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 -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 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
725 -mstrict-align -mno-strict-align -mrelocatable @gol
726 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
727 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
728 -mdynamic-no-pic -maltivec -mswdiv @gol
729 -mprioritize-restricted-insns=@var{priority} @gol
730 -msched-costly-dep=@var{dependence_type} @gol
731 -minsert-sched-nops=@var{scheme} @gol
732 -mcall-sysv -mcall-netbsd @gol
733 -maix-struct-return -msvr4-struct-return @gol
734 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
735 -misel -mno-isel @gol
736 -misel=yes -misel=no @gol
738 -mspe=yes -mspe=no @gol
740 -mgen-cell-microcode -mwarn-cell-microcode @gol
741 -mvrsave -mno-vrsave @gol
742 -mmulhw -mno-mulhw @gol
743 -mdlmzb -mno-dlmzb @gol
744 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
745 -mprototype -mno-prototype @gol
746 -msim -mmvme -mads -myellowknife -memb -msdata @gol
747 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
749 @emph{S/390 and zSeries Options}
750 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
751 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
752 -mlong-double-64 -mlong-double-128 @gol
753 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
754 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
755 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
756 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
757 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
760 @gccoptlist{-meb -mel @gol
764 -mscore5 -mscore5u -mscore7 -mscore7d}
767 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
768 -m4-nofpu -m4-single-only -m4-single -m4 @gol
769 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
770 -m5-64media -m5-64media-nofpu @gol
771 -m5-32media -m5-32media-nofpu @gol
772 -m5-compact -m5-compact-nofpu @gol
773 -mb -ml -mdalign -mrelax @gol
774 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
775 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
776 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
777 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
778 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
782 @gccoptlist{-mcpu=@var{cpu-type} @gol
783 -mtune=@var{cpu-type} @gol
784 -mcmodel=@var{code-model} @gol
785 -m32 -m64 -mapp-regs -mno-app-regs @gol
786 -mfaster-structs -mno-faster-structs @gol
787 -mfpu -mno-fpu -mhard-float -msoft-float @gol
788 -mhard-quad-float -msoft-quad-float @gol
789 -mimpure-text -mno-impure-text -mlittle-endian @gol
790 -mstack-bias -mno-stack-bias @gol
791 -munaligned-doubles -mno-unaligned-doubles @gol
792 -mv8plus -mno-v8plus -mvis -mno-vis
793 -threads -pthreads -pthread}
796 @gccoptlist{-mwarn-reloc -merror-reloc @gol
797 -msafe-dma -munsafe-dma @gol
799 -msmall-mem -mlarge-mem -mstdmain @gol
800 -mfixed-range=@var{register-range}}
802 @emph{System V Options}
803 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
806 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
807 -mprolog-function -mno-prolog-function -mspace @gol
808 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
809 -mapp-regs -mno-app-regs @gol
810 -mdisable-callt -mno-disable-callt @gol
816 @gccoptlist{-mg -mgnu -munix}
818 @emph{VxWorks Options}
819 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
820 -Xbind-lazy -Xbind-now}
822 @emph{x86-64 Options}
823 See i386 and x86-64 Options.
825 @emph{Xstormy16 Options}
828 @emph{Xtensa Options}
829 @gccoptlist{-mconst16 -mno-const16 @gol
830 -mfused-madd -mno-fused-madd @gol
831 -mserialize-volatile -mno-serialize-volatile @gol
832 -mtext-section-literals -mno-text-section-literals @gol
833 -mtarget-align -mno-target-align @gol
834 -mlongcalls -mno-longcalls}
836 @emph{zSeries Options}
837 See S/390 and zSeries Options.
839 @item Code Generation Options
840 @xref{Code Gen Options,,Options for Code Generation Conventions}.
841 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
842 -ffixed-@var{reg} -fexceptions @gol
843 -fnon-call-exceptions -funwind-tables @gol
844 -fasynchronous-unwind-tables @gol
845 -finhibit-size-directive -finstrument-functions @gol
846 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
847 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
848 -fno-common -fno-ident @gol
849 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
850 -fno-jump-tables @gol
851 -frecord-gcc-switches @gol
852 -freg-struct-return -fshort-enums @gol
853 -fshort-double -fshort-wchar @gol
854 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
855 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
856 -fno-stack-limit -fargument-alias -fargument-noalias @gol
857 -fargument-noalias-global -fargument-noalias-anything @gol
858 -fleading-underscore -ftls-model=@var{model} @gol
859 -ftrapv -fwrapv -fbounds-check @gol
864 * Overall Options:: Controlling the kind of output:
865 an executable, object files, assembler files,
866 or preprocessed source.
867 * C Dialect Options:: Controlling the variant of C language compiled.
868 * C++ Dialect Options:: Variations on C++.
869 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
871 * Language Independent Options:: Controlling how diagnostics should be
873 * Warning Options:: How picky should the compiler be?
874 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
875 * Optimize Options:: How much optimization?
876 * Preprocessor Options:: Controlling header files and macro definitions.
877 Also, getting dependency information for Make.
878 * Assembler Options:: Passing options to the assembler.
879 * Link Options:: Specifying libraries and so on.
880 * Directory Options:: Where to find header files and libraries.
881 Where to find the compiler executable files.
882 * Spec Files:: How to pass switches to sub-processes.
883 * Target Options:: Running a cross-compiler, or an old version of GCC.
886 @node Overall Options
887 @section Options Controlling the Kind of Output
889 Compilation can involve up to four stages: preprocessing, compilation
890 proper, assembly and linking, always in that order. GCC is capable of
891 preprocessing and compiling several files either into several
892 assembler input files, or into one assembler input file; then each
893 assembler input file produces an object file, and linking combines all
894 the object files (those newly compiled, and those specified as input)
895 into an executable file.
897 @cindex file name suffix
898 For any given input file, the file name suffix determines what kind of
903 C source code which must be preprocessed.
906 C source code which should not be preprocessed.
909 C++ source code which should not be preprocessed.
912 Objective-C source code. Note that you must link with the @file{libobjc}
913 library to make an Objective-C program work.
916 Objective-C source code which should not be preprocessed.
920 Objective-C++ source code. Note that you must link with the @file{libobjc}
921 library to make an Objective-C++ program work. Note that @samp{.M} refers
922 to a literal capital M@.
925 Objective-C++ source code which should not be preprocessed.
928 C, C++, Objective-C or Objective-C++ header file to be turned into a
933 @itemx @var{file}.cxx
934 @itemx @var{file}.cpp
935 @itemx @var{file}.CPP
936 @itemx @var{file}.c++
938 C++ source code which must be preprocessed. Note that in @samp{.cxx},
939 the last two letters must both be literally @samp{x}. Likewise,
940 @samp{.C} refers to a literal capital C@.
944 Objective-C++ source code which must be preprocessed.
947 Objective-C++ source code which should not be preprocessed.
952 @itemx @var{file}.hxx
953 @itemx @var{file}.hpp
954 @itemx @var{file}.HPP
955 @itemx @var{file}.h++
956 @itemx @var{file}.tcc
957 C++ header file to be turned into a precompiled header.
960 @itemx @var{file}.for
961 @itemx @var{file}.ftn
962 Fixed form Fortran source code which should not be preprocessed.
965 @itemx @var{file}.FOR
966 @itemx @var{file}.fpp
967 @itemx @var{file}.FPP
968 @itemx @var{file}.FTN
969 Fixed form Fortran source code which must be preprocessed (with the traditional
973 @itemx @var{file}.f95
974 @itemx @var{file}.f03
975 @itemx @var{file}.f08
976 Free form Fortran source code which should not be preprocessed.
979 @itemx @var{file}.F95
980 @itemx @var{file}.F03
981 @itemx @var{file}.F08
982 Free form Fortran source code which must be preprocessed (with the
983 traditional preprocessor).
985 @c FIXME: Descriptions of Java file types.
992 Ada source code file which contains a library unit declaration (a
993 declaration of a package, subprogram, or generic, or a generic
994 instantiation), or a library unit renaming declaration (a package,
995 generic, or subprogram renaming declaration). Such files are also
999 Ada source code file containing a library unit body (a subprogram or
1000 package body). Such files are also called @dfn{bodies}.
1002 @c GCC also knows about some suffixes for languages not yet included:
1013 @itemx @var{file}.sx
1014 Assembler code which must be preprocessed.
1017 An object file to be fed straight into linking.
1018 Any file name with no recognized suffix is treated this way.
1022 You can specify the input language explicitly with the @option{-x} option:
1025 @item -x @var{language}
1026 Specify explicitly the @var{language} for the following input files
1027 (rather than letting the compiler choose a default based on the file
1028 name suffix). This option applies to all following input files until
1029 the next @option{-x} option. Possible values for @var{language} are:
1031 c c-header c-cpp-output
1032 c++ c++-header c++-cpp-output
1033 objective-c objective-c-header objective-c-cpp-output
1034 objective-c++ objective-c++-header objective-c++-cpp-output
1035 assembler assembler-with-cpp
1037 f77 f77-cpp-input f95 f95-cpp-input
1042 Turn off any specification of a language, so that subsequent files are
1043 handled according to their file name suffixes (as they are if @option{-x}
1044 has not been used at all).
1046 @item -pass-exit-codes
1047 @opindex pass-exit-codes
1048 Normally the @command{gcc} program will exit with the code of 1 if any
1049 phase of the compiler returns a non-success return code. If you specify
1050 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1051 numerically highest error produced by any phase that returned an error
1052 indication. The C, C++, and Fortran frontends return 4, if an internal
1053 compiler error is encountered.
1056 If you only want some of the stages of compilation, you can use
1057 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1058 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1059 @command{gcc} is to stop. Note that some combinations (for example,
1060 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1065 Compile or assemble the source files, but do not link. The linking
1066 stage simply is not done. The ultimate output is in the form of an
1067 object file for each source file.
1069 By default, the object file name for a source file is made by replacing
1070 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1072 Unrecognized input files, not requiring compilation or assembly, are
1077 Stop after the stage of compilation proper; do not assemble. The output
1078 is in the form of an assembler code file for each non-assembler input
1081 By default, the assembler file name for a source file is made by
1082 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1084 Input files that don't require compilation are ignored.
1088 Stop after the preprocessing stage; do not run the compiler proper. The
1089 output is in the form of preprocessed source code, which is sent to the
1092 Input files which don't require preprocessing are ignored.
1094 @cindex output file option
1097 Place output in file @var{file}. This applies regardless to whatever
1098 sort of output is being produced, whether it be an executable file,
1099 an object file, an assembler file or preprocessed C code.
1101 If @option{-o} is not specified, the default is to put an executable
1102 file in @file{a.out}, the object file for
1103 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1104 assembler file in @file{@var{source}.s}, a precompiled header file in
1105 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1110 Print (on standard error output) the commands executed to run the stages
1111 of compilation. Also print the version number of the compiler driver
1112 program and of the preprocessor and the compiler proper.
1116 Like @option{-v} except the commands are not executed and all command
1117 arguments are quoted. This is useful for shell scripts to capture the
1118 driver-generated command lines.
1122 Use pipes rather than temporary files for communication between the
1123 various stages of compilation. This fails to work on some systems where
1124 the assembler is unable to read from a pipe; but the GNU assembler has
1129 If you are compiling multiple source files, this option tells the driver
1130 to pass all the source files to the compiler at once (for those
1131 languages for which the compiler can handle this). This will allow
1132 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1133 language for which this is supported is C@. If you pass source files for
1134 multiple languages to the driver, using this option, the driver will invoke
1135 the compiler(s) that support IMA once each, passing each compiler all the
1136 source files appropriate for it. For those languages that do not support
1137 IMA this option will be ignored, and the compiler will be invoked once for
1138 each source file in that language. If you use this option in conjunction
1139 with @option{-save-temps}, the compiler will generate multiple
1141 (one for each source file), but only one (combined) @file{.o} or
1146 Print (on the standard output) a description of the command line options
1147 understood by @command{gcc}. If the @option{-v} option is also specified
1148 then @option{--help} will also be passed on to the various processes
1149 invoked by @command{gcc}, so that they can display the command line options
1150 they accept. If the @option{-Wextra} option has also been specified
1151 (prior to the @option{--help} option), then command line options which
1152 have no documentation associated with them will also be displayed.
1155 @opindex target-help
1156 Print (on the standard output) a description of target-specific command
1157 line options for each tool. For some targets extra target-specific
1158 information may also be printed.
1160 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1161 Print (on the standard output) a description of the command line
1162 options understood by the compiler that fit into a specific class.
1163 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1164 @samp{params}, or @var{language}:
1167 @item @samp{optimizers}
1168 This will display all of the optimization options supported by the
1171 @item @samp{warnings}
1172 This will display all of the options controlling warning messages
1173 produced by the compiler.
1176 This will display target-specific options. Unlike the
1177 @option{--target-help} option however, target-specific options of the
1178 linker and assembler will not be displayed. This is because those
1179 tools do not currently support the extended @option{--help=} syntax.
1182 This will display the values recognized by the @option{--param}
1185 @item @var{language}
1186 This will display the options supported for @var{language}, where
1187 @var{language} is the name of one of the languages supported in this
1191 This will display the options that are common to all languages.
1194 It is possible to further refine the output of the @option{--help=}
1195 option by adding a comma separated list of qualifiers after the
1196 class. These can be any from the following list:
1199 @item @samp{undocumented}
1200 Display only those options which are undocumented.
1203 Display options which take an argument that appears after an equal
1204 sign in the same continuous piece of text, such as:
1205 @samp{--help=target}.
1207 @item @samp{separate}
1208 Display options which take an argument that appears as a separate word
1209 following the original option, such as: @samp{-o output-file}.
1212 Thus for example to display all the undocumented target-specific
1213 switches supported by the compiler the following can be used:
1216 --help=target,undocumented
1219 The sense of a qualifier can be inverted by prefixing it with the
1220 @var{^} character, so for example to display all binary warning
1221 options (i.e., ones that are either on or off and that do not take an
1222 argument), which have a description the following can be used:
1225 --help=warnings,^joined,^undocumented
1228 A class can also be used as a qualifier, although this usually
1229 restricts the output by so much that there is nothing to display. One
1230 case where it does work however is when one of the classes is
1231 @var{target}. So for example to display all the target-specific
1232 optimization options the following can be used:
1235 --help=target,optimizers
1238 The @option{--help=} option can be repeated on the command line. Each
1239 successive use will display its requested class of options, skipping
1240 those that have already been displayed.
1242 If the @option{-Q} option appears on the command line before the
1243 @option{--help=} option, then the descriptive text displayed by
1244 @option{--help=} is changed. Instead of describing the displayed
1245 options, an indication is given as to whether the option is enabled,
1246 disabled or set to a specific value (assuming that the compiler
1247 knows this at the point where the @option{--help=} option is used).
1249 Here is a truncated example from the ARM port of @command{gcc}:
1252 % gcc -Q -mabi=2 --help=target -c
1253 The following options are target specific:
1255 -mabort-on-noreturn [disabled]
1259 The output is sensitive to the effects of previous command line
1260 options, so for example it is possible to find out which optimizations
1261 are enabled at @option{-O2} by using:
1264 -O2 --help=optimizers
1267 Alternatively you can discover which binary optimizations are enabled
1268 by @option{-O3} by using:
1271 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1272 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1273 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1278 Display the version number and copyrights of the invoked GCC@.
1282 Invoke all subcommands under a wrapper program. It takes a single
1283 comma separated list as an argument, which will be used to invoke
1287 gcc -c t.c -wrapper gdb,--args
1290 This will invoke all subprograms of gcc under "gdb --args",
1291 thus cc1 invocation will be "gdb --args cc1 ...".
1293 @include @value{srcdir}/../libiberty/at-file.texi
1297 @section Compiling C++ Programs
1299 @cindex suffixes for C++ source
1300 @cindex C++ source file suffixes
1301 C++ source files conventionally use one of the suffixes @samp{.C},
1302 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1303 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1304 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1305 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1306 files with these names and compiles them as C++ programs even if you
1307 call the compiler the same way as for compiling C programs (usually
1308 with the name @command{gcc}).
1312 However, the use of @command{gcc} does not add the C++ library.
1313 @command{g++} is a program that calls GCC and treats @samp{.c},
1314 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1315 files unless @option{-x} is used, and automatically specifies linking
1316 against the C++ library. This program is also useful when
1317 precompiling a C header file with a @samp{.h} extension for use in C++
1318 compilations. On many systems, @command{g++} is also installed with
1319 the name @command{c++}.
1321 @cindex invoking @command{g++}
1322 When you compile C++ programs, you may specify many of the same
1323 command-line options that you use for compiling programs in any
1324 language; or command-line options meaningful for C and related
1325 languages; or options that are meaningful only for C++ programs.
1326 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1327 explanations of options for languages related to C@.
1328 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1329 explanations of options that are meaningful only for C++ programs.
1331 @node C Dialect Options
1332 @section Options Controlling C Dialect
1333 @cindex dialect options
1334 @cindex language dialect options
1335 @cindex options, dialect
1337 The following options control the dialect of C (or languages derived
1338 from C, such as C++, Objective-C and Objective-C++) that the compiler
1342 @cindex ANSI support
1346 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1347 equivalent to @samp{-std=c++98}.
1349 This turns off certain features of GCC that are incompatible with ISO
1350 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1351 such as the @code{asm} and @code{typeof} keywords, and
1352 predefined macros such as @code{unix} and @code{vax} that identify the
1353 type of system you are using. It also enables the undesirable and
1354 rarely used ISO trigraph feature. For the C compiler,
1355 it disables recognition of C++ style @samp{//} comments as well as
1356 the @code{inline} keyword.
1358 The alternate keywords @code{__asm__}, @code{__extension__},
1359 @code{__inline__} and @code{__typeof__} continue to work despite
1360 @option{-ansi}. You would not want to use them in an ISO C program, of
1361 course, but it is useful to put them in header files that might be included
1362 in compilations done with @option{-ansi}. Alternate predefined macros
1363 such as @code{__unix__} and @code{__vax__} are also available, with or
1364 without @option{-ansi}.
1366 The @option{-ansi} option does not cause non-ISO programs to be
1367 rejected gratuitously. For that, @option{-pedantic} is required in
1368 addition to @option{-ansi}. @xref{Warning Options}.
1370 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1371 option is used. Some header files may notice this macro and refrain
1372 from declaring certain functions or defining certain macros that the
1373 ISO standard doesn't call for; this is to avoid interfering with any
1374 programs that might use these names for other things.
1376 Functions that would normally be built in but do not have semantics
1377 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1378 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1379 built-in functions provided by GCC}, for details of the functions
1384 Determine the language standard. @xref{Standards,,Language Standards
1385 Supported by GCC}, for details of these standard versions. This option
1386 is currently only supported when compiling C or C++.
1388 The compiler can accept several base standards, such as @samp{c89} or
1389 @samp{c++98}, and GNU dialects of those standards, such as
1390 @samp{gnu89} or @samp{gnu++98}. By specifying a base standard, the
1391 compiler will accept all programs following that standard and those
1392 using GNU extensions that do not contradict it. For example,
1393 @samp{-std=c89} turns off certain features of GCC that are
1394 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1395 keywords, but not other GNU extensions that do not have a meaning in
1396 ISO C90, such as omitting the middle term of a @code{?:}
1397 expression. On the other hand, by specifying a GNU dialect of a
1398 standard, all features the compiler support are enabled, even when
1399 those features change the meaning of the base standard and some
1400 strict-conforming programs may be rejected. The particular standard
1401 is used by @option{-pedantic} to identify which features are GNU
1402 extensions given that version of the standard. For example
1403 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1404 comments, while @samp{-std=gnu99 -pedantic} would not.
1406 A value for this option must be provided; possible values are
1411 Support all ISO C90 programs (certain GNU extensions that conflict
1412 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1414 @item iso9899:199409
1415 ISO C90 as modified in amendment 1.
1421 ISO C99. Note that this standard is not yet fully supported; see
1422 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1423 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1426 GNU dialect of ISO C90 (including some C99 features). This
1427 is the default for C code.
1431 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1432 this will become the default. The name @samp{gnu9x} is deprecated.
1435 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1439 GNU dialect of @option{-std=c++98}. This is the default for
1443 The working draft of the upcoming ISO C++0x standard. This option
1444 enables experimental features that are likely to be included in
1445 C++0x. The working draft is constantly changing, and any feature that is
1446 enabled by this flag may be removed from future versions of GCC if it is
1447 not part of the C++0x standard.
1450 GNU dialect of @option{-std=c++0x}. This option enables
1451 experimental features that may be removed in future versions of GCC.
1454 @item -fgnu89-inline
1455 @opindex fgnu89-inline
1456 The option @option{-fgnu89-inline} tells GCC to use the traditional
1457 GNU semantics for @code{inline} functions when in C99 mode.
1458 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1459 is accepted and ignored by GCC versions 4.1.3 up to but not including
1460 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1461 C99 mode. Using this option is roughly equivalent to adding the
1462 @code{gnu_inline} function attribute to all inline functions
1463 (@pxref{Function Attributes}).
1465 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1466 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1467 specifies the default behavior). This option was first supported in
1468 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1470 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1471 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1472 in effect for @code{inline} functions. @xref{Common Predefined
1473 Macros,,,cpp,The C Preprocessor}.
1475 @item -aux-info @var{filename}
1477 Output to the given filename prototyped declarations for all functions
1478 declared and/or defined in a translation unit, including those in header
1479 files. This option is silently ignored in any language other than C@.
1481 Besides declarations, the file indicates, in comments, the origin of
1482 each declaration (source file and line), whether the declaration was
1483 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1484 @samp{O} for old, respectively, in the first character after the line
1485 number and the colon), and whether it came from a declaration or a
1486 definition (@samp{C} or @samp{F}, respectively, in the following
1487 character). In the case of function definitions, a K&R-style list of
1488 arguments followed by their declarations is also provided, inside
1489 comments, after the declaration.
1493 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1494 keyword, so that code can use these words as identifiers. You can use
1495 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1496 instead. @option{-ansi} implies @option{-fno-asm}.
1498 In C++, this switch only affects the @code{typeof} keyword, since
1499 @code{asm} and @code{inline} are standard keywords. You may want to
1500 use the @option{-fno-gnu-keywords} flag instead, which has the same
1501 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1502 switch only affects the @code{asm} and @code{typeof} keywords, since
1503 @code{inline} is a standard keyword in ISO C99.
1506 @itemx -fno-builtin-@var{function}
1507 @opindex fno-builtin
1508 @cindex built-in functions
1509 Don't recognize built-in functions that do not begin with
1510 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1511 functions provided by GCC}, for details of the functions affected,
1512 including those which are not built-in functions when @option{-ansi} or
1513 @option{-std} options for strict ISO C conformance are used because they
1514 do not have an ISO standard meaning.
1516 GCC normally generates special code to handle certain built-in functions
1517 more efficiently; for instance, calls to @code{alloca} may become single
1518 instructions that adjust the stack directly, and calls to @code{memcpy}
1519 may become inline copy loops. The resulting code is often both smaller
1520 and faster, but since the function calls no longer appear as such, you
1521 cannot set a breakpoint on those calls, nor can you change the behavior
1522 of the functions by linking with a different library. In addition,
1523 when a function is recognized as a built-in function, GCC may use
1524 information about that function to warn about problems with calls to
1525 that function, or to generate more efficient code, even if the
1526 resulting code still contains calls to that function. For example,
1527 warnings are given with @option{-Wformat} for bad calls to
1528 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1529 known not to modify global memory.
1531 With the @option{-fno-builtin-@var{function}} option
1532 only the built-in function @var{function} is
1533 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1534 function is named that is not built-in in this version of GCC, this
1535 option is ignored. There is no corresponding
1536 @option{-fbuiltin-@var{function}} option; if you wish to enable
1537 built-in functions selectively when using @option{-fno-builtin} or
1538 @option{-ffreestanding}, you may define macros such as:
1541 #define abs(n) __builtin_abs ((n))
1542 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1547 @cindex hosted environment
1549 Assert that compilation takes place in a hosted environment. This implies
1550 @option{-fbuiltin}. A hosted environment is one in which the
1551 entire standard library is available, and in which @code{main} has a return
1552 type of @code{int}. Examples are nearly everything except a kernel.
1553 This is equivalent to @option{-fno-freestanding}.
1555 @item -ffreestanding
1556 @opindex ffreestanding
1557 @cindex hosted environment
1559 Assert that compilation takes place in a freestanding environment. This
1560 implies @option{-fno-builtin}. A freestanding environment
1561 is one in which the standard library may not exist, and program startup may
1562 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1563 This is equivalent to @option{-fno-hosted}.
1565 @xref{Standards,,Language Standards Supported by GCC}, for details of
1566 freestanding and hosted environments.
1570 @cindex openmp parallel
1571 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1572 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1573 compiler generates parallel code according to the OpenMP Application
1574 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1575 implies @option{-pthread}, and thus is only supported on targets that
1576 have support for @option{-pthread}.
1578 @item -fms-extensions
1579 @opindex fms-extensions
1580 Accept some non-standard constructs used in Microsoft header files.
1582 Some cases of unnamed fields in structures and unions are only
1583 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1584 fields within structs/unions}, for details.
1588 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1589 options for strict ISO C conformance) implies @option{-trigraphs}.
1591 @item -no-integrated-cpp
1592 @opindex no-integrated-cpp
1593 Performs a compilation in two passes: preprocessing and compiling. This
1594 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1595 @option{-B} option. The user supplied compilation step can then add in
1596 an additional preprocessing step after normal preprocessing but before
1597 compiling. The default is to use the integrated cpp (internal cpp)
1599 The semantics of this option will change if "cc1", "cc1plus", and
1600 "cc1obj" are merged.
1602 @cindex traditional C language
1603 @cindex C language, traditional
1605 @itemx -traditional-cpp
1606 @opindex traditional-cpp
1607 @opindex traditional
1608 Formerly, these options caused GCC to attempt to emulate a pre-standard
1609 C compiler. They are now only supported with the @option{-E} switch.
1610 The preprocessor continues to support a pre-standard mode. See the GNU
1611 CPP manual for details.
1613 @item -fcond-mismatch
1614 @opindex fcond-mismatch
1615 Allow conditional expressions with mismatched types in the second and
1616 third arguments. The value of such an expression is void. This option
1617 is not supported for C++.
1619 @item -flax-vector-conversions
1620 @opindex flax-vector-conversions
1621 Allow implicit conversions between vectors with differing numbers of
1622 elements and/or incompatible element types. This option should not be
1625 @item -funsigned-char
1626 @opindex funsigned-char
1627 Let the type @code{char} be unsigned, like @code{unsigned char}.
1629 Each kind of machine has a default for what @code{char} should
1630 be. It is either like @code{unsigned char} by default or like
1631 @code{signed char} by default.
1633 Ideally, a portable program should always use @code{signed char} or
1634 @code{unsigned char} when it depends on the signedness of an object.
1635 But many programs have been written to use plain @code{char} and
1636 expect it to be signed, or expect it to be unsigned, depending on the
1637 machines they were written for. This option, and its inverse, let you
1638 make such a program work with the opposite default.
1640 The type @code{char} is always a distinct type from each of
1641 @code{signed char} or @code{unsigned char}, even though its behavior
1642 is always just like one of those two.
1645 @opindex fsigned-char
1646 Let the type @code{char} be signed, like @code{signed char}.
1648 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1649 the negative form of @option{-funsigned-char}. Likewise, the option
1650 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1652 @item -fsigned-bitfields
1653 @itemx -funsigned-bitfields
1654 @itemx -fno-signed-bitfields
1655 @itemx -fno-unsigned-bitfields
1656 @opindex fsigned-bitfields
1657 @opindex funsigned-bitfields
1658 @opindex fno-signed-bitfields
1659 @opindex fno-unsigned-bitfields
1660 These options control whether a bit-field is signed or unsigned, when the
1661 declaration does not use either @code{signed} or @code{unsigned}. By
1662 default, such a bit-field is signed, because this is consistent: the
1663 basic integer types such as @code{int} are signed types.
1666 @node C++ Dialect Options
1667 @section Options Controlling C++ Dialect
1669 @cindex compiler options, C++
1670 @cindex C++ options, command line
1671 @cindex options, C++
1672 This section describes the command-line options that are only meaningful
1673 for C++ programs; but you can also use most of the GNU compiler options
1674 regardless of what language your program is in. For example, you
1675 might compile a file @code{firstClass.C} like this:
1678 g++ -g -frepo -O -c firstClass.C
1682 In this example, only @option{-frepo} is an option meant
1683 only for C++ programs; you can use the other options with any
1684 language supported by GCC@.
1686 Here is a list of options that are @emph{only} for compiling C++ programs:
1690 @item -fabi-version=@var{n}
1691 @opindex fabi-version
1692 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1693 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1694 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1695 the version that conforms most closely to the C++ ABI specification.
1696 Therefore, the ABI obtained using version 0 will change as ABI bugs
1699 The default is version 2.
1701 @item -fno-access-control
1702 @opindex fno-access-control
1703 Turn off all access checking. This switch is mainly useful for working
1704 around bugs in the access control code.
1708 Check that the pointer returned by @code{operator new} is non-null
1709 before attempting to modify the storage allocated. This check is
1710 normally unnecessary because the C++ standard specifies that
1711 @code{operator new} will only return @code{0} if it is declared
1712 @samp{throw()}, in which case the compiler will always check the
1713 return value even without this option. In all other cases, when
1714 @code{operator new} has a non-empty exception specification, memory
1715 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1716 @samp{new (nothrow)}.
1718 @item -fconserve-space
1719 @opindex fconserve-space
1720 Put uninitialized or runtime-initialized global variables into the
1721 common segment, as C does. This saves space in the executable at the
1722 cost of not diagnosing duplicate definitions. If you compile with this
1723 flag and your program mysteriously crashes after @code{main()} has
1724 completed, you may have an object that is being destroyed twice because
1725 two definitions were merged.
1727 This option is no longer useful on most targets, now that support has
1728 been added for putting variables into BSS without making them common.
1730 @item -ffriend-injection
1731 @opindex ffriend-injection
1732 Inject friend functions into the enclosing namespace, so that they are
1733 visible outside the scope of the class in which they are declared.
1734 Friend functions were documented to work this way in the old Annotated
1735 C++ Reference Manual, and versions of G++ before 4.1 always worked
1736 that way. However, in ISO C++ a friend function which is not declared
1737 in an enclosing scope can only be found using argument dependent
1738 lookup. This option causes friends to be injected as they were in
1741 This option is for compatibility, and may be removed in a future
1744 @item -fno-elide-constructors
1745 @opindex fno-elide-constructors
1746 The C++ standard allows an implementation to omit creating a temporary
1747 which is only used to initialize another object of the same type.
1748 Specifying this option disables that optimization, and forces G++ to
1749 call the copy constructor in all cases.
1751 @item -fno-enforce-eh-specs
1752 @opindex fno-enforce-eh-specs
1753 Don't generate code to check for violation of exception specifications
1754 at runtime. This option violates the C++ standard, but may be useful
1755 for reducing code size in production builds, much like defining
1756 @samp{NDEBUG}. This does not give user code permission to throw
1757 exceptions in violation of the exception specifications; the compiler
1758 will still optimize based on the specifications, so throwing an
1759 unexpected exception will result in undefined behavior.
1762 @itemx -fno-for-scope
1764 @opindex fno-for-scope
1765 If @option{-ffor-scope} is specified, the scope of variables declared in
1766 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1767 as specified by the C++ standard.
1768 If @option{-fno-for-scope} is specified, the scope of variables declared in
1769 a @i{for-init-statement} extends to the end of the enclosing scope,
1770 as was the case in old versions of G++, and other (traditional)
1771 implementations of C++.
1773 The default if neither flag is given to follow the standard,
1774 but to allow and give a warning for old-style code that would
1775 otherwise be invalid, or have different behavior.
1777 @item -fno-gnu-keywords
1778 @opindex fno-gnu-keywords
1779 Do not recognize @code{typeof} as a keyword, so that code can use this
1780 word as an identifier. You can use the keyword @code{__typeof__} instead.
1781 @option{-ansi} implies @option{-fno-gnu-keywords}.
1783 @item -fno-implicit-templates
1784 @opindex fno-implicit-templates
1785 Never emit code for non-inline templates which are instantiated
1786 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1787 @xref{Template Instantiation}, for more information.
1789 @item -fno-implicit-inline-templates
1790 @opindex fno-implicit-inline-templates
1791 Don't emit code for implicit instantiations of inline templates, either.
1792 The default is to handle inlines differently so that compiles with and
1793 without optimization will need the same set of explicit instantiations.
1795 @item -fno-implement-inlines
1796 @opindex fno-implement-inlines
1797 To save space, do not emit out-of-line copies of inline functions
1798 controlled by @samp{#pragma implementation}. This will cause linker
1799 errors if these functions are not inlined everywhere they are called.
1801 @item -fms-extensions
1802 @opindex fms-extensions
1803 Disable pedantic warnings about constructs used in MFC, such as implicit
1804 int and getting a pointer to member function via non-standard syntax.
1806 @item -fno-nonansi-builtins
1807 @opindex fno-nonansi-builtins
1808 Disable built-in declarations of functions that are not mandated by
1809 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1810 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1812 @item -fno-operator-names
1813 @opindex fno-operator-names
1814 Do not treat the operator name keywords @code{and}, @code{bitand},
1815 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1816 synonyms as keywords.
1818 @item -fno-optional-diags
1819 @opindex fno-optional-diags
1820 Disable diagnostics that the standard says a compiler does not need to
1821 issue. Currently, the only such diagnostic issued by G++ is the one for
1822 a name having multiple meanings within a class.
1825 @opindex fpermissive
1826 Downgrade some diagnostics about nonconformant code from errors to
1827 warnings. Thus, using @option{-fpermissive} will allow some
1828 nonconforming code to compile.
1832 Enable automatic template instantiation at link time. This option also
1833 implies @option{-fno-implicit-templates}. @xref{Template
1834 Instantiation}, for more information.
1838 Disable generation of information about every class with virtual
1839 functions for use by the C++ runtime type identification features
1840 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1841 of the language, you can save some space by using this flag. Note that
1842 exception handling uses the same information, but it will generate it as
1843 needed. The @samp{dynamic_cast} operator can still be used for casts that
1844 do not require runtime type information, i.e.@: casts to @code{void *} or to
1845 unambiguous base classes.
1849 Emit statistics about front-end processing at the end of the compilation.
1850 This information is generally only useful to the G++ development team.
1852 @item -ftemplate-depth-@var{n}
1853 @opindex ftemplate-depth
1854 Set the maximum instantiation depth for template classes to @var{n}.
1855 A limit on the template instantiation depth is needed to detect
1856 endless recursions during template class instantiation. ANSI/ISO C++
1857 conforming programs must not rely on a maximum depth greater than 17.
1859 @item -fno-threadsafe-statics
1860 @opindex fno-threadsafe-statics
1861 Do not emit the extra code to use the routines specified in the C++
1862 ABI for thread-safe initialization of local statics. You can use this
1863 option to reduce code size slightly in code that doesn't need to be
1866 @item -fuse-cxa-atexit
1867 @opindex fuse-cxa-atexit
1868 Register destructors for objects with static storage duration with the
1869 @code{__cxa_atexit} function rather than the @code{atexit} function.
1870 This option is required for fully standards-compliant handling of static
1871 destructors, but will only work if your C library supports
1872 @code{__cxa_atexit}.
1874 @item -fno-use-cxa-get-exception-ptr
1875 @opindex fno-use-cxa-get-exception-ptr
1876 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1877 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1878 if the runtime routine is not available.
1880 @item -fvisibility-inlines-hidden
1881 @opindex fvisibility-inlines-hidden
1882 This switch declares that the user does not attempt to compare
1883 pointers to inline methods where the addresses of the two functions
1884 were taken in different shared objects.
1886 The effect of this is that GCC may, effectively, mark inline methods with
1887 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1888 appear in the export table of a DSO and do not require a PLT indirection
1889 when used within the DSO@. Enabling this option can have a dramatic effect
1890 on load and link times of a DSO as it massively reduces the size of the
1891 dynamic export table when the library makes heavy use of templates.
1893 The behavior of this switch is not quite the same as marking the
1894 methods as hidden directly, because it does not affect static variables
1895 local to the function or cause the compiler to deduce that
1896 the function is defined in only one shared object.
1898 You may mark a method as having a visibility explicitly to negate the
1899 effect of the switch for that method. For example, if you do want to
1900 compare pointers to a particular inline method, you might mark it as
1901 having default visibility. Marking the enclosing class with explicit
1902 visibility will have no effect.
1904 Explicitly instantiated inline methods are unaffected by this option
1905 as their linkage might otherwise cross a shared library boundary.
1906 @xref{Template Instantiation}.
1908 @item -fvisibility-ms-compat
1909 @opindex fvisibility-ms-compat
1910 This flag attempts to use visibility settings to make GCC's C++
1911 linkage model compatible with that of Microsoft Visual Studio.
1913 The flag makes these changes to GCC's linkage model:
1917 It sets the default visibility to @code{hidden}, like
1918 @option{-fvisibility=hidden}.
1921 Types, but not their members, are not hidden by default.
1924 The One Definition Rule is relaxed for types without explicit
1925 visibility specifications which are defined in more than one different
1926 shared object: those declarations are permitted if they would have
1927 been permitted when this option was not used.
1930 In new code it is better to use @option{-fvisibility=hidden} and
1931 export those classes which are intended to be externally visible.
1932 Unfortunately it is possible for code to rely, perhaps accidentally,
1933 on the Visual Studio behavior.
1935 Among the consequences of these changes are that static data members
1936 of the same type with the same name but defined in different shared
1937 objects will be different, so changing one will not change the other;
1938 and that pointers to function members defined in different shared
1939 objects may not compare equal. When this flag is given, it is a
1940 violation of the ODR to define types with the same name differently.
1944 Do not use weak symbol support, even if it is provided by the linker.
1945 By default, G++ will use weak symbols if they are available. This
1946 option exists only for testing, and should not be used by end-users;
1947 it will result in inferior code and has no benefits. This option may
1948 be removed in a future release of G++.
1952 Do not search for header files in the standard directories specific to
1953 C++, but do still search the other standard directories. (This option
1954 is used when building the C++ library.)
1957 In addition, these optimization, warning, and code generation options
1958 have meanings only for C++ programs:
1961 @item -fno-default-inline
1962 @opindex fno-default-inline
1963 Do not assume @samp{inline} for functions defined inside a class scope.
1964 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1965 functions will have linkage like inline functions; they just won't be
1968 @item -Wabi @r{(C++ and Objective-C++ only)}
1971 Warn when G++ generates code that is probably not compatible with the
1972 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1973 all such cases, there are probably some cases that are not warned about,
1974 even though G++ is generating incompatible code. There may also be
1975 cases where warnings are emitted even though the code that is generated
1978 You should rewrite your code to avoid these warnings if you are
1979 concerned about the fact that code generated by G++ may not be binary
1980 compatible with code generated by other compilers.
1982 The known incompatibilities at this point include:
1987 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1988 pack data into the same byte as a base class. For example:
1991 struct A @{ virtual void f(); int f1 : 1; @};
1992 struct B : public A @{ int f2 : 1; @};
1996 In this case, G++ will place @code{B::f2} into the same byte
1997 as@code{A::f1}; other compilers will not. You can avoid this problem
1998 by explicitly padding @code{A} so that its size is a multiple of the
1999 byte size on your platform; that will cause G++ and other compilers to
2000 layout @code{B} identically.
2003 Incorrect handling of tail-padding for virtual bases. G++ does not use
2004 tail padding when laying out virtual bases. For example:
2007 struct A @{ virtual void f(); char c1; @};
2008 struct B @{ B(); char c2; @};
2009 struct C : public A, public virtual B @{@};
2013 In this case, G++ will not place @code{B} into the tail-padding for
2014 @code{A}; other compilers will. You can avoid this problem by
2015 explicitly padding @code{A} so that its size is a multiple of its
2016 alignment (ignoring virtual base classes); that will cause G++ and other
2017 compilers to layout @code{C} identically.
2020 Incorrect handling of bit-fields with declared widths greater than that
2021 of their underlying types, when the bit-fields appear in a union. For
2025 union U @{ int i : 4096; @};
2029 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2030 union too small by the number of bits in an @code{int}.
2033 Empty classes can be placed at incorrect offsets. For example:
2043 struct C : public B, public A @{@};
2047 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2048 it should be placed at offset zero. G++ mistakenly believes that the
2049 @code{A} data member of @code{B} is already at offset zero.
2052 Names of template functions whose types involve @code{typename} or
2053 template template parameters can be mangled incorrectly.
2056 template <typename Q>
2057 void f(typename Q::X) @{@}
2059 template <template <typename> class Q>
2060 void f(typename Q<int>::X) @{@}
2064 Instantiations of these templates may be mangled incorrectly.
2068 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2069 @opindex Wctor-dtor-privacy
2070 @opindex Wno-ctor-dtor-privacy
2071 Warn when a class seems unusable because all the constructors or
2072 destructors in that class are private, and it has neither friends nor
2073 public static member functions.
2075 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2076 @opindex Wnon-virtual-dtor
2077 @opindex Wno-non-virtual-dtor
2078 Warn when a class has virtual functions and accessible non-virtual
2079 destructor, in which case it would be possible but unsafe to delete
2080 an instance of a derived class through a pointer to the base class.
2081 This warning is also enabled if -Weffc++ is specified.
2083 @item -Wreorder @r{(C++ and Objective-C++ only)}
2085 @opindex Wno-reorder
2086 @cindex reordering, warning
2087 @cindex warning for reordering of member initializers
2088 Warn when the order of member initializers given in the code does not
2089 match the order in which they must be executed. For instance:
2095 A(): j (0), i (1) @{ @}
2099 The compiler will rearrange the member initializers for @samp{i}
2100 and @samp{j} to match the declaration order of the members, emitting
2101 a warning to that effect. This warning is enabled by @option{-Wall}.
2104 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2107 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2110 Warn about violations of the following style guidelines from Scott Meyers'
2111 @cite{Effective C++} book:
2115 Item 11: Define a copy constructor and an assignment operator for classes
2116 with dynamically allocated memory.
2119 Item 12: Prefer initialization to assignment in constructors.
2122 Item 14: Make destructors virtual in base classes.
2125 Item 15: Have @code{operator=} return a reference to @code{*this}.
2128 Item 23: Don't try to return a reference when you must return an object.
2132 Also warn about violations of the following style guidelines from
2133 Scott Meyers' @cite{More Effective C++} book:
2137 Item 6: Distinguish between prefix and postfix forms of increment and
2138 decrement operators.
2141 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2145 When selecting this option, be aware that the standard library
2146 headers do not obey all of these guidelines; use @samp{grep -v}
2147 to filter out those warnings.
2149 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2150 @opindex Wstrict-null-sentinel
2151 @opindex Wno-strict-null-sentinel
2152 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2153 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2154 to @code{__null}. Although it is a null pointer constant not a null pointer,
2155 it is guaranteed to be of the same size as a pointer. But this use is
2156 not portable across different compilers.
2158 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2159 @opindex Wno-non-template-friend
2160 @opindex Wnon-template-friend
2161 Disable warnings when non-templatized friend functions are declared
2162 within a template. Since the advent of explicit template specification
2163 support in G++, if the name of the friend is an unqualified-id (i.e.,
2164 @samp{friend foo(int)}), the C++ language specification demands that the
2165 friend declare or define an ordinary, nontemplate function. (Section
2166 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2167 could be interpreted as a particular specialization of a templatized
2168 function. Because this non-conforming behavior is no longer the default
2169 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2170 check existing code for potential trouble spots and is on by default.
2171 This new compiler behavior can be turned off with
2172 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2173 but disables the helpful warning.
2175 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2176 @opindex Wold-style-cast
2177 @opindex Wno-old-style-cast
2178 Warn if an old-style (C-style) cast to a non-void type is used within
2179 a C++ program. The new-style casts (@samp{dynamic_cast},
2180 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2181 less vulnerable to unintended effects and much easier to search for.
2183 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2184 @opindex Woverloaded-virtual
2185 @opindex Wno-overloaded-virtual
2186 @cindex overloaded virtual fn, warning
2187 @cindex warning for overloaded virtual fn
2188 Warn when a function declaration hides virtual functions from a
2189 base class. For example, in:
2196 struct B: public A @{
2201 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2209 will fail to compile.
2211 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2212 @opindex Wno-pmf-conversions
2213 @opindex Wpmf-conversions
2214 Disable the diagnostic for converting a bound pointer to member function
2217 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2218 @opindex Wsign-promo
2219 @opindex Wno-sign-promo
2220 Warn when overload resolution chooses a promotion from unsigned or
2221 enumerated type to a signed type, over a conversion to an unsigned type of
2222 the same size. Previous versions of G++ would try to preserve
2223 unsignedness, but the standard mandates the current behavior.
2228 A& operator = (int);
2238 In this example, G++ will synthesize a default @samp{A& operator =
2239 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2242 @node Objective-C and Objective-C++ Dialect Options
2243 @section Options Controlling Objective-C and Objective-C++ Dialects
2245 @cindex compiler options, Objective-C and Objective-C++
2246 @cindex Objective-C and Objective-C++ options, command line
2247 @cindex options, Objective-C and Objective-C++
2248 (NOTE: This manual does not describe the Objective-C and Objective-C++
2249 languages themselves. See @xref{Standards,,Language Standards
2250 Supported by GCC}, for references.)
2252 This section describes the command-line options that are only meaningful
2253 for Objective-C and Objective-C++ programs, but you can also use most of
2254 the language-independent GNU compiler options.
2255 For example, you might compile a file @code{some_class.m} like this:
2258 gcc -g -fgnu-runtime -O -c some_class.m
2262 In this example, @option{-fgnu-runtime} is an option meant only for
2263 Objective-C and Objective-C++ programs; you can use the other options with
2264 any language supported by GCC@.
2266 Note that since Objective-C is an extension of the C language, Objective-C
2267 compilations may also use options specific to the C front-end (e.g.,
2268 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2269 C++-specific options (e.g., @option{-Wabi}).
2271 Here is a list of options that are @emph{only} for compiling Objective-C
2272 and Objective-C++ programs:
2275 @item -fconstant-string-class=@var{class-name}
2276 @opindex fconstant-string-class
2277 Use @var{class-name} as the name of the class to instantiate for each
2278 literal string specified with the syntax @code{@@"@dots{}"}. The default
2279 class name is @code{NXConstantString} if the GNU runtime is being used, and
2280 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2281 @option{-fconstant-cfstrings} option, if also present, will override the
2282 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2283 to be laid out as constant CoreFoundation strings.
2286 @opindex fgnu-runtime
2287 Generate object code compatible with the standard GNU Objective-C
2288 runtime. This is the default for most types of systems.
2290 @item -fnext-runtime
2291 @opindex fnext-runtime
2292 Generate output compatible with the NeXT runtime. This is the default
2293 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2294 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2297 @item -fno-nil-receivers
2298 @opindex fno-nil-receivers
2299 Assume that all Objective-C message dispatches (e.g.,
2300 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2301 is not @code{nil}. This allows for more efficient entry points in the runtime
2302 to be used. Currently, this option is only available in conjunction with
2303 the NeXT runtime on Mac OS X 10.3 and later.
2305 @item -fobjc-call-cxx-cdtors
2306 @opindex fobjc-call-cxx-cdtors
2307 For each Objective-C class, check if any of its instance variables is a
2308 C++ object with a non-trivial default constructor. If so, synthesize a
2309 special @code{- (id) .cxx_construct} instance method that will run
2310 non-trivial default constructors on any such instance variables, in order,
2311 and then return @code{self}. Similarly, check if any instance variable
2312 is a C++ object with a non-trivial destructor, and if so, synthesize a
2313 special @code{- (void) .cxx_destruct} method that will run
2314 all such default destructors, in reverse order.
2316 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2317 thusly generated will only operate on instance variables declared in the
2318 current Objective-C class, and not those inherited from superclasses. It
2319 is the responsibility of the Objective-C runtime to invoke all such methods
2320 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2321 will be invoked by the runtime immediately after a new object
2322 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2323 be invoked immediately before the runtime deallocates an object instance.
2325 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2326 support for invoking the @code{- (id) .cxx_construct} and
2327 @code{- (void) .cxx_destruct} methods.
2329 @item -fobjc-direct-dispatch
2330 @opindex fobjc-direct-dispatch
2331 Allow fast jumps to the message dispatcher. On Darwin this is
2332 accomplished via the comm page.
2334 @item -fobjc-exceptions
2335 @opindex fobjc-exceptions
2336 Enable syntactic support for structured exception handling in Objective-C,
2337 similar to what is offered by C++ and Java. This option is
2338 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2347 @@catch (AnObjCClass *exc) @{
2354 @@catch (AnotherClass *exc) @{
2357 @@catch (id allOthers) @{
2367 The @code{@@throw} statement may appear anywhere in an Objective-C or
2368 Objective-C++ program; when used inside of a @code{@@catch} block, the
2369 @code{@@throw} may appear without an argument (as shown above), in which case
2370 the object caught by the @code{@@catch} will be rethrown.
2372 Note that only (pointers to) Objective-C objects may be thrown and
2373 caught using this scheme. When an object is thrown, it will be caught
2374 by the nearest @code{@@catch} clause capable of handling objects of that type,
2375 analogously to how @code{catch} blocks work in C++ and Java. A
2376 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2377 any and all Objective-C exceptions not caught by previous @code{@@catch}
2380 The @code{@@finally} clause, if present, will be executed upon exit from the
2381 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2382 regardless of whether any exceptions are thrown, caught or rethrown
2383 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2384 of the @code{finally} clause in Java.
2386 There are several caveats to using the new exception mechanism:
2390 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2391 idioms provided by the @code{NSException} class, the new
2392 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2393 systems, due to additional functionality needed in the (NeXT) Objective-C
2397 As mentioned above, the new exceptions do not support handling
2398 types other than Objective-C objects. Furthermore, when used from
2399 Objective-C++, the Objective-C exception model does not interoperate with C++
2400 exceptions at this time. This means you cannot @code{@@throw} an exception
2401 from Objective-C and @code{catch} it in C++, or vice versa
2402 (i.e., @code{throw @dots{} @@catch}).
2405 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2406 blocks for thread-safe execution:
2409 @@synchronized (ObjCClass *guard) @{
2414 Upon entering the @code{@@synchronized} block, a thread of execution shall
2415 first check whether a lock has been placed on the corresponding @code{guard}
2416 object by another thread. If it has, the current thread shall wait until
2417 the other thread relinquishes its lock. Once @code{guard} becomes available,
2418 the current thread will place its own lock on it, execute the code contained in
2419 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2420 making @code{guard} available to other threads).
2422 Unlike Java, Objective-C does not allow for entire methods to be marked
2423 @code{@@synchronized}. Note that throwing exceptions out of
2424 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2425 to be unlocked properly.
2429 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2431 @item -freplace-objc-classes
2432 @opindex freplace-objc-classes
2433 Emit a special marker instructing @command{ld(1)} not to statically link in
2434 the resulting object file, and allow @command{dyld(1)} to load it in at
2435 run time instead. This is used in conjunction with the Fix-and-Continue
2436 debugging mode, where the object file in question may be recompiled and
2437 dynamically reloaded in the course of program execution, without the need
2438 to restart the program itself. Currently, Fix-and-Continue functionality
2439 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2444 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2445 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2446 compile time) with static class references that get initialized at load time,
2447 which improves run-time performance. Specifying the @option{-fzero-link} flag
2448 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2449 to be retained. This is useful in Zero-Link debugging mode, since it allows
2450 for individual class implementations to be modified during program execution.
2454 Dump interface declarations for all classes seen in the source file to a
2455 file named @file{@var{sourcename}.decl}.
2457 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2458 @opindex Wassign-intercept
2459 @opindex Wno-assign-intercept
2460 Warn whenever an Objective-C assignment is being intercepted by the
2463 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2464 @opindex Wno-protocol
2466 If a class is declared to implement a protocol, a warning is issued for
2467 every method in the protocol that is not implemented by the class. The
2468 default behavior is to issue a warning for every method not explicitly
2469 implemented in the class, even if a method implementation is inherited
2470 from the superclass. If you use the @option{-Wno-protocol} option, then
2471 methods inherited from the superclass are considered to be implemented,
2472 and no warning is issued for them.
2474 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2476 @opindex Wno-selector
2477 Warn if multiple methods of different types for the same selector are
2478 found during compilation. The check is performed on the list of methods
2479 in the final stage of compilation. Additionally, a check is performed
2480 for each selector appearing in a @code{@@selector(@dots{})}
2481 expression, and a corresponding method for that selector has been found
2482 during compilation. Because these checks scan the method table only at
2483 the end of compilation, these warnings are not produced if the final
2484 stage of compilation is not reached, for example because an error is
2485 found during compilation, or because the @option{-fsyntax-only} option is
2488 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2489 @opindex Wstrict-selector-match
2490 @opindex Wno-strict-selector-match
2491 Warn if multiple methods with differing argument and/or return types are
2492 found for a given selector when attempting to send a message using this
2493 selector to a receiver of type @code{id} or @code{Class}. When this flag
2494 is off (which is the default behavior), the compiler will omit such warnings
2495 if any differences found are confined to types which share the same size
2498 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2499 @opindex Wundeclared-selector
2500 @opindex Wno-undeclared-selector
2501 Warn if a @code{@@selector(@dots{})} expression referring to an
2502 undeclared selector is found. A selector is considered undeclared if no
2503 method with that name has been declared before the
2504 @code{@@selector(@dots{})} expression, either explicitly in an
2505 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2506 an @code{@@implementation} section. This option always performs its
2507 checks as soon as a @code{@@selector(@dots{})} expression is found,
2508 while @option{-Wselector} only performs its checks in the final stage of
2509 compilation. This also enforces the coding style convention
2510 that methods and selectors must be declared before being used.
2512 @item -print-objc-runtime-info
2513 @opindex print-objc-runtime-info
2514 Generate C header describing the largest structure that is passed by
2519 @node Language Independent Options
2520 @section Options to Control Diagnostic Messages Formatting
2521 @cindex options to control diagnostics formatting
2522 @cindex diagnostic messages
2523 @cindex message formatting
2525 Traditionally, diagnostic messages have been formatted irrespective of
2526 the output device's aspect (e.g.@: its width, @dots{}). The options described
2527 below can be used to control the diagnostic messages formatting
2528 algorithm, e.g.@: how many characters per line, how often source location
2529 information should be reported. Right now, only the C++ front end can
2530 honor these options. However it is expected, in the near future, that
2531 the remaining front ends would be able to digest them correctly.
2534 @item -fmessage-length=@var{n}
2535 @opindex fmessage-length
2536 Try to format error messages so that they fit on lines of about @var{n}
2537 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2538 the front ends supported by GCC@. If @var{n} is zero, then no
2539 line-wrapping will be done; each error message will appear on a single
2542 @opindex fdiagnostics-show-location
2543 @item -fdiagnostics-show-location=once
2544 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2545 reporter to emit @emph{once} source location information; that is, in
2546 case the message is too long to fit on a single physical line and has to
2547 be wrapped, the source location won't be emitted (as prefix) again,
2548 over and over, in subsequent continuation lines. This is the default
2551 @item -fdiagnostics-show-location=every-line
2552 Only meaningful in line-wrapping mode. Instructs the diagnostic
2553 messages reporter to emit the same source location information (as
2554 prefix) for physical lines that result from the process of breaking
2555 a message which is too long to fit on a single line.
2557 @item -fdiagnostics-show-option
2558 @opindex fdiagnostics-show-option
2559 This option instructs the diagnostic machinery to add text to each
2560 diagnostic emitted, which indicates which command line option directly
2561 controls that diagnostic, when such an option is known to the
2562 diagnostic machinery.
2564 @item -Wcoverage-mismatch
2565 @opindex Wcoverage-mismatch
2566 Warn if feedback profiles do not match when using the
2567 @option{-fprofile-use} option.
2568 If a source file was changed between @option{-fprofile-gen} and
2569 @option{-fprofile-use}, the files with the profile feedback can fail
2570 to match the source file and GCC can not use the profile feedback
2571 information. By default, GCC emits an error message in this case.
2572 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2573 error. GCC does not use appropriate feedback profiles, so using this
2574 option can result in poorly optimized code. This option is useful
2575 only in the case of very minor changes such as bug fixes to an
2580 @node Warning Options
2581 @section Options to Request or Suppress Warnings
2582 @cindex options to control warnings
2583 @cindex warning messages
2584 @cindex messages, warning
2585 @cindex suppressing warnings
2587 Warnings are diagnostic messages that report constructions which
2588 are not inherently erroneous but which are risky or suggest there
2589 may have been an error.
2591 The following language-independent options do not enable specific
2592 warnings but control the kinds of diagnostics produced by GCC.
2595 @cindex syntax checking
2597 @opindex fsyntax-only
2598 Check the code for syntax errors, but don't do anything beyond that.
2602 Inhibit all warning messages.
2607 Make all warnings into errors.
2612 Make the specified warning into an error. The specifier for a warning
2613 is appended, for example @option{-Werror=switch} turns the warnings
2614 controlled by @option{-Wswitch} into errors. This switch takes a
2615 negative form, to be used to negate @option{-Werror} for specific
2616 warnings, for example @option{-Wno-error=switch} makes
2617 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2618 is in effect. You can use the @option{-fdiagnostics-show-option}
2619 option to have each controllable warning amended with the option which
2620 controls it, to determine what to use with this option.
2622 Note that specifying @option{-Werror=}@var{foo} automatically implies
2623 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2626 @item -Wfatal-errors
2627 @opindex Wfatal-errors
2628 @opindex Wno-fatal-errors
2629 This option causes the compiler to abort compilation on the first error
2630 occurred rather than trying to keep going and printing further error
2635 You can request many specific warnings with options beginning
2636 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2637 implicit declarations. Each of these specific warning options also
2638 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2639 example, @option{-Wno-implicit}. This manual lists only one of the
2640 two forms, whichever is not the default. For further,
2641 language-specific options also refer to @ref{C++ Dialect Options} and
2642 @ref{Objective-C and Objective-C++ Dialect Options}.
2647 Issue all the warnings demanded by strict ISO C and ISO C++;
2648 reject all programs that use forbidden extensions, and some other
2649 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2650 version of the ISO C standard specified by any @option{-std} option used.
2652 Valid ISO C and ISO C++ programs should compile properly with or without
2653 this option (though a rare few will require @option{-ansi} or a
2654 @option{-std} option specifying the required version of ISO C)@. However,
2655 without this option, certain GNU extensions and traditional C and C++
2656 features are supported as well. With this option, they are rejected.
2658 @option{-pedantic} does not cause warning messages for use of the
2659 alternate keywords whose names begin and end with @samp{__}. Pedantic
2660 warnings are also disabled in the expression that follows
2661 @code{__extension__}. However, only system header files should use
2662 these escape routes; application programs should avoid them.
2663 @xref{Alternate Keywords}.
