)
8148 As an alternative to providing a spec string, the text that follows a
8149 suffix directive can be one of the following:
8152 @item @@@var{language}
8153 This says that the suffix is an alias for a known @var{language}. This is
8154 similar to using the @option{-x} command-line switch to GCC to specify a
8155 language explicitly. For example:
8162 Says that .ZZ files are, in fact, C++ source files.
8165 This causes an error messages saying:
8168 @var{name} compiler not installed on this system.
8172 GCC already has an extensive list of suffixes built into it.
8173 This directive will add an entry to the end of the list of suffixes, but
8174 since the list is searched from the end backwards, it is effectively
8175 possible to override earlier entries using this technique.
8179 GCC has the following spec strings built into it. Spec files can
8180 override these strings or create their own. Note that individual
8181 targets can also add their own spec strings to this list.
8184 asm Options to pass to the assembler
8185 asm_final Options to pass to the assembler post-processor
8186 cpp Options to pass to the C preprocessor
8187 cc1 Options to pass to the C compiler
8188 cc1plus Options to pass to the C++ compiler
8189 endfile Object files to include at the end of the link
8190 link Options to pass to the linker
8191 lib Libraries to include on the command line to the linker
8192 libgcc Decides which GCC support library to pass to the linker
8193 linker Sets the name of the linker
8194 predefines Defines to be passed to the C preprocessor
8195 signed_char Defines to pass to CPP to say whether @code{char} is signed
8197 startfile Object files to include at the start of the link
8200 Here is a small example of a spec file:
8206 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
8209 This example renames the spec called @samp{lib} to @samp{old_lib} and
8210 then overrides the previous definition of @samp{lib} with a new one.
8211 The new definition adds in some extra command-line options before
8212 including the text of the old definition.
8214 @dfn{Spec strings} are a list of command-line options to be passed to their
8215 corresponding program. In addition, the spec strings can contain
8216 @samp{%}-prefixed sequences to substitute variable text or to
8217 conditionally insert text into the command line. Using these constructs
8218 it is possible to generate quite complex command lines.
8220 Here is a table of all defined @samp{%}-sequences for spec
8221 strings. Note that spaces are not generated automatically around the
8222 results of expanding these sequences. Therefore you can concatenate them
8223 together or combine them with constant text in a single argument.
8227 Substitute one @samp{%} into the program name or argument.
8230 Substitute the name of the input file being processed.
8233 Substitute the basename of the input file being processed.
8234 This is the substring up to (and not including) the last period
8235 and not including the directory.
8238 This is the same as @samp{%b}, but include the file suffix (text after
8242 Marks the argument containing or following the @samp{%d} as a
8243 temporary file name, so that that file will be deleted if GCC exits
8244 successfully. Unlike @samp{%g}, this contributes no text to the
8247 @item %g@var{suffix}
8248 Substitute a file name that has suffix @var{suffix} and is chosen
8249 once per compilation, and mark the argument in the same way as
8250 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
8251 name is now chosen in a way that is hard to predict even when previously
8252 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
8253 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
8254 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
8255 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
8256 was simply substituted with a file name chosen once per compilation,
8257 without regard to any appended suffix (which was therefore treated
8258 just like ordinary text), making such attacks more likely to succeed.
8260 @item %u@var{suffix}
8261 Like @samp{%g}, but generates a new temporary file name even if
8262 @samp{%u@var{suffix}} was already seen.
8264 @item %U@var{suffix}
8265 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
8266 new one if there is no such last file name. In the absence of any
8267 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
8268 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
8269 would involve the generation of two distinct file names, one
8270 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
8271 simply substituted with a file name chosen for the previous @samp{%u},
8272 without regard to any appended suffix.
8274 @item %j@var{suffix}
8275 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
8276 writable, and if save-temps is off; otherwise, substitute the name
8277 of a temporary file, just like @samp{%u}. This temporary file is not
8278 meant for communication between processes, but rather as a junk
8281 @item %|@var{suffix}
8282 @itemx %m@var{suffix}
8283 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
8284 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
8285 all. These are the two most common ways to instruct a program that it
8286 should read from standard input or write to standard output. If you
8287 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
8288 construct: see for example @file{f/lang-specs.h}.
8290 @item %.@var{SUFFIX}
8291 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
8292 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
8293 terminated by the next space or %.
8296 Marks the argument containing or following the @samp{%w} as the
8297 designated output file of this compilation. This puts the argument
8298 into the sequence of arguments that @samp{%o} will substitute later.
8301 Substitutes the names of all the output files, with spaces
8302 automatically placed around them. You should write spaces
8303 around the @samp{%o} as well or the results are undefined.
8304 @samp{%o} is for use in the specs for running the linker.
8305 Input files whose names have no recognized suffix are not compiled
8306 at all, but they are included among the output files, so they will
8310 Substitutes the suffix for object files. Note that this is
8311 handled specially when it immediately follows @samp{%g, %u, or %U},
8312 because of the need for those to form complete file names. The
8313 handling is such that @samp{%O} is treated exactly as if it had already
8314 been substituted, except that @samp{%g, %u, and %U} do not currently
8315 support additional @var{suffix} characters following @samp{%O} as they would
8316 following, for example, @samp{.o}.
8319 Substitutes the standard macro predefinitions for the
8320 current target machine. Use this when running @code{cpp}.
8323 Like @samp{%p}, but puts @samp{__} before and after the name of each
8324 predefined macro, except for macros that start with @samp{__} or with
8325 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8329 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8330 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8331 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8332 and @option{-imultilib} as necessary.
8335 Current argument is the name of a library or startup file of some sort.
8336 Search for that file in a standard list of directories and substitute
8337 the full name found.
8340 Print @var{str} as an error message. @var{str} is terminated by a newline.
8341 Use this when inconsistent options are detected.
8344 Substitute the contents of spec string @var{name} at this point.
8347 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8349 @item %x@{@var{option}@}
8350 Accumulate an option for @samp{%X}.
8353 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8357 Output the accumulated assembler options specified by @option{-Wa}.
8360 Output the accumulated preprocessor options specified by @option{-Wp}.
8363 Process the @code{asm} spec. This is used to compute the
8364 switches to be passed to the assembler.
8367 Process the @code{asm_final} spec. This is a spec string for
8368 passing switches to an assembler post-processor, if such a program is
8372 Process the @code{link} spec. This is the spec for computing the
8373 command line passed to the linker. Typically it will make use of the
8374 @samp{%L %G %S %D and %E} sequences.
8377 Dump out a @option{-L} option for each directory that GCC believes might
8378 contain startup files. If the target supports multilibs then the
8379 current multilib directory will be prepended to each of these paths.
8382 Process the @code{lib} spec. This is a spec string for deciding which
8383 libraries should be included on the command line to the linker.
8386 Process the @code{libgcc} spec. This is a spec string for deciding
8387 which GCC support library should be included on the command line to the linker.
8390 Process the @code{startfile} spec. This is a spec for deciding which
8391 object files should be the first ones passed to the linker. Typically
8392 this might be a file named @file{crt0.o}.
8395 Process the @code{endfile} spec. This is a spec string that specifies
8396 the last object files that will be passed to the linker.
8399 Process the @code{cpp} spec. This is used to construct the arguments
8400 to be passed to the C preprocessor.
8403 Process the @code{cc1} spec. This is used to construct the options to be
8404 passed to the actual C compiler (@samp{cc1}).
8407 Process the @code{cc1plus} spec. This is used to construct the options to be
8408 passed to the actual C++ compiler (@samp{cc1plus}).
8411 Substitute the variable part of a matched option. See below.
8412 Note that each comma in the substituted string is replaced by
8416 Remove all occurrences of @code{-S} from the command line. Note---this
8417 command is position dependent. @samp{%} commands in the spec string
8418 before this one will see @code{-S}, @samp{%} commands in the spec string
8419 after this one will not.
8421 @item %:@var{function}(@var{args})
8422 Call the named function @var{function}, passing it @var{args}.
8423 @var{args} is first processed as a nested spec string, then split
8424 into an argument vector in the usual fashion. The function returns
8425 a string which is processed as if it had appeared literally as part
8426 of the current spec.
8428 The following built-in spec functions are provided:
8432 The @code{getenv} spec function takes two arguments: an environment
8433 variable name and a string. If the environment variable is not
8434 defined, a fatal error is issued. Otherwise, the return value is the
8435 value of the environment variable concatenated with the string. For
8436 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8439 %:getenv(TOPDIR /include)
8442 expands to @file{/path/to/top/include}.
8444 @item @code{if-exists}
8445 The @code{if-exists} spec function takes one argument, an absolute
8446 pathname to a file. If the file exists, @code{if-exists} returns the
8447 pathname. Here is a small example of its usage:
8451 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8454 @item @code{if-exists-else}
8455 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8456 spec function, except that it takes two arguments. The first argument is
8457 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8458 returns the pathname. If it does not exist, it returns the second argument.
8459 This way, @code{if-exists-else} can be used to select one file or another,
8460 based on the existence of the first. Here is a small example of its usage:
8464 crt0%O%s %:if-exists(crti%O%s) \
8465 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8468 @item @code{replace-outfile}
8469 The @code{replace-outfile} spec function takes two arguments. It looks for the
8470 first argument in the outfiles array and replaces it with the second argument. Here
8471 is a small example of its usage:
8474 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8477 @item @code{print-asm-header}
8478 The @code{print-asm-header} function takes no arguments and simply
8479 prints a banner like:
8485 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8488 It is used to separate compiler options from assembler options
8489 in the @option{--target-help} output.
8493 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8494 If that switch was not specified, this substitutes nothing. Note that
8495 the leading dash is omitted when specifying this option, and it is
8496 automatically inserted if the substitution is performed. Thus the spec
8497 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8498 and would output the command line option @option{-foo}.
8500 @item %W@{@code{S}@}
8501 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8504 @item %@{@code{S}*@}
8505 Substitutes all the switches specified to GCC whose names start
8506 with @code{-S}, but which also take an argument. This is used for
8507 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8508 GCC considers @option{-o foo} as being
8509 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8510 text, including the space. Thus two arguments would be generated.
8512 @item %@{@code{S}*&@code{T}*@}
8513 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8514 (the order of @code{S} and @code{T} in the spec is not significant).
8515 There can be any number of ampersand-separated variables; for each the
8516 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8518 @item %@{@code{S}:@code{X}@}
8519 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8521 @item %@{!@code{S}:@code{X}@}
8522 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8524 @item %@{@code{S}*:@code{X}@}
8525 Substitutes @code{X} if one or more switches whose names start with
8526 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8527 once, no matter how many such switches appeared. However, if @code{%*}
8528 appears somewhere in @code{X}, then @code{X} will be substituted once
8529 for each matching switch, with the @code{%*} replaced by the part of
8530 that switch that matched the @code{*}.
8532 @item %@{.@code{S}:@code{X}@}
8533 Substitutes @code{X}, if processing a file with suffix @code{S}.
8535 @item %@{!.@code{S}:@code{X}@}
8536 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8538 @item %@{,@code{S}:@code{X}@}
8539 Substitutes @code{X}, if processing a file for language @code{S}.
8541 @item %@{!,@code{S}:@code{X}@}
8542 Substitutes @code{X}, if not processing a file for language @code{S}.
8544 @item %@{@code{S}|@code{P}:@code{X}@}
8545 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8546 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8547 @code{*} sequences as well, although they have a stronger binding than
8548 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8549 alternatives must be starred, and only the first matching alternative
8552 For example, a spec string like this:
8555 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8558 will output the following command-line options from the following input
8559 command-line options:
8564 -d fred.c -foo -baz -boggle
8565 -d jim.d -bar -baz -boggle
8568 @item %@{S:X; T:Y; :D@}
8570 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8571 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8572 be as many clauses as you need. This may be combined with @code{.},
8573 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8578 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8579 construct may contain other nested @samp{%} constructs or spaces, or
8580 even newlines. They are processed as usual, as described above.
8581 Trailing white space in @code{X} is ignored. White space may also
8582 appear anywhere on the left side of the colon in these constructs,
8583 except between @code{.} or @code{*} and the corresponding word.
8585 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8586 handled specifically in these constructs. If another value of
8587 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8588 @option{-W} switch is found later in the command line, the earlier
8589 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8590 just one letter, which passes all matching options.
8592 The character @samp{|} at the beginning of the predicate text is used to
8593 indicate that a command should be piped to the following command, but
8594 only if @option{-pipe} is specified.
8596 It is built into GCC which switches take arguments and which do not.
8597 (You might think it would be useful to generalize this to allow each
8598 compiler's spec to say which switches take arguments. But this cannot
8599 be done in a consistent fashion. GCC cannot even decide which input
8600 files have been specified without knowing which switches take arguments,
8601 and it must know which input files to compile in order to tell which
8604 GCC also knows implicitly that arguments starting in @option{-l} are to be
8605 treated as compiler output files, and passed to the linker in their
8606 proper position among the other output files.
8608 @c man begin OPTIONS
8610 @node Target Options
8611 @section Specifying Target Machine and Compiler Version
8612 @cindex target options
8613 @cindex cross compiling
8614 @cindex specifying machine version
8615 @cindex specifying compiler version and target machine
8616 @cindex compiler version, specifying
8617 @cindex target machine, specifying
8619 The usual way to run GCC is to run the executable called @file{gcc}, or
8620 @file{<machine>-gcc} when cross-compiling, or
8621 @file{<machine>-gcc-<version>} to run a version other than the one that
8622 was installed last. Sometimes this is inconvenient, so GCC provides
8623 options that will switch to another cross-compiler or version.
8626 @item -b @var{machine}
8628 The argument @var{machine} specifies the target machine for compilation.
8630 The value to use for @var{machine} is the same as was specified as the
8631 machine type when configuring GCC as a cross-compiler. For
8632 example, if a cross-compiler was configured with @samp{configure
8633 arm-elf}, meaning to compile for an arm processor with elf binaries,
8634 then you would specify @option{-b arm-elf} to run that cross compiler.
8635 Because there are other options beginning with @option{-b}, the
8636 configuration must contain a hyphen, or @option{-b} alone should be one
8637 argument followed by the configuration in the next argument.
8639 @item -V @var{version}
8641 The argument @var{version} specifies which version of GCC to run.
8642 This is useful when multiple versions are installed. For example,
8643 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8646 The @option{-V} and @option{-b} options work by running the
8647 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8648 use them if you can just run that directly.
8650 @node Submodel Options
8651 @section Hardware Models and Configurations
8652 @cindex submodel options
8653 @cindex specifying hardware config
8654 @cindex hardware models and configurations, specifying
8655 @cindex machine dependent options
8657 Earlier we discussed the standard option @option{-b} which chooses among
8658 different installed compilers for completely different target
8659 machines, such as VAX vs.@: 68000 vs.@: 80386.
8661 In addition, each of these target machine types can have its own
8662 special options, starting with @samp{-m}, to choose among various
8663 hardware models or configurations---for example, 68010 vs 68020,
8664 floating coprocessor or none. A single installed version of the
8665 compiler can compile for any model or configuration, according to the
8668 Some configurations of the compiler also support additional special
8669 options, usually for compatibility with other compilers on the same
8672 @c This list is ordered alphanumerically by subsection name.
8673 @c It should be the same order and spelling as these options are listed
8674 @c in Machine Dependent Options
8680 * Blackfin Options::
8684 * DEC Alpha Options::
8685 * DEC Alpha/VMS Options::
8687 * GNU/Linux Options::
8690 * i386 and x86-64 Options::
8701 * picoChip Options::
8703 * RS/6000 and PowerPC Options::
8704 * S/390 and zSeries Options::
8709 * System V Options::
8714 * Xstormy16 Options::
8720 @subsection ARC Options
8723 These options are defined for ARC implementations:
8728 Compile code for little endian mode. This is the default.
8732 Compile code for big endian mode.
8735 @opindex mmangle-cpu
8736 Prepend the name of the cpu to all public symbol names.
8737 In multiple-processor systems, there are many ARC variants with different
8738 instruction and register set characteristics. This flag prevents code
8739 compiled for one cpu to be linked with code compiled for another.
8740 No facility exists for handling variants that are ``almost identical''.
8741 This is an all or nothing option.
8743 @item -mcpu=@var{cpu}
8745 Compile code for ARC variant @var{cpu}.
8746 Which variants are supported depend on the configuration.
8747 All variants support @option{-mcpu=base}, this is the default.
8749 @item -mtext=@var{text-section}
8750 @itemx -mdata=@var{data-section}
8751 @itemx -mrodata=@var{readonly-data-section}
8755 Put functions, data, and readonly data in @var{text-section},
8756 @var{data-section}, and @var{readonly-data-section} respectively
8757 by default. This can be overridden with the @code{section} attribute.
8758 @xref{Variable Attributes}.
8760 @item -mfix-cortex-m3-ldrd
8761 @opindex mfix-cortex-m3-ldrd
8762 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
8763 with overlapping destination and base registers are used. This option avoids
8764 generating these instructions. This option is enabled by default when
8765 @option{-mcpu=cortex-m3} is specified.
8770 @subsection ARM Options
8773 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8777 @item -mabi=@var{name}
8779 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8780 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8783 @opindex mapcs-frame
8784 Generate a stack frame that is compliant with the ARM Procedure Call
8785 Standard for all functions, even if this is not strictly necessary for
8786 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8787 with this option will cause the stack frames not to be generated for
8788 leaf functions. The default is @option{-mno-apcs-frame}.
8792 This is a synonym for @option{-mapcs-frame}.
8795 @c not currently implemented
8796 @item -mapcs-stack-check
8797 @opindex mapcs-stack-check
8798 Generate code to check the amount of stack space available upon entry to
8799 every function (that actually uses some stack space). If there is
8800 insufficient space available then either the function
8801 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8802 called, depending upon the amount of stack space required. The run time
8803 system is required to provide these functions. The default is
8804 @option{-mno-apcs-stack-check}, since this produces smaller code.
8806 @c not currently implemented
8808 @opindex mapcs-float
8809 Pass floating point arguments using the float point registers. This is
8810 one of the variants of the APCS@. This option is recommended if the
8811 target hardware has a floating point unit or if a lot of floating point
8812 arithmetic is going to be performed by the code. The default is
8813 @option{-mno-apcs-float}, since integer only code is slightly increased in
8814 size if @option{-mapcs-float} is used.
8816 @c not currently implemented
8817 @item -mapcs-reentrant
8818 @opindex mapcs-reentrant
8819 Generate reentrant, position independent code. The default is
8820 @option{-mno-apcs-reentrant}.
8823 @item -mthumb-interwork
8824 @opindex mthumb-interwork
8825 Generate code which supports calling between the ARM and Thumb
8826 instruction sets. Without this option the two instruction sets cannot
8827 be reliably used inside one program. The default is
8828 @option{-mno-thumb-interwork}, since slightly larger code is generated
8829 when @option{-mthumb-interwork} is specified.
8831 @item -mno-sched-prolog
8832 @opindex mno-sched-prolog
8833 Prevent the reordering of instructions in the function prolog, or the
8834 merging of those instruction with the instructions in the function's
8835 body. This means that all functions will start with a recognizable set
8836 of instructions (or in fact one of a choice from a small set of
8837 different function prologues), and this information can be used to
8838 locate the start if functions inside an executable piece of code. The
8839 default is @option{-msched-prolog}.
8841 @item -mfloat-abi=@var{name}
8843 Specifies which floating-point ABI to use. Permissible values
8844 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8846 Specifying @samp{soft} causes GCC to generate output containing
8847 library calls for floating-point operations.
8848 @samp{softfp} allows the generation of code using hardware floating-point
8849 instructions, but still uses the soft-float calling conventions.
8850 @samp{hard} allows generation of floating-point instructions
8851 and uses FPU-specific calling conventions.
8853 Using @option{-mfloat-abi=hard} with VFP coprocessors is not supported.
8854 Use @option{-mfloat-abi=softfp} with the appropriate @option{-mfpu} option
8855 to allow the compiler to generate code that makes use of the hardware
8856 floating-point capabilities for these CPUs.
8858 The default depends on the specific target configuration. Note that
8859 the hard-float and soft-float ABIs are not link-compatible; you must
8860 compile your entire program with the same ABI, and link with a
8861 compatible set of libraries.
8864 @opindex mhard-float
8865 Equivalent to @option{-mfloat-abi=hard}.
8868 @opindex msoft-float
8869 Equivalent to @option{-mfloat-abi=soft}.
8871 @item -mlittle-endian
8872 @opindex mlittle-endian
8873 Generate code for a processor running in little-endian mode. This is
8874 the default for all standard configurations.
8877 @opindex mbig-endian
8878 Generate code for a processor running in big-endian mode; the default is
8879 to compile code for a little-endian processor.
8881 @item -mwords-little-endian
8882 @opindex mwords-little-endian
8883 This option only applies when generating code for big-endian processors.
8884 Generate code for a little-endian word order but a big-endian byte
8885 order. That is, a byte order of the form @samp{32107654}. Note: this
8886 option should only be used if you require compatibility with code for
8887 big-endian ARM processors generated by versions of the compiler prior to
8890 @item -mcpu=@var{name}
8892 This specifies the name of the target ARM processor. GCC uses this name
8893 to determine what kind of instructions it can emit when generating
8894 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8895 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8896 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8897 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8898 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8900 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8901 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
8902 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8903 @samp{strongarm1110},
8904 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8905 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8906 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8907 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8908 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8909 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8910 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8911 @samp{cortex-a8}, @samp{cortex-a9},
8912 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
8914 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
8916 @item -mtune=@var{name}
8918 This option is very similar to the @option{-mcpu=} option, except that
8919 instead of specifying the actual target processor type, and hence
8920 restricting which instructions can be used, it specifies that GCC should
8921 tune the performance of the code as if the target were of the type
8922 specified in this option, but still choosing the instructions that it
8923 will generate based on the cpu specified by a @option{-mcpu=} option.
8924 For some ARM implementations better performance can be obtained by using
8927 @item -march=@var{name}
8929 This specifies the name of the target ARM architecture. GCC uses this
8930 name to determine what kind of instructions it can emit when generating
8931 assembly code. This option can be used in conjunction with or instead
8932 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8933 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8934 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
8935 @samp{armv6}, @samp{armv6j},
8936 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
8937 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
8938 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
8940 @item -mfpu=@var{name}
8941 @itemx -mfpe=@var{number}
8942 @itemx -mfp=@var{number}
8946 This specifies what floating point hardware (or hardware emulation) is
8947 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8948 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16} and
8949 @samp{neon}. @option{-mfp} and @option{-mfpe}
8950 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8951 with older versions of GCC@.
8953 If @option{-msoft-float} is specified this specifies the format of
8954 floating point values.
8956 @item -mstructure-size-boundary=@var{n}
8957 @opindex mstructure-size-boundary
8958 The size of all structures and unions will be rounded up to a multiple
8959 of the number of bits set by this option. Permissible values are 8, 32
8960 and 64. The default value varies for different toolchains. For the COFF
8961 targeted toolchain the default value is 8. A value of 64 is only allowed
8962 if the underlying ABI supports it.
8964 Specifying the larger number can produce faster, more efficient code, but
8965 can also increase the size of the program. Different values are potentially
8966 incompatible. Code compiled with one value cannot necessarily expect to
8967 work with code or libraries compiled with another value, if they exchange
8968 information using structures or unions.
8970 @item -mabort-on-noreturn
8971 @opindex mabort-on-noreturn
8972 Generate a call to the function @code{abort} at the end of a
8973 @code{noreturn} function. It will be executed if the function tries to
8977 @itemx -mno-long-calls
8978 @opindex mlong-calls
8979 @opindex mno-long-calls
8980 Tells the compiler to perform function calls by first loading the
8981 address of the function into a register and then performing a subroutine
8982 call on this register. This switch is needed if the target function
8983 will lie outside of the 64 megabyte addressing range of the offset based
8984 version of subroutine call instruction.
8986 Even if this switch is enabled, not all function calls will be turned
8987 into long calls. The heuristic is that static functions, functions
8988 which have the @samp{short-call} attribute, functions that are inside
8989 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8990 definitions have already been compiled within the current compilation
8991 unit, will not be turned into long calls. The exception to this rule is
8992 that weak function definitions, functions with the @samp{long-call}
8993 attribute or the @samp{section} attribute, and functions that are within
8994 the scope of a @samp{#pragma long_calls} directive, will always be
8995 turned into long calls.
8997 This feature is not enabled by default. Specifying
8998 @option{-mno-long-calls} will restore the default behavior, as will
8999 placing the function calls within the scope of a @samp{#pragma
9000 long_calls_off} directive. Note these switches have no effect on how
9001 the compiler generates code to handle function calls via function
9004 @item -mnop-fun-dllimport
9005 @opindex mnop-fun-dllimport
9006 Disable support for the @code{dllimport} attribute.
9008 @item -msingle-pic-base
9009 @opindex msingle-pic-base
9010 Treat the register used for PIC addressing as read-only, rather than
9011 loading it in the prologue for each function. The run-time system is
9012 responsible for initializing this register with an appropriate value
9013 before execution begins.
9015 @item -mpic-register=@var{reg}
9016 @opindex mpic-register
9017 Specify the register to be used for PIC addressing. The default is R10
9018 unless stack-checking is enabled, when R9 is used.
9020 @item -mcirrus-fix-invalid-insns
9021 @opindex mcirrus-fix-invalid-insns
9022 @opindex mno-cirrus-fix-invalid-insns
9023 Insert NOPs into the instruction stream to in order to work around
9024 problems with invalid Maverick instruction combinations. This option
9025 is only valid if the @option{-mcpu=ep9312} option has been used to
9026 enable generation of instructions for the Cirrus Maverick floating
9027 point co-processor. This option is not enabled by default, since the
9028 problem is only present in older Maverick implementations. The default
9029 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
9032 @item -mpoke-function-name
9033 @opindex mpoke-function-name
9034 Write the name of each function into the text section, directly
9035 preceding the function prologue. The generated code is similar to this:
9039 .ascii "arm_poke_function_name", 0
9042 .word 0xff000000 + (t1 - t0)
9043 arm_poke_function_name
9045 stmfd sp!, @{fp, ip, lr, pc@}
9049 When performing a stack backtrace, code can inspect the value of
9050 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
9051 location @code{pc - 12} and the top 8 bits are set, then we know that
9052 there is a function name embedded immediately preceding this location
9053 and has length @code{((pc[-3]) & 0xff000000)}.
9057 Generate code for the Thumb instruction set. The default is to
9058 use the 32-bit ARM instruction set.
9059 This option automatically enables either 16-bit Thumb-1 or
9060 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
9061 and @option{-march=@var{name}} options.
9064 @opindex mtpcs-frame
9065 Generate a stack frame that is compliant with the Thumb Procedure Call
9066 Standard for all non-leaf functions. (A leaf function is one that does
9067 not call any other functions.) The default is @option{-mno-tpcs-frame}.
9069 @item -mtpcs-leaf-frame
9070 @opindex mtpcs-leaf-frame
9071 Generate a stack frame that is compliant with the Thumb Procedure Call
9072 Standard for all leaf functions. (A leaf function is one that does
9073 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
9075 @item -mcallee-super-interworking
9076 @opindex mcallee-super-interworking
9077 Gives all externally visible functions in the file being compiled an ARM
9078 instruction set header which switches to Thumb mode before executing the
9079 rest of the function. This allows these functions to be called from
9080 non-interworking code.
9082 @item -mcaller-super-interworking
9083 @opindex mcaller-super-interworking
9084 Allows calls via function pointers (including virtual functions) to
9085 execute correctly regardless of whether the target code has been
9086 compiled for interworking or not. There is a small overhead in the cost
9087 of executing a function pointer if this option is enabled.
9089 @item -mtp=@var{name}
9091 Specify the access model for the thread local storage pointer. The valid
9092 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
9093 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
9094 (supported in the arm6k architecture), and @option{auto}, which uses the
9095 best available method for the selected processor. The default setting is
9098 @item -mword-relocations
9099 @opindex mword-relocations
9100 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
9101 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
9102 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
9108 @subsection AVR Options
9111 These options are defined for AVR implementations:
9114 @item -mmcu=@var{mcu}
9116 Specify ATMEL AVR instruction set or MCU type.
9118 Instruction set avr1 is for the minimal AVR core, not supported by the C
9119 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9120 attiny11, attiny12, attiny15, attiny28).
9122 Instruction set avr2 (default) is for the classic AVR core with up to
9123 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9124 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9125 at90c8534, at90s8535).
9127 Instruction set avr3 is for the classic AVR core with up to 128K program
9128 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9130 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9131 memory space (MCU types: atmega8, atmega83, atmega85).
9133 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9134 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9135 atmega64, atmega128, at43usb355, at94k).
9139 Output instruction sizes to the asm file.
9141 @item -minit-stack=@var{N}
9142 @opindex minit-stack
9143 Specify the initial stack address, which may be a symbol or numeric value,
9144 @samp{__stack} is the default.
9146 @item -mno-interrupts
9147 @opindex mno-interrupts
9148 Generated code is not compatible with hardware interrupts.
9149 Code size will be smaller.
9151 @item -mcall-prologues
9152 @opindex mcall-prologues
9153 Functions prologues/epilogues expanded as call to appropriate
9154 subroutines. Code size will be smaller.
9156 @item -mno-tablejump
9157 @opindex mno-tablejump
9158 Do not generate tablejump insns which sometimes increase code size.
9161 @opindex mtiny-stack
9162 Change only the low 8 bits of the stack pointer.
9166 Assume int to be 8 bit integer. This affects the sizes of all types: A
9167 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
9168 and long long will be 4 bytes. Please note that this option does not
9169 comply to the C standards, but it will provide you with smaller code
9173 @node Blackfin Options
9174 @subsection Blackfin Options
9175 @cindex Blackfin Options
9178 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
9180 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
9181 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
9182 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
9183 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
9184 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
9185 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
9187 The optional @var{sirevision} specifies the silicon revision of the target
9188 Blackfin processor. Any workarounds available for the targeted silicon revision
9189 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
9190 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
9191 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
9192 hexadecimal digits representing the major and minor numbers in the silicon
9193 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
9194 is not defined. If @var{sirevision} is @samp{any}, the
9195 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
9196 If this optional @var{sirevision} is not used, GCC assumes the latest known
9197 silicon revision of the targeted Blackfin processor.
9199 Support for @samp{bf561} is incomplete. For @samp{bf561},
9200 Only the processor macro is defined.
9201 Without this option, @samp{bf532} is used as the processor by default.
9202 The corresponding predefined processor macros for @var{cpu} is to
9203 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
9204 provided by libgloss to be linked in if @option{-msim} is not given.
9208 Specifies that the program will be run on the simulator. This causes
9209 the simulator BSP provided by libgloss to be linked in. This option
9210 has effect only for @samp{bfin-elf} toolchain.