2665 Some users try to use @option{-pedantic} to check programs for strict ISO
2666 C conformance. They soon find that it does not do quite what they want:
2667 it finds some non-ISO practices, but not all---only those for which
2668 ISO C @emph{requires} a diagnostic, and some others for which
2669 diagnostics have been added.
2671 A feature to report any failure to conform to ISO C might be useful in
2672 some instances, but would require considerable additional work and would
2673 be quite different from @option{-pedantic}. We don't have plans to
2674 support such a feature in the near future.
2676 Where the standard specified with @option{-std} represents a GNU
2677 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2678 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2679 extended dialect is based. Warnings from @option{-pedantic} are given
2680 where they are required by the base standard. (It would not make sense
2681 for such warnings to be given only for features not in the specified GNU
2682 C dialect, since by definition the GNU dialects of C include all
2683 features the compiler supports with the given option, and there would be
2684 nothing to warn about.)
2686 @item -pedantic-errors
2687 @opindex pedantic-errors
2688 Like @option{-pedantic}, except that errors are produced rather than
2694 This enables all the warnings about constructions that some users
2695 consider questionable, and that are easy to avoid (or modify to
2696 prevent the warning), even in conjunction with macros. This also
2697 enables some language-specific warnings described in @ref{C++ Dialect
2698 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2700 @option{-Wall} turns on the following warning flags:
2702 @gccoptlist{-Waddress @gol
2703 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2705 -Wchar-subscripts @gol
2707 -Wimplicit-function-declaration @gol
2710 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2711 -Wmissing-braces @gol
2717 -Wsequence-point @gol
2718 -Wsign-compare @r{(only in C++)} @gol
2719 -Wstrict-aliasing @gol
2720 -Wstrict-overflow=1 @gol
2723 -Wuninitialized @gol
2724 -Wunknown-pragmas @gol
2725 -Wunused-function @gol
2728 -Wunused-variable @gol
2729 -Wvolatile-register-var @gol
2732 Note that some warning flags are not implied by @option{-Wall}. Some of
2733 them warn about constructions that users generally do not consider
2734 questionable, but which occasionally you might wish to check for;
2735 others warn about constructions that are necessary or hard to avoid in
2736 some cases, and there is no simple way to modify the code to suppress
2737 the warning. Some of them are enabled by @option{-Wextra} but many of
2738 them must be enabled individually.
2744 This enables some extra warning flags that are not enabled by
2745 @option{-Wall}. (This option used to be called @option{-W}. The older
2746 name is still supported, but the newer name is more descriptive.)
2748 @gccoptlist{-Wclobbered @gol
2750 -Wignored-qualifiers @gol
2751 -Wmissing-field-initializers @gol
2752 -Wmissing-parameter-type @r{(C only)} @gol
2753 -Wold-style-declaration @r{(C only)} @gol
2754 -Woverride-init @gol
2757 -Wuninitialized @gol
2758 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2761 The option @option{-Wextra} also prints warning messages for the
2767 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2768 @samp{>}, or @samp{>=}.
2771 (C++ only) An enumerator and a non-enumerator both appear in a
2772 conditional expression.
2775 (C++ only) Ambiguous virtual bases.
2778 (C++ only) Subscripting an array which has been declared @samp{register}.
2781 (C++ only) Taking the address of a variable which has been declared
2785 (C++ only) A base class is not initialized in a derived class' copy
2790 @item -Wchar-subscripts
2791 @opindex Wchar-subscripts
2792 @opindex Wno-char-subscripts
2793 Warn if an array subscript has type @code{char}. This is a common cause
2794 of error, as programmers often forget that this type is signed on some
2796 This warning is enabled by @option{-Wall}.
2800 @opindex Wno-comment
2801 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2802 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2803 This warning is enabled by @option{-Wall}.
2808 @opindex ffreestanding
2809 @opindex fno-builtin
2810 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2811 the arguments supplied have types appropriate to the format string
2812 specified, and that the conversions specified in the format string make
2813 sense. This includes standard functions, and others specified by format
2814 attributes (@pxref{Function Attributes}), in the @code{printf},
2815 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2816 not in the C standard) families (or other target-specific families).
2817 Which functions are checked without format attributes having been
2818 specified depends on the standard version selected, and such checks of
2819 functions without the attribute specified are disabled by
2820 @option{-ffreestanding} or @option{-fno-builtin}.
2822 The formats are checked against the format features supported by GNU
2823 libc version 2.2. These include all ISO C90 and C99 features, as well
2824 as features from the Single Unix Specification and some BSD and GNU
2825 extensions. Other library implementations may not support all these
2826 features; GCC does not support warning about features that go beyond a
2827 particular library's limitations. However, if @option{-pedantic} is used
2828 with @option{-Wformat}, warnings will be given about format features not
2829 in the selected standard version (but not for @code{strfmon} formats,
2830 since those are not in any version of the C standard). @xref{C Dialect
2831 Options,,Options Controlling C Dialect}.
2833 Since @option{-Wformat} also checks for null format arguments for
2834 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2836 @option{-Wformat} is included in @option{-Wall}. For more control over some
2837 aspects of format checking, the options @option{-Wformat-y2k},
2838 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2839 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2840 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2843 @opindex Wformat-y2k
2844 @opindex Wno-format-y2k
2845 If @option{-Wformat} is specified, also warn about @code{strftime}
2846 formats which may yield only a two-digit year.
2848 @item -Wno-format-contains-nul
2849 @opindex Wno-format-contains-nul
2850 @opindex Wformat-contains-nul
2851 If @option{-Wformat} is specified, do not warn about format strings that
2854 @item -Wno-format-extra-args
2855 @opindex Wno-format-extra-args
2856 @opindex Wformat-extra-args
2857 If @option{-Wformat} is specified, do not warn about excess arguments to a
2858 @code{printf} or @code{scanf} format function. The C standard specifies
2859 that such arguments are ignored.
2861 Where the unused arguments lie between used arguments that are
2862 specified with @samp{$} operand number specifications, normally
2863 warnings are still given, since the implementation could not know what
2864 type to pass to @code{va_arg} to skip the unused arguments. However,
2865 in the case of @code{scanf} formats, this option will suppress the
2866 warning if the unused arguments are all pointers, since the Single
2867 Unix Specification says that such unused arguments are allowed.
2869 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2870 @opindex Wno-format-zero-length
2871 @opindex Wformat-zero-length
2872 If @option{-Wformat} is specified, do not warn about zero-length formats.
2873 The C standard specifies that zero-length formats are allowed.
2875 @item -Wformat-nonliteral
2876 @opindex Wformat-nonliteral
2877 @opindex Wno-format-nonliteral
2878 If @option{-Wformat} is specified, also warn if the format string is not a
2879 string literal and so cannot be checked, unless the format function
2880 takes its format arguments as a @code{va_list}.
2882 @item -Wformat-security
2883 @opindex Wformat-security
2884 @opindex Wno-format-security
2885 If @option{-Wformat} is specified, also warn about uses of format
2886 functions that represent possible security problems. At present, this
2887 warns about calls to @code{printf} and @code{scanf} functions where the
2888 format string is not a string literal and there are no format arguments,
2889 as in @code{printf (foo);}. This may be a security hole if the format
2890 string came from untrusted input and contains @samp{%n}. (This is
2891 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2892 in future warnings may be added to @option{-Wformat-security} that are not
2893 included in @option{-Wformat-nonliteral}.)
2897 @opindex Wno-format=2
2898 Enable @option{-Wformat} plus format checks not included in
2899 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2900 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2902 @item -Wnonnull @r{(C and Objective-C only)}
2904 @opindex Wno-nonnull
2905 Warn about passing a null pointer for arguments marked as
2906 requiring a non-null value by the @code{nonnull} function attribute.
2908 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2909 can be disabled with the @option{-Wno-nonnull} option.
2911 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2913 @opindex Wno-init-self
2914 Warn about uninitialized variables which are initialized with themselves.
2915 Note this option can only be used with the @option{-Wuninitialized} option.
2917 For example, GCC will warn about @code{i} being uninitialized in the
2918 following snippet only when @option{-Winit-self} has been specified:
2929 @item -Wimplicit-int @r{(C and Objective-C only)}
2930 @opindex Wimplicit-int
2931 @opindex Wno-implicit-int
2932 Warn when a declaration does not specify a type.
2933 This warning is enabled by @option{-Wall}.
2935 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2936 @opindex Wimplicit-function-declaration
2937 @opindex Wno-implicit-function-declaration
2938 Give a warning whenever a function is used before being declared. In
2939 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2940 enabled by default and it is made into an error by
2941 @option{-pedantic-errors}. This warning is also enabled by
2946 @opindex Wno-implicit
2947 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2948 This warning is enabled by @option{-Wall}.
2950 @item -Wignored-qualifiers @r{(C and C++ only)}
2951 @opindex Wignored-qualifiers
2952 @opindex Wno-ignored-qualifiers
2953 Warn if the return type of a function has a type qualifier
2954 such as @code{const}. For ISO C such a type qualifier has no effect,
2955 since the value returned by a function is not an lvalue.
2956 For C++, the warning is only emitted for scalar types or @code{void}.
2957 ISO C prohibits qualified @code{void} return types on function
2958 definitions, so such return types always receive a warning
2959 even without this option.
2961 This warning is also enabled by @option{-Wextra}.
2966 Warn if the type of @samp{main} is suspicious. @samp{main} should be
2967 a function with external linkage, returning int, taking either zero
2968 arguments, two, or three arguments of appropriate types. This warning
2969 is enabled by default in C++ and is enabled by either @option{-Wall}
2970 or @option{-pedantic}.
2972 @item -Wmissing-braces
2973 @opindex Wmissing-braces
2974 @opindex Wno-missing-braces
2975 Warn if an aggregate or union initializer is not fully bracketed. In
2976 the following example, the initializer for @samp{a} is not fully
2977 bracketed, but that for @samp{b} is fully bracketed.
2980 int a[2][2] = @{ 0, 1, 2, 3 @};
2981 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2984 This warning is enabled by @option{-Wall}.
2986 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2987 @opindex Wmissing-include-dirs
2988 @opindex Wno-missing-include-dirs
2989 Warn if a user-supplied include directory does not exist.
2992 @opindex Wparentheses
2993 @opindex Wno-parentheses
2994 Warn if parentheses are omitted in certain contexts, such
2995 as when there is an assignment in a context where a truth value
2996 is expected, or when operators are nested whose precedence people
2997 often get confused about.
2999 Also warn if a comparison like @samp{x<=y<=z} appears; this is
3000 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
3001 interpretation from that of ordinary mathematical notation.
3003 Also warn about constructions where there may be confusion to which
3004 @code{if} statement an @code{else} branch belongs. Here is an example of
3019 In C/C++, every @code{else} branch belongs to the innermost possible
3020 @code{if} statement, which in this example is @code{if (b)}. This is
3021 often not what the programmer expected, as illustrated in the above
3022 example by indentation the programmer chose. When there is the
3023 potential for this confusion, GCC will issue a warning when this flag
3024 is specified. To eliminate the warning, add explicit braces around
3025 the innermost @code{if} statement so there is no way the @code{else}
3026 could belong to the enclosing @code{if}. The resulting code would
3043 This warning is enabled by @option{-Wall}.
3045 @item -Wsequence-point
3046 @opindex Wsequence-point
3047 @opindex Wno-sequence-point
3048 Warn about code that may have undefined semantics because of violations
3049 of sequence point rules in the C and C++ standards.
3051 The C and C++ standards defines the order in which expressions in a C/C++
3052 program are evaluated in terms of @dfn{sequence points}, which represent
3053 a partial ordering between the execution of parts of the program: those
3054 executed before the sequence point, and those executed after it. These
3055 occur after the evaluation of a full expression (one which is not part
3056 of a larger expression), after the evaluation of the first operand of a
3057 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3058 function is called (but after the evaluation of its arguments and the
3059 expression denoting the called function), and in certain other places.
3060 Other than as expressed by the sequence point rules, the order of
3061 evaluation of subexpressions of an expression is not specified. All
3062 these rules describe only a partial order rather than a total order,
3063 since, for example, if two functions are called within one expression
3064 with no sequence point between them, the order in which the functions
3065 are called is not specified. However, the standards committee have
3066 ruled that function calls do not overlap.
3068 It is not specified when between sequence points modifications to the
3069 values of objects take effect. Programs whose behavior depends on this
3070 have undefined behavior; the C and C++ standards specify that ``Between
3071 the previous and next sequence point an object shall have its stored
3072 value modified at most once by the evaluation of an expression.
3073 Furthermore, the prior value shall be read only to determine the value
3074 to be stored.''. If a program breaks these rules, the results on any
3075 particular implementation are entirely unpredictable.
3077 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3078 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3079 diagnosed by this option, and it may give an occasional false positive
3080 result, but in general it has been found fairly effective at detecting
3081 this sort of problem in programs.
3083 The standard is worded confusingly, therefore there is some debate
3084 over the precise meaning of the sequence point rules in subtle cases.
3085 Links to discussions of the problem, including proposed formal
3086 definitions, may be found on the GCC readings page, at
3087 @w{@uref{http://gcc.gnu.org/readings.html}}.
3089 This warning is enabled by @option{-Wall} for C and C++.
3092 @opindex Wreturn-type
3093 @opindex Wno-return-type
3094 Warn whenever a function is defined with a return-type that defaults
3095 to @code{int}. Also warn about any @code{return} statement with no
3096 return-value in a function whose return-type is not @code{void}
3097 (falling off the end of the function body is considered returning
3098 without a value), and about a @code{return} statement with a
3099 expression in a function whose return-type is @code{void}.
3101 For C++, a function without return type always produces a diagnostic
3102 message, even when @option{-Wno-return-type} is specified. The only
3103 exceptions are @samp{main} and functions defined in system headers.
3105 This warning is enabled by @option{-Wall}.
3110 Warn whenever a @code{switch} statement has an index of enumerated type
3111 and lacks a @code{case} for one or more of the named codes of that
3112 enumeration. (The presence of a @code{default} label prevents this
3113 warning.) @code{case} labels outside the enumeration range also
3114 provoke warnings when this option is used.
3115 This warning is enabled by @option{-Wall}.
3117 @item -Wswitch-default
3118 @opindex Wswitch-default
3119 @opindex Wno-switch-default
3120 Warn whenever a @code{switch} statement does not have a @code{default}
3124 @opindex Wswitch-enum
3125 @opindex Wno-switch-enum
3126 Warn whenever a @code{switch} statement has an index of enumerated type
3127 and lacks a @code{case} for one or more of the named codes of that
3128 enumeration. @code{case} labels outside the enumeration range also
3129 provoke warnings when this option is used.
3133 @opindex Wno-sync-nand
3134 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
3135 built-in functions are used. These functions changed semantics in GCC 4.4.
3139 @opindex Wno-trigraphs
3140 Warn if any trigraphs are encountered that might change the meaning of
3141 the program (trigraphs within comments are not warned about).
3142 This warning is enabled by @option{-Wall}.
3144 @item -Wunused-function
3145 @opindex Wunused-function
3146 @opindex Wno-unused-function
3147 Warn whenever a static function is declared but not defined or a
3148 non-inline static function is unused.
3149 This warning is enabled by @option{-Wall}.
3151 @item -Wunused-label
3152 @opindex Wunused-label
3153 @opindex Wno-unused-label
3154 Warn whenever a label is declared but not used.
3155 This warning is enabled by @option{-Wall}.
3157 To suppress this warning use the @samp{unused} attribute
3158 (@pxref{Variable Attributes}).
3160 @item -Wunused-parameter
3161 @opindex Wunused-parameter
3162 @opindex Wno-unused-parameter
3163 Warn whenever a function parameter is unused aside from its declaration.
3165 To suppress this warning use the @samp{unused} attribute
3166 (@pxref{Variable Attributes}).
3168 @item -Wunused-variable
3169 @opindex Wunused-variable
3170 @opindex Wno-unused-variable
3171 Warn whenever a local variable or non-constant static variable is unused
3172 aside from its declaration.
3173 This warning is enabled by @option{-Wall}.
3175 To suppress this warning use the @samp{unused} attribute
3176 (@pxref{Variable Attributes}).
3178 @item -Wunused-value
3179 @opindex Wunused-value
3180 @opindex Wno-unused-value
3181 Warn whenever a statement computes a result that is explicitly not
3182 used. To suppress this warning cast the unused expression to
3183 @samp{void}. This includes an expression-statement or the left-hand
3184 side of a comma expression that contains no side effects. For example,
3185 an expression such as @samp{x[i,j]} will cause a warning, while
3186 @samp{x[(void)i,j]} will not.
3188 This warning is enabled by @option{-Wall}.
3193 All the above @option{-Wunused} options combined.
3195 In order to get a warning about an unused function parameter, you must
3196 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3197 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3199 @item -Wuninitialized
3200 @opindex Wuninitialized
3201 @opindex Wno-uninitialized
3202 Warn if an automatic variable is used without first being initialized
3203 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3204 warn if a non-static reference or non-static @samp{const} member
3205 appears in a class without constructors.
3207 If you want to warn about code which uses the uninitialized value of the
3208 variable in its own initializer, use the @option{-Winit-self} option.
3210 These warnings occur for individual uninitialized or clobbered
3211 elements of structure, union or array variables as well as for
3212 variables which are uninitialized or clobbered as a whole. They do
3213 not occur for variables or elements declared @code{volatile}. Because
3214 these warnings depend on optimization, the exact variables or elements
3215 for which there are warnings will depend on the precise optimization
3216 options and version of GCC used.
3218 Note that there may be no warning about a variable that is used only
3219 to compute a value that itself is never used, because such
3220 computations may be deleted by data flow analysis before the warnings
3223 These warnings are made optional because GCC is not smart
3224 enough to see all the reasons why the code might be correct
3225 despite appearing to have an error. Here is one example of how
3246 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3247 always initialized, but GCC doesn't know this. Here is
3248 another common case:
3253 if (change_y) save_y = y, y = new_y;
3255 if (change_y) y = save_y;
3260 This has no bug because @code{save_y} is used only if it is set.
3262 @cindex @code{longjmp} warnings
3263 This option also warns when a non-volatile automatic variable might be
3264 changed by a call to @code{longjmp}. These warnings as well are possible
3265 only in optimizing compilation.
3267 The compiler sees only the calls to @code{setjmp}. It cannot know
3268 where @code{longjmp} will be called; in fact, a signal handler could
3269 call it at any point in the code. As a result, you may get a warning
3270 even when there is in fact no problem because @code{longjmp} cannot
3271 in fact be called at the place which would cause a problem.
3273 Some spurious warnings can be avoided if you declare all the functions
3274 you use that never return as @code{noreturn}. @xref{Function
3277 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3279 @item -Wunknown-pragmas
3280 @opindex Wunknown-pragmas
3281 @opindex Wno-unknown-pragmas
3282 @cindex warning for unknown pragmas
3283 @cindex unknown pragmas, warning
3284 @cindex pragmas, warning of unknown
3285 Warn when a #pragma directive is encountered which is not understood by
3286 GCC@. If this command line option is used, warnings will even be issued
3287 for unknown pragmas in system header files. This is not the case if
3288 the warnings were only enabled by the @option{-Wall} command line option.
3291 @opindex Wno-pragmas
3293 Do not warn about misuses of pragmas, such as incorrect parameters,
3294 invalid syntax, or conflicts between pragmas. See also
3295 @samp{-Wunknown-pragmas}.
3297 @item -Wstrict-aliasing
3298 @opindex Wstrict-aliasing
3299 @opindex Wno-strict-aliasing
3300 This option is only active when @option{-fstrict-aliasing} is active.
3301 It warns about code which might break the strict aliasing rules that the
3302 compiler is using for optimization. The warning does not catch all
3303 cases, but does attempt to catch the more common pitfalls. It is
3304 included in @option{-Wall}.
3305 It is equivalent to @option{-Wstrict-aliasing=3}
3307 @item -Wstrict-aliasing=n
3308 @opindex Wstrict-aliasing=n
3309 @opindex Wno-strict-aliasing=n
3310 This option is only active when @option{-fstrict-aliasing} is active.
3311 It warns about code which might break the strict aliasing rules that the
3312 compiler is using for optimization.
3313 Higher levels correspond to higher accuracy (fewer false positives).
3314 Higher levels also correspond to more effort, similar to the way -O works.
3315 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3318 Level 1: Most aggressive, quick, least accurate.
3319 Possibly useful when higher levels
3320 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3321 false negatives. However, it has many false positives.
3322 Warns for all pointer conversions between possibly incompatible types,
3323 even if never dereferenced. Runs in the frontend only.
3325 Level 2: Aggressive, quick, not too precise.
3326 May still have many false positives (not as many as level 1 though),
3327 and few false negatives (but possibly more than level 1).
3328 Unlike level 1, it only warns when an address is taken. Warns about
3329 incomplete types. Runs in the frontend only.
3331 Level 3 (default for @option{-Wstrict-aliasing}):
3332 Should have very few false positives and few false
3333 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3334 Takes care of the common punn+dereference pattern in the frontend:
3335 @code{*(int*)&some_float}.
3336 If optimization is enabled, it also runs in the backend, where it deals
3337 with multiple statement cases using flow-sensitive points-to information.
3338 Only warns when the converted pointer is dereferenced.
3339 Does not warn about incomplete types.
3341 @item -Wstrict-overflow
3342 @itemx -Wstrict-overflow=@var{n}
3343 @opindex Wstrict-overflow
3344 @opindex Wno-strict-overflow
3345 This option is only active when @option{-fstrict-overflow} is active.
3346 It warns about cases where the compiler optimizes based on the
3347 assumption that signed overflow does not occur. Note that it does not
3348 warn about all cases where the code might overflow: it only warns
3349 about cases where the compiler implements some optimization. Thus
3350 this warning depends on the optimization level.
3352 An optimization which assumes that signed overflow does not occur is
3353 perfectly safe if the values of the variables involved are such that
3354 overflow never does, in fact, occur. Therefore this warning can
3355 easily give a false positive: a warning about code which is not
3356 actually a problem. To help focus on important issues, several
3357 warning levels are defined. No warnings are issued for the use of
3358 undefined signed overflow when estimating how many iterations a loop
3359 will require, in particular when determining whether a loop will be
3363 @item -Wstrict-overflow=1
3364 Warn about cases which are both questionable and easy to avoid. For
3365 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3366 compiler will simplify this to @code{1}. This level of
3367 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3368 are not, and must be explicitly requested.
3370 @item -Wstrict-overflow=2
3371 Also warn about other cases where a comparison is simplified to a
3372 constant. For example: @code{abs (x) >= 0}. This can only be
3373 simplified when @option{-fstrict-overflow} is in effect, because
3374 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3375 zero. @option{-Wstrict-overflow} (with no level) is the same as
3376 @option{-Wstrict-overflow=2}.
3378 @item -Wstrict-overflow=3
3379 Also warn about other cases where a comparison is simplified. For
3380 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3382 @item -Wstrict-overflow=4
3383 Also warn about other simplifications not covered by the above cases.
3384 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3386 @item -Wstrict-overflow=5
3387 Also warn about cases where the compiler reduces the magnitude of a
3388 constant involved in a comparison. For example: @code{x + 2 > y} will
3389 be simplified to @code{x + 1 >= y}. This is reported only at the
3390 highest warning level because this simplification applies to many
3391 comparisons, so this warning level will give a very large number of
3395 @item -Warray-bounds
3396 @opindex Wno-array-bounds
3397 @opindex Warray-bounds
3398 This option is only active when @option{-ftree-vrp} is active
3399 (default for -O2 and above). It warns about subscripts to arrays
3400 that are always out of bounds. This warning is enabled by @option{-Wall}.
3402 @item -Wno-div-by-zero
3403 @opindex Wno-div-by-zero
3404 @opindex Wdiv-by-zero
3405 Do not warn about compile-time integer division by zero. Floating point
3406 division by zero is not warned about, as it can be a legitimate way of
3407 obtaining infinities and NaNs.
3409 @item -Wsystem-headers
3410 @opindex Wsystem-headers
3411 @opindex Wno-system-headers
3412 @cindex warnings from system headers
3413 @cindex system headers, warnings from
3414 Print warning messages for constructs found in system header files.
3415 Warnings from system headers are normally suppressed, on the assumption
3416 that they usually do not indicate real problems and would only make the
3417 compiler output harder to read. Using this command line option tells
3418 GCC to emit warnings from system headers as if they occurred in user
3419 code. However, note that using @option{-Wall} in conjunction with this
3420 option will @emph{not} warn about unknown pragmas in system
3421 headers---for that, @option{-Wunknown-pragmas} must also be used.
3424 @opindex Wfloat-equal
3425 @opindex Wno-float-equal
3426 Warn if floating point values are used in equality comparisons.
3428 The idea behind this is that sometimes it is convenient (for the
3429 programmer) to consider floating-point values as approximations to
3430 infinitely precise real numbers. If you are doing this, then you need
3431 to compute (by analyzing the code, or in some other way) the maximum or
3432 likely maximum error that the computation introduces, and allow for it
3433 when performing comparisons (and when producing output, but that's a
3434 different problem). In particular, instead of testing for equality, you
3435 would check to see whether the two values have ranges that overlap; and
3436 this is done with the relational operators, so equality comparisons are
3439 @item -Wtraditional @r{(C and Objective-C only)}
3440 @opindex Wtraditional
3441 @opindex Wno-traditional
3442 Warn about certain constructs that behave differently in traditional and
3443 ISO C@. Also warn about ISO C constructs that have no traditional C
3444 equivalent, and/or problematic constructs which should be avoided.
3448 Macro parameters that appear within string literals in the macro body.
3449 In traditional C macro replacement takes place within string literals,
3450 but does not in ISO C@.
3453 In traditional C, some preprocessor directives did not exist.
3454 Traditional preprocessors would only consider a line to be a directive
3455 if the @samp{#} appeared in column 1 on the line. Therefore
3456 @option{-Wtraditional} warns about directives that traditional C
3457 understands but would ignore because the @samp{#} does not appear as the
3458 first character on the line. It also suggests you hide directives like
3459 @samp{#pragma} not understood by traditional C by indenting them. Some
3460 traditional implementations would not recognize @samp{#elif}, so it
3461 suggests avoiding it altogether.
3464 A function-like macro that appears without arguments.
3467 The unary plus operator.
3470 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3471 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3472 constants.) Note, these suffixes appear in macros defined in the system
3473 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3474 Use of these macros in user code might normally lead to spurious
3475 warnings, however GCC's integrated preprocessor has enough context to
3476 avoid warning in these cases.
3479 A function declared external in one block and then used after the end of
3483 A @code{switch} statement has an operand of type @code{long}.
3486 A non-@code{static} function declaration follows a @code{static} one.
3487 This construct is not accepted by some traditional C compilers.
3490 The ISO type of an integer constant has a different width or
3491 signedness from its traditional type. This warning is only issued if
3492 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3493 typically represent bit patterns, are not warned about.
3496 Usage of ISO string concatenation is detected.
3499 Initialization of automatic aggregates.
3502 Identifier conflicts with labels. Traditional C lacks a separate
3503 namespace for labels.
3506 Initialization of unions. If the initializer is zero, the warning is
3507 omitted. This is done under the assumption that the zero initializer in
3508 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3509 initializer warnings and relies on default initialization to zero in the
3513 Conversions by prototypes between fixed/floating point values and vice
3514 versa. The absence of these prototypes when compiling with traditional
3515 C would cause serious problems. This is a subset of the possible
3516 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3519 Use of ISO C style function definitions. This warning intentionally is
3520 @emph{not} issued for prototype declarations or variadic functions
3521 because these ISO C features will appear in your code when using
3522 libiberty's traditional C compatibility macros, @code{PARAMS} and
3523 @code{VPARAMS}. This warning is also bypassed for nested functions
3524 because that feature is already a GCC extension and thus not relevant to
3525 traditional C compatibility.
3528 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3529 @opindex Wtraditional-conversion
3530 @opindex Wno-traditional-conversion
3531 Warn if a prototype causes a type conversion that is different from what
3532 would happen to the same argument in the absence of a prototype. This
3533 includes conversions of fixed point to floating and vice versa, and
3534 conversions changing the width or signedness of a fixed point argument
3535 except when the same as the default promotion.
3537 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3538 @opindex Wdeclaration-after-statement
3539 @opindex Wno-declaration-after-statement
3540 Warn when a declaration is found after a statement in a block. This
3541 construct, known from C++, was introduced with ISO C99 and is by default
3542 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3543 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3548 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3550 @item -Wno-endif-labels
3551 @opindex Wno-endif-labels
3552 @opindex Wendif-labels
3553 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3558 Warn whenever a local variable shadows another local variable, parameter or
3559 global variable or whenever a built-in function is shadowed.
3561 @item -Wlarger-than=@var{len}
3562 @opindex Wlarger-than=@var{len}
3563 @opindex Wlarger-than-@var{len}
3564 Warn whenever an object of larger than @var{len} bytes is defined.
3566 @item -Wframe-larger-than=@var{len}
3567 @opindex Wframe-larger-than
3568 Warn if the size of a function frame is larger than @var{len} bytes.
3569 The computation done to determine the stack frame size is approximate
3570 and not conservative.
3571 The actual requirements may be somewhat greater than @var{len}
3572 even if you do not get a warning. In addition, any space allocated
3573 via @code{alloca}, variable-length arrays, or related constructs
3574 is not included by the compiler when determining
3575 whether or not to issue a warning.
3577 @item -Wunsafe-loop-optimizations
3578 @opindex Wunsafe-loop-optimizations
3579 @opindex Wno-unsafe-loop-optimizations
3580 Warn if the loop cannot be optimized because the compiler could not
3581 assume anything on the bounds of the loop indices. With
3582 @option{-funsafe-loop-optimizations} warn if the compiler made
3585 @item -Wno-pedantic-ms-format
3586 @opindex Wno-pedantic-ms-format
3587 @opindex Wpedantic-ms-format
3588 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3589 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3590 depending on the MS runtime, when you are using the options @option{-Wformat}
3591 and @option{-pedantic} without gnu-extensions.
3593 @item -Wpointer-arith
3594 @opindex Wpointer-arith
3595 @opindex Wno-pointer-arith
3596 Warn about anything that depends on the ``size of'' a function type or
3597 of @code{void}. GNU C assigns these types a size of 1, for
3598 convenience in calculations with @code{void *} pointers and pointers
3599 to functions. In C++, warn also when an arithmetic operation involves
3600 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3603 @opindex Wtype-limits
3604 @opindex Wno-type-limits
3605 Warn if a comparison is always true or always false due to the limited
3606 range of the data type, but do not warn for constant expressions. For
3607 example, warn if an unsigned variable is compared against zero with
3608 @samp{<} or @samp{>=}. This warning is also enabled by
3611 @item -Wbad-function-cast @r{(C and Objective-C only)}
3612 @opindex Wbad-function-cast
3613 @opindex Wno-bad-function-cast
3614 Warn whenever a function call is cast to a non-matching type.
3615 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3617 @item -Wc++-compat @r{(C and Objective-C only)}
3618 Warn about ISO C constructs that are outside of the common subset of
3619 ISO C and ISO C++, e.g.@: request for implicit conversion from
3620 @code{void *} to a pointer to non-@code{void} type.
3622 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3623 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3624 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3625 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3629 @opindex Wno-cast-qual
3630 Warn whenever a pointer is cast so as to remove a type qualifier from
3631 the target type. For example, warn if a @code{const char *} is cast
3632 to an ordinary @code{char *}.
3635 @opindex Wcast-align
3636 @opindex Wno-cast-align
3637 Warn whenever a pointer is cast such that the required alignment of the
3638 target is increased. For example, warn if a @code{char *} is cast to
3639 an @code{int *} on machines where integers can only be accessed at
3640 two- or four-byte boundaries.
3642 @item -Wwrite-strings
3643 @opindex Wwrite-strings
3644 @opindex Wno-write-strings
3645 When compiling C, give string constants the type @code{const
3646 char[@var{length}]} so that copying the address of one into a
3647 non-@code{const} @code{char *} pointer will get a warning. These
3648 warnings will help you find at compile time code that can try to write
3649 into a string constant, but only if you have been very careful about
3650 using @code{const} in declarations and prototypes. Otherwise, it will
3651 just be a nuisance. This is why we did not make @option{-Wall} request
3654 When compiling C++, warn about the deprecated conversion from string
3655 literals to @code{char *}. This warning is enabled by default for C++
3660 @opindex Wno-clobbered
3661 Warn for variables that might be changed by @samp{longjmp} or
3662 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3665 @opindex Wconversion
3666 @opindex Wno-conversion
3667 Warn for implicit conversions that may alter a value. This includes
3668 conversions between real and integer, like @code{abs (x)} when
3669 @code{x} is @code{double}; conversions between signed and unsigned,
3670 like @code{unsigned ui = -1}; and conversions to smaller types, like
3671 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3672 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3673 changed by the conversion like in @code{abs (2.0)}. Warnings about
3674 conversions between signed and unsigned integers can be disabled by
3675 using @option{-Wno-sign-conversion}.
3677 For C++, also warn for conversions between @code{NULL} and non-pointer
3678 types; confusing overload resolution for user-defined conversions; and
3679 conversions that will never use a type conversion operator:
3680 conversions to @code{void}, the same type, a base class or a reference
3681 to them. Warnings about conversions between signed and unsigned
3682 integers are disabled by default in C++ unless
3683 @option{-Wsign-conversion} is explicitly enabled.
3686 @opindex Wempty-body
3687 @opindex Wno-empty-body
3688 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3689 while} statement. This warning is also enabled by @option{-Wextra}.
3691 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3692 @opindex Wenum-compare
3693 @opindex Wno-enum-compare
3694 Warn about a comparison between values of different enum types. This
3695 warning is enabled by default.
3697 @item -Wsign-compare
3698 @opindex Wsign-compare
3699 @opindex Wno-sign-compare
3700 @cindex warning for comparison of signed and unsigned values
3701 @cindex comparison of signed and unsigned values, warning
3702 @cindex signed and unsigned values, comparison warning
3703 Warn when a comparison between signed and unsigned values could produce
3704 an incorrect result when the signed value is converted to unsigned.
3705 This warning is also enabled by @option{-Wextra}; to get the other warnings
3706 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3708 @item -Wsign-conversion
3709 @opindex Wsign-conversion
3710 @opindex Wno-sign-conversion
3711 Warn for implicit conversions that may change the sign of an integer
3712 value, like assigning a signed integer expression to an unsigned
3713 integer variable. An explicit cast silences the warning. In C, this
3714 option is enabled also by @option{-Wconversion}.
3718 @opindex Wno-address
3719 Warn about suspicious uses of memory addresses. These include using
3720 the address of a function in a conditional expression, such as
3721 @code{void func(void); if (func)}, and comparisons against the memory
3722 address of a string literal, such as @code{if (x == "abc")}. Such
3723 uses typically indicate a programmer error: the address of a function
3724 always evaluates to true, so their use in a conditional usually
3725 indicate that the programmer forgot the parentheses in a function
3726 call; and comparisons against string literals result in unspecified
3727 behavior and are not portable in C, so they usually indicate that the
3728 programmer intended to use @code{strcmp}. This warning is enabled by
3732 @opindex Wlogical-op
3733 @opindex Wno-logical-op
3734 Warn about suspicious uses of logical operators in expressions.
3735 This includes using logical operators in contexts where a
3736 bit-wise operator is likely to be expected.
3738 @item -Waggregate-return
3739 @opindex Waggregate-return
3740 @opindex Wno-aggregate-return
3741 Warn if any functions that return structures or unions are defined or
3742 called. (In languages where you can return an array, this also elicits
3745 @item -Wno-attributes
3746 @opindex Wno-attributes
3747 @opindex Wattributes
3748 Do not warn if an unexpected @code{__attribute__} is used, such as
3749 unrecognized attributes, function attributes applied to variables,
3750 etc. This will not stop errors for incorrect use of supported
3753 @item -Wno-builtin-macro-redefined
3754 @opindex Wno-builtin-macro-redefined
3755 @opindex Wbuiltin-macro-redefined
3756 Do not warn if certain built-in macros are redefined. This suppresses
3757 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
3758 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
3760 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3761 @opindex Wstrict-prototypes
3762 @opindex Wno-strict-prototypes
3763 Warn if a function is declared or defined without specifying the
3764 argument types. (An old-style function definition is permitted without
3765 a warning if preceded by a declaration which specifies the argument
3768 @item -Wold-style-declaration @r{(C and Objective-C only)}
3769 @opindex Wold-style-declaration
3770 @opindex Wno-old-style-declaration
3771 Warn for obsolescent usages, according to the C Standard, in a
3772 declaration. For example, warn if storage-class specifiers like
3773 @code{static} are not the first things in a declaration. This warning
3774 is also enabled by @option{-Wextra}.
3776 @item -Wold-style-definition @r{(C and Objective-C only)}
3777 @opindex Wold-style-definition
3778 @opindex Wno-old-style-definition
3779 Warn if an old-style function definition is used. A warning is given
3780 even if there is a previous prototype.
3782 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3783 @opindex Wmissing-parameter-type
3784 @opindex Wno-missing-parameter-type
3785 A function parameter is declared without a type specifier in K&R-style
3792 This warning is also enabled by @option{-Wextra}.
3794 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3795 @opindex Wmissing-prototypes
3796 @opindex Wno-missing-prototypes
3797 Warn if a global function is defined without a previous prototype
3798 declaration. This warning is issued even if the definition itself
3799 provides a prototype. The aim is to detect global functions that fail
3800 to be declared in header files.
3802 @item -Wmissing-declarations
3803 @opindex Wmissing-declarations
3804 @opindex Wno-missing-declarations
3805 Warn if a global function is defined without a previous declaration.
3806 Do so even if the definition itself provides a prototype.
3807 Use this option to detect global functions that are not declared in
3808 header files. In C++, no warnings are issued for function templates,
3809 or for inline functions, or for functions in anonymous namespaces.
3811 @item -Wmissing-field-initializers
3812 @opindex Wmissing-field-initializers
3813 @opindex Wno-missing-field-initializers
3817 Warn if a structure's initializer has some fields missing. For
3818 example, the following code would cause such a warning, because
3819 @code{x.h} is implicitly zero:
3822 struct s @{ int f, g, h; @};
3823 struct s x = @{ 3, 4 @};
3826 This option does not warn about designated initializers, so the following
3827 modification would not trigger a warning:
3830 struct s @{ int f, g, h; @};
3831 struct s x = @{ .f = 3, .g = 4 @};
3834 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3835 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3837 @item -Wmissing-noreturn
3838 @opindex Wmissing-noreturn
3839 @opindex Wno-missing-noreturn
3840 Warn about functions which might be candidates for attribute @code{noreturn}.
3841 Note these are only possible candidates, not absolute ones. Care should
3842 be taken to manually verify functions actually do not ever return before
3843 adding the @code{noreturn} attribute, otherwise subtle code generation
3844 bugs could be introduced. You will not get a warning for @code{main} in
3845 hosted C environments.
3847 @item -Wmissing-format-attribute
3848 @opindex Wmissing-format-attribute
3849 @opindex Wno-missing-format-attribute
3852 Warn about function pointers which might be candidates for @code{format}
3853 attributes. Note these are only possible candidates, not absolute ones.
3854 GCC will guess that function pointers with @code{format} attributes that
3855 are used in assignment, initialization, parameter passing or return
3856 statements should have a corresponding @code{format} attribute in the
3857 resulting type. I.e.@: the left-hand side of the assignment or
3858 initialization, the type of the parameter variable, or the return type
3859 of the containing function respectively should also have a @code{format}
3860 attribute to avoid the warning.
3862 GCC will also warn about function definitions which might be
3863 candidates for @code{format} attributes. Again, these are only
3864 possible candidates. GCC will guess that @code{format} attributes
3865 might be appropriate for any function that calls a function like
3866 @code{vprintf} or @code{vscanf}, but this might not always be the
3867 case, and some functions for which @code{format} attributes are
3868 appropriate may not be detected.
3870 @item -Wno-multichar
3871 @opindex Wno-multichar
3873 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3874 Usually they indicate a typo in the user's code, as they have
3875 implementation-defined values, and should not be used in portable code.
3877 @item -Wnormalized=<none|id|nfc|nfkc>
3878 @opindex Wnormalized=
3881 @cindex character set, input normalization
3882 In ISO C and ISO C++, two identifiers are different if they are
3883 different sequences of characters. However, sometimes when characters
3884 outside the basic ASCII character set are used, you can have two
3885 different character sequences that look the same. To avoid confusion,
3886 the ISO 10646 standard sets out some @dfn{normalization rules} which
3887 when applied ensure that two sequences that look the same are turned into
3888 the same sequence. GCC can warn you if you are using identifiers which
3889 have not been normalized; this option controls that warning.
3891 There are four levels of warning that GCC supports. The default is
3892 @option{-Wnormalized=nfc}, which warns about any identifier which is
3893 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3894 recommended form for most uses.
3896 Unfortunately, there are some characters which ISO C and ISO C++ allow
3897 in identifiers that when turned into NFC aren't allowable as
3898 identifiers. That is, there's no way to use these symbols in portable
3899 ISO C or C++ and have all your identifiers in NFC@.
3900 @option{-Wnormalized=id} suppresses the warning for these characters.
3901 It is hoped that future versions of the standards involved will correct
3902 this, which is why this option is not the default.
3904 You can switch the warning off for all characters by writing
3905 @option{-Wnormalized=none}. You would only want to do this if you
3906 were using some other normalization scheme (like ``D''), because
3907 otherwise you can easily create bugs that are literally impossible to see.
3909 Some characters in ISO 10646 have distinct meanings but look identical
3910 in some fonts or display methodologies, especially once formatting has
3911 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3912 LETTER N'', will display just like a regular @code{n} which has been
3913 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3914 normalization scheme to convert all these into a standard form as
3915 well, and GCC will warn if your code is not in NFKC if you use
3916 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3917 about every identifier that contains the letter O because it might be
3918 confused with the digit 0, and so is not the default, but may be
3919 useful as a local coding convention if the programming environment is
3920 unable to be fixed to display these characters distinctly.
3922 @item -Wno-deprecated
3923 @opindex Wno-deprecated
3924 @opindex Wdeprecated
3925 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3927 @item -Wno-deprecated-declarations
3928 @opindex Wno-deprecated-declarations
3929 @opindex Wdeprecated-declarations
3930 Do not warn about uses of functions (@pxref{Function Attributes}),
3931 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3932 Attributes}) marked as deprecated by using the @code{deprecated}
3936 @opindex Wno-overflow
3938 Do not warn about compile-time overflow in constant expressions.
3940 @item -Woverride-init @r{(C and Objective-C only)}
3941 @opindex Woverride-init
3942 @opindex Wno-override-init
3946 Warn if an initialized field without side effects is overridden when
3947 using designated initializers (@pxref{Designated Inits, , Designated
3950 This warning is included in @option{-Wextra}. To get other
3951 @option{-Wextra} warnings without this one, use @samp{-Wextra
3952 -Wno-override-init}.
3957 Warn if a structure is given the packed attribute, but the packed
3958 attribute has no effect on the layout or size of the structure.
3959 Such structures may be mis-aligned for little benefit. For
3960 instance, in this code, the variable @code{f.x} in @code{struct bar}
3961 will be misaligned even though @code{struct bar} does not itself
3962 have the packed attribute:
3969 @} __attribute__((packed));
3980 Warn if padding is included in a structure, either to align an element
3981 of the structure or to align the whole structure. Sometimes when this
3982 happens it is possible to rearrange the fields of the structure to
3983 reduce the padding and so make the structure smaller.
3985 @item -Wredundant-decls
3986 @opindex Wredundant-decls
3987 @opindex Wno-redundant-decls
3988 Warn if anything is declared more than once in the same scope, even in
3989 cases where multiple declaration is valid and changes nothing.
3991 @item -Wnested-externs @r{(C and Objective-C only)}
3992 @opindex Wnested-externs
3993 @opindex Wno-nested-externs
3994 Warn if an @code{extern} declaration is encountered within a function.
3996 @item -Wunreachable-code
3997 @opindex Wunreachable-code
3998 @opindex Wno-unreachable-code
3999 Warn if the compiler detects that code will never be executed.
4001 This option is intended to warn when the compiler detects that at
4002 least a whole line of source code will never be executed, because
4003 some condition is never satisfied or because it is after a
4004 procedure that never returns.
4006 It is possible for this option to produce a warning even though there
4007 are circumstances under which part of the affected line can be executed,
4008 so care should be taken when removing apparently-unreachable code.
4010 For instance, when a function is inlined, a warning may mean that the
4011 line is unreachable in only one inlined copy of the function.
4013 This option is not made part of @option{-Wall} because in a debugging
4014 version of a program there is often substantial code which checks
4015 correct functioning of the program and is, hopefully, unreachable
4016 because the program does work. Another common use of unreachable
4017 code is to provide behavior which is selectable at compile-time.
4022 Warn if a function can not be inlined and it was declared as inline.
4023 Even with this option, the compiler will not warn about failures to
4024 inline functions declared in system headers.
4026 The compiler uses a variety of heuristics to determine whether or not
4027 to inline a function. For example, the compiler takes into account
4028 the size of the function being inlined and the amount of inlining
4029 that has already been done in the current function. Therefore,
4030 seemingly insignificant changes in the source program can cause the
4031 warnings produced by @option{-Winline} to appear or disappear.
4033 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4034 @opindex Wno-invalid-offsetof
4035 @opindex Winvalid-offsetof
4036 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4037 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4038 to a non-POD type is undefined. In existing C++ implementations,
4039 however, @samp{offsetof} typically gives meaningful results even when
4040 applied to certain kinds of non-POD types. (Such as a simple
4041 @samp{struct} that fails to be a POD type only by virtue of having a
4042 constructor.) This flag is for users who are aware that they are
4043 writing nonportable code and who have deliberately chosen to ignore the
4046 The restrictions on @samp{offsetof} may be relaxed in a future version
4047 of the C++ standard.
4049 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4050 @opindex Wno-int-to-pointer-cast
4051 @opindex Wint-to-pointer-cast
4052 Suppress warnings from casts to pointer type of an integer of a
4055 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4056 @opindex Wno-pointer-to-int-cast
4057 @opindex Wpointer-to-int-cast
4058 Suppress warnings from casts from a pointer to an integer type of a
4062 @opindex Winvalid-pch
4063 @opindex Wno-invalid-pch
4064 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4065 the search path but can't be used.
4069 @opindex Wno-long-long
4070 Warn if @samp{long long} type is used. This is default. To inhibit
4071 the warning messages, use @option{-Wno-long-long}. Flags
4072 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4073 only when @option{-pedantic} flag is used.
4075 @item -Wvariadic-macros
4076 @opindex Wvariadic-macros
4077 @opindex Wno-variadic-macros
4078 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4079 alternate syntax when in pedantic ISO C99 mode. This is default.
4080 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4085 Warn if variable length array is used in the code.
4086 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4087 the variable length array.
4089 @item -Wvolatile-register-var
4090 @opindex Wvolatile-register-var
4091 @opindex Wno-volatile-register-var
4092 Warn if a register variable is declared volatile. The volatile
4093 modifier does not inhibit all optimizations that may eliminate reads
4094 and/or writes to register variables. This warning is enabled by
4097 @item -Wdisabled-optimization
4098 @opindex Wdisabled-optimization
4099 @opindex Wno-disabled-optimization
4100 Warn if a requested optimization pass is disabled. This warning does
4101 not generally indicate that there is anything wrong with your code; it
4102 merely indicates that GCC's optimizers were unable to handle the code
4103 effectively. Often, the problem is that your code is too big or too
4104 complex; GCC will refuse to optimize programs when the optimization
4105 itself is likely to take inordinate amounts of time.
4107 @item -Wpointer-sign @r{(C and Objective-C only)}
4108 @opindex Wpointer-sign
4109 @opindex Wno-pointer-sign
4110 Warn for pointer argument passing or assignment with different signedness.
4111 This option is only supported for C and Objective-C@. It is implied by
4112 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4113 @option{-Wno-pointer-sign}.
4115 @item -Wstack-protector
4116 @opindex Wstack-protector
4117 @opindex Wno-stack-protector
4118 This option is only active when @option{-fstack-protector} is active. It
4119 warns about functions that will not be protected against stack smashing.
4122 @opindex Wno-mudflap
4123 Suppress warnings about constructs that cannot be instrumented by
4126 @item -Woverlength-strings
4127 @opindex Woverlength-strings
4128 @opindex Wno-overlength-strings
4129 Warn about string constants which are longer than the ``minimum
4130 maximum'' length specified in the C standard. Modern compilers
4131 generally allow string constants which are much longer than the
4132 standard's minimum limit, but very portable programs should avoid
4133 using longer strings.
4135 The limit applies @emph{after} string constant concatenation, and does
4136 not count the trailing NUL@. In C89, the limit was 509 characters; in
4137 C99, it was raised to 4095. C++98 does not specify a normative
4138 minimum maximum, so we do not diagnose overlength strings in C++@.
4140 This option is implied by @option{-pedantic}, and can be disabled with
4141 @option{-Wno-overlength-strings}.
4143 @item -Wdisallowed-function-list=@var{sym},@var{sym},@dots{}
4144 @opindex Wdisallowed-function-list
4146 If any of @var{sym} is called, GCC will issue a warning. This can be useful
4147 in enforcing coding conventions that ban calls to certain functions, for
4148 example, @code{alloca}, @code{malloc}, etc.
4151 @node Debugging Options
4152 @section Options for Debugging Your Program or GCC
4153 @cindex options, debugging
4154 @cindex debugging information options
4156 GCC has various special options that are used for debugging
4157 either your program or GCC:
4162 Produce debugging information in the operating system's native format
4163 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4166 On most systems that use stabs format, @option{-g} enables use of extra
4167 debugging information that only GDB can use; this extra information
4168 makes debugging work better in GDB but will probably make other debuggers
4170 refuse to read the program. If you want to control for certain whether
4171 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4172 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4174 GCC allows you to use @option{-g} with
4175 @option{-O}. The shortcuts taken by optimized code may occasionally
4176 produce surprising results: some variables you declared may not exist
4177 at all; flow of control may briefly move where you did not expect it;
4178 some statements may not be executed because they compute constant
4179 results or their values were already at hand; some statements may
4180 execute in different places because they were moved out of loops.
4182 Nevertheless it proves possible to debug optimized output. This makes
4183 it reasonable to use the optimizer for programs that might have bugs.
4185 The following options are useful when GCC is generated with the
4186 capability for more than one debugging format.
4190 Produce debugging information for use by GDB@. This means to use the
4191 most expressive format available (DWARF 2, stabs, or the native format
4192 if neither of those are supported), including GDB extensions if at all
4197 Produce debugging information in stabs format (if that is supported),
4198 without GDB extensions. This is the format used by DBX on most BSD
4199 systems. On MIPS, Alpha and System V Release 4 systems this option
4200 produces stabs debugging output which is not understood by DBX or SDB@.
4201 On System V Release 4 systems this option requires the GNU assembler.
4203 @item -feliminate-unused-debug-symbols
4204 @opindex feliminate-unused-debug-symbols
4205 Produce debugging information in stabs format (if that is supported),
4206 for only symbols that are actually used.
4208 @item -femit-class-debug-always
4209 Instead of emitting debugging information for a C++ class in only one
4210 object file, emit it in all object files using the class. This option
4211 should be used only with debuggers that are unable to handle the way GCC
4212 normally emits debugging information for classes because using this
4213 option will increase the size of debugging information by as much as a
4218 Produce debugging information in stabs format (if that is supported),
4219 using GNU extensions understood only by the GNU debugger (GDB)@. The
4220 use of these extensions is likely to make other debuggers crash or
4221 refuse to read the program.
4225 Produce debugging information in COFF format (if that is supported).
4226 This is the format used by SDB on most System V systems prior to
4231 Produce debugging information in XCOFF format (if that is supported).
4232 This is the format used by the DBX debugger on IBM RS/6000 systems.
4236 Produce debugging information in XCOFF format (if that is supported),
4237 using GNU extensions understood only by the GNU debugger (GDB)@. The
4238 use of these extensions is likely to make other debuggers crash or
4239 refuse to read the program, and may cause assemblers other than the GNU
4240 assembler (GAS) to fail with an error.
4244 Produce debugging information in DWARF version 2 format (if that is
4245 supported). This is the format used by DBX on IRIX 6. With this
4246 option, GCC uses features of DWARF version 3 when they are useful;
4247 version 3 is upward compatible with version 2, but may still cause
4248 problems for older debuggers.
4252 Produce debugging information in VMS debug format (if that is
4253 supported). This is the format used by DEBUG on VMS systems.
4256 @itemx -ggdb@var{level}
4257 @itemx -gstabs@var{level}
4258 @itemx -gcoff@var{level}
4259 @itemx -gxcoff@var{level}
4260 @itemx -gvms@var{level}
4261 Request debugging information and also use @var{level} to specify how
4262 much information. The default level is 2.
4264 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4267 Level 1 produces minimal information, enough for making backtraces in
4268 parts of the program that you don't plan to debug. This includes
4269 descriptions of functions and external variables, but no information
4270 about local variables and no line numbers.
4272 Level 3 includes extra information, such as all the macro definitions
4273 present in the program. Some debuggers support macro expansion when
4274 you use @option{-g3}.
4276 @option{-gdwarf-2} does not accept a concatenated debug level, because
4277 GCC used to support an option @option{-gdwarf} that meant to generate
4278 debug information in version 1 of the DWARF format (which is very
4279 different from version 2), and it would have been too confusing. That
4280 debug format is long obsolete, but the option cannot be changed now.
4281 Instead use an additional @option{-g@var{level}} option to change the
4282 debug level for DWARF2.
4284 @item -feliminate-dwarf2-dups
4285 @opindex feliminate-dwarf2-dups
4286 Compress DWARF2 debugging information by eliminating duplicated
4287 information about each symbol. This option only makes sense when
4288 generating DWARF2 debugging information with @option{-gdwarf-2}.
4290 @item -femit-struct-debug-baseonly
4291 Emit debug information for struct-like types
4292 only when the base name of the compilation source file
4293 matches the base name of file in which the struct was defined.
4295 This option substantially reduces the size of debugging information,
4296 but at significant potential loss in type information to the debugger.
4297 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4298 See @option{-femit-struct-debug-detailed} for more detailed control.
4300 This option works only with DWARF 2.
4302 @item -femit-struct-debug-reduced
4303 Emit debug information for struct-like types
4304 only when the base name of the compilation source file
4305 matches the base name of file in which the type was defined,
4306 unless the struct is a template or defined in a system header.
4308 This option significantly reduces the size of debugging information,
4309 with some potential loss in type information to the debugger.
4310 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4311 See @option{-femit-struct-debug-detailed} for more detailed control.
4313 This option works only with DWARF 2.
4315 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4316 Specify the struct-like types
4317 for which the compiler will generate debug information.
4318 The intent is to reduce duplicate struct debug information
4319 between different object files within the same program.
4321 This option is a detailed version of
4322 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4323 which will serve for most needs.
4325 A specification has the syntax
4326 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4328 The optional first word limits the specification to
4329 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4330 A struct type is used directly when it is the type of a variable, member.
4331 Indirect uses arise through pointers to structs.
4332 That is, when use of an incomplete struct would be legal, the use is indirect.
4334 @samp{struct one direct; struct two * indirect;}.
4336 The optional second word limits the specification to
4337 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4338 Generic structs are a bit complicated to explain.
4339 For C++, these are non-explicit specializations of template classes,
4340 or non-template classes within the above.
4341 Other programming languages have generics,
4342 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4344 The third word specifies the source files for those
4345 structs for which the compiler will emit debug information.
4346 The values @samp{none} and @samp{any} have the normal meaning.
4347 The value @samp{base} means that
4348 the base of name of the file in which the type declaration appears
4349 must match the base of the name of the main compilation file.
4350 In practice, this means that
4351 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4352 but types declared in other header will not.
4353 The value @samp{sys} means those types satisfying @samp{base}
4354 or declared in system or compiler headers.
4356 You may need to experiment to determine the best settings for your application.
4358 The default is @samp{-femit-struct-debug-detailed=all}.
4360 This option works only with DWARF 2.
4362 @item -fno-merge-debug-strings
4363 @opindex fmerge-debug-strings
4364 @opindex fno-merge-debug-strings
4365 Direct the linker to merge together strings which are identical in
4366 different object files. This is not supported by all assemblers or
4367 linker. This decreases the size of the debug information in the
4368 output file at the cost of increasing link processing time. This is
4371 @item -fdebug-prefix-map=@var{old}=@var{new}
4372 @opindex fdebug-prefix-map
4373 When compiling files in directory @file{@var{old}}, record debugging
4374 information describing them as in @file{@var{new}} instead.
4376 @item -fno-dwarf2-cfi-asm
4377 @opindex fdwarf2-cfi-asm
4378 @opindex fno-dwarf2-cfi-asm
4379 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4380 instead of using GAS @code{.cfi_*} directives.
4382 @cindex @command{prof}
4385 Generate extra code to write profile information suitable for the
4386 analysis program @command{prof}. You must use this option when compiling
4387 the source files you want data about, and you must also use it when
4390 @cindex @command{gprof}
4393 Generate extra code to write profile information suitable for the
4394 analysis program @command{gprof}. You must use this option when compiling
4395 the source files you want data about, and you must also use it when
4400 Makes the compiler print out each function name as it is compiled, and
4401 print some statistics about each pass when it finishes.
4404 @opindex ftime-report
4405 Makes the compiler print some statistics about the time consumed by each
4406 pass when it finishes.
4409 @opindex fmem-report
4410 Makes the compiler print some statistics about permanent memory
4411 allocation when it finishes.
4413 @item -fpre-ipa-mem-report
4414 @opindex fpre-ipa-mem-report
4415 @item -fpost-ipa-mem-report
4416 @opindex fpost-ipa-mem-report
4417 Makes the compiler print some statistics about permanent memory
4418 allocation before or after interprocedural optimization.
4420 @item -fprofile-arcs
4421 @opindex fprofile-arcs
4422 Add code so that program flow @dfn{arcs} are instrumented. During
4423 execution the program records how many times each branch and call is
4424 executed and how many times it is taken or returns. When the compiled
4425 program exits it saves this data to a file called
4426 @file{@var{auxname}.gcda} for each source file. The data may be used for
4427 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4428 test coverage analysis (@option{-ftest-coverage}). Each object file's
4429 @var{auxname} is generated from the name of the output file, if
4430 explicitly specified and it is not the final executable, otherwise it is
4431 the basename of the source file. In both cases any suffix is removed
4432 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4433 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4434 @xref{Cross-profiling}.
4436 @cindex @command{gcov}
4440 This option is used to compile and link code instrumented for coverage
4441 analysis. The option is a synonym for @option{-fprofile-arcs}
4442 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4443 linking). See the documentation for those options for more details.
4448 Compile the source files with @option{-fprofile-arcs} plus optimization
4449 and code generation options. For test coverage analysis, use the
4450 additional @option{-ftest-coverage} option. You do not need to profile
4451 every source file in a program.
4454 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4455 (the latter implies the former).