9211 Certain other options, such as @option{-mid-shared-library} and
9212 @option{-mfdpic}, imply @option{-msim}.
9214 @item -momit-leaf-frame-pointer
9215 @opindex momit-leaf-frame-pointer
9216 Don't keep the frame pointer in a register for leaf functions. This
9217 avoids the instructions to save, set up and restore frame pointers and
9218 makes an extra register available in leaf functions. The option
9219 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9220 which might make debugging harder.
9222 @item -mspecld-anomaly
9223 @opindex mspecld-anomaly
9224 When enabled, the compiler will ensure that the generated code does not
9225 contain speculative loads after jump instructions. If this option is used,
9226 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
9228 @item -mno-specld-anomaly
9229 @opindex mno-specld-anomaly
9230 Don't generate extra code to prevent speculative loads from occurring.
9232 @item -mcsync-anomaly
9233 @opindex mcsync-anomaly
9234 When enabled, the compiler will ensure that the generated code does not
9235 contain CSYNC or SSYNC instructions too soon after conditional branches.
9236 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
9238 @item -mno-csync-anomaly
9239 @opindex mno-csync-anomaly
9240 Don't generate extra code to prevent CSYNC or SSYNC instructions from
9241 occurring too soon after a conditional branch.
9245 When enabled, the compiler is free to take advantage of the knowledge that
9246 the entire program fits into the low 64k of memory.
9249 @opindex mno-low-64k
9250 Assume that the program is arbitrarily large. This is the default.
9252 @item -mstack-check-l1
9253 @opindex mstack-check-l1
9254 Do stack checking using information placed into L1 scratchpad memory by the
9257 @item -mid-shared-library
9258 @opindex mid-shared-library
9259 Generate code that supports shared libraries via the library ID method.
9260 This allows for execute in place and shared libraries in an environment
9261 without virtual memory management. This option implies @option{-fPIC}.
9262 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9264 @item -mno-id-shared-library
9265 @opindex mno-id-shared-library
9266 Generate code that doesn't assume ID based shared libraries are being used.
9267 This is the default.
9269 @item -mleaf-id-shared-library
9270 @opindex mleaf-id-shared-library
9271 Generate code that supports shared libraries via the library ID method,
9272 but assumes that this library or executable won't link against any other
9273 ID shared libraries. That allows the compiler to use faster code for jumps
9276 @item -mno-leaf-id-shared-library
9277 @opindex mno-leaf-id-shared-library
9278 Do not assume that the code being compiled won't link against any ID shared
9279 libraries. Slower code will be generated for jump and call insns.
9281 @item -mshared-library-id=n
9282 @opindex mshared-library-id
9283 Specified the identification number of the ID based shared library being
9284 compiled. Specifying a value of 0 will generate more compact code, specifying
9285 other values will force the allocation of that number to the current
9286 library but is no more space or time efficient than omitting this option.
9290 Generate code that allows the data segment to be located in a different
9291 area of memory from the text segment. This allows for execute in place in
9292 an environment without virtual memory management by eliminating relocations
9293 against the text section.
9296 @opindex mno-sep-data
9297 Generate code that assumes that the data segment follows the text segment.
9298 This is the default.
9301 @itemx -mno-long-calls
9302 @opindex mlong-calls
9303 @opindex mno-long-calls
9304 Tells the compiler to perform function calls by first loading the
9305 address of the function into a register and then performing a subroutine
9306 call on this register. This switch is needed if the target function
9307 will lie outside of the 24 bit addressing range of the offset based
9308 version of subroutine call instruction.
9310 This feature is not enabled by default. Specifying
9311 @option{-mno-long-calls} will restore the default behavior. Note these
9312 switches have no effect on how the compiler generates code to handle
9313 function calls via function pointers.
9317 Link with the fast floating-point library. This library relaxes some of
9318 the IEEE floating-point standard's rules for checking inputs against
9319 Not-a-Number (NAN), in the interest of performance.
9322 @opindex minline-plt
9323 Enable inlining of PLT entries in function calls to functions that are
9324 not known to bind locally. It has no effect without @option{-mfdpic}.
9328 Build standalone application for multicore Blackfin processor. Proper
9329 start files and link scripts will be used to support multicore.
9330 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9331 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9332 @option{-mcorea} or @option{-mcoreb}. If it's used without
9333 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9334 programming model is used. In this model, the main function of Core B
9335 should be named as coreb_main. If it's used with @option{-mcorea} or
9336 @option{-mcoreb}, one application per core programming model is used.
9337 If this option is not used, single core application programming
9342 Build standalone application for Core A of BF561 when using
9343 one application per core programming model. Proper start files
9344 and link scripts will be used to support Core A. This option
9345 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9349 Build standalone application for Core B of BF561 when using
9350 one application per core programming model. Proper start files
9351 and link scripts will be used to support Core B. This option
9352 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9353 should be used instead of main. It must be used with
9354 @option{-mmulticore}.
9358 Build standalone application for SDRAM. Proper start files and
9359 link scripts will be used to put the application into SDRAM.
9360 Loader should initialize SDRAM before loading the application
9361 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9365 Assume that ICPLBs are enabled at runtime. This has an effect on certain
9366 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
9367 are enabled; for standalone applications the default is off.
9371 @subsection CRIS Options
9372 @cindex CRIS Options
9374 These options are defined specifically for the CRIS ports.
9377 @item -march=@var{architecture-type}
9378 @itemx -mcpu=@var{architecture-type}
9381 Generate code for the specified architecture. The choices for
9382 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9383 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9384 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9387 @item -mtune=@var{architecture-type}
9389 Tune to @var{architecture-type} everything applicable about the generated
9390 code, except for the ABI and the set of available instructions. The
9391 choices for @var{architecture-type} are the same as for
9392 @option{-march=@var{architecture-type}}.
9394 @item -mmax-stack-frame=@var{n}
9395 @opindex mmax-stack-frame
9396 Warn when the stack frame of a function exceeds @var{n} bytes.
9402 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9403 @option{-march=v3} and @option{-march=v8} respectively.
9405 @item -mmul-bug-workaround
9406 @itemx -mno-mul-bug-workaround
9407 @opindex mmul-bug-workaround
9408 @opindex mno-mul-bug-workaround
9409 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9410 models where it applies. This option is active by default.
9414 Enable CRIS-specific verbose debug-related information in the assembly
9415 code. This option also has the effect to turn off the @samp{#NO_APP}
9416 formatted-code indicator to the assembler at the beginning of the
9421 Do not use condition-code results from previous instruction; always emit
9422 compare and test instructions before use of condition codes.
9424 @item -mno-side-effects
9425 @opindex mno-side-effects
9426 Do not emit instructions with side-effects in addressing modes other than
9430 @itemx -mno-stack-align
9432 @itemx -mno-data-align
9433 @itemx -mconst-align
9434 @itemx -mno-const-align
9435 @opindex mstack-align
9436 @opindex mno-stack-align
9437 @opindex mdata-align
9438 @opindex mno-data-align
9439 @opindex mconst-align
9440 @opindex mno-const-align
9441 These options (no-options) arranges (eliminate arrangements) for the
9442 stack-frame, individual data and constants to be aligned for the maximum
9443 single data access size for the chosen CPU model. The default is to
9444 arrange for 32-bit alignment. ABI details such as structure layout are
9445 not affected by these options.
9453 Similar to the stack- data- and const-align options above, these options
9454 arrange for stack-frame, writable data and constants to all be 32-bit,
9455 16-bit or 8-bit aligned. The default is 32-bit alignment.
9457 @item -mno-prologue-epilogue
9458 @itemx -mprologue-epilogue
9459 @opindex mno-prologue-epilogue
9460 @opindex mprologue-epilogue
9461 With @option{-mno-prologue-epilogue}, the normal function prologue and
9462 epilogue that sets up the stack-frame are omitted and no return
9463 instructions or return sequences are generated in the code. Use this
9464 option only together with visual inspection of the compiled code: no
9465 warnings or errors are generated when call-saved registers must be saved,
9466 or storage for local variable needs to be allocated.
9472 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9473 instruction sequences that load addresses for functions from the PLT part
9474 of the GOT rather than (traditional on other architectures) calls to the
9475 PLT@. The default is @option{-mgotplt}.
9479 Legacy no-op option only recognized with the cris-axis-elf and
9480 cris-axis-linux-gnu targets.
9484 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9488 This option, recognized for the cris-axis-elf arranges
9489 to link with input-output functions from a simulator library. Code,
9490 initialized data and zero-initialized data are allocated consecutively.
9494 Like @option{-sim}, but pass linker options to locate initialized data at
9495 0x40000000 and zero-initialized data at 0x80000000.
9499 @subsection CRX Options
9502 These options are defined specifically for the CRX ports.
9508 Enable the use of multiply-accumulate instructions. Disabled by default.
9512 Push instructions will be used to pass outgoing arguments when functions
9513 are called. Enabled by default.
9516 @node Darwin Options
9517 @subsection Darwin Options
9518 @cindex Darwin options
9520 These options are defined for all architectures running the Darwin operating
9523 FSF GCC on Darwin does not create ``fat'' object files; it will create
9524 an object file for the single architecture that it was built to
9525 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9526 @option{-arch} options are used; it does so by running the compiler or
9527 linker multiple times and joining the results together with
9530 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9531 @samp{i686}) is determined by the flags that specify the ISA
9532 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9533 @option{-force_cpusubtype_ALL} option can be used to override this.
9535 The Darwin tools vary in their behavior when presented with an ISA
9536 mismatch. The assembler, @file{as}, will only permit instructions to
9537 be used that are valid for the subtype of the file it is generating,
9538 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9539 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9540 and print an error if asked to create a shared library with a less
9541 restrictive subtype than its input files (for instance, trying to put
9542 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9543 for executables, @file{ld}, will quietly give the executable the most
9544 restrictive subtype of any of its input files.
9549 Add the framework directory @var{dir} to the head of the list of
9550 directories to be searched for header files. These directories are
9551 interleaved with those specified by @option{-I} options and are
9552 scanned in a left-to-right order.
9554 A framework directory is a directory with frameworks in it. A
9555 framework is a directory with a @samp{"Headers"} and/or
9556 @samp{"PrivateHeaders"} directory contained directly in it that ends
9557 in @samp{".framework"}. The name of a framework is the name of this
9558 directory excluding the @samp{".framework"}. Headers associated with
9559 the framework are found in one of those two directories, with
9560 @samp{"Headers"} being searched first. A subframework is a framework
9561 directory that is in a framework's @samp{"Frameworks"} directory.
9562 Includes of subframework headers can only appear in a header of a
9563 framework that contains the subframework, or in a sibling subframework
9564 header. Two subframeworks are siblings if they occur in the same
9565 framework. A subframework should not have the same name as a
9566 framework, a warning will be issued if this is violated. Currently a
9567 subframework cannot have subframeworks, in the future, the mechanism
9568 may be extended to support this. The standard frameworks can be found
9569 in @samp{"/System/Library/Frameworks"} and
9570 @samp{"/Library/Frameworks"}. An example include looks like
9571 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9572 the name of the framework and header.h is found in the
9573 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9575 @item -iframework@var{dir}
9577 Like @option{-F} except the directory is a treated as a system
9578 directory. The main difference between this @option{-iframework} and
9579 @option{-F} is that with @option{-iframework} the compiler does not
9580 warn about constructs contained within header files found via
9581 @var{dir}. This option is valid only for the C family of languages.
9585 Emit debugging information for symbols that are used. For STABS
9586 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9587 This is by default ON@.
9591 Emit debugging information for all symbols and types.
9593 @item -mmacosx-version-min=@var{version}
9594 The earliest version of MacOS X that this executable will run on
9595 is @var{version}. Typical values of @var{version} include @code{10.1},
9596 @code{10.2}, and @code{10.3.9}.
9598 If the compiler was built to use the system's headers by default,
9599 then the default for this option is the system version on which the
9600 compiler is running, otherwise the default is to make choices which
9601 are compatible with as many systems and code bases as possible.
9605 Enable kernel development mode. The @option{-mkernel} option sets
9606 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9607 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9608 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9609 applicable. This mode also sets @option{-mno-altivec},
9610 @option{-msoft-float}, @option{-fno-builtin} and
9611 @option{-mlong-branch} for PowerPC targets.
9613 @item -mone-byte-bool
9614 @opindex mone-byte-bool
9615 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9616 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9617 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9618 option has no effect on x86.
9620 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9621 to generate code that is not binary compatible with code generated
9622 without that switch. Using this switch may require recompiling all
9623 other modules in a program, including system libraries. Use this
9624 switch to conform to a non-default data model.
9626 @item -mfix-and-continue
9627 @itemx -ffix-and-continue
9628 @itemx -findirect-data
9629 @opindex mfix-and-continue
9630 @opindex ffix-and-continue
9631 @opindex findirect-data
9632 Generate code suitable for fast turn around development. Needed to
9633 enable gdb to dynamically load @code{.o} files into already running
9634 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9635 are provided for backwards compatibility.
9639 Loads all members of static archive libraries.
9640 See man ld(1) for more information.
9642 @item -arch_errors_fatal
9643 @opindex arch_errors_fatal
9644 Cause the errors having to do with files that have the wrong architecture
9648 @opindex bind_at_load
9649 Causes the output file to be marked such that the dynamic linker will
9650 bind all undefined references when the file is loaded or launched.
9654 Produce a Mach-o bundle format file.
9655 See man ld(1) for more information.
9657 @item -bundle_loader @var{executable}
9658 @opindex bundle_loader
9659 This option specifies the @var{executable} that will be loading the build
9660 output file being linked. See man ld(1) for more information.
9664 When passed this option, GCC will produce a dynamic library instead of
9665 an executable when linking, using the Darwin @file{libtool} command.
9667 @item -force_cpusubtype_ALL
9668 @opindex force_cpusubtype_ALL
9669 This causes GCC's output file to have the @var{ALL} subtype, instead of
9670 one controlled by the @option{-mcpu} or @option{-march} option.
9672 @item -allowable_client @var{client_name}
9674 @itemx -compatibility_version
9675 @itemx -current_version
9677 @itemx -dependency-file
9679 @itemx -dylinker_install_name
9681 @itemx -exported_symbols_list
9683 @itemx -flat_namespace
9684 @itemx -force_flat_namespace
9685 @itemx -headerpad_max_install_names
9688 @itemx -install_name
9689 @itemx -keep_private_externs
9690 @itemx -multi_module
9691 @itemx -multiply_defined
9692 @itemx -multiply_defined_unused
9694 @itemx -no_dead_strip_inits_and_terms
9695 @itemx -nofixprebinding
9698 @itemx -noseglinkedit
9699 @itemx -pagezero_size
9701 @itemx -prebind_all_twolevel_modules
9702 @itemx -private_bundle
9703 @itemx -read_only_relocs
9705 @itemx -sectobjectsymbols
9709 @itemx -sectobjectsymbols
9712 @itemx -segs_read_only_addr
9713 @itemx -segs_read_write_addr
9714 @itemx -seg_addr_table
9715 @itemx -seg_addr_table_filename
9718 @itemx -segs_read_only_addr
9719 @itemx -segs_read_write_addr
9720 @itemx -single_module
9723 @itemx -sub_umbrella
9724 @itemx -twolevel_namespace
9727 @itemx -unexported_symbols_list
9728 @itemx -weak_reference_mismatches
9730 @opindex allowable_client
9731 @opindex client_name
9732 @opindex compatibility_version
9733 @opindex current_version
9735 @opindex dependency-file
9737 @opindex dylinker_install_name
9739 @opindex exported_symbols_list
9741 @opindex flat_namespace
9742 @opindex force_flat_namespace
9743 @opindex headerpad_max_install_names
9746 @opindex install_name
9747 @opindex keep_private_externs
9748 @opindex multi_module
9749 @opindex multiply_defined
9750 @opindex multiply_defined_unused
9752 @opindex no_dead_strip_inits_and_terms
9753 @opindex nofixprebinding
9754 @opindex nomultidefs
9756 @opindex noseglinkedit
9757 @opindex pagezero_size
9759 @opindex prebind_all_twolevel_modules
9760 @opindex private_bundle
9761 @opindex read_only_relocs
9763 @opindex sectobjectsymbols
9767 @opindex sectobjectsymbols
9770 @opindex segs_read_only_addr
9771 @opindex segs_read_write_addr
9772 @opindex seg_addr_table
9773 @opindex seg_addr_table_filename
9774 @opindex seglinkedit
9776 @opindex segs_read_only_addr
9777 @opindex segs_read_write_addr
9778 @opindex single_module
9780 @opindex sub_library
9781 @opindex sub_umbrella
9782 @opindex twolevel_namespace
9785 @opindex unexported_symbols_list
9786 @opindex weak_reference_mismatches
9787 @opindex whatsloaded
9788 These options are passed to the Darwin linker. The Darwin linker man page
9789 describes them in detail.
9792 @node DEC Alpha Options
9793 @subsection DEC Alpha Options
9795 These @samp{-m} options are defined for the DEC Alpha implementations:
9798 @item -mno-soft-float
9800 @opindex mno-soft-float
9801 @opindex msoft-float
9802 Use (do not use) the hardware floating-point instructions for
9803 floating-point operations. When @option{-msoft-float} is specified,
9804 functions in @file{libgcc.a} will be used to perform floating-point
9805 operations. Unless they are replaced by routines that emulate the
9806 floating-point operations, or compiled in such a way as to call such
9807 emulations routines, these routines will issue floating-point
9808 operations. If you are compiling for an Alpha without floating-point
9809 operations, you must ensure that the library is built so as not to call
9812 Note that Alpha implementations without floating-point operations are
9813 required to have floating-point registers.
9818 @opindex mno-fp-regs
9819 Generate code that uses (does not use) the floating-point register set.
9820 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9821 register set is not used, floating point operands are passed in integer
9822 registers as if they were integers and floating-point results are passed
9823 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9824 so any function with a floating-point argument or return value called by code
9825 compiled with @option{-mno-fp-regs} must also be compiled with that
9828 A typical use of this option is building a kernel that does not use,
9829 and hence need not save and restore, any floating-point registers.
9833 The Alpha architecture implements floating-point hardware optimized for
9834 maximum performance. It is mostly compliant with the IEEE floating
9835 point standard. However, for full compliance, software assistance is
9836 required. This option generates code fully IEEE compliant code
9837 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9838 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9839 defined during compilation. The resulting code is less efficient but is
9840 able to correctly support denormalized numbers and exceptional IEEE
9841 values such as not-a-number and plus/minus infinity. Other Alpha
9842 compilers call this option @option{-ieee_with_no_inexact}.
9844 @item -mieee-with-inexact
9845 @opindex mieee-with-inexact
9846 This is like @option{-mieee} except the generated code also maintains
9847 the IEEE @var{inexact-flag}. Turning on this option causes the
9848 generated code to implement fully-compliant IEEE math. In addition to
9849 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9850 macro. On some Alpha implementations the resulting code may execute
9851 significantly slower than the code generated by default. Since there is
9852 very little code that depends on the @var{inexact-flag}, you should
9853 normally not specify this option. Other Alpha compilers call this
9854 option @option{-ieee_with_inexact}.
9856 @item -mfp-trap-mode=@var{trap-mode}
9857 @opindex mfp-trap-mode
9858 This option controls what floating-point related traps are enabled.
9859 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9860 The trap mode can be set to one of four values:
9864 This is the default (normal) setting. The only traps that are enabled
9865 are the ones that cannot be disabled in software (e.g., division by zero
9869 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9873 Like @samp{u}, but the instructions are marked to be safe for software
9874 completion (see Alpha architecture manual for details).
9877 Like @samp{su}, but inexact traps are enabled as well.
9880 @item -mfp-rounding-mode=@var{rounding-mode}
9881 @opindex mfp-rounding-mode
9882 Selects the IEEE rounding mode. Other Alpha compilers call this option
9883 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9888 Normal IEEE rounding mode. Floating point numbers are rounded towards
9889 the nearest machine number or towards the even machine number in case
9893 Round towards minus infinity.
9896 Chopped rounding mode. Floating point numbers are rounded towards zero.
9899 Dynamic rounding mode. A field in the floating point control register
9900 (@var{fpcr}, see Alpha architecture reference manual) controls the
9901 rounding mode in effect. The C library initializes this register for
9902 rounding towards plus infinity. Thus, unless your program modifies the
9903 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9906 @item -mtrap-precision=@var{trap-precision}
9907 @opindex mtrap-precision
9908 In the Alpha architecture, floating point traps are imprecise. This
9909 means without software assistance it is impossible to recover from a
9910 floating trap and program execution normally needs to be terminated.
9911 GCC can generate code that can assist operating system trap handlers
9912 in determining the exact location that caused a floating point trap.
9913 Depending on the requirements of an application, different levels of
9914 precisions can be selected:
9918 Program precision. This option is the default and means a trap handler
9919 can only identify which program caused a floating point exception.
9922 Function precision. The trap handler can determine the function that
9923 caused a floating point exception.
9926 Instruction precision. The trap handler can determine the exact
9927 instruction that caused a floating point exception.
9930 Other Alpha compilers provide the equivalent options called
9931 @option{-scope_safe} and @option{-resumption_safe}.
9933 @item -mieee-conformant
9934 @opindex mieee-conformant
9935 This option marks the generated code as IEEE conformant. You must not
9936 use this option unless you also specify @option{-mtrap-precision=i} and either
9937 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9938 is to emit the line @samp{.eflag 48} in the function prologue of the
9939 generated assembly file. Under DEC Unix, this has the effect that
9940 IEEE-conformant math library routines will be linked in.
9942 @item -mbuild-constants
9943 @opindex mbuild-constants
9944 Normally GCC examines a 32- or 64-bit integer constant to
9945 see if it can construct it from smaller constants in two or three
9946 instructions. If it cannot, it will output the constant as a literal and
9947 generate code to load it from the data segment at runtime.
9949 Use this option to require GCC to construct @emph{all} integer constants
9950 using code, even if it takes more instructions (the maximum is six).
9952 You would typically use this option to build a shared library dynamic
9953 loader. Itself a shared library, it must relocate itself in memory
9954 before it can find the variables and constants in its own data segment.
9960 Select whether to generate code to be assembled by the vendor-supplied
9961 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9979 Indicate whether GCC should generate code to use the optional BWX,
9980 CIX, FIX and MAX instruction sets. The default is to use the instruction
9981 sets supported by the CPU type specified via @option{-mcpu=} option or that
9982 of the CPU on which GCC was built if none was specified.
9987 @opindex mfloat-ieee
9988 Generate code that uses (does not use) VAX F and G floating point
9989 arithmetic instead of IEEE single and double precision.
9991 @item -mexplicit-relocs
9992 @itemx -mno-explicit-relocs
9993 @opindex mexplicit-relocs
9994 @opindex mno-explicit-relocs
9995 Older Alpha assemblers provided no way to generate symbol relocations
9996 except via assembler macros. Use of these macros does not allow
9997 optimal instruction scheduling. GNU binutils as of version 2.12
9998 supports a new syntax that allows the compiler to explicitly mark
9999 which relocations should apply to which instructions. This option
10000 is mostly useful for debugging, as GCC detects the capabilities of
10001 the assembler when it is built and sets the default accordingly.
10004 @itemx -mlarge-data
10005 @opindex msmall-data
10006 @opindex mlarge-data
10007 When @option{-mexplicit-relocs} is in effect, static data is
10008 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
10009 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
10010 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
10011 16-bit relocations off of the @code{$gp} register. This limits the
10012 size of the small data area to 64KB, but allows the variables to be
10013 directly accessed via a single instruction.
10015 The default is @option{-mlarge-data}. With this option the data area
10016 is limited to just below 2GB@. Programs that require more than 2GB of
10017 data must use @code{malloc} or @code{mmap} to allocate the data in the
10018 heap instead of in the program's data segment.
10020 When generating code for shared libraries, @option{-fpic} implies
10021 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
10024 @itemx -mlarge-text
10025 @opindex msmall-text
10026 @opindex mlarge-text
10027 When @option{-msmall-text} is used, the compiler assumes that the
10028 code of the entire program (or shared library) fits in 4MB, and is
10029 thus reachable with a branch instruction. When @option{-msmall-data}
10030 is used, the compiler can assume that all local symbols share the
10031 same @code{$gp} value, and thus reduce the number of instructions
10032 required for a function call from 4 to 1.
10034 The default is @option{-mlarge-text}.
10036 @item -mcpu=@var{cpu_type}
10038 Set the instruction set and instruction scheduling parameters for
10039 machine type @var{cpu_type}. You can specify either the @samp{EV}
10040 style name or the corresponding chip number. GCC supports scheduling
10041 parameters for the EV4, EV5 and EV6 family of processors and will
10042 choose the default values for the instruction set from the processor
10043 you specify. If you do not specify a processor type, GCC will default
10044 to the processor on which the compiler was built.
10046 Supported values for @var{cpu_type} are
10052 Schedules as an EV4 and has no instruction set extensions.
10056 Schedules as an EV5 and has no instruction set extensions.
10060 Schedules as an EV5 and supports the BWX extension.
10065 Schedules as an EV5 and supports the BWX and MAX extensions.
10069 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
10073 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
10076 @item -mtune=@var{cpu_type}
10078 Set only the instruction scheduling parameters for machine type
10079 @var{cpu_type}. The instruction set is not changed.
10081 @item -mmemory-latency=@var{time}
10082 @opindex mmemory-latency
10083 Sets the latency the scheduler should assume for typical memory
10084 references as seen by the application. This number is highly
10085 dependent on the memory access patterns used by the application
10086 and the size of the external cache on the machine.
10088 Valid options for @var{time} are
10092 A decimal number representing clock cycles.
10098 The compiler contains estimates of the number of clock cycles for
10099 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
10100 (also called Dcache, Scache, and Bcache), as well as to main memory.
10101 Note that L3 is only valid for EV5.
10106 @node DEC Alpha/VMS Options
10107 @subsection DEC Alpha/VMS Options
10109 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
10112 @item -mvms-return-codes
10113 @opindex mvms-return-codes
10114 Return VMS condition codes from main. The default is to return POSIX
10115 style condition (e.g.@: error) codes.
10119 @subsection FRV Options
10120 @cindex FRV Options
10126 Only use the first 32 general purpose registers.
10131 Use all 64 general purpose registers.
10136 Use only the first 32 floating point registers.
10141 Use all 64 floating point registers
10144 @opindex mhard-float
10146 Use hardware instructions for floating point operations.
10149 @opindex msoft-float
10151 Use library routines for floating point operations.
10156 Dynamically allocate condition code registers.
10161 Do not try to dynamically allocate condition code registers, only
10162 use @code{icc0} and @code{fcc0}.
10167 Change ABI to use double word insns.
10172 Do not use double word instructions.
10177 Use floating point double instructions.
10180 @opindex mno-double
10182 Do not use floating point double instructions.
10187 Use media instructions.
10192 Do not use media instructions.
10197 Use multiply and add/subtract instructions.
10200 @opindex mno-muladd
10202 Do not use multiply and add/subtract instructions.
10207 Select the FDPIC ABI, that uses function descriptors to represent
10208 pointers to functions. Without any PIC/PIE-related options, it
10209 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
10210 assumes GOT entries and small data are within a 12-bit range from the
10211 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
10212 are computed with 32 bits.
10213 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10216 @opindex minline-plt
10218 Enable inlining of PLT entries in function calls to functions that are
10219 not known to bind locally. It has no effect without @option{-mfdpic}.
10220 It's enabled by default if optimizing for speed and compiling for
10221 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
10222 optimization option such as @option{-O3} or above is present in the
10228 Assume a large TLS segment when generating thread-local code.
10233 Do not assume a large TLS segment when generating thread-local code.
10238 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
10239 that is known to be in read-only sections. It's enabled by default,
10240 except for @option{-fpic} or @option{-fpie}: even though it may help
10241 make the global offset table smaller, it trades 1 instruction for 4.
10242 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
10243 one of which may be shared by multiple symbols, and it avoids the need
10244 for a GOT entry for the referenced symbol, so it's more likely to be a
10245 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
10247 @item -multilib-library-pic
10248 @opindex multilib-library-pic
10250 Link with the (library, not FD) pic libraries. It's implied by
10251 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
10252 @option{-fpic} without @option{-mfdpic}. You should never have to use
10256 @opindex mlinked-fp
10258 Follow the EABI requirement of always creating a frame pointer whenever
10259 a stack frame is allocated. This option is enabled by default and can
10260 be disabled with @option{-mno-linked-fp}.
10263 @opindex mlong-calls
10265 Use indirect addressing to call functions outside the current
10266 compilation unit. This allows the functions to be placed anywhere
10267 within the 32-bit address space.
10269 @item -malign-labels
10270 @opindex malign-labels
10272 Try to align labels to an 8-byte boundary by inserting nops into the
10273 previous packet. This option only has an effect when VLIW packing
10274 is enabled. It doesn't create new packets; it merely adds nops to
10277 @item -mlibrary-pic
10278 @opindex mlibrary-pic
10280 Generate position-independent EABI code.
10285 Use only the first four media accumulator registers.
10290 Use all eight media accumulator registers.
10295 Pack VLIW instructions.
10300 Do not pack VLIW instructions.
10303 @opindex mno-eflags
10305 Do not mark ABI switches in e_flags.
10308 @opindex mcond-move
10310 Enable the use of conditional-move instructions (default).
10312 This switch is mainly for debugging the compiler and will likely be removed
10313 in a future version.
10315 @item -mno-cond-move
10316 @opindex mno-cond-move
10318 Disable the use of conditional-move instructions.
10320 This switch is mainly for debugging the compiler and will likely be removed
10321 in a future version.
10326 Enable the use of conditional set instructions (default).
10328 This switch is mainly for debugging the compiler and will likely be removed
10329 in a future version.
10334 Disable the use of conditional set instructions.
10336 This switch is mainly for debugging the compiler and will likely be removed
10337 in a future version.
10340 @opindex mcond-exec
10342 Enable the use of conditional execution (default).
10344 This switch is mainly for debugging the compiler and will likely be removed
10345 in a future version.
10347 @item -mno-cond-exec
10348 @opindex mno-cond-exec
10350 Disable the use of conditional execution.
10352 This switch is mainly for debugging the compiler and will likely be removed
10353 in a future version.
10355 @item -mvliw-branch
10356 @opindex mvliw-branch
10358 Run a pass to pack branches into VLIW instructions (default).
10360 This switch is mainly for debugging the compiler and will likely be removed
10361 in a future version.
10363 @item -mno-vliw-branch
10364 @opindex mno-vliw-branch
10366 Do not run a pass to pack branches into VLIW instructions.
10368 This switch is mainly for debugging the compiler and will likely be removed
10369 in a future version.