4458 Run the program on a representative workload to generate the arc profile
4459 information. This may be repeated any number of times. You can run
4460 concurrent instances of your program, and provided that the file system
4461 supports locking, the data files will be correctly updated. Also
4462 @code{fork} calls are detected and correctly handled (double counting
4466 For profile-directed optimizations, compile the source files again with
4467 the same optimization and code generation options plus
4468 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4469 Control Optimization}).
4472 For test coverage analysis, use @command{gcov} to produce human readable
4473 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4474 @command{gcov} documentation for further information.
4478 With @option{-fprofile-arcs}, for each function of your program GCC
4479 creates a program flow graph, then finds a spanning tree for the graph.
4480 Only arcs that are not on the spanning tree have to be instrumented: the
4481 compiler adds code to count the number of times that these arcs are
4482 executed. When an arc is the only exit or only entrance to a block, the
4483 instrumentation code can be added to the block; otherwise, a new basic
4484 block must be created to hold the instrumentation code.
4487 @item -ftest-coverage
4488 @opindex ftest-coverage
4489 Produce a notes file that the @command{gcov} code-coverage utility
4490 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4491 show program coverage. Each source file's note file is called
4492 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4493 above for a description of @var{auxname} and instructions on how to
4494 generate test coverage data. Coverage data will match the source files
4495 more closely, if you do not optimize.
4497 @item -fdbg-cnt-list
4498 @opindex fdbg-cnt-list
4499 Print the name and the counter upperbound for all debug counters.
4501 @item -fdbg-cnt=@var{counter-value-list}
4503 Set the internal debug counter upperbound. @var{counter-value-list}
4504 is a comma-separated list of @var{name}:@var{value} pairs
4505 which sets the upperbound of each debug counter @var{name} to @var{value}.
4506 All debug counters have the initial upperbound of @var{UINT_MAX},
4507 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4508 e.g. With -fdbg-cnt=dce:10,tail_call:0
4509 dbg_cnt(dce) will return true only for first 10 invocations
4510 and dbg_cnt(tail_call) will return false always.
4512 @item -d@var{letters}
4513 @itemx -fdump-rtl-@var{pass}
4515 Says to make debugging dumps during compilation at times specified by
4516 @var{letters}. This is used for debugging the RTL-based passes of the
4517 compiler. The file names for most of the dumps are made by appending a
4518 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4519 from the name of the output file, if explicitly specified and it is not
4520 an executable, otherwise it is the basename of the source file. These
4521 switches may have different effects when @option{-E} is used for
4524 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
4525 @option{-d} option @var{letters}. Here are the possible
4526 letters for use in @var{letters} and @var{pass}, and their meanings:
4531 Annotate the assembler output with miscellaneous debugging information.
4533 @item -fdump-rtl-bbro
4534 @opindex fdump-rtl-bbro
4535 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4537 @item -fdump-rtl-combine
4538 @opindex fdump-rtl-combine
4539 Dump after the RTL instruction combination pass, to the file
4540 @file{@var{file}.129r.combine}.
4542 @item -fdump-rtl-ce1
4543 @itemx -fdump-rtl-ce2
4544 @opindex fdump-rtl-ce1
4545 @opindex fdump-rtl-ce2
4546 @option{-fdump-rtl-ce1} enable dumping after the
4547 first if conversion, to the file @file{@var{file}.117r.ce1}.
4548 @option{-fdump-rtl-ce2} enable dumping after the second if
4549 conversion, to the file @file{@var{file}.130r.ce2}.
4551 @item -fdump-rtl-btl
4552 @itemx -fdump-rtl-dbr
4553 @opindex fdump-rtl-btl
4554 @opindex fdump-rtl-dbr
4555 @option{-fdump-rtl-btl} enable dumping after branch
4556 target load optimization, to @file{@var{file}.31.btl}.
4557 @option{-fdump-rtl-dbr} enable dumping after delayed branch
4558 scheduling, to @file{@var{file}.36.dbr}.
4562 Dump all macro definitions, at the end of preprocessing, in addition to
4565 @item -fdump-rtl-ce3
4566 @opindex fdump-rtl-ce3
4567 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4569 @item -fdump-rtl-cfg
4570 @itemx -fdump-rtl-life
4571 @opindex fdump-rtl-cfg
4572 @opindex fdump-rtl-life
4573 @option{-fdump-rtl-cfg} enable dumping after control
4574 and data flow analysis, to @file{@var{file}.116r.cfg}.
4575 @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4576 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4578 @item -fdump-rtl-greg
4579 @opindex fdump-rtl-greg
4580 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4582 @item -fdump-rtl-gcse
4583 @itemx -fdump-rtl-bypass
4584 @opindex fdump-rtl-gcse
4585 @opindex fdump-rtl-bypass
4586 @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4587 @file{@var{file}.114r.gcse}. @option{-fdump-rtl-bypass}
4588 enable dumping after jump bypassing and control flow optimizations, to
4589 @file{@var{file}.115r.bypass}.
4592 @opindex fdump-rtl-eh
4593 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4595 @item -fdump-rtl-sibling
4596 @opindex fdump-rtl-sibling
4597 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4599 @item -fdump-rtl-jump
4600 @opindex fdump-rtl-jump
4601 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4603 @item -fdump-rtl-stack
4604 @opindex fdump-rtl-stack
4605 Dump after conversion from GCC's "flat register file" registers to the
4606 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4608 @item -fdump-rtl-lreg
4609 @opindex fdump-rtl-lreg
4610 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4612 @item -fdump-rtl-loop2
4613 @opindex fdump-rtl-loop2
4614 @option{-fdump-rtl-loop2} enables dumping after the
4615 loop optimization pass, to @file{@var{file}.119r.loop2},
4616 @file{@var{file}.120r.loop2_init},
4617 @file{@var{file}.121r.loop2_invariant}, and
4618 @file{@var{file}.125r.loop2_done}.
4620 @item -fdump-rtl-sms
4621 @opindex fdump-rtl-sms
4622 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4624 @item -fdump-rtl-mach
4625 @opindex fdump-rtl-mach
4626 Dump after performing the machine dependent reorganization pass, to
4627 @file{@var{file}.155r.mach} if that pass exists.
4629 @item -fdump-rtl-rnreg
4630 @opindex fdump-rtl-rnreg
4631 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4633 @item -fdump-rtl-regmove
4634 @opindex fdump-rtl-regmove
4635 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4637 @item -fdump-rtl-postreload
4638 @opindex fdump-rtl-postreload
4639 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4641 @item -fdump-rtl-expand
4642 @opindex fdump-rtl-expand
4643 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4645 @item -fdump-rtl-sched2
4646 @opindex fdump-rtl-sched2
4647 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4649 @item -fdump-rtl-cse
4650 @opindex fdump-rtl-cse
4651 Dump after CSE (including the jump optimization that sometimes follows
4652 CSE), to @file{@var{file}.113r.cse}.
4654 @item -fdump-rtl-sched1
4655 @opindex fdump-rtl-sched1
4656 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4658 @item -fdump-rtl-cse2
4659 @opindex fdump-rtl-cse2
4660 Dump after the second CSE pass (including the jump optimization that
4661 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4663 @item -fdump-rtl-tracer
4664 @opindex fdump-rtl-tracer
4665 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4667 @item -fdump-rtl-vpt
4668 @itemx -fdump-rtl-vartrack
4669 @opindex fdump-rtl-vpt
4670 @opindex fdump-rtl-vartrack
4671 @option{-fdump-rtl-vpt} enable dumping after the value
4672 profile transformations, to @file{@var{file}.10.vpt}.
4673 @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4674 to @file{@var{file}.154r.vartrack}.
4676 @item -fdump-rtl-flow2
4677 @opindex fdump-rtl-flow2
4678 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4680 @item -fdump-rtl-peephole2
4681 @opindex fdump-rtl-peephole2
4682 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4684 @item -fdump-rtl-web
4685 @opindex fdump-rtl-web
4686 Dump after live range splitting, to @file{@var{file}.126r.web}.
4688 @item -fdump-rtl-all
4689 @opindex fdump-rtl-all
4690 Produce all the dumps listed above.
4694 Produce a core dump whenever an error occurs.
4698 Print statistics on memory usage, at the end of the run, to
4703 Annotate the assembler output with a comment indicating which
4704 pattern and alternative was used. The length of each instruction is
4709 Dump the RTL in the assembler output as a comment before each instruction.
4710 Also turns on @option{-dp} annotation.
4714 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
4715 dump a representation of the control flow graph suitable for viewing with VCG
4716 to @file{@var{file}.@var{pass}.vcg}.
4720 Just generate RTL for a function instead of compiling it. Usually used
4721 with @option{-fdump-rtl-expand}.
4725 Dump debugging information during parsing, to standard error.
4729 @opindex fdump-noaddr
4730 When doing debugging dumps, suppress address output. This makes it more
4731 feasible to use diff on debugging dumps for compiler invocations with
4732 different compiler binaries and/or different
4733 text / bss / data / heap / stack / dso start locations.
4735 @item -fdump-unnumbered
4736 @opindex fdump-unnumbered
4737 When doing debugging dumps, suppress instruction numbers and address output.
4738 This makes it more feasible to use diff on debugging dumps for compiler
4739 invocations with different options, in particular with and without
4742 @item -fdump-translation-unit @r{(C++ only)}
4743 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4744 @opindex fdump-translation-unit
4745 Dump a representation of the tree structure for the entire translation
4746 unit to a file. The file name is made by appending @file{.tu} to the
4747 source file name. If the @samp{-@var{options}} form is used, @var{options}
4748 controls the details of the dump as described for the
4749 @option{-fdump-tree} options.
4751 @item -fdump-class-hierarchy @r{(C++ only)}
4752 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4753 @opindex fdump-class-hierarchy
4754 Dump a representation of each class's hierarchy and virtual function
4755 table layout to a file. The file name is made by appending @file{.class}
4756 to the source file name. If the @samp{-@var{options}} form is used,
4757 @var{options} controls the details of the dump as described for the
4758 @option{-fdump-tree} options.
4760 @item -fdump-ipa-@var{switch}
4762 Control the dumping at various stages of inter-procedural analysis
4763 language tree to a file. The file name is generated by appending a switch
4764 specific suffix to the source file name. The following dumps are possible:
4768 Enables all inter-procedural analysis dumps.
4771 Dumps information about call-graph optimization, unused function removal,
4772 and inlining decisions.
4775 Dump after function inlining.
4779 @item -fdump-statistics-@var{option}
4780 @opindex -fdump-statistics
4781 Enable and control dumping of pass statistics in a separate file. The
4782 file name is generated by appending a suffix ending in @samp{.statistics}
4783 to the source file name. If the @samp{-@var{option}} form is used,
4784 @samp{-stats} will cause counters to be summed over the whole compilation unit
4785 while @samp{-details} will dump every event as the passes generate them.
4786 The default with no option is to sum counters for each function compiled.
4788 @item -fdump-tree-@var{switch}
4789 @itemx -fdump-tree-@var{switch}-@var{options}
4791 Control the dumping at various stages of processing the intermediate
4792 language tree to a file. The file name is generated by appending a switch
4793 specific suffix to the source file name. If the @samp{-@var{options}}
4794 form is used, @var{options} is a list of @samp{-} separated options that
4795 control the details of the dump. Not all options are applicable to all
4796 dumps, those which are not meaningful will be ignored. The following
4797 options are available
4801 Print the address of each node. Usually this is not meaningful as it
4802 changes according to the environment and source file. Its primary use
4803 is for tying up a dump file with a debug environment.
4805 Inhibit dumping of members of a scope or body of a function merely
4806 because that scope has been reached. Only dump such items when they
4807 are directly reachable by some other path. When dumping pretty-printed
4808 trees, this option inhibits dumping the bodies of control structures.
4810 Print a raw representation of the tree. By default, trees are
4811 pretty-printed into a C-like representation.
4813 Enable more detailed dumps (not honored by every dump option).
4815 Enable dumping various statistics about the pass (not honored by every dump
4818 Enable showing basic block boundaries (disabled in raw dumps).
4820 Enable showing virtual operands for every statement.
4822 Enable showing line numbers for statements.
4824 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4826 Enable showing the tree dump for each statement.
4828 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4829 and @option{lineno}.
4832 The following tree dumps are possible:
4836 Dump before any tree based optimization, to @file{@var{file}.original}.
4839 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4842 @opindex fdump-tree-gimple
4843 Dump each function before and after the gimplification pass to a file. The
4844 file name is made by appending @file{.gimple} to the source file name.
4847 @opindex fdump-tree-cfg
4848 Dump the control flow graph of each function to a file. The file name is
4849 made by appending @file{.cfg} to the source file name.
4852 @opindex fdump-tree-vcg
4853 Dump the control flow graph of each function to a file in VCG format. The
4854 file name is made by appending @file{.vcg} to the source file name. Note
4855 that if the file contains more than one function, the generated file cannot
4856 be used directly by VCG@. You will need to cut and paste each function's
4857 graph into its own separate file first.
4860 @opindex fdump-tree-ch
4861 Dump each function after copying loop headers. The file name is made by
4862 appending @file{.ch} to the source file name.
4865 @opindex fdump-tree-ssa
4866 Dump SSA related information to a file. The file name is made by appending
4867 @file{.ssa} to the source file name.
4870 @opindex fdump-tree-alias
4871 Dump aliasing information for each function. The file name is made by
4872 appending @file{.alias} to the source file name.
4875 @opindex fdump-tree-ccp
4876 Dump each function after CCP@. The file name is made by appending
4877 @file{.ccp} to the source file name.
4880 @opindex fdump-tree-storeccp
4881 Dump each function after STORE-CCP@. The file name is made by appending
4882 @file{.storeccp} to the source file name.
4885 @opindex fdump-tree-pre
4886 Dump trees after partial redundancy elimination. The file name is made
4887 by appending @file{.pre} to the source file name.
4890 @opindex fdump-tree-fre
4891 Dump trees after full redundancy elimination. The file name is made
4892 by appending @file{.fre} to the source file name.
4895 @opindex fdump-tree-copyprop
4896 Dump trees after copy propagation. The file name is made
4897 by appending @file{.copyprop} to the source file name.
4899 @item store_copyprop
4900 @opindex fdump-tree-store_copyprop
4901 Dump trees after store copy-propagation. The file name is made
4902 by appending @file{.store_copyprop} to the source file name.
4905 @opindex fdump-tree-dce
4906 Dump each function after dead code elimination. The file name is made by
4907 appending @file{.dce} to the source file name.
4910 @opindex fdump-tree-mudflap
4911 Dump each function after adding mudflap instrumentation. The file name is
4912 made by appending @file{.mudflap} to the source file name.
4915 @opindex fdump-tree-sra
4916 Dump each function after performing scalar replacement of aggregates. The
4917 file name is made by appending @file{.sra} to the source file name.
4920 @opindex fdump-tree-sink
4921 Dump each function after performing code sinking. The file name is made
4922 by appending @file{.sink} to the source file name.
4925 @opindex fdump-tree-dom
4926 Dump each function after applying dominator tree optimizations. The file
4927 name is made by appending @file{.dom} to the source file name.
4930 @opindex fdump-tree-dse
4931 Dump each function after applying dead store elimination. The file
4932 name is made by appending @file{.dse} to the source file name.
4935 @opindex fdump-tree-phiopt
4936 Dump each function after optimizing PHI nodes into straightline code. The file
4937 name is made by appending @file{.phiopt} to the source file name.
4940 @opindex fdump-tree-forwprop
4941 Dump each function after forward propagating single use variables. The file
4942 name is made by appending @file{.forwprop} to the source file name.
4945 @opindex fdump-tree-copyrename
4946 Dump each function after applying the copy rename optimization. The file
4947 name is made by appending @file{.copyrename} to the source file name.
4950 @opindex fdump-tree-nrv
4951 Dump each function after applying the named return value optimization on
4952 generic trees. The file name is made by appending @file{.nrv} to the source
4956 @opindex fdump-tree-vect
4957 Dump each function after applying vectorization of loops. The file name is
4958 made by appending @file{.vect} to the source file name.
4961 @opindex fdump-tree-vrp
4962 Dump each function after Value Range Propagation (VRP). The file name
4963 is made by appending @file{.vrp} to the source file name.
4966 @opindex fdump-tree-all
4967 Enable all the available tree dumps with the flags provided in this option.
4970 @item -ftree-vectorizer-verbose=@var{n}
4971 @opindex ftree-vectorizer-verbose
4972 This option controls the amount of debugging output the vectorizer prints.
4973 This information is written to standard error, unless
4974 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4975 in which case it is output to the usual dump listing file, @file{.vect}.
4976 For @var{n}=0 no diagnostic information is reported.
4977 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4978 and the total number of loops that got vectorized.
4979 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4980 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
4981 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4982 level that @option{-fdump-tree-vect-stats} uses.
4983 Higher verbosity levels mean either more information dumped for each
4984 reported loop, or same amount of information reported for more loops:
4985 If @var{n}=3, alignment related information is added to the reports.
4986 If @var{n}=4, data-references related information (e.g.@: memory dependences,
4987 memory access-patterns) is added to the reports.
4988 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4989 that did not pass the first analysis phase (i.e., may not be countable, or
4990 may have complicated control-flow).
4991 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4992 For @var{n}=7, all the information the vectorizer generates during its
4993 analysis and transformation is reported. This is the same verbosity level
4994 that @option{-fdump-tree-vect-details} uses.
4996 @item -frandom-seed=@var{string}
4997 @opindex frandom-string
4998 This option provides a seed that GCC uses when it would otherwise use
4999 random numbers. It is used to generate certain symbol names
5000 that have to be different in every compiled file. It is also used to
5001 place unique stamps in coverage data files and the object files that
5002 produce them. You can use the @option{-frandom-seed} option to produce
5003 reproducibly identical object files.
5005 The @var{string} should be different for every file you compile.
5007 @item -fsched-verbose=@var{n}
5008 @opindex fsched-verbose
5009 On targets that use instruction scheduling, this option controls the
5010 amount of debugging output the scheduler prints. This information is
5011 written to standard error, unless @option{-fdump-rtl-sched1} or
5012 @option{-fdump-rtl-sched2} is specified, in which case it is output
5013 to the usual dump listing file, @file{.sched} or @file{.sched2}
5014 respectively. However for @var{n} greater than nine, the output is
5015 always printed to standard error.
5017 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5018 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5019 For @var{n} greater than one, it also output basic block probabilities,
5020 detailed ready list information and unit/insn info. For @var{n} greater
5021 than two, it includes RTL at abort point, control-flow and regions info.
5022 And for @var{n} over four, @option{-fsched-verbose} also includes
5027 Store the usual ``temporary'' intermediate files permanently; place them
5028 in the current directory and name them based on the source file. Thus,
5029 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5030 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5031 preprocessed @file{foo.i} output file even though the compiler now
5032 normally uses an integrated preprocessor.
5034 When used in combination with the @option{-x} command line option,
5035 @option{-save-temps} is sensible enough to avoid over writing an
5036 input source file with the same extension as an intermediate file.
5037 The corresponding intermediate file may be obtained by renaming the
5038 source file before using @option{-save-temps}.
5042 Report the CPU time taken by each subprocess in the compilation
5043 sequence. For C source files, this is the compiler proper and assembler
5044 (plus the linker if linking is done). The output looks like this:
5051 The first number on each line is the ``user time'', that is time spent
5052 executing the program itself. The second number is ``system time'',
5053 time spent executing operating system routines on behalf of the program.
5054 Both numbers are in seconds.
5056 @item -fvar-tracking
5057 @opindex fvar-tracking
5058 Run variable tracking pass. It computes where variables are stored at each
5059 position in code. Better debugging information is then generated
5060 (if the debugging information format supports this information).
5062 It is enabled by default when compiling with optimization (@option{-Os},
5063 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5064 the debug info format supports it.
5066 @item -print-file-name=@var{library}
5067 @opindex print-file-name
5068 Print the full absolute name of the library file @var{library} that
5069 would be used when linking---and don't do anything else. With this
5070 option, GCC does not compile or link anything; it just prints the
5073 @item -print-multi-directory
5074 @opindex print-multi-directory
5075 Print the directory name corresponding to the multilib selected by any
5076 other switches present in the command line. This directory is supposed
5077 to exist in @env{GCC_EXEC_PREFIX}.
5079 @item -print-multi-lib
5080 @opindex print-multi-lib
5081 Print the mapping from multilib directory names to compiler switches
5082 that enable them. The directory name is separated from the switches by
5083 @samp{;}, and each switch starts with an @samp{@@} instead of the
5084 @samp{-}, without spaces between multiple switches. This is supposed to
5085 ease shell-processing.
5087 @item -print-prog-name=@var{program}
5088 @opindex print-prog-name
5089 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5091 @item -print-libgcc-file-name
5092 @opindex print-libgcc-file-name
5093 Same as @option{-print-file-name=libgcc.a}.
5095 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5096 but you do want to link with @file{libgcc.a}. You can do
5099 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5102 @item -print-search-dirs
5103 @opindex print-search-dirs
5104 Print the name of the configured installation directory and a list of
5105 program and library directories @command{gcc} will search---and don't do anything else.
5107 This is useful when @command{gcc} prints the error message
5108 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5109 To resolve this you either need to put @file{cpp0} and the other compiler
5110 components where @command{gcc} expects to find them, or you can set the environment
5111 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5112 Don't forget the trailing @samp{/}.
5113 @xref{Environment Variables}.
5115 @item -print-sysroot
5116 @opindex print-sysroot
5117 Print the target sysroot directory that will be used during
5118 compilation. This is the target sysroot specified either at configure
5119 time or using the @option{--sysroot} option, possibly with an extra
5120 suffix that depends on compilation options. If no target sysroot is
5121 specified, the option prints nothing.
5123 @item -print-sysroot-headers-suffix
5124 @opindex print-sysroot-headers-suffix
5125 Print the suffix added to the target sysroot when searching for
5126 headers, or give an error if the compiler is not configured with such
5127 a suffix---and don't do anything else.
5130 @opindex dumpmachine
5131 Print the compiler's target machine (for example,
5132 @samp{i686-pc-linux-gnu})---and don't do anything else.
5135 @opindex dumpversion
5136 Print the compiler version (for example, @samp{3.0})---and don't do
5141 Print the compiler's built-in specs---and don't do anything else. (This
5142 is used when GCC itself is being built.) @xref{Spec Files}.
5144 @item -feliminate-unused-debug-types
5145 @opindex feliminate-unused-debug-types
5146 Normally, when producing DWARF2 output, GCC will emit debugging
5147 information for all types declared in a compilation
5148 unit, regardless of whether or not they are actually used
5149 in that compilation unit. Sometimes this is useful, such as
5150 if, in the debugger, you want to cast a value to a type that is
5151 not actually used in your program (but is declared). More often,
5152 however, this results in a significant amount of wasted space.
5153 With this option, GCC will avoid producing debug symbol output
5154 for types that are nowhere used in the source file being compiled.
5157 @node Optimize Options
5158 @section Options That Control Optimization
5159 @cindex optimize options
5160 @cindex options, optimization
5162 These options control various sorts of optimizations.
5164 Without any optimization option, the compiler's goal is to reduce the
5165 cost of compilation and to make debugging produce the expected
5166 results. Statements are independent: if you stop the program with a
5167 breakpoint between statements, you can then assign a new value to any
5168 variable or change the program counter to any other statement in the
5169 function and get exactly the results you would expect from the source
5172 Turning on optimization flags makes the compiler attempt to improve
5173 the performance and/or code size at the expense of compilation time
5174 and possibly the ability to debug the program.
5176 The compiler performs optimization based on the knowledge it has of the
5177 program. Compiling multiple files at once to a single output file mode allows
5178 the compiler to use information gained from all of the files when compiling
5181 Not all optimizations are controlled directly by a flag. Only
5182 optimizations that have a flag are listed.
5189 Optimize. Optimizing compilation takes somewhat more time, and a lot
5190 more memory for a large function.
5192 With @option{-O}, the compiler tries to reduce code size and execution
5193 time, without performing any optimizations that take a great deal of
5196 @option{-O} turns on the following optimization flags:
5199 -fcprop-registers @gol
5202 -fdelayed-branch @gol
5204 -fguess-branch-probability @gol
5205 -fif-conversion2 @gol
5206 -fif-conversion @gol
5207 -finline-small-functions @gol
5208 -fipa-pure-const @gol
5209 -fipa-reference @gol
5211 -fsplit-wide-types @gol
5212 -ftree-builtin-call-dce @gol
5215 -ftree-copyrename @gol
5217 -ftree-dominator-opts @gol
5224 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5225 where doing so does not interfere with debugging.
5229 Optimize even more. GCC performs nearly all supported optimizations
5230 that do not involve a space-speed tradeoff. The compiler does not
5231 perform loop unrolling or function inlining when you specify @option{-O2}.
5232 As compared to @option{-O}, this option increases both compilation time
5233 and the performance of the generated code.
5235 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5236 also turns on the following optimization flags:
5237 @gccoptlist{-fthread-jumps @gol
5238 -falign-functions -falign-jumps @gol
5239 -falign-loops -falign-labels @gol
5242 -fcse-follow-jumps -fcse-skip-blocks @gol
5243 -fdelete-null-pointer-checks @gol
5244 -fexpensive-optimizations @gol
5245 -fgcse -fgcse-lm @gol
5246 -findirect-inlining @gol
5247 -foptimize-sibling-calls @gol
5250 -freorder-blocks -freorder-functions @gol
5251 -frerun-cse-after-loop @gol
5252 -fsched-interblock -fsched-spec @gol
5253 -fschedule-insns -fschedule-insns2 @gol
5254 -fstrict-aliasing -fstrict-overflow @gol
5255 -ftree-switch-conversion @gol
5259 Please note the warning under @option{-fgcse} about
5260 invoking @option{-O2} on programs that use computed gotos.
5264 Optimize yet more. @option{-O3} turns on all optimizations specified
5265 by @option{-O2} and also turns on the @option{-finline-functions},
5266 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5267 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5271 Reduce compilation time and make debugging produce the expected
5272 results. This is the default.
5276 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5277 do not typically increase code size. It also performs further
5278 optimizations designed to reduce code size.
5280 @option{-Os} disables the following optimization flags:
5281 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5282 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5283 -fprefetch-loop-arrays -ftree-vect-loop-version}
5285 If you use multiple @option{-O} options, with or without level numbers,
5286 the last such option is the one that is effective.
5289 Options of the form @option{-f@var{flag}} specify machine-independent
5290 flags. Most flags have both positive and negative forms; the negative
5291 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5292 below, only one of the forms is listed---the one you typically will
5293 use. You can figure out the other form by either removing @samp{no-}
5296 The following options control specific optimizations. They are either
5297 activated by @option{-O} options or are related to ones that are. You
5298 can use the following flags in the rare cases when ``fine-tuning'' of
5299 optimizations to be performed is desired.
5302 @item -fno-default-inline
5303 @opindex fno-default-inline
5304 Do not make member functions inline by default merely because they are
5305 defined inside the class scope (C++ only). Otherwise, when you specify
5306 @w{@option{-O}}, member functions defined inside class scope are compiled
5307 inline by default; i.e., you don't need to add @samp{inline} in front of
5308 the member function name.
5310 @item -fno-defer-pop
5311 @opindex fno-defer-pop
5312 Always pop the arguments to each function call as soon as that function
5313 returns. For machines which must pop arguments after a function call,
5314 the compiler normally lets arguments accumulate on the stack for several
5315 function calls and pops them all at once.
5317 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5319 @item -fforward-propagate
5320 @opindex fforward-propagate
5321 Perform a forward propagation pass on RTL@. The pass tries to combine two
5322 instructions and checks if the result can be simplified. If loop unrolling
5323 is active, two passes are performed and the second is scheduled after
5326 This option is enabled by default at optimization levels @option{-O2},
5327 @option{-O3}, @option{-Os}.
5329 @item -fomit-frame-pointer
5330 @opindex fomit-frame-pointer
5331 Don't keep the frame pointer in a register for functions that
5332 don't need one. This avoids the instructions to save, set up and
5333 restore frame pointers; it also makes an extra register available
5334 in many functions. @strong{It also makes debugging impossible on
5337 On some machines, such as the VAX, this flag has no effect, because
5338 the standard calling sequence automatically handles the frame pointer
5339 and nothing is saved by pretending it doesn't exist. The
5340 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5341 whether a target machine supports this flag. @xref{Registers,,Register
5342 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5344 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5346 @item -foptimize-sibling-calls
5347 @opindex foptimize-sibling-calls
5348 Optimize sibling and tail recursive calls.
5350 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5354 Don't pay attention to the @code{inline} keyword. Normally this option
5355 is used to keep the compiler from expanding any functions inline.
5356 Note that if you are not optimizing, no functions can be expanded inline.
5358 @item -finline-small-functions
5359 @opindex finline-small-functions
5360 Integrate functions into their callers when their body is smaller than expected
5361 function call code (so overall size of program gets smaller). The compiler
5362 heuristically decides which functions are simple enough to be worth integrating
5365 Enabled at level @option{-O2}.
5367 @item -findirect-inlining
5368 @opindex findirect-inlining
5369 Inline also indirect calls that are discovered to be known at compile
5370 time thanks to previous inlining. This option has any effect only
5371 when inlining itself is turned on by the @option{-finline-functions}
5372 or @option{-finline-small-functions} options.
5374 Enabled at level @option{-O2}.
5376 @item -finline-functions
5377 @opindex finline-functions
5378 Integrate all simple functions into their callers. The compiler
5379 heuristically decides which functions are simple enough to be worth
5380 integrating in this way.
5382 If all calls to a given function are integrated, and the function is
5383 declared @code{static}, then the function is normally not output as
5384 assembler code in its own right.
5386 Enabled at level @option{-O3}.
5388 @item -finline-functions-called-once
5389 @opindex finline-functions-called-once
5390 Consider all @code{static} functions called once for inlining into their
5391 caller even if they are not marked @code{inline}. If a call to a given
5392 function is integrated, then the function is not output as assembler code
5395 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5397 @item -fearly-inlining
5398 @opindex fearly-inlining
5399 Inline functions marked by @code{always_inline} and functions whose body seems
5400 smaller than the function call overhead early before doing
5401 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5402 makes profiling significantly cheaper and usually inlining faster on programs
5403 having large chains of nested wrapper functions.
5407 @item -finline-limit=@var{n}
5408 @opindex finline-limit
5409 By default, GCC limits the size of functions that can be inlined. This flag
5410 allows coarse control of this limit. @var{n} is the size of functions that
5411 can be inlined in number of pseudo instructions.
5413 Inlining is actually controlled by a number of parameters, which may be
5414 specified individually by using @option{--param @var{name}=@var{value}}.
5415 The @option{-finline-limit=@var{n}} option sets some of these parameters
5419 @item max-inline-insns-single
5420 is set to @var{n}/2.
5421 @item max-inline-insns-auto
5422 is set to @var{n}/2.
5425 See below for a documentation of the individual
5426 parameters controlling inlining and for the defaults of these parameters.
5428 @emph{Note:} there may be no value to @option{-finline-limit} that results
5429 in default behavior.
5431 @emph{Note:} pseudo instruction represents, in this particular context, an
5432 abstract measurement of function's size. In no way does it represent a count
5433 of assembly instructions and as such its exact meaning might change from one
5434 release to an another.
5436 @item -fkeep-inline-functions
5437 @opindex fkeep-inline-functions
5438 In C, emit @code{static} functions that are declared @code{inline}
5439 into the object file, even if the function has been inlined into all
5440 of its callers. This switch does not affect functions using the
5441 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5442 inline functions into the object file.
5444 @item -fkeep-static-consts
5445 @opindex fkeep-static-consts
5446 Emit variables declared @code{static const} when optimization isn't turned
5447 on, even if the variables aren't referenced.
5449 GCC enables this option by default. If you want to force the compiler to
5450 check if the variable was referenced, regardless of whether or not
5451 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5453 @item -fmerge-constants
5454 @opindex fmerge-constants
5455 Attempt to merge identical constants (string constants and floating point
5456 constants) across compilation units.
5458 This option is the default for optimized compilation if the assembler and
5459 linker support it. Use @option{-fno-merge-constants} to inhibit this
5462 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5464 @item -fmerge-all-constants
5465 @opindex fmerge-all-constants
5466 Attempt to merge identical constants and identical variables.
5468 This option implies @option{-fmerge-constants}. In addition to
5469 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5470 arrays or initialized constant variables with integral or floating point
5471 types. Languages like C or C++ require each non-automatic variable to
5472 have distinct location, so using this option will result in non-conforming
5475 @item -fmodulo-sched
5476 @opindex fmodulo-sched
5477 Perform swing modulo scheduling immediately before the first scheduling
5478 pass. This pass looks at innermost loops and reorders their
5479 instructions by overlapping different iterations.
5481 @item -fmodulo-sched-allow-regmoves
5482 @opindex fmodulo-sched-allow-regmoves
5483 Perform more aggressive SMS based modulo scheduling with register moves
5484 allowed. By setting this flag certain anti-dependences edges will be
5485 deleted which will trigger the generation of reg-moves based on the
5486 life-range analysis. This option is effective only with
5487 @option{-fmodulo-sched} enabled.
5489 @item -fno-branch-count-reg
5490 @opindex fno-branch-count-reg
5491 Do not use ``decrement and branch'' instructions on a count register,
5492 but instead generate a sequence of instructions that decrement a
5493 register, compare it against zero, then branch based upon the result.
5494 This option is only meaningful on architectures that support such
5495 instructions, which include x86, PowerPC, IA-64 and S/390.
5497 The default is @option{-fbranch-count-reg}.
5499 @item -fno-function-cse
5500 @opindex fno-function-cse
5501 Do not put function addresses in registers; make each instruction that
5502 calls a constant function contain the function's address explicitly.
5504 This option results in less efficient code, but some strange hacks
5505 that alter the assembler output may be confused by the optimizations
5506 performed when this option is not used.
5508 The default is @option{-ffunction-cse}
5510 @item -fno-zero-initialized-in-bss
5511 @opindex fno-zero-initialized-in-bss
5512 If the target supports a BSS section, GCC by default puts variables that
5513 are initialized to zero into BSS@. This can save space in the resulting
5516 This option turns off this behavior because some programs explicitly
5517 rely on variables going to the data section. E.g., so that the
5518 resulting executable can find the beginning of that section and/or make
5519 assumptions based on that.
5521 The default is @option{-fzero-initialized-in-bss}.
5523 @item -fmudflap -fmudflapth -fmudflapir
5527 @cindex bounds checking
5529 For front-ends that support it (C and C++), instrument all risky
5530 pointer/array dereferencing operations, some standard library
5531 string/heap functions, and some other associated constructs with
5532 range/validity tests. Modules so instrumented should be immune to
5533 buffer overflows, invalid heap use, and some other classes of C/C++
5534 programming errors. The instrumentation relies on a separate runtime
5535 library (@file{libmudflap}), which will be linked into a program if
5536 @option{-fmudflap} is given at link time. Run-time behavior of the
5537 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5538 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5541 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5542 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5543 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5544 instrumentation should ignore pointer reads. This produces less
5545 instrumentation (and therefore faster execution) and still provides
5546 some protection against outright memory corrupting writes, but allows
5547 erroneously read data to propagate within a program.
5549 @item -fthread-jumps
5550 @opindex fthread-jumps
5551 Perform optimizations where we check to see if a jump branches to a
5552 location where another comparison subsumed by the first is found. If
5553 so, the first branch is redirected to either the destination of the
5554 second branch or a point immediately following it, depending on whether
5555 the condition is known to be true or false.
5557 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5559 @item -fsplit-wide-types
5560 @opindex fsplit-wide-types
5561 When using a type that occupies multiple registers, such as @code{long
5562 long} on a 32-bit system, split the registers apart and allocate them
5563 independently. This normally generates better code for those types,
5564 but may make debugging more difficult.
5566 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5569 @item -fcse-follow-jumps
5570 @opindex fcse-follow-jumps
5571 In common subexpression elimination (CSE), scan through jump instructions
5572 when the target of the jump is not reached by any other path. For
5573 example, when CSE encounters an @code{if} statement with an
5574 @code{else} clause, CSE will follow the jump when the condition
5577 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5579 @item -fcse-skip-blocks
5580 @opindex fcse-skip-blocks
5581 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5582 follow jumps which conditionally skip over blocks. When CSE
5583 encounters a simple @code{if} statement with no else clause,
5584 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5585 body of the @code{if}.
5587 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5589 @item -frerun-cse-after-loop
5590 @opindex frerun-cse-after-loop
5591 Re-run common subexpression elimination after loop optimizations has been
5594 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5598 Perform a global common subexpression elimination pass.
5599 This pass also performs global constant and copy propagation.
5601 @emph{Note:} When compiling a program using computed gotos, a GCC
5602 extension, you may get better runtime performance if you disable
5603 the global common subexpression elimination pass by adding
5604 @option{-fno-gcse} to the command line.
5606 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5610 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5611 attempt to move loads which are only killed by stores into themselves. This
5612 allows a loop containing a load/store sequence to be changed to a load outside
5613 the loop, and a copy/store within the loop.
5615 Enabled by default when gcse is enabled.
5619 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5620 global common subexpression elimination. This pass will attempt to move
5621 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5622 loops containing a load/store sequence can be changed to a load before
5623 the loop and a store after the loop.
5625 Not enabled at any optimization level.
5629 When @option{-fgcse-las} is enabled, the global common subexpression
5630 elimination pass eliminates redundant loads that come after stores to the
5631 same memory location (both partial and full redundancies).
5633 Not enabled at any optimization level.
5635 @item -fgcse-after-reload
5636 @opindex fgcse-after-reload
5637 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5638 pass is performed after reload. The purpose of this pass is to cleanup
5641 @item -funsafe-loop-optimizations
5642 @opindex funsafe-loop-optimizations
5643 If given, the loop optimizer will assume that loop indices do not
5644 overflow, and that the loops with nontrivial exit condition are not
5645 infinite. This enables a wider range of loop optimizations even if
5646 the loop optimizer itself cannot prove that these assumptions are valid.
5647 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5648 if it finds this kind of loop.
5650 @item -fcrossjumping
5651 @opindex fcrossjumping
5652 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5653 resulting code may or may not perform better than without cross-jumping.
5655 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5657 @item -fauto-inc-dec
5658 @opindex fauto-inc-dec
5659 Combine increments or decrements of addresses with memory accesses.
5660 This pass is always skipped on architectures that do not have
5661 instructions to support this. Enabled by default at @option{-O} and
5662 higher on architectures that support this.
5666 Perform dead code elimination (DCE) on RTL@.
5667 Enabled by default at @option{-O} and higher.
5671 Perform dead store elimination (DSE) on RTL@.
5672 Enabled by default at @option{-O} and higher.
5674 @item -fif-conversion
5675 @opindex fif-conversion
5676 Attempt to transform conditional jumps into branch-less equivalents. This
5677 include use of conditional moves, min, max, set flags and abs instructions, and
5678 some tricks doable by standard arithmetics. The use of conditional execution
5679 on chips where it is available is controlled by @code{if-conversion2}.
5681 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5683 @item -fif-conversion2
5684 @opindex fif-conversion2
5685 Use conditional execution (where available) to transform conditional jumps into
5686 branch-less equivalents.
5688 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5690 @item -fdelete-null-pointer-checks
5691 @opindex fdelete-null-pointer-checks
5692 Use global dataflow analysis to identify and eliminate useless checks
5693 for null pointers. The compiler assumes that dereferencing a null
5694 pointer would have halted the program. If a pointer is checked after
5695 it has already been dereferenced, it cannot be null.
5697 In some environments, this assumption is not true, and programs can
5698 safely dereference null pointers. Use
5699 @option{-fno-delete-null-pointer-checks} to disable this optimization
5700 for programs which depend on that behavior.
5702 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5704 @item -fexpensive-optimizations
5705 @opindex fexpensive-optimizations
5706 Perform a number of minor optimizations that are relatively expensive.
5708 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5710 @item -foptimize-register-move
5712 @opindex foptimize-register-move
5714 Attempt to reassign register numbers in move instructions and as
5715 operands of other simple instructions in order to maximize the amount of
5716 register tying. This is especially helpful on machines with two-operand
5719 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5722 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5726 Use the integrated register allocator (@acronym{IRA}) for register
5727 allocation. It is a default if @acronym{IRA} has been ported for the
5730 @item -fira-algorithm=@var{algorithm}
5731 Use specified coloring algorithm for the integrated register
5732 allocator. The @var{algorithm} argument should be @code{priority} or
5733 @code{CB}. The first algorithm specifies Chow's priority coloring,
5734 the second one specifies Chaitin-Briggs coloring. The second
5735 algorithm can be unimplemented for some architectures. If it is
5736 implemented, it is the default because Chaitin-Briggs coloring as a
5737 rule generates a better code.
5739 @item -fira-region=@var{region}
5740 Use specified regions for the integrated register allocator. The
5741 @var{region} argument should be one of @code{all}, @code{mixed}, or
5742 @code{one}. The first value means using all loops as register
5743 allocation regions, the second value which is the default means using
5744 all loops except for loops with small register pressure as the
5745 regions, and third one means using all function as a single region.
5746 The first value can give best result for machines with small size and
5747 irregular register set, the third one results in faster and generates
5748 decent code and the smallest size code, and the default value usually
5749 give the best results in most cases and for most architectures.
5751 @item -fira-coalesce
5752 @opindex fira-coalesce
5753 Do optimistic register coalescing. This option might be profitable for
5754 architectures with big regular register files.
5756 @item -fno-ira-share-save-slots
5757 @opindex fno-ira-share-save-slots
5758 Switch off sharing stack slots used for saving call used hard
5759 registers living through a call. Each hard register will get a
5760 separate stack slot and as a result function stack frame will be
5763 @item -fno-ira-share-spill-slots
5764 @opindex fno-ira-share-spill-slots
5765 Switch off sharing stack slots allocated for pseudo-registers. Each
5766 pseudo-register which did not get a hard register will get a separate
5767 stack slot and as a result function stack frame will be bigger.
5769 @item -fira-verbose=@var{n}
5770 @opindex fira-verbose
5771 Set up how verbose dump file for the integrated register allocator
5772 will be. Default value is 5. If the value is greater or equal to 10,
5773 the dump file will be stderr as if the value were @var{n} minus 10.
5775 @item -fdelayed-branch
5776 @opindex fdelayed-branch
5777 If supported for the target machine, attempt to reorder instructions
5778 to exploit instruction slots available after delayed branch
5781 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5783 @item -fschedule-insns
5784 @opindex fschedule-insns
5785 If supported for the target machine, attempt to reorder instructions to
5786 eliminate execution stalls due to required data being unavailable. This
5787 helps machines that have slow floating point or memory load instructions
5788 by allowing other instructions to be issued until the result of the load
5789 or floating point instruction is required.
5791 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5793 @item -fschedule-insns2
5794 @opindex fschedule-insns2
5795 Similar to @option{-fschedule-insns}, but requests an additional pass of
5796 instruction scheduling after register allocation has been done. This is
5797 especially useful on machines with a relatively small number of
5798 registers and where memory load instructions take more than one cycle.
5800 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5802 @item -fno-sched-interblock
5803 @opindex fno-sched-interblock
5804 Don't schedule instructions across basic blocks. This is normally
5805 enabled by default when scheduling before register allocation, i.e.@:
5806 with @option{-fschedule-insns} or at @option{-O2} or higher.
5808 @item -fno-sched-spec
5809 @opindex fno-sched-spec
5810 Don't allow speculative motion of non-load instructions. This is normally
5811 enabled by default when scheduling before register allocation, i.e.@:
5812 with @option{-fschedule-insns} or at @option{-O2} or higher.
5814 @item -fsched-spec-load
5815 @opindex fsched-spec-load
5816 Allow speculative motion of some load instructions. This only makes
5817 sense when scheduling before register allocation, i.e.@: with
5818 @option{-fschedule-insns} or at @option{-O2} or higher.
5820 @item -fsched-spec-load-dangerous
5821 @opindex fsched-spec-load-dangerous
5822 Allow speculative motion of more load instructions. This only makes
5823 sense when scheduling before register allocation, i.e.@: with
5824 @option{-fschedule-insns} or at @option{-O2} or higher.
5826 @item -fsched-stalled-insns
5827 @itemx -fsched-stalled-insns=@var{n}
5828 @opindex fsched-stalled-insns
5829 Define how many insns (if any) can be moved prematurely from the queue
5830 of stalled insns into the ready list, during the second scheduling pass.
5831 @option{-fno-sched-stalled-insns} means that no insns will be moved
5832 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5833 on how many queued insns can be moved prematurely.
5834 @option{-fsched-stalled-insns} without a value is equivalent to
5835 @option{-fsched-stalled-insns=1}.
5837 @item -fsched-stalled-insns-dep
5838 @itemx -fsched-stalled-insns-dep=@var{n}
5839 @opindex fsched-stalled-insns-dep
5840 Define how many insn groups (cycles) will be examined for a dependency
5841 on a stalled insn that is candidate for premature removal from the queue
5842 of stalled insns. This has an effect only during the second scheduling pass,
5843 and only if @option{-fsched-stalled-insns} is used.
5844 @option{-fno-sched-stalled-insns-dep} is equivalent to
5845 @option{-fsched-stalled-insns-dep=0}.
5846 @option{-fsched-stalled-insns-dep} without a value is equivalent to
5847 @option{-fsched-stalled-insns-dep=1}.
5849 @item -fsched2-use-superblocks
5850 @opindex fsched2-use-superblocks
5851 When scheduling after register allocation, do use superblock scheduling
5852 algorithm. Superblock scheduling allows motion across basic block boundaries
5853 resulting on faster schedules. This option is experimental, as not all machine
5854 descriptions used by GCC model the CPU closely enough to avoid unreliable
5855 results from the algorithm.
5857 This only makes sense when scheduling after register allocation, i.e.@: with
5858 @option{-fschedule-insns2} or at @option{-O2} or higher.
5860 @item -fsched2-use-traces
5861 @opindex fsched2-use-traces
5862 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5863 allocation and additionally perform code duplication in order to increase the
5864 size of superblocks using tracer pass. See @option{-ftracer} for details on
5867 This mode should produce faster but significantly longer programs. Also
5868 without @option{-fbranch-probabilities} the traces constructed may not
5869 match the reality and hurt the performance. This only makes
5870 sense when scheduling after register allocation, i.e.@: with
5871 @option{-fschedule-insns2} or at @option{-O2} or higher.
5875 Eliminate redundant sign extension instructions and move the non-redundant
5876 ones to optimal placement using lazy code motion (LCM).
5878 @item -freschedule-modulo-scheduled-loops
5879 @opindex freschedule-modulo-scheduled-loops
5880 The modulo scheduling comes before the traditional scheduling, if a loop
5881 was modulo scheduled we may want to prevent the later scheduling passes
5882 from changing its schedule, we use this option to control that.
5884 @item -fselective-scheduling
5885 @opindex fselective-scheduling
5886 Schedule instructions using selective scheduling algorithm. Selective
5887 scheduling runs instead of the first scheduler pass.
5889 @item -fselective-scheduling2
5890 @opindex fselective-scheduling2
5891 Schedule instructions using selective scheduling algorithm. Selective
5892 scheduling runs instead of the second scheduler pass.
5894 @item -fsel-sched-pipelining
5895 @opindex fsel-sched-pipelining
5896 Enable software pipelining of innermost loops during selective scheduling.
5897 This option has no effect until one of @option{-fselective-scheduling} or
5898 @option{-fselective-scheduling2} is turned on.
5900 @item -fsel-sched-pipelining-outer-loops
5901 @opindex fsel-sched-pipelining-outer-loops
5902 When pipelining loops during selective scheduling, also pipeline outer loops.
5903 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
5905 @item -fcaller-saves
5906 @opindex fcaller-saves
5907 Enable values to be allocated in registers that will be clobbered by
5908 function calls, by emitting extra instructions to save and restore the
5909 registers around such calls. Such allocation is done only when it
5910 seems to result in better code than would otherwise be produced.
5912 This option is always enabled by default on certain machines, usually
5913 those which have no call-preserved registers to use instead.
5915 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5917 @item -fconserve-stack
5918 @opindex fconserve-stack
5919 Attempt to minimize stack usage. The compiler will attempt to use less
5920 stack space, even if that makes the program slower. This option
5921 implies setting the @option{large-stack-frame} parameter to 100
5922 and the @option{large-stack-frame-growth} parameter to 400.
5924 @item -ftree-reassoc
5925 @opindex ftree-reassoc
5926 Perform reassociation on trees. This flag is enabled by default
5927 at @option{-O} and higher.
5931 Perform partial redundancy elimination (PRE) on trees. This flag is
5932 enabled by default at @option{-O2} and @option{-O3}.
5936 Perform full redundancy elimination (FRE) on trees. The difference
5937 between FRE and PRE is that FRE only considers expressions
5938 that are computed on all paths leading to the redundant computation.
5939 This analysis is faster than PRE, though it exposes fewer redundancies.
5940 This flag is enabled by default at @option{-O} and higher.
5942 @item -ftree-copy-prop
5943 @opindex ftree-copy-prop
5944 Perform copy propagation on trees. This pass eliminates unnecessary
5945 copy operations. This flag is enabled by default at @option{-O} and
5948 @item -fipa-pure-const
5949 @opindex fipa-pure-const
5950 Discover which functions are pure or constant.
5951 Enabled by default at @option{-O} and higher.
5953 @item -fipa-reference
5954 @opindex fipa-reference
5955 Discover which static variables do not escape cannot escape the
5957 Enabled by default at @option{-O} and higher.
5959 @item -fipa-struct-reorg
5960 @opindex fipa-struct-reorg
5961 Perform structure reorganization optimization, that change C-like structures
5962 layout in order to better utilize spatial locality. This transformation is
5963 affective for programs containing arrays of structures. Available in two
5964 compilation modes: profile-based (enabled with @option{-fprofile-generate})
5965 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
5966 to provide the safety of this transformation. It works only in whole program
5967 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
5968 enabled. Structures considered @samp{cold} by this transformation are not
5969 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
5971 With this flag, the program debug info reflects a new structure layout.
5975 Perform interprocedural pointer analysis. This option is experimental
5976 and does not affect generated code.
5980 Perform interprocedural constant propagation.
5981 This optimization analyzes the program to determine when values passed
5982 to functions are constants and then optimizes accordingly.
5983 This optimization can substantially increase performance
5984 if the application has constants passed to functions.
5985 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
5987 @item -fipa-cp-clone
5988 @opindex fipa-cp-clone
5989 Perform function cloning to make interprocedural constant propagation stronger.
5990 When enabled, interprocedural constant propagation will perform function cloning
5991 when externally visible function can be called with constant arguments.
5992 Because this optimization can create multiple copies of functions,
5993 it may significantly increase code size
5994 (see @option{--param ipcp-unit-growth=@var{value}}).
5995 This flag is enabled by default at @option{-O3}.
5997 @item -fipa-matrix-reorg
5998 @opindex fipa-matrix-reorg
5999 Perform matrix flattening and transposing.
6000 Matrix flattening tries to replace a m-dimensional matrix
6001 with its equivalent n-dimensional matrix, where n < m.
6002 This reduces the level of indirection needed for accessing the elements
6003 of the matrix. The second optimization is matrix transposing that
6004 attemps to change the order of the matrix's dimensions in order to
6005 improve cache locality.
6006 Both optimizations need the @option{-fwhole-program} flag.
6007 Transposing is enabled only if profiling information is available.
6012 Perform forward store motion on trees. This flag is
6013 enabled by default at @option{-O} and higher.
6017 Perform sparse conditional constant propagation (CCP) on trees. This
6018 pass only operates on local scalar variables and is enabled by default
6019 at @option{-O} and higher.
6021 @item -ftree-switch-conversion
6022 Perform conversion of simple initializations in a switch to
6023 initializations from a scalar array. This flag is enabled by default
6024 at @option{-O2} and higher.
6028 Perform dead code elimination (DCE) on trees. This flag is enabled by
6029 default at @option{-O} and higher.
6031 @item -ftree-builtin-call-dce
6032 @opindex ftree-builtin-call-dce
6033 Perform conditional dead code elimination (DCE) for calls to builtin functions
6034 that may set @code{errno} but are otherwise side-effect free. This flag is
6035 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6038 @item -ftree-dominator-opts
6039 @opindex ftree-dominator-opts
6040 Perform a variety of simple scalar cleanups (constant/copy
6041 propagation, redundancy elimination, range propagation and expression
6042 simplification) based on a dominator tree traversal. This also
6043 performs jump threading (to reduce jumps to jumps). This flag is
6044 enabled by default at @option{-O} and higher.
6048 Perform dead store elimination (DSE) on trees. A dead store is a store into
6049 a memory location which will later be overwritten by another store without
6050 any intervening loads. In this case the earlier store can be deleted. This
6051 flag is enabled by default at @option{-O} and higher.
6055 Perform loop header copying on trees. This is beneficial since it increases
6056 effectiveness of code motion optimizations. It also saves one jump. This flag
6057 is enabled by default at @option{-O} and higher. It is not enabled
6058 for @option{-Os}, since it usually increases code size.
6060 @item -ftree-loop-optimize
6061 @opindex ftree-loop-optimize
6062 Perform loop optimizations on trees. This flag is enabled by default
6063 at @option{-O} and higher.
6065 @item -ftree-loop-linear
6066 @opindex ftree-loop-linear
6067 Perform linear loop transformations on tree. This flag can improve cache
6068 performance and allow further loop optimizations to take place.
6070 @item -floop-interchange
6071 Perform loop interchange transformations on loops. Interchanging two
6072 nested loops switches the inner and outer loops. For example, given a
6077 A(J, I) = A(J, I) * C
6081 loop interchange will transform the loop as if the user had written:
6085 A(J, I) = A(J, I) * C
6089 which can be beneficial when @code{N} is larger than the caches,
6090 because in Fortran, the elements of an array are stored in memory
6091 contiguously by column, and the original loop iterates over rows,
6092 potentially creating at each access a cache miss. This optimization
6093 applies to all the languages supported by GCC and is not limited to
6096 @item -floop-strip-mine
6097 Perform loop strip mining transformations on loops. Strip mining
6098 splits a loop into two nested loops. The outer loop has strides
6099 equal to the strip size and the inner loop has strides of the
6100 original loop within a strip. For example, given a loop like:
6106 loop strip mining will transform the loop as if the user had written:
6109 DO I = II, min (II + 3, N)
6114 This optimization applies to all the languages supported by GCC and is
6115 not limited to Fortran.
6118 Perform loop blocking transformations on loops. Blocking strip mines
6119 each loop in the loop nest such that the memory accesses of the
6120 element loops fit inside caches. For example, given a loop like:
6124 A(J, I) = B(I) + C(J)
6128 loop blocking will transform the loop as if the user had written:
6132 DO I = II, min (II + 63, N)
6133 DO J = JJ, min (JJ + 63, M)
6134 A(J, I) = B(I) + C(J)
6140 which can be beneficial when @code{M} is larger than the caches,
6141 because the innermost loop will iterate over a smaller amount of data
6142 that can be kept in the caches. This optimization applies to all the
6143 languages supported by GCC and is not limited to Fortran.
6145 @item -fcheck-data-deps
6146 @opindex fcheck-data-deps
6147 Compare the results of several data dependence analyzers. This option
6148 is used for debugging the data dependence analyzers.
6150 @item -ftree-loop-distribution
6151 Perform loop distribution. This flag can improve cache performance on
6152 big loop bodies and allow further loop optimizations, like
6153 parallelization or vectorization, to take place. For example, the loop
6170 @item -ftree-loop-im
6171 @opindex ftree-loop-im
6172 Perform loop invariant motion on trees. This pass moves only invariants that
6173 would be hard to handle at RTL level (function calls, operations that expand to
6174 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
6175 operands of conditions that are invariant out of the loop, so that we can use
6176 just trivial invariantness analysis in loop unswitching. The pass also includes
6179 @item -ftree-loop-ivcanon
6180 @opindex ftree-loop-ivcanon
6181 Create a canonical counter for number of iterations in the loop for that
6182 determining number of iterations requires complicated analysis. Later
6183 optimizations then may determine the number easily. Useful especially
6184 in connection with unrolling.
6188 Perform induction variable optimizations (strength reduction, induction
6189 variable merging and induction variable elimination) on trees.
6191 @item -ftree-parallelize-loops=n
6192 @opindex ftree-parallelize-loops
6193 Parallelize loops, i.e., split their iteration space to run in n threads.
6194 This is only possible for loops whose iterations are independent
6195 and can be arbitrarily reordered. The optimization is only
6196 profitable on multiprocessor machines, for loops that are CPU-intensive,
6197 rather than constrained e.g.@: by memory bandwidth. This option
6198 implies @option{-pthread}, and thus is only supported on targets
6199 that have support for @option{-pthread}.
6203 Perform scalar replacement of aggregates. This pass replaces structure
6204 references with scalars to prevent committing structures to memory too
6205 early. This flag is enabled by default at @option{-O} and higher.
6207 @item -ftree-copyrename
6208 @opindex ftree-copyrename
6209 Perform copy renaming on trees. This pass attempts to rename compiler
6210 temporaries to other variables at copy locations, usually resulting in
6211 variable names which more closely resemble the original variables. This flag
6212 is enabled by default at @option{-O} and higher.
6216 Perform temporary expression replacement during the SSA->normal phase. Single
6217 use/single def temporaries are replaced at their use location with their
6218 defining expression. This results in non-GIMPLE code, but gives the expanders
6219 much more complex trees to work on resulting in better RTL generation. This is
6220 enabled by default at @option{-O} and higher.
6222 @item -ftree-vectorize
6223 @opindex ftree-vectorize
6224 Perform loop vectorization on trees. This flag is enabled by default at
6227 @item -ftree-vect-loop-version
6228 @opindex ftree-vect-loop-version
6229 Perform loop versioning when doing loop vectorization on trees. When a loop
6230 appears to be vectorizable except that data alignment or data dependence cannot
6231 be determined at compile time then vectorized and non-vectorized versions of
6232 the loop are generated along with runtime checks for alignment or dependence
6233 to control which version is executed. This option is enabled by default
6234 except at level @option{-Os} where it is disabled.
6236 @item -fvect-cost-model
6237 @opindex fvect-cost-model
6238 Enable cost model for vectorization.
6242 Perform Value Range Propagation on trees. This is similar to the
6243 constant propagation pass, but instead of values, ranges of values are
6244 propagated. This allows the optimizers to remove unnecessary range
6245 checks like array bound checks and null pointer checks. This is
6246 enabled by default at @option{-O2} and higher. Null pointer check
6247 elimination is only done if @option{-fdelete-null-pointer-checks} is
6252 Perform tail duplication to enlarge superblock size. This transformation
6253 simplifies the control flow of the function allowing other optimizations to do
6256 @item -funroll-loops
6257 @opindex funroll-loops
6258 Unroll loops whose number of iterations can be determined at compile
6259 time or upon entry to the loop. @option{-funroll-loops} implies
6260 @option{-frerun-cse-after-loop}. This option makes code larger,
6261 and may or may not make it run faster.