10371 @item -mmulti-cond-exec
10372 @opindex mmulti-cond-exec
10374 Enable optimization of @code{&&} and @code{||} in conditional execution
10377 This switch is mainly for debugging the compiler and will likely be removed
10378 in a future version.
10380 @item -mno-multi-cond-exec
10381 @opindex mno-multi-cond-exec
10383 Disable optimization of @code{&&} and @code{||} in conditional execution.
10385 This switch is mainly for debugging the compiler and will likely be removed
10386 in a future version.
10388 @item -mnested-cond-exec
10389 @opindex mnested-cond-exec
10391 Enable nested conditional execution optimizations (default).
10393 This switch is mainly for debugging the compiler and will likely be removed
10394 in a future version.
10396 @item -mno-nested-cond-exec
10397 @opindex mno-nested-cond-exec
10399 Disable nested conditional execution optimizations.
10401 This switch is mainly for debugging the compiler and will likely be removed
10402 in a future version.
10404 @item -moptimize-membar
10405 @opindex moptimize-membar
10407 This switch removes redundant @code{membar} instructions from the
10408 compiler generated code. It is enabled by default.
10410 @item -mno-optimize-membar
10411 @opindex mno-optimize-membar
10413 This switch disables the automatic removal of redundant @code{membar}
10414 instructions from the generated code.
10416 @item -mtomcat-stats
10417 @opindex mtomcat-stats
10419 Cause gas to print out tomcat statistics.
10421 @item -mcpu=@var{cpu}
10424 Select the processor type for which to generate code. Possible values are
10425 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10426 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10430 @node GNU/Linux Options
10431 @subsection GNU/Linux Options
10433 These @samp{-m} options are defined for GNU/Linux targets:
10438 Use the GNU C library instead of uClibc. This is the default except
10439 on @samp{*-*-linux-*uclibc*} targets.
10443 Use uClibc instead of the GNU C library. This is the default on
10444 @samp{*-*-linux-*uclibc*} targets.
10447 @node H8/300 Options
10448 @subsection H8/300 Options
10450 These @samp{-m} options are defined for the H8/300 implementations:
10455 Shorten some address references at link time, when possible; uses the
10456 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10457 ld, Using ld}, for a fuller description.
10461 Generate code for the H8/300H@.
10465 Generate code for the H8S@.
10469 Generate code for the H8S and H8/300H in the normal mode. This switch
10470 must be used either with @option{-mh} or @option{-ms}.
10474 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10478 Make @code{int} data 32 bits by default.
10481 @opindex malign-300
10482 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10483 The default for the H8/300H and H8S is to align longs and floats on 4
10485 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10486 This option has no effect on the H8/300.
10490 @subsection HPPA Options
10491 @cindex HPPA Options
10493 These @samp{-m} options are defined for the HPPA family of computers:
10496 @item -march=@var{architecture-type}
10498 Generate code for the specified architecture. The choices for
10499 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10500 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10501 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10502 architecture option for your machine. Code compiled for lower numbered
10503 architectures will run on higher numbered architectures, but not the
10506 @item -mpa-risc-1-0
10507 @itemx -mpa-risc-1-1
10508 @itemx -mpa-risc-2-0
10509 @opindex mpa-risc-1-0
10510 @opindex mpa-risc-1-1
10511 @opindex mpa-risc-2-0
10512 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10515 @opindex mbig-switch
10516 Generate code suitable for big switch tables. Use this option only if
10517 the assembler/linker complain about out of range branches within a switch
10520 @item -mjump-in-delay
10521 @opindex mjump-in-delay
10522 Fill delay slots of function calls with unconditional jump instructions
10523 by modifying the return pointer for the function call to be the target
10524 of the conditional jump.
10526 @item -mdisable-fpregs
10527 @opindex mdisable-fpregs
10528 Prevent floating point registers from being used in any manner. This is
10529 necessary for compiling kernels which perform lazy context switching of
10530 floating point registers. If you use this option and attempt to perform
10531 floating point operations, the compiler will abort.
10533 @item -mdisable-indexing
10534 @opindex mdisable-indexing
10535 Prevent the compiler from using indexing address modes. This avoids some
10536 rather obscure problems when compiling MIG generated code under MACH@.
10538 @item -mno-space-regs
10539 @opindex mno-space-regs
10540 Generate code that assumes the target has no space registers. This allows
10541 GCC to generate faster indirect calls and use unscaled index address modes.
10543 Such code is suitable for level 0 PA systems and kernels.
10545 @item -mfast-indirect-calls
10546 @opindex mfast-indirect-calls
10547 Generate code that assumes calls never cross space boundaries. This
10548 allows GCC to emit code which performs faster indirect calls.
10550 This option will not work in the presence of shared libraries or nested
10553 @item -mfixed-range=@var{register-range}
10554 @opindex mfixed-range
10555 Generate code treating the given register range as fixed registers.
10556 A fixed register is one that the register allocator can not use. This is
10557 useful when compiling kernel code. A register range is specified as
10558 two registers separated by a dash. Multiple register ranges can be
10559 specified separated by a comma.
10561 @item -mlong-load-store
10562 @opindex mlong-load-store
10563 Generate 3-instruction load and store sequences as sometimes required by
10564 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10567 @item -mportable-runtime
10568 @opindex mportable-runtime
10569 Use the portable calling conventions proposed by HP for ELF systems.
10573 Enable the use of assembler directives only GAS understands.
10575 @item -mschedule=@var{cpu-type}
10577 Schedule code according to the constraints for the machine type
10578 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10579 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10580 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10581 proper scheduling option for your machine. The default scheduling is
10585 @opindex mlinker-opt
10586 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10587 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10588 linkers in which they give bogus error messages when linking some programs.
10591 @opindex msoft-float
10592 Generate output containing library calls for floating point.
10593 @strong{Warning:} the requisite libraries are not available for all HPPA
10594 targets. Normally the facilities of the machine's usual C compiler are
10595 used, but this cannot be done directly in cross-compilation. You must make
10596 your own arrangements to provide suitable library functions for
10599 @option{-msoft-float} changes the calling convention in the output file;
10600 therefore, it is only useful if you compile @emph{all} of a program with
10601 this option. In particular, you need to compile @file{libgcc.a}, the
10602 library that comes with GCC, with @option{-msoft-float} in order for
10607 Generate the predefine, @code{_SIO}, for server IO@. The default is
10608 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10609 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10610 options are available under HP-UX and HI-UX@.
10614 Use GNU ld specific options. This passes @option{-shared} to ld when
10615 building a shared library. It is the default when GCC is configured,
10616 explicitly or implicitly, with the GNU linker. This option does not
10617 have any affect on which ld is called, it only changes what parameters
10618 are passed to that ld. The ld that is called is determined by the
10619 @option{--with-ld} configure option, GCC's program search path, and
10620 finally by the user's @env{PATH}. The linker used by GCC can be printed
10621 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10622 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10626 Use HP ld specific options. This passes @option{-b} to ld when building
10627 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10628 links. It is the default when GCC is configured, explicitly or
10629 implicitly, with the HP linker. This option does not have any affect on
10630 which ld is called, it only changes what parameters are passed to that
10631 ld. The ld that is called is determined by the @option{--with-ld}
10632 configure option, GCC's program search path, and finally by the user's
10633 @env{PATH}. The linker used by GCC can be printed using @samp{which
10634 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10635 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10638 @opindex mno-long-calls
10639 Generate code that uses long call sequences. This ensures that a call
10640 is always able to reach linker generated stubs. The default is to generate
10641 long calls only when the distance from the call site to the beginning
10642 of the function or translation unit, as the case may be, exceeds a
10643 predefined limit set by the branch type being used. The limits for
10644 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10645 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10648 Distances are measured from the beginning of functions when using the
10649 @option{-ffunction-sections} option, or when using the @option{-mgas}
10650 and @option{-mno-portable-runtime} options together under HP-UX with
10653 It is normally not desirable to use this option as it will degrade
10654 performance. However, it may be useful in large applications,
10655 particularly when partial linking is used to build the application.
10657 The types of long calls used depends on the capabilities of the
10658 assembler and linker, and the type of code being generated. The
10659 impact on systems that support long absolute calls, and long pic
10660 symbol-difference or pc-relative calls should be relatively small.
10661 However, an indirect call is used on 32-bit ELF systems in pic code
10662 and it is quite long.
10664 @item -munix=@var{unix-std}
10666 Generate compiler predefines and select a startfile for the specified
10667 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10668 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10669 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10670 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10671 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10674 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10675 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10676 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10677 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10678 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10679 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10681 It is @emph{important} to note that this option changes the interfaces
10682 for various library routines. It also affects the operational behavior
10683 of the C library. Thus, @emph{extreme} care is needed in using this
10686 Library code that is intended to operate with more than one UNIX
10687 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10688 as appropriate. Most GNU software doesn't provide this capability.
10692 Suppress the generation of link options to search libdld.sl when the
10693 @option{-static} option is specified on HP-UX 10 and later.
10697 The HP-UX implementation of setlocale in libc has a dependency on
10698 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10699 when the @option{-static} option is specified, special link options
10700 are needed to resolve this dependency.
10702 On HP-UX 10 and later, the GCC driver adds the necessary options to
10703 link with libdld.sl when the @option{-static} option is specified.
10704 This causes the resulting binary to be dynamic. On the 64-bit port,
10705 the linkers generate dynamic binaries by default in any case. The
10706 @option{-nolibdld} option can be used to prevent the GCC driver from
10707 adding these link options.
10711 Add support for multithreading with the @dfn{dce thread} library
10712 under HP-UX@. This option sets flags for both the preprocessor and
10716 @node i386 and x86-64 Options
10717 @subsection Intel 386 and AMD x86-64 Options
10718 @cindex i386 Options
10719 @cindex x86-64 Options
10720 @cindex Intel 386 Options
10721 @cindex AMD x86-64 Options
10723 These @samp{-m} options are defined for the i386 and x86-64 family of
10727 @item -mtune=@var{cpu-type}
10729 Tune to @var{cpu-type} everything applicable about the generated code, except
10730 for the ABI and the set of available instructions. The choices for
10731 @var{cpu-type} are:
10734 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10735 If you know the CPU on which your code will run, then you should use
10736 the corresponding @option{-mtune} option instead of
10737 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10738 of your application will have, then you should use this option.
10740 As new processors are deployed in the marketplace, the behavior of this
10741 option will change. Therefore, if you upgrade to a newer version of
10742 GCC, the code generated option will change to reflect the processors
10743 that were most common when that version of GCC was released.
10745 There is no @option{-march=generic} option because @option{-march}
10746 indicates the instruction set the compiler can use, and there is no
10747 generic instruction set applicable to all processors. In contrast,
10748 @option{-mtune} indicates the processor (or, in this case, collection of
10749 processors) for which the code is optimized.
10751 This selects the CPU to tune for at compilation time by determining
10752 the processor type of the compiling machine. Using @option{-mtune=native}
10753 will produce code optimized for the local machine under the constraints
10754 of the selected instruction set. Using @option{-march=native} will
10755 enable all instruction subsets supported by the local machine (hence
10756 the result might not run on different machines).
10758 Original Intel's i386 CPU@.
10760 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10761 @item i586, pentium
10762 Intel Pentium CPU with no MMX support.
10764 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10766 Intel PentiumPro CPU@.
10768 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10769 instruction set will be used, so the code will run on all i686 family chips.
10771 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10772 @item pentium3, pentium3m
10773 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10776 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10777 support. Used by Centrino notebooks.
10778 @item pentium4, pentium4m
10779 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10781 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10784 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10785 SSE2 and SSE3 instruction set support.
10787 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10788 instruction set support.
10790 AMD K6 CPU with MMX instruction set support.
10792 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10793 @item athlon, athlon-tbird
10794 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10796 @item athlon-4, athlon-xp, athlon-mp
10797 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10798 instruction set support.
10799 @item k8, opteron, athlon64, athlon-fx
10800 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10801 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10802 @item k8-sse3, opteron-sse3, athlon64-sse3
10803 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10804 @item amdfam10, barcelona
10805 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10806 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10807 instruction set extensions.)
10809 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10812 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
10813 instruction set support.
10815 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
10816 implemented for this chip.)
10818 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10819 implemented for this chip.)
10821 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10824 While picking a specific @var{cpu-type} will schedule things appropriately
10825 for that particular chip, the compiler will not generate any code that
10826 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10829 @item -march=@var{cpu-type}
10831 Generate instructions for the machine type @var{cpu-type}. The choices
10832 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10833 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10835 @item -mcpu=@var{cpu-type}
10837 A deprecated synonym for @option{-mtune}.
10839 @item -mfpmath=@var{unit}
10841 Generate floating point arithmetics for selected unit @var{unit}. The choices
10842 for @var{unit} are:
10846 Use the standard 387 floating point coprocessor present majority of chips and
10847 emulated otherwise. Code compiled with this option will run almost everywhere.
10848 The temporary results are computed in 80bit precision instead of precision
10849 specified by the type resulting in slightly different results compared to most
10850 of other chips. See @option{-ffloat-store} for more detailed description.
10852 This is the default choice for i386 compiler.
10855 Use scalar floating point instructions present in the SSE instruction set.
10856 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10857 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10858 instruction set supports only single precision arithmetics, thus the double and
10859 extended precision arithmetics is still done using 387. Later version, present
10860 only in Pentium4 and the future AMD x86-64 chips supports double precision
10863 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10864 or @option{-msse2} switches to enable SSE extensions and make this option
10865 effective. For the x86-64 compiler, these extensions are enabled by default.
10867 The resulting code should be considerably faster in the majority of cases and avoid
10868 the numerical instability problems of 387 code, but may break some existing
10869 code that expects temporaries to be 80bit.
10871 This is the default choice for the x86-64 compiler.
10876 Attempt to utilize both instruction sets at once. This effectively double the
10877 amount of available registers and on chips with separate execution units for
10878 387 and SSE the execution resources too. Use this option with care, as it is
10879 still experimental, because the GCC register allocator does not model separate
10880 functional units well resulting in instable performance.
10883 @item -masm=@var{dialect}
10884 @opindex masm=@var{dialect}
10885 Output asm instructions using selected @var{dialect}. Supported
10886 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10887 not support @samp{intel}.
10890 @itemx -mno-ieee-fp
10892 @opindex mno-ieee-fp
10893 Control whether or not the compiler uses IEEE floating point
10894 comparisons. These handle correctly the case where the result of a
10895 comparison is unordered.
10898 @opindex msoft-float
10899 Generate output containing library calls for floating point.
10900 @strong{Warning:} the requisite libraries are not part of GCC@.
10901 Normally the facilities of the machine's usual C compiler are used, but
10902 this can't be done directly in cross-compilation. You must make your
10903 own arrangements to provide suitable library functions for
10906 On machines where a function returns floating point results in the 80387
10907 register stack, some floating point opcodes may be emitted even if
10908 @option{-msoft-float} is used.
10910 @item -mno-fp-ret-in-387
10911 @opindex mno-fp-ret-in-387
10912 Do not use the FPU registers for return values of functions.
10914 The usual calling convention has functions return values of types
10915 @code{float} and @code{double} in an FPU register, even if there
10916 is no FPU@. The idea is that the operating system should emulate
10919 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10920 in ordinary CPU registers instead.
10922 @item -mno-fancy-math-387
10923 @opindex mno-fancy-math-387
10924 Some 387 emulators do not support the @code{sin}, @code{cos} and
10925 @code{sqrt} instructions for the 387. Specify this option to avoid
10926 generating those instructions. This option is the default on FreeBSD,
10927 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10928 indicates that the target cpu will always have an FPU and so the
10929 instruction will not need emulation. As of revision 2.6.1, these
10930 instructions are not generated unless you also use the
10931 @option{-funsafe-math-optimizations} switch.
10933 @item -malign-double
10934 @itemx -mno-align-double
10935 @opindex malign-double
10936 @opindex mno-align-double
10937 Control whether GCC aligns @code{double}, @code{long double}, and
10938 @code{long long} variables on a two word boundary or a one word
10939 boundary. Aligning @code{double} variables on a two word boundary will
10940 produce code that runs somewhat faster on a @samp{Pentium} at the
10941 expense of more memory.
10943 On x86-64, @option{-malign-double} is enabled by default.
10945 @strong{Warning:} if you use the @option{-malign-double} switch,
10946 structures containing the above types will be aligned differently than
10947 the published application binary interface specifications for the 386
10948 and will not be binary compatible with structures in code compiled
10949 without that switch.
10951 @item -m96bit-long-double
10952 @itemx -m128bit-long-double
10953 @opindex m96bit-long-double
10954 @opindex m128bit-long-double
10955 These switches control the size of @code{long double} type. The i386
10956 application binary interface specifies the size to be 96 bits,
10957 so @option{-m96bit-long-double} is the default in 32 bit mode.
10959 Modern architectures (Pentium and newer) would prefer @code{long double}
10960 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10961 conforming to the ABI, this would not be possible. So specifying a
10962 @option{-m128bit-long-double} will align @code{long double}
10963 to a 16 byte boundary by padding the @code{long double} with an additional
10966 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10967 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10969 Notice that neither of these options enable any extra precision over the x87
10970 standard of 80 bits for a @code{long double}.
10972 @strong{Warning:} if you override the default value for your target ABI, the
10973 structures and arrays containing @code{long double} variables will change
10974 their size as well as function calling convention for function taking
10975 @code{long double} will be modified. Hence they will not be binary
10976 compatible with arrays or structures in code compiled without that switch.
10978 @item -mlarge-data-threshold=@var{number}
10979 @opindex mlarge-data-threshold=@var{number}
10980 When @option{-mcmodel=medium} is specified, the data greater than
10981 @var{threshold} are placed in large data section. This value must be the
10982 same across all object linked into the binary and defaults to 65535.
10986 Use a different function-calling convention, in which functions that
10987 take a fixed number of arguments return with the @code{ret} @var{num}
10988 instruction, which pops their arguments while returning. This saves one
10989 instruction in the caller since there is no need to pop the arguments
10992 You can specify that an individual function is called with this calling
10993 sequence with the function attribute @samp{stdcall}. You can also
10994 override the @option{-mrtd} option by using the function attribute
10995 @samp{cdecl}. @xref{Function Attributes}.
10997 @strong{Warning:} this calling convention is incompatible with the one
10998 normally used on Unix, so you cannot use it if you need to call
10999 libraries compiled with the Unix compiler.
11001 Also, you must provide function prototypes for all functions that
11002 take variable numbers of arguments (including @code{printf});
11003 otherwise incorrect code will be generated for calls to those
11006 In addition, seriously incorrect code will result if you call a
11007 function with too many arguments. (Normally, extra arguments are
11008 harmlessly ignored.)
11010 @item -mregparm=@var{num}
11012 Control how many registers are used to pass integer arguments. By
11013 default, no registers are used to pass arguments, and at most 3
11014 registers can be used. You can control this behavior for a specific
11015 function by using the function attribute @samp{regparm}.
11016 @xref{Function Attributes}.
11018 @strong{Warning:} if you use this switch, and
11019 @var{num} is nonzero, then you must build all modules with the same
11020 value, including any libraries. This includes the system libraries and
11024 @opindex msseregparm
11025 Use SSE register passing conventions for float and double arguments
11026 and return values. You can control this behavior for a specific
11027 function by using the function attribute @samp{sseregparm}.
11028 @xref{Function Attributes}.
11030 @strong{Warning:} if you use this switch then you must build all
11031 modules with the same value, including any libraries. This includes
11032 the system libraries and startup modules.
11041 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
11042 is specified, the significands of results of floating-point operations are
11043 rounded to 24 bits (single precision); @option{-mpc64} rounds the
11044 significands of results of floating-point operations to 53 bits (double
11045 precision) and @option{-mpc80} rounds the significands of results of
11046 floating-point operations to 64 bits (extended double precision), which is
11047 the default. When this option is used, floating-point operations in higher
11048 precisions are not available to the programmer without setting the FPU
11049 control word explicitly.
11051 Setting the rounding of floating-point operations to less than the default
11052 80 bits can speed some programs by 2% or more. Note that some mathematical
11053 libraries assume that extended precision (80 bit) floating-point operations
11054 are enabled by default; routines in such libraries could suffer significant
11055 loss of accuracy, typically through so-called "catastrophic cancellation",
11056 when this option is used to set the precision to less than extended precision.
11058 @item -mstackrealign
11059 @opindex mstackrealign
11060 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
11061 option will generate an alternate prologue and epilogue that realigns the
11062 runtime stack if necessary. This supports mixing legacy codes that keep
11063 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
11064 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
11065 applicable to individual functions.
11067 @item -mpreferred-stack-boundary=@var{num}
11068 @opindex mpreferred-stack-boundary
11069 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
11070 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
11071 the default is 4 (16 bytes or 128 bits).
11073 @item -mincoming-stack-boundary=@var{num}
11074 @opindex mincoming-stack-boundary
11075 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
11076 boundary. If @option{-mincoming-stack-boundary} is not specified,
11077 the one specified by @option{-mpreferred-stack-boundary} will be used.
11079 On Pentium and PentiumPro, @code{double} and @code{long double} values
11080 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
11081 suffer significant run time performance penalties. On Pentium III, the
11082 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
11083 properly if it is not 16 byte aligned.
11085 To ensure proper alignment of this values on the stack, the stack boundary
11086 must be as aligned as that required by any value stored on the stack.
11087 Further, every function must be generated such that it keeps the stack
11088 aligned. Thus calling a function compiled with a higher preferred
11089 stack boundary from a function compiled with a lower preferred stack
11090 boundary will most likely misalign the stack. It is recommended that
11091 libraries that use callbacks always use the default setting.
11093 This extra alignment does consume extra stack space, and generally
11094 increases code size. Code that is sensitive to stack space usage, such
11095 as embedded systems and operating system kernels, may want to reduce the
11096 preferred alignment to @option{-mpreferred-stack-boundary=2}.
11136 These switches enable or disable the use of instructions in the MMX,
11137 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, SSE5, ABM or
11138 3DNow!@: extended instruction sets.
11139 These extensions are also available as built-in functions: see
11140 @ref{X86 Built-in Functions}, for details of the functions enabled and
11141 disabled by these switches.
11143 To have SSE/SSE2 instructions generated automatically from floating-point
11144 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
11146 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
11147 generates new AVX instructions or AVX equivalence for all SSEx instructions
11150 These options will enable GCC to use these extended instructions in
11151 generated code, even without @option{-mfpmath=sse}. Applications which
11152 perform runtime CPU detection must compile separate files for each
11153 supported architecture, using the appropriate flags. In particular,
11154 the file containing the CPU detection code should be compiled without
11159 This option instructs GCC to emit a @code{cld} instruction in the prologue
11160 of functions that use string instructions. String instructions depend on
11161 the DF flag to select between autoincrement or autodecrement mode. While the
11162 ABI specifies the DF flag to be cleared on function entry, some operating
11163 systems violate this specification by not clearing the DF flag in their
11164 exception dispatchers. The exception handler can be invoked with the DF flag
11165 set which leads to wrong direction mode, when string instructions are used.
11166 This option can be enabled by default on 32-bit x86 targets by configuring
11167 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
11168 instructions can be suppressed with the @option{-mno-cld} compiler option
11173 This option will enable GCC to use CMPXCHG16B instruction in generated code.
11174 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
11175 data types. This is useful for high resolution counters that could be updated
11176 by multiple processors (or cores). This instruction is generated as part of
11177 atomic built-in functions: see @ref{Atomic Builtins} for details.
11181 This option will enable GCC to use SAHF instruction in generated 64-bit code.
11182 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
11183 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
11184 SAHF are load and store instructions, respectively, for certain status flags.
11185 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
11186 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
11190 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
11191 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Rhapson step
11192 to increase precision instead of DIVSS and SQRTSS (and their vectorized
11193 variants) for single precision floating point arguments. These instructions
11194 are generated only when @option{-funsafe-math-optimizations} is enabled
11195 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
11196 Note that while the throughput of the sequence is higher than the throughput
11197 of the non-reciprocal instruction, the precision of the sequence can be
11198 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
11200 @item -mveclibabi=@var{type}
11201 @opindex mveclibabi
11202 Specifies the ABI type to use for vectorizing intrinsics using an
11203 external library. Supported types are @code{svml} for the Intel short
11204 vector math library and @code{acml} for the AMD math core library style
11205 of interfacing. GCC will currently emit calls to @code{vmldExp2},
11206 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
11207 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
11208 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
11209 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
11210 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
11211 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
11212 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
11213 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
11214 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
11215 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
11216 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
11217 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
11218 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
11219 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
11220 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
11221 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
11222 compatible library will have to be specified at link time.
11225 @itemx -mno-push-args
11226 @opindex mpush-args
11227 @opindex mno-push-args
11228 Use PUSH operations to store outgoing parameters. This method is shorter
11229 and usually equally fast as method using SUB/MOV operations and is enabled
11230 by default. In some cases disabling it may improve performance because of
11231 improved scheduling and reduced dependencies.
11233 @item -maccumulate-outgoing-args
11234 @opindex maccumulate-outgoing-args
11235 If enabled, the maximum amount of space required for outgoing arguments will be
11236 computed in the function prologue. This is faster on most modern CPUs
11237 because of reduced dependencies, improved scheduling and reduced stack usage
11238 when preferred stack boundary is not equal to 2. The drawback is a notable
11239 increase in code size. This switch implies @option{-mno-push-args}.
11243 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
11244 on thread-safe exception handling must compile and link all code with the
11245 @option{-mthreads} option. When compiling, @option{-mthreads} defines
11246 @option{-D_MT}; when linking, it links in a special thread helper library
11247 @option{-lmingwthrd} which cleans up per thread exception handling data.
11249 @item -mno-align-stringops
11250 @opindex mno-align-stringops
11251 Do not align destination of inlined string operations. This switch reduces
11252 code size and improves performance in case the destination is already aligned,
11253 but GCC doesn't know about it.
11255 @item -minline-all-stringops
11256 @opindex minline-all-stringops
11257 By default GCC inlines string operations only when destination is known to be
11258 aligned at least to 4 byte boundary. This enables more inlining, increase code
11259 size, but may improve performance of code that depends on fast memcpy, strlen
11260 and memset for short lengths.
11262 @item -minline-stringops-dynamically
11263 @opindex minline-stringops-dynamically
11264 For string operation of unknown size, inline runtime checks so for small
11265 blocks inline code is used, while for large blocks library call is used.
11267 @item -mstringop-strategy=@var{alg}
11268 @opindex mstringop-strategy=@var{alg}
11269 Overwrite internal decision heuristic about particular algorithm to inline
11270 string operation with. The allowed values are @code{rep_byte},
11271 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
11272 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
11273 expanding inline loop, @code{libcall} for always expanding library call.
11275 @item -momit-leaf-frame-pointer
11276 @opindex momit-leaf-frame-pointer
11277 Don't keep the frame pointer in a register for leaf functions. This
11278 avoids the instructions to save, set up and restore frame pointers and
11279 makes an extra register available in leaf functions. The option
11280 @option{-fomit-frame-pointer} removes the frame pointer for all functions
11281 which might make debugging harder.
11283 @item -mtls-direct-seg-refs
11284 @itemx -mno-tls-direct-seg-refs
11285 @opindex mtls-direct-seg-refs
11286 Controls whether TLS variables may be accessed with offsets from the
11287 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
11288 or whether the thread base pointer must be added. Whether or not this
11289 is legal depends on the operating system, and whether it maps the
11290 segment to cover the entire TLS area.
11292 For systems that use GNU libc, the default is on.
11295 @itemx -mno-fused-madd
11296 @opindex mfused-madd
11297 Enable automatic generation of fused floating point multiply-add instructions
11298 if the ISA supports such instructions. The -mfused-madd option is on by
11299 default. The fused multiply-add instructions have a different
11300 rounding behavior compared to executing a multiply followed by an add.
11303 @itemx -mno-sse2avx
11305 Specify that the assembler should encode SSE instructions with VEX
11306 prefix. The option @option{-mavx} turns this on by default.
11309 These @samp{-m} switches are supported in addition to the above
11310 on AMD x86-64 processors in 64-bit environments.
11317 Generate code for a 32-bit or 64-bit environment.
11318 The 32-bit environment sets int, long and pointer to 32 bits and
11319 generates code that runs on any i386 system.
11320 The 64-bit environment sets int to 32 bits and long and pointer
11321 to 64 bits and generates code for AMD's x86-64 architecture. For
11322 darwin only the -m64 option turns off the @option{-fno-pic} and
11323 @option{-mdynamic-no-pic} options.
11325 @item -mno-red-zone
11326 @opindex no-red-zone
11327 Do not use a so called red zone for x86-64 code. The red zone is mandated
11328 by the x86-64 ABI, it is a 128-byte area beyond the location of the
11329 stack pointer that will not be modified by signal or interrupt handlers
11330 and therefore can be used for temporary data without adjusting the stack
11331 pointer. The flag @option{-mno-red-zone} disables this red zone.
11333 @item -mcmodel=small
11334 @opindex mcmodel=small
11335 Generate code for the small code model: the program and its symbols must
11336 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11337 Programs can be statically or dynamically linked. This is the default
11340 @item -mcmodel=kernel
11341 @opindex mcmodel=kernel
11342 Generate code for the kernel code model. The kernel runs in the
11343 negative 2 GB of the address space.
11344 This model has to be used for Linux kernel code.
11346 @item -mcmodel=medium
11347 @opindex mcmodel=medium
11348 Generate code for the medium model: The program is linked in the lower 2
11349 GB of the address space. Small symbols are also placed there. Symbols
11350 with sizes larger than @option{-mlarge-data-threshold} are put into
11351 large data or bss sections and can be located above 2GB. Programs can
11352 be statically or dynamically linked.
11354 @item -mcmodel=large
11355 @opindex mcmodel=large
11356 Generate code for the large model: This model makes no assumptions
11357 about addresses and sizes of sections.
11360 @node IA-64 Options
11361 @subsection IA-64 Options
11362 @cindex IA-64 Options
11364 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11368 @opindex mbig-endian
11369 Generate code for a big endian target. This is the default for HP-UX@.
11371 @item -mlittle-endian
11372 @opindex mlittle-endian
11373 Generate code for a little endian target. This is the default for AIX5
11379 @opindex mno-gnu-as
11380 Generate (or don't) code for the GNU assembler. This is the default.
11381 @c Also, this is the default if the configure option @option{--with-gnu-as}
11387 @opindex mno-gnu-ld
11388 Generate (or don't) code for the GNU linker. This is the default.
11389 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11394 Generate code that does not use a global pointer register. The result
11395 is not position independent code, and violates the IA-64 ABI@.
11397 @item -mvolatile-asm-stop
11398 @itemx -mno-volatile-asm-stop
11399 @opindex mvolatile-asm-stop
11400 @opindex mno-volatile-asm-stop
11401 Generate (or don't) a stop bit immediately before and after volatile asm
11404 @item -mregister-names
11405 @itemx -mno-register-names
11406 @opindex mregister-names
11407 @opindex mno-register-names
11408 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11409 the stacked registers. This may make assembler output more readable.
11415 Disable (or enable) optimizations that use the small data section. This may
11416 be useful for working around optimizer bugs.
11418 @item -mconstant-gp
11419 @opindex mconstant-gp
11420 Generate code that uses a single constant global pointer value. This is
11421 useful when compiling kernel code.
11425 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11426 This is useful when compiling firmware code.
11428 @item -minline-float-divide-min-latency
11429 @opindex minline-float-divide-min-latency
11430 Generate code for inline divides of floating point values
11431 using the minimum latency algorithm.
11433 @item -minline-float-divide-max-throughput
11434 @opindex minline-float-divide-max-throughput
11435 Generate code for inline divides of floating point values
11436 using the maximum throughput algorithm.
11438 @item -minline-int-divide-min-latency
11439 @opindex minline-int-divide-min-latency
11440 Generate code for inline divides of integer values
11441 using the minimum latency algorithm.
11443 @item -minline-int-divide-max-throughput
11444 @opindex minline-int-divide-max-throughput
11445 Generate code for inline divides of integer values
11446 using the maximum throughput algorithm.
11448 @item -minline-sqrt-min-latency
11449 @opindex minline-sqrt-min-latency
11450 Generate code for inline square roots
11451 using the minimum latency algorithm.
11453 @item -minline-sqrt-max-throughput
11454 @opindex minline-sqrt-max-throughput
11455 Generate code for inline square roots
11456 using the maximum throughput algorithm.
11458 @item -mno-dwarf2-asm
11459 @itemx -mdwarf2-asm
11460 @opindex mno-dwarf2-asm
11461 @opindex mdwarf2-asm
11462 Don't (or do) generate assembler code for the DWARF2 line number debugging
11463 info. This may be useful when not using the GNU assembler.
11465 @item -mearly-stop-bits
11466 @itemx -mno-early-stop-bits
11467 @opindex mearly-stop-bits
11468 @opindex mno-early-stop-bits
11469 Allow stop bits to be placed earlier than immediately preceding the
11470 instruction that triggered the stop bit. This can improve instruction
11471 scheduling, but does not always do so.
11473 @item -mfixed-range=@var{register-range}
11474 @opindex mfixed-range
11475 Generate code treating the given register range as fixed registers.
11476 A fixed register is one that the register allocator can not use. This is
11477 useful when compiling kernel code. A register range is specified as
11478 two registers separated by a dash. Multiple register ranges can be
11479 specified separated by a comma.
11481 @item -mtls-size=@var{tls-size}
11483 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11486 @item -mtune=@var{cpu-type}
11488 Tune the instruction scheduling for a particular CPU, Valid values are
11489 itanium, itanium1, merced, itanium2, and mckinley.
11495 Add support for multithreading using the POSIX threads library. This
11496 option sets flags for both the preprocessor and linker. It does
11497 not affect the thread safety of object code produced by the compiler or
11498 that of libraries supplied with it. These are HP-UX specific flags.
11504 Generate code for a 32-bit or 64-bit environment.
11505 The 32-bit environment sets int, long and pointer to 32 bits.
11506 The 64-bit environment sets int to 32 bits and long and pointer
11507 to 64 bits. These are HP-UX specific flags.
11509 @item -mno-sched-br-data-spec
11510 @itemx -msched-br-data-spec
11511 @opindex mno-sched-br-data-spec
11512 @opindex msched-br-data-spec
11513 (Dis/En)able data speculative scheduling before reload.
11514 This will result in generation of the ld.a instructions and
11515 the corresponding check instructions (ld.c / chk.a).
11516 The default is 'disable'.
11518 @item -msched-ar-data-spec
11519 @itemx -mno-sched-ar-data-spec
11520 @opindex msched-ar-data-spec
11521 @opindex mno-sched-ar-data-spec
11522 (En/Dis)able data speculative scheduling after reload.
11523 This will result in generation of the ld.a instructions and
11524 the corresponding check instructions (ld.c / chk.a).
11525 The default is 'enable'.
11527 @item -mno-sched-control-spec
11528 @itemx -msched-control-spec
11529 @opindex mno-sched-control-spec
11530 @opindex msched-control-spec
11531 (Dis/En)able control speculative scheduling. This feature is
11532 available only during region scheduling (i.e.@: before reload).
11533 This will result in generation of the ld.s instructions and
11534 the corresponding check instructions chk.s .
11535 The default is 'disable'.
11537 @item -msched-br-in-data-spec
11538 @itemx -mno-sched-br-in-data-spec
11539 @opindex msched-br-in-data-spec
11540 @opindex mno-sched-br-in-data-spec
11541 (En/Dis)able speculative scheduling of the instructions that
11542 are dependent on the data speculative loads before reload.
11543 This is effective only with @option{-msched-br-data-spec} enabled.
11544 The default is 'enable'.
11546 @item -msched-ar-in-data-spec
11547 @itemx -mno-sched-ar-in-data-spec
11548 @opindex msched-ar-in-data-spec
11549 @opindex mno-sched-ar-in-data-spec
11550 (En/Dis)able speculative scheduling of the instructions that
11551 are dependent on the data speculative loads after reload.
11552 This is effective only with @option{-msched-ar-data-spec} enabled.
11553 The default is 'enable'.
11555 @item -msched-in-control-spec
11556 @itemx -mno-sched-in-control-spec
11557 @opindex msched-in-control-spec
11558 @opindex mno-sched-in-control-spec
11559 (En/Dis)able speculative scheduling of the instructions that
11560 are dependent on the control speculative loads.
11561 This is effective only with @option{-msched-control-spec} enabled.
11562 The default is 'enable'.
11565 @itemx -mno-sched-ldc
11566 @opindex msched-ldc
11567 @opindex mno-sched-ldc
11568 (En/Dis)able use of simple data speculation checks ld.c .
11569 If disabled, only chk.a instructions will be emitted to check
11570 data speculative loads.
11571 The default is 'enable'.
11573 @item -mno-sched-control-ldc
11574 @itemx -msched-control-ldc
11575 @opindex mno-sched-control-ldc
11576 @opindex msched-control-ldc
11577 (Dis/En)able use of ld.c instructions to check control speculative loads.
11578 If enabled, in case of control speculative load with no speculatively
11579 scheduled dependent instructions this load will be emitted as ld.sa and
11580 ld.c will be used to check it.
11581 The default is 'disable'.
11583 @item -mno-sched-spec-verbose
11584 @itemx -msched-spec-verbose
11585 @opindex mno-sched-spec-verbose
11586 @opindex msched-spec-verbose
11587 (Dis/En)able printing of the information about speculative motions.
11589 @item -mno-sched-prefer-non-data-spec-insns
11590 @itemx -msched-prefer-non-data-spec-insns
11591 @opindex mno-sched-prefer-non-data-spec-insns
11592 @opindex msched-prefer-non-data-spec-insns
11593 If enabled, data speculative instructions will be chosen for schedule
11594 only if there are no other choices at the moment. This will make
11595 the use of the data speculation much more conservative.
11596 The default is 'disable'.
11598 @item -mno-sched-prefer-non-control-spec-insns
11599 @itemx -msched-prefer-non-control-spec-insns
11600 @opindex mno-sched-prefer-non-control-spec-insns
11601 @opindex msched-prefer-non-control-spec-insns
11602 If enabled, control speculative instructions will be chosen for schedule
11603 only if there are no other choices at the moment. This will make
11604 the use of the control speculation much more conservative.
11605 The default is 'disable'.
11607 @item -mno-sched-count-spec-in-critical-path
11608 @itemx -msched-count-spec-in-critical-path
11609 @opindex mno-sched-count-spec-in-critical-path
11610 @opindex msched-count-spec-in-critical-path
11611 If enabled, speculative dependencies will be considered during
11612 computation of the instructions priorities. This will make the use of the
11613 speculation a bit more conservative.
11614 The default is 'disable'.
11619 @subsection M32C Options
11620 @cindex M32C options
11623 @item -mcpu=@var{name}
11625 Select the CPU for which code is generated. @var{name} may be one of
11626 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11627 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11628 the M32C/80 series.
11632 Specifies that the program will be run on the simulator. This causes
11633 an alternate runtime library to be linked in which supports, for
11634 example, file I/O@. You must not use this option when generating
11635 programs that will run on real hardware; you must provide your own
11636 runtime library for whatever I/O functions are needed.
11638 @item -memregs=@var{number}
11640 Specifies the number of memory-based pseudo-registers GCC will use
11641 during code generation. These pseudo-registers will be used like real
11642 registers, so there is a tradeoff between GCC's ability to fit the
11643 code into available registers, and the performance penalty of using
11644 memory instead of registers. Note that all modules in a program must
11645 be compiled with the same value for this option. Because of that, you
11646 must not use this option with the default runtime libraries gcc
11651 @node M32R/D Options
11652 @subsection M32R/D Options
11653 @cindex M32R/D options
11655 These @option{-m} options are defined for Renesas M32R/D architectures:
11660 Generate code for the M32R/2@.
11664 Generate code for the M32R/X@.
11668 Generate code for the M32R@. This is the default.
11670 @item -mmodel=small
11671 @opindex mmodel=small
11672 Assume all objects live in the lower 16MB of memory (so that their addresses
11673 can be loaded with the @code{ld24} instruction), and assume all subroutines
11674 are reachable with the @code{bl} instruction.
11675 This is the default.
11677 The addressability of a particular object can be set with the
11678 @code{model} attribute.
11680 @item -mmodel=medium
11681 @opindex mmodel=medium
11682 Assume objects may be anywhere in the 32-bit address space (the compiler
11683 will generate @code{seth/add3} instructions to load their addresses), and
11684 assume all subroutines are reachable with the @code{bl} instruction.
11686 @item -mmodel=large
11687 @opindex mmodel=large
11688 Assume objects may be anywhere in the 32-bit address space (the compiler
11689 will generate @code{seth/add3} instructions to load their addresses), and
11690 assume subroutines may not be reachable with the @code{bl} instruction
11691 (the compiler will generate the much slower @code{seth/add3/jl}
11692 instruction sequence).
11695 @opindex msdata=none
11696 Disable use of the small data area. Variables will be put into
11697 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11698 @code{section} attribute has been specified).
11699 This is the default.
11701 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11702 Objects may be explicitly put in the small data area with the
11703 @code{section} attribute using one of these sections.
11705 @item -msdata=sdata
11706 @opindex msdata=sdata
11707 Put small global and static data in the small data area, but do not
11708 generate special code to reference them.
11711 @opindex msdata=use
11712 Put small global and static data in the small data area, and generate
11713 special instructions to reference them.
11717 @cindex smaller data references
11718 Put global and static objects less than or equal to @var{num} bytes
11719 into the small data or bss sections instead of the normal data or bss
11720 sections. The default value of @var{num} is 8.
11721 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11722 for this option to have any effect.
11724 All modules should be compiled with the same @option{-G @var{num}} value.
11725 Compiling with different values of @var{num} may or may not work; if it
11726 doesn't the linker will give an error message---incorrect code will not be
11731 Makes the M32R specific code in the compiler display some statistics
11732 that might help in debugging programs.
11734 @item -malign-loops
11735 @opindex malign-loops
11736 Align all loops to a 32-byte boundary.
11738 @item -mno-align-loops
11739 @opindex mno-align-loops
11740 Do not enforce a 32-byte alignment for loops. This is the default.
11742 @item -missue-rate=@var{number}
11743 @opindex missue-rate=@var{number}
11744 Issue @var{number} instructions per cycle. @var{number} can only be 1
11747 @item -mbranch-cost=@var{number}
11748 @opindex mbranch-cost=@var{number}
11749 @var{number} can only be 1 or 2. If it is 1 then branches will be
11750 preferred over conditional code, if it is 2, then the opposite will
11753 @item -mflush-trap=@var{number}
11754 @opindex mflush-trap=@var{number}
11755 Specifies the trap number to use to flush the cache. The default is
11756 12. Valid numbers are between 0 and 15 inclusive.
11758 @item -mno-flush-trap
11759 @opindex mno-flush-trap
11760 Specifies that the cache cannot be flushed by using a trap.
11762 @item -mflush-func=@var{name}
11763 @opindex mflush-func=@var{name}
11764 Specifies the name of the operating system function to call to flush
11765 the cache. The default is @emph{_flush_cache}, but a function call
11766 will only be used if a trap is not available.
11768 @item -mno-flush-func
11769 @opindex mno-flush-func
11770 Indicates that there is no OS function for flushing the cache.
11774 @node M680x0 Options
11775 @subsection M680x0 Options
11776 @cindex M680x0 options
11778 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11779 The default settings depend on which architecture was selected when
11780 the compiler was configured; the defaults for the most common choices
11784 @item -march=@var{arch}
11786 Generate code for a specific M680x0 or ColdFire instruction set
11787 architecture. Permissible values of @var{arch} for M680x0
11788 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11789 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11790 architectures are selected according to Freescale's ISA classification
11791 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11792 @samp{isab} and @samp{isac}.
11794 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11795 code for a ColdFire target. The @var{arch} in this macro is one of the
11796 @option{-march} arguments given above.
11798 When used together, @option{-march} and @option{-mtune} select code
11799 that runs on a family of similar processors but that is optimized
11800 for a particular microarchitecture.
11802 @item -mcpu=@var{cpu}
11804 Generate code for a specific M680x0 or ColdFire processor.
11805 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
11806 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
11807 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
11808 below, which also classifies the CPUs into families:
11810 @multitable @columnfractions 0.20 0.80
11811 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
11812 @item @samp{51qe} @tab @samp{51qe}
11813 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
11814 @item @samp{5206e} @tab @samp{5206e}
11815 @item @samp{5208} @tab @samp{5207} @samp{5208}
11816 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
11817 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
11818 @item @samp{5216} @tab @samp{5214} @samp{5216}
11819 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
11820 @item @samp{5225} @tab @samp{5224} @samp{5225}
11821 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
11822 @item @samp{5249} @tab @samp{5249}
11823 @item @samp{5250} @tab @samp{5250}
11824 @item @samp{5271} @tab @samp{5270} @samp{5271}
11825 @item @samp{5272} @tab @samp{5272}
11826 @item @samp{5275} @tab @samp{5274} @samp{5275}
11827 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
11828 @item @samp{5307} @tab @samp{5307}
11829 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
11830 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
11831 @item @samp{5407} @tab @samp{5407}
11832 @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}
11835 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
11836 @var{arch} is compatible with @var{cpu}. Other combinations of
11837 @option{-mcpu} and @option{-march} are rejected.
11839 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
11840 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
11841 where the value of @var{family} is given by the table above.
11843 @item -mtune=@var{tune}
11845 Tune the code for a particular microarchitecture, within the
11846 constraints set by @option{-march} and @option{-mcpu}.
11847 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11848 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11849 and @samp{cpu32}. The ColdFire microarchitectures
11850 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11852 You can also use @option{-mtune=68020-40} for code that needs
11853 to run relatively well on 68020, 68030 and 68040 targets.
11854 @option{-mtune=68020-60} is similar but includes 68060 targets
11855 as well. These two options select the same tuning decisions as
11856 @option{-m68020-40} and @option{-m68020-60} respectively.
11858 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11859 when tuning for 680x0 architecture @var{arch}. It also defines
11860 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11861 option is used. If gcc is tuning for a range of architectures,
11862 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11863 it defines the macros for every architecture in the range.
11865 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11866 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11867 of the arguments given above.
11873 Generate output for a 68000. This is the default
11874 when the compiler is configured for 68000-based systems.
11875 It is equivalent to @option{-march=68000}.
11877 Use this option for microcontrollers with a 68000 or EC000 core,
11878 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11882 Generate output for a 68010. This is the default
11883 when the compiler is configured for 68010-based systems.
11884 It is equivalent to @option{-march=68010}.
11890 Generate output for a 68020. This is the default
11891 when the compiler is configured for 68020-based systems.
11892 It is equivalent to @option{-march=68020}.
11896 Generate output for a 68030. This is the default when the compiler is
11897 configured for 68030-based systems. It is equivalent to
11898 @option{-march=68030}.
11902 Generate output for a 68040. This is the default when the compiler is
11903 configured for 68040-based systems. It is equivalent to
11904 @option{-march=68040}.
11906 This option inhibits the use of 68881/68882 instructions that have to be
11907 emulated by software on the 68040. Use this option if your 68040 does not
11908 have code to emulate those instructions.
11912 Generate output for a 68060. This is the default when the compiler is
11913 configured for 68060-based systems. It is equivalent to
11914 @option{-march=68060}.
11916 This option inhibits the use of 68020 and 68881/68882 instructions that
11917 have to be emulated by software on the 68060. Use this option if your 68060
11918 does not have code to emulate those instructions.
11922 Generate output for a CPU32. This is the default
11923 when the compiler is configured for CPU32-based systems.
11924 It is equivalent to @option{-march=cpu32}.
11926 Use this option for microcontrollers with a
11927 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11928 68336, 68340, 68341, 68349 and 68360.
11932 Generate output for a 520X ColdFire CPU@. This is the default
11933 when the compiler is configured for 520X-based systems.
11934 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11935 in favor of that option.
11937 Use this option for microcontroller with a 5200 core, including
11938 the MCF5202, MCF5203, MCF5204 and MCF5206.
11942 Generate output for a 5206e ColdFire CPU@. The option is now
11943 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11947 Generate output for a member of the ColdFire 528X family.
11948 The option is now deprecated in favor of the equivalent
11949 @option{-mcpu=528x}.
11953 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
11954 in favor of the equivalent @option{-mcpu=5307}.
11958 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
11959 in favor of the equivalent @option{-mcpu=5407}.
11963 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11964 This includes use of hardware floating point instructions.
11965 The option is equivalent to @option{-mcpu=547x}, and is now
11966 deprecated in favor of that option.
11970 Generate output for a 68040, without using any of the new instructions.
11971 This results in code which can run relatively efficiently on either a
11972 68020/68881 or a 68030 or a 68040. The generated code does use the
11973 68881 instructions that are emulated on the 68040.
11975 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11979 Generate output for a 68060, without using any of the new instructions.
11980 This results in code which can run relatively efficiently on either a
11981 68020/68881 or a 68030 or a 68040. The generated code does use the
11982 68881 instructions that are emulated on the 68060.
11984 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11988 @opindex mhard-float
11990 Generate floating-point instructions. This is the default for 68020
11991 and above, and for ColdFire devices that have an FPU@. It defines the
11992 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11993 on ColdFire targets.
11996 @opindex msoft-float
11997 Do not generate floating-point instructions; use library calls instead.
11998 This is the default for 68000, 68010, and 68832 targets. It is also
11999 the default for ColdFire devices that have no FPU.
12005 Generate (do not generate) ColdFire hardware divide and remainder
12006 instructions. If @option{-march} is used without @option{-mcpu},
12007 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
12008 architectures. Otherwise, the default is taken from the target CPU
12009 (either the default CPU, or the one specified by @option{-mcpu}). For
12010 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
12011 @option{-mcpu=5206e}.
12013 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
12017 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12018 Additionally, parameters passed on the stack are also aligned to a
12019 16-bit boundary even on targets whose API mandates promotion to 32-bit.
12023 Do not consider type @code{int} to be 16 bits wide. This is the default.
12026 @itemx -mno-bitfield
12027 @opindex mnobitfield
12028 @opindex mno-bitfield
12029 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
12030 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
12034 Do use the bit-field instructions. The @option{-m68020} option implies
12035 @option{-mbitfield}. This is the default if you use a configuration
12036 designed for a 68020.
12040 Use a different function-calling convention, in which functions
12041 that take a fixed number of arguments return with the @code{rtd}
12042 instruction, which pops their arguments while returning. This
12043 saves one instruction in the caller since there is no need to pop
12044 the arguments there.
12046 This calling convention is incompatible with the one normally
12047 used on Unix, so you cannot use it if you need to call libraries
12048 compiled with the Unix compiler.
12050 Also, you must provide function prototypes for all functions that
12051 take variable numbers of arguments (including @code{printf});
12052 otherwise incorrect code will be generated for calls to those
12055 In addition, seriously incorrect code will result if you call a
12056 function with too many arguments. (Normally, extra arguments are
12057 harmlessly ignored.)
12059 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
12060 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
12064 Do not use the calling conventions selected by @option{-mrtd}.
12065 This is the default.
12068 @itemx -mno-align-int
12069 @opindex malign-int
12070 @opindex mno-align-int
12071 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
12072 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
12073 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
12074 Aligning variables on 32-bit boundaries produces code that runs somewhat
12075 faster on processors with 32-bit busses at the expense of more memory.
12077 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
12078 align structures containing the above types differently than
12079 most published application binary interface specifications for the m68k.
12083 Use the pc-relative addressing mode of the 68000 directly, instead of
12084 using a global offset table. At present, this option implies @option{-fpic},
12085 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
12086 not presently supported with @option{-mpcrel}, though this could be supported for
12087 68020 and higher processors.
12089 @item -mno-strict-align
12090 @itemx -mstrict-align
12091 @opindex mno-strict-align
12092 @opindex mstrict-align
12093 Do not (do) assume that unaligned memory references will be handled by
12097 Generate code that allows the data segment to be located in a different
12098 area of memory from the text segment. This allows for execute in place in
12099 an environment without virtual memory management. This option implies
12102 @item -mno-sep-data
12103 Generate code that assumes that the data segment follows the text segment.
12104 This is the default.
12106 @item -mid-shared-library
12107 Generate code that supports shared libraries via the library ID method.
12108 This allows for execute in place and shared libraries in an environment
12109 without virtual memory management. This option implies @option{-fPIC}.
12111 @item -mno-id-shared-library
12112 Generate code that doesn't assume ID based shared libraries are being used.
12113 This is the default.
12115 @item -mshared-library-id=n
12116 Specified the identification number of the ID based shared library being
12117 compiled. Specifying a value of 0 will generate more compact code, specifying
12118 other values will force the allocation of that number to the current
12119 library but is no more space or time efficient than omitting this option.
12125 When generating position-independent code for ColdFire, generate code
12126 that works if the GOT has more than 8192 entries. This code is
12127 larger and slower than code generated without this option. On M680x0
12128 processors, this option is not needed; @option{-fPIC} suffices.
12130 GCC normally uses a single instruction to load values from the GOT@.
12131 While this is relatively efficient, it only works if the GOT
12132 is smaller than about 64k. Anything larger causes the linker
12133 to report an error such as:
12135 @cindex relocation truncated to fit (ColdFire)
12137 relocation truncated to fit: R_68K_GOT16O foobar
12140 If this happens, you should recompile your code with @option{-mxgot}.
12141 It should then work with very large GOTs. However, code generated with
12142 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
12143 the value of a global symbol.
12145 Note that some linkers, including newer versions of the GNU linker,
12146 can create multiple GOTs and sort GOT entries. If you have such a linker,
12147 you should only need to use @option{-mxgot} when compiling a single
12148 object file that accesses more than 8192 GOT entries. Very few do.
12150 These options have no effect unless GCC is generating
12151 position-independent code.
12155 @node M68hc1x Options
12156 @subsection M68hc1x Options
12157 @cindex M68hc1x options
12159 These are the @samp{-m} options defined for the 68hc11 and 68hc12
12160 microcontrollers. The default values for these options depends on
12161 which style of microcontroller was selected when the compiler was configured;
12162 the defaults for the most common choices are given below.
12169 Generate output for a 68HC11. This is the default
12170 when the compiler is configured for 68HC11-based systems.
12176 Generate output for a 68HC12. This is the default
12177 when the compiler is configured for 68HC12-based systems.
12183 Generate output for a 68HCS12.
12185 @item -mauto-incdec
12186 @opindex mauto-incdec
12187 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
12194 Enable the use of 68HC12 min and max instructions.
12197 @itemx -mno-long-calls
12198 @opindex mlong-calls
12199 @opindex mno-long-calls
12200 Treat all calls as being far away (near). If calls are assumed to be
12201 far away, the compiler will use the @code{call} instruction to
12202 call a function and the @code{rtc} instruction for returning.
12206 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12208 @item -msoft-reg-count=@var{count}
12209 @opindex msoft-reg-count
12210 Specify the number of pseudo-soft registers which are used for the
12211 code generation. The maximum number is 32. Using more pseudo-soft
12212 register may or may not result in better code depending on the program.
12213 The default is 4 for 68HC11 and 2 for 68HC12.
12217 @node MCore Options
12218 @subsection MCore Options
12219 @cindex MCore options
12221 These are the @samp{-m} options defined for the Motorola M*Core
12227 @itemx -mno-hardlit
12229 @opindex mno-hardlit
12230 Inline constants into the code stream if it can be done in two
12231 instructions or less.
12237 Use the divide instruction. (Enabled by default).
12239 @item -mrelax-immediate
12240 @itemx -mno-relax-immediate
12241 @opindex mrelax-immediate
12242 @opindex mno-relax-immediate
12243 Allow arbitrary sized immediates in bit operations.
12245 @item -mwide-bitfields
12246 @itemx -mno-wide-bitfields
12247 @opindex mwide-bitfields
12248 @opindex mno-wide-bitfields
12249 Always treat bit-fields as int-sized.
12251 @item -m4byte-functions
12252 @itemx -mno-4byte-functions
12253 @opindex m4byte-functions
12254 @opindex mno-4byte-functions
12255 Force all functions to be aligned to a four byte boundary.
12257 @item -mcallgraph-data
12258 @itemx -mno-callgraph-data
12259 @opindex mcallgraph-data
12260 @opindex mno-callgraph-data
12261 Emit callgraph information.
12264 @itemx -mno-slow-bytes
12265 @opindex mslow-bytes
12266 @opindex mno-slow-bytes
12267 Prefer word access when reading byte quantities.
12269 @item -mlittle-endian
12270 @itemx -mbig-endian
12271 @opindex mlittle-endian
12272 @opindex mbig-endian
12273 Generate code for a little endian target.
12279 Generate code for the 210 processor.
12283 @subsection MIPS Options
12284 @cindex MIPS options
12290 Generate big-endian code.
12294 Generate little-endian code. This is the default for @samp{mips*el-*-*}
12297 @item -march=@var{arch}
12299 Generate code that will run on @var{arch}, which can be the name of a
12300 generic MIPS ISA, or the name of a particular processor.
12302 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
12303 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
12304 The processor names are:
12305 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
12306 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
12307 @samp{5kc}, @samp{5kf},
12309 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
12310 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
12311 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
12312 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
12313 @samp{loongson2e}, @samp{loongson2f},
12317 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
12318 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
12319 @samp{rm7000}, @samp{rm9000},
12320 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
12323 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
12324 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
12326 The special value @samp{from-abi} selects the
12327 most compatible architecture for the selected ABI (that is,
12328 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
12330 Native Linux/GNU toolchains also support the value @samp{native},
12331 which selects the best architecture option for the host processor.
12332 @option{-march=native} has no effect if GCC does not recognize
12335 In processor names, a final @samp{000} can be abbreviated as @samp{k}
12336 (for example, @samp{-march=r2k}). Prefixes are optional, and
12337 @samp{vr} may be written @samp{r}.
12339 Names of the form @samp{@var{n}f2_1} refer to processors with
12340 FPUs clocked at half the rate of the core, names of the form
12341 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
12342 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
12343 processors with FPUs clocked a ratio of 3:2 with respect to the core.
12344 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12345 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12346 accepted as synonyms for @samp{@var{n}f1_1}.
12348 GCC defines two macros based on the value of this option. The first
12349 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12350 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12351 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12352 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12353 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12355 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12356 above. In other words, it will have the full prefix and will not
12357 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12358 the macro names the resolved architecture (either @samp{"mips1"} or
12359 @samp{"mips3"}). It names the default architecture when no
12360 @option{-march} option is given.
12362 @item -mtune=@var{arch}
12364 Optimize for @var{arch}. Among other things, this option controls
12365 the way instructions are scheduled, and the perceived cost of arithmetic
12366 operations. The list of @var{arch} values is the same as for
12369 When this option is not used, GCC will optimize for the processor
12370 specified by @option{-march}. By using @option{-march} and
12371 @option{-mtune} together, it is possible to generate code that will
12372 run on a family of processors, but optimize the code for one
12373 particular member of that family.
12375 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12376 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12377 @samp{-march} ones described above.
12381 Equivalent to @samp{-march=mips1}.
12385 Equivalent to @samp{-march=mips2}.
12389 Equivalent to @samp{-march=mips3}.
12393 Equivalent to @samp{-march=mips4}.
12397 Equivalent to @samp{-march=mips32}.
12401 Equivalent to @samp{-march=mips32r2}.
12405 Equivalent to @samp{-march=mips64}.
12409 Equivalent to @samp{-march=mips64r2}.
12414 @opindex mno-mips16
12415 Generate (do not generate) MIPS16 code. If GCC is targetting a
12416 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12418 MIPS16 code generation can also be controlled on a per-function basis
12419 by means of @code{mips16} and @code{nomips16} attributes.
12420 @xref{Function Attributes}, for more information.
12422 @item -mflip-mips16
12423 @opindex mflip-mips16
12424 Generate MIPS16 code on alternating functions. This option is provided
12425 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12426 not intended for ordinary use in compiling user code.
12428 @item -minterlink-mips16
12429 @itemx -mno-interlink-mips16
12430 @opindex minterlink-mips16
12431 @opindex mno-interlink-mips16
12432 Require (do not require) that non-MIPS16 code be link-compatible with
12435 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12436 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12437 therefore disables direct jumps unless GCC knows that the target of the
12438 jump is not MIPS16.
12450 Generate code for the given ABI@.
12452 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12453 generates 64-bit code when you select a 64-bit architecture, but you
12454 can use @option{-mgp32} to get 32-bit code instead.
12456 For information about the O64 ABI, see
12457 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12459 GCC supports a variant of the o32 ABI in which floating-point registers
12460 are 64 rather than 32 bits wide. You can select this combination with
12461 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12462 and @samp{mfhc1} instructions and is therefore only supported for
12463 MIPS32R2 processors.
12465 The register assignments for arguments and return values remain the
12466 same, but each scalar value is passed in a single 64-bit register
12467 rather than a pair of 32-bit registers. For example, scalar
12468 floating-point values are returned in @samp{$f0} only, not a
12469 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12470 remains the same, but all 64 bits are saved.
12473 @itemx -mno-abicalls
12475 @opindex mno-abicalls
12476 Generate (do not generate) code that is suitable for SVR4-style
12477 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12482 Generate (do not generate) code that is fully position-independent,
12483 and that can therefore be linked into shared libraries. This option
12484 only affects @option{-mabicalls}.