6263 @item -funroll-all-loops
6264 @opindex funroll-all-loops
6265 Unroll all loops, even if their number of iterations is uncertain when
6266 the loop is entered. This usually makes programs run more slowly.
6267 @option{-funroll-all-loops} implies the same options as
6268 @option{-funroll-loops},
6270 @item -fsplit-ivs-in-unroller
6271 @opindex fsplit-ivs-in-unroller
6272 Enables expressing of values of induction variables in later iterations
6273 of the unrolled loop using the value in the first iteration. This breaks
6274 long dependency chains, thus improving efficiency of the scheduling passes.
6276 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6277 same effect. However in cases the loop body is more complicated than
6278 a single basic block, this is not reliable. It also does not work at all
6279 on some of the architectures due to restrictions in the CSE pass.
6281 This optimization is enabled by default.
6283 @item -fvariable-expansion-in-unroller
6284 @opindex fvariable-expansion-in-unroller
6285 With this option, the compiler will create multiple copies of some
6286 local variables when unrolling a loop which can result in superior code.
6288 @item -fpredictive-commoning
6289 @opindex fpredictive-commoning
6290 Perform predictive commoning optimization, i.e., reusing computations
6291 (especially memory loads and stores) performed in previous
6292 iterations of loops.
6294 This option is enabled at level @option{-O3}.
6296 @item -fprefetch-loop-arrays
6297 @opindex fprefetch-loop-arrays
6298 If supported by the target machine, generate instructions to prefetch
6299 memory to improve the performance of loops that access large arrays.
6301 This option may generate better or worse code; results are highly
6302 dependent on the structure of loops within the source code.
6304 Disabled at level @option{-Os}.
6307 @itemx -fno-peephole2
6308 @opindex fno-peephole
6309 @opindex fno-peephole2
6310 Disable any machine-specific peephole optimizations. The difference
6311 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6312 are implemented in the compiler; some targets use one, some use the
6313 other, a few use both.
6315 @option{-fpeephole} is enabled by default.
6316 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6318 @item -fno-guess-branch-probability
6319 @opindex fno-guess-branch-probability
6320 Do not guess branch probabilities using heuristics.
6322 GCC will use heuristics to guess branch probabilities if they are
6323 not provided by profiling feedback (@option{-fprofile-arcs}). These
6324 heuristics are based on the control flow graph. If some branch probabilities
6325 are specified by @samp{__builtin_expect}, then the heuristics will be
6326 used to guess branch probabilities for the rest of the control flow graph,
6327 taking the @samp{__builtin_expect} info into account. The interactions
6328 between the heuristics and @samp{__builtin_expect} can be complex, and in
6329 some cases, it may be useful to disable the heuristics so that the effects
6330 of @samp{__builtin_expect} are easier to understand.
6332 The default is @option{-fguess-branch-probability} at levels
6333 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6335 @item -freorder-blocks
6336 @opindex freorder-blocks
6337 Reorder basic blocks in the compiled function in order to reduce number of
6338 taken branches and improve code locality.
6340 Enabled at levels @option{-O2}, @option{-O3}.
6342 @item -freorder-blocks-and-partition
6343 @opindex freorder-blocks-and-partition
6344 In addition to reordering basic blocks in the compiled function, in order
6345 to reduce number of taken branches, partitions hot and cold basic blocks
6346 into separate sections of the assembly and .o files, to improve
6347 paging and cache locality performance.
6349 This optimization is automatically turned off in the presence of
6350 exception handling, for linkonce sections, for functions with a user-defined
6351 section attribute and on any architecture that does not support named
6354 @item -freorder-functions
6355 @opindex freorder-functions
6356 Reorder functions in the object file in order to
6357 improve code locality. This is implemented by using special
6358 subsections @code{.text.hot} for most frequently executed functions and
6359 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6360 the linker so object file format must support named sections and linker must
6361 place them in a reasonable way.
6363 Also profile feedback must be available in to make this option effective. See
6364 @option{-fprofile-arcs} for details.
6366 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6368 @item -fstrict-aliasing
6369 @opindex fstrict-aliasing
6370 Allows the compiler to assume the strictest aliasing rules applicable to
6371 the language being compiled. For C (and C++), this activates
6372 optimizations based on the type of expressions. In particular, an
6373 object of one type is assumed never to reside at the same address as an
6374 object of a different type, unless the types are almost the same. For
6375 example, an @code{unsigned int} can alias an @code{int}, but not a
6376 @code{void*} or a @code{double}. A character type may alias any other
6379 @anchor{Type-punning}Pay special attention to code like this:
6392 The practice of reading from a different union member than the one most
6393 recently written to (called ``type-punning'') is common. Even with
6394 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6395 is accessed through the union type. So, the code above will work as
6396 expected. @xref{Structures unions enumerations and bit-fields
6397 implementation}. However, this code might not:
6408 Similarly, access by taking the address, casting the resulting pointer
6409 and dereferencing the result has undefined behavior, even if the cast
6410 uses a union type, e.g.:
6414 return ((union a_union *) &d)->i;
6418 The @option{-fstrict-aliasing} option is enabled at levels
6419 @option{-O2}, @option{-O3}, @option{-Os}.
6421 @item -fstrict-overflow
6422 @opindex fstrict-overflow
6423 Allow the compiler to assume strict signed overflow rules, depending
6424 on the language being compiled. For C (and C++) this means that
6425 overflow when doing arithmetic with signed numbers is undefined, which
6426 means that the compiler may assume that it will not happen. This
6427 permits various optimizations. For example, the compiler will assume
6428 that an expression like @code{i + 10 > i} will always be true for
6429 signed @code{i}. This assumption is only valid if signed overflow is
6430 undefined, as the expression is false if @code{i + 10} overflows when
6431 using twos complement arithmetic. When this option is in effect any
6432 attempt to determine whether an operation on signed numbers will
6433 overflow must be written carefully to not actually involve overflow.
6435 This option also allows the compiler to assume strict pointer
6436 semantics: given a pointer to an object, if adding an offset to that
6437 pointer does not produce a pointer to the same object, the addition is
6438 undefined. This permits the compiler to conclude that @code{p + u >
6439 p} is always true for a pointer @code{p} and unsigned integer
6440 @code{u}. This assumption is only valid because pointer wraparound is
6441 undefined, as the expression is false if @code{p + u} overflows using
6442 twos complement arithmetic.
6444 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6445 that integer signed overflow is fully defined: it wraps. When
6446 @option{-fwrapv} is used, there is no difference between
6447 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6448 integers. With @option{-fwrapv} certain types of overflow are
6449 permitted. For example, if the compiler gets an overflow when doing
6450 arithmetic on constants, the overflowed value can still be used with
6451 @option{-fwrapv}, but not otherwise.
6453 The @option{-fstrict-overflow} option is enabled at levels
6454 @option{-O2}, @option{-O3}, @option{-Os}.
6456 @item -falign-functions
6457 @itemx -falign-functions=@var{n}
6458 @opindex falign-functions
6459 Align the start of functions to the next power-of-two greater than
6460 @var{n}, skipping up to @var{n} bytes. For instance,
6461 @option{-falign-functions=32} aligns functions to the next 32-byte
6462 boundary, but @option{-falign-functions=24} would align to the next
6463 32-byte boundary only if this can be done by skipping 23 bytes or less.
6465 @option{-fno-align-functions} and @option{-falign-functions=1} are
6466 equivalent and mean that functions will not be aligned.
6468 Some assemblers only support this flag when @var{n} is a power of two;
6469 in that case, it is rounded up.
6471 If @var{n} is not specified or is zero, use a machine-dependent default.
6473 Enabled at levels @option{-O2}, @option{-O3}.
6475 @item -falign-labels
6476 @itemx -falign-labels=@var{n}
6477 @opindex falign-labels
6478 Align all branch targets to a power-of-two boundary, skipping up to
6479 @var{n} bytes like @option{-falign-functions}. This option can easily
6480 make code slower, because it must insert dummy operations for when the
6481 branch target is reached in the usual flow of the code.
6483 @option{-fno-align-labels} and @option{-falign-labels=1} are
6484 equivalent and mean that labels will not be aligned.
6486 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6487 are greater than this value, then their values are used instead.
6489 If @var{n} is not specified or is zero, use a machine-dependent default
6490 which is very likely to be @samp{1}, meaning no alignment.
6492 Enabled at levels @option{-O2}, @option{-O3}.
6495 @itemx -falign-loops=@var{n}
6496 @opindex falign-loops
6497 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6498 like @option{-falign-functions}. The hope is that the loop will be
6499 executed many times, which will make up for any execution of the dummy
6502 @option{-fno-align-loops} and @option{-falign-loops=1} are
6503 equivalent and mean that loops will not be aligned.
6505 If @var{n} is not specified or is zero, use a machine-dependent default.
6507 Enabled at levels @option{-O2}, @option{-O3}.
6510 @itemx -falign-jumps=@var{n}
6511 @opindex falign-jumps
6512 Align branch targets to a power-of-two boundary, for branch targets
6513 where the targets can only be reached by jumping, skipping up to @var{n}
6514 bytes like @option{-falign-functions}. In this case, no dummy operations
6517 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6518 equivalent and mean that loops will not be aligned.
6520 If @var{n} is not specified or is zero, use a machine-dependent default.
6522 Enabled at levels @option{-O2}, @option{-O3}.
6524 @item -funit-at-a-time
6525 @opindex funit-at-a-time
6526 This option is left for compatibility reasons. @option{-funit-at-a-time}
6527 has no effect, while @option{-fno-unit-at-a-time} implies
6528 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
6532 @item -fno-toplevel-reorder
6533 @opindex fno-toplevel-reorder
6534 Do not reorder top-level functions, variables, and @code{asm}
6535 statements. Output them in the same order that they appear in the
6536 input file. When this option is used, unreferenced static variables
6537 will not be removed. This option is intended to support existing code
6538 which relies on a particular ordering. For new code, it is better to
6541 Enabled at level @option{-O0}. When disabled explicitly, it also imply
6542 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
6547 Constructs webs as commonly used for register allocation purposes and assign
6548 each web individual pseudo register. This allows the register allocation pass
6549 to operate on pseudos directly, but also strengthens several other optimization
6550 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6551 however, make debugging impossible, since variables will no longer stay in a
6554 Enabled by default with @option{-funroll-loops}.
6556 @item -fwhole-program
6557 @opindex fwhole-program
6558 Assume that the current compilation unit represents whole program being
6559 compiled. All public functions and variables with the exception of @code{main}
6560 and those merged by attribute @code{externally_visible} become static functions
6561 and in a affect gets more aggressively optimized by interprocedural optimizers.
6562 While this option is equivalent to proper use of @code{static} keyword for
6563 programs consisting of single file, in combination with option
6564 @option{--combine} this flag can be used to compile most of smaller scale C
6565 programs since the functions and variables become local for the whole combined
6566 compilation unit, not for the single source file itself.
6568 This option is not supported for Fortran programs.
6570 @item -fcprop-registers
6571 @opindex fcprop-registers
6572 After register allocation and post-register allocation instruction splitting,
6573 we perform a copy-propagation pass to try to reduce scheduling dependencies
6574 and occasionally eliminate the copy.
6576 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6578 @item -fprofile-correction
6579 @opindex fprofile-correction
6580 Profiles collected using an instrumented binary for multi-threaded programs may
6581 be inconsistent due to missed counter updates. When this option is specified,
6582 GCC will use heuristics to correct or smooth out such inconsistencies. By
6583 default, GCC will emit an error message when an inconsistent profile is detected.
6585 @item -fprofile-dir=@var{path}
6586 @opindex fprofile-dir
6588 Set the directory to search the profile data files in to @var{path}.
6589 This option affects only the profile data generated by
6590 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6591 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6592 and its related options.
6593 By default, GCC will use the current directory as @var{path}
6594 thus the profile data file will appear in the same directory as the object file.
6596 @item -fprofile-generate
6597 @itemx -fprofile-generate=@var{path}
6598 @opindex fprofile-generate
6600 Enable options usually used for instrumenting application to produce
6601 profile useful for later recompilation with profile feedback based
6602 optimization. You must use @option{-fprofile-generate} both when
6603 compiling and when linking your program.
6605 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6607 If @var{path} is specified, GCC will look at the @var{path} to find
6608 the profile feedback data files. See @option{-fprofile-dir}.
6611 @itemx -fprofile-use=@var{path}
6612 @opindex fprofile-use
6613 Enable profile feedback directed optimizations, and optimizations
6614 generally profitable only with profile feedback available.
6616 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6617 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6619 By default, GCC emits an error message if the feedback profiles do not
6620 match the source code. This error can be turned into a warning by using
6621 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6624 If @var{path} is specified, GCC will look at the @var{path} to find
6625 the profile feedback data files. See @option{-fprofile-dir}.
6628 The following options control compiler behavior regarding floating
6629 point arithmetic. These options trade off between speed and
6630 correctness. All must be specifically enabled.
6634 @opindex ffloat-store
6635 Do not store floating point variables in registers, and inhibit other
6636 options that might change whether a floating point value is taken from a
6639 @cindex floating point precision
6640 This option prevents undesirable excess precision on machines such as
6641 the 68000 where the floating registers (of the 68881) keep more
6642 precision than a @code{double} is supposed to have. Similarly for the
6643 x86 architecture. For most programs, the excess precision does only
6644 good, but a few programs rely on the precise definition of IEEE floating
6645 point. Use @option{-ffloat-store} for such programs, after modifying
6646 them to store all pertinent intermediate computations into variables.
6650 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6651 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6652 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6654 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6656 This option is not turned on by any @option{-O} option since
6657 it can result in incorrect output for programs which depend on
6658 an exact implementation of IEEE or ISO rules/specifications for
6659 math functions. It may, however, yield faster code for programs
6660 that do not require the guarantees of these specifications.
6662 @item -fno-math-errno
6663 @opindex fno-math-errno
6664 Do not set ERRNO after calling math functions that are executed
6665 with a single instruction, e.g., sqrt. A program that relies on
6666 IEEE exceptions for math error handling may want to use this flag
6667 for speed while maintaining IEEE arithmetic compatibility.
6669 This option is not turned on by any @option{-O} option since
6670 it can result in incorrect output for programs which depend on
6671 an exact implementation of IEEE or ISO rules/specifications for
6672 math functions. It may, however, yield faster code for programs
6673 that do not require the guarantees of these specifications.
6675 The default is @option{-fmath-errno}.
6677 On Darwin systems, the math library never sets @code{errno}. There is
6678 therefore no reason for the compiler to consider the possibility that
6679 it might, and @option{-fno-math-errno} is the default.
6681 @item -funsafe-math-optimizations
6682 @opindex funsafe-math-optimizations
6684 Allow optimizations for floating-point arithmetic that (a) assume
6685 that arguments and results are valid and (b) may violate IEEE or
6686 ANSI standards. When used at link-time, it may include libraries
6687 or startup files that change the default FPU control word or other
6688 similar optimizations.
6690 This option is not turned on by any @option{-O} option since
6691 it can result in incorrect output for programs which depend on
6692 an exact implementation of IEEE or ISO rules/specifications for
6693 math functions. It may, however, yield faster code for programs
6694 that do not require the guarantees of these specifications.
6695 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6696 @option{-fassociative-math} and @option{-freciprocal-math}.
6698 The default is @option{-fno-unsafe-math-optimizations}.
6700 @item -fassociative-math
6701 @opindex fassociative-math
6703 Allow re-association of operands in series of floating-point operations.
6704 This violates the ISO C and C++ language standard by possibly changing
6705 computation result. NOTE: re-ordering may change the sign of zero as
6706 well as ignore NaNs and inhibit or create underflow or overflow (and
6707 thus cannot be used on a code which relies on rounding behavior like
6708 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6709 and thus may not be used when ordered comparisons are required.
6710 This option requires that both @option{-fno-signed-zeros} and
6711 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6712 much sense with @option{-frounding-math}.
6714 The default is @option{-fno-associative-math}.
6716 @item -freciprocal-math
6717 @opindex freciprocal-math
6719 Allow the reciprocal of a value to be used instead of dividing by
6720 the value if this enables optimizations. For example @code{x / y}
6721 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6722 is subject to common subexpression elimination. Note that this loses
6723 precision and increases the number of flops operating on the value.
6725 The default is @option{-fno-reciprocal-math}.
6727 @item -ffinite-math-only
6728 @opindex ffinite-math-only
6729 Allow optimizations for floating-point arithmetic that assume
6730 that arguments and results are not NaNs or +-Infs.
6732 This option is not turned on by any @option{-O} option since
6733 it can result in incorrect output for programs which depend on
6734 an exact implementation of IEEE or ISO rules/specifications for
6735 math functions. It may, however, yield faster code for programs
6736 that do not require the guarantees of these specifications.
6738 The default is @option{-fno-finite-math-only}.
6740 @item -fno-signed-zeros
6741 @opindex fno-signed-zeros
6742 Allow optimizations for floating point arithmetic that ignore the
6743 signedness of zero. IEEE arithmetic specifies the behavior of
6744 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6745 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6746 This option implies that the sign of a zero result isn't significant.
6748 The default is @option{-fsigned-zeros}.
6750 @item -fno-trapping-math
6751 @opindex fno-trapping-math
6752 Compile code assuming that floating-point operations cannot generate
6753 user-visible traps. These traps include division by zero, overflow,
6754 underflow, inexact result and invalid operation. This option requires
6755 that @option{-fno-signaling-nans} be in effect. Setting this option may
6756 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6758 This option should never be turned on by any @option{-O} option since
6759 it can result in incorrect output for programs which depend on
6760 an exact implementation of IEEE or ISO rules/specifications for
6763 The default is @option{-ftrapping-math}.
6765 @item -frounding-math
6766 @opindex frounding-math
6767 Disable transformations and optimizations that assume default floating
6768 point rounding behavior. This is round-to-zero for all floating point
6769 to integer conversions, and round-to-nearest for all other arithmetic
6770 truncations. This option should be specified for programs that change
6771 the FP rounding mode dynamically, or that may be executed with a
6772 non-default rounding mode. This option disables constant folding of
6773 floating point expressions at compile-time (which may be affected by
6774 rounding mode) and arithmetic transformations that are unsafe in the
6775 presence of sign-dependent rounding modes.
6777 The default is @option{-fno-rounding-math}.
6779 This option is experimental and does not currently guarantee to
6780 disable all GCC optimizations that are affected by rounding mode.
6781 Future versions of GCC may provide finer control of this setting
6782 using C99's @code{FENV_ACCESS} pragma. This command line option
6783 will be used to specify the default state for @code{FENV_ACCESS}.
6785 @item -frtl-abstract-sequences
6786 @opindex frtl-abstract-sequences
6787 It is a size optimization method. This option is to find identical
6788 sequences of code, which can be turned into pseudo-procedures and
6789 then replace all occurrences with calls to the newly created
6790 subroutine. It is kind of an opposite of @option{-finline-functions}.
6791 This optimization runs at RTL level.
6793 @item -fsignaling-nans
6794 @opindex fsignaling-nans
6795 Compile code assuming that IEEE signaling NaNs may generate user-visible
6796 traps during floating-point operations. Setting this option disables
6797 optimizations that may change the number of exceptions visible with
6798 signaling NaNs. This option implies @option{-ftrapping-math}.
6800 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6803 The default is @option{-fno-signaling-nans}.
6805 This option is experimental and does not currently guarantee to
6806 disable all GCC optimizations that affect signaling NaN behavior.
6808 @item -fsingle-precision-constant
6809 @opindex fsingle-precision-constant
6810 Treat floating point constant as single precision constant instead of
6811 implicitly converting it to double precision constant.
6813 @item -fcx-limited-range
6814 @opindex fcx-limited-range
6815 When enabled, this option states that a range reduction step is not
6816 needed when performing complex division. Also, there is no checking
6817 whether the result of a complex multiplication or division is @code{NaN
6818 + I*NaN}, with an attempt to rescue the situation in that case. The
6819 default is @option{-fno-cx-limited-range}, but is enabled by
6820 @option{-ffast-math}.
6822 This option controls the default setting of the ISO C99
6823 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6826 @item -fcx-fortran-rules
6827 @opindex fcx-fortran-rules
6828 Complex multiplication and division follow Fortran rules. Range
6829 reduction is done as part of complex division, but there is no checking
6830 whether the result of a complex multiplication or division is @code{NaN
6831 + I*NaN}, with an attempt to rescue the situation in that case.
6833 The default is @option{-fno-cx-fortran-rules}.
6837 The following options control optimizations that may improve
6838 performance, but are not enabled by any @option{-O} options. This
6839 section includes experimental options that may produce broken code.
6842 @item -fbranch-probabilities
6843 @opindex fbranch-probabilities
6844 After running a program compiled with @option{-fprofile-arcs}
6845 (@pxref{Debugging Options,, Options for Debugging Your Program or
6846 @command{gcc}}), you can compile it a second time using
6847 @option{-fbranch-probabilities}, to improve optimizations based on
6848 the number of times each branch was taken. When the program
6849 compiled with @option{-fprofile-arcs} exits it saves arc execution
6850 counts to a file called @file{@var{sourcename}.gcda} for each source
6851 file. The information in this data file is very dependent on the
6852 structure of the generated code, so you must use the same source code
6853 and the same optimization options for both compilations.
6855 With @option{-fbranch-probabilities}, GCC puts a
6856 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6857 These can be used to improve optimization. Currently, they are only
6858 used in one place: in @file{reorg.c}, instead of guessing which path a
6859 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6860 exactly determine which path is taken more often.
6862 @item -fprofile-values
6863 @opindex fprofile-values
6864 If combined with @option{-fprofile-arcs}, it adds code so that some
6865 data about values of expressions in the program is gathered.
6867 With @option{-fbranch-probabilities}, it reads back the data gathered
6868 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6869 notes to instructions for their later usage in optimizations.
6871 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6875 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6876 a code to gather information about values of expressions.
6878 With @option{-fbranch-probabilities}, it reads back the data gathered
6879 and actually performs the optimizations based on them.
6880 Currently the optimizations include specialization of division operation
6881 using the knowledge about the value of the denominator.
6883 @item -frename-registers
6884 @opindex frename-registers
6885 Attempt to avoid false dependencies in scheduled code by making use
6886 of registers left over after register allocation. This optimization
6887 will most benefit processors with lots of registers. Depending on the
6888 debug information format adopted by the target, however, it can
6889 make debugging impossible, since variables will no longer stay in
6890 a ``home register''.
6892 Enabled by default with @option{-funroll-loops}.
6896 Perform tail duplication to enlarge superblock size. This transformation
6897 simplifies the control flow of the function allowing other optimizations to do
6900 Enabled with @option{-fprofile-use}.
6902 @item -funroll-loops
6903 @opindex funroll-loops
6904 Unroll loops whose number of iterations can be determined at compile time or
6905 upon entry to the loop. @option{-funroll-loops} implies
6906 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6907 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6908 small constant number of iterations). This option makes code larger, and may
6909 or may not make it run faster.
6911 Enabled with @option{-fprofile-use}.
6913 @item -funroll-all-loops
6914 @opindex funroll-all-loops
6915 Unroll all loops, even if their number of iterations is uncertain when
6916 the loop is entered. This usually makes programs run more slowly.
6917 @option{-funroll-all-loops} implies the same options as
6918 @option{-funroll-loops}.
6921 @opindex fpeel-loops
6922 Peels the loops for that there is enough information that they do not
6923 roll much (from profile feedback). It also turns on complete loop peeling
6924 (i.e.@: complete removal of loops with small constant number of iterations).
6926 Enabled with @option{-fprofile-use}.
6928 @item -fmove-loop-invariants
6929 @opindex fmove-loop-invariants
6930 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6931 at level @option{-O1}
6933 @item -funswitch-loops
6934 @opindex funswitch-loops
6935 Move branches with loop invariant conditions out of the loop, with duplicates
6936 of the loop on both branches (modified according to result of the condition).
6938 @item -ffunction-sections
6939 @itemx -fdata-sections
6940 @opindex ffunction-sections
6941 @opindex fdata-sections
6942 Place each function or data item into its own section in the output
6943 file if the target supports arbitrary sections. The name of the
6944 function or the name of the data item determines the section's name
6947 Use these options on systems where the linker can perform optimizations
6948 to improve locality of reference in the instruction space. Most systems
6949 using the ELF object format and SPARC processors running Solaris 2 have
6950 linkers with such optimizations. AIX may have these optimizations in
6953 Only use these options when there are significant benefits from doing
6954 so. When you specify these options, the assembler and linker will
6955 create larger object and executable files and will also be slower.
6956 You will not be able to use @code{gprof} on all systems if you
6957 specify this option and you may have problems with debugging if
6958 you specify both this option and @option{-g}.
6960 @item -fbranch-target-load-optimize
6961 @opindex fbranch-target-load-optimize
6962 Perform branch target register load optimization before prologue / epilogue
6964 The use of target registers can typically be exposed only during reload,
6965 thus hoisting loads out of loops and doing inter-block scheduling needs
6966 a separate optimization pass.
6968 @item -fbranch-target-load-optimize2
6969 @opindex fbranch-target-load-optimize2
6970 Perform branch target register load optimization after prologue / epilogue
6973 @item -fbtr-bb-exclusive
6974 @opindex fbtr-bb-exclusive
6975 When performing branch target register load optimization, don't reuse
6976 branch target registers in within any basic block.
6978 @item -fstack-protector
6979 @opindex fstack-protector
6980 Emit extra code to check for buffer overflows, such as stack smashing
6981 attacks. This is done by adding a guard variable to functions with
6982 vulnerable objects. This includes functions that call alloca, and
6983 functions with buffers larger than 8 bytes. The guards are initialized
6984 when a function is entered and then checked when the function exits.
6985 If a guard check fails, an error message is printed and the program exits.
6987 @item -fstack-protector-all
6988 @opindex fstack-protector-all
6989 Like @option{-fstack-protector} except that all functions are protected.
6991 @item -fsection-anchors
6992 @opindex fsection-anchors
6993 Try to reduce the number of symbolic address calculations by using
6994 shared ``anchor'' symbols to address nearby objects. This transformation
6995 can help to reduce the number of GOT entries and GOT accesses on some
6998 For example, the implementation of the following function @code{foo}:
7002 int foo (void) @{ return a + b + c; @}
7005 would usually calculate the addresses of all three variables, but if you
7006 compile it with @option{-fsection-anchors}, it will access the variables
7007 from a common anchor point instead. The effect is similar to the
7008 following pseudocode (which isn't valid C):
7013 register int *xr = &x;
7014 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
7018 Not all targets support this option.
7020 @item --param @var{name}=@var{value}
7022 In some places, GCC uses various constants to control the amount of
7023 optimization that is done. For example, GCC will not inline functions
7024 that contain more that a certain number of instructions. You can
7025 control some of these constants on the command-line using the
7026 @option{--param} option.
7028 The names of specific parameters, and the meaning of the values, are
7029 tied to the internals of the compiler, and are subject to change
7030 without notice in future releases.
7032 In each case, the @var{value} is an integer. The allowable choices for
7033 @var{name} are given in the following table:
7036 @item sra-max-structure-size
7037 The maximum structure size, in bytes, at which the scalar replacement
7038 of aggregates (SRA) optimization will perform block copies. The
7039 default value, 0, implies that GCC will select the most appropriate
7042 @item sra-field-structure-ratio
7043 The threshold ratio (as a percentage) between instantiated fields and
7044 the complete structure size. We say that if the ratio of the number
7045 of bytes in instantiated fields to the number of bytes in the complete
7046 structure exceeds this parameter, then block copies are not used. The
7049 @item struct-reorg-cold-struct-ratio
7050 The threshold ratio (as a percentage) between a structure frequency
7051 and the frequency of the hottest structure in the program. This parameter
7052 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
7053 We say that if the ratio of a structure frequency, calculated by profiling,
7054 to the hottest structure frequency in the program is less than this
7055 parameter, then structure reorganization is not applied to this structure.
7058 @item predictable-branch-cost-outcome
7059 When branch is predicted to be taken with probability lower than this threshold
7060 (in percent), then it is considered well predictable. The default is 10.
7062 @item max-crossjump-edges
7063 The maximum number of incoming edges to consider for crossjumping.
7064 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
7065 the number of edges incoming to each block. Increasing values mean
7066 more aggressive optimization, making the compile time increase with
7067 probably small improvement in executable size.
7069 @item min-crossjump-insns
7070 The minimum number of instructions which must be matched at the end
7071 of two blocks before crossjumping will be performed on them. This
7072 value is ignored in the case where all instructions in the block being
7073 crossjumped from are matched. The default value is 5.
7075 @item max-grow-copy-bb-insns
7076 The maximum code size expansion factor when copying basic blocks
7077 instead of jumping. The expansion is relative to a jump instruction.
7078 The default value is 8.
7080 @item max-goto-duplication-insns
7081 The maximum number of instructions to duplicate to a block that jumps
7082 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
7083 passes, GCC factors computed gotos early in the compilation process,
7084 and unfactors them as late as possible. Only computed jumps at the
7085 end of a basic blocks with no more than max-goto-duplication-insns are
7086 unfactored. The default value is 8.
7088 @item max-delay-slot-insn-search
7089 The maximum number of instructions to consider when looking for an
7090 instruction to fill a delay slot. If more than this arbitrary number of
7091 instructions is searched, the time savings from filling the delay slot
7092 will be minimal so stop searching. Increasing values mean more
7093 aggressive optimization, making the compile time increase with probably
7094 small improvement in executable run time.
7096 @item max-delay-slot-live-search
7097 When trying to fill delay slots, the maximum number of instructions to
7098 consider when searching for a block with valid live register
7099 information. Increasing this arbitrarily chosen value means more
7100 aggressive optimization, increasing the compile time. This parameter
7101 should be removed when the delay slot code is rewritten to maintain the
7104 @item max-gcse-memory
7105 The approximate maximum amount of memory that will be allocated in
7106 order to perform the global common subexpression elimination
7107 optimization. If more memory than specified is required, the
7108 optimization will not be done.
7110 @item max-gcse-passes
7111 The maximum number of passes of GCSE to run. The default is 1.
7113 @item max-pending-list-length
7114 The maximum number of pending dependencies scheduling will allow
7115 before flushing the current state and starting over. Large functions
7116 with few branches or calls can create excessively large lists which
7117 needlessly consume memory and resources.
7119 @item max-inline-insns-single
7120 Several parameters control the tree inliner used in gcc.
7121 This number sets the maximum number of instructions (counted in GCC's
7122 internal representation) in a single function that the tree inliner
7123 will consider for inlining. This only affects functions declared
7124 inline and methods implemented in a class declaration (C++).
7125 The default value is 450.
7127 @item max-inline-insns-auto
7128 When you use @option{-finline-functions} (included in @option{-O3}),
7129 a lot of functions that would otherwise not be considered for inlining
7130 by the compiler will be investigated. To those functions, a different
7131 (more restrictive) limit compared to functions declared inline can
7133 The default value is 90.
7135 @item large-function-insns
7136 The limit specifying really large functions. For functions larger than this
7137 limit after inlining, inlining is constrained by
7138 @option{--param large-function-growth}. This parameter is useful primarily
7139 to avoid extreme compilation time caused by non-linear algorithms used by the
7141 The default value is 2700.
7143 @item large-function-growth
7144 Specifies maximal growth of large function caused by inlining in percents.
7145 The default value is 100 which limits large function growth to 2.0 times
7148 @item large-unit-insns
7149 The limit specifying large translation unit. Growth caused by inlining of
7150 units larger than this limit is limited by @option{--param inline-unit-growth}.
7151 For small units this might be too tight (consider unit consisting of function A
7152 that is inline and B that just calls A three time. If B is small relative to
7153 A, the growth of unit is 300\% and yet such inlining is very sane. For very
7154 large units consisting of small inlineable functions however the overall unit
7155 growth limit is needed to avoid exponential explosion of code size. Thus for
7156 smaller units, the size is increased to @option{--param large-unit-insns}
7157 before applying @option{--param inline-unit-growth}. The default is 10000
7159 @item inline-unit-growth
7160 Specifies maximal overall growth of the compilation unit caused by inlining.
7161 The default value is 30 which limits unit growth to 1.3 times the original
7164 @item ipcp-unit-growth
7165 Specifies maximal overall growth of the compilation unit caused by
7166 interprocedural constant propagation. The default value is 10 which limits
7167 unit growth to 1.1 times the original size.
7169 @item large-stack-frame
7170 The limit specifying large stack frames. While inlining the algorithm is trying
7171 to not grow past this limit too much. Default value is 256 bytes.
7173 @item large-stack-frame-growth
7174 Specifies maximal growth of large stack frames caused by inlining in percents.
7175 The default value is 1000 which limits large stack frame growth to 11 times
7178 @item max-inline-insns-recursive
7179 @itemx max-inline-insns-recursive-auto
7180 Specifies maximum number of instructions out-of-line copy of self recursive inline
7181 function can grow into by performing recursive inlining.
7183 For functions declared inline @option{--param max-inline-insns-recursive} is
7184 taken into account. For function not declared inline, recursive inlining
7185 happens only when @option{-finline-functions} (included in @option{-O3}) is
7186 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
7187 default value is 450.
7189 @item max-inline-recursive-depth
7190 @itemx max-inline-recursive-depth-auto
7191 Specifies maximum recursion depth used by the recursive inlining.
7193 For functions declared inline @option{--param max-inline-recursive-depth} is
7194 taken into account. For function not declared inline, recursive inlining
7195 happens only when @option{-finline-functions} (included in @option{-O3}) is
7196 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
7199 @item min-inline-recursive-probability
7200 Recursive inlining is profitable only for function having deep recursion
7201 in average and can hurt for function having little recursion depth by
7202 increasing the prologue size or complexity of function body to other
7205 When profile feedback is available (see @option{-fprofile-generate}) the actual
7206 recursion depth can be guessed from probability that function will recurse via
7207 given call expression. This parameter limits inlining only to call expression
7208 whose probability exceeds given threshold (in percents). The default value is
7211 @item inline-call-cost
7212 Specify cost of call instruction relative to simple arithmetics operations
7213 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
7214 functions and at the same time increases size of leaf function that is believed to
7215 reduce function size by being inlined. In effect it increases amount of
7216 inlining for code having large abstraction penalty (many functions that just
7217 pass the arguments to other functions) and decrease inlining for code with low
7218 abstraction penalty. The default value is 12.
7220 @item min-vect-loop-bound
7221 The minimum number of iterations under which a loop will not get vectorized
7222 when @option{-ftree-vectorize} is used. The number of iterations after
7223 vectorization needs to be greater than the value specified by this option
7224 to allow vectorization. The default value is 0.
7226 @item max-unrolled-insns
7227 The maximum number of instructions that a loop should have if that loop
7228 is unrolled, and if the loop is unrolled, it determines how many times
7229 the loop code is unrolled.
7231 @item max-average-unrolled-insns
7232 The maximum number of instructions biased by probabilities of their execution
7233 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7234 it determines how many times the loop code is unrolled.
7236 @item max-unroll-times
7237 The maximum number of unrollings of a single loop.
7239 @item max-peeled-insns
7240 The maximum number of instructions that a loop should have if that loop
7241 is peeled, and if the loop is peeled, it determines how many times
7242 the loop code is peeled.
7244 @item max-peel-times
7245 The maximum number of peelings of a single loop.
7247 @item max-completely-peeled-insns
7248 The maximum number of insns of a completely peeled loop.
7250 @item max-completely-peel-times
7251 The maximum number of iterations of a loop to be suitable for complete peeling.
7253 @item max-unswitch-insns
7254 The maximum number of insns of an unswitched loop.
7256 @item max-unswitch-level
7257 The maximum number of branches unswitched in a single loop.
7260 The minimum cost of an expensive expression in the loop invariant motion.
7262 @item iv-consider-all-candidates-bound
7263 Bound on number of candidates for induction variables below that
7264 all candidates are considered for each use in induction variable
7265 optimizations. Only the most relevant candidates are considered
7266 if there are more candidates, to avoid quadratic time complexity.
7268 @item iv-max-considered-uses
7269 The induction variable optimizations give up on loops that contain more
7270 induction variable uses.
7272 @item iv-always-prune-cand-set-bound
7273 If number of candidates in the set is smaller than this value,
7274 we always try to remove unnecessary ivs from the set during its
7275 optimization when a new iv is added to the set.
7277 @item scev-max-expr-size
7278 Bound on size of expressions used in the scalar evolutions analyzer.
7279 Large expressions slow the analyzer.
7281 @item omega-max-vars
7282 The maximum number of variables in an Omega constraint system.
7283 The default value is 128.
7285 @item omega-max-geqs
7286 The maximum number of inequalities in an Omega constraint system.
7287 The default value is 256.
7290 The maximum number of equalities in an Omega constraint system.
7291 The default value is 128.
7293 @item omega-max-wild-cards
7294 The maximum number of wildcard variables that the Omega solver will
7295 be able to insert. The default value is 18.
7297 @item omega-hash-table-size
7298 The size of the hash table in the Omega solver. The default value is
7301 @item omega-max-keys
7302 The maximal number of keys used by the Omega solver. The default
7305 @item omega-eliminate-redundant-constraints
7306 When set to 1, use expensive methods to eliminate all redundant
7307 constraints. The default value is 0.
7309 @item vect-max-version-for-alignment-checks
7310 The maximum number of runtime checks that can be performed when
7311 doing loop versioning for alignment in the vectorizer. See option
7312 ftree-vect-loop-version for more information.
7314 @item vect-max-version-for-alias-checks
7315 The maximum number of runtime checks that can be performed when
7316 doing loop versioning for alias in the vectorizer. See option
7317 ftree-vect-loop-version for more information.
7319 @item max-iterations-to-track
7321 The maximum number of iterations of a loop the brute force algorithm
7322 for analysis of # of iterations of the loop tries to evaluate.
7324 @item hot-bb-count-fraction
7325 Select fraction of the maximal count of repetitions of basic block in program
7326 given basic block needs to have to be considered hot.
7328 @item hot-bb-frequency-fraction
7329 Select fraction of the maximal frequency of executions of basic block in
7330 function given basic block needs to have to be considered hot
7332 @item max-predicted-iterations
7333 The maximum number of loop iterations we predict statically. This is useful
7334 in cases where function contain single loop with known bound and other loop
7335 with unknown. We predict the known number of iterations correctly, while
7336 the unknown number of iterations average to roughly 10. This means that the
7337 loop without bounds would appear artificially cold relative to the other one.
7339 @item align-threshold
7341 Select fraction of the maximal frequency of executions of basic block in
7342 function given basic block will get aligned.
7344 @item align-loop-iterations
7346 A loop expected to iterate at lest the selected number of iterations will get
7349 @item tracer-dynamic-coverage
7350 @itemx tracer-dynamic-coverage-feedback
7352 This value is used to limit superblock formation once the given percentage of
7353 executed instructions is covered. This limits unnecessary code size
7356 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7357 feedback is available. The real profiles (as opposed to statically estimated
7358 ones) are much less balanced allowing the threshold to be larger value.
7360 @item tracer-max-code-growth
7361 Stop tail duplication once code growth has reached given percentage. This is
7362 rather hokey argument, as most of the duplicates will be eliminated later in
7363 cross jumping, so it may be set to much higher values than is the desired code
7366 @item tracer-min-branch-ratio
7368 Stop reverse growth when the reverse probability of best edge is less than this
7369 threshold (in percent).
7371 @item tracer-min-branch-ratio
7372 @itemx tracer-min-branch-ratio-feedback
7374 Stop forward growth if the best edge do have probability lower than this
7377 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7378 compilation for profile feedback and one for compilation without. The value
7379 for compilation with profile feedback needs to be more conservative (higher) in
7380 order to make tracer effective.
7382 @item max-cse-path-length
7384 Maximum number of basic blocks on path that cse considers. The default is 10.
7387 The maximum instructions CSE process before flushing. The default is 1000.
7389 @item max-aliased-vops
7391 Maximum number of virtual operands per function allowed to represent
7392 aliases before triggering the alias partitioning heuristic. Alias
7393 partitioning reduces compile times and memory consumption needed for
7394 aliasing at the expense of precision loss in alias information. The
7395 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7398 Notice that if a function contains more memory statements than the
7399 value of this parameter, it is not really possible to achieve this
7400 reduction. In this case, the compiler will use the number of memory
7401 statements as the value for @option{max-aliased-vops}.
7403 @item avg-aliased-vops
7405 Average number of virtual operands per statement allowed to represent
7406 aliases before triggering the alias partitioning heuristic. This
7407 works in conjunction with @option{max-aliased-vops}. If a function
7408 contains more than @option{max-aliased-vops} virtual operators, then
7409 memory symbols will be grouped into memory partitions until either the
7410 total number of virtual operators is below @option{max-aliased-vops}
7411 or the average number of virtual operators per memory statement is
7412 below @option{avg-aliased-vops}. The default value for this parameter
7413 is 1 for -O1 and -O2, and 3 for -O3.
7415 @item ggc-min-expand
7417 GCC uses a garbage collector to manage its own memory allocation. This
7418 parameter specifies the minimum percentage by which the garbage
7419 collector's heap should be allowed to expand between collections.
7420 Tuning this may improve compilation speed; it has no effect on code
7423 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7424 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7425 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7426 GCC is not able to calculate RAM on a particular platform, the lower
7427 bound of 30% is used. Setting this parameter and
7428 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7429 every opportunity. This is extremely slow, but can be useful for
7432 @item ggc-min-heapsize
7434 Minimum size of the garbage collector's heap before it begins bothering
7435 to collect garbage. The first collection occurs after the heap expands
7436 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7437 tuning this may improve compilation speed, and has no effect on code
7440 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7441 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7442 with a lower bound of 4096 (four megabytes) and an upper bound of
7443 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7444 particular platform, the lower bound is used. Setting this parameter
7445 very large effectively disables garbage collection. Setting this
7446 parameter and @option{ggc-min-expand} to zero causes a full collection
7447 to occur at every opportunity.
7449 @item max-reload-search-insns
7450 The maximum number of instruction reload should look backward for equivalent
7451 register. Increasing values mean more aggressive optimization, making the
7452 compile time increase with probably slightly better performance. The default
7455 @item max-cselib-memory-locations
7456 The maximum number of memory locations cselib should take into account.
7457 Increasing values mean more aggressive optimization, making the compile time
7458 increase with probably slightly better performance. The default value is 500.
7460 @item reorder-blocks-duplicate
7461 @itemx reorder-blocks-duplicate-feedback
7463 Used by basic block reordering pass to decide whether to use unconditional
7464 branch or duplicate the code on its destination. Code is duplicated when its
7465 estimated size is smaller than this value multiplied by the estimated size of
7466 unconditional jump in the hot spots of the program.
7468 The @option{reorder-block-duplicate-feedback} is used only when profile
7469 feedback is available and may be set to higher values than
7470 @option{reorder-block-duplicate} since information about the hot spots is more
7473 @item max-sched-ready-insns
7474 The maximum number of instructions ready to be issued the scheduler should
7475 consider at any given time during the first scheduling pass. Increasing
7476 values mean more thorough searches, making the compilation time increase
7477 with probably little benefit. The default value is 100.
7479 @item max-sched-region-blocks
7480 The maximum number of blocks in a region to be considered for
7481 interblock scheduling. The default value is 10.
7483 @item max-pipeline-region-blocks
7484 The maximum number of blocks in a region to be considered for
7485 pipelining in the selective scheduler. The default value is 15.
7487 @item max-sched-region-insns
7488 The maximum number of insns in a region to be considered for
7489 interblock scheduling. The default value is 100.
7491 @item max-pipeline-region-insns
7492 The maximum number of insns in a region to be considered for
7493 pipelining in the selective scheduler. The default value is 200.
7496 The minimum probability (in percents) of reaching a source block
7497 for interblock speculative scheduling. The default value is 40.
7499 @item max-sched-extend-regions-iters
7500 The maximum number of iterations through CFG to extend regions.
7501 0 - disable region extension,
7502 N - do at most N iterations.
7503 The default value is 0.
7505 @item max-sched-insn-conflict-delay
7506 The maximum conflict delay for an insn to be considered for speculative motion.
7507 The default value is 3.
7509 @item sched-spec-prob-cutoff
7510 The minimal probability of speculation success (in percents), so that
7511 speculative insn will be scheduled.
7512 The default value is 40.
7514 @item sched-mem-true-dep-cost
7515 Minimal distance (in CPU cycles) between store and load targeting same
7516 memory locations. The default value is 1.
7518 @item selsched-max-lookahead
7519 The maximum size of the lookahead window of selective scheduling. It is a
7520 depth of search for available instructions.
7521 The default value is 50.
7523 @item selsched-max-sched-times
7524 The maximum number of times that an instruction will be scheduled during
7525 selective scheduling. This is the limit on the number of iterations
7526 through which the instruction may be pipelined. The default value is 2.
7528 @item selsched-max-insns-to-rename
7529 The maximum number of best instructions in the ready list that are considered
7530 for renaming in the selective scheduler. The default value is 2.
7532 @item max-last-value-rtl
7533 The maximum size measured as number of RTLs that can be recorded in an expression
7534 in combiner for a pseudo register as last known value of that register. The default
7537 @item integer-share-limit
7538 Small integer constants can use a shared data structure, reducing the
7539 compiler's memory usage and increasing its speed. This sets the maximum
7540 value of a shared integer constant. The default value is 256.
7542 @item min-virtual-mappings
7543 Specifies the minimum number of virtual mappings in the incremental
7544 SSA updater that should be registered to trigger the virtual mappings
7545 heuristic defined by virtual-mappings-ratio. The default value is
7548 @item virtual-mappings-ratio
7549 If the number of virtual mappings is virtual-mappings-ratio bigger
7550 than the number of virtual symbols to be updated, then the incremental
7551 SSA updater switches to a full update for those symbols. The default
7554 @item ssp-buffer-size
7555 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7556 protection when @option{-fstack-protection} is used.
7558 @item max-jump-thread-duplication-stmts
7559 Maximum number of statements allowed in a block that needs to be
7560 duplicated when threading jumps.
7562 @item max-fields-for-field-sensitive
7563 Maximum number of fields in a structure we will treat in
7564 a field sensitive manner during pointer analysis. The default is zero
7565 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7567 @item prefetch-latency
7568 Estimate on average number of instructions that are executed before
7569 prefetch finishes. The distance we prefetch ahead is proportional
7570 to this constant. Increasing this number may also lead to less
7571 streams being prefetched (see @option{simultaneous-prefetches}).
7573 @item simultaneous-prefetches
7574 Maximum number of prefetches that can run at the same time.
7576 @item l1-cache-line-size
7577 The size of cache line in L1 cache, in bytes.
7580 The size of L1 cache, in kilobytes.
7583 The size of L2 cache, in kilobytes.
7585 @item use-canonical-types
7586 Whether the compiler should use the ``canonical'' type system. By
7587 default, this should always be 1, which uses a more efficient internal
7588 mechanism for comparing types in C++ and Objective-C++. However, if
7589 bugs in the canonical type system are causing compilation failures,
7590 set this value to 0 to disable canonical types.
7592 @item switch-conversion-max-branch-ratio
7593 Switch initialization conversion will refuse to create arrays that are
7594 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7595 branches in the switch.
7597 @item max-partial-antic-length
7598 Maximum length of the partial antic set computed during the tree
7599 partial redundancy elimination optimization (@option{-ftree-pre}) when
7600 optimizing at @option{-O3} and above. For some sorts of source code
7601 the enhanced partial redundancy elimination optimization can run away,
7602 consuming all of the memory available on the host machine. This
7603 parameter sets a limit on the length of the sets that are computed,
7604 which prevents the runaway behavior. Setting a value of 0 for
7605 this parameter will allow an unlimited set length.
7607 @item sccvn-max-scc-size
7608 Maximum size of a strongly connected component (SCC) during SCCVN
7609 processing. If this limit is hit, SCCVN processing for the whole
7610 function will not be done and optimizations depending on it will
7611 be disabled. The default maximum SCC size is 10000.
7613 @item ira-max-loops-num
7614 IRA uses a regional register allocation by default. If a function
7615 contains loops more than number given by the parameter, only at most
7616 given number of the most frequently executed loops will form regions
7617 for the regional register allocation. The default value of the
7620 @item ira-max-conflict-table-size
7621 Although IRA uses a sophisticated algorithm of compression conflict
7622 table, the table can be still big for huge functions. If the conflict
7623 table for a function could be more than size in MB given by the
7624 parameter, the conflict table is not built and faster, simpler, and
7625 lower quality register allocation algorithm will be used. The
7626 algorithm do not use pseudo-register conflicts. The default value of
7627 the parameter is 2000.
7632 @node Preprocessor Options
7633 @section Options Controlling the Preprocessor
7634 @cindex preprocessor options
7635 @cindex options, preprocessor
7637 These options control the C preprocessor, which is run on each C source
7638 file before actual compilation.
7640 If you use the @option{-E} option, nothing is done except preprocessing.
7641 Some of these options make sense only together with @option{-E} because
7642 they cause the preprocessor output to be unsuitable for actual
7647 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7648 and pass @var{option} directly through to the preprocessor. If
7649 @var{option} contains commas, it is split into multiple options at the
7650 commas. However, many options are modified, translated or interpreted
7651 by the compiler driver before being passed to the preprocessor, and
7652 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7653 interface is undocumented and subject to change, so whenever possible
7654 you should avoid using @option{-Wp} and let the driver handle the
7657 @item -Xpreprocessor @var{option}
7658 @opindex preprocessor
7659 Pass @var{option} as an option to the preprocessor. You can use this to
7660 supply system-specific preprocessor options which GCC does not know how to
7663 If you want to pass an option that takes an argument, you must use
7664 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7667 @include cppopts.texi
7669 @node Assembler Options
7670 @section Passing Options to the Assembler
7672 @c prevent bad page break with this line
7673 You can pass options to the assembler.
7676 @item -Wa,@var{option}
7678 Pass @var{option} as an option to the assembler. If @var{option}
7679 contains commas, it is split into multiple options at the commas.
7681 @item -Xassembler @var{option}
7683 Pass @var{option} as an option to the assembler. You can use this to
7684 supply system-specific assembler options which GCC does not know how to
7687 If you want to pass an option that takes an argument, you must use
7688 @option{-Xassembler} twice, once for the option and once for the argument.
7693 @section Options for Linking
7694 @cindex link options
7695 @cindex options, linking
7697 These options come into play when the compiler links object files into
7698 an executable output file. They are meaningless if the compiler is
7699 not doing a link step.
7703 @item @var{object-file-name}
7704 A file name that does not end in a special recognized suffix is
7705 considered to name an object file or library. (Object files are
7706 distinguished from libraries by the linker according to the file
7707 contents.) If linking is done, these object files are used as input
7716 If any of these options is used, then the linker is not run, and
7717 object file names should not be used as arguments. @xref{Overall
7721 @item -l@var{library}
7722 @itemx -l @var{library}
7724 Search the library named @var{library} when linking. (The second
7725 alternative with the library as a separate argument is only for
7726 POSIX compliance and is not recommended.)
7728 It makes a difference where in the command you write this option; the
7729 linker searches and processes libraries and object files in the order they
7730 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7731 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7732 to functions in @samp{z}, those functions may not be loaded.
7734 The linker searches a standard list of directories for the library,
7735 which is actually a file named @file{lib@var{library}.a}. The linker
7736 then uses this file as if it had been specified precisely by name.
7738 The directories searched include several standard system directories
7739 plus any that you specify with @option{-L}.
7741 Normally the files found this way are library files---archive files
7742 whose members are object files. The linker handles an archive file by
7743 scanning through it for members which define symbols that have so far
7744 been referenced but not defined. But if the file that is found is an
7745 ordinary object file, it is linked in the usual fashion. The only
7746 difference between using an @option{-l} option and specifying a file name
7747 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7748 and searches several directories.
7752 You need this special case of the @option{-l} option in order to
7753 link an Objective-C or Objective-C++ program.
7756 @opindex nostartfiles
7757 Do not use the standard system startup files when linking.
7758 The standard system libraries are used normally, unless @option{-nostdlib}
7759 or @option{-nodefaultlibs} is used.
7761 @item -nodefaultlibs
7762 @opindex nodefaultlibs
7763 Do not use the standard system libraries when linking.
7764 Only the libraries you specify will be passed to the linker.
7765 The standard startup files are used normally, unless @option{-nostartfiles}
7766 is used. The compiler may generate calls to @code{memcmp},
7767 @code{memset}, @code{memcpy} and @code{memmove}.
7768 These entries are usually resolved by entries in
7769 libc. These entry points should be supplied through some other
7770 mechanism when this option is specified.
7774 Do not use the standard system startup files or libraries when linking.
7775 No startup files and only the libraries you specify will be passed to
7776 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7777 @code{memcpy} and @code{memmove}.
7778 These entries are usually resolved by entries in
7779 libc. These entry points should be supplied through some other
7780 mechanism when this option is specified.
7782 @cindex @option{-lgcc}, use with @option{-nostdlib}
7783 @cindex @option{-nostdlib} and unresolved references
7784 @cindex unresolved references and @option{-nostdlib}
7785 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7786 @cindex @option{-nodefaultlibs} and unresolved references
7787 @cindex unresolved references and @option{-nodefaultlibs}
7788 One of the standard libraries bypassed by @option{-nostdlib} and
7789 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7790 that GCC uses to overcome shortcomings of particular machines, or special
7791 needs for some languages.
7792 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7793 Collection (GCC) Internals},
7794 for more discussion of @file{libgcc.a}.)
7795 In most cases, you need @file{libgcc.a} even when you want to avoid
7796 other standard libraries. In other words, when you specify @option{-nostdlib}
7797 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7798 This ensures that you have no unresolved references to internal GCC
7799 library subroutines. (For example, @samp{__main}, used to ensure C++
7800 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7801 GNU Compiler Collection (GCC) Internals}.)
7805 Produce a position independent executable on targets which support it.
7806 For predictable results, you must also specify the same set of options
7807 that were used to generate code (@option{-fpie}, @option{-fPIE},
7808 or model suboptions) when you specify this option.
7812 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7813 that support it. This instructs the linker to add all symbols, not
7814 only used ones, to the dynamic symbol table. This option is needed
7815 for some uses of @code{dlopen} or to allow obtaining backtraces
7816 from within a program.
7820 Remove all symbol table and relocation information from the executable.
7824 On systems that support dynamic linking, this prevents linking with the shared
7825 libraries. On other systems, this option has no effect.
7829 Produce a shared object which can then be linked with other objects to
7830 form an executable. Not all systems support this option. For predictable
7831 results, you must also specify the same set of options that were used to
7832 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7833 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7834 needs to build supplementary stub code for constructors to work. On
7835 multi-libbed systems, @samp{gcc -shared} must select the correct support
7836 libraries to link against. Failing to supply the correct flags may lead
7837 to subtle defects. Supplying them in cases where they are not necessary
7840 @item -shared-libgcc
7841 @itemx -static-libgcc
7842 @opindex shared-libgcc
7843 @opindex static-libgcc
7844 On systems that provide @file{libgcc} as a shared library, these options
7845 force the use of either the shared or static version respectively.
7846 If no shared version of @file{libgcc} was built when the compiler was
7847 configured, these options have no effect.
7849 There are several situations in which an application should use the
7850 shared @file{libgcc} instead of the static version. The most common
7851 of these is when the application wishes to throw and catch exceptions
7852 across different shared libraries. In that case, each of the libraries
7853 as well as the application itself should use the shared @file{libgcc}.
7855 Therefore, the G++ and GCJ drivers automatically add
7856 @option{-shared-libgcc} whenever you build a shared library or a main
7857 executable, because C++ and Java programs typically use exceptions, so
7858 this is the right thing to do.
7860 If, instead, you use the GCC driver to create shared libraries, you may
7861 find that they will not always be linked with the shared @file{libgcc}.
7862 If GCC finds, at its configuration time, that you have a non-GNU linker
7863 or a GNU linker that does not support option @option{--eh-frame-hdr},
7864 it will link the shared version of @file{libgcc} into shared libraries
7865 by default. Otherwise, it will take advantage of the linker and optimize
7866 away the linking with the shared version of @file{libgcc}, linking with
7867 the static version of libgcc by default. This allows exceptions to
7868 propagate through such shared libraries, without incurring relocation
7869 costs at library load time.
7871 However, if a library or main executable is supposed to throw or catch
7872 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7873 for the languages used in the program, or using the option
7874 @option{-shared-libgcc}, such that it is linked with the shared
7879 Bind references to global symbols when building a shared object. Warn
7880 about any unresolved references (unless overridden by the link editor
7881 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7884 @item -T @var{script}
7886 @cindex linker script
7887 Use @var{script} as the linker script. This option is supported by most
7888 systems using the GNU linker. On some targets, such as bare-board
7889 targets without an operating system, the @option{-T} option may be required
7890 when linking to avoid references to undefined symbols.
7892 @item -Xlinker @var{option}
7894 Pass @var{option} as an option to the linker. You can use this to
7895 supply system-specific linker options which GCC does not know how to
7898 If you want to pass an option that takes an argument, you must use
7899 @option{-Xlinker} twice, once for the option and once for the argument.
7900 For example, to pass @option{-assert definitions}, you must write
7901 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7902 @option{-Xlinker "-assert definitions"}, because this passes the entire
7903 string as a single argument, which is not what the linker expects.
7905 @item -Wl,@var{option}
7907 Pass @var{option} as an option to the linker. If @var{option} contains
7908 commas, it is split into multiple options at the commas.
7910 @item -u @var{symbol}
7912 Pretend the symbol @var{symbol} is undefined, to force linking of
7913 library modules to define it. You can use @option{-u} multiple times with
7914 different symbols to force loading of additional library modules.
7917 @node Directory Options
7918 @section Options for Directory Search
7919 @cindex directory options
7920 @cindex options, directory search
7923 These options specify directories to search for header files, for
7924 libraries and for parts of the compiler:
7929 Add the directory @var{dir} to the head of the list of directories to be
7930 searched for header files. This can be used to override a system header
7931 file, substituting your own version, since these directories are
7932 searched before the system header file directories. However, you should
7933 not use this option to add directories that contain vendor-supplied
7934 system header files (use @option{-isystem} for that). If you use more than
7935 one @option{-I} option, the directories are scanned in left-to-right
7936 order; the standard system directories come after.
7938 If a standard system include directory, or a directory specified with
7939 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7940 option will be ignored. The directory will still be searched but as a
7941 system directory at its normal position in the system include chain.
7942 This is to ensure that GCC's procedure to fix buggy system headers and
7943 the ordering for the include_next directive are not inadvertently changed.
7944 If you really need to change the search order for system directories,
7945 use the @option{-nostdinc} and/or @option{-isystem} options.
7947 @item -iquote@var{dir}
7949 Add the directory @var{dir} to the head of the list of directories to
7950 be searched for header files only for the case of @samp{#include
7951 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7952 otherwise just like @option{-I}.
7956 Add directory @var{dir} to the list of directories to be searched
7959 @item -B@var{prefix}
7961 This option specifies where to find the executables, libraries,
7962 include files, and data files of the compiler itself.