12486 All @option{-mabicalls} code has traditionally been position-independent,
12487 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12488 as an extension, the GNU toolchain allows executables to use absolute
12489 accesses for locally-binding symbols. It can also use shorter GP
12490 initialization sequences and generate direct calls to locally-defined
12491 functions. This mode is selected by @option{-mno-shared}.
12493 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12494 objects that can only be linked by the GNU linker. However, the option
12495 does not affect the ABI of the final executable; it only affects the ABI
12496 of relocatable objects. Using @option{-mno-shared} will generally make
12497 executables both smaller and quicker.
12499 @option{-mshared} is the default.
12505 Assume (do not assume) that the static and dynamic linkers
12506 support PLTs and copy relocations. This option only affects
12507 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
12508 has no effect without @samp{-msym32}.
12510 You can make @option{-mplt} the default by configuring
12511 GCC with @option{--with-mips-plt}. The default is
12512 @option{-mno-plt} otherwise.
12518 Lift (do not lift) the usual restrictions on the size of the global
12521 GCC normally uses a single instruction to load values from the GOT@.
12522 While this is relatively efficient, it will only work if the GOT
12523 is smaller than about 64k. Anything larger will cause the linker
12524 to report an error such as:
12526 @cindex relocation truncated to fit (MIPS)
12528 relocation truncated to fit: R_MIPS_GOT16 foobar
12531 If this happens, you should recompile your code with @option{-mxgot}.
12532 It should then work with very large GOTs, although it will also be
12533 less efficient, since it will take three instructions to fetch the
12534 value of a global symbol.
12536 Note that some linkers can create multiple GOTs. If you have such a
12537 linker, you should only need to use @option{-mxgot} when a single object
12538 file accesses more than 64k's worth of GOT entries. Very few do.
12540 These options have no effect unless GCC is generating position
12545 Assume that general-purpose registers are 32 bits wide.
12549 Assume that general-purpose registers are 64 bits wide.
12553 Assume that floating-point registers are 32 bits wide.
12557 Assume that floating-point registers are 64 bits wide.
12560 @opindex mhard-float
12561 Use floating-point coprocessor instructions.
12564 @opindex msoft-float
12565 Do not use floating-point coprocessor instructions. Implement
12566 floating-point calculations using library calls instead.
12568 @item -msingle-float
12569 @opindex msingle-float
12570 Assume that the floating-point coprocessor only supports single-precision
12573 @item -mdouble-float
12574 @opindex mdouble-float
12575 Assume that the floating-point coprocessor supports double-precision
12576 operations. This is the default.
12582 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12583 implement atomic memory built-in functions. When neither option is
12584 specified, GCC will use the instructions if the target architecture
12587 @option{-mllsc} is useful if the runtime environment can emulate the
12588 instructions and @option{-mno-llsc} can be useful when compiling for
12589 nonstandard ISAs. You can make either option the default by
12590 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12591 respectively. @option{--with-llsc} is the default for some
12592 configurations; see the installation documentation for details.
12598 Use (do not use) revision 1 of the MIPS DSP ASE@.
12599 @xref{MIPS DSP Built-in Functions}. This option defines the
12600 preprocessor macro @samp{__mips_dsp}. It also defines
12601 @samp{__mips_dsp_rev} to 1.
12607 Use (do not use) revision 2 of the MIPS DSP ASE@.
12608 @xref{MIPS DSP Built-in Functions}. This option defines the
12609 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12610 It also defines @samp{__mips_dsp_rev} to 2.
12613 @itemx -mno-smartmips
12614 @opindex msmartmips
12615 @opindex mno-smartmips
12616 Use (do not use) the MIPS SmartMIPS ASE.
12618 @item -mpaired-single
12619 @itemx -mno-paired-single
12620 @opindex mpaired-single
12621 @opindex mno-paired-single
12622 Use (do not use) paired-single floating-point instructions.
12623 @xref{MIPS Paired-Single Support}. This option requires
12624 hardware floating-point support to be enabled.
12630 Use (do not use) MIPS Digital Media Extension instructions.
12631 This option can only be used when generating 64-bit code and requires
12632 hardware floating-point support to be enabled.
12637 @opindex mno-mips3d
12638 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12639 The option @option{-mips3d} implies @option{-mpaired-single}.
12645 Use (do not use) MT Multithreading instructions.
12649 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12650 an explanation of the default and the way that the pointer size is
12655 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12657 The default size of @code{int}s, @code{long}s and pointers depends on
12658 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12659 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12660 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12661 or the same size as integer registers, whichever is smaller.
12667 Assume (do not assume) that all symbols have 32-bit values, regardless
12668 of the selected ABI@. This option is useful in combination with
12669 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12670 to generate shorter and faster references to symbolic addresses.
12674 Put definitions of externally-visible data in a small data section
12675 if that data is no bigger than @var{num} bytes. GCC can then access
12676 the data more efficiently; see @option{-mgpopt} for details.
12678 The default @option{-G} option depends on the configuration.
12680 @item -mlocal-sdata
12681 @itemx -mno-local-sdata
12682 @opindex mlocal-sdata
12683 @opindex mno-local-sdata
12684 Extend (do not extend) the @option{-G} behavior to local data too,
12685 such as to static variables in C@. @option{-mlocal-sdata} is the
12686 default for all configurations.
12688 If the linker complains that an application is using too much small data,
12689 you might want to try rebuilding the less performance-critical parts with
12690 @option{-mno-local-sdata}. You might also want to build large
12691 libraries with @option{-mno-local-sdata}, so that the libraries leave
12692 more room for the main program.
12694 @item -mextern-sdata
12695 @itemx -mno-extern-sdata
12696 @opindex mextern-sdata
12697 @opindex mno-extern-sdata
12698 Assume (do not assume) that externally-defined data will be in
12699 a small data section if that data is within the @option{-G} limit.
12700 @option{-mextern-sdata} is the default for all configurations.
12702 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12703 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12704 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12705 is placed in a small data section. If @var{Var} is defined by another
12706 module, you must either compile that module with a high-enough
12707 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12708 definition. If @var{Var} is common, you must link the application
12709 with a high-enough @option{-G} setting.
12711 The easiest way of satisfying these restrictions is to compile
12712 and link every module with the same @option{-G} option. However,
12713 you may wish to build a library that supports several different
12714 small data limits. You can do this by compiling the library with
12715 the highest supported @option{-G} setting and additionally using
12716 @option{-mno-extern-sdata} to stop the library from making assumptions
12717 about externally-defined data.
12723 Use (do not use) GP-relative accesses for symbols that are known to be
12724 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12725 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12728 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12729 might not hold the value of @code{_gp}. For example, if the code is
12730 part of a library that might be used in a boot monitor, programs that
12731 call boot monitor routines will pass an unknown value in @code{$gp}.
12732 (In such situations, the boot monitor itself would usually be compiled
12733 with @option{-G0}.)
12735 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12736 @option{-mno-extern-sdata}.
12738 @item -membedded-data
12739 @itemx -mno-embedded-data
12740 @opindex membedded-data
12741 @opindex mno-embedded-data
12742 Allocate variables to the read-only data section first if possible, then
12743 next in the small data section if possible, otherwise in data. This gives
12744 slightly slower code than the default, but reduces the amount of RAM required
12745 when executing, and thus may be preferred for some embedded systems.
12747 @item -muninit-const-in-rodata
12748 @itemx -mno-uninit-const-in-rodata
12749 @opindex muninit-const-in-rodata
12750 @opindex mno-uninit-const-in-rodata
12751 Put uninitialized @code{const} variables in the read-only data section.
12752 This option is only meaningful in conjunction with @option{-membedded-data}.
12754 @item -mcode-readable=@var{setting}
12755 @opindex mcode-readable
12756 Specify whether GCC may generate code that reads from executable sections.
12757 There are three possible settings:
12760 @item -mcode-readable=yes
12761 Instructions may freely access executable sections. This is the
12764 @item -mcode-readable=pcrel
12765 MIPS16 PC-relative load instructions can access executable sections,
12766 but other instructions must not do so. This option is useful on 4KSc
12767 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12768 It is also useful on processors that can be configured to have a dual
12769 instruction/data SRAM interface and that, like the M4K, automatically
12770 redirect PC-relative loads to the instruction RAM.
12772 @item -mcode-readable=no
12773 Instructions must not access executable sections. This option can be
12774 useful on targets that are configured to have a dual instruction/data
12775 SRAM interface but that (unlike the M4K) do not automatically redirect
12776 PC-relative loads to the instruction RAM.
12779 @item -msplit-addresses
12780 @itemx -mno-split-addresses
12781 @opindex msplit-addresses
12782 @opindex mno-split-addresses
12783 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12784 relocation operators. This option has been superseded by
12785 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12787 @item -mexplicit-relocs
12788 @itemx -mno-explicit-relocs
12789 @opindex mexplicit-relocs
12790 @opindex mno-explicit-relocs
12791 Use (do not use) assembler relocation operators when dealing with symbolic
12792 addresses. The alternative, selected by @option{-mno-explicit-relocs},
12793 is to use assembler macros instead.
12795 @option{-mexplicit-relocs} is the default if GCC was configured
12796 to use an assembler that supports relocation operators.
12798 @item -mcheck-zero-division
12799 @itemx -mno-check-zero-division
12800 @opindex mcheck-zero-division
12801 @opindex mno-check-zero-division
12802 Trap (do not trap) on integer division by zero.
12804 The default is @option{-mcheck-zero-division}.
12806 @item -mdivide-traps
12807 @itemx -mdivide-breaks
12808 @opindex mdivide-traps
12809 @opindex mdivide-breaks
12810 MIPS systems check for division by zero by generating either a
12811 conditional trap or a break instruction. Using traps results in
12812 smaller code, but is only supported on MIPS II and later. Also, some
12813 versions of the Linux kernel have a bug that prevents trap from
12814 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
12815 allow conditional traps on architectures that support them and
12816 @option{-mdivide-breaks} to force the use of breaks.
12818 The default is usually @option{-mdivide-traps}, but this can be
12819 overridden at configure time using @option{--with-divide=breaks}.
12820 Divide-by-zero checks can be completely disabled using
12821 @option{-mno-check-zero-division}.
12826 @opindex mno-memcpy
12827 Force (do not force) the use of @code{memcpy()} for non-trivial block
12828 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
12829 most constant-sized copies.
12832 @itemx -mno-long-calls
12833 @opindex mlong-calls
12834 @opindex mno-long-calls
12835 Disable (do not disable) use of the @code{jal} instruction. Calling
12836 functions using @code{jal} is more efficient but requires the caller
12837 and callee to be in the same 256 megabyte segment.
12839 This option has no effect on abicalls code. The default is
12840 @option{-mno-long-calls}.
12846 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
12847 instructions, as provided by the R4650 ISA@.
12850 @itemx -mno-fused-madd
12851 @opindex mfused-madd
12852 @opindex mno-fused-madd
12853 Enable (disable) use of the floating point multiply-accumulate
12854 instructions, when they are available. The default is
12855 @option{-mfused-madd}.
12857 When multiply-accumulate instructions are used, the intermediate
12858 product is calculated to infinite precision and is not subject to
12859 the FCSR Flush to Zero bit. This may be undesirable in some
12864 Tell the MIPS assembler to not run its preprocessor over user
12865 assembler files (with a @samp{.s} suffix) when assembling them.
12868 @itemx -mno-fix-r4000
12869 @opindex mfix-r4000
12870 @opindex mno-fix-r4000
12871 Work around certain R4000 CPU errata:
12874 A double-word or a variable shift may give an incorrect result if executed
12875 immediately after starting an integer division.
12877 A double-word or a variable shift may give an incorrect result if executed
12878 while an integer multiplication is in progress.
12880 An integer division may give an incorrect result if started in a delay slot
12881 of a taken branch or a jump.
12885 @itemx -mno-fix-r4400
12886 @opindex mfix-r4400
12887 @opindex mno-fix-r4400
12888 Work around certain R4400 CPU errata:
12891 A double-word or a variable shift may give an incorrect result if executed
12892 immediately after starting an integer division.
12896 @itemx -mno-fix-r10000
12897 @opindex mfix-r10000
12898 @opindex mno-fix-r10000
12899 Work around certain R10000 errata:
12902 @code{ll}/@code{sc} sequences may not behave atomically on revisions
12903 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
12906 This option can only be used if the target architecture supports
12907 branch-likely instructions. @option{-mfix-r10000} is the default when
12908 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
12912 @itemx -mno-fix-vr4120
12913 @opindex mfix-vr4120
12914 Work around certain VR4120 errata:
12917 @code{dmultu} does not always produce the correct result.
12919 @code{div} and @code{ddiv} do not always produce the correct result if one
12920 of the operands is negative.
12922 The workarounds for the division errata rely on special functions in
12923 @file{libgcc.a}. At present, these functions are only provided by
12924 the @code{mips64vr*-elf} configurations.
12926 Other VR4120 errata require a nop to be inserted between certain pairs of
12927 instructions. These errata are handled by the assembler, not by GCC itself.
12930 @opindex mfix-vr4130
12931 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
12932 workarounds are implemented by the assembler rather than by GCC,
12933 although GCC will avoid using @code{mflo} and @code{mfhi} if the
12934 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
12935 instructions are available instead.
12938 @itemx -mno-fix-sb1
12940 Work around certain SB-1 CPU core errata.
12941 (This flag currently works around the SB-1 revision 2
12942 ``F1'' and ``F2'' floating point errata.)
12944 @item -mr10k-cache-barrier=@var{setting}
12945 @opindex mr10k-cache-barrier
12946 Specify whether GCC should insert cache barriers to avoid the
12947 side-effects of speculation on R10K processors.
12949 In common with many processors, the R10K tries to predict the outcome
12950 of a conditional branch and speculatively executes instructions from
12951 the ``taken'' branch. It later aborts these instructions if the
12952 predicted outcome was wrong. However, on the R10K, even aborted
12953 instructions can have side effects.
12955 This problem only affects kernel stores and, depending on the system,
12956 kernel loads. As an example, a speculatively-executed store may load
12957 the target memory into cache and mark the cache line as dirty, even if
12958 the store itself is later aborted. If a DMA operation writes to the
12959 same area of memory before the ``dirty'' line is flushed, the cached
12960 data will overwrite the DMA-ed data. See the R10K processor manual
12961 for a full description, including other potential problems.
12963 One workaround is to insert cache barrier instructions before every memory
12964 access that might be speculatively executed and that might have side
12965 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
12966 controls GCC's implementation of this workaround. It assumes that
12967 aborted accesses to any byte in the following regions will not have
12972 the memory occupied by the current function's stack frame;
12975 the memory occupied by an incoming stack argument;
12978 the memory occupied by an object with a link-time-constant address.
12981 It is the kernel's responsibility to ensure that speculative
12982 accesses to these regions are indeed safe.
12984 If the input program contains a function declaration such as:
12990 then the implementation of @code{foo} must allow @code{j foo} and
12991 @code{jal foo} to be executed speculatively. GCC honors this
12992 restriction for functions it compiles itself. It expects non-GCC
12993 functions (such as hand-written assembly code) to do the same.
12995 The option has three forms:
12998 @item -mr10k-cache-barrier=load-store
12999 Insert a cache barrier before a load or store that might be
13000 speculatively executed and that might have side effects even
13003 @item -mr10k-cache-barrier=store
13004 Insert a cache barrier before a store that might be speculatively
13005 executed and that might have side effects even if aborted.
13007 @item -mr10k-cache-barrier=none
13008 Disable the insertion of cache barriers. This is the default setting.
13011 @item -mflush-func=@var{func}
13012 @itemx -mno-flush-func
13013 @opindex mflush-func
13014 Specifies the function to call to flush the I and D caches, or to not
13015 call any such function. If called, the function must take the same
13016 arguments as the common @code{_flush_func()}, that is, the address of the
13017 memory range for which the cache is being flushed, the size of the
13018 memory range, and the number 3 (to flush both caches). The default
13019 depends on the target GCC was configured for, but commonly is either
13020 @samp{_flush_func} or @samp{__cpu_flush}.
13022 @item mbranch-cost=@var{num}
13023 @opindex mbranch-cost
13024 Set the cost of branches to roughly @var{num} ``simple'' instructions.
13025 This cost is only a heuristic and is not guaranteed to produce
13026 consistent results across releases. A zero cost redundantly selects
13027 the default, which is based on the @option{-mtune} setting.
13029 @item -mbranch-likely
13030 @itemx -mno-branch-likely
13031 @opindex mbranch-likely
13032 @opindex mno-branch-likely
13033 Enable or disable use of Branch Likely instructions, regardless of the
13034 default for the selected architecture. By default, Branch Likely
13035 instructions may be generated if they are supported by the selected
13036 architecture. An exception is for the MIPS32 and MIPS64 architectures
13037 and processors which implement those architectures; for those, Branch
13038 Likely instructions will not be generated by default because the MIPS32
13039 and MIPS64 architectures specifically deprecate their use.
13041 @item -mfp-exceptions
13042 @itemx -mno-fp-exceptions
13043 @opindex mfp-exceptions
13044 Specifies whether FP exceptions are enabled. This affects how we schedule
13045 FP instructions for some processors. The default is that FP exceptions are
13048 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
13049 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
13052 @item -mvr4130-align
13053 @itemx -mno-vr4130-align
13054 @opindex mvr4130-align
13055 The VR4130 pipeline is two-way superscalar, but can only issue two
13056 instructions together if the first one is 8-byte aligned. When this
13057 option is enabled, GCC will align pairs of instructions that it
13058 thinks should execute in parallel.
13060 This option only has an effect when optimizing for the VR4130.
13061 It normally makes code faster, but at the expense of making it bigger.
13062 It is enabled by default at optimization level @option{-O3}.
13066 @subsection MMIX Options
13067 @cindex MMIX Options
13069 These options are defined for the MMIX:
13073 @itemx -mno-libfuncs
13075 @opindex mno-libfuncs
13076 Specify that intrinsic library functions are being compiled, passing all
13077 values in registers, no matter the size.
13080 @itemx -mno-epsilon
13082 @opindex mno-epsilon
13083 Generate floating-point comparison instructions that compare with respect
13084 to the @code{rE} epsilon register.
13086 @item -mabi=mmixware
13088 @opindex mabi-mmixware
13090 Generate code that passes function parameters and return values that (in
13091 the called function) are seen as registers @code{$0} and up, as opposed to
13092 the GNU ABI which uses global registers @code{$231} and up.
13094 @item -mzero-extend
13095 @itemx -mno-zero-extend
13096 @opindex mzero-extend
13097 @opindex mno-zero-extend
13098 When reading data from memory in sizes shorter than 64 bits, use (do not
13099 use) zero-extending load instructions by default, rather than
13100 sign-extending ones.
13103 @itemx -mno-knuthdiv
13105 @opindex mno-knuthdiv
13106 Make the result of a division yielding a remainder have the same sign as
13107 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
13108 remainder follows the sign of the dividend. Both methods are
13109 arithmetically valid, the latter being almost exclusively used.
13111 @item -mtoplevel-symbols
13112 @itemx -mno-toplevel-symbols
13113 @opindex mtoplevel-symbols
13114 @opindex mno-toplevel-symbols
13115 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
13116 code can be used with the @code{PREFIX} assembly directive.
13120 Generate an executable in the ELF format, rather than the default
13121 @samp{mmo} format used by the @command{mmix} simulator.
13123 @item -mbranch-predict
13124 @itemx -mno-branch-predict
13125 @opindex mbranch-predict
13126 @opindex mno-branch-predict
13127 Use (do not use) the probable-branch instructions, when static branch
13128 prediction indicates a probable branch.
13130 @item -mbase-addresses
13131 @itemx -mno-base-addresses
13132 @opindex mbase-addresses
13133 @opindex mno-base-addresses
13134 Generate (do not generate) code that uses @emph{base addresses}. Using a
13135 base address automatically generates a request (handled by the assembler
13136 and the linker) for a constant to be set up in a global register. The
13137 register is used for one or more base address requests within the range 0
13138 to 255 from the value held in the register. The generally leads to short
13139 and fast code, but the number of different data items that can be
13140 addressed is limited. This means that a program that uses lots of static
13141 data may require @option{-mno-base-addresses}.
13143 @item -msingle-exit
13144 @itemx -mno-single-exit
13145 @opindex msingle-exit
13146 @opindex mno-single-exit
13147 Force (do not force) generated code to have a single exit point in each
13151 @node MN10300 Options
13152 @subsection MN10300 Options
13153 @cindex MN10300 options
13155 These @option{-m} options are defined for Matsushita MN10300 architectures:
13160 Generate code to avoid bugs in the multiply instructions for the MN10300
13161 processors. This is the default.
13163 @item -mno-mult-bug
13164 @opindex mno-mult-bug
13165 Do not generate code to avoid bugs in the multiply instructions for the
13166 MN10300 processors.
13170 Generate code which uses features specific to the AM33 processor.
13174 Do not generate code which uses features specific to the AM33 processor. This
13177 @item -mreturn-pointer-on-d0
13178 @opindex mreturn-pointer-on-d0
13179 When generating a function which returns a pointer, return the pointer
13180 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
13181 only in a0, and attempts to call such functions without a prototype
13182 would result in errors. Note that this option is on by default; use
13183 @option{-mno-return-pointer-on-d0} to disable it.
13187 Do not link in the C run-time initialization object file.
13191 Indicate to the linker that it should perform a relaxation optimization pass
13192 to shorten branches, calls and absolute memory addresses. This option only
13193 has an effect when used on the command line for the final link step.
13195 This option makes symbolic debugging impossible.
13198 @node PDP-11 Options
13199 @subsection PDP-11 Options
13200 @cindex PDP-11 Options
13202 These options are defined for the PDP-11:
13207 Use hardware FPP floating point. This is the default. (FIS floating
13208 point on the PDP-11/40 is not supported.)
13211 @opindex msoft-float
13212 Do not use hardware floating point.
13216 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
13220 Return floating-point results in memory. This is the default.
13224 Generate code for a PDP-11/40.
13228 Generate code for a PDP-11/45. This is the default.
13232 Generate code for a PDP-11/10.
13234 @item -mbcopy-builtin
13235 @opindex bcopy-builtin
13236 Use inline @code{movmemhi} patterns for copying memory. This is the
13241 Do not use inline @code{movmemhi} patterns for copying memory.
13247 Use 16-bit @code{int}. This is the default.
13253 Use 32-bit @code{int}.
13256 @itemx -mno-float32
13258 @opindex mno-float32
13259 Use 64-bit @code{float}. This is the default.
13262 @itemx -mno-float64
13264 @opindex mno-float64
13265 Use 32-bit @code{float}.
13269 Use @code{abshi2} pattern. This is the default.
13273 Do not use @code{abshi2} pattern.
13275 @item -mbranch-expensive
13276 @opindex mbranch-expensive
13277 Pretend that branches are expensive. This is for experimenting with
13278 code generation only.
13280 @item -mbranch-cheap
13281 @opindex mbranch-cheap
13282 Do not pretend that branches are expensive. This is the default.
13286 Generate code for a system with split I&D@.
13290 Generate code for a system without split I&D@. This is the default.
13294 Use Unix assembler syntax. This is the default when configured for
13295 @samp{pdp11-*-bsd}.
13299 Use DEC assembler syntax. This is the default when configured for any
13300 PDP-11 target other than @samp{pdp11-*-bsd}.
13303 @node picoChip Options
13304 @subsection picoChip Options
13305 @cindex picoChip options
13307 These @samp{-m} options are defined for picoChip implementations:
13311 @item -mae=@var{ae_type}
13313 Set the instruction set, register set, and instruction scheduling
13314 parameters for array element type @var{ae_type}. Supported values
13315 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
13317 @option{-mae=ANY} selects a completely generic AE type. Code
13318 generated with this option will run on any of the other AE types. The
13319 code will not be as efficient as it would be if compiled for a specific
13320 AE type, and some types of operation (e.g., multiplication) will not
13321 work properly on all types of AE.
13323 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
13324 for compiled code, and is the default.
13326 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
13327 option may suffer from poor performance of byte (char) manipulation,
13328 since the DSP AE does not provide hardware support for byte load/stores.
13330 @item -msymbol-as-address
13331 Enable the compiler to directly use a symbol name as an address in a
13332 load/store instruction, without first loading it into a
13333 register. Typically, the use of this option will generate larger
13334 programs, which run faster than when the option isn't used. However, the
13335 results vary from program to program, so it is left as a user option,
13336 rather than being permanently enabled.
13338 @item -mno-inefficient-warnings
13339 Disables warnings about the generation of inefficient code. These
13340 warnings can be generated, for example, when compiling code which
13341 performs byte-level memory operations on the MAC AE type. The MAC AE has
13342 no hardware support for byte-level memory operations, so all byte
13343 load/stores must be synthesized from word load/store operations. This is
13344 inefficient and a warning will be generated indicating to the programmer
13345 that they should rewrite the code to avoid byte operations, or to target
13346 an AE type which has the necessary hardware support. This option enables
13347 the warning to be turned off.
13351 @node PowerPC Options
13352 @subsection PowerPC Options
13353 @cindex PowerPC options
13355 These are listed under @xref{RS/6000 and PowerPC Options}.
13357 @node RS/6000 and PowerPC Options
13358 @subsection IBM RS/6000 and PowerPC Options
13359 @cindex RS/6000 and PowerPC Options
13360 @cindex IBM RS/6000 and PowerPC Options
13362 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
13369 @itemx -mno-powerpc
13370 @itemx -mpowerpc-gpopt
13371 @itemx -mno-powerpc-gpopt
13372 @itemx -mpowerpc-gfxopt
13373 @itemx -mno-powerpc-gfxopt
13375 @itemx -mno-powerpc64
13379 @itemx -mno-popcntb
13387 @itemx -mno-hard-dfp
13391 @opindex mno-power2
13393 @opindex mno-powerpc
13394 @opindex mpowerpc-gpopt
13395 @opindex mno-powerpc-gpopt
13396 @opindex mpowerpc-gfxopt
13397 @opindex mno-powerpc-gfxopt
13398 @opindex mpowerpc64
13399 @opindex mno-powerpc64
13403 @opindex mno-popcntb
13409 @opindex mno-mfpgpr
13411 @opindex mno-hard-dfp
13412 GCC supports two related instruction set architectures for the
13413 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
13414 instructions supported by the @samp{rios} chip set used in the original
13415 RS/6000 systems and the @dfn{PowerPC} instruction set is the
13416 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
13417 the IBM 4xx, 6xx, and follow-on microprocessors.
13419 Neither architecture is a subset of the other. However there is a
13420 large common subset of instructions supported by both. An MQ
13421 register is included in processors supporting the POWER architecture.
13423 You use these options to specify which instructions are available on the
13424 processor you are using. The default value of these options is
13425 determined when configuring GCC@. Specifying the
13426 @option{-mcpu=@var{cpu_type}} overrides the specification of these
13427 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
13428 rather than the options listed above.
13430 The @option{-mpower} option allows GCC to generate instructions that
13431 are found only in the POWER architecture and to use the MQ register.
13432 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
13433 to generate instructions that are present in the POWER2 architecture but
13434 not the original POWER architecture.
13436 The @option{-mpowerpc} option allows GCC to generate instructions that
13437 are found only in the 32-bit subset of the PowerPC architecture.
13438 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
13439 GCC to use the optional PowerPC architecture instructions in the
13440 General Purpose group, including floating-point square root. Specifying
13441 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
13442 use the optional PowerPC architecture instructions in the Graphics
13443 group, including floating-point select.
13445 The @option{-mmfcrf} option allows GCC to generate the move from
13446 condition register field instruction implemented on the POWER4
13447 processor and other processors that support the PowerPC V2.01
13449 The @option{-mpopcntb} option allows GCC to generate the popcount and
13450 double precision FP reciprocal estimate instruction implemented on the
13451 POWER5 processor and other processors that support the PowerPC V2.02
13453 The @option{-mfprnd} option allows GCC to generate the FP round to
13454 integer instructions implemented on the POWER5+ processor and other
13455 processors that support the PowerPC V2.03 architecture.
13456 The @option{-mcmpb} option allows GCC to generate the compare bytes
13457 instruction implemented on the POWER6 processor and other processors
13458 that support the PowerPC V2.05 architecture.
13459 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
13460 general purpose register instructions implemented on the POWER6X
13461 processor and other processors that support the extended PowerPC V2.05
13463 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
13464 point instructions implemented on some POWER processors.
13466 The @option{-mpowerpc64} option allows GCC to generate the additional
13467 64-bit instructions that are found in the full PowerPC64 architecture
13468 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
13469 @option{-mno-powerpc64}.
13471 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
13472 will use only the instructions in the common subset of both
13473 architectures plus some special AIX common-mode calls, and will not use
13474 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
13475 permits GCC to use any instruction from either architecture and to
13476 allow use of the MQ register; specify this for the Motorola MPC601.
13478 @item -mnew-mnemonics
13479 @itemx -mold-mnemonics
13480 @opindex mnew-mnemonics
13481 @opindex mold-mnemonics
13482 Select which mnemonics to use in the generated assembler code. With
13483 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
13484 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
13485 assembler mnemonics defined for the POWER architecture. Instructions
13486 defined in only one architecture have only one mnemonic; GCC uses that
13487 mnemonic irrespective of which of these options is specified.
13489 GCC defaults to the mnemonics appropriate for the architecture in
13490 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
13491 value of these option. Unless you are building a cross-compiler, you
13492 should normally not specify either @option{-mnew-mnemonics} or
13493 @option{-mold-mnemonics}, but should instead accept the default.
13495 @item -mcpu=@var{cpu_type}
13497 Set architecture type, register usage, choice of mnemonics, and
13498 instruction scheduling parameters for machine type @var{cpu_type}.
13499 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13500 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13501 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13502 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13503 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13504 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13505 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13506 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13507 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}
13508 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13509 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13511 @option{-mcpu=common} selects a completely generic processor. Code
13512 generated under this option will run on any POWER or PowerPC processor.
13513 GCC will use only the instructions in the common subset of both
13514 architectures, and will not use the MQ register. GCC assumes a generic
13515 processor model for scheduling purposes.
13517 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13518 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13519 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13520 types, with an appropriate, generic processor model assumed for
13521 scheduling purposes.
13523 The other options specify a specific processor. Code generated under
13524 those options will run best on that processor, and may not run at all on
13527 The @option{-mcpu} options automatically enable or disable the
13530 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13531 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13532 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
13533 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr}
13535 The particular options set for any particular CPU will vary between
13536 compiler versions, depending on what setting seems to produce optimal
13537 code for that CPU; it doesn't necessarily reflect the actual hardware's
13538 capabilities. If you wish to set an individual option to a particular
13539 value, you may specify it after the @option{-mcpu} option, like
13540 @samp{-mcpu=970 -mno-altivec}.
13542 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13543 not enabled or disabled by the @option{-mcpu} option at present because
13544 AIX does not have full support for these options. You may still
13545 enable or disable them individually if you're sure it'll work in your
13548 @item -mtune=@var{cpu_type}
13550 Set the instruction scheduling parameters for machine type
13551 @var{cpu_type}, but do not set the architecture type, register usage, or
13552 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13553 values for @var{cpu_type} are used for @option{-mtune} as for
13554 @option{-mcpu}. If both are specified, the code generated will use the
13555 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13556 scheduling parameters set by @option{-mtune}.
13562 Generate code to compute division as reciprocal estimate and iterative
13563 refinement, creating opportunities for increased throughput. This
13564 feature requires: optional PowerPC Graphics instruction set for single
13565 precision and FRE instruction for double precision, assuming divides
13566 cannot generate user-visible traps, and the domain values not include
13567 Infinities, denormals or zero denominator.
13570 @itemx -mno-altivec
13572 @opindex mno-altivec
13573 Generate code that uses (does not use) AltiVec instructions, and also
13574 enable the use of built-in functions that allow more direct access to
13575 the AltiVec instruction set. You may also need to set
13576 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13582 @opindex mno-vrsave
13583 Generate VRSAVE instructions when generating AltiVec code.
13585 @item -mgen-cell-microcode
13586 @opindex mgen-cell-microcode
13587 Generate Cell microcode instructions
13589 @item -mwarn-cell-microcode
13590 @opindex mwarn-cell-microcode
13591 Warning when a Cell microcode instruction is going to emitted. An example
13592 of a Cell microcode instruction is a variable shift.
13595 @opindex msecure-plt
13596 Generate code that allows ld and ld.so to build executables and shared
13597 libraries with non-exec .plt and .got sections. This is a PowerPC
13598 32-bit SYSV ABI option.
13602 Generate code that uses a BSS .plt section that ld.so fills in, and
13603 requires .plt and .got sections that are both writable and executable.
13604 This is a PowerPC 32-bit SYSV ABI option.
13610 This switch enables or disables the generation of ISEL instructions.
13612 @item -misel=@var{yes/no}
13613 This switch has been deprecated. Use @option{-misel} and
13614 @option{-mno-isel} instead.
13620 This switch enables or disables the generation of SPE simd
13626 @opindex mno-paired
13627 This switch enables or disables the generation of PAIRED simd
13630 @item -mspe=@var{yes/no}
13631 This option has been deprecated. Use @option{-mspe} and
13632 @option{-mno-spe} instead.
13634 @item -mfloat-gprs=@var{yes/single/double/no}
13635 @itemx -mfloat-gprs
13636 @opindex mfloat-gprs
13637 This switch enables or disables the generation of floating point
13638 operations on the general purpose registers for architectures that
13641 The argument @var{yes} or @var{single} enables the use of
13642 single-precision floating point operations.
13644 The argument @var{double} enables the use of single and
13645 double-precision floating point operations.
13647 The argument @var{no} disables floating point operations on the
13648 general purpose registers.
13650 This option is currently only available on the MPC854x.
13656 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13657 targets (including GNU/Linux). The 32-bit environment sets int, long
13658 and pointer to 32 bits and generates code that runs on any PowerPC
13659 variant. The 64-bit environment sets int to 32 bits and long and
13660 pointer to 64 bits, and generates code for PowerPC64, as for
13661 @option{-mpowerpc64}.
13664 @itemx -mno-fp-in-toc
13665 @itemx -mno-sum-in-toc
13666 @itemx -mminimal-toc
13668 @opindex mno-fp-in-toc
13669 @opindex mno-sum-in-toc
13670 @opindex mminimal-toc
13671 Modify generation of the TOC (Table Of Contents), which is created for
13672 every executable file. The @option{-mfull-toc} option is selected by
13673 default. In that case, GCC will allocate at least one TOC entry for
13674 each unique non-automatic variable reference in your program. GCC
13675 will also place floating-point constants in the TOC@. However, only
13676 16,384 entries are available in the TOC@.
13678 If you receive a linker error message that saying you have overflowed
13679 the available TOC space, you can reduce the amount of TOC space used
13680 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13681 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13682 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13683 generate code to calculate the sum of an address and a constant at
13684 run-time instead of putting that sum into the TOC@. You may specify one
13685 or both of these options. Each causes GCC to produce very slightly
13686 slower and larger code at the expense of conserving TOC space.
13688 If you still run out of space in the TOC even when you specify both of
13689 these options, specify @option{-mminimal-toc} instead. This option causes
13690 GCC to make only one TOC entry for every file. When you specify this
13691 option, GCC will produce code that is slower and larger but which
13692 uses extremely little TOC space. You may wish to use this option
13693 only on files that contain less frequently executed code.
13699 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13700 @code{long} type, and the infrastructure needed to support them.
13701 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13702 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13703 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13706 @itemx -mno-xl-compat
13707 @opindex mxl-compat
13708 @opindex mno-xl-compat
13709 Produce code that conforms more closely to IBM XL compiler semantics
13710 when using AIX-compatible ABI@. Pass floating-point arguments to
13711 prototyped functions beyond the register save area (RSA) on the stack
13712 in addition to argument FPRs. Do not assume that most significant
13713 double in 128-bit long double value is properly rounded when comparing
13714 values and converting to double. Use XL symbol names for long double
13717 The AIX calling convention was extended but not initially documented to
13718 handle an obscure K&R C case of calling a function that takes the
13719 address of its arguments with fewer arguments than declared. IBM XL
13720 compilers access floating point arguments which do not fit in the
13721 RSA from the stack when a subroutine is compiled without
13722 optimization. Because always storing floating-point arguments on the
13723 stack is inefficient and rarely needed, this option is not enabled by
13724 default and only is necessary when calling subroutines compiled by IBM
13725 XL compilers without optimization.
13729 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13730 application written to use message passing with special startup code to
13731 enable the application to run. The system must have PE installed in the
13732 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13733 must be overridden with the @option{-specs=} option to specify the
13734 appropriate directory location. The Parallel Environment does not
13735 support threads, so the @option{-mpe} option and the @option{-pthread}
13736 option are incompatible.
13738 @item -malign-natural
13739 @itemx -malign-power
13740 @opindex malign-natural
13741 @opindex malign-power
13742 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13743 @option{-malign-natural} overrides the ABI-defined alignment of larger
13744 types, such as floating-point doubles, on their natural size-based boundary.
13745 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13746 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13748 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13752 @itemx -mhard-float
13753 @opindex msoft-float
13754 @opindex mhard-float
13755 Generate code that does not use (uses) the floating-point register set.
13756 Software floating point emulation is provided if you use the
13757 @option{-msoft-float} option, and pass the option to GCC when linking.
13759 @item -msingle-float
13760 @itemx -mdouble-float
13761 @opindex msingle-float
13762 @opindex mdouble-float
13763 Generate code for single or double-precision floating point operations.
13764 @option{-mdouble-float} implies @option{-msingle-float}.
13767 @opindex msimple-fpu
13768 Do not generate sqrt and div instructions for hardware floating point unit.
13772 Specify type of floating point unit. Valid values are @var{sp_lite}
13773 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
13774 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
13775 and @var{dp_full} (equivalent to -mdouble-float).
13778 @opindex mxilinx-fpu
13779 Perform optimizations for floating point unit on Xilinx PPC 405/440.
13782 @itemx -mno-multiple
13784 @opindex mno-multiple
13785 Generate code that uses (does not use) the load multiple word
13786 instructions and the store multiple word instructions. These
13787 instructions are generated by default on POWER systems, and not
13788 generated on PowerPC systems. Do not use @option{-mmultiple} on little
13789 endian PowerPC systems, since those instructions do not work when the
13790 processor is in little endian mode. The exceptions are PPC740 and
13791 PPC750 which permit the instructions usage in little endian mode.
13796 @opindex mno-string
13797 Generate code that uses (does not use) the load string instructions
13798 and the store string word instructions to save multiple registers and
13799 do small block moves. These instructions are generated by default on
13800 POWER systems, and not generated on PowerPC systems. Do not use
13801 @option{-mstring} on little endian PowerPC systems, since those
13802 instructions do not work when the processor is in little endian mode.
13803 The exceptions are PPC740 and PPC750 which permit the instructions
13804 usage in little endian mode.
13809 @opindex mno-update
13810 Generate code that uses (does not use) the load or store instructions
13811 that update the base register to the address of the calculated memory
13812 location. These instructions are generated by default. If you use
13813 @option{-mno-update}, there is a small window between the time that the
13814 stack pointer is updated and the address of the previous frame is
13815 stored, which means code that walks the stack frame across interrupts or
13816 signals may get corrupted data.
13818 @item -mavoid-indexed-addresses
13819 @item -mno-avoid-indexed-addresses
13820 @opindex mavoid-indexed-addresses
13821 @opindex mno-avoid-indexed-addresses
13822 Generate code that tries to avoid (not avoid) the use of indexed load
13823 or store instructions. These instructions can incur a performance
13824 penalty on Power6 processors in certain situations, such as when
13825 stepping through large arrays that cross a 16M boundary. This option
13826 is enabled by default when targetting Power6 and disabled otherwise.
13829 @itemx -mno-fused-madd
13830 @opindex mfused-madd
13831 @opindex mno-fused-madd
13832 Generate code that uses (does not use) the floating point multiply and
13833 accumulate instructions. These instructions are generated by default if
13834 hardware floating is used.
13840 Generate code that uses (does not use) the half-word multiply and
13841 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
13842 These instructions are generated by default when targetting those
13849 Generate code that uses (does not use) the string-search @samp{dlmzb}
13850 instruction on the IBM 405, 440 and 464 processors. This instruction is
13851 generated by default when targetting those processors.
13853 @item -mno-bit-align
13855 @opindex mno-bit-align
13856 @opindex mbit-align
13857 On System V.4 and embedded PowerPC systems do not (do) force structures
13858 and unions that contain bit-fields to be aligned to the base type of the
13861 For example, by default a structure containing nothing but 8
13862 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
13863 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
13864 the structure would be aligned to a 1 byte boundary and be one byte in
13867 @item -mno-strict-align
13868 @itemx -mstrict-align
13869 @opindex mno-strict-align
13870 @opindex mstrict-align
13871 On System V.4 and embedded PowerPC systems do not (do) assume that
13872 unaligned memory references will be handled by the system.
13874 @item -mrelocatable
13875 @itemx -mno-relocatable
13876 @opindex mrelocatable
13877 @opindex mno-relocatable
13878 On embedded PowerPC systems generate code that allows (does not allow)
13879 the program to be relocated to a different address at runtime. If you
13880 use @option{-mrelocatable} on any module, all objects linked together must
13881 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
13883 @item -mrelocatable-lib
13884 @itemx -mno-relocatable-lib
13885 @opindex mrelocatable-lib
13886 @opindex mno-relocatable-lib
13887 On embedded PowerPC systems generate code that allows (does not allow)
13888 the program to be relocated to a different address at runtime. Modules
13889 compiled with @option{-mrelocatable-lib} can be linked with either modules
13890 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
13891 with modules compiled with the @option{-mrelocatable} options.
13897 On System V.4 and embedded PowerPC systems do not (do) assume that
13898 register 2 contains a pointer to a global area pointing to the addresses
13899 used in the program.
13902 @itemx -mlittle-endian
13904 @opindex mlittle-endian
13905 On System V.4 and embedded PowerPC systems compile code for the
13906 processor in little endian mode. The @option{-mlittle-endian} option is
13907 the same as @option{-mlittle}.
13910 @itemx -mbig-endian
13912 @opindex mbig-endian
13913 On System V.4 and embedded PowerPC systems compile code for the
13914 processor in big endian mode. The @option{-mbig-endian} option is
13915 the same as @option{-mbig}.
13917 @item -mdynamic-no-pic
13918 @opindex mdynamic-no-pic
13919 On Darwin and Mac OS X systems, compile code so that it is not
13920 relocatable, but that its external references are relocatable. The
13921 resulting code is suitable for applications, but not shared
13924 @item -mprioritize-restricted-insns=@var{priority}
13925 @opindex mprioritize-restricted-insns
13926 This option controls the priority that is assigned to
13927 dispatch-slot restricted instructions during the second scheduling
13928 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
13929 @var{no/highest/second-highest} priority to dispatch slot restricted
13932 @item -msched-costly-dep=@var{dependence_type}
13933 @opindex msched-costly-dep
13934 This option controls which dependences are considered costly
13935 by the target during instruction scheduling. The argument
13936 @var{dependence_type} takes one of the following values:
13937 @var{no}: no dependence is costly,
13938 @var{all}: all dependences are costly,
13939 @var{true_store_to_load}: a true dependence from store to load is costly,
13940 @var{store_to_load}: any dependence from store to load is costly,
13941 @var{number}: any dependence which latency >= @var{number} is costly.
13943 @item -minsert-sched-nops=@var{scheme}
13944 @opindex minsert-sched-nops
13945 This option controls which nop insertion scheme will be used during
13946 the second scheduling pass. The argument @var{scheme} takes one of the
13948 @var{no}: Don't insert nops.
13949 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
13950 according to the scheduler's grouping.
13951 @var{regroup_exact}: Insert nops to force costly dependent insns into
13952 separate groups. Insert exactly as many nops as needed to force an insn
13953 to a new group, according to the estimated processor grouping.
13954 @var{number}: Insert nops to force costly dependent insns into
13955 separate groups. Insert @var{number} nops to force an insn to a new group.
13958 @opindex mcall-sysv
13959 On System V.4 and embedded PowerPC systems compile code using calling
13960 conventions that adheres to the March 1995 draft of the System V
13961 Application Binary Interface, PowerPC processor supplement. This is the
13962 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
13964 @item -mcall-sysv-eabi
13965 @opindex mcall-sysv-eabi
13966 Specify both @option{-mcall-sysv} and @option{-meabi} options.
13968 @item -mcall-sysv-noeabi
13969 @opindex mcall-sysv-noeabi
13970 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
13972 @item -mcall-solaris
13973 @opindex mcall-solaris
13974 On System V.4 and embedded PowerPC systems compile code for the Solaris
13978 @opindex mcall-linux
13979 On System V.4 and embedded PowerPC systems compile code for the
13980 Linux-based GNU system.
13984 On System V.4 and embedded PowerPC systems compile code for the
13985 Hurd-based GNU system.
13987 @item -mcall-netbsd
13988 @opindex mcall-netbsd
13989 On System V.4 and embedded PowerPC systems compile code for the
13990 NetBSD operating system.
13992 @item -maix-struct-return
13993 @opindex maix-struct-return
13994 Return all structures in memory (as specified by the AIX ABI)@.
13996 @item -msvr4-struct-return
13997 @opindex msvr4-struct-return
13998 Return structures smaller than 8 bytes in registers (as specified by the
14001 @item -mabi=@var{abi-type}
14003 Extend the current ABI with a particular extension, or remove such extension.
14004 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
14005 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
14009 Extend the current ABI with SPE ABI extensions. This does not change
14010 the default ABI, instead it adds the SPE ABI extensions to the current
14014 @opindex mabi=no-spe
14015 Disable Booke SPE ABI extensions for the current ABI@.
14017 @item -mabi=ibmlongdouble
14018 @opindex mabi=ibmlongdouble
14019 Change the current ABI to use IBM extended precision long double.
14020 This is a PowerPC 32-bit SYSV ABI option.
14022 @item -mabi=ieeelongdouble
14023 @opindex mabi=ieeelongdouble
14024 Change the current ABI to use IEEE extended precision long double.
14025 This is a PowerPC 32-bit Linux ABI option.
14028 @itemx -mno-prototype
14029 @opindex mprototype
14030 @opindex mno-prototype
14031 On System V.4 and embedded PowerPC systems assume that all calls to
14032 variable argument functions are properly prototyped. Otherwise, the
14033 compiler must insert an instruction before every non prototyped call to
14034 set or clear bit 6 of the condition code register (@var{CR}) to
14035 indicate whether floating point values were passed in the floating point
14036 registers in case the function takes a variable arguments. With
14037 @option{-mprototype}, only calls to prototyped variable argument functions
14038 will set or clear the bit.
14042 On embedded PowerPC systems, assume that the startup module is called
14043 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
14044 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
14049 On embedded PowerPC systems, assume that the startup module is called
14050 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
14055 On embedded PowerPC systems, assume that the startup module is called
14056 @file{crt0.o} and the standard C libraries are @file{libads.a} and
14059 @item -myellowknife
14060 @opindex myellowknife
14061 On embedded PowerPC systems, assume that the startup module is called
14062 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
14067 On System V.4 and embedded PowerPC systems, specify that you are
14068 compiling for a VxWorks system.
14072 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
14073 header to indicate that @samp{eabi} extended relocations are used.
14079 On System V.4 and embedded PowerPC systems do (do not) adhere to the
14080 Embedded Applications Binary Interface (eabi) which is a set of
14081 modifications to the System V.4 specifications. Selecting @option{-meabi}
14082 means that the stack is aligned to an 8 byte boundary, a function
14083 @code{__eabi} is called to from @code{main} to set up the eabi
14084 environment, and the @option{-msdata} option can use both @code{r2} and
14085 @code{r13} to point to two separate small data areas. Selecting
14086 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
14087 do not call an initialization function from @code{main}, and the
14088 @option{-msdata} option will only use @code{r13} to point to a single
14089 small data area. The @option{-meabi} option is on by default if you
14090 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
14093 @opindex msdata=eabi
14094 On System V.4 and embedded PowerPC systems, put small initialized
14095 @code{const} global and static data in the @samp{.sdata2} section, which
14096 is pointed to by register @code{r2}. Put small initialized
14097 non-@code{const} global and static data in the @samp{.sdata} section,
14098 which is pointed to by register @code{r13}. Put small uninitialized
14099 global and static data in the @samp{.sbss} section, which is adjacent to
14100 the @samp{.sdata} section. The @option{-msdata=eabi} option is
14101 incompatible with the @option{-mrelocatable} option. The
14102 @option{-msdata=eabi} option also sets the @option{-memb} option.
14105 @opindex msdata=sysv
14106 On System V.4 and embedded PowerPC systems, put small global and static
14107 data in the @samp{.sdata} section, which is pointed to by register
14108 @code{r13}. Put small uninitialized global and static data in the
14109 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
14110 The @option{-msdata=sysv} option is incompatible with the
14111 @option{-mrelocatable} option.
14113 @item -msdata=default
14115 @opindex msdata=default
14117 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
14118 compile code the same as @option{-msdata=eabi}, otherwise compile code the
14119 same as @option{-msdata=sysv}.
14122 @opindex msdata-data
14123 On System V.4 and embedded PowerPC systems, put small global
14124 data in the @samp{.sdata} section. Put small uninitialized global
14125 data in the @samp{.sbss} section. Do not use register @code{r13}
14126 to address small data however. This is the default behavior unless
14127 other @option{-msdata} options are used.
14131 @opindex msdata=none
14133 On embedded PowerPC systems, put all initialized global and static data
14134 in the @samp{.data} section, and all uninitialized data in the
14135 @samp{.bss} section.
14139 @cindex smaller data references (PowerPC)
14140 @cindex .sdata/.sdata2 references (PowerPC)
14141 On embedded PowerPC systems, put global and static items less than or
14142 equal to @var{num} bytes into the small data or bss sections instead of
14143 the normal data or bss section. By default, @var{num} is 8. The
14144 @option{-G @var{num}} switch is also passed to the linker.
14145 All modules should be compiled with the same @option{-G @var{num}} value.
14148 @itemx -mno-regnames
14150 @opindex mno-regnames
14151 On System V.4 and embedded PowerPC systems do (do not) emit register
14152 names in the assembly language output using symbolic forms.
14155 @itemx -mno-longcall
14157 @opindex mno-longcall
14158 By default assume that all calls are far away so that a longer more
14159 expensive calling sequence is required. This is required for calls
14160 further than 32 megabytes (33,554,432 bytes) from the current location.
14161 A short call will be generated if the compiler knows
14162 the call cannot be that far away. This setting can be overridden by
14163 the @code{shortcall} function attribute, or by @code{#pragma
14166 Some linkers are capable of detecting out-of-range calls and generating
14167 glue code on the fly. On these systems, long calls are unnecessary and
14168 generate slower code. As of this writing, the AIX linker can do this,
14169 as can the GNU linker for PowerPC/64. It is planned to add this feature
14170 to the GNU linker for 32-bit PowerPC systems as well.
14172 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
14173 callee, L42'', plus a ``branch island'' (glue code). The two target
14174 addresses represent the callee and the ``branch island''. The
14175 Darwin/PPC linker will prefer the first address and generate a ``bl
14176 callee'' if the PPC ``bl'' instruction will reach the callee directly;
14177 otherwise, the linker will generate ``bl L42'' to call the ``branch
14178 island''. The ``branch island'' is appended to the body of the
14179 calling function; it computes the full 32-bit address of the callee
14182 On Mach-O (Darwin) systems, this option directs the compiler emit to
14183 the glue for every direct call, and the Darwin linker decides whether
14184 to use or discard it.
14186 In the future, we may cause GCC to ignore all longcall specifications
14187 when the linker is known to generate glue.
14191 Adds support for multithreading with the @dfn{pthreads} library.
14192 This option sets flags for both the preprocessor and linker.
14196 @node S/390 and zSeries Options
14197 @subsection S/390 and zSeries Options
14198 @cindex S/390 and zSeries Options
14200 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
14204 @itemx -msoft-float
14205 @opindex mhard-float
14206 @opindex msoft-float
14207 Use (do not use) the hardware floating-point instructions and registers
14208 for floating-point operations. When @option{-msoft-float} is specified,
14209 functions in @file{libgcc.a} will be used to perform floating-point
14210 operations. When @option{-mhard-float} is specified, the compiler
14211 generates IEEE floating-point instructions. This is the default.
14214 @itemx -mno-hard-dfp
14216 @opindex mno-hard-dfp
14217 Use (do not use) the hardware decimal-floating-point instructions for
14218 decimal-floating-point operations. When @option{-mno-hard-dfp} is
14219 specified, functions in @file{libgcc.a} will be used to perform
14220 decimal-floating-point operations. When @option{-mhard-dfp} is
14221 specified, the compiler generates decimal-floating-point hardware
14222 instructions. This is the default for @option{-march=z9-ec} or higher.
14224 @item -mlong-double-64
14225 @itemx -mlong-double-128
14226 @opindex mlong-double-64
14227 @opindex mlong-double-128
14228 These switches control the size of @code{long double} type. A size
14229 of 64bit makes the @code{long double} type equivalent to the @code{double}
14230 type. This is the default.
14233 @itemx -mno-backchain
14234 @opindex mbackchain
14235 @opindex mno-backchain
14236 Store (do not store) the address of the caller's frame as backchain pointer
14237 into the callee's stack frame.
14238 A backchain may be needed to allow debugging using tools that do not understand
14239 DWARF-2 call frame information.
14240 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
14241 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
14242 the backchain is placed into the topmost word of the 96/160 byte register
14245 In general, code compiled with @option{-mbackchain} is call-compatible with
14246 code compiled with @option{-mmo-backchain}; however, use of the backchain
14247 for debugging purposes usually requires that the whole binary is built with
14248 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
14249 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14250 to build a linux kernel use @option{-msoft-float}.
14252 The default is to not maintain the backchain.
14254 @item -mpacked-stack
14255 @itemx -mno-packed-stack
14256 @opindex mpacked-stack
14257 @opindex mno-packed-stack
14258 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
14259 specified, the compiler uses the all fields of the 96/160 byte register save
14260 area only for their default purpose; unused fields still take up stack space.
14261 When @option{-mpacked-stack} is specified, register save slots are densely
14262 packed at the top of the register save area; unused space is reused for other
14263 purposes, allowing for more efficient use of the available stack space.
14264 However, when @option{-mbackchain} is also in effect, the topmost word of
14265 the save area is always used to store the backchain, and the return address
14266 register is always saved two words below the backchain.
14268 As long as the stack frame backchain is not used, code generated with
14269 @option{-mpacked-stack} is call-compatible with code generated with
14270 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
14271 S/390 or zSeries generated code that uses the stack frame backchain at run
14272 time, not just for debugging purposes. Such code is not call-compatible
14273 with code compiled with @option{-mpacked-stack}. Also, note that the
14274 combination of @option{-mbackchain},
14275 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14276 to build a linux kernel use @option{-msoft-float}.
14278 The default is to not use the packed stack layout.
14281 @itemx -mno-small-exec
14282 @opindex msmall-exec
14283 @opindex mno-small-exec
14284 Generate (or do not generate) code using the @code{bras} instruction
14285 to do subroutine calls.
14286 This only works reliably if the total executable size does not
14287 exceed 64k. The default is to use the @code{basr} instruction instead,
14288 which does not have this limitation.
14294 When @option{-m31} is specified, generate code compliant to the
14295 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
14296 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
14297 particular to generate 64-bit instructions. For the @samp{s390}
14298 targets, the default is @option{-m31}, while the @samp{s390x}
14299 targets default to @option{-m64}.
14305 When @option{-mzarch} is specified, generate code using the
14306 instructions available on z/Architecture.
14307 When @option{-mesa} is specified, generate code using the
14308 instructions available on ESA/390. Note that @option{-mesa} is
14309 not possible with @option{-m64}.
14310 When generating code compliant to the GNU/Linux for S/390 ABI,
14311 the default is @option{-mesa}. When generating code compliant
14312 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
14318 Generate (or do not generate) code using the @code{mvcle} instruction
14319 to perform block moves. When @option{-mno-mvcle} is specified,
14320 use a @code{mvc} loop instead. This is the default unless optimizing for
14327 Print (or do not print) additional debug information when compiling.
14328 The default is to not print debug information.
14330 @item -march=@var{cpu-type}
14332 Generate code that will run on @var{cpu-type}, which is the name of a system
14333 representing a certain processor type. Possible values for
14334 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
14335 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
14336 When generating code using the instructions available on z/Architecture,
14337 the default is @option{-march=z900}. Otherwise, the default is
14338 @option{-march=g5}.
14340 @item -mtune=@var{cpu-type}
14342 Tune to @var{cpu-type} everything applicable about the generated code,
14343 except for the ABI and the set of available instructions.
14344 The list of @var{cpu-type} values is the same as for @option{-march}.
14345 The default is the value used for @option{-march}.
14348 @itemx -mno-tpf-trace
14349 @opindex mtpf-trace
14350 @opindex mno-tpf-trace
14351 Generate code that adds (does not add) in TPF OS specific branches to trace
14352 routines in the operating system. This option is off by default, even
14353 when compiling for the TPF OS@.
14356 @itemx -mno-fused-madd
14357 @opindex mfused-madd
14358 @opindex mno-fused-madd
14359 Generate code that uses (does not use) the floating point multiply and
14360 accumulate instructions. These instructions are generated by default if
14361 hardware floating point is used.
14363 @item -mwarn-framesize=@var{framesize}
14364 @opindex mwarn-framesize
14365 Emit a warning if the current function exceeds the given frame size. Because
14366 this is a compile time check it doesn't need to be a real problem when the program
14367 runs. It is intended to identify functions which most probably cause
14368 a stack overflow. It is useful to be used in an environment with limited stack
14369 size e.g.@: the linux kernel.
14371 @item -mwarn-dynamicstack
14372 @opindex mwarn-dynamicstack
14373 Emit a warning if the function calls alloca or uses dynamically
14374 sized arrays. This is generally a bad idea with a limited stack size.
14376 @item -mstack-guard=@var{stack-guard}
14377 @itemx -mstack-size=@var{stack-size}
14378 @opindex mstack-guard
14379 @opindex mstack-size
14380 If these options are provided the s390 back end emits additional instructions in
14381 the function prologue which trigger a trap if the stack size is @var{stack-guard}
14382 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
14383 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
14384 the frame size of the compiled function is chosen.
14385 These options are intended to be used to help debugging stack overflow problems.
14386 The additionally emitted code causes only little overhead and hence can also be
14387 used in production like systems without greater performance degradation. The given
14388 values have to be exact powers of 2 and @var{stack-size} has to be greater than
14389 @var{stack-guard} without exceeding 64k.
14390 In order to be efficient the extra code makes the assumption that the stack starts
14391 at an address aligned to the value given by @var{stack-size}.
14392 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
14395 @node Score Options
14396 @subsection Score Options
14397 @cindex Score Options
14399 These options are defined for Score implementations:
14404 Compile code for big endian mode. This is the default.
14408 Compile code for little endian mode.
14412 Disable generate bcnz instruction.
14416 Enable generate unaligned load and store instruction.
14420 Enable the use of multiply-accumulate instructions. Disabled by default.
14424 Specify the SCORE5 as the target architecture.
14428 Specify the SCORE5U of the target architecture.
14432 Specify the SCORE7 as the target architecture. This is the default.
14436 Specify the SCORE7D as the target architecture.
14440 @subsection SH Options
14442 These @samp{-m} options are defined for the SH implementations:
14447 Generate code for the SH1.
14451 Generate code for the SH2.
14454 Generate code for the SH2e.
14458 Generate code for the SH3.
14462 Generate code for the SH3e.
14466 Generate code for the SH4 without a floating-point unit.
14468 @item -m4-single-only
14469 @opindex m4-single-only
14470 Generate code for the SH4 with a floating-point unit that only
14471 supports single-precision arithmetic.
14475 Generate code for the SH4 assuming the floating-point unit is in
14476 single-precision mode by default.
14480 Generate code for the SH4.
14484 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
14485 floating-point unit is not used.
14487 @item -m4a-single-only
14488 @opindex m4a-single-only
14489 Generate code for the SH4a, in such a way that no double-precision
14490 floating point operations are used.
14493 @opindex m4a-single
14494 Generate code for the SH4a assuming the floating-point unit is in
14495 single-precision mode by default.
14499 Generate code for the SH4a.
14503 Same as @option{-m4a-nofpu}, except that it implicitly passes
14504 @option{-dsp} to the assembler. GCC doesn't generate any DSP
14505 instructions at the moment.
14509 Compile code for the processor in big endian mode.
14513 Compile code for the processor in little endian mode.
14517 Align doubles at 64-bit boundaries. Note that this changes the calling
14518 conventions, and thus some functions from the standard C library will
14519 not work unless you recompile it first with @option{-mdalign}.
14523 Shorten some address references at link time, when possible; uses the
14524 linker option @option{-relax}.
14528 Use 32-bit offsets in @code{switch} tables. The default is to use
14533 Enable the use of bit manipulation instructions on SH2A.
14537 Enable the use of the instruction @code{fmovd}.
14541 Comply with the calling conventions defined by Renesas.
14545 Comply with the calling conventions defined by Renesas.
14549 Comply with the calling conventions defined for GCC before the Renesas
14550 conventions were available. This option is the default for all
14551 targets of the SH toolchain except for @samp{sh-symbianelf}.