7964 The compiler driver program runs one or more of the subprograms
7965 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7966 @var{prefix} as a prefix for each program it tries to run, both with and
7967 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7969 For each subprogram to be run, the compiler driver first tries the
7970 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7971 was not specified, the driver tries two standard prefixes, which are
7972 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7973 those results in a file name that is found, the unmodified program
7974 name is searched for using the directories specified in your
7975 @env{PATH} environment variable.
7977 The compiler will check to see if the path provided by the @option{-B}
7978 refers to a directory, and if necessary it will add a directory
7979 separator character at the end of the path.
7981 @option{-B} prefixes that effectively specify directory names also apply
7982 to libraries in the linker, because the compiler translates these
7983 options into @option{-L} options for the linker. They also apply to
7984 includes files in the preprocessor, because the compiler translates these
7985 options into @option{-isystem} options for the preprocessor. In this case,
7986 the compiler appends @samp{include} to the prefix.
7988 The run-time support file @file{libgcc.a} can also be searched for using
7989 the @option{-B} prefix, if needed. If it is not found there, the two
7990 standard prefixes above are tried, and that is all. The file is left
7991 out of the link if it is not found by those means.
7993 Another way to specify a prefix much like the @option{-B} prefix is to use
7994 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
7997 As a special kludge, if the path provided by @option{-B} is
7998 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
7999 9, then it will be replaced by @file{[dir/]include}. This is to help
8000 with boot-strapping the compiler.
8002 @item -specs=@var{file}
8004 Process @var{file} after the compiler reads in the standard @file{specs}
8005 file, in order to override the defaults that the @file{gcc} driver
8006 program uses when determining what switches to pass to @file{cc1},
8007 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
8008 @option{-specs=@var{file}} can be specified on the command line, and they
8009 are processed in order, from left to right.
8011 @item --sysroot=@var{dir}
8013 Use @var{dir} as the logical root directory for headers and libraries.
8014 For example, if the compiler would normally search for headers in
8015 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
8016 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
8018 If you use both this option and the @option{-isysroot} option, then
8019 the @option{--sysroot} option will apply to libraries, but the
8020 @option{-isysroot} option will apply to header files.
8022 The GNU linker (beginning with version 2.16) has the necessary support
8023 for this option. If your linker does not support this option, the
8024 header file aspect of @option{--sysroot} will still work, but the
8025 library aspect will not.
8029 This option has been deprecated. Please use @option{-iquote} instead for
8030 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
8031 Any directories you specify with @option{-I} options before the @option{-I-}
8032 option are searched only for the case of @samp{#include "@var{file}"};
8033 they are not searched for @samp{#include <@var{file}>}.
8035 If additional directories are specified with @option{-I} options after
8036 the @option{-I-}, these directories are searched for all @samp{#include}
8037 directives. (Ordinarily @emph{all} @option{-I} directories are used
8040 In addition, the @option{-I-} option inhibits the use of the current
8041 directory (where the current input file came from) as the first search
8042 directory for @samp{#include "@var{file}"}. There is no way to
8043 override this effect of @option{-I-}. With @option{-I.} you can specify
8044 searching the directory which was current when the compiler was
8045 invoked. That is not exactly the same as what the preprocessor does
8046 by default, but it is often satisfactory.
8048 @option{-I-} does not inhibit the use of the standard system directories
8049 for header files. Thus, @option{-I-} and @option{-nostdinc} are
8056 @section Specifying subprocesses and the switches to pass to them
8059 @command{gcc} is a driver program. It performs its job by invoking a
8060 sequence of other programs to do the work of compiling, assembling and
8061 linking. GCC interprets its command-line parameters and uses these to
8062 deduce which programs it should invoke, and which command-line options
8063 it ought to place on their command lines. This behavior is controlled
8064 by @dfn{spec strings}. In most cases there is one spec string for each
8065 program that GCC can invoke, but a few programs have multiple spec
8066 strings to control their behavior. The spec strings built into GCC can
8067 be overridden by using the @option{-specs=} command-line switch to specify
8070 @dfn{Spec files} are plaintext files that are used to construct spec
8071 strings. They consist of a sequence of directives separated by blank
8072 lines. The type of directive is determined by the first non-whitespace
8073 character on the line and it can be one of the following:
8076 @item %@var{command}
8077 Issues a @var{command} to the spec file processor. The commands that can
8081 @item %include <@var{file}>
8083 Search for @var{file} and insert its text at the current point in the
8086 @item %include_noerr <@var{file}>
8087 @cindex %include_noerr
8088 Just like @samp{%include}, but do not generate an error message if the include
8089 file cannot be found.
8091 @item %rename @var{old_name} @var{new_name}
8093 Rename the spec string @var{old_name} to @var{new_name}.
8097 @item *[@var{spec_name}]:
8098 This tells the compiler to create, override or delete the named spec
8099 string. All lines after this directive up to the next directive or
8100 blank line are considered to be the text for the spec string. If this
8101 results in an empty string then the spec will be deleted. (Or, if the
8102 spec did not exist, then nothing will happened.) Otherwise, if the spec
8103 does not currently exist a new spec will be created. If the spec does
8104 exist then its contents will be overridden by the text of this
8105 directive, unless the first character of that text is the @samp{+}
8106 character, in which case the text will be appended to the spec.
8108 @item [@var{suffix}]:
8109 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
8110 and up to the next directive or blank line are considered to make up the
8111 spec string for the indicated suffix. When the compiler encounters an
8112 input file with the named suffix, it will processes the spec string in
8113 order to work out how to compile that file. For example:
8120 This says that any input file whose name ends in @samp{.ZZ} should be
8121 passed to the program @samp{z-compile}, which should be invoked with the
8122 command-line switch @option{-input} and with the result of performing the
8123 @samp{%i} substitution. (See below.)
8125 As an alternative to providing a spec string, the text that follows a
8126 suffix directive can be one of the following:
8129 @item @@@var{language}
8130 This says that the suffix is an alias for a known @var{language}. This is
8131 similar to using the @option{-x} command-line switch to GCC to specify a
8132 language explicitly. For example:
8139 Says that .ZZ files are, in fact, C++ source files.
8142 This causes an error messages saying:
8145 @var{name} compiler not installed on this system.
8149 GCC already has an extensive list of suffixes built into it.
8150 This directive will add an entry to the end of the list of suffixes, but
8151 since the list is searched from the end backwards, it is effectively
8152 possible to override earlier entries using this technique.
8156 GCC has the following spec strings built into it. Spec files can
8157 override these strings or create their own. Note that individual
8158 targets can also add their own spec strings to this list.
8161 asm Options to pass to the assembler
8162 asm_final Options to pass to the assembler post-processor
8163 cpp Options to pass to the C preprocessor
8164 cc1 Options to pass to the C compiler
8165 cc1plus Options to pass to the C++ compiler
8166 endfile Object files to include at the end of the link
8167 link Options to pass to the linker
8168 lib Libraries to include on the command line to the linker
8169 libgcc Decides which GCC support library to pass to the linker
8170 linker Sets the name of the linker
8171 predefines Defines to be passed to the C preprocessor
8172 signed_char Defines to pass to CPP to say whether @code{char} is signed
8174 startfile Object files to include at the start of the link
8177 Here is a small example of a spec file:
8183 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
8186 This example renames the spec called @samp{lib} to @samp{old_lib} and
8187 then overrides the previous definition of @samp{lib} with a new one.
8188 The new definition adds in some extra command-line options before
8189 including the text of the old definition.
8191 @dfn{Spec strings} are a list of command-line options to be passed to their
8192 corresponding program. In addition, the spec strings can contain
8193 @samp{%}-prefixed sequences to substitute variable text or to
8194 conditionally insert text into the command line. Using these constructs
8195 it is possible to generate quite complex command lines.
8197 Here is a table of all defined @samp{%}-sequences for spec
8198 strings. Note that spaces are not generated automatically around the
8199 results of expanding these sequences. Therefore you can concatenate them
8200 together or combine them with constant text in a single argument.
8204 Substitute one @samp{%} into the program name or argument.
8207 Substitute the name of the input file being processed.
8210 Substitute the basename of the input file being processed.
8211 This is the substring up to (and not including) the last period
8212 and not including the directory.
8215 This is the same as @samp{%b}, but include the file suffix (text after
8219 Marks the argument containing or following the @samp{%d} as a
8220 temporary file name, so that that file will be deleted if GCC exits
8221 successfully. Unlike @samp{%g}, this contributes no text to the
8224 @item %g@var{suffix}
8225 Substitute a file name that has suffix @var{suffix} and is chosen
8226 once per compilation, and mark the argument in the same way as
8227 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
8228 name is now chosen in a way that is hard to predict even when previously
8229 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
8230 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
8231 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
8232 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
8233 was simply substituted with a file name chosen once per compilation,
8234 without regard to any appended suffix (which was therefore treated
8235 just like ordinary text), making such attacks more likely to succeed.
8237 @item %u@var{suffix}
8238 Like @samp{%g}, but generates a new temporary file name even if
8239 @samp{%u@var{suffix}} was already seen.
8241 @item %U@var{suffix}
8242 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
8243 new one if there is no such last file name. In the absence of any
8244 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
8245 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
8246 would involve the generation of two distinct file names, one
8247 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
8248 simply substituted with a file name chosen for the previous @samp{%u},
8249 without regard to any appended suffix.
8251 @item %j@var{suffix}
8252 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
8253 writable, and if save-temps is off; otherwise, substitute the name
8254 of a temporary file, just like @samp{%u}. This temporary file is not
8255 meant for communication between processes, but rather as a junk
8258 @item %|@var{suffix}
8259 @itemx %m@var{suffix}
8260 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
8261 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
8262 all. These are the two most common ways to instruct a program that it
8263 should read from standard input or write to standard output. If you
8264 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
8265 construct: see for example @file{f/lang-specs.h}.
8267 @item %.@var{SUFFIX}
8268 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
8269 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
8270 terminated by the next space or %.
8273 Marks the argument containing or following the @samp{%w} as the
8274 designated output file of this compilation. This puts the argument
8275 into the sequence of arguments that @samp{%o} will substitute later.
8278 Substitutes the names of all the output files, with spaces
8279 automatically placed around them. You should write spaces
8280 around the @samp{%o} as well or the results are undefined.
8281 @samp{%o} is for use in the specs for running the linker.
8282 Input files whose names have no recognized suffix are not compiled
8283 at all, but they are included among the output files, so they will
8287 Substitutes the suffix for object files. Note that this is
8288 handled specially when it immediately follows @samp{%g, %u, or %U},
8289 because of the need for those to form complete file names. The
8290 handling is such that @samp{%O} is treated exactly as if it had already
8291 been substituted, except that @samp{%g, %u, and %U} do not currently
8292 support additional @var{suffix} characters following @samp{%O} as they would
8293 following, for example, @samp{.o}.
8296 Substitutes the standard macro predefinitions for the
8297 current target machine. Use this when running @code{cpp}.
8300 Like @samp{%p}, but puts @samp{__} before and after the name of each
8301 predefined macro, except for macros that start with @samp{__} or with
8302 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8306 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8307 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8308 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8309 and @option{-imultilib} as necessary.
8312 Current argument is the name of a library or startup file of some sort.
8313 Search for that file in a standard list of directories and substitute
8314 the full name found.
8317 Print @var{str} as an error message. @var{str} is terminated by a newline.
8318 Use this when inconsistent options are detected.
8321 Substitute the contents of spec string @var{name} at this point.
8324 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8326 @item %x@{@var{option}@}
8327 Accumulate an option for @samp{%X}.
8330 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8334 Output the accumulated assembler options specified by @option{-Wa}.
8337 Output the accumulated preprocessor options specified by @option{-Wp}.
8340 Process the @code{asm} spec. This is used to compute the
8341 switches to be passed to the assembler.
8344 Process the @code{asm_final} spec. This is a spec string for
8345 passing switches to an assembler post-processor, if such a program is
8349 Process the @code{link} spec. This is the spec for computing the
8350 command line passed to the linker. Typically it will make use of the
8351 @samp{%L %G %S %D and %E} sequences.
8354 Dump out a @option{-L} option for each directory that GCC believes might
8355 contain startup files. If the target supports multilibs then the
8356 current multilib directory will be prepended to each of these paths.
8359 Process the @code{lib} spec. This is a spec string for deciding which
8360 libraries should be included on the command line to the linker.
8363 Process the @code{libgcc} spec. This is a spec string for deciding
8364 which GCC support library should be included on the command line to the linker.
8367 Process the @code{startfile} spec. This is a spec for deciding which
8368 object files should be the first ones passed to the linker. Typically
8369 this might be a file named @file{crt0.o}.
8372 Process the @code{endfile} spec. This is a spec string that specifies
8373 the last object files that will be passed to the linker.
8376 Process the @code{cpp} spec. This is used to construct the arguments
8377 to be passed to the C preprocessor.
8380 Process the @code{cc1} spec. This is used to construct the options to be
8381 passed to the actual C compiler (@samp{cc1}).
8384 Process the @code{cc1plus} spec. This is used to construct the options to be
8385 passed to the actual C++ compiler (@samp{cc1plus}).
8388 Substitute the variable part of a matched option. See below.
8389 Note that each comma in the substituted string is replaced by
8393 Remove all occurrences of @code{-S} from the command line. Note---this
8394 command is position dependent. @samp{%} commands in the spec string
8395 before this one will see @code{-S}, @samp{%} commands in the spec string
8396 after this one will not.
8398 @item %:@var{function}(@var{args})
8399 Call the named function @var{function}, passing it @var{args}.
8400 @var{args} is first processed as a nested spec string, then split
8401 into an argument vector in the usual fashion. The function returns
8402 a string which is processed as if it had appeared literally as part
8403 of the current spec.
8405 The following built-in spec functions are provided:
8409 The @code{getenv} spec function takes two arguments: an environment
8410 variable name and a string. If the environment variable is not
8411 defined, a fatal error is issued. Otherwise, the return value is the
8412 value of the environment variable concatenated with the string. For
8413 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8416 %:getenv(TOPDIR /include)
8419 expands to @file{/path/to/top/include}.
8421 @item @code{if-exists}
8422 The @code{if-exists} spec function takes one argument, an absolute
8423 pathname to a file. If the file exists, @code{if-exists} returns the
8424 pathname. Here is a small example of its usage:
8428 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8431 @item @code{if-exists-else}
8432 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8433 spec function, except that it takes two arguments. The first argument is
8434 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8435 returns the pathname. If it does not exist, it returns the second argument.
8436 This way, @code{if-exists-else} can be used to select one file or another,
8437 based on the existence of the first. Here is a small example of its usage:
8441 crt0%O%s %:if-exists(crti%O%s) \
8442 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8445 @item @code{replace-outfile}
8446 The @code{replace-outfile} spec function takes two arguments. It looks for the
8447 first argument in the outfiles array and replaces it with the second argument. Here
8448 is a small example of its usage:
8451 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8454 @item @code{print-asm-header}
8455 The @code{print-asm-header} function takes no arguments and simply
8456 prints a banner like:
8462 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8465 It is used to separate compiler options from assembler options
8466 in the @option{--target-help} output.
8470 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8471 If that switch was not specified, this substitutes nothing. Note that
8472 the leading dash is omitted when specifying this option, and it is
8473 automatically inserted if the substitution is performed. Thus the spec
8474 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8475 and would output the command line option @option{-foo}.
8477 @item %W@{@code{S}@}
8478 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8481 @item %@{@code{S}*@}
8482 Substitutes all the switches specified to GCC whose names start
8483 with @code{-S}, but which also take an argument. This is used for
8484 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8485 GCC considers @option{-o foo} as being
8486 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8487 text, including the space. Thus two arguments would be generated.
8489 @item %@{@code{S}*&@code{T}*@}
8490 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8491 (the order of @code{S} and @code{T} in the spec is not significant).
8492 There can be any number of ampersand-separated variables; for each the
8493 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8495 @item %@{@code{S}:@code{X}@}
8496 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8498 @item %@{!@code{S}:@code{X}@}
8499 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8501 @item %@{@code{S}*:@code{X}@}
8502 Substitutes @code{X} if one or more switches whose names start with
8503 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8504 once, no matter how many such switches appeared. However, if @code{%*}
8505 appears somewhere in @code{X}, then @code{X} will be substituted once
8506 for each matching switch, with the @code{%*} replaced by the part of
8507 that switch that matched the @code{*}.
8509 @item %@{.@code{S}:@code{X}@}
8510 Substitutes @code{X}, if processing a file with suffix @code{S}.
8512 @item %@{!.@code{S}:@code{X}@}
8513 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8515 @item %@{,@code{S}:@code{X}@}
8516 Substitutes @code{X}, if processing a file for language @code{S}.
8518 @item %@{!,@code{S}:@code{X}@}
8519 Substitutes @code{X}, if not processing a file for language @code{S}.
8521 @item %@{@code{S}|@code{P}:@code{X}@}
8522 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8523 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8524 @code{*} sequences as well, although they have a stronger binding than
8525 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8526 alternatives must be starred, and only the first matching alternative
8529 For example, a spec string like this:
8532 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8535 will output the following command-line options from the following input
8536 command-line options:
8541 -d fred.c -foo -baz -boggle
8542 -d jim.d -bar -baz -boggle
8545 @item %@{S:X; T:Y; :D@}
8547 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8548 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8549 be as many clauses as you need. This may be combined with @code{.},
8550 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8555 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8556 construct may contain other nested @samp{%} constructs or spaces, or
8557 even newlines. They are processed as usual, as described above.
8558 Trailing white space in @code{X} is ignored. White space may also
8559 appear anywhere on the left side of the colon in these constructs,
8560 except between @code{.} or @code{*} and the corresponding word.
8562 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8563 handled specifically in these constructs. If another value of
8564 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8565 @option{-W} switch is found later in the command line, the earlier
8566 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8567 just one letter, which passes all matching options.
8569 The character @samp{|} at the beginning of the predicate text is used to
8570 indicate that a command should be piped to the following command, but
8571 only if @option{-pipe} is specified.
8573 It is built into GCC which switches take arguments and which do not.
8574 (You might think it would be useful to generalize this to allow each
8575 compiler's spec to say which switches take arguments. But this cannot
8576 be done in a consistent fashion. GCC cannot even decide which input
8577 files have been specified without knowing which switches take arguments,
8578 and it must know which input files to compile in order to tell which
8581 GCC also knows implicitly that arguments starting in @option{-l} are to be
8582 treated as compiler output files, and passed to the linker in their
8583 proper position among the other output files.
8585 @c man begin OPTIONS
8587 @node Target Options
8588 @section Specifying Target Machine and Compiler Version
8589 @cindex target options
8590 @cindex cross compiling
8591 @cindex specifying machine version
8592 @cindex specifying compiler version and target machine
8593 @cindex compiler version, specifying
8594 @cindex target machine, specifying
8596 The usual way to run GCC is to run the executable called @file{gcc}, or
8597 @file{<machine>-gcc} when cross-compiling, or
8598 @file{<machine>-gcc-<version>} to run a version other than the one that
8599 was installed last. Sometimes this is inconvenient, so GCC provides
8600 options that will switch to another cross-compiler or version.
8603 @item -b @var{machine}
8605 The argument @var{machine} specifies the target machine for compilation.
8607 The value to use for @var{machine} is the same as was specified as the
8608 machine type when configuring GCC as a cross-compiler. For
8609 example, if a cross-compiler was configured with @samp{configure
8610 arm-elf}, meaning to compile for an arm processor with elf binaries,
8611 then you would specify @option{-b arm-elf} to run that cross compiler.
8612 Because there are other options beginning with @option{-b}, the
8613 configuration must contain a hyphen, or @option{-b} alone should be one
8614 argument followed by the configuration in the next argument.
8616 @item -V @var{version}
8618 The argument @var{version} specifies which version of GCC to run.
8619 This is useful when multiple versions are installed. For example,
8620 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8623 The @option{-V} and @option{-b} options work by running the
8624 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8625 use them if you can just run that directly.
8627 @node Submodel Options
8628 @section Hardware Models and Configurations
8629 @cindex submodel options
8630 @cindex specifying hardware config
8631 @cindex hardware models and configurations, specifying
8632 @cindex machine dependent options
8634 Earlier we discussed the standard option @option{-b} which chooses among
8635 different installed compilers for completely different target
8636 machines, such as VAX vs.@: 68000 vs.@: 80386.
8638 In addition, each of these target machine types can have its own
8639 special options, starting with @samp{-m}, to choose among various
8640 hardware models or configurations---for example, 68010 vs 68020,
8641 floating coprocessor or none. A single installed version of the
8642 compiler can compile for any model or configuration, according to the
8645 Some configurations of the compiler also support additional special
8646 options, usually for compatibility with other compilers on the same
8649 @c This list is ordered alphanumerically by subsection name.
8650 @c It should be the same order and spelling as these options are listed
8651 @c in Machine Dependent Options
8657 * Blackfin Options::
8661 * DEC Alpha Options::
8662 * DEC Alpha/VMS Options::
8664 * GNU/Linux Options::
8667 * i386 and x86-64 Options::
8678 * picoChip Options::
8680 * RS/6000 and PowerPC Options::
8681 * S/390 and zSeries Options::
8686 * System V Options::
8691 * Xstormy16 Options::
8697 @subsection ARC Options
8700 These options are defined for ARC implementations:
8705 Compile code for little endian mode. This is the default.
8709 Compile code for big endian mode.
8712 @opindex mmangle-cpu
8713 Prepend the name of the cpu to all public symbol names.
8714 In multiple-processor systems, there are many ARC variants with different
8715 instruction and register set characteristics. This flag prevents code
8716 compiled for one cpu to be linked with code compiled for another.
8717 No facility exists for handling variants that are ``almost identical''.
8718 This is an all or nothing option.
8720 @item -mcpu=@var{cpu}
8722 Compile code for ARC variant @var{cpu}.
8723 Which variants are supported depend on the configuration.
8724 All variants support @option{-mcpu=base}, this is the default.
8726 @item -mtext=@var{text-section}
8727 @itemx -mdata=@var{data-section}
8728 @itemx -mrodata=@var{readonly-data-section}
8732 Put functions, data, and readonly data in @var{text-section},
8733 @var{data-section}, and @var{readonly-data-section} respectively
8734 by default. This can be overridden with the @code{section} attribute.
8735 @xref{Variable Attributes}.
8737 @item -mfix-cortex-m3-ldrd
8738 @opindex mfix-cortex-m3-ldrd
8739 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
8740 with overlapping destination and base registers are used. This option avoids
8741 generating these instructions. This option is enabled by default when
8742 @option{-mcpu=cortex-m3} is specified.
8747 @subsection ARM Options
8750 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8754 @item -mabi=@var{name}
8756 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8757 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8760 @opindex mapcs-frame
8761 Generate a stack frame that is compliant with the ARM Procedure Call
8762 Standard for all functions, even if this is not strictly necessary for
8763 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8764 with this option will cause the stack frames not to be generated for
8765 leaf functions. The default is @option{-mno-apcs-frame}.
8769 This is a synonym for @option{-mapcs-frame}.
8772 @c not currently implemented
8773 @item -mapcs-stack-check
8774 @opindex mapcs-stack-check
8775 Generate code to check the amount of stack space available upon entry to
8776 every function (that actually uses some stack space). If there is
8777 insufficient space available then either the function
8778 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8779 called, depending upon the amount of stack space required. The run time
8780 system is required to provide these functions. The default is
8781 @option{-mno-apcs-stack-check}, since this produces smaller code.
8783 @c not currently implemented
8785 @opindex mapcs-float
8786 Pass floating point arguments using the float point registers. This is
8787 one of the variants of the APCS@. This option is recommended if the
8788 target hardware has a floating point unit or if a lot of floating point
8789 arithmetic is going to be performed by the code. The default is
8790 @option{-mno-apcs-float}, since integer only code is slightly increased in
8791 size if @option{-mapcs-float} is used.
8793 @c not currently implemented
8794 @item -mapcs-reentrant
8795 @opindex mapcs-reentrant
8796 Generate reentrant, position independent code. The default is
8797 @option{-mno-apcs-reentrant}.
8800 @item -mthumb-interwork
8801 @opindex mthumb-interwork
8802 Generate code which supports calling between the ARM and Thumb
8803 instruction sets. Without this option the two instruction sets cannot
8804 be reliably used inside one program. The default is
8805 @option{-mno-thumb-interwork}, since slightly larger code is generated
8806 when @option{-mthumb-interwork} is specified.
8808 @item -mno-sched-prolog
8809 @opindex mno-sched-prolog
8810 Prevent the reordering of instructions in the function prolog, or the
8811 merging of those instruction with the instructions in the function's
8812 body. This means that all functions will start with a recognizable set
8813 of instructions (or in fact one of a choice from a small set of
8814 different function prologues), and this information can be used to
8815 locate the start if functions inside an executable piece of code. The
8816 default is @option{-msched-prolog}.
8818 @item -mfloat-abi=@var{name}
8820 Specifies which floating-point ABI to use. Permissible values
8821 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8823 Specifying @samp{soft} causes GCC to generate output containing
8824 library calls for floating-point operations.
8825 @samp{softfp} allows the generation of code using hardware floating-point
8826 instructions, but still uses the soft-float calling conventions.
8827 @samp{hard} allows generation of floating-point instructions
8828 and uses FPU-specific calling conventions.
8830 Using @option{-mfloat-abi=hard} with VFP coprocessors is not supported.
8831 Use @option{-mfloat-abi=softfp} with the appropriate @option{-mfpu} option
8832 to allow the compiler to generate code that makes use of the hardware
8833 floating-point capabilities for these CPUs.
8835 The default depends on the specific target configuration. Note that
8836 the hard-float and soft-float ABIs are not link-compatible; you must
8837 compile your entire program with the same ABI, and link with a
8838 compatible set of libraries.
8841 @opindex mhard-float
8842 Equivalent to @option{-mfloat-abi=hard}.
8845 @opindex msoft-float
8846 Equivalent to @option{-mfloat-abi=soft}.
8848 @item -mlittle-endian
8849 @opindex mlittle-endian
8850 Generate code for a processor running in little-endian mode. This is
8851 the default for all standard configurations.
8854 @opindex mbig-endian
8855 Generate code for a processor running in big-endian mode; the default is
8856 to compile code for a little-endian processor.
8858 @item -mwords-little-endian
8859 @opindex mwords-little-endian
8860 This option only applies when generating code for big-endian processors.
8861 Generate code for a little-endian word order but a big-endian byte
8862 order. That is, a byte order of the form @samp{32107654}. Note: this
8863 option should only be used if you require compatibility with code for
8864 big-endian ARM processors generated by versions of the compiler prior to
8867 @item -mcpu=@var{name}
8869 This specifies the name of the target ARM processor. GCC uses this name
8870 to determine what kind of instructions it can emit when generating
8871 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8872 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8873 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8874 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8875 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8877 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8878 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
8879 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8880 @samp{strongarm1110},
8881 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8882 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8883 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8884 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8885 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8886 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8887 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8888 @samp{cortex-a8}, @samp{cortex-a9},
8889 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
8891 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
8893 @item -mtune=@var{name}
8895 This option is very similar to the @option{-mcpu=} option, except that
8896 instead of specifying the actual target processor type, and hence
8897 restricting which instructions can be used, it specifies that GCC should
8898 tune the performance of the code as if the target were of the type
8899 specified in this option, but still choosing the instructions that it
8900 will generate based on the cpu specified by a @option{-mcpu=} option.
8901 For some ARM implementations better performance can be obtained by using
8904 @item -march=@var{name}
8906 This specifies the name of the target ARM architecture. GCC uses this
8907 name to determine what kind of instructions it can emit when generating
8908 assembly code. This option can be used in conjunction with or instead
8909 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8910 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8911 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
8912 @samp{armv6}, @samp{armv6j},
8913 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
8914 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
8915 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
8917 @item -mfpu=@var{name}
8918 @itemx -mfpe=@var{number}
8919 @itemx -mfp=@var{number}
8923 This specifies what floating point hardware (or hardware emulation) is
8924 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8925 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16} and
8926 @samp{neon}. @option{-mfp} and @option{-mfpe}
8927 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8928 with older versions of GCC@.
8930 If @option{-msoft-float} is specified this specifies the format of
8931 floating point values.
8933 @item -mstructure-size-boundary=@var{n}
8934 @opindex mstructure-size-boundary
8935 The size of all structures and unions will be rounded up to a multiple
8936 of the number of bits set by this option. Permissible values are 8, 32
8937 and 64. The default value varies for different toolchains. For the COFF
8938 targeted toolchain the default value is 8. A value of 64 is only allowed
8939 if the underlying ABI supports it.
8941 Specifying the larger number can produce faster, more efficient code, but
8942 can also increase the size of the program. Different values are potentially
8943 incompatible. Code compiled with one value cannot necessarily expect to
8944 work with code or libraries compiled with another value, if they exchange
8945 information using structures or unions.
8947 @item -mabort-on-noreturn
8948 @opindex mabort-on-noreturn
8949 Generate a call to the function @code{abort} at the end of a
8950 @code{noreturn} function. It will be executed if the function tries to
8954 @itemx -mno-long-calls
8955 @opindex mlong-calls
8956 @opindex mno-long-calls
8957 Tells the compiler to perform function calls by first loading the
8958 address of the function into a register and then performing a subroutine
8959 call on this register. This switch is needed if the target function
8960 will lie outside of the 64 megabyte addressing range of the offset based
8961 version of subroutine call instruction.
8963 Even if this switch is enabled, not all function calls will be turned
8964 into long calls. The heuristic is that static functions, functions
8965 which have the @samp{short-call} attribute, functions that are inside
8966 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8967 definitions have already been compiled within the current compilation
8968 unit, will not be turned into long calls. The exception to this rule is
8969 that weak function definitions, functions with the @samp{long-call}
8970 attribute or the @samp{section} attribute, and functions that are within
8971 the scope of a @samp{#pragma long_calls} directive, will always be
8972 turned into long calls.
8974 This feature is not enabled by default. Specifying
8975 @option{-mno-long-calls} will restore the default behavior, as will
8976 placing the function calls within the scope of a @samp{#pragma
8977 long_calls_off} directive. Note these switches have no effect on how
8978 the compiler generates code to handle function calls via function
8981 @item -mnop-fun-dllimport
8982 @opindex mnop-fun-dllimport
8983 Disable support for the @code{dllimport} attribute.
8985 @item -msingle-pic-base
8986 @opindex msingle-pic-base
8987 Treat the register used for PIC addressing as read-only, rather than
8988 loading it in the prologue for each function. The run-time system is
8989 responsible for initializing this register with an appropriate value
8990 before execution begins.
8992 @item -mpic-register=@var{reg}
8993 @opindex mpic-register
8994 Specify the register to be used for PIC addressing. The default is R10
8995 unless stack-checking is enabled, when R9 is used.
8997 @item -mcirrus-fix-invalid-insns
8998 @opindex mcirrus-fix-invalid-insns
8999 @opindex mno-cirrus-fix-invalid-insns
9000 Insert NOPs into the instruction stream to in order to work around
9001 problems with invalid Maverick instruction combinations. This option
9002 is only valid if the @option{-mcpu=ep9312} option has been used to
9003 enable generation of instructions for the Cirrus Maverick floating
9004 point co-processor. This option is not enabled by default, since the
9005 problem is only present in older Maverick implementations. The default
9006 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
9009 @item -mpoke-function-name
9010 @opindex mpoke-function-name
9011 Write the name of each function into the text section, directly
9012 preceding the function prologue. The generated code is similar to this:
9016 .ascii "arm_poke_function_name", 0
9019 .word 0xff000000 + (t1 - t0)
9020 arm_poke_function_name
9022 stmfd sp!, @{fp, ip, lr, pc@}
9026 When performing a stack backtrace, code can inspect the value of
9027 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
9028 location @code{pc - 12} and the top 8 bits are set, then we know that
9029 there is a function name embedded immediately preceding this location
9030 and has length @code{((pc[-3]) & 0xff000000)}.
9034 Generate code for the Thumb instruction set. The default is to
9035 use the 32-bit ARM instruction set.
9036 This option automatically enables either 16-bit Thumb-1 or
9037 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
9038 and @option{-march=@var{name}} options.
9041 @opindex mtpcs-frame
9042 Generate a stack frame that is compliant with the Thumb Procedure Call
9043 Standard for all non-leaf functions. (A leaf function is one that does
9044 not call any other functions.) The default is @option{-mno-tpcs-frame}.
9046 @item -mtpcs-leaf-frame
9047 @opindex mtpcs-leaf-frame
9048 Generate a stack frame that is compliant with the Thumb Procedure Call
9049 Standard for all leaf functions. (A leaf function is one that does
9050 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
9052 @item -mcallee-super-interworking
9053 @opindex mcallee-super-interworking
9054 Gives all externally visible functions in the file being compiled an ARM
9055 instruction set header which switches to Thumb mode before executing the
9056 rest of the function. This allows these functions to be called from
9057 non-interworking code.
9059 @item -mcaller-super-interworking
9060 @opindex mcaller-super-interworking
9061 Allows calls via function pointers (including virtual functions) to
9062 execute correctly regardless of whether the target code has been
9063 compiled for interworking or not. There is a small overhead in the cost
9064 of executing a function pointer if this option is enabled.
9066 @item -mtp=@var{name}
9068 Specify the access model for the thread local storage pointer. The valid
9069 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
9070 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
9071 (supported in the arm6k architecture), and @option{auto}, which uses the
9072 best available method for the selected processor. The default setting is
9075 @item -mword-relocations
9076 @opindex mword-relocations
9077 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
9078 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
9079 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
9085 @subsection AVR Options
9088 These options are defined for AVR implementations:
9091 @item -mmcu=@var{mcu}
9093 Specify ATMEL AVR instruction set or MCU type.
9095 Instruction set avr1 is for the minimal AVR core, not supported by the C
9096 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9097 attiny11, attiny12, attiny15, attiny28).
9099 Instruction set avr2 (default) is for the classic AVR core with up to
9100 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9101 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9102 at90c8534, at90s8535).
9104 Instruction set avr3 is for the classic AVR core with up to 128K program
9105 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9107 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9108 memory space (MCU types: atmega8, atmega83, atmega85).
9110 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9111 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9112 atmega64, atmega128, at43usb355, at94k).
9116 Output instruction sizes to the asm file.
9118 @item -minit-stack=@var{N}
9119 @opindex minit-stack
9120 Specify the initial stack address, which may be a symbol or numeric value,
9121 @samp{__stack} is the default.
9123 @item -mno-interrupts
9124 @opindex mno-interrupts
9125 Generated code is not compatible with hardware interrupts.
9126 Code size will be smaller.
9128 @item -mcall-prologues
9129 @opindex mcall-prologues
9130 Functions prologues/epilogues expanded as call to appropriate
9131 subroutines. Code size will be smaller.
9133 @item -mno-tablejump
9134 @opindex mno-tablejump
9135 Do not generate tablejump insns which sometimes increase code size.
9138 @opindex mtiny-stack
9139 Change only the low 8 bits of the stack pointer.
9143 Assume int to be 8 bit integer. This affects the sizes of all types: A
9144 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
9145 and long long will be 4 bytes. Please note that this option does not
9146 comply to the C standards, but it will provide you with smaller code
9150 @node Blackfin Options
9151 @subsection Blackfin Options
9152 @cindex Blackfin Options
9155 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
9157 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
9158 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
9159 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
9160 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
9161 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
9162 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
9164 The optional @var{sirevision} specifies the silicon revision of the target
9165 Blackfin processor. Any workarounds available for the targeted silicon revision
9166 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
9167 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
9168 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
9169 hexadecimal digits representing the major and minor numbers in the silicon
9170 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
9171 is not defined. If @var{sirevision} is @samp{any}, the
9172 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
9173 If this optional @var{sirevision} is not used, GCC assumes the latest known
9174 silicon revision of the targeted Blackfin processor.
9176 Support for @samp{bf561} is incomplete. For @samp{bf561},
9177 Only the processor macro is defined.
9178 Without this option, @samp{bf532} is used as the processor by default.
9179 The corresponding predefined processor macros for @var{cpu} is to
9180 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
9181 provided by libgloss to be linked in if @option{-msim} is not given.
9185 Specifies that the program will be run on the simulator. This causes
9186 the simulator BSP provided by libgloss to be linked in. This option
9187 has effect only for @samp{bfin-elf} toolchain.
9188 Certain other options, such as @option{-mid-shared-library} and
9189 @option{-mfdpic}, imply @option{-msim}.
9191 @item -momit-leaf-frame-pointer
9192 @opindex momit-leaf-frame-pointer
9193 Don't keep the frame pointer in a register for leaf functions. This
9194 avoids the instructions to save, set up and restore frame pointers and
9195 makes an extra register available in leaf functions. The option
9196 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9197 which might make debugging harder.
9199 @item -mspecld-anomaly
9200 @opindex mspecld-anomaly
9201 When enabled, the compiler will ensure that the generated code does not
9202 contain speculative loads after jump instructions. If this option is used,
9203 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
9205 @item -mno-specld-anomaly
9206 @opindex mno-specld-anomaly
9207 Don't generate extra code to prevent speculative loads from occurring.
9209 @item -mcsync-anomaly
9210 @opindex mcsync-anomaly
9211 When enabled, the compiler will ensure that the generated code does not
9212 contain CSYNC or SSYNC instructions too soon after conditional branches.
9213 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
9215 @item -mno-csync-anomaly
9216 @opindex mno-csync-anomaly
9217 Don't generate extra code to prevent CSYNC or SSYNC instructions from
9218 occurring too soon after a conditional branch.
9222 When enabled, the compiler is free to take advantage of the knowledge that
9223 the entire program fits into the low 64k of memory.
9226 @opindex mno-low-64k
9227 Assume that the program is arbitrarily large. This is the default.
9229 @item -mstack-check-l1
9230 @opindex mstack-check-l1
9231 Do stack checking using information placed into L1 scratchpad memory by the
9234 @item -mid-shared-library
9235 @opindex mid-shared-library
9236 Generate code that supports shared libraries via the library ID method.
9237 This allows for execute in place and shared libraries in an environment
9238 without virtual memory management. This option implies @option{-fPIC}.
9239 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9241 @item -mno-id-shared-library
9242 @opindex mno-id-shared-library
9243 Generate code that doesn't assume ID based shared libraries are being used.
9244 This is the default.
9246 @item -mleaf-id-shared-library
9247 @opindex mleaf-id-shared-library
9248 Generate code that supports shared libraries via the library ID method,
9249 but assumes that this library or executable won't link against any other
9250 ID shared libraries. That allows the compiler to use faster code for jumps
9253 @item -mno-leaf-id-shared-library
9254 @opindex mno-leaf-id-shared-library
9255 Do not assume that the code being compiled won't link against any ID shared
9256 libraries. Slower code will be generated for jump and call insns.
9258 @item -mshared-library-id=n
9259 @opindex mshared-library-id
9260 Specified the identification number of the ID based shared library being
9261 compiled. Specifying a value of 0 will generate more compact code, specifying
9262 other values will force the allocation of that number to the current
9263 library but is no more space or time efficient than omitting this option.
9267 Generate code that allows the data segment to be located in a different
9268 area of memory from the text segment. This allows for execute in place in
9269 an environment without virtual memory management by eliminating relocations
9270 against the text section.
9273 @opindex mno-sep-data
9274 Generate code that assumes that the data segment follows the text segment.
9275 This is the default.
9278 @itemx -mno-long-calls
9279 @opindex mlong-calls
9280 @opindex mno-long-calls
9281 Tells the compiler to perform function calls by first loading the
9282 address of the function into a register and then performing a subroutine
9283 call on this register. This switch is needed if the target function
9284 will lie outside of the 24 bit addressing range of the offset based
9285 version of subroutine call instruction.
9287 This feature is not enabled by default. Specifying
9288 @option{-mno-long-calls} will restore the default behavior. Note these
9289 switches have no effect on how the compiler generates code to handle
9290 function calls via function pointers.
9294 Link with the fast floating-point library. This library relaxes some of
9295 the IEEE floating-point standard's rules for checking inputs against
9296 Not-a-Number (NAN), in the interest of performance.
9299 @opindex minline-plt
9300 Enable inlining of PLT entries in function calls to functions that are
9301 not known to bind locally. It has no effect without @option{-mfdpic}.
9305 Build standalone application for multicore Blackfin processor. Proper
9306 start files and link scripts will be used to support multicore.
9307 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9308 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9309 @option{-mcorea} or @option{-mcoreb}. If it's used without
9310 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9311 programming model is used. In this model, the main function of Core B
9312 should be named as coreb_main. If it's used with @option{-mcorea} or
9313 @option{-mcoreb}, one application per core programming model is used.
9314 If this option is not used, single core application programming
9319 Build standalone application for Core A of BF561 when using
9320 one application per core programming model. Proper start files
9321 and link scripts will be used to support Core A. This option
9322 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9326 Build standalone application for Core B of BF561 when using
9327 one application per core programming model. Proper start files
9328 and link scripts will be used to support Core B. This option
9329 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9330 should be used instead of main. It must be used with
9331 @option{-mmulticore}.
9335 Build standalone application for SDRAM. Proper start files and
9336 link scripts will be used to put the application into SDRAM.
9337 Loader should initialize SDRAM before loading the application
9338 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9342 Assume that ICPLBs are enabled at runtime. This has an effect on certain
9343 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
9344 are enabled; for standalone applications the default is off.
9348 @subsection CRIS Options
9349 @cindex CRIS Options
9351 These options are defined specifically for the CRIS ports.
9354 @item -march=@var{architecture-type}
9355 @itemx -mcpu=@var{architecture-type}
9358 Generate code for the specified architecture. The choices for
9359 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9360 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9361 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9364 @item -mtune=@var{architecture-type}
9366 Tune to @var{architecture-type} everything applicable about the generated
9367 code, except for the ABI and the set of available instructions. The
9368 choices for @var{architecture-type} are the same as for
9369 @option{-march=@var{architecture-type}}.
9371 @item -mmax-stack-frame=@var{n}
9372 @opindex mmax-stack-frame
9373 Warn when the stack frame of a function exceeds @var{n} bytes.
9379 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9380 @option{-march=v3} and @option{-march=v8} respectively.
9382 @item -mmul-bug-workaround
9383 @itemx -mno-mul-bug-workaround
9384 @opindex mmul-bug-workaround
9385 @opindex mno-mul-bug-workaround
9386 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9387 models where it applies. This option is active by default.
9391 Enable CRIS-specific verbose debug-related information in the assembly
9392 code. This option also has the effect to turn off the @samp{#NO_APP}
9393 formatted-code indicator to the assembler at the beginning of the
9398 Do not use condition-code results from previous instruction; always emit
9399 compare and test instructions before use of condition codes.
9401 @item -mno-side-effects
9402 @opindex mno-side-effects
9403 Do not emit instructions with side-effects in addressing modes other than
9407 @itemx -mno-stack-align
9409 @itemx -mno-data-align
9410 @itemx -mconst-align
9411 @itemx -mno-const-align
9412 @opindex mstack-align
9413 @opindex mno-stack-align
9414 @opindex mdata-align
9415 @opindex mno-data-align
9416 @opindex mconst-align
9417 @opindex mno-const-align
9418 These options (no-options) arranges (eliminate arrangements) for the
9419 stack-frame, individual data and constants to be aligned for the maximum
9420 single data access size for the chosen CPU model. The default is to
9421 arrange for 32-bit alignment. ABI details such as structure layout are
9422 not affected by these options.
9430 Similar to the stack- data- and const-align options above, these options
9431 arrange for stack-frame, writable data and constants to all be 32-bit,
9432 16-bit or 8-bit aligned. The default is 32-bit alignment.
9434 @item -mno-prologue-epilogue
9435 @itemx -mprologue-epilogue
9436 @opindex mno-prologue-epilogue
9437 @opindex mprologue-epilogue
9438 With @option{-mno-prologue-epilogue}, the normal function prologue and
9439 epilogue that sets up the stack-frame are omitted and no return
9440 instructions or return sequences are generated in the code. Use this
9441 option only together with visual inspection of the compiled code: no
9442 warnings or errors are generated when call-saved registers must be saved,
9443 or storage for local variable needs to be allocated.
9449 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9450 instruction sequences that load addresses for functions from the PLT part
9451 of the GOT rather than (traditional on other architectures) calls to the
9452 PLT@. The default is @option{-mgotplt}.
9456 Legacy no-op option only recognized with the cris-axis-elf and
9457 cris-axis-linux-gnu targets.
9461 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9465 This option, recognized for the cris-axis-elf arranges
9466 to link with input-output functions from a simulator library. Code,
9467 initialized data and zero-initialized data are allocated consecutively.
9471 Like @option{-sim}, but pass linker options to locate initialized data at
9472 0x40000000 and zero-initialized data at 0x80000000.
9476 @subsection CRX Options
9479 These options are defined specifically for the CRX ports.
9485 Enable the use of multiply-accumulate instructions. Disabled by default.
9489 Push instructions will be used to pass outgoing arguments when functions
9490 are called. Enabled by default.
9493 @node Darwin Options
9494 @subsection Darwin Options
9495 @cindex Darwin options
9497 These options are defined for all architectures running the Darwin operating
9500 FSF GCC on Darwin does not create ``fat'' object files; it will create
9501 an object file for the single architecture that it was built to
9502 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9503 @option{-arch} options are used; it does so by running the compiler or
9504 linker multiple times and joining the results together with
9507 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9508 @samp{i686}) is determined by the flags that specify the ISA
9509 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9510 @option{-force_cpusubtype_ALL} option can be used to override this.
9512 The Darwin tools vary in their behavior when presented with an ISA
9513 mismatch. The assembler, @file{as}, will only permit instructions to
9514 be used that are valid for the subtype of the file it is generating,
9515 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9516 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9517 and print an error if asked to create a shared library with a less
9518 restrictive subtype than its input files (for instance, trying to put
9519 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9520 for executables, @file{ld}, will quietly give the executable the most
9521 restrictive subtype of any of its input files.
9526 Add the framework directory @var{dir} to the head of the list of
9527 directories to be searched for header files. These directories are
9528 interleaved with those specified by @option{-I} options and are
9529 scanned in a left-to-right order.
9531 A framework directory is a directory with frameworks in it. A
9532 framework is a directory with a @samp{"Headers"} and/or
9533 @samp{"PrivateHeaders"} directory contained directly in it that ends
9534 in @samp{".framework"}. The name of a framework is the name of this
9535 directory excluding the @samp{".framework"}. Headers associated with
9536 the framework are found in one of those two directories, with
9537 @samp{"Headers"} being searched first. A subframework is a framework
9538 directory that is in a framework's @samp{"Frameworks"} directory.
9539 Includes of subframework headers can only appear in a header of a
9540 framework that contains the subframework, or in a sibling subframework
9541 header. Two subframeworks are siblings if they occur in the same
9542 framework. A subframework should not have the same name as a
9543 framework, a warning will be issued if this is violated. Currently a
9544 subframework cannot have subframeworks, in the future, the mechanism
9545 may be extended to support this. The standard frameworks can be found
9546 in @samp{"/System/Library/Frameworks"} and
9547 @samp{"/Library/Frameworks"}. An example include looks like
9548 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9549 the name of the framework and header.h is found in the
9550 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9552 @item -iframework@var{dir}
9554 Like @option{-F} except the directory is a treated as a system
9555 directory. The main difference between this @option{-iframework} and
9556 @option{-F} is that with @option{-iframework} the compiler does not
9557 warn about constructs contained within header files found via
9558 @var{dir}. This option is valid only for the C family of languages.
9562 Emit debugging information for symbols that are used. For STABS
9563 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9564 This is by default ON@.
9568 Emit debugging information for all symbols and types.
9570 @item -mmacosx-version-min=@var{version}
9571 The earliest version of MacOS X that this executable will run on
9572 is @var{version}. Typical values of @var{version} include @code{10.1},
9573 @code{10.2}, and @code{10.3.9}.
9575 If the compiler was built to use the system's headers by default,
9576 then the default for this option is the system version on which the
9577 compiler is running, otherwise the default is to make choices which
9578 are compatible with as many systems and code bases as possible.
9582 Enable kernel development mode. The @option{-mkernel} option sets
9583 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9584 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9585 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9586 applicable. This mode also sets @option{-mno-altivec},
9587 @option{-msoft-float}, @option{-fno-builtin} and
9588 @option{-mlong-branch} for PowerPC targets.
9590 @item -mone-byte-bool
9591 @opindex mone-byte-bool
9592 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9593 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9594 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9595 option has no effect on x86.
9597 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9598 to generate code that is not binary compatible with code generated
9599 without that switch. Using this switch may require recompiling all
9600 other modules in a program, including system libraries. Use this
9601 switch to conform to a non-default data model.
9603 @item -mfix-and-continue
9604 @itemx -ffix-and-continue
9605 @itemx -findirect-data
9606 @opindex mfix-and-continue
9607 @opindex ffix-and-continue
9608 @opindex findirect-data
9609 Generate code suitable for fast turn around development. Needed to
9610 enable gdb to dynamically load @code{.o} files into already running
9611 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9612 are provided for backwards compatibility.
9616 Loads all members of static archive libraries.
9617 See man ld(1) for more information.
9619 @item -arch_errors_fatal
9620 @opindex arch_errors_fatal
9621 Cause the errors having to do with files that have the wrong architecture
9625 @opindex bind_at_load
9626 Causes the output file to be marked such that the dynamic linker will
9627 bind all undefined references when the file is loaded or launched.
9631 Produce a Mach-o bundle format file.
9632 See man ld(1) for more information.
9634 @item -bundle_loader @var{executable}
9635 @opindex bundle_loader
9636 This option specifies the @var{executable} that will be loading the build
9637 output file being linked. See man ld(1) for more information.
9641 When passed this option, GCC will produce a dynamic library instead of
9642 an executable when linking, using the Darwin @file{libtool} command.
9644 @item -force_cpusubtype_ALL
9645 @opindex force_cpusubtype_ALL
9646 This causes GCC's output file to have the @var{ALL} subtype, instead of
9647 one controlled by the @option{-mcpu} or @option{-march} option.
9649 @item -allowable_client @var{client_name}
9651 @itemx -compatibility_version
9652 @itemx -current_version
9654 @itemx -dependency-file
9656 @itemx -dylinker_install_name
9658 @itemx -exported_symbols_list
9660 @itemx -flat_namespace
9661 @itemx -force_flat_namespace
9662 @itemx -headerpad_max_install_names
9665 @itemx -install_name
9666 @itemx -keep_private_externs
9667 @itemx -multi_module
9668 @itemx -multiply_defined
9669 @itemx -multiply_defined_unused
9671 @itemx -no_dead_strip_inits_and_terms
9672 @itemx -nofixprebinding
9675 @itemx -noseglinkedit
9676 @itemx -pagezero_size
9678 @itemx -prebind_all_twolevel_modules
9679 @itemx -private_bundle
9680 @itemx -read_only_relocs
9682 @itemx -sectobjectsymbols
9686 @itemx -sectobjectsymbols
9689 @itemx -segs_read_only_addr
9690 @itemx -segs_read_write_addr
9691 @itemx -seg_addr_table
9692 @itemx -seg_addr_table_filename
9695 @itemx -segs_read_only_addr
9696 @itemx -segs_read_write_addr
9697 @itemx -single_module
9700 @itemx -sub_umbrella
9701 @itemx -twolevel_namespace
9704 @itemx -unexported_symbols_list
9705 @itemx -weak_reference_mismatches
9707 @opindex allowable_client
9708 @opindex client_name
9709 @opindex compatibility_version
9710 @opindex current_version
9712 @opindex dependency-file
9714 @opindex dylinker_install_name
9716 @opindex exported_symbols_list
9718 @opindex flat_namespace
9719 @opindex force_flat_namespace
9720 @opindex headerpad_max_install_names
9723 @opindex install_name
9724 @opindex keep_private_externs
9725 @opindex multi_module
9726 @opindex multiply_defined
9727 @opindex multiply_defined_unused
9729 @opindex no_dead_strip_inits_and_terms
9730 @opindex nofixprebinding
9731 @opindex nomultidefs
9733 @opindex noseglinkedit
9734 @opindex pagezero_size
9736 @opindex prebind_all_twolevel_modules
9737 @opindex private_bundle
9738 @opindex read_only_relocs
9740 @opindex sectobjectsymbols
9744 @opindex sectobjectsymbols
9747 @opindex segs_read_only_addr
9748 @opindex segs_read_write_addr
9749 @opindex seg_addr_table
9750 @opindex seg_addr_table_filename
9751 @opindex seglinkedit
9753 @opindex segs_read_only_addr
9754 @opindex segs_read_write_addr
9755 @opindex single_module
9757 @opindex sub_library
9758 @opindex sub_umbrella
9759 @opindex twolevel_namespace
9762 @opindex unexported_symbols_list
9763 @opindex weak_reference_mismatches
9764 @opindex whatsloaded
9765 These options are passed to the Darwin linker. The Darwin linker man page
9766 describes them in detail.
9769 @node DEC Alpha Options
9770 @subsection DEC Alpha Options
9772 These @samp{-m} options are defined for the DEC Alpha implementations:
9775 @item -mno-soft-float
9777 @opindex mno-soft-float
9778 @opindex msoft-float
9779 Use (do not use) the hardware floating-point instructions for
9780 floating-point operations. When @option{-msoft-float} is specified,
9781 functions in @file{libgcc.a} will be used to perform floating-point
9782 operations. Unless they are replaced by routines that emulate the
9783 floating-point operations, or compiled in such a way as to call such
9784 emulations routines, these routines will issue floating-point
9785 operations. If you are compiling for an Alpha without floating-point
9786 operations, you must ensure that the library is built so as not to call
9789 Note that Alpha implementations without floating-point operations are
9790 required to have floating-point registers.
9795 @opindex mno-fp-regs
9796 Generate code that uses (does not use) the floating-point register set.
9797 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9798 register set is not used, floating point operands are passed in integer
9799 registers as if they were integers and floating-point results are passed
9800 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9801 so any function with a floating-point argument or return value called by code
9802 compiled with @option{-mno-fp-regs} must also be compiled with that
9805 A typical use of this option is building a kernel that does not use,
9806 and hence need not save and restore, any floating-point registers.
9810 The Alpha architecture implements floating-point hardware optimized for
9811 maximum performance. It is mostly compliant with the IEEE floating
9812 point standard. However, for full compliance, software assistance is
9813 required. This option generates code fully IEEE compliant code
9814 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9815 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9816 defined during compilation. The resulting code is less efficient but is
9817 able to correctly support denormalized numbers and exceptional IEEE
9818 values such as not-a-number and plus/minus infinity. Other Alpha
9819 compilers call this option @option{-ieee_with_no_inexact}.
9821 @item -mieee-with-inexact
9822 @opindex mieee-with-inexact
9823 This is like @option{-mieee} except the generated code also maintains
9824 the IEEE @var{inexact-flag}. Turning on this option causes the
9825 generated code to implement fully-compliant IEEE math. In addition to
9826 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9827 macro. On some Alpha implementations the resulting code may execute
9828 significantly slower than the code generated by default. Since there is
9829 very little code that depends on the @var{inexact-flag}, you should
9830 normally not specify this option. Other Alpha compilers call this
9831 option @option{-ieee_with_inexact}.
9833 @item -mfp-trap-mode=@var{trap-mode}
9834 @opindex mfp-trap-mode
9835 This option controls what floating-point related traps are enabled.
9836 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9837 The trap mode can be set to one of four values:
9841 This is the default (normal) setting. The only traps that are enabled
9842 are the ones that cannot be disabled in software (e.g., division by zero
9846 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9850 Like @samp{u}, but the instructions are marked to be safe for software
9851 completion (see Alpha architecture manual for details).
9854 Like @samp{su}, but inexact traps are enabled as well.
9857 @item -mfp-rounding-mode=@var{rounding-mode}
9858 @opindex mfp-rounding-mode
9859 Selects the IEEE rounding mode. Other Alpha compilers call this option
9860 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9865 Normal IEEE rounding mode. Floating point numbers are rounded towards
9866 the nearest machine number or towards the even machine number in case
9870 Round towards minus infinity.
9873 Chopped rounding mode. Floating point numbers are rounded towards zero.
9876 Dynamic rounding mode. A field in the floating point control register
9877 (@var{fpcr}, see Alpha architecture reference manual) controls the
9878 rounding mode in effect. The C library initializes this register for
9879 rounding towards plus infinity. Thus, unless your program modifies the
9880 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9883 @item -mtrap-precision=@var{trap-precision}
9884 @opindex mtrap-precision
9885 In the Alpha architecture, floating point traps are imprecise. This
9886 means without software assistance it is impossible to recover from a
9887 floating trap and program execution normally needs to be terminated.
9888 GCC can generate code that can assist operating system trap handlers
9889 in determining the exact location that caused a floating point trap.
9890 Depending on the requirements of an application, different levels of
9891 precisions can be selected:
9895 Program precision. This option is the default and means a trap handler
9896 can only identify which program caused a floating point exception.
9899 Function precision. The trap handler can determine the function that
9900 caused a floating point exception.
9903 Instruction precision. The trap handler can determine the exact
9904 instruction that caused a floating point exception.
9907 Other Alpha compilers provide the equivalent options called
9908 @option{-scope_safe} and @option{-resumption_safe}.
9910 @item -mieee-conformant
9911 @opindex mieee-conformant
9912 This option marks the generated code as IEEE conformant. You must not
9913 use this option unless you also specify @option{-mtrap-precision=i} and either
9914 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9915 is to emit the line @samp{.eflag 48} in the function prologue of the
9916 generated assembly file. Under DEC Unix, this has the effect that
9917 IEEE-conformant math library routines will be linked in.
9919 @item -mbuild-constants
9920 @opindex mbuild-constants
9921 Normally GCC examines a 32- or 64-bit integer constant to
9922 see if it can construct it from smaller constants in two or three
9923 instructions. If it cannot, it will output the constant as a literal and
9924 generate code to load it from the data segment at runtime.
9926 Use this option to require GCC to construct @emph{all} integer constants
9927 using code, even if it takes more instructions (the maximum is six).
9929 You would typically use this option to build a shared library dynamic
9930 loader. Itself a shared library, it must relocate itself in memory
9931 before it can find the variables and constants in its own data segment.
9937 Select whether to generate code to be assembled by the vendor-supplied
9938 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9956 Indicate whether GCC should generate code to use the optional BWX,
9957 CIX, FIX and MAX instruction sets. The default is to use the instruction
9958 sets supported by the CPU type specified via @option{-mcpu=} option or that
9959 of the CPU on which GCC was built if none was specified.
9964 @opindex mfloat-ieee
9965 Generate code that uses (does not use) VAX F and G floating point
9966 arithmetic instead of IEEE single and double precision.
9968 @item -mexplicit-relocs
9969 @itemx -mno-explicit-relocs
9970 @opindex mexplicit-relocs
9971 @opindex mno-explicit-relocs
9972 Older Alpha assemblers provided no way to generate symbol relocations
9973 except via assembler macros. Use of these macros does not allow
9974 optimal instruction scheduling. GNU binutils as of version 2.12
9975 supports a new syntax that allows the compiler to explicitly mark
9976 which relocations should apply to which instructions. This option
9977 is mostly useful for debugging, as GCC detects the capabilities of
9978 the assembler when it is built and sets the default accordingly.
9982 @opindex msmall-data
9983 @opindex mlarge-data
9984 When @option{-mexplicit-relocs} is in effect, static data is
9985 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9986 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9987 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9988 16-bit relocations off of the @code{$gp} register. This limits the
9989 size of the small data area to 64KB, but allows the variables to be
9990 directly accessed via a single instruction.
9992 The default is @option{-mlarge-data}. With this option the data area
9993 is limited to just below 2GB@. Programs that require more than 2GB of
9994 data must use @code{malloc} or @code{mmap} to allocate the data in the
9995 heap instead of in the program's data segment.
9997 When generating code for shared libraries, @option{-fpic} implies
9998 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
10001 @itemx -mlarge-text
10002 @opindex msmall-text
10003 @opindex mlarge-text
10004 When @option{-msmall-text} is used, the compiler assumes that the
10005 code of the entire program (or shared library) fits in 4MB, and is
10006 thus reachable with a branch instruction. When @option{-msmall-data}
10007 is used, the compiler can assume that all local symbols share the
10008 same @code{$gp} value, and thus reduce the number of instructions
10009 required for a function call from 4 to 1.
10011 The default is @option{-mlarge-text}.
10013 @item -mcpu=@var{cpu_type}
10015 Set the instruction set and instruction scheduling parameters for
10016 machine type @var{cpu_type}. You can specify either the @samp{EV}
10017 style name or the corresponding chip number. GCC supports scheduling
10018 parameters for the EV4, EV5 and EV6 family of processors and will
10019 choose the default values for the instruction set from the processor
10020 you specify. If you do not specify a processor type, GCC will default
10021 to the processor on which the compiler was built.
10023 Supported values for @var{cpu_type} are
10029 Schedules as an EV4 and has no instruction set extensions.
10033 Schedules as an EV5 and has no instruction set extensions.
10037 Schedules as an EV5 and supports the BWX extension.
10042 Schedules as an EV5 and supports the BWX and MAX extensions.
10046 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
10050 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
10053 @item -mtune=@var{cpu_type}
10055 Set only the instruction scheduling parameters for machine type
10056 @var{cpu_type}. The instruction set is not changed.
10058 @item -mmemory-latency=@var{time}
10059 @opindex mmemory-latency
10060 Sets the latency the scheduler should assume for typical memory
10061 references as seen by the application. This number is highly
10062 dependent on the memory access patterns used by the application
10063 and the size of the external cache on the machine.
10065 Valid options for @var{time} are
10069 A decimal number representing clock cycles.
10075 The compiler contains estimates of the number of clock cycles for
10076 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
10077 (also called Dcache, Scache, and Bcache), as well as to main memory.
10078 Note that L3 is only valid for EV5.
10083 @node DEC Alpha/VMS Options
10084 @subsection DEC Alpha/VMS Options
10086 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
10089 @item -mvms-return-codes
10090 @opindex mvms-return-codes
10091 Return VMS condition codes from main. The default is to return POSIX
10092 style condition (e.g.@: error) codes.
10096 @subsection FRV Options
10097 @cindex FRV Options
10103 Only use the first 32 general purpose registers.
10108 Use all 64 general purpose registers.
10113 Use only the first 32 floating point registers.
10118 Use all 64 floating point registers
10121 @opindex mhard-float
10123 Use hardware instructions for floating point operations.
10126 @opindex msoft-float
10128 Use library routines for floating point operations.
10133 Dynamically allocate condition code registers.
10138 Do not try to dynamically allocate condition code registers, only
10139 use @code{icc0} and @code{fcc0}.
10144 Change ABI to use double word insns.
10149 Do not use double word instructions.
10154 Use floating point double instructions.
10157 @opindex mno-double
10159 Do not use floating point double instructions.
10164 Use media instructions.
10169 Do not use media instructions.
10174 Use multiply and add/subtract instructions.
10177 @opindex mno-muladd
10179 Do not use multiply and add/subtract instructions.
10184 Select the FDPIC ABI, that uses function descriptors to represent
10185 pointers to functions. Without any PIC/PIE-related options, it
10186 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
10187 assumes GOT entries and small data are within a 12-bit range from the
10188 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
10189 are computed with 32 bits.
10190 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10193 @opindex minline-plt
10195 Enable inlining of PLT entries in function calls to functions that are
10196 not known to bind locally. It has no effect without @option{-mfdpic}.
10197 It's enabled by default if optimizing for speed and compiling for
10198 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
10199 optimization option such as @option{-O3} or above is present in the
10205 Assume a large TLS segment when generating thread-local code.
10210 Do not assume a large TLS segment when generating thread-local code.
10215 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
10216 that is known to be in read-only sections. It's enabled by default,
10217 except for @option{-fpic} or @option{-fpie}: even though it may help
10218 make the global offset table smaller, it trades 1 instruction for 4.
10219 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
10220 one of which may be shared by multiple symbols, and it avoids the need
10221 for a GOT entry for the referenced symbol, so it's more likely to be a
10222 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
10224 @item -multilib-library-pic
10225 @opindex multilib-library-pic
10227 Link with the (library, not FD) pic libraries. It's implied by
10228 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
10229 @option{-fpic} without @option{-mfdpic}. You should never have to use
10233 @opindex mlinked-fp
10235 Follow the EABI requirement of always creating a frame pointer whenever
10236 a stack frame is allocated. This option is enabled by default and can
10237 be disabled with @option{-mno-linked-fp}.
10240 @opindex mlong-calls
10242 Use indirect addressing to call functions outside the current
10243 compilation unit. This allows the functions to be placed anywhere
10244 within the 32-bit address space.
10246 @item -malign-labels
10247 @opindex malign-labels
10249 Try to align labels to an 8-byte boundary by inserting nops into the
10250 previous packet. This option only has an effect when VLIW packing
10251 is enabled. It doesn't create new packets; it merely adds nops to
10254 @item -mlibrary-pic
10255 @opindex mlibrary-pic
10257 Generate position-independent EABI code.
10262 Use only the first four media accumulator registers.
10267 Use all eight media accumulator registers.
10272 Pack VLIW instructions.
10277 Do not pack VLIW instructions.
10280 @opindex mno-eflags
10282 Do not mark ABI switches in e_flags.
10285 @opindex mcond-move
10287 Enable the use of conditional-move instructions (default).
10289 This switch is mainly for debugging the compiler and will likely be removed
10290 in a future version.
10292 @item -mno-cond-move
10293 @opindex mno-cond-move
10295 Disable the use of conditional-move instructions.
10297 This switch is mainly for debugging the compiler and will likely be removed
10298 in a future version.
10303 Enable the use of conditional set instructions (default).
10305 This switch is mainly for debugging the compiler and will likely be removed
10306 in a future version.
10311 Disable the use of conditional set instructions.
10313 This switch is mainly for debugging the compiler and will likely be removed
10314 in a future version.
10317 @opindex mcond-exec
10319 Enable the use of conditional execution (default).
10321 This switch is mainly for debugging the compiler and will likely be removed
10322 in a future version.
10324 @item -mno-cond-exec
10325 @opindex mno-cond-exec
10327 Disable the use of conditional execution.
10329 This switch is mainly for debugging the compiler and will likely be removed
10330 in a future version.
10332 @item -mvliw-branch
10333 @opindex mvliw-branch
10335 Run a pass to pack branches into VLIW instructions (default).
10337 This switch is mainly for debugging the compiler and will likely be removed
10338 in a future version.
10340 @item -mno-vliw-branch
10341 @opindex mno-vliw-branch
10343 Do not run a pass to pack branches into VLIW instructions.
10345 This switch is mainly for debugging the compiler and will likely be removed
10346 in a future version.
10348 @item -mmulti-cond-exec
10349 @opindex mmulti-cond-exec
10351 Enable optimization of @code{&&} and @code{||} in conditional execution
10354 This switch is mainly for debugging the compiler and will likely be removed
10355 in a future version.
10357 @item -mno-multi-cond-exec
10358 @opindex mno-multi-cond-exec
10360 Disable optimization of @code{&&} and @code{||} in conditional execution.
10362 This switch is mainly for debugging the compiler and will likely be removed
10363 in a future version.
10365 @item -mnested-cond-exec
10366 @opindex mnested-cond-exec
10368 Enable nested conditional execution optimizations (default).
10370 This switch is mainly for debugging the compiler and will likely be removed
10371 in a future version.
10373 @item -mno-nested-cond-exec
10374 @opindex mno-nested-cond-exec
10376 Disable nested conditional execution optimizations.
10378 This switch is mainly for debugging the compiler and will likely be removed
10379 in a future version.
10381 @item -moptimize-membar
10382 @opindex moptimize-membar
10384 This switch removes redundant @code{membar} instructions from the
10385 compiler generated code. It is enabled by default.
10387 @item -mno-optimize-membar
10388 @opindex mno-optimize-membar
10390 This switch disables the automatic removal of redundant @code{membar}
10391 instructions from the generated code.
10393 @item -mtomcat-stats
10394 @opindex mtomcat-stats
10396 Cause gas to print out tomcat statistics.
10398 @item -mcpu=@var{cpu}
10401 Select the processor type for which to generate code. Possible values are
10402 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10403 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10407 @node GNU/Linux Options
10408 @subsection GNU/Linux Options
10410 These @samp{-m} options are defined for GNU/Linux targets:
10415 Use the GNU C library instead of uClibc. This is the default except
10416 on @samp{*-*-linux-*uclibc*} targets.
10420 Use uClibc instead of the GNU C library. This is the default on
10421 @samp{*-*-linux-*uclibc*} targets.
10424 @node H8/300 Options
10425 @subsection H8/300 Options
10427 These @samp{-m} options are defined for the H8/300 implementations:
10432 Shorten some address references at link time, when possible; uses the
10433 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10434 ld, Using ld}, for a fuller description.
10438 Generate code for the H8/300H@.
10442 Generate code for the H8S@.
10446 Generate code for the H8S and H8/300H in the normal mode. This switch
10447 must be used either with @option{-mh} or @option{-ms}.
10451 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10455 Make @code{int} data 32 bits by default.
10458 @opindex malign-300
10459 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10460 The default for the H8/300H and H8S is to align longs and floats on 4
10462 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10463 This option has no effect on the H8/300.
10467 @subsection HPPA Options
10468 @cindex HPPA Options
10470 These @samp{-m} options are defined for the HPPA family of computers:
10473 @item -march=@var{architecture-type}
10475 Generate code for the specified architecture. The choices for
10476 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10477 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10478 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10479 architecture option for your machine. Code compiled for lower numbered
10480 architectures will run on higher numbered architectures, but not the
10483 @item -mpa-risc-1-0
10484 @itemx -mpa-risc-1-1
10485 @itemx -mpa-risc-2-0
10486 @opindex mpa-risc-1-0
10487 @opindex mpa-risc-1-1
10488 @opindex mpa-risc-2-0
10489 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10492 @opindex mbig-switch
10493 Generate code suitable for big switch tables. Use this option only if
10494 the assembler/linker complain about out of range branches within a switch
10497 @item -mjump-in-delay
10498 @opindex mjump-in-delay
10499 Fill delay slots of function calls with unconditional jump instructions
10500 by modifying the return pointer for the function call to be the target
10501 of the conditional jump.
10503 @item -mdisable-fpregs
10504 @opindex mdisable-fpregs
10505 Prevent floating point registers from being used in any manner. This is
10506 necessary for compiling kernels which perform lazy context switching of
10507 floating point registers. If you use this option and attempt to perform
10508 floating point operations, the compiler will abort.
10510 @item -mdisable-indexing
10511 @opindex mdisable-indexing
10512 Prevent the compiler from using indexing address modes. This avoids some
10513 rather obscure problems when compiling MIG generated code under MACH@.
10515 @item -mno-space-regs
10516 @opindex mno-space-regs
10517 Generate code that assumes the target has no space registers. This allows
10518 GCC to generate faster indirect calls and use unscaled index address modes.
10520 Such code is suitable for level 0 PA systems and kernels.
10522 @item -mfast-indirect-calls
10523 @opindex mfast-indirect-calls
10524 Generate code that assumes calls never cross space boundaries. This
10525 allows GCC to emit code which performs faster indirect calls.
10527 This option will not work in the presence of shared libraries or nested
10530 @item -mfixed-range=@var{register-range}
10531 @opindex mfixed-range
10532 Generate code treating the given register range as fixed registers.
10533 A fixed register is one that the register allocator can not use. This is
10534 useful when compiling kernel code. A register range is specified as
10535 two registers separated by a dash. Multiple register ranges can be
10536 specified separated by a comma.
10538 @item -mlong-load-store
10539 @opindex mlong-load-store
10540 Generate 3-instruction load and store sequences as sometimes required by
10541 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10544 @item -mportable-runtime
10545 @opindex mportable-runtime
10546 Use the portable calling conventions proposed by HP for ELF systems.
10550 Enable the use of assembler directives only GAS understands.
10552 @item -mschedule=@var{cpu-type}
10554 Schedule code according to the constraints for the machine type
10555 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10556 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10557 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10558 proper scheduling option for your machine. The default scheduling is
10562 @opindex mlinker-opt
10563 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10564 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10565 linkers in which they give bogus error messages when linking some programs.
10568 @opindex msoft-float
10569 Generate output containing library calls for floating point.
10570 @strong{Warning:} the requisite libraries are not available for all HPPA
10571 targets. Normally the facilities of the machine's usual C compiler are
10572 used, but this cannot be done directly in cross-compilation. You must make
10573 your own arrangements to provide suitable library functions for
10576 @option{-msoft-float} changes the calling convention in the output file;
10577 therefore, it is only useful if you compile @emph{all} of a program with
10578 this option. In particular, you need to compile @file{libgcc.a}, the
10579 library that comes with GCC, with @option{-msoft-float} in order for
10584 Generate the predefine, @code{_SIO}, for server IO@. The default is
10585 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10586 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10587 options are available under HP-UX and HI-UX@.
10591 Use GNU ld specific options. This passes @option{-shared} to ld when
10592 building a shared library. It is the default when GCC is configured,
10593 explicitly or implicitly, with the GNU linker. This option does not
10594 have any affect on which ld is called, it only changes what parameters
10595 are passed to that ld. The ld that is called is determined by the
10596 @option{--with-ld} configure option, GCC's program search path, and
10597 finally by the user's @env{PATH}. The linker used by GCC can be printed
10598 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10599 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10603 Use HP ld specific options. This passes @option{-b} to ld when building
10604 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10605 links. It is the default when GCC is configured, explicitly or
10606 implicitly, with the HP linker. This option does not have any affect on
10607 which ld is called, it only changes what parameters are passed to that
10608 ld. The ld that is called is determined by the @option{--with-ld}
10609 configure option, GCC's program search path, and finally by the user's
10610 @env{PATH}. The linker used by GCC can be printed using @samp{which
10611 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10612 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10615 @opindex mno-long-calls
10616 Generate code that uses long call sequences. This ensures that a call
10617 is always able to reach linker generated stubs. The default is to generate
10618 long calls only when the distance from the call site to the beginning
10619 of the function or translation unit, as the case may be, exceeds a
10620 predefined limit set by the branch type being used. The limits for
10621 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10622 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10625 Distances are measured from the beginning of functions when using the
10626 @option{-ffunction-sections} option, or when using the @option{-mgas}
10627 and @option{-mno-portable-runtime} options together under HP-UX with
10630 It is normally not desirable to use this option as it will degrade
10631 performance. However, it may be useful in large applications,
10632 particularly when partial linking is used to build the application.
10634 The types of long calls used depends on the capabilities of the
10635 assembler and linker, and the type of code being generated. The
10636 impact on systems that support long absolute calls, and long pic
10637 symbol-difference or pc-relative calls should be relatively small.
10638 However, an indirect call is used on 32-bit ELF systems in pic code
10639 and it is quite long.
10641 @item -munix=@var{unix-std}
10643 Generate compiler predefines and select a startfile for the specified
10644 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10645 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10646 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10647 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10648 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10651 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10652 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10653 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10654 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10655 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10656 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10658 It is @emph{important} to note that this option changes the interfaces
10659 for various library routines. It also affects the operational behavior
10660 of the C library. Thus, @emph{extreme} care is needed in using this
10663 Library code that is intended to operate with more than one UNIX
10664 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10665 as appropriate. Most GNU software doesn't provide this capability.
10669 Suppress the generation of link options to search libdld.sl when the
10670 @option{-static} option is specified on HP-UX 10 and later.
10674 The HP-UX implementation of setlocale in libc has a dependency on
10675 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10676 when the @option{-static} option is specified, special link options
10677 are needed to resolve this dependency.
10679 On HP-UX 10 and later, the GCC driver adds the necessary options to
10680 link with libdld.sl when the @option{-static} option is specified.
10681 This causes the resulting binary to be dynamic. On the 64-bit port,
10682 the linkers generate dynamic binaries by default in any case. The
10683 @option{-nolibdld} option can be used to prevent the GCC driver from
10684 adding these link options.
10688 Add support for multithreading with the @dfn{dce thread} library
10689 under HP-UX@. This option sets flags for both the preprocessor and
10693 @node i386 and x86-64 Options
10694 @subsection Intel 386 and AMD x86-64 Options
10695 @cindex i386 Options
10696 @cindex x86-64 Options
10697 @cindex Intel 386 Options
10698 @cindex AMD x86-64 Options
10700 These @samp{-m} options are defined for the i386 and x86-64 family of
10704 @item -mtune=@var{cpu-type}
10706 Tune to @var{cpu-type} everything applicable about the generated code, except
10707 for the ABI and the set of available instructions. The choices for
10708 @var{cpu-type} are:
10711 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10712 If you know the CPU on which your code will run, then you should use
10713 the corresponding @option{-mtune} option instead of
10714 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10715 of your application will have, then you should use this option.
10717 As new processors are deployed in the marketplace, the behavior of this
10718 option will change. Therefore, if you upgrade to a newer version of
10719 GCC, the code generated option will change to reflect the processors
10720 that were most common when that version of GCC was released.
10722 There is no @option{-march=generic} option because @option{-march}
10723 indicates the instruction set the compiler can use, and there is no
10724 generic instruction set applicable to all processors. In contrast,
10725 @option{-mtune} indicates the processor (or, in this case, collection of
10726 processors) for which the code is optimized.
10728 This selects the CPU to tune for at compilation time by determining
10729 the processor type of the compiling machine. Using @option{-mtune=native}
10730 will produce code optimized for the local machine under the constraints
10731 of the selected instruction set. Using @option{-march=native} will
10732 enable all instruction subsets supported by the local machine (hence
10733 the result might not run on different machines).
10735 Original Intel's i386 CPU@.
10737 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10738 @item i586, pentium
10739 Intel Pentium CPU with no MMX support.
10741 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10743 Intel PentiumPro CPU@.
10745 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10746 instruction set will be used, so the code will run on all i686 family chips.
10748 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10749 @item pentium3, pentium3m
10750 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10753 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10754 support. Used by Centrino notebooks.
10755 @item pentium4, pentium4m
10756 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10758 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10761 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10762 SSE2 and SSE3 instruction set support.
10764 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10765 instruction set support.
10767 AMD K6 CPU with MMX instruction set support.
10769 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10770 @item athlon, athlon-tbird
10771 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10773 @item athlon-4, athlon-xp, athlon-mp
10774 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10775 instruction set support.
10776 @item k8, opteron, athlon64, athlon-fx
10777 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10778 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10779 @item k8-sse3, opteron-sse3, athlon64-sse3
10780 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10781 @item amdfam10, barcelona
10782 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10783 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10784 instruction set extensions.)
10786 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10789 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
10790 instruction set support.
10792 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
10793 implemented for this chip.)
10795 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10796 implemented for this chip.)
10798 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10801 While picking a specific @var{cpu-type} will schedule things appropriately
10802 for that particular chip, the compiler will not generate any code that
10803 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10806 @item -march=@var{cpu-type}
10808 Generate instructions for the machine type @var{cpu-type}. The choices
10809 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10810 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10812 @item -mcpu=@var{cpu-type}
10814 A deprecated synonym for @option{-mtune}.
10816 @item -mfpmath=@var{unit}
10818 Generate floating point arithmetics for selected unit @var{unit}. The choices
10819 for @var{unit} are:
10823 Use the standard 387 floating point coprocessor present majority of chips and
10824 emulated otherwise. Code compiled with this option will run almost everywhere.
10825 The temporary results are computed in 80bit precision instead of precision
10826 specified by the type resulting in slightly different results compared to most
10827 of other chips. See @option{-ffloat-store} for more detailed description.
10829 This is the default choice for i386 compiler.
10832 Use scalar floating point instructions present in the SSE instruction set.
10833 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10834 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10835 instruction set supports only single precision arithmetics, thus the double and
10836 extended precision arithmetics is still done using 387. Later version, present
10837 only in Pentium4 and the future AMD x86-64 chips supports double precision
10840 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10841 or @option{-msse2} switches to enable SSE extensions and make this option
10842 effective. For the x86-64 compiler, these extensions are enabled by default.
10844 The resulting code should be considerably faster in the majority of cases and avoid
10845 the numerical instability problems of 387 code, but may break some existing
10846 code that expects temporaries to be 80bit.
10848 This is the default choice for the x86-64 compiler.
10853 Attempt to utilize both instruction sets at once. This effectively double the
10854 amount of available registers and on chips with separate execution units for
10855 387 and SSE the execution resources too. Use this option with care, as it is
10856 still experimental, because the GCC register allocator does not model separate
10857 functional units well resulting in instable performance.
10860 @item -masm=@var{dialect}
10861 @opindex masm=@var{dialect}
10862 Output asm instructions using selected @var{dialect}. Supported
10863 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10864 not support @samp{intel}.
10867 @itemx -mno-ieee-fp
10869 @opindex mno-ieee-fp
10870 Control whether or not the compiler uses IEEE floating point
10871 comparisons. These handle correctly the case where the result of a
10872 comparison is unordered.
10875 @opindex msoft-float
10876 Generate output containing library calls for floating point.
10877 @strong{Warning:} the requisite libraries are not part of GCC@.
10878 Normally the facilities of the machine's usual C compiler are used, but
10879 this can't be done directly in cross-compilation. You must make your
10880 own arrangements to provide suitable library functions for
10883 On machines where a function returns floating point results in the 80387
10884 register stack, some floating point opcodes may be emitted even if
10885 @option{-msoft-float} is used.
10887 @item -mno-fp-ret-in-387
10888 @opindex mno-fp-ret-in-387
10889 Do not use the FPU registers for return values of functions.
10891 The usual calling convention has functions return values of types
10892 @code{float} and @code{double} in an FPU register, even if there
10893 is no FPU@. The idea is that the operating system should emulate
10896 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10897 in ordinary CPU registers instead.
10899 @item -mno-fancy-math-387
10900 @opindex mno-fancy-math-387
10901 Some 387 emulators do not support the @code{sin}, @code{cos} and
10902 @code{sqrt} instructions for the 387. Specify this option to avoid
10903 generating those instructions. This option is the default on FreeBSD,
10904 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10905 indicates that the target cpu will always have an FPU and so the
10906 instruction will not need emulation. As of revision 2.6.1, these
10907 instructions are not generated unless you also use the
10908 @option{-funsafe-math-optimizations} switch.
10910 @item -malign-double
10911 @itemx -mno-align-double
10912 @opindex malign-double
10913 @opindex mno-align-double
10914 Control whether GCC aligns @code{double}, @code{long double}, and
10915 @code{long long} variables on a two word boundary or a one word
10916 boundary. Aligning @code{double} variables on a two word boundary will
10917 produce code that runs somewhat faster on a @samp{Pentium} at the
10918 expense of more memory.
10920 On x86-64, @option{-malign-double} is enabled by default.
10922 @strong{Warning:} if you use the @option{-malign-double} switch,
10923 structures containing the above types will be aligned differently than
10924 the published application binary interface specifications for the 386
10925 and will not be binary compatible with structures in code compiled
10926 without that switch.
10928 @item -m96bit-long-double
10929 @itemx -m128bit-long-double
10930 @opindex m96bit-long-double
10931 @opindex m128bit-long-double
10932 These switches control the size of @code{long double} type. The i386
10933 application binary interface specifies the size to be 96 bits,
10934 so @option{-m96bit-long-double} is the default in 32 bit mode.
10936 Modern architectures (Pentium and newer) would prefer @code{long double}
10937 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10938 conforming to the ABI, this would not be possible. So specifying a
10939 @option{-m128bit-long-double} will align @code{long double}
10940 to a 16 byte boundary by padding the @code{long double} with an additional
10943 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10944 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10946 Notice that neither of these options enable any extra precision over the x87
10947 standard of 80 bits for a @code{long double}.
10949 @strong{Warning:} if you override the default value for your target ABI, the
10950 structures and arrays containing @code{long double} variables will change
10951 their size as well as function calling convention for function taking
10952 @code{long double} will be modified. Hence they will not be binary
10953 compatible with arrays or structures in code compiled without that switch.
10955 @item -mlarge-data-threshold=@var{number}
10956 @opindex mlarge-data-threshold=@var{number}
10957 When @option{-mcmodel=medium} is specified, the data greater than
10958 @var{threshold} are placed in large data section. This value must be the
10959 same across all object linked into the binary and defaults to 65535.
10963 Use a different function-calling convention, in which functions that
10964 take a fixed number of arguments return with the @code{ret} @var{num}
10965 instruction, which pops their arguments while returning. This saves one
10966 instruction in the caller since there is no need to pop the arguments
10969 You can specify that an individual function is called with this calling
10970 sequence with the function attribute @samp{stdcall}. You can also
10971 override the @option{-mrtd} option by using the function attribute
10972 @samp{cdecl}. @xref{Function Attributes}.
10974 @strong{Warning:} this calling convention is incompatible with the one
10975 normally used on Unix, so you cannot use it if you need to call
10976 libraries compiled with the Unix compiler.
10978 Also, you must provide function prototypes for all functions that
10979 take variable numbers of arguments (including @code{printf});
10980 otherwise incorrect code will be generated for calls to those
10983 In addition, seriously incorrect code will result if you call a
10984 function with too many arguments. (Normally, extra arguments are
10985 harmlessly ignored.)
10987 @item -mregparm=@var{num}
10989 Control how many registers are used to pass integer arguments. By
10990 default, no registers are used to pass arguments, and at most 3
10991 registers can be used. You can control this behavior for a specific
10992 function by using the function attribute @samp{regparm}.
10993 @xref{Function Attributes}.
10995 @strong{Warning:} if you use this switch, and
10996 @var{num} is nonzero, then you must build all modules with the same
10997 value, including any libraries. This includes the system libraries and
11001 @opindex msseregparm
11002 Use SSE register passing conventions for float and double arguments
11003 and return values. You can control this behavior for a specific
11004 function by using the function attribute @samp{sseregparm}.
11005 @xref{Function Attributes}.
11007 @strong{Warning:} if you use this switch then you must build all
11008 modules with the same value, including any libraries. This includes
11009 the system libraries and startup modules.
11018 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
11019 is specified, the significands of results of floating-point operations are
11020 rounded to 24 bits (single precision); @option{-mpc64} rounds the
11021 significands of results of floating-point operations to 53 bits (double
11022 precision) and @option{-mpc80} rounds the significands of results of
11023 floating-point operations to 64 bits (extended double precision), which is
11024 the default. When this option is used, floating-point operations in higher
11025 precisions are not available to the programmer without setting the FPU
11026 control word explicitly.
11028 Setting the rounding of floating-point operations to less than the default
11029 80 bits can speed some programs by 2% or more. Note that some mathematical
11030 libraries assume that extended precision (80 bit) floating-point operations
11031 are enabled by default; routines in such libraries could suffer significant
11032 loss of accuracy, typically through so-called "catastrophic cancellation",
11033 when this option is used to set the precision to less than extended precision.
11035 @item -mstackrealign
11036 @opindex mstackrealign
11037 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
11038 option will generate an alternate prologue and epilogue that realigns the
11039 runtime stack if necessary. This supports mixing legacy codes that keep
11040 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
11041 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
11042 applicable to individual functions.
11044 @item -mpreferred-stack-boundary=@var{num}
11045 @opindex mpreferred-stack-boundary
11046 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
11047 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
11048 the default is 4 (16 bytes or 128 bits).
11050 @item -mincoming-stack-boundary=@var{num}
11051 @opindex mincoming-stack-boundary
11052 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
11053 boundary. If @option{-mincoming-stack-boundary} is not specified,
11054 the one specified by @option{-mpreferred-stack-boundary} will be used.
11056 On Pentium and PentiumPro, @code{double} and @code{long double} values
11057 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
11058 suffer significant run time performance penalties. On Pentium III, the
11059 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
11060 properly if it is not 16 byte aligned.
11062 To ensure proper alignment of this values on the stack, the stack boundary
11063 must be as aligned as that required by any value stored on the stack.
11064 Further, every function must be generated such that it keeps the stack
11065 aligned. Thus calling a function compiled with a higher preferred
11066 stack boundary from a function compiled with a lower preferred stack
11067 boundary will most likely misalign the stack. It is recommended that
11068 libraries that use callbacks always use the default setting.
11070 This extra alignment does consume extra stack space, and generally
11071 increases code size. Code that is sensitive to stack space usage, such
11072 as embedded systems and operating system kernels, may want to reduce the
11073 preferred alignment to @option{-mpreferred-stack-boundary=2}.
11113 These switches enable or disable the use of instructions in the MMX,
11114 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, SSE5, ABM or
11115 3DNow!@: extended instruction sets.
11116 These extensions are also available as built-in functions: see
11117 @ref{X86 Built-in Functions}, for details of the functions enabled and
11118 disabled by these switches.
11120 To have SSE/SSE2 instructions generated automatically from floating-point
11121 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
11123 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
11124 generates new AVX instructions or AVX equivalence for all SSEx instructions
11127 These options will enable GCC to use these extended instructions in
11128 generated code, even without @option{-mfpmath=sse}. Applications which
11129 perform runtime CPU detection must compile separate files for each
11130 supported architecture, using the appropriate flags. In particular,
11131 the file containing the CPU detection code should be compiled without
11136 This option instructs GCC to emit a @code{cld} instruction in the prologue
11137 of functions that use string instructions. String instructions depend on
11138 the DF flag to select between autoincrement or autodecrement mode. While the
11139 ABI specifies the DF flag to be cleared on function entry, some operating
11140 systems violate this specification by not clearing the DF flag in their
11141 exception dispatchers. The exception handler can be invoked with the DF flag
11142 set which leads to wrong direction mode, when string instructions are used.
11143 This option can be enabled by default on 32-bit x86 targets by configuring
11144 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
11145 instructions can be suppressed with the @option{-mno-cld} compiler option
11150 This option will enable GCC to use CMPXCHG16B instruction in generated code.
11151 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
11152 data types. This is useful for high resolution counters that could be updated
11153 by multiple processors (or cores). This instruction is generated as part of
11154 atomic built-in functions: see @ref{Atomic Builtins} for details.
11158 This option will enable GCC to use SAHF instruction in generated 64-bit code.
11159 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
11160 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
11161 SAHF are load and store instructions, respectively, for certain status flags.
11162 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
11163 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
11167 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
11168 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Rhapson step
11169 to increase precision instead of DIVSS and SQRTSS (and their vectorized
11170 variants) for single precision floating point arguments. These instructions
11171 are generated only when @option{-funsafe-math-optimizations} is enabled
11172 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
11173 Note that while the throughput of the sequence is higher than the throughput
11174 of the non-reciprocal instruction, the precision of the sequence can be
11175 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
11177 @item -mveclibabi=@var{type}
11178 @opindex mveclibabi
11179 Specifies the ABI type to use for vectorizing intrinsics using an
11180 external library. Supported types are @code{svml} for the Intel short
11181 vector math library and @code{acml} for the AMD math core library style
11182 of interfacing. GCC will currently emit calls to @code{vmldExp2},
11183 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
11184 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
11185 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
11186 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
11187 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
11188 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
11189 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
11190 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
11191 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
11192 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
11193 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
11194 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
11195 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
11196 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
11197 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
11198 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
11199 compatible library will have to be specified at link time.
11202 @itemx -mno-push-args
11203 @opindex mpush-args
11204 @opindex mno-push-args
11205 Use PUSH operations to store outgoing parameters. This method is shorter
11206 and usually equally fast as method using SUB/MOV operations and is enabled
11207 by default. In some cases disabling it may improve performance because of
11208 improved scheduling and reduced dependencies.
11210 @item -maccumulate-outgoing-args
11211 @opindex maccumulate-outgoing-args
11212 If enabled, the maximum amount of space required for outgoing arguments will be
11213 computed in the function prologue. This is faster on most modern CPUs
11214 because of reduced dependencies, improved scheduling and reduced stack usage
11215 when preferred stack boundary is not equal to 2. The drawback is a notable
11216 increase in code size. This switch implies @option{-mno-push-args}.
11220 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
11221 on thread-safe exception handling must compile and link all code with the
11222 @option{-mthreads} option. When compiling, @option{-mthreads} defines
11223 @option{-D_MT}; when linking, it links in a special thread helper library
11224 @option{-lmingwthrd} which cleans up per thread exception handling data.
11226 @item -mno-align-stringops
11227 @opindex mno-align-stringops
11228 Do not align destination of inlined string operations. This switch reduces
11229 code size and improves performance in case the destination is already aligned,
11230 but GCC doesn't know about it.
11232 @item -minline-all-stringops
11233 @opindex minline-all-stringops
11234 By default GCC inlines string operations only when destination is known to be
11235 aligned at least to 4 byte boundary. This enables more inlining, increase code
11236 size, but may improve performance of code that depends on fast memcpy, strlen
11237 and memset for short lengths.
11239 @item -minline-stringops-dynamically
11240 @opindex minline-stringops-dynamically
11241 For string operation of unknown size, inline runtime checks so for small
11242 blocks inline code is used, while for large blocks library call is used.
11244 @item -mstringop-strategy=@var{alg}
11245 @opindex mstringop-strategy=@var{alg}
11246 Overwrite internal decision heuristic about particular algorithm to inline
11247 string operation with. The allowed values are @code{rep_byte},
11248 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
11249 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
11250 expanding inline loop, @code{libcall} for always expanding library call.
11252 @item -momit-leaf-frame-pointer
11253 @opindex momit-leaf-frame-pointer
11254 Don't keep the frame pointer in a register for leaf functions. This
11255 avoids the instructions to save, set up and restore frame pointers and
11256 makes an extra register available in leaf functions. The option
11257 @option{-fomit-frame-pointer} removes the frame pointer for all functions
11258 which might make debugging harder.
11260 @item -mtls-direct-seg-refs
11261 @itemx -mno-tls-direct-seg-refs
11262 @opindex mtls-direct-seg-refs
11263 Controls whether TLS variables may be accessed with offsets from the
11264 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
11265 or whether the thread base pointer must be added. Whether or not this
11266 is legal depends on the operating system, and whether it maps the
11267 segment to cover the entire TLS area.
11269 For systems that use GNU libc, the default is on.
11272 @itemx -mno-fused-madd
11273 @opindex mfused-madd
11274 Enable automatic generation of fused floating point multiply-add instructions
11275 if the ISA supports such instructions. The -mfused-madd option is on by
11276 default. The fused multiply-add instructions have a different
11277 rounding behavior compared to executing a multiply followed by an add.
11280 @itemx -mno-sse2avx
11282 Specify that the assembler should encode SSE instructions with VEX
11283 prefix. The option @option{-mavx} turns this on by default.
11286 These @samp{-m} switches are supported in addition to the above
11287 on AMD x86-64 processors in 64-bit environments.
11294 Generate code for a 32-bit or 64-bit environment.
11295 The 32-bit environment sets int, long and pointer to 32 bits and
11296 generates code that runs on any i386 system.
11297 The 64-bit environment sets int to 32 bits and long and pointer
11298 to 64 bits and generates code for AMD's x86-64 architecture. For
11299 darwin only the -m64 option turns off the @option{-fno-pic} and
11300 @option{-mdynamic-no-pic} options.
11302 @item -mno-red-zone
11303 @opindex no-red-zone
11304 Do not use a so called red zone for x86-64 code. The red zone is mandated
11305 by the x86-64 ABI, it is a 128-byte area beyond the location of the
11306 stack pointer that will not be modified by signal or interrupt handlers
11307 and therefore can be used for temporary data without adjusting the stack
11308 pointer. The flag @option{-mno-red-zone} disables this red zone.
11310 @item -mcmodel=small
11311 @opindex mcmodel=small
11312 Generate code for the small code model: the program and its symbols must
11313 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11314 Programs can be statically or dynamically linked. This is the default
11317 @item -mcmodel=kernel
11318 @opindex mcmodel=kernel
11319 Generate code for the kernel code model. The kernel runs in the
11320 negative 2 GB of the address space.
11321 This model has to be used for Linux kernel code.
11323 @item -mcmodel=medium
11324 @opindex mcmodel=medium
11325 Generate code for the medium model: The program is linked in the lower 2
11326 GB of the address space. Small symbols are also placed there. Symbols
11327 with sizes larger than @option{-mlarge-data-threshold} are put into
11328 large data or bss sections and can be located above 2GB. Programs can
11329 be statically or dynamically linked.
11331 @item -mcmodel=large
11332 @opindex mcmodel=large
11333 Generate code for the large model: This model makes no assumptions
11334 about addresses and sizes of sections.
11337 @node IA-64 Options
11338 @subsection IA-64 Options
11339 @cindex IA-64 Options
11341 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11345 @opindex mbig-endian
11346 Generate code for a big endian target. This is the default for HP-UX@.
11348 @item -mlittle-endian
11349 @opindex mlittle-endian
11350 Generate code for a little endian target. This is the default for AIX5
11356 @opindex mno-gnu-as
11357 Generate (or don't) code for the GNU assembler. This is the default.
11358 @c Also, this is the default if the configure option @option{--with-gnu-as}
11364 @opindex mno-gnu-ld
11365 Generate (or don't) code for the GNU linker. This is the default.
11366 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11371 Generate code that does not use a global pointer register. The result
11372 is not position independent code, and violates the IA-64 ABI@.
11374 @item -mvolatile-asm-stop
11375 @itemx -mno-volatile-asm-stop
11376 @opindex mvolatile-asm-stop
11377 @opindex mno-volatile-asm-stop
11378 Generate (or don't) a stop bit immediately before and after volatile asm
11381 @item -mregister-names
11382 @itemx -mno-register-names
11383 @opindex mregister-names
11384 @opindex mno-register-names
11385 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11386 the stacked registers. This may make assembler output more readable.
11392 Disable (or enable) optimizations that use the small data section. This may
11393 be useful for working around optimizer bugs.
11395 @item -mconstant-gp
11396 @opindex mconstant-gp
11397 Generate code that uses a single constant global pointer value. This is
11398 useful when compiling kernel code.
11402 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11403 This is useful when compiling firmware code.
11405 @item -minline-float-divide-min-latency
11406 @opindex minline-float-divide-min-latency
11407 Generate code for inline divides of floating point values
11408 using the minimum latency algorithm.
11410 @item -minline-float-divide-max-throughput
11411 @opindex minline-float-divide-max-throughput
11412 Generate code for inline divides of floating point values
11413 using the maximum throughput algorithm.
11415 @item -minline-int-divide-min-latency
11416 @opindex minline-int-divide-min-latency
11417 Generate code for inline divides of integer values
11418 using the minimum latency algorithm.
11420 @item -minline-int-divide-max-throughput
11421 @opindex minline-int-divide-max-throughput
11422 Generate code for inline divides of integer values
11423 using the maximum throughput algorithm.
11425 @item -minline-sqrt-min-latency
11426 @opindex minline-sqrt-min-latency
11427 Generate code for inline square roots
11428 using the minimum latency algorithm.
11430 @item -minline-sqrt-max-throughput
11431 @opindex minline-sqrt-max-throughput
11432 Generate code for inline square roots
11433 using the maximum throughput algorithm.
11435 @item -mno-dwarf2-asm
11436 @itemx -mdwarf2-asm
11437 @opindex mno-dwarf2-asm
11438 @opindex mdwarf2-asm
11439 Don't (or do) generate assembler code for the DWARF2 line number debugging
11440 info. This may be useful when not using the GNU assembler.
11442 @item -mearly-stop-bits
11443 @itemx -mno-early-stop-bits
11444 @opindex mearly-stop-bits
11445 @opindex mno-early-stop-bits
11446 Allow stop bits to be placed earlier than immediately preceding the
11447 instruction that triggered the stop bit. This can improve instruction
11448 scheduling, but does not always do so.
11450 @item -mfixed-range=@var{register-range}
11451 @opindex mfixed-range
11452 Generate code treating the given register range as fixed registers.
11453 A fixed register is one that the register allocator can not use. This is
11454 useful when compiling kernel code. A register range is specified as
11455 two registers separated by a dash. Multiple register ranges can be
11456 specified separated by a comma.
11458 @item -mtls-size=@var{tls-size}
11460 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11463 @item -mtune=@var{cpu-type}
11465 Tune the instruction scheduling for a particular CPU, Valid values are
11466 itanium, itanium1, merced, itanium2, and mckinley.
11472 Add support for multithreading using the POSIX threads library. This
11473 option sets flags for both the preprocessor and linker. It does
11474 not affect the thread safety of object code produced by the compiler or
11475 that of libraries supplied with it. These are HP-UX specific flags.
11481 Generate code for a 32-bit or 64-bit environment.
11482 The 32-bit environment sets int, long and pointer to 32 bits.
11483 The 64-bit environment sets int to 32 bits and long and pointer
11484 to 64 bits. These are HP-UX specific flags.
11486 @item -mno-sched-br-data-spec
11487 @itemx -msched-br-data-spec
11488 @opindex mno-sched-br-data-spec
11489 @opindex msched-br-data-spec
11490 (Dis/En)able data speculative scheduling before reload.
11491 This will result in generation of the ld.a instructions and
11492 the corresponding check instructions (ld.c / chk.a).
11493 The default is 'disable'.
11495 @item -msched-ar-data-spec
11496 @itemx -mno-sched-ar-data-spec
11497 @opindex msched-ar-data-spec
11498 @opindex mno-sched-ar-data-spec
11499 (En/Dis)able data speculative scheduling after reload.
11500 This will result in generation of the ld.a instructions and
11501 the corresponding check instructions (ld.c / chk.a).
11502 The default is 'enable'.
11504 @item -mno-sched-control-spec
11505 @itemx -msched-control-spec
11506 @opindex mno-sched-control-spec
11507 @opindex msched-control-spec
11508 (Dis/En)able control speculative scheduling. This feature is
11509 available only during region scheduling (i.e.@: before reload).
11510 This will result in generation of the ld.s instructions and
11511 the corresponding check instructions chk.s .
11512 The default is 'disable'.
11514 @item -msched-br-in-data-spec
11515 @itemx -mno-sched-br-in-data-spec
11516 @opindex msched-br-in-data-spec
11517 @opindex mno-sched-br-in-data-spec
11518 (En/Dis)able speculative scheduling of the instructions that
11519 are dependent on the data speculative loads before reload.
11520 This is effective only with @option{-msched-br-data-spec} enabled.
11521 The default is 'enable'.
11523 @item -msched-ar-in-data-spec
11524 @itemx -mno-sched-ar-in-data-spec
11525 @opindex msched-ar-in-data-spec
11526 @opindex mno-sched-ar-in-data-spec
11527 (En/Dis)able speculative scheduling of the instructions that
11528 are dependent on the data speculative loads after reload.
11529 This is effective only with @option{-msched-ar-data-spec} enabled.
11530 The default is 'enable'.
11532 @item -msched-in-control-spec
11533 @itemx -mno-sched-in-control-spec
11534 @opindex msched-in-control-spec
11535 @opindex mno-sched-in-control-spec
11536 (En/Dis)able speculative scheduling of the instructions that
11537 are dependent on the control speculative loads.
11538 This is effective only with @option{-msched-control-spec} enabled.
11539 The default is 'enable'.
11542 @itemx -mno-sched-ldc
11543 @opindex msched-ldc
11544 @opindex mno-sched-ldc
11545 (En/Dis)able use of simple data speculation checks ld.c .
11546 If disabled, only chk.a instructions will be emitted to check
11547 data speculative loads.
11548 The default is 'enable'.
11550 @item -mno-sched-control-ldc
11551 @itemx -msched-control-ldc
11552 @opindex mno-sched-control-ldc
11553 @opindex msched-control-ldc
11554 (Dis/En)able use of ld.c instructions to check control speculative loads.
11555 If enabled, in case of control speculative load with no speculatively
11556 scheduled dependent instructions this load will be emitted as ld.sa and
11557 ld.c will be used to check it.
11558 The default is 'disable'.
11560 @item -mno-sched-spec-verbose
11561 @itemx -msched-spec-verbose
11562 @opindex mno-sched-spec-verbose
11563 @opindex msched-spec-verbose
11564 (Dis/En)able printing of the information about speculative motions.
11566 @item -mno-sched-prefer-non-data-spec-insns
11567 @itemx -msched-prefer-non-data-spec-insns
11568 @opindex mno-sched-prefer-non-data-spec-insns
11569 @opindex msched-prefer-non-data-spec-insns
11570 If enabled, data speculative instructions will be chosen for schedule
11571 only if there are no other choices at the moment. This will make
11572 the use of the data speculation much more conservative.
11573 The default is 'disable'.
11575 @item -mno-sched-prefer-non-control-spec-insns
11576 @itemx -msched-prefer-non-control-spec-insns
11577 @opindex mno-sched-prefer-non-control-spec-insns
11578 @opindex msched-prefer-non-control-spec-insns
11579 If enabled, control speculative instructions will be chosen for schedule
11580 only if there are no other choices at the moment. This will make
11581 the use of the control speculation much more conservative.
11582 The default is 'disable'.
11584 @item -mno-sched-count-spec-in-critical-path
11585 @itemx -msched-count-spec-in-critical-path
11586 @opindex mno-sched-count-spec-in-critical-path
11587 @opindex msched-count-spec-in-critical-path
11588 If enabled, speculative dependencies will be considered during
11589 computation of the instructions priorities. This will make the use of the
11590 speculation a bit more conservative.
11591 The default is 'disable'.
11596 @subsection M32C Options
11597 @cindex M32C options
11600 @item -mcpu=@var{name}
11602 Select the CPU for which code is generated. @var{name} may be one of
11603 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11604 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11605 the M32C/80 series.
11609 Specifies that the program will be run on the simulator. This causes
11610 an alternate runtime library to be linked in which supports, for
11611 example, file I/O@. You must not use this option when generating
11612 programs that will run on real hardware; you must provide your own
11613 runtime library for whatever I/O functions are needed.
11615 @item -memregs=@var{number}
11617 Specifies the number of memory-based pseudo-registers GCC will use
11618 during code generation. These pseudo-registers will be used like real
11619 registers, so there is a tradeoff between GCC's ability to fit the
11620 code into available registers, and the performance penalty of using
11621 memory instead of registers. Note that all modules in a program must
11622 be compiled with the same value for this option. Because of that, you
11623 must not use this option with the default runtime libraries gcc
11628 @node M32R/D Options
11629 @subsection M32R/D Options
11630 @cindex M32R/D options
11632 These @option{-m} options are defined for Renesas M32R/D architectures:
11637 Generate code for the M32R/2@.
11641 Generate code for the M32R/X@.
11645 Generate code for the M32R@. This is the default.
11647 @item -mmodel=small
11648 @opindex mmodel=small
11649 Assume all objects live in the lower 16MB of memory (so that their addresses
11650 can be loaded with the @code{ld24} instruction), and assume all subroutines
11651 are reachable with the @code{bl} instruction.
11652 This is the default.
11654 The addressability of a particular object can be set with the
11655 @code{model} attribute.
11657 @item -mmodel=medium
11658 @opindex mmodel=medium
11659 Assume objects may be anywhere in the 32-bit address space (the compiler
11660 will generate @code{seth/add3} instructions to load their addresses), and
11661 assume all subroutines are reachable with the @code{bl} instruction.
11663 @item -mmodel=large
11664 @opindex mmodel=large
11665 Assume objects may be anywhere in the 32-bit address space (the compiler
11666 will generate @code{seth/add3} instructions to load their addresses), and
11667 assume subroutines may not be reachable with the @code{bl} instruction
11668 (the compiler will generate the much slower @code{seth/add3/jl}
11669 instruction sequence).
11672 @opindex msdata=none
11673 Disable use of the small data area. Variables will be put into
11674 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11675 @code{section} attribute has been specified).
11676 This is the default.
11678 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11679 Objects may be explicitly put in the small data area with the
11680 @code{section} attribute using one of these sections.
11682 @item -msdata=sdata
11683 @opindex msdata=sdata
11684 Put small global and static data in the small data area, but do not
11685 generate special code to reference them.
11688 @opindex msdata=use
11689 Put small global and static data in the small data area, and generate
11690 special instructions to reference them.
11694 @cindex smaller data references
11695 Put global and static objects less than or equal to @var{num} bytes
11696 into the small data or bss sections instead of the normal data or bss
11697 sections. The default value of @var{num} is 8.
11698 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11699 for this option to have any effect.
11701 All modules should be compiled with the same @option{-G @var{num}} value.
11702 Compiling with different values of @var{num} may or may not work; if it
11703 doesn't the linker will give an error message---incorrect code will not be
11708 Makes the M32R specific code in the compiler display some statistics
11709 that might help in debugging programs.
11711 @item -malign-loops
11712 @opindex malign-loops
11713 Align all loops to a 32-byte boundary.
11715 @item -mno-align-loops
11716 @opindex mno-align-loops
11717 Do not enforce a 32-byte alignment for loops. This is the default.
11719 @item -missue-rate=@var{number}
11720 @opindex missue-rate=@var{number}
11721 Issue @var{number} instructions per cycle. @var{number} can only be 1
11724 @item -mbranch-cost=@var{number}
11725 @opindex mbranch-cost=@var{number}
11726 @var{number} can only be 1 or 2. If it is 1 then branches will be
11727 preferred over conditional code, if it is 2, then the opposite will
11730 @item -mflush-trap=@var{number}
11731 @opindex mflush-trap=@var{number}
11732 Specifies the trap number to use to flush the cache. The default is
11733 12. Valid numbers are between 0 and 15 inclusive.
11735 @item -mno-flush-trap
11736 @opindex mno-flush-trap
11737 Specifies that the cache cannot be flushed by using a trap.
11739 @item -mflush-func=@var{name}
11740 @opindex mflush-func=@var{name}
11741 Specifies the name of the operating system function to call to flush
11742 the cache. The default is @emph{_flush_cache}, but a function call
11743 will only be used if a trap is not available.
11745 @item -mno-flush-func
11746 @opindex mno-flush-func
11747 Indicates that there is no OS function for flushing the cache.
11751 @node M680x0 Options
11752 @subsection M680x0 Options
11753 @cindex M680x0 options
11755 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11756 The default settings depend on which architecture was selected when
11757 the compiler was configured; the defaults for the most common choices
11761 @item -march=@var{arch}
11763 Generate code for a specific M680x0 or ColdFire instruction set
11764 architecture. Permissible values of @var{arch} for M680x0
11765 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11766 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11767 architectures are selected according to Freescale's ISA classification
11768 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11769 @samp{isab} and @samp{isac}.
11771 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11772 code for a ColdFire target. The @var{arch} in this macro is one of the
11773 @option{-march} arguments given above.
11775 When used together, @option{-march} and @option{-mtune} select code
11776 that runs on a family of similar processors but that is optimized
11777 for a particular microarchitecture.
11779 @item -mcpu=@var{cpu}
11781 Generate code for a specific M680x0 or ColdFire processor.
11782 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
11783 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
11784 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
11785 below, which also classifies the CPUs into families:
11787 @multitable @columnfractions 0.20 0.80
11788 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
11789 @item @samp{51qe} @tab @samp{51qe}
11790 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
11791 @item @samp{5206e} @tab @samp{5206e}
11792 @item @samp{5208} @tab @samp{5207} @samp{5208}
11793 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
11794 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
11795 @item @samp{5216} @tab @samp{5214} @samp{5216}
11796 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
11797 @item @samp{5225} @tab @samp{5224} @samp{5225}
11798 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
11799 @item @samp{5249} @tab @samp{5249}
11800 @item @samp{5250} @tab @samp{5250}
11801 @item @samp{5271} @tab @samp{5270} @samp{5271}
11802 @item @samp{5272} @tab @samp{5272}
11803 @item @samp{5275} @tab @samp{5274} @samp{5275}
11804 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
11805 @item @samp{5307} @tab @samp{5307}
11806 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
11807 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
11808 @item @samp{5407} @tab @samp{5407}
11809 @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}
11812 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
11813 @var{arch} is compatible with @var{cpu}. Other combinations of
11814 @option{-mcpu} and @option{-march} are rejected.
11816 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
11817 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
11818 where the value of @var{family} is given by the table above.
11820 @item -mtune=@var{tune}
11822 Tune the code for a particular microarchitecture, within the
11823 constraints set by @option{-march} and @option{-mcpu}.
11824 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11825 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11826 and @samp{cpu32}. The ColdFire microarchitectures
11827 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11829 You can also use @option{-mtune=68020-40} for code that needs
11830 to run relatively well on 68020, 68030 and 68040 targets.
11831 @option{-mtune=68020-60} is similar but includes 68060 targets
11832 as well. These two options select the same tuning decisions as
11833 @option{-m68020-40} and @option{-m68020-60} respectively.
11835 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11836 when tuning for 680x0 architecture @var{arch}. It also defines
11837 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11838 option is used. If gcc is tuning for a range of architectures,
11839 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11840 it defines the macros for every architecture in the range.
11842 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11843 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11844 of the arguments given above.
11850 Generate output for a 68000. This is the default
11851 when the compiler is configured for 68000-based systems.
11852 It is equivalent to @option{-march=68000}.
11854 Use this option for microcontrollers with a 68000 or EC000 core,
11855 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11859 Generate output for a 68010. This is the default
11860 when the compiler is configured for 68010-based systems.
11861 It is equivalent to @option{-march=68010}.
11867 Generate output for a 68020. This is the default
11868 when the compiler is configured for 68020-based systems.
11869 It is equivalent to @option{-march=68020}.
11873 Generate output for a 68030. This is the default when the compiler is
11874 configured for 68030-based systems. It is equivalent to
11875 @option{-march=68030}.
11879 Generate output for a 68040. This is the default when the compiler is
11880 configured for 68040-based systems. It is equivalent to
11881 @option{-march=68040}.
11883 This option inhibits the use of 68881/68882 instructions that have to be
11884 emulated by software on the 68040. Use this option if your 68040 does not
11885 have code to emulate those instructions.
11889 Generate output for a 68060. This is the default when the compiler is
11890 configured for 68060-based systems. It is equivalent to
11891 @option{-march=68060}.
11893 This option inhibits the use of 68020 and 68881/68882 instructions that
11894 have to be emulated by software on the 68060. Use this option if your 68060
11895 does not have code to emulate those instructions.
11899 Generate output for a CPU32. This is the default
11900 when the compiler is configured for CPU32-based systems.
11901 It is equivalent to @option{-march=cpu32}.
11903 Use this option for microcontrollers with a
11904 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11905 68336, 68340, 68341, 68349 and 68360.
11909 Generate output for a 520X ColdFire CPU@. This is the default
11910 when the compiler is configured for 520X-based systems.
11911 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11912 in favor of that option.
11914 Use this option for microcontroller with a 5200 core, including
11915 the MCF5202, MCF5203, MCF5204 and MCF5206.
11919 Generate output for a 5206e ColdFire CPU@. The option is now
11920 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11924 Generate output for a member of the ColdFire 528X family.
11925 The option is now deprecated in favor of the equivalent
11926 @option{-mcpu=528x}.
11930 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
11931 in favor of the equivalent @option{-mcpu=5307}.
11935 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
11936 in favor of the equivalent @option{-mcpu=5407}.
11940 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11941 This includes use of hardware floating point instructions.
11942 The option is equivalent to @option{-mcpu=547x}, and is now
11943 deprecated in favor of that option.
11947 Generate output for a 68040, without using any of the new instructions.
11948 This results in code which can run relatively efficiently on either a
11949 68020/68881 or a 68030 or a 68040. The generated code does use the
11950 68881 instructions that are emulated on the 68040.
11952 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11956 Generate output for a 68060, without using any of the new instructions.
11957 This results in code which can run relatively efficiently on either a
11958 68020/68881 or a 68030 or a 68040. The generated code does use the
11959 68881 instructions that are emulated on the 68060.
11961 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11965 @opindex mhard-float
11967 Generate floating-point instructions. This is the default for 68020
11968 and above, and for ColdFire devices that have an FPU@. It defines the
11969 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11970 on ColdFire targets.
11973 @opindex msoft-float
11974 Do not generate floating-point instructions; use library calls instead.
11975 This is the default for 68000, 68010, and 68832 targets. It is also
11976 the default for ColdFire devices that have no FPU.
11982 Generate (do not generate) ColdFire hardware divide and remainder
11983 instructions. If @option{-march} is used without @option{-mcpu},
11984 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
11985 architectures. Otherwise, the default is taken from the target CPU
11986 (either the default CPU, or the one specified by @option{-mcpu}). For
11987 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
11988 @option{-mcpu=5206e}.
11990 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
11994 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11995 Additionally, parameters passed on the stack are also aligned to a
11996 16-bit boundary even on targets whose API mandates promotion to 32-bit.
12000 Do not consider type @code{int} to be 16 bits wide. This is the default.
12003 @itemx -mno-bitfield
12004 @opindex mnobitfield
12005 @opindex mno-bitfield
12006 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
12007 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
12011 Do use the bit-field instructions. The @option{-m68020} option implies
12012 @option{-mbitfield}. This is the default if you use a configuration
12013 designed for a 68020.
12017 Use a different function-calling convention, in which functions
12018 that take a fixed number of arguments return with the @code{rtd}
12019 instruction, which pops their arguments while returning. This
12020 saves one instruction in the caller since there is no need to pop
12021 the arguments there.
12023 This calling convention is incompatible with the one normally
12024 used on Unix, so you cannot use it if you need to call libraries
12025 compiled with the Unix compiler.
12027 Also, you must provide function prototypes for all functions that
12028 take variable numbers of arguments (including @code{printf});
12029 otherwise incorrect code will be generated for calls to those
12032 In addition, seriously incorrect code will result if you call a
12033 function with too many arguments. (Normally, extra arguments are
12034 harmlessly ignored.)
12036 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
12037 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
12041 Do not use the calling conventions selected by @option{-mrtd}.
12042 This is the default.
12045 @itemx -mno-align-int
12046 @opindex malign-int
12047 @opindex mno-align-int
12048 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
12049 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
12050 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
12051 Aligning variables on 32-bit boundaries produces code that runs somewhat
12052 faster on processors with 32-bit busses at the expense of more memory.
12054 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
12055 align structures containing the above types differently than
12056 most published application binary interface specifications for the m68k.
12060 Use the pc-relative addressing mode of the 68000 directly, instead of
12061 using a global offset table. At present, this option implies @option{-fpic},
12062 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
12063 not presently supported with @option{-mpcrel}, though this could be supported for
12064 68020 and higher processors.