14554 @opindex mnomacsave
14555 Mark the @code{MAC} register as call-clobbered, even if
14556 @option{-mhitachi} is given.
14560 Increase IEEE-compliance of floating-point code.
14561 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14562 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14563 comparisons of NANs / infinities incurs extra overhead in every
14564 floating point comparison, therefore the default is set to
14565 @option{-ffinite-math-only}.
14567 @item -minline-ic_invalidate
14568 @opindex minline-ic_invalidate
14569 Inline code to invalidate instruction cache entries after setting up
14570 nested function trampolines.
14571 This option has no effect if -musermode is in effect and the selected
14572 code generation option (e.g. -m4) does not allow the use of the icbi
14574 If the selected code generation option does not allow the use of the icbi
14575 instruction, and -musermode is not in effect, the inlined code will
14576 manipulate the instruction cache address array directly with an associative
14577 write. This not only requires privileged mode, but it will also
14578 fail if the cache line had been mapped via the TLB and has become unmapped.
14582 Dump instruction size and location in the assembly code.
14585 @opindex mpadstruct
14586 This option is deprecated. It pads structures to multiple of 4 bytes,
14587 which is incompatible with the SH ABI@.
14591 Optimize for space instead of speed. Implied by @option{-Os}.
14594 @opindex mprefergot
14595 When generating position-independent code, emit function calls using
14596 the Global Offset Table instead of the Procedure Linkage Table.
14600 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14601 if the inlined code would not work in user mode.
14602 This is the default when the target is @code{sh-*-linux*}.
14604 @item -multcost=@var{number}
14605 @opindex multcost=@var{number}
14606 Set the cost to assume for a multiply insn.
14608 @item -mdiv=@var{strategy}
14609 @opindex mdiv=@var{strategy}
14610 Set the division strategy to use for SHmedia code. @var{strategy} must be
14611 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14612 inv:call2, inv:fp .
14613 "fp" performs the operation in floating point. This has a very high latency,
14614 but needs only a few instructions, so it might be a good choice if
14615 your code has enough easily exploitable ILP to allow the compiler to
14616 schedule the floating point instructions together with other instructions.
14617 Division by zero causes a floating point exception.
14618 "inv" uses integer operations to calculate the inverse of the divisor,
14619 and then multiplies the dividend with the inverse. This strategy allows
14620 cse and hoisting of the inverse calculation. Division by zero calculates
14621 an unspecified result, but does not trap.
14622 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14623 have been found, or if the entire operation has been hoisted to the same
14624 place, the last stages of the inverse calculation are intertwined with the
14625 final multiply to reduce the overall latency, at the expense of using a few
14626 more instructions, and thus offering fewer scheduling opportunities with
14628 "call" calls a library function that usually implements the inv:minlat
14630 This gives high code density for m5-*media-nofpu compilations.
14631 "call2" uses a different entry point of the same library function, where it
14632 assumes that a pointer to a lookup table has already been set up, which
14633 exposes the pointer load to cse / code hoisting optimizations.
14634 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14635 code generation, but if the code stays unoptimized, revert to the "call",
14636 "call2", or "fp" strategies, respectively. Note that the
14637 potentially-trapping side effect of division by zero is carried by a
14638 separate instruction, so it is possible that all the integer instructions
14639 are hoisted out, but the marker for the side effect stays where it is.
14640 A recombination to fp operations or a call is not possible in that case.
14641 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14642 that the inverse calculation was nor separated from the multiply, they speed
14643 up division where the dividend fits into 20 bits (plus sign where applicable),
14644 by inserting a test to skip a number of operations in this case; this test
14645 slows down the case of larger dividends. inv20u assumes the case of a such
14646 a small dividend to be unlikely, and inv20l assumes it to be likely.
14648 @item -mdivsi3_libfunc=@var{name}
14649 @opindex mdivsi3_libfunc=@var{name}
14650 Set the name of the library function used for 32 bit signed division to
14651 @var{name}. This only affect the name used in the call and inv:call
14652 division strategies, and the compiler will still expect the same
14653 sets of input/output/clobbered registers as if this option was not present.
14655 @item -mfixed-range=@var{register-range}
14656 @opindex mfixed-range
14657 Generate code treating the given register range as fixed registers.
14658 A fixed register is one that the register allocator can not use. This is
14659 useful when compiling kernel code. A register range is specified as
14660 two registers separated by a dash. Multiple register ranges can be
14661 specified separated by a comma.
14663 @item -madjust-unroll
14664 @opindex madjust-unroll
14665 Throttle unrolling to avoid thrashing target registers.
14666 This option only has an effect if the gcc code base supports the
14667 TARGET_ADJUST_UNROLL_MAX target hook.
14669 @item -mindexed-addressing
14670 @opindex mindexed-addressing
14671 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14672 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14673 semantics for the indexed addressing mode. The architecture allows the
14674 implementation of processors with 64 bit MMU, which the OS could use to
14675 get 32 bit addressing, but since no current hardware implementation supports
14676 this or any other way to make the indexed addressing mode safe to use in
14677 the 32 bit ABI, the default is -mno-indexed-addressing.
14679 @item -mgettrcost=@var{number}
14680 @opindex mgettrcost=@var{number}
14681 Set the cost assumed for the gettr instruction to @var{number}.
14682 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14686 Assume pt* instructions won't trap. This will generally generate better
14687 scheduled code, but is unsafe on current hardware. The current architecture
14688 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14689 This has the unintentional effect of making it unsafe to schedule ptabs /
14690 ptrel before a branch, or hoist it out of a loop. For example,
14691 __do_global_ctors, a part of libgcc that runs constructors at program
14692 startup, calls functions in a list which is delimited by @minus{}1. With the
14693 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14694 That means that all the constructors will be run a bit quicker, but when
14695 the loop comes to the end of the list, the program crashes because ptabs
14696 loads @minus{}1 into a target register. Since this option is unsafe for any
14697 hardware implementing the current architecture specification, the default
14698 is -mno-pt-fixed. Unless the user specifies a specific cost with
14699 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14700 this deters register allocation using target registers for storing
14703 @item -minvalid-symbols
14704 @opindex minvalid-symbols
14705 Assume symbols might be invalid. Ordinary function symbols generated by
14706 the compiler will always be valid to load with movi/shori/ptabs or
14707 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14708 to generate symbols that will cause ptabs / ptrel to trap.
14709 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14710 It will then prevent cross-basic-block cse, hoisting and most scheduling
14711 of symbol loads. The default is @option{-mno-invalid-symbols}.
14714 @node SPARC Options
14715 @subsection SPARC Options
14716 @cindex SPARC options
14718 These @samp{-m} options are supported on the SPARC:
14721 @item -mno-app-regs
14723 @opindex mno-app-regs
14725 Specify @option{-mapp-regs} to generate output using the global registers
14726 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14729 To be fully SVR4 ABI compliant at the cost of some performance loss,
14730 specify @option{-mno-app-regs}. You should compile libraries and system
14731 software with this option.
14734 @itemx -mhard-float
14736 @opindex mhard-float
14737 Generate output containing floating point instructions. This is the
14741 @itemx -msoft-float
14743 @opindex msoft-float
14744 Generate output containing library calls for floating point.
14745 @strong{Warning:} the requisite libraries are not available for all SPARC
14746 targets. Normally the facilities of the machine's usual C compiler are
14747 used, but this cannot be done directly in cross-compilation. You must make
14748 your own arrangements to provide suitable library functions for
14749 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14750 @samp{sparclite-*-*} do provide software floating point support.
14752 @option{-msoft-float} changes the calling convention in the output file;
14753 therefore, it is only useful if you compile @emph{all} of a program with
14754 this option. In particular, you need to compile @file{libgcc.a}, the
14755 library that comes with GCC, with @option{-msoft-float} in order for
14758 @item -mhard-quad-float
14759 @opindex mhard-quad-float
14760 Generate output containing quad-word (long double) floating point
14763 @item -msoft-quad-float
14764 @opindex msoft-quad-float
14765 Generate output containing library calls for quad-word (long double)
14766 floating point instructions. The functions called are those specified
14767 in the SPARC ABI@. This is the default.
14769 As of this writing, there are no SPARC implementations that have hardware
14770 support for the quad-word floating point instructions. They all invoke
14771 a trap handler for one of these instructions, and then the trap handler
14772 emulates the effect of the instruction. Because of the trap handler overhead,
14773 this is much slower than calling the ABI library routines. Thus the
14774 @option{-msoft-quad-float} option is the default.
14776 @item -mno-unaligned-doubles
14777 @itemx -munaligned-doubles
14778 @opindex mno-unaligned-doubles
14779 @opindex munaligned-doubles
14780 Assume that doubles have 8 byte alignment. This is the default.
14782 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14783 alignment only if they are contained in another type, or if they have an
14784 absolute address. Otherwise, it assumes they have 4 byte alignment.
14785 Specifying this option avoids some rare compatibility problems with code
14786 generated by other compilers. It is not the default because it results
14787 in a performance loss, especially for floating point code.
14789 @item -mno-faster-structs
14790 @itemx -mfaster-structs
14791 @opindex mno-faster-structs
14792 @opindex mfaster-structs
14793 With @option{-mfaster-structs}, the compiler assumes that structures
14794 should have 8 byte alignment. This enables the use of pairs of
14795 @code{ldd} and @code{std} instructions for copies in structure
14796 assignment, in place of twice as many @code{ld} and @code{st} pairs.
14797 However, the use of this changed alignment directly violates the SPARC
14798 ABI@. Thus, it's intended only for use on targets where the developer
14799 acknowledges that their resulting code will not be directly in line with
14800 the rules of the ABI@.
14802 @item -mimpure-text
14803 @opindex mimpure-text
14804 @option{-mimpure-text}, used in addition to @option{-shared}, tells
14805 the compiler to not pass @option{-z text} to the linker when linking a
14806 shared object. Using this option, you can link position-dependent
14807 code into a shared object.
14809 @option{-mimpure-text} suppresses the ``relocations remain against
14810 allocatable but non-writable sections'' linker error message.
14811 However, the necessary relocations will trigger copy-on-write, and the
14812 shared object is not actually shared across processes. Instead of
14813 using @option{-mimpure-text}, you should compile all source code with
14814 @option{-fpic} or @option{-fPIC}.
14816 This option is only available on SunOS and Solaris.
14818 @item -mcpu=@var{cpu_type}
14820 Set the instruction set, register set, and instruction scheduling parameters
14821 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
14822 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
14823 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
14824 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
14825 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
14827 Default instruction scheduling parameters are used for values that select
14828 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
14829 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
14831 Here is a list of each supported architecture and their supported
14836 v8: supersparc, hypersparc
14837 sparclite: f930, f934, sparclite86x
14839 v9: ultrasparc, ultrasparc3, niagara, niagara2
14842 By default (unless configured otherwise), GCC generates code for the V7
14843 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
14844 additionally optimizes it for the Cypress CY7C602 chip, as used in the
14845 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
14846 SPARCStation 1, 2, IPX etc.
14848 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
14849 architecture. The only difference from V7 code is that the compiler emits
14850 the integer multiply and integer divide instructions which exist in SPARC-V8
14851 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
14852 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
14855 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
14856 the SPARC architecture. This adds the integer multiply, integer divide step
14857 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
14858 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
14859 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
14860 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
14861 MB86934 chip, which is the more recent SPARClite with FPU@.
14863 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
14864 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
14865 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
14866 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
14867 optimizes it for the TEMIC SPARClet chip.
14869 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
14870 architecture. This adds 64-bit integer and floating-point move instructions,
14871 3 additional floating-point condition code registers and conditional move
14872 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
14873 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
14874 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
14875 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
14876 @option{-mcpu=niagara}, the compiler additionally optimizes it for
14877 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
14878 additionally optimizes it for Sun UltraSPARC T2 chips.
14880 @item -mtune=@var{cpu_type}
14882 Set the instruction scheduling parameters for machine type
14883 @var{cpu_type}, but do not set the instruction set or register set that the
14884 option @option{-mcpu=@var{cpu_type}} would.
14886 The same values for @option{-mcpu=@var{cpu_type}} can be used for
14887 @option{-mtune=@var{cpu_type}}, but the only useful values are those
14888 that select a particular cpu implementation. Those are @samp{cypress},
14889 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
14890 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
14891 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
14896 @opindex mno-v8plus
14897 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
14898 difference from the V8 ABI is that the global and out registers are
14899 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
14900 mode for all SPARC-V9 processors.
14906 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
14907 Visual Instruction Set extensions. The default is @option{-mno-vis}.
14910 These @samp{-m} options are supported in addition to the above
14911 on SPARC-V9 processors in 64-bit environments:
14914 @item -mlittle-endian
14915 @opindex mlittle-endian
14916 Generate code for a processor running in little-endian mode. It is only
14917 available for a few configurations and most notably not on Solaris and Linux.
14923 Generate code for a 32-bit or 64-bit environment.
14924 The 32-bit environment sets int, long and pointer to 32 bits.
14925 The 64-bit environment sets int to 32 bits and long and pointer
14928 @item -mcmodel=medlow
14929 @opindex mcmodel=medlow
14930 Generate code for the Medium/Low code model: 64-bit addresses, programs
14931 must be linked in the low 32 bits of memory. Programs can be statically
14932 or dynamically linked.
14934 @item -mcmodel=medmid
14935 @opindex mcmodel=medmid
14936 Generate code for the Medium/Middle code model: 64-bit addresses, programs
14937 must be linked in the low 44 bits of memory, the text and data segments must
14938 be less than 2GB in size and the data segment must be located within 2GB of
14941 @item -mcmodel=medany
14942 @opindex mcmodel=medany
14943 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
14944 may be linked anywhere in memory, the text and data segments must be less
14945 than 2GB in size and the data segment must be located within 2GB of the
14948 @item -mcmodel=embmedany
14949 @opindex mcmodel=embmedany
14950 Generate code for the Medium/Anywhere code model for embedded systems:
14951 64-bit addresses, the text and data segments must be less than 2GB in
14952 size, both starting anywhere in memory (determined at link time). The
14953 global register %g4 points to the base of the data segment. Programs
14954 are statically linked and PIC is not supported.
14957 @itemx -mno-stack-bias
14958 @opindex mstack-bias
14959 @opindex mno-stack-bias
14960 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
14961 frame pointer if present, are offset by @minus{}2047 which must be added back
14962 when making stack frame references. This is the default in 64-bit mode.
14963 Otherwise, assume no such offset is present.
14966 These switches are supported in addition to the above on Solaris:
14971 Add support for multithreading using the Solaris threads library. This
14972 option sets flags for both the preprocessor and linker. This option does
14973 not affect the thread safety of object code produced by the compiler or
14974 that of libraries supplied with it.
14978 Add support for multithreading using the POSIX threads library. This
14979 option sets flags for both the preprocessor and linker. This option does
14980 not affect the thread safety of object code produced by the compiler or
14981 that of libraries supplied with it.
14985 This is a synonym for @option{-pthreads}.
14989 @subsection SPU Options
14990 @cindex SPU options
14992 These @samp{-m} options are supported on the SPU:
14996 @itemx -merror-reloc
14997 @opindex mwarn-reloc
14998 @opindex merror-reloc
15000 The loader for SPU does not handle dynamic relocations. By default, GCC
15001 will give an error when it generates code that requires a dynamic
15002 relocation. @option{-mno-error-reloc} disables the error,
15003 @option{-mwarn-reloc} will generate a warning instead.
15006 @itemx -munsafe-dma
15008 @opindex munsafe-dma
15010 Instructions which initiate or test completion of DMA must not be
15011 reordered with respect to loads and stores of the memory which is being
15012 accessed. Users typically address this problem using the volatile
15013 keyword, but that can lead to inefficient code in places where the
15014 memory is known to not change. Rather than mark the memory as volatile
15015 we treat the DMA instructions as potentially effecting all memory. With
15016 @option{-munsafe-dma} users must use the volatile keyword to protect
15019 @item -mbranch-hints
15020 @opindex mbranch-hints
15022 By default, GCC will generate a branch hint instruction to avoid
15023 pipeline stalls for always taken or probably taken branches. A hint
15024 will not be generated closer than 8 instructions away from its branch.
15025 There is little reason to disable them, except for debugging purposes,
15026 or to make an object a little bit smaller.
15030 @opindex msmall-mem
15031 @opindex mlarge-mem
15033 By default, GCC generates code assuming that addresses are never larger
15034 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
15035 a full 32 bit address.
15040 By default, GCC links against startup code that assumes the SPU-style
15041 main function interface (which has an unconventional parameter list).
15042 With @option{-mstdmain}, GCC will link your program against startup
15043 code that assumes a C99-style interface to @code{main}, including a
15044 local copy of @code{argv} strings.
15046 @item -mfixed-range=@var{register-range}
15047 @opindex mfixed-range
15048 Generate code treating the given register range as fixed registers.
15049 A fixed register is one that the register allocator can not use. This is
15050 useful when compiling kernel code. A register range is specified as
15051 two registers separated by a dash. Multiple register ranges can be
15052 specified separated by a comma.
15055 @itemx -mdual-nops=@var{n}
15056 @opindex mdual-nops
15057 By default, GCC will insert nops to increase dual issue when it expects
15058 it to increase performance. @var{n} can be a value from 0 to 10. A
15059 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
15060 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
15062 @item -mhint-max-nops=@var{n}
15063 @opindex mhint-max-nops
15064 Maximum number of nops to insert for a branch hint. A branch hint must
15065 be at least 8 instructions away from the branch it is effecting. GCC
15066 will insert up to @var{n} nops to enforce this, otherwise it will not
15067 generate the branch hint.
15069 @item -mhint-max-distance=@var{n}
15070 @opindex mhint-max-distance
15071 The encoding of the branch hint instruction limits the hint to be within
15072 256 instructions of the branch it is effecting. By default, GCC makes
15073 sure it is within 125.
15076 @opindex msafe-hints
15077 Work around a hardware bug which causes the SPU to stall indefinitely.
15078 By default, GCC will insert the @code{hbrp} instruction to make sure
15079 this stall won't happen.
15083 @node System V Options
15084 @subsection Options for System V
15086 These additional options are available on System V Release 4 for
15087 compatibility with other compilers on those systems:
15092 Create a shared object.
15093 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
15097 Identify the versions of each tool used by the compiler, in a
15098 @code{.ident} assembler directive in the output.
15102 Refrain from adding @code{.ident} directives to the output file (this is
15105 @item -YP,@var{dirs}
15107 Search the directories @var{dirs}, and no others, for libraries
15108 specified with @option{-l}.
15110 @item -Ym,@var{dir}
15112 Look in the directory @var{dir} to find the M4 preprocessor.
15113 The assembler uses this option.
15114 @c This is supposed to go with a -Yd for predefined M4 macro files, but
15115 @c the generic assembler that comes with Solaris takes just -Ym.
15119 @subsection V850 Options
15120 @cindex V850 Options
15122 These @samp{-m} options are defined for V850 implementations:
15126 @itemx -mno-long-calls
15127 @opindex mlong-calls
15128 @opindex mno-long-calls
15129 Treat all calls as being far away (near). If calls are assumed to be
15130 far away, the compiler will always load the functions address up into a
15131 register, and call indirect through the pointer.
15137 Do not optimize (do optimize) basic blocks that use the same index
15138 pointer 4 or more times to copy pointer into the @code{ep} register, and
15139 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
15140 option is on by default if you optimize.
15142 @item -mno-prolog-function
15143 @itemx -mprolog-function
15144 @opindex mno-prolog-function
15145 @opindex mprolog-function
15146 Do not use (do use) external functions to save and restore registers
15147 at the prologue and epilogue of a function. The external functions
15148 are slower, but use less code space if more than one function saves
15149 the same number of registers. The @option{-mprolog-function} option
15150 is on by default if you optimize.
15154 Try to make the code as small as possible. At present, this just turns
15155 on the @option{-mep} and @option{-mprolog-function} options.
15157 @item -mtda=@var{n}
15159 Put static or global variables whose size is @var{n} bytes or less into
15160 the tiny data area that register @code{ep} points to. The tiny data
15161 area can hold up to 256 bytes in total (128 bytes for byte references).
15163 @item -msda=@var{n}
15165 Put static or global variables whose size is @var{n} bytes or less into
15166 the small data area that register @code{gp} points to. The small data
15167 area can hold up to 64 kilobytes.
15169 @item -mzda=@var{n}
15171 Put static or global variables whose size is @var{n} bytes or less into
15172 the first 32 kilobytes of memory.
15176 Specify that the target processor is the V850.
15179 @opindex mbig-switch
15180 Generate code suitable for big switch tables. Use this option only if
15181 the assembler/linker complain about out of range branches within a switch
15186 This option will cause r2 and r5 to be used in the code generated by
15187 the compiler. This setting is the default.
15189 @item -mno-app-regs
15190 @opindex mno-app-regs
15191 This option will cause r2 and r5 to be treated as fixed registers.
15195 Specify that the target processor is the V850E1. The preprocessor
15196 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
15197 this option is used.
15201 Specify that the target processor is the V850E@. The preprocessor
15202 constant @samp{__v850e__} will be defined if this option is used.
15204 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
15205 are defined then a default target processor will be chosen and the
15206 relevant @samp{__v850*__} preprocessor constant will be defined.
15208 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
15209 defined, regardless of which processor variant is the target.
15211 @item -mdisable-callt
15212 @opindex mdisable-callt
15213 This option will suppress generation of the CALLT instruction for the
15214 v850e and v850e1 flavors of the v850 architecture. The default is
15215 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
15220 @subsection VAX Options
15221 @cindex VAX options
15223 These @samp{-m} options are defined for the VAX:
15228 Do not output certain jump instructions (@code{aobleq} and so on)
15229 that the Unix assembler for the VAX cannot handle across long
15234 Do output those jump instructions, on the assumption that you
15235 will assemble with the GNU assembler.
15239 Output code for g-format floating point numbers instead of d-format.
15242 @node VxWorks Options
15243 @subsection VxWorks Options
15244 @cindex VxWorks Options
15246 The options in this section are defined for all VxWorks targets.
15247 Options specific to the target hardware are listed with the other
15248 options for that target.
15253 GCC can generate code for both VxWorks kernels and real time processes
15254 (RTPs). This option switches from the former to the latter. It also
15255 defines the preprocessor macro @code{__RTP__}.
15258 @opindex non-static
15259 Link an RTP executable against shared libraries rather than static
15260 libraries. The options @option{-static} and @option{-shared} can
15261 also be used for RTPs (@pxref{Link Options}); @option{-static}
15268 These options are passed down to the linker. They are defined for
15269 compatibility with Diab.
15272 @opindex Xbind-lazy
15273 Enable lazy binding of function calls. This option is equivalent to
15274 @option{-Wl,-z,now} and is defined for compatibility with Diab.
15278 Disable lazy binding of function calls. This option is the default and
15279 is defined for compatibility with Diab.
15282 @node x86-64 Options
15283 @subsection x86-64 Options
15284 @cindex x86-64 options
15286 These are listed under @xref{i386 and x86-64 Options}.
15288 @node Xstormy16 Options
15289 @subsection Xstormy16 Options
15290 @cindex Xstormy16 Options
15292 These options are defined for Xstormy16:
15297 Choose startup files and linker script suitable for the simulator.
15300 @node Xtensa Options
15301 @subsection Xtensa Options
15302 @cindex Xtensa Options
15304 These options are supported for Xtensa targets:
15308 @itemx -mno-const16
15310 @opindex mno-const16
15311 Enable or disable use of @code{CONST16} instructions for loading
15312 constant values. The @code{CONST16} instruction is currently not a
15313 standard option from Tensilica. When enabled, @code{CONST16}
15314 instructions are always used in place of the standard @code{L32R}
15315 instructions. The use of @code{CONST16} is enabled by default only if
15316 the @code{L32R} instruction is not available.
15319 @itemx -mno-fused-madd
15320 @opindex mfused-madd
15321 @opindex mno-fused-madd
15322 Enable or disable use of fused multiply/add and multiply/subtract
15323 instructions in the floating-point option. This has no effect if the
15324 floating-point option is not also enabled. Disabling fused multiply/add
15325 and multiply/subtract instructions forces the compiler to use separate
15326 instructions for the multiply and add/subtract operations. This may be
15327 desirable in some cases where strict IEEE 754-compliant results are
15328 required: the fused multiply add/subtract instructions do not round the
15329 intermediate result, thereby producing results with @emph{more} bits of
15330 precision than specified by the IEEE standard. Disabling fused multiply
15331 add/subtract instructions also ensures that the program output is not
15332 sensitive to the compiler's ability to combine multiply and add/subtract
15335 @item -mserialize-volatile
15336 @itemx -mno-serialize-volatile
15337 @opindex mserialize-volatile
15338 @opindex mno-serialize-volatile
15339 When this option is enabled, GCC inserts @code{MEMW} instructions before
15340 @code{volatile} memory references to guarantee sequential consistency.
15341 The default is @option{-mserialize-volatile}. Use
15342 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
15344 @item -mtext-section-literals
15345 @itemx -mno-text-section-literals
15346 @opindex mtext-section-literals
15347 @opindex mno-text-section-literals
15348 Control the treatment of literal pools. The default is
15349 @option{-mno-text-section-literals}, which places literals in a separate
15350 section in the output file. This allows the literal pool to be placed
15351 in a data RAM/ROM, and it also allows the linker to combine literal
15352 pools from separate object files to remove redundant literals and
15353 improve code size. With @option{-mtext-section-literals}, the literals
15354 are interspersed in the text section in order to keep them as close as
15355 possible to their references. This may be necessary for large assembly
15358 @item -mtarget-align
15359 @itemx -mno-target-align
15360 @opindex mtarget-align
15361 @opindex mno-target-align
15362 When this option is enabled, GCC instructs the assembler to
15363 automatically align instructions to reduce branch penalties at the
15364 expense of some code density. The assembler attempts to widen density
15365 instructions to align branch targets and the instructions following call
15366 instructions. If there are not enough preceding safe density
15367 instructions to align a target, no widening will be performed. The
15368 default is @option{-mtarget-align}. These options do not affect the
15369 treatment of auto-aligned instructions like @code{LOOP}, which the
15370 assembler will always align, either by widening density instructions or
15371 by inserting no-op instructions.
15374 @itemx -mno-longcalls
15375 @opindex mlongcalls
15376 @opindex mno-longcalls
15377 When this option is enabled, GCC instructs the assembler to translate
15378 direct calls to indirect calls unless it can determine that the target
15379 of a direct call is in the range allowed by the call instruction. This
15380 translation typically occurs for calls to functions in other source
15381 files. Specifically, the assembler translates a direct @code{CALL}
15382 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
15383 The default is @option{-mno-longcalls}. This option should be used in
15384 programs where the call target can potentially be out of range. This
15385 option is implemented in the assembler, not the compiler, so the
15386 assembly code generated by GCC will still show direct call
15387 instructions---look at the disassembled object code to see the actual
15388 instructions. Note that the assembler will use an indirect call for
15389 every cross-file call, not just those that really will be out of range.
15392 @node zSeries Options
15393 @subsection zSeries Options
15394 @cindex zSeries options
15396 These are listed under @xref{S/390 and zSeries Options}.
15398 @node Code Gen Options
15399 @section Options for Code Generation Conventions
15400 @cindex code generation conventions
15401 @cindex options, code generation
15402 @cindex run-time options
15404 These machine-independent options control the interface conventions
15405 used in code generation.
15407 Most of them have both positive and negative forms; the negative form
15408 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
15409 one of the forms is listed---the one which is not the default. You
15410 can figure out the other form by either removing @samp{no-} or adding
15414 @item -fbounds-check
15415 @opindex fbounds-check
15416 For front-ends that support it, generate additional code to check that
15417 indices used to access arrays are within the declared range. This is
15418 currently only supported by the Java and Fortran front-ends, where
15419 this option defaults to true and false respectively.
15423 This option generates traps for signed overflow on addition, subtraction,
15424 multiplication operations.
15428 This option instructs the compiler to assume that signed arithmetic
15429 overflow of addition, subtraction and multiplication wraps around
15430 using twos-complement representation. This flag enables some optimizations
15431 and disables others. This option is enabled by default for the Java
15432 front-end, as required by the Java language specification.
15435 @opindex fexceptions
15436 Enable exception handling. Generates extra code needed to propagate
15437 exceptions. For some targets, this implies GCC will generate frame
15438 unwind information for all functions, which can produce significant data
15439 size overhead, although it does not affect execution. If you do not
15440 specify this option, GCC will enable it by default for languages like
15441 C++ which normally require exception handling, and disable it for
15442 languages like C that do not normally require it. However, you may need
15443 to enable this option when compiling C code that needs to interoperate
15444 properly with exception handlers written in C++. You may also wish to
15445 disable this option if you are compiling older C++ programs that don't
15446 use exception handling.
15448 @item -fnon-call-exceptions
15449 @opindex fnon-call-exceptions
15450 Generate code that allows trapping instructions to throw exceptions.
15451 Note that this requires platform-specific runtime support that does
15452 not exist everywhere. Moreover, it only allows @emph{trapping}
15453 instructions to throw exceptions, i.e.@: memory references or floating
15454 point instructions. It does not allow exceptions to be thrown from
15455 arbitrary signal handlers such as @code{SIGALRM}.
15457 @item -funwind-tables
15458 @opindex funwind-tables
15459 Similar to @option{-fexceptions}, except that it will just generate any needed
15460 static data, but will not affect the generated code in any other way.
15461 You will normally not enable this option; instead, a language processor
15462 that needs this handling would enable it on your behalf.
15464 @item -fasynchronous-unwind-tables
15465 @opindex fasynchronous-unwind-tables
15466 Generate unwind table in dwarf2 format, if supported by target machine. The
15467 table is exact at each instruction boundary, so it can be used for stack
15468 unwinding from asynchronous events (such as debugger or garbage collector).
15470 @item -fpcc-struct-return
15471 @opindex fpcc-struct-return
15472 Return ``short'' @code{struct} and @code{union} values in memory like
15473 longer ones, rather than in registers. This convention is less
15474 efficient, but it has the advantage of allowing intercallability between
15475 GCC-compiled files and files compiled with other compilers, particularly
15476 the Portable C Compiler (pcc).
15478 The precise convention for returning structures in memory depends
15479 on the target configuration macros.
15481 Short structures and unions are those whose size and alignment match
15482 that of some integer type.
15484 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
15485 switch is not binary compatible with code compiled with the
15486 @option{-freg-struct-return} switch.
15487 Use it to conform to a non-default application binary interface.
15489 @item -freg-struct-return
15490 @opindex freg-struct-return
15491 Return @code{struct} and @code{union} values in registers when possible.
15492 This is more efficient for small structures than
15493 @option{-fpcc-struct-return}.