12066 @item -mno-strict-align
12067 @itemx -mstrict-align
12068 @opindex mno-strict-align
12069 @opindex mstrict-align
12070 Do not (do) assume that unaligned memory references will be handled by
12074 Generate code that allows the data segment to be located in a different
12075 area of memory from the text segment. This allows for execute in place in
12076 an environment without virtual memory management. This option implies
12079 @item -mno-sep-data
12080 Generate code that assumes that the data segment follows the text segment.
12081 This is the default.
12083 @item -mid-shared-library
12084 Generate code that supports shared libraries via the library ID method.
12085 This allows for execute in place and shared libraries in an environment
12086 without virtual memory management. This option implies @option{-fPIC}.
12088 @item -mno-id-shared-library
12089 Generate code that doesn't assume ID based shared libraries are being used.
12090 This is the default.
12092 @item -mshared-library-id=n
12093 Specified the identification number of the ID based shared library being
12094 compiled. Specifying a value of 0 will generate more compact code, specifying
12095 other values will force the allocation of that number to the current
12096 library but is no more space or time efficient than omitting this option.
12102 When generating position-independent code for ColdFire, generate code
12103 that works if the GOT has more than 8192 entries. This code is
12104 larger and slower than code generated without this option. On M680x0
12105 processors, this option is not needed; @option{-fPIC} suffices.
12107 GCC normally uses a single instruction to load values from the GOT@.
12108 While this is relatively efficient, it only works if the GOT
12109 is smaller than about 64k. Anything larger causes the linker
12110 to report an error such as:
12112 @cindex relocation truncated to fit (ColdFire)
12114 relocation truncated to fit: R_68K_GOT16O foobar
12117 If this happens, you should recompile your code with @option{-mxgot}.
12118 It should then work with very large GOTs. However, code generated with
12119 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
12120 the value of a global symbol.
12122 Note that some linkers, including newer versions of the GNU linker,
12123 can create multiple GOTs and sort GOT entries. If you have such a linker,
12124 you should only need to use @option{-mxgot} when compiling a single
12125 object file that accesses more than 8192 GOT entries. Very few do.
12127 These options have no effect unless GCC is generating
12128 position-independent code.
12132 @node M68hc1x Options
12133 @subsection M68hc1x Options
12134 @cindex M68hc1x options
12136 These are the @samp{-m} options defined for the 68hc11 and 68hc12
12137 microcontrollers. The default values for these options depends on
12138 which style of microcontroller was selected when the compiler was configured;
12139 the defaults for the most common choices are given below.
12146 Generate output for a 68HC11. This is the default
12147 when the compiler is configured for 68HC11-based systems.
12153 Generate output for a 68HC12. This is the default
12154 when the compiler is configured for 68HC12-based systems.
12160 Generate output for a 68HCS12.
12162 @item -mauto-incdec
12163 @opindex mauto-incdec
12164 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
12171 Enable the use of 68HC12 min and max instructions.
12174 @itemx -mno-long-calls
12175 @opindex mlong-calls
12176 @opindex mno-long-calls
12177 Treat all calls as being far away (near). If calls are assumed to be
12178 far away, the compiler will use the @code{call} instruction to
12179 call a function and the @code{rtc} instruction for returning.
12183 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12185 @item -msoft-reg-count=@var{count}
12186 @opindex msoft-reg-count
12187 Specify the number of pseudo-soft registers which are used for the
12188 code generation. The maximum number is 32. Using more pseudo-soft
12189 register may or may not result in better code depending on the program.
12190 The default is 4 for 68HC11 and 2 for 68HC12.
12194 @node MCore Options
12195 @subsection MCore Options
12196 @cindex MCore options
12198 These are the @samp{-m} options defined for the Motorola M*Core
12204 @itemx -mno-hardlit
12206 @opindex mno-hardlit
12207 Inline constants into the code stream if it can be done in two
12208 instructions or less.
12214 Use the divide instruction. (Enabled by default).
12216 @item -mrelax-immediate
12217 @itemx -mno-relax-immediate
12218 @opindex mrelax-immediate
12219 @opindex mno-relax-immediate
12220 Allow arbitrary sized immediates in bit operations.
12222 @item -mwide-bitfields
12223 @itemx -mno-wide-bitfields
12224 @opindex mwide-bitfields
12225 @opindex mno-wide-bitfields
12226 Always treat bit-fields as int-sized.
12228 @item -m4byte-functions
12229 @itemx -mno-4byte-functions
12230 @opindex m4byte-functions
12231 @opindex mno-4byte-functions
12232 Force all functions to be aligned to a four byte boundary.
12234 @item -mcallgraph-data
12235 @itemx -mno-callgraph-data
12236 @opindex mcallgraph-data
12237 @opindex mno-callgraph-data
12238 Emit callgraph information.
12241 @itemx -mno-slow-bytes
12242 @opindex mslow-bytes
12243 @opindex mno-slow-bytes
12244 Prefer word access when reading byte quantities.
12246 @item -mlittle-endian
12247 @itemx -mbig-endian
12248 @opindex mlittle-endian
12249 @opindex mbig-endian
12250 Generate code for a little endian target.
12256 Generate code for the 210 processor.
12260 @subsection MIPS Options
12261 @cindex MIPS options
12267 Generate big-endian code.
12271 Generate little-endian code. This is the default for @samp{mips*el-*-*}
12274 @item -march=@var{arch}
12276 Generate code that will run on @var{arch}, which can be the name of a
12277 generic MIPS ISA, or the name of a particular processor.
12279 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
12280 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
12281 The processor names are:
12282 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
12283 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
12284 @samp{5kc}, @samp{5kf},
12286 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
12287 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
12288 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
12289 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
12290 @samp{loongson2e}, @samp{loongson2f},
12294 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
12295 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
12296 @samp{rm7000}, @samp{rm9000},
12297 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
12300 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
12301 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
12303 The special value @samp{from-abi} selects the
12304 most compatible architecture for the selected ABI (that is,
12305 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
12307 Native Linux/GNU toolchains also support the value @samp{native},
12308 which selects the best architecture option for the host processor.
12309 @option{-march=native} has no effect if GCC does not recognize
12312 In processor names, a final @samp{000} can be abbreviated as @samp{k}
12313 (for example, @samp{-march=r2k}). Prefixes are optional, and
12314 @samp{vr} may be written @samp{r}.
12316 Names of the form @samp{@var{n}f2_1} refer to processors with
12317 FPUs clocked at half the rate of the core, names of the form
12318 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
12319 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
12320 processors with FPUs clocked a ratio of 3:2 with respect to the core.
12321 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12322 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12323 accepted as synonyms for @samp{@var{n}f1_1}.
12325 GCC defines two macros based on the value of this option. The first
12326 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12327 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12328 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12329 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12330 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12332 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12333 above. In other words, it will have the full prefix and will not
12334 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12335 the macro names the resolved architecture (either @samp{"mips1"} or
12336 @samp{"mips3"}). It names the default architecture when no
12337 @option{-march} option is given.
12339 @item -mtune=@var{arch}
12341 Optimize for @var{arch}. Among other things, this option controls
12342 the way instructions are scheduled, and the perceived cost of arithmetic
12343 operations. The list of @var{arch} values is the same as for
12346 When this option is not used, GCC will optimize for the processor
12347 specified by @option{-march}. By using @option{-march} and
12348 @option{-mtune} together, it is possible to generate code that will
12349 run on a family of processors, but optimize the code for one
12350 particular member of that family.
12352 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12353 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12354 @samp{-march} ones described above.
12358 Equivalent to @samp{-march=mips1}.
12362 Equivalent to @samp{-march=mips2}.
12366 Equivalent to @samp{-march=mips3}.
12370 Equivalent to @samp{-march=mips4}.
12374 Equivalent to @samp{-march=mips32}.
12378 Equivalent to @samp{-march=mips32r2}.
12382 Equivalent to @samp{-march=mips64}.
12386 Equivalent to @samp{-march=mips64r2}.
12391 @opindex mno-mips16
12392 Generate (do not generate) MIPS16 code. If GCC is targetting a
12393 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12395 MIPS16 code generation can also be controlled on a per-function basis
12396 by means of @code{mips16} and @code{nomips16} attributes.
12397 @xref{Function Attributes}, for more information.
12399 @item -mflip-mips16
12400 @opindex mflip-mips16
12401 Generate MIPS16 code on alternating functions. This option is provided
12402 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12403 not intended for ordinary use in compiling user code.
12405 @item -minterlink-mips16
12406 @itemx -mno-interlink-mips16
12407 @opindex minterlink-mips16
12408 @opindex mno-interlink-mips16
12409 Require (do not require) that non-MIPS16 code be link-compatible with
12412 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12413 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12414 therefore disables direct jumps unless GCC knows that the target of the
12415 jump is not MIPS16.
12427 Generate code for the given ABI@.
12429 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12430 generates 64-bit code when you select a 64-bit architecture, but you
12431 can use @option{-mgp32} to get 32-bit code instead.
12433 For information about the O64 ABI, see
12434 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12436 GCC supports a variant of the o32 ABI in which floating-point registers
12437 are 64 rather than 32 bits wide. You can select this combination with
12438 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12439 and @samp{mfhc1} instructions and is therefore only supported for
12440 MIPS32R2 processors.
12442 The register assignments for arguments and return values remain the
12443 same, but each scalar value is passed in a single 64-bit register
12444 rather than a pair of 32-bit registers. For example, scalar
12445 floating-point values are returned in @samp{$f0} only, not a
12446 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12447 remains the same, but all 64 bits are saved.
12450 @itemx -mno-abicalls
12452 @opindex mno-abicalls
12453 Generate (do not generate) code that is suitable for SVR4-style
12454 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12459 Generate (do not generate) code that is fully position-independent,
12460 and that can therefore be linked into shared libraries. This option
12461 only affects @option{-mabicalls}.
12463 All @option{-mabicalls} code has traditionally been position-independent,
12464 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12465 as an extension, the GNU toolchain allows executables to use absolute
12466 accesses for locally-binding symbols. It can also use shorter GP
12467 initialization sequences and generate direct calls to locally-defined
12468 functions. This mode is selected by @option{-mno-shared}.
12470 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12471 objects that can only be linked by the GNU linker. However, the option
12472 does not affect the ABI of the final executable; it only affects the ABI
12473 of relocatable objects. Using @option{-mno-shared} will generally make
12474 executables both smaller and quicker.
12476 @option{-mshared} is the default.
12482 Assume (do not assume) that the static and dynamic linkers
12483 support PLTs and copy relocations. This option only affects
12484 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
12485 has no effect without @samp{-msym32}.
12487 You can make @option{-mplt} the default by configuring
12488 GCC with @option{--with-mips-plt}. The default is
12489 @option{-mno-plt} otherwise.
12495 Lift (do not lift) the usual restrictions on the size of the global
12498 GCC normally uses a single instruction to load values from the GOT@.
12499 While this is relatively efficient, it will only work if the GOT
12500 is smaller than about 64k. Anything larger will cause the linker
12501 to report an error such as:
12503 @cindex relocation truncated to fit (MIPS)
12505 relocation truncated to fit: R_MIPS_GOT16 foobar
12508 If this happens, you should recompile your code with @option{-mxgot}.
12509 It should then work with very large GOTs, although it will also be
12510 less efficient, since it will take three instructions to fetch the
12511 value of a global symbol.
12513 Note that some linkers can create multiple GOTs. If you have such a
12514 linker, you should only need to use @option{-mxgot} when a single object
12515 file accesses more than 64k's worth of GOT entries. Very few do.
12517 These options have no effect unless GCC is generating position
12522 Assume that general-purpose registers are 32 bits wide.
12526 Assume that general-purpose registers are 64 bits wide.
12530 Assume that floating-point registers are 32 bits wide.
12534 Assume that floating-point registers are 64 bits wide.
12537 @opindex mhard-float
12538 Use floating-point coprocessor instructions.
12541 @opindex msoft-float
12542 Do not use floating-point coprocessor instructions. Implement
12543 floating-point calculations using library calls instead.
12545 @item -msingle-float
12546 @opindex msingle-float
12547 Assume that the floating-point coprocessor only supports single-precision
12550 @item -mdouble-float
12551 @opindex mdouble-float
12552 Assume that the floating-point coprocessor supports double-precision
12553 operations. This is the default.
12559 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12560 implement atomic memory built-in functions. When neither option is
12561 specified, GCC will use the instructions if the target architecture
12564 @option{-mllsc} is useful if the runtime environment can emulate the
12565 instructions and @option{-mno-llsc} can be useful when compiling for
12566 nonstandard ISAs. You can make either option the default by
12567 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12568 respectively. @option{--with-llsc} is the default for some
12569 configurations; see the installation documentation for details.
12575 Use (do not use) revision 1 of the MIPS DSP ASE@.
12576 @xref{MIPS DSP Built-in Functions}. This option defines the
12577 preprocessor macro @samp{__mips_dsp}. It also defines
12578 @samp{__mips_dsp_rev} to 1.
12584 Use (do not use) revision 2 of the MIPS DSP ASE@.
12585 @xref{MIPS DSP Built-in Functions}. This option defines the
12586 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12587 It also defines @samp{__mips_dsp_rev} to 2.
12590 @itemx -mno-smartmips
12591 @opindex msmartmips
12592 @opindex mno-smartmips
12593 Use (do not use) the MIPS SmartMIPS ASE.
12595 @item -mpaired-single
12596 @itemx -mno-paired-single
12597 @opindex mpaired-single
12598 @opindex mno-paired-single
12599 Use (do not use) paired-single floating-point instructions.
12600 @xref{MIPS Paired-Single Support}. This option requires
12601 hardware floating-point support to be enabled.
12607 Use (do not use) MIPS Digital Media Extension instructions.
12608 This option can only be used when generating 64-bit code and requires
12609 hardware floating-point support to be enabled.
12614 @opindex mno-mips3d
12615 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12616 The option @option{-mips3d} implies @option{-mpaired-single}.
12622 Use (do not use) MT Multithreading instructions.
12626 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12627 an explanation of the default and the way that the pointer size is
12632 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12634 The default size of @code{int}s, @code{long}s and pointers depends on
12635 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12636 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12637 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12638 or the same size as integer registers, whichever is smaller.
12644 Assume (do not assume) that all symbols have 32-bit values, regardless
12645 of the selected ABI@. This option is useful in combination with
12646 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12647 to generate shorter and faster references to symbolic addresses.
12651 Put definitions of externally-visible data in a small data section
12652 if that data is no bigger than @var{num} bytes. GCC can then access
12653 the data more efficiently; see @option{-mgpopt} for details.
12655 The default @option{-G} option depends on the configuration.
12657 @item -mlocal-sdata
12658 @itemx -mno-local-sdata
12659 @opindex mlocal-sdata
12660 @opindex mno-local-sdata
12661 Extend (do not extend) the @option{-G} behavior to local data too,
12662 such as to static variables in C@. @option{-mlocal-sdata} is the
12663 default for all configurations.
12665 If the linker complains that an application is using too much small data,
12666 you might want to try rebuilding the less performance-critical parts with
12667 @option{-mno-local-sdata}. You might also want to build large
12668 libraries with @option{-mno-local-sdata}, so that the libraries leave
12669 more room for the main program.
12671 @item -mextern-sdata
12672 @itemx -mno-extern-sdata
12673 @opindex mextern-sdata
12674 @opindex mno-extern-sdata
12675 Assume (do not assume) that externally-defined data will be in
12676 a small data section if that data is within the @option{-G} limit.
12677 @option{-mextern-sdata} is the default for all configurations.
12679 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12680 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12681 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12682 is placed in a small data section. If @var{Var} is defined by another
12683 module, you must either compile that module with a high-enough
12684 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12685 definition. If @var{Var} is common, you must link the application
12686 with a high-enough @option{-G} setting.
12688 The easiest way of satisfying these restrictions is to compile
12689 and link every module with the same @option{-G} option. However,
12690 you may wish to build a library that supports several different
12691 small data limits. You can do this by compiling the library with
12692 the highest supported @option{-G} setting and additionally using
12693 @option{-mno-extern-sdata} to stop the library from making assumptions
12694 about externally-defined data.
12700 Use (do not use) GP-relative accesses for symbols that are known to be
12701 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12702 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12705 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12706 might not hold the value of @code{_gp}. For example, if the code is
12707 part of a library that might be used in a boot monitor, programs that
12708 call boot monitor routines will pass an unknown value in @code{$gp}.
12709 (In such situations, the boot monitor itself would usually be compiled
12710 with @option{-G0}.)
12712 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12713 @option{-mno-extern-sdata}.
12715 @item -membedded-data
12716 @itemx -mno-embedded-data
12717 @opindex membedded-data
12718 @opindex mno-embedded-data
12719 Allocate variables to the read-only data section first if possible, then
12720 next in the small data section if possible, otherwise in data. This gives
12721 slightly slower code than the default, but reduces the amount of RAM required
12722 when executing, and thus may be preferred for some embedded systems.
12724 @item -muninit-const-in-rodata
12725 @itemx -mno-uninit-const-in-rodata
12726 @opindex muninit-const-in-rodata
12727 @opindex mno-uninit-const-in-rodata
12728 Put uninitialized @code{const} variables in the read-only data section.
12729 This option is only meaningful in conjunction with @option{-membedded-data}.
12731 @item -mcode-readable=@var{setting}
12732 @opindex mcode-readable
12733 Specify whether GCC may generate code that reads from executable sections.
12734 There are three possible settings:
12737 @item -mcode-readable=yes
12738 Instructions may freely access executable sections. This is the
12741 @item -mcode-readable=pcrel
12742 MIPS16 PC-relative load instructions can access executable sections,
12743 but other instructions must not do so. This option is useful on 4KSc
12744 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12745 It is also useful on processors that can be configured to have a dual
12746 instruction/data SRAM interface and that, like the M4K, automatically
12747 redirect PC-relative loads to the instruction RAM.
12749 @item -mcode-readable=no
12750 Instructions must not access executable sections. This option can be
12751 useful on targets that are configured to have a dual instruction/data
12752 SRAM interface but that (unlike the M4K) do not automatically redirect
12753 PC-relative loads to the instruction RAM.
12756 @item -msplit-addresses
12757 @itemx -mno-split-addresses
12758 @opindex msplit-addresses
12759 @opindex mno-split-addresses
12760 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12761 relocation operators. This option has been superseded by
12762 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12764 @item -mexplicit-relocs
12765 @itemx -mno-explicit-relocs
12766 @opindex mexplicit-relocs
12767 @opindex mno-explicit-relocs
12768 Use (do not use) assembler relocation operators when dealing with symbolic
12769 addresses. The alternative, selected by @option{-mno-explicit-relocs},
12770 is to use assembler macros instead.
12772 @option{-mexplicit-relocs} is the default if GCC was configured
12773 to use an assembler that supports relocation operators.
12775 @item -mcheck-zero-division
12776 @itemx -mno-check-zero-division
12777 @opindex mcheck-zero-division
12778 @opindex mno-check-zero-division
12779 Trap (do not trap) on integer division by zero.
12781 The default is @option{-mcheck-zero-division}.
12783 @item -mdivide-traps
12784 @itemx -mdivide-breaks
12785 @opindex mdivide-traps
12786 @opindex mdivide-breaks
12787 MIPS systems check for division by zero by generating either a
12788 conditional trap or a break instruction. Using traps results in
12789 smaller code, but is only supported on MIPS II and later. Also, some
12790 versions of the Linux kernel have a bug that prevents trap from
12791 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
12792 allow conditional traps on architectures that support them and
12793 @option{-mdivide-breaks} to force the use of breaks.
12795 The default is usually @option{-mdivide-traps}, but this can be
12796 overridden at configure time using @option{--with-divide=breaks}.
12797 Divide-by-zero checks can be completely disabled using
12798 @option{-mno-check-zero-division}.
12803 @opindex mno-memcpy
12804 Force (do not force) the use of @code{memcpy()} for non-trivial block
12805 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
12806 most constant-sized copies.
12809 @itemx -mno-long-calls
12810 @opindex mlong-calls
12811 @opindex mno-long-calls
12812 Disable (do not disable) use of the @code{jal} instruction. Calling
12813 functions using @code{jal} is more efficient but requires the caller
12814 and callee to be in the same 256 megabyte segment.
12816 This option has no effect on abicalls code. The default is
12817 @option{-mno-long-calls}.
12823 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
12824 instructions, as provided by the R4650 ISA@.
12827 @itemx -mno-fused-madd
12828 @opindex mfused-madd
12829 @opindex mno-fused-madd
12830 Enable (disable) use of the floating point multiply-accumulate
12831 instructions, when they are available. The default is
12832 @option{-mfused-madd}.
12834 When multiply-accumulate instructions are used, the intermediate
12835 product is calculated to infinite precision and is not subject to
12836 the FCSR Flush to Zero bit. This may be undesirable in some
12841 Tell the MIPS assembler to not run its preprocessor over user
12842 assembler files (with a @samp{.s} suffix) when assembling them.
12845 @itemx -mno-fix-r4000
12846 @opindex mfix-r4000
12847 @opindex mno-fix-r4000
12848 Work around certain R4000 CPU errata:
12851 A double-word or a variable shift may give an incorrect result if executed
12852 immediately after starting an integer division.
12854 A double-word or a variable shift may give an incorrect result if executed
12855 while an integer multiplication is in progress.
12857 An integer division may give an incorrect result if started in a delay slot
12858 of a taken branch or a jump.
12862 @itemx -mno-fix-r4400
12863 @opindex mfix-r4400
12864 @opindex mno-fix-r4400
12865 Work around certain R4400 CPU errata:
12868 A double-word or a variable shift may give an incorrect result if executed
12869 immediately after starting an integer division.
12873 @itemx -mno-fix-r10000
12874 @opindex mfix-r10000
12875 @opindex mno-fix-r10000
12876 Work around certain R10000 errata:
12879 @code{ll}/@code{sc} sequences may not behave atomically on revisions
12880 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
12883 This option can only be used if the target architecture supports
12884 branch-likely instructions. @option{-mfix-r10000} is the default when
12885 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
12889 @itemx -mno-fix-vr4120
12890 @opindex mfix-vr4120
12891 Work around certain VR4120 errata:
12894 @code{dmultu} does not always produce the correct result.
12896 @code{div} and @code{ddiv} do not always produce the correct result if one
12897 of the operands is negative.
12899 The workarounds for the division errata rely on special functions in
12900 @file{libgcc.a}. At present, these functions are only provided by
12901 the @code{mips64vr*-elf} configurations.
12903 Other VR4120 errata require a nop to be inserted between certain pairs of
12904 instructions. These errata are handled by the assembler, not by GCC itself.
12907 @opindex mfix-vr4130
12908 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
12909 workarounds are implemented by the assembler rather than by GCC,
12910 although GCC will avoid using @code{mflo} and @code{mfhi} if the
12911 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
12912 instructions are available instead.
12915 @itemx -mno-fix-sb1
12917 Work around certain SB-1 CPU core errata.
12918 (This flag currently works around the SB-1 revision 2
12919 ``F1'' and ``F2'' floating point errata.)
12921 @item -mr10k-cache-barrier=@var{setting}
12922 @opindex mr10k-cache-barrier
12923 Specify whether GCC should insert cache barriers to avoid the
12924 side-effects of speculation on R10K processors.
12926 In common with many processors, the R10K tries to predict the outcome
12927 of a conditional branch and speculatively executes instructions from
12928 the ``taken'' branch. It later aborts these instructions if the
12929 predicted outcome was wrong. However, on the R10K, even aborted
12930 instructions can have side effects.
12932 This problem only affects kernel stores and, depending on the system,
12933 kernel loads. As an example, a speculatively-executed store may load
12934 the target memory into cache and mark the cache line as dirty, even if
12935 the store itself is later aborted. If a DMA operation writes to the
12936 same area of memory before the ``dirty'' line is flushed, the cached
12937 data will overwrite the DMA-ed data. See the R10K processor manual
12938 for a full description, including other potential problems.
12940 One workaround is to insert cache barrier instructions before every memory
12941 access that might be speculatively executed and that might have side
12942 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
12943 controls GCC's implementation of this workaround. It assumes that
12944 aborted accesses to any byte in the following regions will not have
12949 the memory occupied by the current function's stack frame;
12952 the memory occupied by an incoming stack argument;
12955 the memory occupied by an object with a link-time-constant address.
12958 It is the kernel's responsibility to ensure that speculative
12959 accesses to these regions are indeed safe.
12961 If the input program contains a function declaration such as:
12967 then the implementation of @code{foo} must allow @code{j foo} and
12968 @code{jal foo} to be executed speculatively. GCC honors this
12969 restriction for functions it compiles itself. It expects non-GCC
12970 functions (such as hand-written assembly code) to do the same.
12972 The option has three forms:
12975 @item -mr10k-cache-barrier=load-store
12976 Insert a cache barrier before a load or store that might be
12977 speculatively executed and that might have side effects even
12980 @item -mr10k-cache-barrier=store
12981 Insert a cache barrier before a store that might be speculatively
12982 executed and that might have side effects even if aborted.
12984 @item -mr10k-cache-barrier=none
12985 Disable the insertion of cache barriers. This is the default setting.
12988 @item -mflush-func=@var{func}
12989 @itemx -mno-flush-func
12990 @opindex mflush-func
12991 Specifies the function to call to flush the I and D caches, or to not
12992 call any such function. If called, the function must take the same
12993 arguments as the common @code{_flush_func()}, that is, the address of the
12994 memory range for which the cache is being flushed, the size of the
12995 memory range, and the number 3 (to flush both caches). The default
12996 depends on the target GCC was configured for, but commonly is either
12997 @samp{_flush_func} or @samp{__cpu_flush}.
12999 @item mbranch-cost=@var{num}
13000 @opindex mbranch-cost
13001 Set the cost of branches to roughly @var{num} ``simple'' instructions.
13002 This cost is only a heuristic and is not guaranteed to produce
13003 consistent results across releases. A zero cost redundantly selects
13004 the default, which is based on the @option{-mtune} setting.
13006 @item -mbranch-likely
13007 @itemx -mno-branch-likely
13008 @opindex mbranch-likely
13009 @opindex mno-branch-likely
13010 Enable or disable use of Branch Likely instructions, regardless of the
13011 default for the selected architecture. By default, Branch Likely
13012 instructions may be generated if they are supported by the selected
13013 architecture. An exception is for the MIPS32 and MIPS64 architectures
13014 and processors which implement those architectures; for those, Branch
13015 Likely instructions will not be generated by default because the MIPS32
13016 and MIPS64 architectures specifically deprecate their use.
13018 @item -mfp-exceptions
13019 @itemx -mno-fp-exceptions
13020 @opindex mfp-exceptions
13021 Specifies whether FP exceptions are enabled. This affects how we schedule
13022 FP instructions for some processors. The default is that FP exceptions are
13025 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
13026 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
13029 @item -mvr4130-align
13030 @itemx -mno-vr4130-align
13031 @opindex mvr4130-align
13032 The VR4130 pipeline is two-way superscalar, but can only issue two
13033 instructions together if the first one is 8-byte aligned. When this
13034 option is enabled, GCC will align pairs of instructions that it
13035 thinks should execute in parallel.
13037 This option only has an effect when optimizing for the VR4130.
13038 It normally makes code faster, but at the expense of making it bigger.
13039 It is enabled by default at optimization level @option{-O3}.
13043 @subsection MMIX Options
13044 @cindex MMIX Options
13046 These options are defined for the MMIX:
13050 @itemx -mno-libfuncs
13052 @opindex mno-libfuncs
13053 Specify that intrinsic library functions are being compiled, passing all
13054 values in registers, no matter the size.
13057 @itemx -mno-epsilon
13059 @opindex mno-epsilon
13060 Generate floating-point comparison instructions that compare with respect
13061 to the @code{rE} epsilon register.
13063 @item -mabi=mmixware
13065 @opindex mabi-mmixware
13067 Generate code that passes function parameters and return values that (in
13068 the called function) are seen as registers @code{$0} and up, as opposed to
13069 the GNU ABI which uses global registers @code{$231} and up.
13071 @item -mzero-extend
13072 @itemx -mno-zero-extend
13073 @opindex mzero-extend
13074 @opindex mno-zero-extend
13075 When reading data from memory in sizes shorter than 64 bits, use (do not
13076 use) zero-extending load instructions by default, rather than
13077 sign-extending ones.
13080 @itemx -mno-knuthdiv
13082 @opindex mno-knuthdiv
13083 Make the result of a division yielding a remainder have the same sign as
13084 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
13085 remainder follows the sign of the dividend. Both methods are
13086 arithmetically valid, the latter being almost exclusively used.
13088 @item -mtoplevel-symbols
13089 @itemx -mno-toplevel-symbols
13090 @opindex mtoplevel-symbols
13091 @opindex mno-toplevel-symbols
13092 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
13093 code can be used with the @code{PREFIX} assembly directive.
13097 Generate an executable in the ELF format, rather than the default
13098 @samp{mmo} format used by the @command{mmix} simulator.
13100 @item -mbranch-predict
13101 @itemx -mno-branch-predict
13102 @opindex mbranch-predict
13103 @opindex mno-branch-predict
13104 Use (do not use) the probable-branch instructions, when static branch
13105 prediction indicates a probable branch.
13107 @item -mbase-addresses
13108 @itemx -mno-base-addresses
13109 @opindex mbase-addresses
13110 @opindex mno-base-addresses
13111 Generate (do not generate) code that uses @emph{base addresses}. Using a
13112 base address automatically generates a request (handled by the assembler
13113 and the linker) for a constant to be set up in a global register. The
13114 register is used for one or more base address requests within the range 0
13115 to 255 from the value held in the register. The generally leads to short
13116 and fast code, but the number of different data items that can be
13117 addressed is limited. This means that a program that uses lots of static
13118 data may require @option{-mno-base-addresses}.
13120 @item -msingle-exit
13121 @itemx -mno-single-exit
13122 @opindex msingle-exit
13123 @opindex mno-single-exit
13124 Force (do not force) generated code to have a single exit point in each
13128 @node MN10300 Options
13129 @subsection MN10300 Options
13130 @cindex MN10300 options
13132 These @option{-m} options are defined for Matsushita MN10300 architectures:
13137 Generate code to avoid bugs in the multiply instructions for the MN10300
13138 processors. This is the default.
13140 @item -mno-mult-bug
13141 @opindex mno-mult-bug
13142 Do not generate code to avoid bugs in the multiply instructions for the
13143 MN10300 processors.
13147 Generate code which uses features specific to the AM33 processor.
13151 Do not generate code which uses features specific to the AM33 processor. This
13154 @item -mreturn-pointer-on-d0
13155 @opindex mreturn-pointer-on-d0
13156 When generating a function which returns a pointer, return the pointer
13157 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
13158 only in a0, and attempts to call such functions without a prototype
13159 would result in errors. Note that this option is on by default; use
13160 @option{-mno-return-pointer-on-d0} to disable it.
13164 Do not link in the C run-time initialization object file.
13168 Indicate to the linker that it should perform a relaxation optimization pass
13169 to shorten branches, calls and absolute memory addresses. This option only
13170 has an effect when used on the command line for the final link step.
13172 This option makes symbolic debugging impossible.
13175 @node PDP-11 Options
13176 @subsection PDP-11 Options
13177 @cindex PDP-11 Options
13179 These options are defined for the PDP-11:
13184 Use hardware FPP floating point. This is the default. (FIS floating
13185 point on the PDP-11/40 is not supported.)
13188 @opindex msoft-float
13189 Do not use hardware floating point.
13193 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
13197 Return floating-point results in memory. This is the default.
13201 Generate code for a PDP-11/40.
13205 Generate code for a PDP-11/45. This is the default.
13209 Generate code for a PDP-11/10.
13211 @item -mbcopy-builtin
13212 @opindex bcopy-builtin
13213 Use inline @code{movmemhi} patterns for copying memory. This is the
13218 Do not use inline @code{movmemhi} patterns for copying memory.
13224 Use 16-bit @code{int}. This is the default.
13230 Use 32-bit @code{int}.
13233 @itemx -mno-float32
13235 @opindex mno-float32
13236 Use 64-bit @code{float}. This is the default.
13239 @itemx -mno-float64
13241 @opindex mno-float64
13242 Use 32-bit @code{float}.
13246 Use @code{abshi2} pattern. This is the default.
13250 Do not use @code{abshi2} pattern.
13252 @item -mbranch-expensive
13253 @opindex mbranch-expensive
13254 Pretend that branches are expensive. This is for experimenting with
13255 code generation only.
13257 @item -mbranch-cheap
13258 @opindex mbranch-cheap
13259 Do not pretend that branches are expensive. This is the default.
13263 Generate code for a system with split I&D@.
13267 Generate code for a system without split I&D@. This is the default.
13271 Use Unix assembler syntax. This is the default when configured for
13272 @samp{pdp11-*-bsd}.
13276 Use DEC assembler syntax. This is the default when configured for any
13277 PDP-11 target other than @samp{pdp11-*-bsd}.
13280 @node picoChip Options
13281 @subsection picoChip Options
13282 @cindex picoChip options
13284 These @samp{-m} options are defined for picoChip implementations:
13288 @item -mae=@var{ae_type}
13290 Set the instruction set, register set, and instruction scheduling
13291 parameters for array element type @var{ae_type}. Supported values
13292 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
13294 @option{-mae=ANY} selects a completely generic AE type. Code
13295 generated with this option will run on any of the other AE types. The
13296 code will not be as efficient as it would be if compiled for a specific
13297 AE type, and some types of operation (e.g., multiplication) will not
13298 work properly on all types of AE.
13300 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
13301 for compiled code, and is the default.
13303 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
13304 option may suffer from poor performance of byte (char) manipulation,
13305 since the DSP AE does not provide hardware support for byte load/stores.
13307 @item -msymbol-as-address
13308 Enable the compiler to directly use a symbol name as an address in a
13309 load/store instruction, without first loading it into a
13310 register. Typically, the use of this option will generate larger
13311 programs, which run faster than when the option isn't used. However, the
13312 results vary from program to program, so it is left as a user option,
13313 rather than being permanently enabled.
13315 @item -mno-inefficient-warnings
13316 Disables warnings about the generation of inefficient code. These
13317 warnings can be generated, for example, when compiling code which
13318 performs byte-level memory operations on the MAC AE type. The MAC AE has
13319 no hardware support for byte-level memory operations, so all byte
13320 load/stores must be synthesized from word load/store operations. This is
13321 inefficient and a warning will be generated indicating to the programmer
13322 that they should rewrite the code to avoid byte operations, or to target
13323 an AE type which has the necessary hardware support. This option enables
13324 the warning to be turned off.
13328 @node PowerPC Options
13329 @subsection PowerPC Options
13330 @cindex PowerPC options
13332 These are listed under @xref{RS/6000 and PowerPC Options}.
13334 @node RS/6000 and PowerPC Options
13335 @subsection IBM RS/6000 and PowerPC Options
13336 @cindex RS/6000 and PowerPC Options
13337 @cindex IBM RS/6000 and PowerPC Options
13339 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
13346 @itemx -mno-powerpc
13347 @itemx -mpowerpc-gpopt
13348 @itemx -mno-powerpc-gpopt
13349 @itemx -mpowerpc-gfxopt
13350 @itemx -mno-powerpc-gfxopt
13352 @itemx -mno-powerpc64
13356 @itemx -mno-popcntb
13364 @itemx -mno-hard-dfp
13368 @opindex mno-power2
13370 @opindex mno-powerpc
13371 @opindex mpowerpc-gpopt
13372 @opindex mno-powerpc-gpopt
13373 @opindex mpowerpc-gfxopt
13374 @opindex mno-powerpc-gfxopt
13375 @opindex mpowerpc64
13376 @opindex mno-powerpc64
13380 @opindex mno-popcntb
13386 @opindex mno-mfpgpr
13388 @opindex mno-hard-dfp
13389 GCC supports two related instruction set architectures for the
13390 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
13391 instructions supported by the @samp{rios} chip set used in the original
13392 RS/6000 systems and the @dfn{PowerPC} instruction set is the
13393 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
13394 the IBM 4xx, 6xx, and follow-on microprocessors.
13396 Neither architecture is a subset of the other. However there is a
13397 large common subset of instructions supported by both. An MQ
13398 register is included in processors supporting the POWER architecture.
13400 You use these options to specify which instructions are available on the
13401 processor you are using. The default value of these options is
13402 determined when configuring GCC@. Specifying the
13403 @option{-mcpu=@var{cpu_type}} overrides the specification of these
13404 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
13405 rather than the options listed above.
13407 The @option{-mpower} option allows GCC to generate instructions that
13408 are found only in the POWER architecture and to use the MQ register.
13409 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
13410 to generate instructions that are present in the POWER2 architecture but
13411 not the original POWER architecture.
13413 The @option{-mpowerpc} option allows GCC to generate instructions that
13414 are found only in the 32-bit subset of the PowerPC architecture.
13415 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
13416 GCC to use the optional PowerPC architecture instructions in the
13417 General Purpose group, including floating-point square root. Specifying
13418 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
13419 use the optional PowerPC architecture instructions in the Graphics
13420 group, including floating-point select.
13422 The @option{-mmfcrf} option allows GCC to generate the move from
13423 condition register field instruction implemented on the POWER4
13424 processor and other processors that support the PowerPC V2.01
13426 The @option{-mpopcntb} option allows GCC to generate the popcount and
13427 double precision FP reciprocal estimate instruction implemented on the
13428 POWER5 processor and other processors that support the PowerPC V2.02
13430 The @option{-mfprnd} option allows GCC to generate the FP round to
13431 integer instructions implemented on the POWER5+ processor and other
13432 processors that support the PowerPC V2.03 architecture.
13433 The @option{-mcmpb} option allows GCC to generate the compare bytes
13434 instruction implemented on the POWER6 processor and other processors
13435 that support the PowerPC V2.05 architecture.
13436 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
13437 general purpose register instructions implemented on the POWER6X
13438 processor and other processors that support the extended PowerPC V2.05
13440 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
13441 point instructions implemented on some POWER processors.
13443 The @option{-mpowerpc64} option allows GCC to generate the additional
13444 64-bit instructions that are found in the full PowerPC64 architecture
13445 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
13446 @option{-mno-powerpc64}.
13448 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
13449 will use only the instructions in the common subset of both
13450 architectures plus some special AIX common-mode calls, and will not use
13451 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
13452 permits GCC to use any instruction from either architecture and to
13453 allow use of the MQ register; specify this for the Motorola MPC601.
13455 @item -mnew-mnemonics
13456 @itemx -mold-mnemonics
13457 @opindex mnew-mnemonics
13458 @opindex mold-mnemonics
13459 Select which mnemonics to use in the generated assembler code. With
13460 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
13461 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
13462 assembler mnemonics defined for the POWER architecture. Instructions
13463 defined in only one architecture have only one mnemonic; GCC uses that
13464 mnemonic irrespective of which of these options is specified.
13466 GCC defaults to the mnemonics appropriate for the architecture in
13467 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
13468 value of these option. Unless you are building a cross-compiler, you
13469 should normally not specify either @option{-mnew-mnemonics} or
13470 @option{-mold-mnemonics}, but should instead accept the default.
13472 @item -mcpu=@var{cpu_type}
13474 Set architecture type, register usage, choice of mnemonics, and
13475 instruction scheduling parameters for machine type @var{cpu_type}.
13476 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13477 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13478 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13479 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13480 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13481 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13482 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13483 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13484 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}
13485 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13486 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13488 @option{-mcpu=common} selects a completely generic processor. Code
13489 generated under this option will run on any POWER or PowerPC processor.
13490 GCC will use only the instructions in the common subset of both
13491 architectures, and will not use the MQ register. GCC assumes a generic
13492 processor model for scheduling purposes.
13494 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13495 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13496 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13497 types, with an appropriate, generic processor model assumed for
13498 scheduling purposes.
13500 The other options specify a specific processor. Code generated under
13501 those options will run best on that processor, and may not run at all on
13504 The @option{-mcpu} options automatically enable or disable the
13507 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13508 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13509 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
13510 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr}
13512 The particular options set for any particular CPU will vary between
13513 compiler versions, depending on what setting seems to produce optimal
13514 code for that CPU; it doesn't necessarily reflect the actual hardware's
13515 capabilities. If you wish to set an individual option to a particular
13516 value, you may specify it after the @option{-mcpu} option, like
13517 @samp{-mcpu=970 -mno-altivec}.
13519 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13520 not enabled or disabled by the @option{-mcpu} option at present because
13521 AIX does not have full support for these options. You may still
13522 enable or disable them individually if you're sure it'll work in your
13525 @item -mtune=@var{cpu_type}
13527 Set the instruction scheduling parameters for machine type
13528 @var{cpu_type}, but do not set the architecture type, register usage, or
13529 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13530 values for @var{cpu_type} are used for @option{-mtune} as for
13531 @option{-mcpu}. If both are specified, the code generated will use the
13532 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13533 scheduling parameters set by @option{-mtune}.
13539 Generate code to compute division as reciprocal estimate and iterative
13540 refinement, creating opportunities for increased throughput. This
13541 feature requires: optional PowerPC Graphics instruction set for single
13542 precision and FRE instruction for double precision, assuming divides
13543 cannot generate user-visible traps, and the domain values not include
13544 Infinities, denormals or zero denominator.
13547 @itemx -mno-altivec
13549 @opindex mno-altivec
13550 Generate code that uses (does not use) AltiVec instructions, and also
13551 enable the use of built-in functions that allow more direct access to
13552 the AltiVec instruction set. You may also need to set
13553 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13559 @opindex mno-vrsave
13560 Generate VRSAVE instructions when generating AltiVec code.
13562 @item -mgen-cell-microcode
13563 @opindex mgen-cell-microcode
13564 Generate Cell microcode instructions
13566 @item -mwarn-cell-microcode
13567 @opindex mwarn-cell-microcode
13568 Warning when a Cell microcode instruction is going to emitted. An example
13569 of a Cell microcode instruction is a variable shift.
13572 @opindex msecure-plt
13573 Generate code that allows ld and ld.so to build executables and shared
13574 libraries with non-exec .plt and .got sections. This is a PowerPC
13575 32-bit SYSV ABI option.
13579 Generate code that uses a BSS .plt section that ld.so fills in, and
13580 requires .plt and .got sections that are both writable and executable.
13581 This is a PowerPC 32-bit SYSV ABI option.
13587 This switch enables or disables the generation of ISEL instructions.
13589 @item -misel=@var{yes/no}
13590 This switch has been deprecated. Use @option{-misel} and
13591 @option{-mno-isel} instead.
13597 This switch enables or disables the generation of SPE simd
13603 @opindex mno-paired
13604 This switch enables or disables the generation of PAIRED simd
13607 @item -mspe=@var{yes/no}
13608 This option has been deprecated. Use @option{-mspe} and
13609 @option{-mno-spe} instead.
13611 @item -mfloat-gprs=@var{yes/single/double/no}
13612 @itemx -mfloat-gprs
13613 @opindex mfloat-gprs
13614 This switch enables or disables the generation of floating point
13615 operations on the general purpose registers for architectures that
13618 The argument @var{yes} or @var{single} enables the use of
13619 single-precision floating point operations.
13621 The argument @var{double} enables the use of single and
13622 double-precision floating point operations.
13624 The argument @var{no} disables floating point operations on the
13625 general purpose registers.
13627 This option is currently only available on the MPC854x.
13633 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13634 targets (including GNU/Linux). The 32-bit environment sets int, long
13635 and pointer to 32 bits and generates code that runs on any PowerPC
13636 variant. The 64-bit environment sets int to 32 bits and long and
13637 pointer to 64 bits, and generates code for PowerPC64, as for
13638 @option{-mpowerpc64}.
13641 @itemx -mno-fp-in-toc
13642 @itemx -mno-sum-in-toc
13643 @itemx -mminimal-toc
13645 @opindex mno-fp-in-toc
13646 @opindex mno-sum-in-toc
13647 @opindex mminimal-toc
13648 Modify generation of the TOC (Table Of Contents), which is created for
13649 every executable file. The @option{-mfull-toc} option is selected by
13650 default. In that case, GCC will allocate at least one TOC entry for
13651 each unique non-automatic variable reference in your program. GCC
13652 will also place floating-point constants in the TOC@. However, only
13653 16,384 entries are available in the TOC@.
13655 If you receive a linker error message that saying you have overflowed
13656 the available TOC space, you can reduce the amount of TOC space used
13657 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13658 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13659 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13660 generate code to calculate the sum of an address and a constant at
13661 run-time instead of putting that sum into the TOC@. You may specify one
13662 or both of these options. Each causes GCC to produce very slightly
13663 slower and larger code at the expense of conserving TOC space.
13665 If you still run out of space in the TOC even when you specify both of
13666 these options, specify @option{-mminimal-toc} instead. This option causes
13667 GCC to make only one TOC entry for every file. When you specify this
13668 option, GCC will produce code that is slower and larger but which
13669 uses extremely little TOC space. You may wish to use this option
13670 only on files that contain less frequently executed code.
13676 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13677 @code{long} type, and the infrastructure needed to support them.
13678 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13679 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13680 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13683 @itemx -mno-xl-compat
13684 @opindex mxl-compat
13685 @opindex mno-xl-compat
13686 Produce code that conforms more closely to IBM XL compiler semantics
13687 when using AIX-compatible ABI@. Pass floating-point arguments to
13688 prototyped functions beyond the register save area (RSA) on the stack
13689 in addition to argument FPRs. Do not assume that most significant
13690 double in 128-bit long double value is properly rounded when comparing
13691 values and converting to double. Use XL symbol names for long double
13694 The AIX calling convention was extended but not initially documented to
13695 handle an obscure K&R C case of calling a function that takes the
13696 address of its arguments with fewer arguments than declared. IBM XL
13697 compilers access floating point arguments which do not fit in the
13698 RSA from the stack when a subroutine is compiled without
13699 optimization. Because always storing floating-point arguments on the
13700 stack is inefficient and rarely needed, this option is not enabled by
13701 default and only is necessary when calling subroutines compiled by IBM
13702 XL compilers without optimization.
13706 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13707 application written to use message passing with special startup code to
13708 enable the application to run. The system must have PE installed in the
13709 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13710 must be overridden with the @option{-specs=} option to specify the
13711 appropriate directory location. The Parallel Environment does not
13712 support threads, so the @option{-mpe} option and the @option{-pthread}
13713 option are incompatible.
13715 @item -malign-natural
13716 @itemx -malign-power
13717 @opindex malign-natural
13718 @opindex malign-power
13719 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13720 @option{-malign-natural} overrides the ABI-defined alignment of larger
13721 types, such as floating-point doubles, on their natural size-based boundary.
13722 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13723 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13725 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13729 @itemx -mhard-float
13730 @opindex msoft-float
13731 @opindex mhard-float
13732 Generate code that does not use (uses) the floating-point register set.
13733 Software floating point emulation is provided if you use the
13734 @option{-msoft-float} option, and pass the option to GCC when linking.
13736 @item -msingle-float
13737 @itemx -mdouble-float
13738 @opindex msingle-float
13739 @opindex mdouble-float
13740 Generate code for single or double-precision floating point operations.
13741 @option{-mdouble-float} implies @option{-msingle-float}.
13744 @opindex msimple-fpu
13745 Do not generate sqrt and div instructions for hardware floating point unit.
13749 Specify type of floating point unit. Valid values are @var{sp_lite}
13750 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
13751 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
13752 and @var{dp_full} (equivalent to -mdouble-float).
13755 @opindex mxilinx-fpu
13756 Perform optimizations for floating point unit on Xilinx PPC 405/440.
13759 @itemx -mno-multiple
13761 @opindex mno-multiple
13762 Generate code that uses (does not use) the load multiple word
13763 instructions and the store multiple word instructions. These
13764 instructions are generated by default on POWER systems, and not
13765 generated on PowerPC systems. Do not use @option{-mmultiple} on little
13766 endian PowerPC systems, since those instructions do not work when the
13767 processor is in little endian mode. The exceptions are PPC740 and
13768 PPC750 which permit the instructions usage in little endian mode.
13773 @opindex mno-string
13774 Generate code that uses (does not use) the load string instructions
13775 and the store string word instructions to save multiple registers and
13776 do small block moves. These instructions are generated by default on
13777 POWER systems, and not generated on PowerPC systems. Do not use
13778 @option{-mstring} on little endian PowerPC systems, since those
13779 instructions do not work when the processor is in little endian mode.
13780 The exceptions are PPC740 and PPC750 which permit the instructions
13781 usage in little endian mode.
13786 @opindex mno-update
13787 Generate code that uses (does not use) the load or store instructions
13788 that update the base register to the address of the calculated memory
13789 location. These instructions are generated by default. If you use
13790 @option{-mno-update}, there is a small window between the time that the
13791 stack pointer is updated and the address of the previous frame is
13792 stored, which means code that walks the stack frame across interrupts or
13793 signals may get corrupted data.
13796 @itemx -mno-fused-madd
13797 @opindex mfused-madd
13798 @opindex mno-fused-madd
13799 Generate code that uses (does not use) the floating point multiply and
13800 accumulate instructions. These instructions are generated by default if
13801 hardware floating is used.
13807 Generate code that uses (does not use) the half-word multiply and
13808 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
13809 These instructions are generated by default when targetting those
13816 Generate code that uses (does not use) the string-search @samp{dlmzb}
13817 instruction on the IBM 405, 440 and 464 processors. This instruction is
13818 generated by default when targetting those processors.
13820 @item -mno-bit-align
13822 @opindex mno-bit-align
13823 @opindex mbit-align
13824 On System V.4 and embedded PowerPC systems do not (do) force structures
13825 and unions that contain bit-fields to be aligned to the base type of the
13828 For example, by default a structure containing nothing but 8
13829 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
13830 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
13831 the structure would be aligned to a 1 byte boundary and be one byte in
13834 @item -mno-strict-align
13835 @itemx -mstrict-align
13836 @opindex mno-strict-align
13837 @opindex mstrict-align
13838 On System V.4 and embedded PowerPC systems do not (do) assume that
13839 unaligned memory references will be handled by the system.
13841 @item -mrelocatable
13842 @itemx -mno-relocatable
13843 @opindex mrelocatable
13844 @opindex mno-relocatable
13845 On embedded PowerPC systems generate code that allows (does not allow)
13846 the program to be relocated to a different address at runtime. If you
13847 use @option{-mrelocatable} on any module, all objects linked together must
13848 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
13850 @item -mrelocatable-lib
13851 @itemx -mno-relocatable-lib
13852 @opindex mrelocatable-lib
13853 @opindex mno-relocatable-lib
13854 On embedded PowerPC systems generate code that allows (does not allow)
13855 the program to be relocated to a different address at runtime. Modules
13856 compiled with @option{-mrelocatable-lib} can be linked with either modules
13857 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
13858 with modules compiled with the @option{-mrelocatable} options.
13864 On System V.4 and embedded PowerPC systems do not (do) assume that
13865 register 2 contains a pointer to a global area pointing to the addresses
13866 used in the program.
13869 @itemx -mlittle-endian
13871 @opindex mlittle-endian
13872 On System V.4 and embedded PowerPC systems compile code for the
13873 processor in little endian mode. The @option{-mlittle-endian} option is
13874 the same as @option{-mlittle}.
13877 @itemx -mbig-endian
13879 @opindex mbig-endian
13880 On System V.4 and embedded PowerPC systems compile code for the
13881 processor in big endian mode. The @option{-mbig-endian} option is
13882 the same as @option{-mbig}.
13884 @item -mdynamic-no-pic
13885 @opindex mdynamic-no-pic
13886 On Darwin and Mac OS X systems, compile code so that it is not
13887 relocatable, but that its external references are relocatable. The
13888 resulting code is suitable for applications, but not shared
13891 @item -mprioritize-restricted-insns=@var{priority}
13892 @opindex mprioritize-restricted-insns
13893 This option controls the priority that is assigned to
13894 dispatch-slot restricted instructions during the second scheduling
13895 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
13896 @var{no/highest/second-highest} priority to dispatch slot restricted
13899 @item -msched-costly-dep=@var{dependence_type}
13900 @opindex msched-costly-dep
13901 This option controls which dependences are considered costly
13902 by the target during instruction scheduling. The argument
13903 @var{dependence_type} takes one of the following values:
13904 @var{no}: no dependence is costly,
13905 @var{all}: all dependences are costly,
13906 @var{true_store_to_load}: a true dependence from store to load is costly,
13907 @var{store_to_load}: any dependence from store to load is costly,
13908 @var{number}: any dependence which latency >= @var{number} is costly.
13910 @item -minsert-sched-nops=@var{scheme}
13911 @opindex minsert-sched-nops
13912 This option controls which nop insertion scheme will be used during
13913 the second scheduling pass. The argument @var{scheme} takes one of the
13915 @var{no}: Don't insert nops.
13916 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
13917 according to the scheduler's grouping.
13918 @var{regroup_exact}: Insert nops to force costly dependent insns into
13919 separate groups. Insert exactly as many nops as needed to force an insn
13920 to a new group, according to the estimated processor grouping.
13921 @var{number}: Insert nops to force costly dependent insns into
13922 separate groups. Insert @var{number} nops to force an insn to a new group.
13925 @opindex mcall-sysv
13926 On System V.4 and embedded PowerPC systems compile code using calling
13927 conventions that adheres to the March 1995 draft of the System V
13928 Application Binary Interface, PowerPC processor supplement. This is the
13929 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
13931 @item -mcall-sysv-eabi
13932 @opindex mcall-sysv-eabi
13933 Specify both @option{-mcall-sysv} and @option{-meabi} options.
13935 @item -mcall-sysv-noeabi
13936 @opindex mcall-sysv-noeabi
13937 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
13939 @item -mcall-solaris
13940 @opindex mcall-solaris
13941 On System V.4 and embedded PowerPC systems compile code for the Solaris
13945 @opindex mcall-linux
13946 On System V.4 and embedded PowerPC systems compile code for the
13947 Linux-based GNU system.
13951 On System V.4 and embedded PowerPC systems compile code for the
13952 Hurd-based GNU system.
13954 @item -mcall-netbsd
13955 @opindex mcall-netbsd
13956 On System V.4 and embedded PowerPC systems compile code for the
13957 NetBSD operating system.
13959 @item -maix-struct-return
13960 @opindex maix-struct-return
13961 Return all structures in memory (as specified by the AIX ABI)@.
13963 @item -msvr4-struct-return
13964 @opindex msvr4-struct-return
13965 Return structures smaller than 8 bytes in registers (as specified by the
13968 @item -mabi=@var{abi-type}
13970 Extend the current ABI with a particular extension, or remove such extension.
13971 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
13972 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
13976 Extend the current ABI with SPE ABI extensions. This does not change
13977 the default ABI, instead it adds the SPE ABI extensions to the current
13981 @opindex mabi=no-spe
13982 Disable Booke SPE ABI extensions for the current ABI@.
13984 @item -mabi=ibmlongdouble
13985 @opindex mabi=ibmlongdouble
13986 Change the current ABI to use IBM extended precision long double.
13987 This is a PowerPC 32-bit SYSV ABI option.
13989 @item -mabi=ieeelongdouble
13990 @opindex mabi=ieeelongdouble
13991 Change the current ABI to use IEEE extended precision long double.
13992 This is a PowerPC 32-bit Linux ABI option.
13995 @itemx -mno-prototype
13996 @opindex mprototype
13997 @opindex mno-prototype
13998 On System V.4 and embedded PowerPC systems assume that all calls to
13999 variable argument functions are properly prototyped. Otherwise, the
14000 compiler must insert an instruction before every non prototyped call to
14001 set or clear bit 6 of the condition code register (@var{CR}) to
14002 indicate whether floating point values were passed in the floating point
14003 registers in case the function takes a variable arguments. With
14004 @option{-mprototype}, only calls to prototyped variable argument functions
14005 will set or clear the bit.
14009 On embedded PowerPC systems, assume that the startup module is called
14010 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
14011 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
14016 On embedded PowerPC systems, assume that the startup module is called
14017 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
14022 On embedded PowerPC systems, assume that the startup module is called
14023 @file{crt0.o} and the standard C libraries are @file{libads.a} and
14026 @item -myellowknife
14027 @opindex myellowknife
14028 On embedded PowerPC systems, assume that the startup module is called
14029 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
14034 On System V.4 and embedded PowerPC systems, specify that you are
14035 compiling for a VxWorks system.
14039 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
14040 header to indicate that @samp{eabi} extended relocations are used.
14046 On System V.4 and embedded PowerPC systems do (do not) adhere to the
14047 Embedded Applications Binary Interface (eabi) which is a set of
14048 modifications to the System V.4 specifications. Selecting @option{-meabi}
14049 means that the stack is aligned to an 8 byte boundary, a function
14050 @code{__eabi} is called to from @code{main} to set up the eabi
14051 environment, and the @option{-msdata} option can use both @code{r2} and
14052 @code{r13} to point to two separate small data areas. Selecting
14053 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
14054 do not call an initialization function from @code{main}, and the
14055 @option{-msdata} option will only use @code{r13} to point to a single
14056 small data area. The @option{-meabi} option is on by default if you
14057 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
14060 @opindex msdata=eabi
14061 On System V.4 and embedded PowerPC systems, put small initialized
14062 @code{const} global and static data in the @samp{.sdata2} section, which
14063 is pointed to by register @code{r2}. Put small initialized
14064 non-@code{const} global and static data in the @samp{.sdata} section,
14065 which is pointed to by register @code{r13}. Put small uninitialized
14066 global and static data in the @samp{.sbss} section, which is adjacent to
14067 the @samp{.sdata} section. The @option{-msdata=eabi} option is
14068 incompatible with the @option{-mrelocatable} option. The
14069 @option{-msdata=eabi} option also sets the @option{-memb} option.
14072 @opindex msdata=sysv
14073 On System V.4 and embedded PowerPC systems, put small global and static
14074 data in the @samp{.sdata} section, which is pointed to by register
14075 @code{r13}. Put small uninitialized global and static data in the
14076 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
14077 The @option{-msdata=sysv} option is incompatible with the
14078 @option{-mrelocatable} option.
14080 @item -msdata=default
14082 @opindex msdata=default
14084 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
14085 compile code the same as @option{-msdata=eabi}, otherwise compile code the
14086 same as @option{-msdata=sysv}.
14089 @opindex msdata-data
14090 On System V.4 and embedded PowerPC systems, put small global
14091 data in the @samp{.sdata} section. Put small uninitialized global
14092 data in the @samp{.sbss} section. Do not use register @code{r13}
14093 to address small data however. This is the default behavior unless
14094 other @option{-msdata} options are used.
14098 @opindex msdata=none
14100 On embedded PowerPC systems, put all initialized global and static data
14101 in the @samp{.data} section, and all uninitialized data in the
14102 @samp{.bss} section.
14106 @cindex smaller data references (PowerPC)
14107 @cindex .sdata/.sdata2 references (PowerPC)
14108 On embedded PowerPC systems, put global and static items less than or
14109 equal to @var{num} bytes into the small data or bss sections instead of
14110 the normal data or bss section. By default, @var{num} is 8. The
14111 @option{-G @var{num}} switch is also passed to the linker.