15495 If you specify neither @option{-fpcc-struct-return} nor
15496 @option{-freg-struct-return}, GCC defaults to whichever convention is
15497 standard for the target. If there is no standard convention, GCC
15498 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
15499 the principal compiler. In those cases, we can choose the standard, and
15500 we chose the more efficient register return alternative.
15502 @strong{Warning:} code compiled with the @option{-freg-struct-return}
15503 switch is not binary compatible with code compiled with the
15504 @option{-fpcc-struct-return} switch.
15505 Use it to conform to a non-default application binary interface.
15507 @item -fshort-enums
15508 @opindex fshort-enums
15509 Allocate to an @code{enum} type only as many bytes as it needs for the
15510 declared range of possible values. Specifically, the @code{enum} type
15511 will be equivalent to the smallest integer type which has enough room.
15513 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
15514 code that is not binary compatible with code generated without that switch.
15515 Use it to conform to a non-default application binary interface.
15517 @item -fshort-double
15518 @opindex fshort-double
15519 Use the same size for @code{double} as for @code{float}.
15521 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
15522 code that is not binary compatible with code generated without that switch.
15523 Use it to conform to a non-default application binary interface.
15525 @item -fshort-wchar
15526 @opindex fshort-wchar
15527 Override the underlying type for @samp{wchar_t} to be @samp{short
15528 unsigned int} instead of the default for the target. This option is
15529 useful for building programs to run under WINE@.
15531 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
15532 code that is not binary compatible with code generated without that switch.
15533 Use it to conform to a non-default application binary interface.
15536 @opindex fno-common
15537 In C, allocate even uninitialized global variables in the data section of the
15538 object file, rather than generating them as common blocks. This has the
15539 effect that if the same variable is declared (without @code{extern}) in
15540 two different compilations, you will get an error when you link them.
15541 The only reason this might be useful is if you wish to verify that the
15542 program will work on other systems which always work this way.
15546 Ignore the @samp{#ident} directive.
15548 @item -finhibit-size-directive
15549 @opindex finhibit-size-directive
15550 Don't output a @code{.size} assembler directive, or anything else that
15551 would cause trouble if the function is split in the middle, and the
15552 two halves are placed at locations far apart in memory. This option is
15553 used when compiling @file{crtstuff.c}; you should not need to use it
15556 @item -fverbose-asm
15557 @opindex fverbose-asm
15558 Put extra commentary information in the generated assembly code to
15559 make it more readable. This option is generally only of use to those
15560 who actually need to read the generated assembly code (perhaps while
15561 debugging the compiler itself).
15563 @option{-fno-verbose-asm}, the default, causes the
15564 extra information to be omitted and is useful when comparing two assembler
15567 @item -frecord-gcc-switches
15568 @opindex frecord-gcc-switches
15569 This switch causes the command line that was used to invoke the
15570 compiler to be recorded into the object file that is being created.
15571 This switch is only implemented on some targets and the exact format
15572 of the recording is target and binary file format dependent, but it
15573 usually takes the form of a section containing ASCII text. This
15574 switch is related to the @option{-fverbose-asm} switch, but that
15575 switch only records information in the assembler output file as
15576 comments, so it never reaches the object file.
15580 @cindex global offset table
15582 Generate position-independent code (PIC) suitable for use in a shared
15583 library, if supported for the target machine. Such code accesses all
15584 constant addresses through a global offset table (GOT)@. The dynamic
15585 loader resolves the GOT entries when the program starts (the dynamic
15586 loader is not part of GCC; it is part of the operating system). If
15587 the GOT size for the linked executable exceeds a machine-specific
15588 maximum size, you get an error message from the linker indicating that
15589 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15590 instead. (These maximums are 8k on the SPARC and 32k
15591 on the m68k and RS/6000. The 386 has no such limit.)
15593 Position-independent code requires special support, and therefore works
15594 only on certain machines. For the 386, GCC supports PIC for System V
15595 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15596 position-independent.
15598 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15603 If supported for the target machine, emit position-independent code,
15604 suitable for dynamic linking and avoiding any limit on the size of the
15605 global offset table. This option makes a difference on the m68k,
15606 PowerPC and SPARC@.
15608 Position-independent code requires special support, and therefore works
15609 only on certain machines.
15611 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15618 These options are similar to @option{-fpic} and @option{-fPIC}, but
15619 generated position independent code can be only linked into executables.
15620 Usually these options are used when @option{-pie} GCC option will be
15621 used during linking.
15623 @option{-fpie} and @option{-fPIE} both define the macros
15624 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15625 for @option{-fpie} and 2 for @option{-fPIE}.
15627 @item -fno-jump-tables
15628 @opindex fno-jump-tables
15629 Do not use jump tables for switch statements even where it would be
15630 more efficient than other code generation strategies. This option is
15631 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15632 building code which forms part of a dynamic linker and cannot
15633 reference the address of a jump table. On some targets, jump tables
15634 do not require a GOT and this option is not needed.
15636 @item -ffixed-@var{reg}
15638 Treat the register named @var{reg} as a fixed register; generated code
15639 should never refer to it (except perhaps as a stack pointer, frame
15640 pointer or in some other fixed role).
15642 @var{reg} must be the name of a register. The register names accepted
15643 are machine-specific and are defined in the @code{REGISTER_NAMES}
15644 macro in the machine description macro file.
15646 This flag does not have a negative form, because it specifies a
15649 @item -fcall-used-@var{reg}
15650 @opindex fcall-used
15651 Treat the register named @var{reg} as an allocable register that is
15652 clobbered by function calls. It may be allocated for temporaries or
15653 variables that do not live across a call. Functions compiled this way
15654 will not save and restore the register @var{reg}.
15656 It is an error to used this flag with the frame pointer or stack pointer.
15657 Use of this flag for other registers that have fixed pervasive roles in
15658 the machine's execution model will produce disastrous results.
15660 This flag does not have a negative form, because it specifies a
15663 @item -fcall-saved-@var{reg}
15664 @opindex fcall-saved
15665 Treat the register named @var{reg} as an allocable register saved by
15666 functions. It may be allocated even for temporaries or variables that
15667 live across a call. Functions compiled this way will save and restore
15668 the register @var{reg} if they use it.
15670 It is an error to used this flag with the frame pointer or stack pointer.
15671 Use of this flag for other registers that have fixed pervasive roles in
15672 the machine's execution model will produce disastrous results.
15674 A different sort of disaster will result from the use of this flag for
15675 a register in which function values may be returned.
15677 This flag does not have a negative form, because it specifies a
15680 @item -fpack-struct[=@var{n}]
15681 @opindex fpack-struct
15682 Without a value specified, pack all structure members together without
15683 holes. When a value is specified (which must be a small power of two), pack
15684 structure members according to this value, representing the maximum
15685 alignment (that is, objects with default alignment requirements larger than
15686 this will be output potentially unaligned at the next fitting location.
15688 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15689 code that is not binary compatible with code generated without that switch.
15690 Additionally, it makes the code suboptimal.
15691 Use it to conform to a non-default application binary interface.
15693 @item -finstrument-functions
15694 @opindex finstrument-functions
15695 Generate instrumentation calls for entry and exit to functions. Just
15696 after function entry and just before function exit, the following
15697 profiling functions will be called with the address of the current
15698 function and its call site. (On some platforms,
15699 @code{__builtin_return_address} does not work beyond the current
15700 function, so the call site information may not be available to the
15701 profiling functions otherwise.)
15704 void __cyg_profile_func_enter (void *this_fn,
15706 void __cyg_profile_func_exit (void *this_fn,
15710 The first argument is the address of the start of the current function,
15711 which may be looked up exactly in the symbol table.
15713 This instrumentation is also done for functions expanded inline in other
15714 functions. The profiling calls will indicate where, conceptually, the
15715 inline function is entered and exited. This means that addressable
15716 versions of such functions must be available. If all your uses of a
15717 function are expanded inline, this may mean an additional expansion of
15718 code size. If you use @samp{extern inline} in your C code, an
15719 addressable version of such functions must be provided. (This is
15720 normally the case anyways, but if you get lucky and the optimizer always
15721 expands the functions inline, you might have gotten away without
15722 providing static copies.)
15724 A function may be given the attribute @code{no_instrument_function}, in
15725 which case this instrumentation will not be done. This can be used, for
15726 example, for the profiling functions listed above, high-priority
15727 interrupt routines, and any functions from which the profiling functions
15728 cannot safely be called (perhaps signal handlers, if the profiling
15729 routines generate output or allocate memory).
15731 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
15732 @opindex finstrument-functions-exclude-file-list
15734 Set the list of functions that are excluded from instrumentation (see
15735 the description of @code{-finstrument-functions}). If the file that
15736 contains a function definition matches with one of @var{file}, then
15737 that function is not instrumented. The match is done on substrings:
15738 if the @var{file} parameter is a substring of the file name, it is
15739 considered to be a match.
15742 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
15743 will exclude any inline function defined in files whose pathnames
15744 contain @code{/bits/stl} or @code{include/sys}.
15746 If, for some reason, you want to include letter @code{','} in one of
15747 @var{sym}, write @code{'\,'}. For example,
15748 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
15749 (note the single quote surrounding the option).
15751 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
15752 @opindex finstrument-functions-exclude-function-list
15754 This is similar to @code{-finstrument-functions-exclude-file-list},
15755 but this option sets the list of function names to be excluded from
15756 instrumentation. The function name to be matched is its user-visible
15757 name, such as @code{vector<int> blah(const vector<int> &)}, not the
15758 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
15759 match is done on substrings: if the @var{sym} parameter is a substring
15760 of the function name, it is considered to be a match.
15762 @item -fstack-check
15763 @opindex fstack-check
15764 Generate code to verify that you do not go beyond the boundary of the
15765 stack. You should specify this flag if you are running in an
15766 environment with multiple threads, but only rarely need to specify it in
15767 a single-threaded environment since stack overflow is automatically
15768 detected on nearly all systems if there is only one stack.
15770 Note that this switch does not actually cause checking to be done; the
15771 operating system or the language runtime must do that. The switch causes
15772 generation of code to ensure that they see the stack being extended.
15774 You can additionally specify a string parameter: @code{no} means no
15775 checking, @code{generic} means force the use of old-style checking,
15776 @code{specific} means use the best checking method and is equivalent
15777 to bare @option{-fstack-check}.
15779 Old-style checking is a generic mechanism that requires no specific
15780 target support in the compiler but comes with the following drawbacks:
15784 Modified allocation strategy for large objects: they will always be
15785 allocated dynamically if their size exceeds a fixed threshold.
15788 Fixed limit on the size of the static frame of functions: when it is
15789 topped by a particular function, stack checking is not reliable and
15790 a warning is issued by the compiler.
15793 Inefficiency: because of both the modified allocation strategy and the
15794 generic implementation, the performances of the code are hampered.
15797 Note that old-style stack checking is also the fallback method for
15798 @code{specific} if no target support has been added in the compiler.
15800 @item -fstack-limit-register=@var{reg}
15801 @itemx -fstack-limit-symbol=@var{sym}
15802 @itemx -fno-stack-limit
15803 @opindex fstack-limit-register
15804 @opindex fstack-limit-symbol
15805 @opindex fno-stack-limit
15806 Generate code to ensure that the stack does not grow beyond a certain value,
15807 either the value of a register or the address of a symbol. If the stack
15808 would grow beyond the value, a signal is raised. For most targets,
15809 the signal is raised before the stack overruns the boundary, so
15810 it is possible to catch the signal without taking special precautions.
15812 For instance, if the stack starts at absolute address @samp{0x80000000}
15813 and grows downwards, you can use the flags
15814 @option{-fstack-limit-symbol=__stack_limit} and
15815 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
15816 of 128KB@. Note that this may only work with the GNU linker.
15818 @cindex aliasing of parameters
15819 @cindex parameters, aliased
15820 @item -fargument-alias
15821 @itemx -fargument-noalias
15822 @itemx -fargument-noalias-global
15823 @itemx -fargument-noalias-anything
15824 @opindex fargument-alias
15825 @opindex fargument-noalias
15826 @opindex fargument-noalias-global
15827 @opindex fargument-noalias-anything
15828 Specify the possible relationships among parameters and between
15829 parameters and global data.
15831 @option{-fargument-alias} specifies that arguments (parameters) may
15832 alias each other and may alias global storage.@*
15833 @option{-fargument-noalias} specifies that arguments do not alias
15834 each other, but may alias global storage.@*
15835 @option{-fargument-noalias-global} specifies that arguments do not
15836 alias each other and do not alias global storage.
15837 @option{-fargument-noalias-anything} specifies that arguments do not
15838 alias any other storage.
15840 Each language will automatically use whatever option is required by
15841 the language standard. You should not need to use these options yourself.
15843 @item -fleading-underscore
15844 @opindex fleading-underscore
15845 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
15846 change the way C symbols are represented in the object file. One use
15847 is to help link with legacy assembly code.
15849 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
15850 generate code that is not binary compatible with code generated without that
15851 switch. Use it to conform to a non-default application binary interface.
15852 Not all targets provide complete support for this switch.
15854 @item -ftls-model=@var{model}
15855 @opindex ftls-model
15856 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
15857 The @var{model} argument should be one of @code{global-dynamic},
15858 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
15860 The default without @option{-fpic} is @code{initial-exec}; with
15861 @option{-fpic} the default is @code{global-dynamic}.
15863 @item -fvisibility=@var{default|internal|hidden|protected}
15864 @opindex fvisibility
15865 Set the default ELF image symbol visibility to the specified option---all
15866 symbols will be marked with this unless overridden within the code.
15867 Using this feature can very substantially improve linking and
15868 load times of shared object libraries, produce more optimized
15869 code, provide near-perfect API export and prevent symbol clashes.
15870 It is @strong{strongly} recommended that you use this in any shared objects
15873 Despite the nomenclature, @code{default} always means public ie;
15874 available to be linked against from outside the shared object.
15875 @code{protected} and @code{internal} are pretty useless in real-world
15876 usage so the only other commonly used option will be @code{hidden}.
15877 The default if @option{-fvisibility} isn't specified is
15878 @code{default}, i.e., make every
15879 symbol public---this causes the same behavior as previous versions of
15882 A good explanation of the benefits offered by ensuring ELF
15883 symbols have the correct visibility is given by ``How To Write
15884 Shared Libraries'' by Ulrich Drepper (which can be found at
15885 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
15886 solution made possible by this option to marking things hidden when
15887 the default is public is to make the default hidden and mark things
15888 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
15889 and @code{__attribute__ ((visibility("default")))} instead of
15890 @code{__declspec(dllexport)} you get almost identical semantics with
15891 identical syntax. This is a great boon to those working with
15892 cross-platform projects.
15894 For those adding visibility support to existing code, you may find
15895 @samp{#pragma GCC visibility} of use. This works by you enclosing
15896 the declarations you wish to set visibility for with (for example)
15897 @samp{#pragma GCC visibility push(hidden)} and
15898 @samp{#pragma GCC visibility pop}.
15899 Bear in mind that symbol visibility should be viewed @strong{as
15900 part of the API interface contract} and thus all new code should
15901 always specify visibility when it is not the default ie; declarations
15902 only for use within the local DSO should @strong{always} be marked explicitly
15903 as hidden as so to avoid PLT indirection overheads---making this
15904 abundantly clear also aids readability and self-documentation of the code.
15905 Note that due to ISO C++ specification requirements, operator new and
15906 operator delete must always be of default visibility.
15908 Be aware that headers from outside your project, in particular system
15909 headers and headers from any other library you use, may not be
15910 expecting to be compiled with visibility other than the default. You
15911 may need to explicitly say @samp{#pragma GCC visibility push(default)}
15912 before including any such headers.
15914 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
15915 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
15916 no modifications. However, this means that calls to @samp{extern}
15917 functions with no explicit visibility will use the PLT, so it is more
15918 effective to use @samp{__attribute ((visibility))} and/or
15919 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
15920 declarations should be treated as hidden.
15922 Note that @samp{-fvisibility} does affect C++ vague linkage
15923 entities. This means that, for instance, an exception class that will
15924 be thrown between DSOs must be explicitly marked with default
15925 visibility so that the @samp{type_info} nodes will be unified between
15928 An overview of these techniques, their benefits and how to use them
15929 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
15935 @node Environment Variables
15936 @section Environment Variables Affecting GCC
15937 @cindex environment variables
15939 @c man begin ENVIRONMENT
15940 This section describes several environment variables that affect how GCC
15941 operates. Some of them work by specifying directories or prefixes to use
15942 when searching for various kinds of files. Some are used to specify other
15943 aspects of the compilation environment.
15945 Note that you can also specify places to search using options such as
15946 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
15947 take precedence over places specified using environment variables, which
15948 in turn take precedence over those specified by the configuration of GCC@.
15949 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
15950 GNU Compiler Collection (GCC) Internals}.
15955 @c @itemx LC_COLLATE
15957 @c @itemx LC_MONETARY
15958 @c @itemx LC_NUMERIC
15963 @c @findex LC_COLLATE
15964 @findex LC_MESSAGES
15965 @c @findex LC_MONETARY
15966 @c @findex LC_NUMERIC
15970 These environment variables control the way that GCC uses
15971 localization information that allow GCC to work with different
15972 national conventions. GCC inspects the locale categories
15973 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
15974 so. These locale categories can be set to any value supported by your
15975 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
15976 Kingdom encoded in UTF-8.
15978 The @env{LC_CTYPE} environment variable specifies character
15979 classification. GCC uses it to determine the character boundaries in
15980 a string; this is needed for some multibyte encodings that contain quote
15981 and escape characters that would otherwise be interpreted as a string
15984 The @env{LC_MESSAGES} environment variable specifies the language to
15985 use in diagnostic messages.
15987 If the @env{LC_ALL} environment variable is set, it overrides the value
15988 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
15989 and @env{LC_MESSAGES} default to the value of the @env{LANG}
15990 environment variable. If none of these variables are set, GCC
15991 defaults to traditional C English behavior.
15995 If @env{TMPDIR} is set, it specifies the directory to use for temporary
15996 files. GCC uses temporary files to hold the output of one stage of
15997 compilation which is to be used as input to the next stage: for example,
15998 the output of the preprocessor, which is the input to the compiler
16001 @item GCC_EXEC_PREFIX
16002 @findex GCC_EXEC_PREFIX
16003 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
16004 names of the subprograms executed by the compiler. No slash is added
16005 when this prefix is combined with the name of a subprogram, but you can
16006 specify a prefix that ends with a slash if you wish.
16008 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
16009 an appropriate prefix to use based on the pathname it was invoked with.
16011 If GCC cannot find the subprogram using the specified prefix, it
16012 tries looking in the usual places for the subprogram.
16014 The default value of @env{GCC_EXEC_PREFIX} is
16015 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
16016 the installed compiler. In many cases @var{prefix} is the value
16017 of @code{prefix} when you ran the @file{configure} script.
16019 Other prefixes specified with @option{-B} take precedence over this prefix.
16021 This prefix is also used for finding files such as @file{crt0.o} that are
16024 In addition, the prefix is used in an unusual way in finding the
16025 directories to search for header files. For each of the standard
16026 directories whose name normally begins with @samp{/usr/local/lib/gcc}
16027 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
16028 replacing that beginning with the specified prefix to produce an
16029 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
16030 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
16031 These alternate directories are searched first; the standard directories
16032 come next. If a standard directory begins with the configured
16033 @var{prefix} then the value of @var{prefix} is replaced by
16034 @env{GCC_EXEC_PREFIX} when looking for header files.
16036 @item COMPILER_PATH
16037 @findex COMPILER_PATH
16038 The value of @env{COMPILER_PATH} is a colon-separated list of
16039 directories, much like @env{PATH}. GCC tries the directories thus
16040 specified when searching for subprograms, if it can't find the
16041 subprograms using @env{GCC_EXEC_PREFIX}.
16044 @findex LIBRARY_PATH
16045 The value of @env{LIBRARY_PATH} is a colon-separated list of
16046 directories, much like @env{PATH}. When configured as a native compiler,
16047 GCC tries the directories thus specified when searching for special
16048 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
16049 using GCC also uses these directories when searching for ordinary
16050 libraries for the @option{-l} option (but directories specified with
16051 @option{-L} come first).
16055 @cindex locale definition
16056 This variable is used to pass locale information to the compiler. One way in
16057 which this information is used is to determine the character set to be used
16058 when character literals, string literals and comments are parsed in C and C++.
16059 When the compiler is configured to allow multibyte characters,
16060 the following values for @env{LANG} are recognized:
16064 Recognize JIS characters.
16066 Recognize SJIS characters.
16068 Recognize EUCJP characters.
16071 If @env{LANG} is not defined, or if it has some other value, then the
16072 compiler will use mblen and mbtowc as defined by the default locale to
16073 recognize and translate multibyte characters.
16077 Some additional environments variables affect the behavior of the
16080 @include cppenv.texi
16084 @node Precompiled Headers
16085 @section Using Precompiled Headers
16086 @cindex precompiled headers
16087 @cindex speed of compilation
16089 Often large projects have many header files that are included in every
16090 source file. The time the compiler takes to process these header files
16091 over and over again can account for nearly all of the time required to
16092 build the project. To make builds faster, GCC allows users to
16093 `precompile' a header file; then, if builds can use the precompiled
16094 header file they will be much faster.
16096 To create a precompiled header file, simply compile it as you would any
16097 other file, if necessary using the @option{-x} option to make the driver
16098 treat it as a C or C++ header file. You will probably want to use a
16099 tool like @command{make} to keep the precompiled header up-to-date when
16100 the headers it contains change.
16102 A precompiled header file will be searched for when @code{#include} is
16103 seen in the compilation. As it searches for the included file
16104 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
16105 compiler looks for a precompiled header in each directory just before it
16106 looks for the include file in that directory. The name searched for is
16107 the name specified in the @code{#include} with @samp{.gch} appended. If
16108 the precompiled header file can't be used, it is ignored.
16110 For instance, if you have @code{#include "all.h"}, and you have
16111 @file{all.h.gch} in the same directory as @file{all.h}, then the
16112 precompiled header file will be used if possible, and the original
16113 header will be used otherwise.
16115 Alternatively, you might decide to put the precompiled header file in a
16116 directory and use @option{-I} to ensure that directory is searched
16117 before (or instead of) the directory containing the original header.
16118 Then, if you want to check that the precompiled header file is always
16119 used, you can put a file of the same name as the original header in this
16120 directory containing an @code{#error} command.
16122 This also works with @option{-include}. So yet another way to use
16123 precompiled headers, good for projects not designed with precompiled
16124 header files in mind, is to simply take most of the header files used by
16125 a project, include them from another header file, precompile that header
16126 file, and @option{-include} the precompiled header. If the header files
16127 have guards against multiple inclusion, they will be skipped because
16128 they've already been included (in the precompiled header).
16130 If you need to precompile the same header file for different
16131 languages, targets, or compiler options, you can instead make a
16132 @emph{directory} named like @file{all.h.gch}, and put each precompiled
16133 header in the directory, perhaps using @option{-o}. It doesn't matter
16134 what you call the files in the directory, every precompiled header in
16135 the directory will be considered. The first precompiled header
16136 encountered in the directory that is valid for this compilation will
16137 be used; they're searched in no particular order.
16139 There are many other possibilities, limited only by your imagination,
16140 good sense, and the constraints of your build system.
16142 A precompiled header file can be used only when these conditions apply:
16146 Only one precompiled header can be used in a particular compilation.
16149 A precompiled header can't be used once the first C token is seen. You
16150 can have preprocessor directives before a precompiled header; you can
16151 even include a precompiled header from inside another header, so long as
16152 there are no C tokens before the @code{#include}.
16155 The precompiled header file must be produced for the same language as
16156 the current compilation. You can't use a C precompiled header for a C++
16160 The precompiled header file must have been produced by the same compiler
16161 binary as the current compilation is using.
16164 Any macros defined before the precompiled header is included must
16165 either be defined in the same way as when the precompiled header was
16166 generated, or must not affect the precompiled header, which usually
16167 means that they don't appear in the precompiled header at all.
16169 The @option{-D} option is one way to define a macro before a
16170 precompiled header is included; using a @code{#define} can also do it.
16171 There are also some options that define macros implicitly, like
16172 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
16175 @item If debugging information is output when using the precompiled
16176 header, using @option{-g} or similar, the same kind of debugging information
16177 must have been output when building the precompiled header. However,
16178 a precompiled header built using @option{-g} can be used in a compilation
16179 when no debugging information is being output.
16181 @item The same @option{-m} options must generally be used when building
16182 and using the precompiled header. @xref{Submodel Options},
16183 for any cases where this rule is relaxed.
16185 @item Each of the following options must be the same when building and using
16186 the precompiled header:
16188 @gccoptlist{-fexceptions}
16191 Some other command-line options starting with @option{-f},
16192 @option{-p}, or @option{-O} must be defined in the same way as when
16193 the precompiled header was generated. At present, it's not clear
16194 which options are safe to change and which are not; the safest choice
16195 is to use exactly the same options when generating and using the
16196 precompiled header. The following are known to be safe:
16198 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
16199 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
16200 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
16205 For all of these except the last, the compiler will automatically
16206 ignore the precompiled header if the conditions aren't met. If you
16207 find an option combination that doesn't work and doesn't cause the
16208 precompiled header to be ignored, please consider filing a bug report,
16211 If you do use differing options when generating and using the
16212 precompiled header, the actual behavior will be a mixture of the
16213 behavior for the options. For instance, if you use @option{-g} to
16214 generate the precompiled header but not when using it, you may or may
16215 not get debugging information for routines in the precompiled header.
16217 @node Running Protoize
16218 @section Running Protoize
16220 The program @code{protoize} is an optional part of GCC@. You can use
16221 it to add prototypes to a program, thus converting the program to ISO
16222 C in one respect. The companion program @code{unprotoize} does the
16223 reverse: it removes argument types from any prototypes that are found.
16225 When you run these programs, you must specify a set of source files as
16226 command line arguments. The conversion programs start out by compiling
16227 these files to see what functions they define. The information gathered
16228 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
16230 After scanning comes actual conversion. The specified files are all
16231 eligible to be converted; any files they include (whether sources or
16232 just headers) are eligible as well.
16234 But not all the eligible files are converted. By default,
16235 @code{protoize} and @code{unprotoize} convert only source and header
16236 files in the current directory. You can specify additional directories
16237 whose files should be converted with the @option{-d @var{directory}}
16238 option. You can also specify particular files to exclude with the
16239 @option{-x @var{file}} option. A file is converted if it is eligible, its
16240 directory name matches one of the specified directory names, and its
16241 name within the directory has not been excluded.
16243 Basic conversion with @code{protoize} consists of rewriting most
16244 function definitions and function declarations to specify the types of
16245 the arguments. The only ones not rewritten are those for varargs
16248 @code{protoize} optionally inserts prototype declarations at the
16249 beginning of the source file, to make them available for any calls that
16250 precede the function's definition. Or it can insert prototype
16251 declarations with block scope in the blocks where undeclared functions
16254 Basic conversion with @code{unprotoize} consists of rewriting most
16255 function declarations to remove any argument types, and rewriting
16256 function definitions to the old-style pre-ISO form.
16258 Both conversion programs print a warning for any function declaration or
16259 definition that they can't convert. You can suppress these warnings
16262 The output from @code{protoize} or @code{unprotoize} replaces the
16263 original source file. The original file is renamed to a name ending
16264 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
16265 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
16266 for DOS) file already exists, then the source file is simply discarded.
16268 @code{protoize} and @code{unprotoize} both depend on GCC itself to
16269 scan the program and collect information about the functions it uses.
16270 So neither of these programs will work until GCC is installed.
16272 Here is a table of the options you can use with @code{protoize} and
16273 @code{unprotoize}. Each option works with both programs unless
16277 @item -B @var{directory}
16278 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
16279 usual directory (normally @file{/usr/local/lib}). This file contains
16280 prototype information about standard system functions. This option
16281 applies only to @code{protoize}.
16283 @item -c @var{compilation-options}
16284 Use @var{compilation-options} as the options when running @command{gcc} to
16285 produce the @samp{.X} files. The special option @option{-aux-info} is
16286 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
16288 Note that the compilation options must be given as a single argument to
16289 @code{protoize} or @code{unprotoize}. If you want to specify several
16290 @command{gcc} options, you must quote the entire set of compilation options
16291 to make them a single word in the shell.
16293 There are certain @command{gcc} arguments that you cannot use, because they
16294 would produce the wrong kind of output. These include @option{-g},
16295 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
16296 the @var{compilation-options}, they are ignored.
16299 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
16300 systems) instead of @samp{.c}. This is convenient if you are converting
16301 a C program to C++. This option applies only to @code{protoize}.
16304 Add explicit global declarations. This means inserting explicit
16305 declarations at the beginning of each source file for each function
16306 that is called in the file and was not declared. These declarations
16307 precede the first function definition that contains a call to an
16308 undeclared function. This option applies only to @code{protoize}.
16310 @item -i @var{string}
16311 Indent old-style parameter declarations with the string @var{string}.
16312 This option applies only to @code{protoize}.
16314 @code{unprotoize} converts prototyped function definitions to old-style
16315 function definitions, where the arguments are declared between the
16316 argument list and the initial @samp{@{}. By default, @code{unprotoize}
16317 uses five spaces as the indentation. If you want to indent with just
16318 one space instead, use @option{-i " "}.
16321 Keep the @samp{.X} files. Normally, they are deleted after conversion
16325 Add explicit local declarations. @code{protoize} with @option{-l} inserts
16326 a prototype declaration for each function in each block which calls the
16327 function without any declaration. This option applies only to
16331 Make no real changes. This mode just prints information about the conversions
16332 that would have been done without @option{-n}.
16335 Make no @samp{.save} files. The original files are simply deleted.
16336 Use this option with caution.
16338 @item -p @var{program}
16339 Use the program @var{program} as the compiler. Normally, the name
16340 @file{gcc} is used.
16343 Work quietly. Most warnings are suppressed.
16346 Print the version number, just like @option{-v} for @command{gcc}.
16349 If you need special compiler options to compile one of your program's
16350 source files, then you should generate that file's @samp{.X} file
16351 specially, by running @command{gcc} on that source file with the
16352 appropriate options and the option @option{-aux-info}. Then run
16353 @code{protoize} on the entire set of files. @code{protoize} will use
16354 the existing @samp{.X} file because it is newer than the source file.
16358 gcc -Dfoo=bar file1.c -aux-info file1.X
16363 You need to include the special files along with the rest in the
16364 @code{protoize} command, even though their @samp{.X} files already
16365 exist, because otherwise they won't get converted.
16367 @xref{Protoize Caveats}, for more information on how to use
16368 @code{protoize} successfully.