14112 All modules should be compiled with the same @option{-G @var{num}} value.
14115 @itemx -mno-regnames
14117 @opindex mno-regnames
14118 On System V.4 and embedded PowerPC systems do (do not) emit register
14119 names in the assembly language output using symbolic forms.
14122 @itemx -mno-longcall
14124 @opindex mno-longcall
14125 By default assume that all calls are far away so that a longer more
14126 expensive calling sequence is required. This is required for calls
14127 further than 32 megabytes (33,554,432 bytes) from the current location.
14128 A short call will be generated if the compiler knows
14129 the call cannot be that far away. This setting can be overridden by
14130 the @code{shortcall} function attribute, or by @code{#pragma
14133 Some linkers are capable of detecting out-of-range calls and generating
14134 glue code on the fly. On these systems, long calls are unnecessary and
14135 generate slower code. As of this writing, the AIX linker can do this,
14136 as can the GNU linker for PowerPC/64. It is planned to add this feature
14137 to the GNU linker for 32-bit PowerPC systems as well.
14139 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
14140 callee, L42'', plus a ``branch island'' (glue code). The two target
14141 addresses represent the callee and the ``branch island''. The
14142 Darwin/PPC linker will prefer the first address and generate a ``bl
14143 callee'' if the PPC ``bl'' instruction will reach the callee directly;
14144 otherwise, the linker will generate ``bl L42'' to call the ``branch
14145 island''. The ``branch island'' is appended to the body of the
14146 calling function; it computes the full 32-bit address of the callee
14149 On Mach-O (Darwin) systems, this option directs the compiler emit to
14150 the glue for every direct call, and the Darwin linker decides whether
14151 to use or discard it.
14153 In the future, we may cause GCC to ignore all longcall specifications
14154 when the linker is known to generate glue.
14158 Adds support for multithreading with the @dfn{pthreads} library.
14159 This option sets flags for both the preprocessor and linker.
14163 @node S/390 and zSeries Options
14164 @subsection S/390 and zSeries Options
14165 @cindex S/390 and zSeries Options
14167 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
14171 @itemx -msoft-float
14172 @opindex mhard-float
14173 @opindex msoft-float
14174 Use (do not use) the hardware floating-point instructions and registers
14175 for floating-point operations. When @option{-msoft-float} is specified,
14176 functions in @file{libgcc.a} will be used to perform floating-point
14177 operations. When @option{-mhard-float} is specified, the compiler
14178 generates IEEE floating-point instructions. This is the default.
14181 @itemx -mno-hard-dfp
14183 @opindex mno-hard-dfp
14184 Use (do not use) the hardware decimal-floating-point instructions for
14185 decimal-floating-point operations. When @option{-mno-hard-dfp} is
14186 specified, functions in @file{libgcc.a} will be used to perform
14187 decimal-floating-point operations. When @option{-mhard-dfp} is
14188 specified, the compiler generates decimal-floating-point hardware
14189 instructions. This is the default for @option{-march=z9-ec} or higher.
14191 @item -mlong-double-64
14192 @itemx -mlong-double-128
14193 @opindex mlong-double-64
14194 @opindex mlong-double-128
14195 These switches control the size of @code{long double} type. A size
14196 of 64bit makes the @code{long double} type equivalent to the @code{double}
14197 type. This is the default.
14200 @itemx -mno-backchain
14201 @opindex mbackchain
14202 @opindex mno-backchain
14203 Store (do not store) the address of the caller's frame as backchain pointer
14204 into the callee's stack frame.
14205 A backchain may be needed to allow debugging using tools that do not understand
14206 DWARF-2 call frame information.
14207 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
14208 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
14209 the backchain is placed into the topmost word of the 96/160 byte register
14212 In general, code compiled with @option{-mbackchain} is call-compatible with
14213 code compiled with @option{-mmo-backchain}; however, use of the backchain
14214 for debugging purposes usually requires that the whole binary is built with
14215 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
14216 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14217 to build a linux kernel use @option{-msoft-float}.
14219 The default is to not maintain the backchain.
14221 @item -mpacked-stack
14222 @itemx -mno-packed-stack
14223 @opindex mpacked-stack
14224 @opindex mno-packed-stack
14225 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
14226 specified, the compiler uses the all fields of the 96/160 byte register save
14227 area only for their default purpose; unused fields still take up stack space.
14228 When @option{-mpacked-stack} is specified, register save slots are densely
14229 packed at the top of the register save area; unused space is reused for other
14230 purposes, allowing for more efficient use of the available stack space.
14231 However, when @option{-mbackchain} is also in effect, the topmost word of
14232 the save area is always used to store the backchain, and the return address
14233 register is always saved two words below the backchain.
14235 As long as the stack frame backchain is not used, code generated with
14236 @option{-mpacked-stack} is call-compatible with code generated with
14237 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
14238 S/390 or zSeries generated code that uses the stack frame backchain at run
14239 time, not just for debugging purposes. Such code is not call-compatible
14240 with code compiled with @option{-mpacked-stack}. Also, note that the
14241 combination of @option{-mbackchain},
14242 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14243 to build a linux kernel use @option{-msoft-float}.
14245 The default is to not use the packed stack layout.
14248 @itemx -mno-small-exec
14249 @opindex msmall-exec
14250 @opindex mno-small-exec
14251 Generate (or do not generate) code using the @code{bras} instruction
14252 to do subroutine calls.
14253 This only works reliably if the total executable size does not
14254 exceed 64k. The default is to use the @code{basr} instruction instead,
14255 which does not have this limitation.
14261 When @option{-m31} is specified, generate code compliant to the
14262 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
14263 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
14264 particular to generate 64-bit instructions. For the @samp{s390}
14265 targets, the default is @option{-m31}, while the @samp{s390x}
14266 targets default to @option{-m64}.
14272 When @option{-mzarch} is specified, generate code using the
14273 instructions available on z/Architecture.
14274 When @option{-mesa} is specified, generate code using the
14275 instructions available on ESA/390. Note that @option{-mesa} is
14276 not possible with @option{-m64}.
14277 When generating code compliant to the GNU/Linux for S/390 ABI,
14278 the default is @option{-mesa}. When generating code compliant
14279 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
14285 Generate (or do not generate) code using the @code{mvcle} instruction
14286 to perform block moves. When @option{-mno-mvcle} is specified,
14287 use a @code{mvc} loop instead. This is the default unless optimizing for
14294 Print (or do not print) additional debug information when compiling.
14295 The default is to not print debug information.
14297 @item -march=@var{cpu-type}
14299 Generate code that will run on @var{cpu-type}, which is the name of a system
14300 representing a certain processor type. Possible values for
14301 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
14302 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
14303 When generating code using the instructions available on z/Architecture,
14304 the default is @option{-march=z900}. Otherwise, the default is
14305 @option{-march=g5}.
14307 @item -mtune=@var{cpu-type}
14309 Tune to @var{cpu-type} everything applicable about the generated code,
14310 except for the ABI and the set of available instructions.
14311 The list of @var{cpu-type} values is the same as for @option{-march}.
14312 The default is the value used for @option{-march}.
14315 @itemx -mno-tpf-trace
14316 @opindex mtpf-trace
14317 @opindex mno-tpf-trace
14318 Generate code that adds (does not add) in TPF OS specific branches to trace
14319 routines in the operating system. This option is off by default, even
14320 when compiling for the TPF OS@.
14323 @itemx -mno-fused-madd
14324 @opindex mfused-madd
14325 @opindex mno-fused-madd
14326 Generate code that uses (does not use) the floating point multiply and
14327 accumulate instructions. These instructions are generated by default if
14328 hardware floating point is used.
14330 @item -mwarn-framesize=@var{framesize}
14331 @opindex mwarn-framesize
14332 Emit a warning if the current function exceeds the given frame size. Because
14333 this is a compile time check it doesn't need to be a real problem when the program
14334 runs. It is intended to identify functions which most probably cause
14335 a stack overflow. It is useful to be used in an environment with limited stack
14336 size e.g.@: the linux kernel.
14338 @item -mwarn-dynamicstack
14339 @opindex mwarn-dynamicstack
14340 Emit a warning if the function calls alloca or uses dynamically
14341 sized arrays. This is generally a bad idea with a limited stack size.
14343 @item -mstack-guard=@var{stack-guard}
14344 @itemx -mstack-size=@var{stack-size}
14345 @opindex mstack-guard
14346 @opindex mstack-size
14347 If these options are provided the s390 back end emits additional instructions in
14348 the function prologue which trigger a trap if the stack size is @var{stack-guard}
14349 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
14350 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
14351 the frame size of the compiled function is chosen.
14352 These options are intended to be used to help debugging stack overflow problems.
14353 The additionally emitted code causes only little overhead and hence can also be
14354 used in production like systems without greater performance degradation. The given
14355 values have to be exact powers of 2 and @var{stack-size} has to be greater than
14356 @var{stack-guard} without exceeding 64k.
14357 In order to be efficient the extra code makes the assumption that the stack starts
14358 at an address aligned to the value given by @var{stack-size}.
14359 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
14362 @node Score Options
14363 @subsection Score Options
14364 @cindex Score Options
14366 These options are defined for Score implementations:
14371 Compile code for big endian mode. This is the default.
14375 Compile code for little endian mode.
14379 Disable generate bcnz instruction.
14383 Enable generate unaligned load and store instruction.
14387 Enable the use of multiply-accumulate instructions. Disabled by default.
14391 Specify the SCORE5 as the target architecture.
14395 Specify the SCORE5U of the target architecture.
14399 Specify the SCORE7 as the target architecture. This is the default.
14403 Specify the SCORE7D as the target architecture.
14407 @subsection SH Options
14409 These @samp{-m} options are defined for the SH implementations:
14414 Generate code for the SH1.
14418 Generate code for the SH2.
14421 Generate code for the SH2e.
14425 Generate code for the SH3.
14429 Generate code for the SH3e.
14433 Generate code for the SH4 without a floating-point unit.
14435 @item -m4-single-only
14436 @opindex m4-single-only
14437 Generate code for the SH4 with a floating-point unit that only
14438 supports single-precision arithmetic.
14442 Generate code for the SH4 assuming the floating-point unit is in
14443 single-precision mode by default.
14447 Generate code for the SH4.
14451 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
14452 floating-point unit is not used.
14454 @item -m4a-single-only
14455 @opindex m4a-single-only
14456 Generate code for the SH4a, in such a way that no double-precision
14457 floating point operations are used.
14460 @opindex m4a-single
14461 Generate code for the SH4a assuming the floating-point unit is in
14462 single-precision mode by default.
14466 Generate code for the SH4a.
14470 Same as @option{-m4a-nofpu}, except that it implicitly passes
14471 @option{-dsp} to the assembler. GCC doesn't generate any DSP
14472 instructions at the moment.
14476 Compile code for the processor in big endian mode.
14480 Compile code for the processor in little endian mode.
14484 Align doubles at 64-bit boundaries. Note that this changes the calling
14485 conventions, and thus some functions from the standard C library will
14486 not work unless you recompile it first with @option{-mdalign}.
14490 Shorten some address references at link time, when possible; uses the
14491 linker option @option{-relax}.
14495 Use 32-bit offsets in @code{switch} tables. The default is to use
14500 Enable the use of bit manipulation instructions on SH2A.
14504 Enable the use of the instruction @code{fmovd}.
14508 Comply with the calling conventions defined by Renesas.
14512 Comply with the calling conventions defined by Renesas.
14516 Comply with the calling conventions defined for GCC before the Renesas
14517 conventions were available. This option is the default for all
14518 targets of the SH toolchain except for @samp{sh-symbianelf}.
14521 @opindex mnomacsave
14522 Mark the @code{MAC} register as call-clobbered, even if
14523 @option{-mhitachi} is given.
14527 Increase IEEE-compliance of floating-point code.
14528 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14529 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14530 comparisons of NANs / infinities incurs extra overhead in every
14531 floating point comparison, therefore the default is set to
14532 @option{-ffinite-math-only}.
14534 @item -minline-ic_invalidate
14535 @opindex minline-ic_invalidate
14536 Inline code to invalidate instruction cache entries after setting up
14537 nested function trampolines.
14538 This option has no effect if -musermode is in effect and the selected
14539 code generation option (e.g. -m4) does not allow the use of the icbi
14541 If the selected code generation option does not allow the use of the icbi
14542 instruction, and -musermode is not in effect, the inlined code will
14543 manipulate the instruction cache address array directly with an associative
14544 write. This not only requires privileged mode, but it will also
14545 fail if the cache line had been mapped via the TLB and has become unmapped.
14549 Dump instruction size and location in the assembly code.
14552 @opindex mpadstruct
14553 This option is deprecated. It pads structures to multiple of 4 bytes,
14554 which is incompatible with the SH ABI@.
14558 Optimize for space instead of speed. Implied by @option{-Os}.
14561 @opindex mprefergot
14562 When generating position-independent code, emit function calls using
14563 the Global Offset Table instead of the Procedure Linkage Table.
14567 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14568 if the inlined code would not work in user mode.
14569 This is the default when the target is @code{sh-*-linux*}.
14571 @item -multcost=@var{number}
14572 @opindex multcost=@var{number}
14573 Set the cost to assume for a multiply insn.
14575 @item -mdiv=@var{strategy}
14576 @opindex mdiv=@var{strategy}
14577 Set the division strategy to use for SHmedia code. @var{strategy} must be
14578 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14579 inv:call2, inv:fp .
14580 "fp" performs the operation in floating point. This has a very high latency,
14581 but needs only a few instructions, so it might be a good choice if
14582 your code has enough easily exploitable ILP to allow the compiler to
14583 schedule the floating point instructions together with other instructions.
14584 Division by zero causes a floating point exception.
14585 "inv" uses integer operations to calculate the inverse of the divisor,
14586 and then multiplies the dividend with the inverse. This strategy allows
14587 cse and hoisting of the inverse calculation. Division by zero calculates
14588 an unspecified result, but does not trap.
14589 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14590 have been found, or if the entire operation has been hoisted to the same
14591 place, the last stages of the inverse calculation are intertwined with the
14592 final multiply to reduce the overall latency, at the expense of using a few
14593 more instructions, and thus offering fewer scheduling opportunities with
14595 "call" calls a library function that usually implements the inv:minlat
14597 This gives high code density for m5-*media-nofpu compilations.
14598 "call2" uses a different entry point of the same library function, where it
14599 assumes that a pointer to a lookup table has already been set up, which
14600 exposes the pointer load to cse / code hoisting optimizations.
14601 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14602 code generation, but if the code stays unoptimized, revert to the "call",
14603 "call2", or "fp" strategies, respectively. Note that the
14604 potentially-trapping side effect of division by zero is carried by a
14605 separate instruction, so it is possible that all the integer instructions
14606 are hoisted out, but the marker for the side effect stays where it is.
14607 A recombination to fp operations or a call is not possible in that case.
14608 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14609 that the inverse calculation was nor separated from the multiply, they speed
14610 up division where the dividend fits into 20 bits (plus sign where applicable),
14611 by inserting a test to skip a number of operations in this case; this test
14612 slows down the case of larger dividends. inv20u assumes the case of a such
14613 a small dividend to be unlikely, and inv20l assumes it to be likely.
14615 @item -mdivsi3_libfunc=@var{name}
14616 @opindex mdivsi3_libfunc=@var{name}
14617 Set the name of the library function used for 32 bit signed division to
14618 @var{name}. This only affect the name used in the call and inv:call
14619 division strategies, and the compiler will still expect the same
14620 sets of input/output/clobbered registers as if this option was not present.
14622 @item -mfixed-range=@var{register-range}
14623 @opindex mfixed-range
14624 Generate code treating the given register range as fixed registers.
14625 A fixed register is one that the register allocator can not use. This is
14626 useful when compiling kernel code. A register range is specified as
14627 two registers separated by a dash. Multiple register ranges can be
14628 specified separated by a comma.
14630 @item -madjust-unroll
14631 @opindex madjust-unroll
14632 Throttle unrolling to avoid thrashing target registers.
14633 This option only has an effect if the gcc code base supports the
14634 TARGET_ADJUST_UNROLL_MAX target hook.
14636 @item -mindexed-addressing
14637 @opindex mindexed-addressing
14638 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14639 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14640 semantics for the indexed addressing mode. The architecture allows the
14641 implementation of processors with 64 bit MMU, which the OS could use to
14642 get 32 bit addressing, but since no current hardware implementation supports
14643 this or any other way to make the indexed addressing mode safe to use in
14644 the 32 bit ABI, the default is -mno-indexed-addressing.
14646 @item -mgettrcost=@var{number}
14647 @opindex mgettrcost=@var{number}
14648 Set the cost assumed for the gettr instruction to @var{number}.
14649 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14653 Assume pt* instructions won't trap. This will generally generate better
14654 scheduled code, but is unsafe on current hardware. The current architecture
14655 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14656 This has the unintentional effect of making it unsafe to schedule ptabs /
14657 ptrel before a branch, or hoist it out of a loop. For example,
14658 __do_global_ctors, a part of libgcc that runs constructors at program
14659 startup, calls functions in a list which is delimited by @minus{}1. With the
14660 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14661 That means that all the constructors will be run a bit quicker, but when
14662 the loop comes to the end of the list, the program crashes because ptabs
14663 loads @minus{}1 into a target register. Since this option is unsafe for any
14664 hardware implementing the current architecture specification, the default
14665 is -mno-pt-fixed. Unless the user specifies a specific cost with
14666 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14667 this deters register allocation using target registers for storing
14670 @item -minvalid-symbols
14671 @opindex minvalid-symbols
14672 Assume symbols might be invalid. Ordinary function symbols generated by
14673 the compiler will always be valid to load with movi/shori/ptabs or
14674 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14675 to generate symbols that will cause ptabs / ptrel to trap.
14676 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14677 It will then prevent cross-basic-block cse, hoisting and most scheduling
14678 of symbol loads. The default is @option{-mno-invalid-symbols}.
14681 @node SPARC Options
14682 @subsection SPARC Options
14683 @cindex SPARC options
14685 These @samp{-m} options are supported on the SPARC:
14688 @item -mno-app-regs
14690 @opindex mno-app-regs
14692 Specify @option{-mapp-regs} to generate output using the global registers
14693 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14696 To be fully SVR4 ABI compliant at the cost of some performance loss,
14697 specify @option{-mno-app-regs}. You should compile libraries and system
14698 software with this option.
14701 @itemx -mhard-float
14703 @opindex mhard-float
14704 Generate output containing floating point instructions. This is the
14708 @itemx -msoft-float
14710 @opindex msoft-float
14711 Generate output containing library calls for floating point.
14712 @strong{Warning:} the requisite libraries are not available for all SPARC
14713 targets. Normally the facilities of the machine's usual C compiler are
14714 used, but this cannot be done directly in cross-compilation. You must make
14715 your own arrangements to provide suitable library functions for
14716 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14717 @samp{sparclite-*-*} do provide software floating point support.
14719 @option{-msoft-float} changes the calling convention in the output file;
14720 therefore, it is only useful if you compile @emph{all} of a program with
14721 this option. In particular, you need to compile @file{libgcc.a}, the
14722 library that comes with GCC, with @option{-msoft-float} in order for
14725 @item -mhard-quad-float
14726 @opindex mhard-quad-float
14727 Generate output containing quad-word (long double) floating point
14730 @item -msoft-quad-float
14731 @opindex msoft-quad-float
14732 Generate output containing library calls for quad-word (long double)
14733 floating point instructions. The functions called are those specified
14734 in the SPARC ABI@. This is the default.
14736 As of this writing, there are no SPARC implementations that have hardware
14737 support for the quad-word floating point instructions. They all invoke
14738 a trap handler for one of these instructions, and then the trap handler
14739 emulates the effect of the instruction. Because of the trap handler overhead,
14740 this is much slower than calling the ABI library routines. Thus the
14741 @option{-msoft-quad-float} option is the default.
14743 @item -mno-unaligned-doubles
14744 @itemx -munaligned-doubles
14745 @opindex mno-unaligned-doubles
14746 @opindex munaligned-doubles
14747 Assume that doubles have 8 byte alignment. This is the default.
14749 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14750 alignment only if they are contained in another type, or if they have an
14751 absolute address. Otherwise, it assumes they have 4 byte alignment.
14752 Specifying this option avoids some rare compatibility problems with code
14753 generated by other compilers. It is not the default because it results
14754 in a performance loss, especially for floating point code.
14756 @item -mno-faster-structs
14757 @itemx -mfaster-structs
14758 @opindex mno-faster-structs
14759 @opindex mfaster-structs
14760 With @option{-mfaster-structs}, the compiler assumes that structures
14761 should have 8 byte alignment. This enables the use of pairs of
14762 @code{ldd} and @code{std} instructions for copies in structure
14763 assignment, in place of twice as many @code{ld} and @code{st} pairs.
14764 However, the use of this changed alignment directly violates the SPARC
14765 ABI@. Thus, it's intended only for use on targets where the developer
14766 acknowledges that their resulting code will not be directly in line with
14767 the rules of the ABI@.
14769 @item -mimpure-text
14770 @opindex mimpure-text
14771 @option{-mimpure-text}, used in addition to @option{-shared}, tells
14772 the compiler to not pass @option{-z text} to the linker when linking a
14773 shared object. Using this option, you can link position-dependent
14774 code into a shared object.
14776 @option{-mimpure-text} suppresses the ``relocations remain against
14777 allocatable but non-writable sections'' linker error message.
14778 However, the necessary relocations will trigger copy-on-write, and the
14779 shared object is not actually shared across processes. Instead of
14780 using @option{-mimpure-text}, you should compile all source code with
14781 @option{-fpic} or @option{-fPIC}.
14783 This option is only available on SunOS and Solaris.
14785 @item -mcpu=@var{cpu_type}
14787 Set the instruction set, register set, and instruction scheduling parameters
14788 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
14789 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
14790 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
14791 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
14792 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
14794 Default instruction scheduling parameters are used for values that select
14795 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
14796 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
14798 Here is a list of each supported architecture and their supported
14803 v8: supersparc, hypersparc
14804 sparclite: f930, f934, sparclite86x
14806 v9: ultrasparc, ultrasparc3, niagara, niagara2
14809 By default (unless configured otherwise), GCC generates code for the V7
14810 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
14811 additionally optimizes it for the Cypress CY7C602 chip, as used in the
14812 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
14813 SPARCStation 1, 2, IPX etc.
14815 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
14816 architecture. The only difference from V7 code is that the compiler emits
14817 the integer multiply and integer divide instructions which exist in SPARC-V8
14818 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
14819 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
14822 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
14823 the SPARC architecture. This adds the integer multiply, integer divide step
14824 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
14825 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
14826 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
14827 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
14828 MB86934 chip, which is the more recent SPARClite with FPU@.
14830 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
14831 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
14832 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
14833 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
14834 optimizes it for the TEMIC SPARClet chip.
14836 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
14837 architecture. This adds 64-bit integer and floating-point move instructions,
14838 3 additional floating-point condition code registers and conditional move
14839 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
14840 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
14841 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
14842 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
14843 @option{-mcpu=niagara}, the compiler additionally optimizes it for
14844 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
14845 additionally optimizes it for Sun UltraSPARC T2 chips.
14847 @item -mtune=@var{cpu_type}
14849 Set the instruction scheduling parameters for machine type
14850 @var{cpu_type}, but do not set the instruction set or register set that the
14851 option @option{-mcpu=@var{cpu_type}} would.
14853 The same values for @option{-mcpu=@var{cpu_type}} can be used for
14854 @option{-mtune=@var{cpu_type}}, but the only useful values are those
14855 that select a particular cpu implementation. Those are @samp{cypress},
14856 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
14857 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
14858 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
14863 @opindex mno-v8plus
14864 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
14865 difference from the V8 ABI is that the global and out registers are
14866 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
14867 mode for all SPARC-V9 processors.
14873 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
14874 Visual Instruction Set extensions. The default is @option{-mno-vis}.
14877 These @samp{-m} options are supported in addition to the above
14878 on SPARC-V9 processors in 64-bit environments:
14881 @item -mlittle-endian
14882 @opindex mlittle-endian
14883 Generate code for a processor running in little-endian mode. It is only
14884 available for a few configurations and most notably not on Solaris and Linux.
14890 Generate code for a 32-bit or 64-bit environment.
14891 The 32-bit environment sets int, long and pointer to 32 bits.
14892 The 64-bit environment sets int to 32 bits and long and pointer
14895 @item -mcmodel=medlow
14896 @opindex mcmodel=medlow
14897 Generate code for the Medium/Low code model: 64-bit addresses, programs
14898 must be linked in the low 32 bits of memory. Programs can be statically
14899 or dynamically linked.
14901 @item -mcmodel=medmid
14902 @opindex mcmodel=medmid
14903 Generate code for the Medium/Middle code model: 64-bit addresses, programs
14904 must be linked in the low 44 bits of memory, the text and data segments must
14905 be less than 2GB in size and the data segment must be located within 2GB of
14908 @item -mcmodel=medany
14909 @opindex mcmodel=medany
14910 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
14911 may be linked anywhere in memory, the text and data segments must be less
14912 than 2GB in size and the data segment must be located within 2GB of the
14915 @item -mcmodel=embmedany
14916 @opindex mcmodel=embmedany
14917 Generate code for the Medium/Anywhere code model for embedded systems:
14918 64-bit addresses, the text and data segments must be less than 2GB in
14919 size, both starting anywhere in memory (determined at link time). The
14920 global register %g4 points to the base of the data segment. Programs
14921 are statically linked and PIC is not supported.
14924 @itemx -mno-stack-bias
14925 @opindex mstack-bias
14926 @opindex mno-stack-bias
14927 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
14928 frame pointer if present, are offset by @minus{}2047 which must be added back
14929 when making stack frame references. This is the default in 64-bit mode.
14930 Otherwise, assume no such offset is present.
14933 These switches are supported in addition to the above on Solaris:
14938 Add support for multithreading using the Solaris threads library. This
14939 option sets flags for both the preprocessor and linker. This option does
14940 not affect the thread safety of object code produced by the compiler or
14941 that of libraries supplied with it.
14945 Add support for multithreading using the POSIX threads library. This
14946 option sets flags for both the preprocessor and linker. This option does
14947 not affect the thread safety of object code produced by the compiler or
14948 that of libraries supplied with it.
14952 This is a synonym for @option{-pthreads}.
14956 @subsection SPU Options
14957 @cindex SPU options
14959 These @samp{-m} options are supported on the SPU:
14963 @itemx -merror-reloc
14964 @opindex mwarn-reloc
14965 @opindex merror-reloc
14967 The loader for SPU does not handle dynamic relocations. By default, GCC
14968 will give an error when it generates code that requires a dynamic
14969 relocation. @option{-mno-error-reloc} disables the error,
14970 @option{-mwarn-reloc} will generate a warning instead.
14973 @itemx -munsafe-dma
14975 @opindex munsafe-dma
14977 Instructions which initiate or test completion of DMA must not be
14978 reordered with respect to loads and stores of the memory which is being
14979 accessed. Users typically address this problem using the volatile
14980 keyword, but that can lead to inefficient code in places where the
14981 memory is known to not change. Rather than mark the memory as volatile
14982 we treat the DMA instructions as potentially effecting all memory. With
14983 @option{-munsafe-dma} users must use the volatile keyword to protect
14986 @item -mbranch-hints
14987 @opindex mbranch-hints
14989 By default, GCC will generate a branch hint instruction to avoid
14990 pipeline stalls for always taken or probably taken branches. A hint
14991 will not be generated closer than 8 instructions away from its branch.
14992 There is little reason to disable them, except for debugging purposes,
14993 or to make an object a little bit smaller.
14997 @opindex msmall-mem
14998 @opindex mlarge-mem
15000 By default, GCC generates code assuming that addresses are never larger
15001 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
15002 a full 32 bit address.
15007 By default, GCC links against startup code that assumes the SPU-style
15008 main function interface (which has an unconventional parameter list).
15009 With @option{-mstdmain}, GCC will link your program against startup
15010 code that assumes a C99-style interface to @code{main}, including a
15011 local copy of @code{argv} strings.
15013 @item -mfixed-range=@var{register-range}
15014 @opindex mfixed-range
15015 Generate code treating the given register range as fixed registers.
15016 A fixed register is one that the register allocator can not use. This is
15017 useful when compiling kernel code. A register range is specified as
15018 two registers separated by a dash. Multiple register ranges can be
15019 specified separated by a comma.
15022 @itemx -mdual-nops=@var{n}
15023 @opindex mdual-nops
15024 By default, GCC will insert nops to increase dual issue when it expects
15025 it to increase performance. @var{n} can be a value from 0 to 10. A
15026 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
15027 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
15029 @item -mhint-max-nops=@var{n}
15030 @opindex mhint-max-nops
15031 Maximum number of nops to insert for a branch hint. A branch hint must
15032 be at least 8 instructions away from the branch it is effecting. GCC
15033 will insert up to @var{n} nops to enforce this, otherwise it will not
15034 generate the branch hint.
15036 @item -mhint-max-distance=@var{n}
15037 @opindex mhint-max-distance
15038 The encoding of the branch hint instruction limits the hint to be within
15039 256 instructions of the branch it is effecting. By default, GCC makes
15040 sure it is within 125.
15043 @opindex msafe-hints
15044 Work around a hardware bug which causes the SPU to stall indefinitely.
15045 By default, GCC will insert the @code{hbrp} instruction to make sure
15046 this stall won't happen.
15050 @node System V Options
15051 @subsection Options for System V
15053 These additional options are available on System V Release 4 for
15054 compatibility with other compilers on those systems:
15059 Create a shared object.
15060 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
15064 Identify the versions of each tool used by the compiler, in a
15065 @code{.ident} assembler directive in the output.
15069 Refrain from adding @code{.ident} directives to the output file (this is
15072 @item -YP,@var{dirs}
15074 Search the directories @var{dirs}, and no others, for libraries
15075 specified with @option{-l}.
15077 @item -Ym,@var{dir}
15079 Look in the directory @var{dir} to find the M4 preprocessor.
15080 The assembler uses this option.
15081 @c This is supposed to go with a -Yd for predefined M4 macro files, but
15082 @c the generic assembler that comes with Solaris takes just -Ym.
15086 @subsection V850 Options
15087 @cindex V850 Options
15089 These @samp{-m} options are defined for V850 implementations:
15093 @itemx -mno-long-calls
15094 @opindex mlong-calls
15095 @opindex mno-long-calls
15096 Treat all calls as being far away (near). If calls are assumed to be
15097 far away, the compiler will always load the functions address up into a
15098 register, and call indirect through the pointer.
15104 Do not optimize (do optimize) basic blocks that use the same index
15105 pointer 4 or more times to copy pointer into the @code{ep} register, and
15106 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
15107 option is on by default if you optimize.
15109 @item -mno-prolog-function
15110 @itemx -mprolog-function
15111 @opindex mno-prolog-function
15112 @opindex mprolog-function
15113 Do not use (do use) external functions to save and restore registers
15114 at the prologue and epilogue of a function. The external functions
15115 are slower, but use less code space if more than one function saves
15116 the same number of registers. The @option{-mprolog-function} option
15117 is on by default if you optimize.
15121 Try to make the code as small as possible. At present, this just turns
15122 on the @option{-mep} and @option{-mprolog-function} options.
15124 @item -mtda=@var{n}
15126 Put static or global variables whose size is @var{n} bytes or less into
15127 the tiny data area that register @code{ep} points to. The tiny data
15128 area can hold up to 256 bytes in total (128 bytes for byte references).
15130 @item -msda=@var{n}
15132 Put static or global variables whose size is @var{n} bytes or less into
15133 the small data area that register @code{gp} points to. The small data
15134 area can hold up to 64 kilobytes.
15136 @item -mzda=@var{n}
15138 Put static or global variables whose size is @var{n} bytes or less into
15139 the first 32 kilobytes of memory.
15143 Specify that the target processor is the V850.
15146 @opindex mbig-switch
15147 Generate code suitable for big switch tables. Use this option only if
15148 the assembler/linker complain about out of range branches within a switch
15153 This option will cause r2 and r5 to be used in the code generated by
15154 the compiler. This setting is the default.
15156 @item -mno-app-regs
15157 @opindex mno-app-regs
15158 This option will cause r2 and r5 to be treated as fixed registers.
15162 Specify that the target processor is the V850E1. The preprocessor
15163 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
15164 this option is used.
15168 Specify that the target processor is the V850E@. The preprocessor
15169 constant @samp{__v850e__} will be defined if this option is used.
15171 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
15172 are defined then a default target processor will be chosen and the
15173 relevant @samp{__v850*__} preprocessor constant will be defined.
15175 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
15176 defined, regardless of which processor variant is the target.
15178 @item -mdisable-callt
15179 @opindex mdisable-callt
15180 This option will suppress generation of the CALLT instruction for the
15181 v850e and v850e1 flavors of the v850 architecture. The default is
15182 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
15187 @subsection VAX Options
15188 @cindex VAX options
15190 These @samp{-m} options are defined for the VAX:
15195 Do not output certain jump instructions (@code{aobleq} and so on)
15196 that the Unix assembler for the VAX cannot handle across long
15201 Do output those jump instructions, on the assumption that you
15202 will assemble with the GNU assembler.
15206 Output code for g-format floating point numbers instead of d-format.
15209 @node VxWorks Options
15210 @subsection VxWorks Options
15211 @cindex VxWorks Options
15213 The options in this section are defined for all VxWorks targets.
15214 Options specific to the target hardware are listed with the other
15215 options for that target.
15220 GCC can generate code for both VxWorks kernels and real time processes
15221 (RTPs). This option switches from the former to the latter. It also
15222 defines the preprocessor macro @code{__RTP__}.
15225 @opindex non-static
15226 Link an RTP executable against shared libraries rather than static
15227 libraries. The options @option{-static} and @option{-shared} can
15228 also be used for RTPs (@pxref{Link Options}); @option{-static}
15235 These options are passed down to the linker. They are defined for
15236 compatibility with Diab.
15239 @opindex Xbind-lazy
15240 Enable lazy binding of function calls. This option is equivalent to
15241 @option{-Wl,-z,now} and is defined for compatibility with Diab.
15245 Disable lazy binding of function calls. This option is the default and
15246 is defined for compatibility with Diab.
15249 @node x86-64 Options
15250 @subsection x86-64 Options
15251 @cindex x86-64 options
15253 These are listed under @xref{i386 and x86-64 Options}.
15255 @node Xstormy16 Options
15256 @subsection Xstormy16 Options
15257 @cindex Xstormy16 Options
15259 These options are defined for Xstormy16:
15264 Choose startup files and linker script suitable for the simulator.
15267 @node Xtensa Options
15268 @subsection Xtensa Options
15269 @cindex Xtensa Options
15271 These options are supported for Xtensa targets:
15275 @itemx -mno-const16
15277 @opindex mno-const16
15278 Enable or disable use of @code{CONST16} instructions for loading
15279 constant values. The @code{CONST16} instruction is currently not a
15280 standard option from Tensilica. When enabled, @code{CONST16}
15281 instructions are always used in place of the standard @code{L32R}
15282 instructions. The use of @code{CONST16} is enabled by default only if
15283 the @code{L32R} instruction is not available.
15286 @itemx -mno-fused-madd
15287 @opindex mfused-madd
15288 @opindex mno-fused-madd
15289 Enable or disable use of fused multiply/add and multiply/subtract
15290 instructions in the floating-point option. This has no effect if the
15291 floating-point option is not also enabled. Disabling fused multiply/add
15292 and multiply/subtract instructions forces the compiler to use separate
15293 instructions for the multiply and add/subtract operations. This may be
15294 desirable in some cases where strict IEEE 754-compliant results are
15295 required: the fused multiply add/subtract instructions do not round the
15296 intermediate result, thereby producing results with @emph{more} bits of
15297 precision than specified by the IEEE standard. Disabling fused multiply
15298 add/subtract instructions also ensures that the program output is not
15299 sensitive to the compiler's ability to combine multiply and add/subtract
15302 @item -mserialize-volatile
15303 @itemx -mno-serialize-volatile
15304 @opindex mserialize-volatile
15305 @opindex mno-serialize-volatile
15306 When this option is enabled, GCC inserts @code{MEMW} instructions before
15307 @code{volatile} memory references to guarantee sequential consistency.
15308 The default is @option{-mserialize-volatile}. Use
15309 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
15311 @item -mtext-section-literals
15312 @itemx -mno-text-section-literals
15313 @opindex mtext-section-literals
15314 @opindex mno-text-section-literals
15315 Control the treatment of literal pools. The default is
15316 @option{-mno-text-section-literals}, which places literals in a separate
15317 section in the output file. This allows the literal pool to be placed
15318 in a data RAM/ROM, and it also allows the linker to combine literal
15319 pools from separate object files to remove redundant literals and
15320 improve code size. With @option{-mtext-section-literals}, the literals
15321 are interspersed in the text section in order to keep them as close as
15322 possible to their references. This may be necessary for large assembly
15325 @item -mtarget-align
15326 @itemx -mno-target-align
15327 @opindex mtarget-align
15328 @opindex mno-target-align
15329 When this option is enabled, GCC instructs the assembler to
15330 automatically align instructions to reduce branch penalties at the
15331 expense of some code density. The assembler attempts to widen density
15332 instructions to align branch targets and the instructions following call
15333 instructions. If there are not enough preceding safe density
15334 instructions to align a target, no widening will be performed. The
15335 default is @option{-mtarget-align}. These options do not affect the
15336 treatment of auto-aligned instructions like @code{LOOP}, which the
15337 assembler will always align, either by widening density instructions or
15338 by inserting no-op instructions.
15341 @itemx -mno-longcalls
15342 @opindex mlongcalls
15343 @opindex mno-longcalls
15344 When this option is enabled, GCC instructs the assembler to translate
15345 direct calls to indirect calls unless it can determine that the target
15346 of a direct call is in the range allowed by the call instruction. This
15347 translation typically occurs for calls to functions in other source
15348 files. Specifically, the assembler translates a direct @code{CALL}
15349 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
15350 The default is @option{-mno-longcalls}. This option should be used in
15351 programs where the call target can potentially be out of range. This
15352 option is implemented in the assembler, not the compiler, so the
15353 assembly code generated by GCC will still show direct call
15354 instructions---look at the disassembled object code to see the actual
15355 instructions. Note that the assembler will use an indirect call for
15356 every cross-file call, not just those that really will be out of range.
15359 @node zSeries Options
15360 @subsection zSeries Options
15361 @cindex zSeries options
15363 These are listed under @xref{S/390 and zSeries Options}.
15365 @node Code Gen Options
15366 @section Options for Code Generation Conventions
15367 @cindex code generation conventions
15368 @cindex options, code generation
15369 @cindex run-time options
15371 These machine-independent options control the interface conventions
15372 used in code generation.
15374 Most of them have both positive and negative forms; the negative form
15375 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
15376 one of the forms is listed---the one which is not the default. You
15377 can figure out the other form by either removing @samp{no-} or adding
15381 @item -fbounds-check
15382 @opindex fbounds-check
15383 For front-ends that support it, generate additional code to check that
15384 indices used to access arrays are within the declared range. This is
15385 currently only supported by the Java and Fortran front-ends, where
15386 this option defaults to true and false respectively.
15390 This option generates traps for signed overflow on addition, subtraction,
15391 multiplication operations.
15395 This option instructs the compiler to assume that signed arithmetic
15396 overflow of addition, subtraction and multiplication wraps around
15397 using twos-complement representation. This flag enables some optimizations
15398 and disables others. This option is enabled by default for the Java
15399 front-end, as required by the Java language specification.
15402 @opindex fexceptions
15403 Enable exception handling. Generates extra code needed to propagate
15404 exceptions. For some targets, this implies GCC will generate frame
15405 unwind information for all functions, which can produce significant data
15406 size overhead, although it does not affect execution. If you do not
15407 specify this option, GCC will enable it by default for languages like
15408 C++ which normally require exception handling, and disable it for
15409 languages like C that do not normally require it. However, you may need
15410 to enable this option when compiling C code that needs to interoperate
15411 properly with exception handlers written in C++. You may also wish to
15412 disable this option if you are compiling older C++ programs that don't
15413 use exception handling.
15415 @item -fnon-call-exceptions
15416 @opindex fnon-call-exceptions
15417 Generate code that allows trapping instructions to throw exceptions.
15418 Note that this requires platform-specific runtime support that does
15419 not exist everywhere. Moreover, it only allows @emph{trapping}
15420 instructions to throw exceptions, i.e.@: memory references or floating
15421 point instructions. It does not allow exceptions to be thrown from
15422 arbitrary signal handlers such as @code{SIGALRM}.
15424 @item -funwind-tables
15425 @opindex funwind-tables
15426 Similar to @option{-fexceptions}, except that it will just generate any needed
15427 static data, but will not affect the generated code in any other way.
15428 You will normally not enable this option; instead, a language processor
15429 that needs this handling would enable it on your behalf.
15431 @item -fasynchronous-unwind-tables
15432 @opindex fasynchronous-unwind-tables
15433 Generate unwind table in dwarf2 format, if supported by target machine. The
15434 table is exact at each instruction boundary, so it can be used for stack
15435 unwinding from asynchronous events (such as debugger or garbage collector).
15437 @item -fpcc-struct-return
15438 @opindex fpcc-struct-return
15439 Return ``short'' @code{struct} and @code{union} values in memory like
15440 longer ones, rather than in registers. This convention is less
15441 efficient, but it has the advantage of allowing intercallability between
15442 GCC-compiled files and files compiled with other compilers, particularly
15443 the Portable C Compiler (pcc).
15445 The precise convention for returning structures in memory depends
15446 on the target configuration macros.
15448 Short structures and unions are those whose size and alignment match
15449 that of some integer type.
15451 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
15452 switch is not binary compatible with code compiled with the
15453 @option{-freg-struct-return} switch.
15454 Use it to conform to a non-default application binary interface.
15456 @item -freg-struct-return
15457 @opindex freg-struct-return
15458 Return @code{struct} and @code{union} values in registers when possible.
15459 This is more efficient for small structures than
15460 @option{-fpcc-struct-return}.
15462 If you specify neither @option{-fpcc-struct-return} nor
15463 @option{-freg-struct-return}, GCC defaults to whichever convention is
15464 standard for the target. If there is no standard convention, GCC
15465 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
15466 the principal compiler. In those cases, we can choose the standard, and
15467 we chose the more efficient register return alternative.
15469 @strong{Warning:} code compiled with the @option{-freg-struct-return}
15470 switch is not binary compatible with code compiled with the
15471 @option{-fpcc-struct-return} switch.
15472 Use it to conform to a non-default application binary interface.
15474 @item -fshort-enums
15475 @opindex fshort-enums
15476 Allocate to an @code{enum} type only as many bytes as it needs for the
15477 declared range of possible values. Specifically, the @code{enum} type
15478 will be equivalent to the smallest integer type which has enough room.
15480 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
15481 code that is not binary compatible with code generated without that switch.
15482 Use it to conform to a non-default application binary interface.
15484 @item -fshort-double
15485 @opindex fshort-double
15486 Use the same size for @code{double} as for @code{float}.
15488 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
15489 code that is not binary compatible with code generated without that switch.
15490 Use it to conform to a non-default application binary interface.
15492 @item -fshort-wchar
15493 @opindex fshort-wchar
15494 Override the underlying type for @samp{wchar_t} to be @samp{short
15495 unsigned int} instead of the default for the target. This option is
15496 useful for building programs to run under WINE@.
15498 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
15499 code that is not binary compatible with code generated without that switch.
15500 Use it to conform to a non-default application binary interface.
15503 @opindex fno-common
15504 In C, allocate even uninitialized global variables in the data section of the
15505 object file, rather than generating them as common blocks. This has the
15506 effect that if the same variable is declared (without @code{extern}) in
15507 two different compilations, you will get an error when you link them.
15508 The only reason this might be useful is if you wish to verify that the
15509 program will work on other systems which always work this way.
15513 Ignore the @samp{#ident} directive.
15515 @item -finhibit-size-directive
15516 @opindex finhibit-size-directive
15517 Don't output a @code{.size} assembler directive, or anything else that
15518 would cause trouble if the function is split in the middle, and the
15519 two halves are placed at locations far apart in memory. This option is
15520 used when compiling @file{crtstuff.c}; you should not need to use it
15523 @item -fverbose-asm
15524 @opindex fverbose-asm
15525 Put extra commentary information in the generated assembly code to
15526 make it more readable. This option is generally only of use to those
15527 who actually need to read the generated assembly code (perhaps while
15528 debugging the compiler itself).
15530 @option{-fno-verbose-asm}, the default, causes the
15531 extra information to be omitted and is useful when comparing two assembler
15534 @item -frecord-gcc-switches
15535 @opindex frecord-gcc-switches
15536 This switch causes the command line that was used to invoke the
15537 compiler to be recorded into the object file that is being created.
15538 This switch is only implemented on some targets and the exact format
15539 of the recording is target and binary file format dependent, but it
15540 usually takes the form of a section containing ASCII text. This
15541 switch is related to the @option{-fverbose-asm} switch, but that
15542 switch only records information in the assembler output file as
15543 comments, so it never reaches the object file.
15547 @cindex global offset table
15549 Generate position-independent code (PIC) suitable for use in a shared
15550 library, if supported for the target machine. Such code accesses all
15551 constant addresses through a global offset table (GOT)@. The dynamic
15552 loader resolves the GOT entries when the program starts (the dynamic
15553 loader is not part of GCC; it is part of the operating system). If
15554 the GOT size for the linked executable exceeds a machine-specific
15555 maximum size, you get an error message from the linker indicating that
15556 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15557 instead. (These maximums are 8k on the SPARC and 32k
15558 on the m68k and RS/6000. The 386 has no such limit.)
15560 Position-independent code requires special support, and therefore works
15561 only on certain machines. For the 386, GCC supports PIC for System V
15562 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15563 position-independent.
15565 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15570 If supported for the target machine, emit position-independent code,
15571 suitable for dynamic linking and avoiding any limit on the size of the
15572 global offset table. This option makes a difference on the m68k,
15573 PowerPC and SPARC@.
15575 Position-independent code requires special support, and therefore works
15576 only on certain machines.
15578 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15585 These options are similar to @option{-fpic} and @option{-fPIC}, but
15586 generated position independent code can be only linked into executables.
15587 Usually these options are used when @option{-pie} GCC option will be
15588 used during linking.
15590 @option{-fpie} and @option{-fPIE} both define the macros
15591 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15592 for @option{-fpie} and 2 for @option{-fPIE}.
15594 @item -fno-jump-tables
15595 @opindex fno-jump-tables
15596 Do not use jump tables for switch statements even where it would be
15597 more efficient than other code generation strategies. This option is
15598 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15599 building code which forms part of a dynamic linker and cannot
15600 reference the address of a jump table. On some targets, jump tables
15601 do not require a GOT and this option is not needed.
15603 @item -ffixed-@var{reg}
15605 Treat the register named @var{reg} as a fixed register; generated code
15606 should never refer to it (except perhaps as a stack pointer, frame
15607 pointer or in some other fixed role).
15609 @var{reg} must be the name of a register. The register names accepted
15610 are machine-specific and are defined in the @code{REGISTER_NAMES}
15611 macro in the machine description macro file.
15613 This flag does not have a negative form, because it specifies a
15616 @item -fcall-used-@var{reg}
15617 @opindex fcall-used
15618 Treat the register named @var{reg} as an allocable register that is
15619 clobbered by function calls. It may be allocated for temporaries or
15620 variables that do not live across a call. Functions compiled this way
15621 will not save and restore the register @var{reg}.
15623 It is an error to used this flag with the frame pointer or stack pointer.
15624 Use of this flag for other registers that have fixed pervasive roles in
15625 the machine's execution model will produce disastrous results.
15627 This flag does not have a negative form, because it specifies a
15630 @item -fcall-saved-@var{reg}
15631 @opindex fcall-saved
15632 Treat the register named @var{reg} as an allocable register saved by
15633 functions. It may be allocated even for temporaries or variables that
15634 live across a call. Functions compiled this way will save and restore
15635 the register @var{reg} if they use it.
15637 It is an error to used this flag with the frame pointer or stack pointer.
15638 Use of this flag for other registers that have fixed pervasive roles in
15639 the machine's execution model will produce disastrous results.
15641 A different sort of disaster will result from the use of this flag for
15642 a register in which function values may be returned.
15644 This flag does not have a negative form, because it specifies a
15647 @item -fpack-struct[=@var{n}]
15648 @opindex fpack-struct
15649 Without a value specified, pack all structure members together without
15650 holes. When a value is specified (which must be a small power of two), pack
15651 structure members according to this value, representing the maximum
15652 alignment (that is, objects with default alignment requirements larger than
15653 this will be output potentially unaligned at the next fitting location.
15655 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15656 code that is not binary compatible with code generated without that switch.
15657 Additionally, it makes the code suboptimal.
15658 Use it to conform to a non-default application binary interface.
15660 @item -finstrument-functions
15661 @opindex finstrument-functions
15662 Generate instrumentation calls for entry and exit to functions. Just
15663 after function entry and just before function exit, the following
15664 profiling functions will be called with the address of the current
15665 function and its call site. (On some platforms,
15666 @code{__builtin_return_address} does not work beyond the current
15667 function, so the call site information may not be available to the
15668 profiling functions otherwise.)
15671 void __cyg_profile_func_enter (void *this_fn,
15673 void __cyg_profile_func_exit (void *this_fn,
15677 The first argument is the address of the start of the current function,
15678 which may be looked up exactly in the symbol table.
15680 This instrumentation is also done for functions expanded inline in other
15681 functions. The profiling calls will indicate where, conceptually, the
15682 inline function is entered and exited. This means that addressable
15683 versions of such functions must be available. If all your uses of a
15684 function are expanded inline, this may mean an additional expansion of
15685 code size. If you use @samp{extern inline} in your C code, an
15686 addressable version of such functions must be provided. (This is
15687 normally the case anyways, but if you get lucky and the optimizer always
15688 expands the functions inline, you might have gotten away without
15689 providing static copies.)
15691 A function may be given the attribute @code{no_instrument_function}, in
15692 which case this instrumentation will not be done. This can be used, for
15693 example, for the profiling functions listed above, high-priority
15694 interrupt routines, and any functions from which the profiling functions
15695 cannot safely be called (perhaps signal handlers, if the profiling
15696 routines generate output or allocate memory).
15698 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
15699 @opindex finstrument-functions-exclude-file-list
15701 Set the list of functions that are excluded from instrumentation (see
15702 the description of @code{-finstrument-functions}). If the file that
15703 contains a function definition matches with one of @var{file}, then
15704 that function is not instrumented. The match is done on substrings:
15705 if the @var{file} parameter is a substring of the file name, it is
15706 considered to be a match.
15709 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
15710 will exclude any inline function defined in files whose pathnames
15711 contain @code{/bits/stl} or @code{include/sys}.
15713 If, for some reason, you want to include letter @code{','} in one of
15714 @var{sym}, write @code{'\,'}. For example,
15715 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
15716 (note the single quote surrounding the option).
15718 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
15719 @opindex finstrument-functions-exclude-function-list
15721 This is similar to @code{-finstrument-functions-exclude-file-list},
15722 but this option sets the list of function names to be excluded from
15723 instrumentation. The function name to be matched is its user-visible
15724 name, such as @code{vector<int> blah(const vector<int> &)}, not the
15725 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
15726 match is done on substrings: if the @var{sym} parameter is a substring
15727 of the function name, it is considered to be a match.
15729 @item -fstack-check
15730 @opindex fstack-check
15731 Generate code to verify that you do not go beyond the boundary of the
15732 stack. You should specify this flag if you are running in an
15733 environment with multiple threads, but only rarely need to specify it in
15734 a single-threaded environment since stack overflow is automatically
15735 detected on nearly all systems if there is only one stack.
15737 Note that this switch does not actually cause checking to be done; the
15738 operating system or the language runtime must do that. The switch causes
15739 generation of code to ensure that they see the stack being extended.
15741 You can additionally specify a string parameter: @code{no} means no
15742 checking, @code{generic} means force the use of old-style checking,
15743 @code{specific} means use the best checking method and is equivalent
15744 to bare @option{-fstack-check}.
15746 Old-style checking is a generic mechanism that requires no specific
15747 target support in the compiler but comes with the following drawbacks:
15751 Modified allocation strategy for large objects: they will always be
15752 allocated dynamically if their size exceeds a fixed threshold.
15755 Fixed limit on the size of the static frame of functions: when it is
15756 topped by a particular function, stack checking is not reliable and
15757 a warning is issued by the compiler.
15760 Inefficiency: because of both the modified allocation strategy and the
15761 generic implementation, the performances of the code are hampered.
15764 Note that old-style stack checking is also the fallback method for
15765 @code{specific} if no target support has been added in the compiler.
15767 @item -fstack-limit-register=@var{reg}
15768 @itemx -fstack-limit-symbol=@var{sym}
15769 @itemx -fno-stack-limit
15770 @opindex fstack-limit-register
15771 @opindex fstack-limit-symbol
15772 @opindex fno-stack-limit
15773 Generate code to ensure that the stack does not grow beyond a certain value,
15774 either the value of a register or the address of a symbol. If the stack
15775 would grow beyond the value, a signal is raised. For most targets,
15776 the signal is raised before the stack overruns the boundary, so
15777 it is possible to catch the signal without taking special precautions.
15779 For instance, if the stack starts at absolute address @samp{0x80000000}
15780 and grows downwards, you can use the flags
15781 @option{-fstack-limit-symbol=__stack_limit} and
15782 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
15783 of 128KB@. Note that this may only work with the GNU linker.
15785 @cindex aliasing of parameters
15786 @cindex parameters, aliased
15787 @item -fargument-alias
15788 @itemx -fargument-noalias
15789 @itemx -fargument-noalias-global
15790 @itemx -fargument-noalias-anything
15791 @opindex fargument-alias
15792 @opindex fargument-noalias
15793 @opindex fargument-noalias-global
15794 @opindex fargument-noalias-anything
15795 Specify the possible relationships among parameters and between
15796 parameters and global data.
15798 @option{-fargument-alias} specifies that arguments (parameters) may
15799 alias each other and may alias global storage.@*
15800 @option{-fargument-noalias} specifies that arguments do not alias
15801 each other, but may alias global storage.@*
15802 @option{-fargument-noalias-global} specifies that arguments do not
15803 alias each other and do not alias global storage.
15804 @option{-fargument-noalias-anything} specifies that arguments do not
15805 alias any other storage.
15807 Each language will automatically use whatever option is required by
15808 the language standard. You should not need to use these options yourself.
15810 @item -fleading-underscore
15811 @opindex fleading-underscore
15812 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
15813 change the way C symbols are represented in the object file. One use
15814 is to help link with legacy assembly code.
15816 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
15817 generate code that is not binary compatible with code generated without that
15818 switch. Use it to conform to a non-default application binary interface.
15819 Not all targets provide complete support for this switch.
15821 @item -ftls-model=@var{model}
15822 @opindex ftls-model
15823 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
15824 The @var{model} argument should be one of @code{global-dynamic},
15825 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
15827 The default without @option{-fpic} is @code{initial-exec}; with
15828 @option{-fpic} the default is @code{global-dynamic}.
15830 @item -fvisibility=@var{default|internal|hidden|protected}
15831 @opindex fvisibility
15832 Set the default ELF image symbol visibility to the specified option---all
15833 symbols will be marked with this unless overridden within the code.
15834 Using this feature can very substantially improve linking and
15835 load times of shared object libraries, produce more optimized
15836 code, provide near-perfect API export and prevent symbol clashes.
15837 It is @strong{strongly} recommended that you use this in any shared objects
15840 Despite the nomenclature, @code{default} always means public ie;
15841 available to be linked against from outside the shared object.
15842 @code{protected} and @code{internal} are pretty useless in real-world
15843 usage so the only other commonly used option will be @code{hidden}.
15844 The default if @option{-fvisibility} isn't specified is
15845 @code{default}, i.e., make every
15846 symbol public---this causes the same behavior as previous versions of
15849 A good explanation of the benefits offered by ensuring ELF
15850 symbols have the correct visibility is given by ``How To Write
15851 Shared Libraries'' by Ulrich Drepper (which can be found at
15852 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
15853 solution made possible by this option to marking things hidden when
15854 the default is public is to make the default hidden and mark things
15855 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
15856 and @code{__attribute__ ((visibility("default")))} instead of
15857 @code{__declspec(dllexport)} you get almost identical semantics with
15858 identical syntax. This is a great boon to those working with
15859 cross-platform projects.
15861 For those adding visibility support to existing code, you may find
15862 @samp{#pragma GCC visibility} of use. This works by you enclosing
15863 the declarations you wish to set visibility for with (for example)
15864 @samp{#pragma GCC visibility push(hidden)} and
15865 @samp{#pragma GCC visibility pop}.
15866 Bear in mind that symbol visibility should be viewed @strong{as
15867 part of the API interface contract} and thus all new code should
15868 always specify visibility when it is not the default ie; declarations
15869 only for use within the local DSO should @strong{always} be marked explicitly
15870 as hidden as so to avoid PLT indirection overheads---making this
15871 abundantly clear also aids readability and self-documentation of the code.
15872 Note that due to ISO C++ specification requirements, operator new and
15873 operator delete must always be of default visibility.
15875 Be aware that headers from outside your project, in particular system
15876 headers and headers from any other library you use, may not be
15877 expecting to be compiled with visibility other than the default. You
15878 may need to explicitly say @samp{#pragma GCC visibility push(default)}
15879 before including any such headers.
15881 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
15882 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
15883 no modifications. However, this means that calls to @samp{extern}
15884 functions with no explicit visibility will use the PLT, so it is more
15885 effective to use @samp{__attribute ((visibility))} and/or
15886 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
15887 declarations should be treated as hidden.
15889 Note that @samp{-fvisibility} does affect C++ vague linkage
15890 entities. This means that, for instance, an exception class that will
15891 be thrown between DSOs must be explicitly marked with default
15892 visibility so that the @samp{type_info} nodes will be unified between
15895 An overview of these techniques, their benefits and how to use them
15896 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
15902 @node Environment Variables
15903 @section Environment Variables Affecting GCC
15904 @cindex environment variables
15906 @c man begin ENVIRONMENT
15907 This section describes several environment variables that affect how GCC
15908 operates. Some of them work by specifying directories or prefixes to use
15909 when searching for various kinds of files. Some are used to specify other
15910 aspects of the compilation environment.
15912 Note that you can also specify places to search using options such as
15913 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
15914 take precedence over places specified using environment variables, which
15915 in turn take precedence over those specified by the configuration of GCC@.
15916 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
15917 GNU Compiler Collection (GCC) Internals}.
15922 @c @itemx LC_COLLATE
15924 @c @itemx LC_MONETARY
15925 @c @itemx LC_NUMERIC
15930 @c @findex LC_COLLATE
15931 @findex LC_MESSAGES
15932 @c @findex LC_MONETARY
15933 @c @findex LC_NUMERIC
15937 These environment variables control the way that GCC uses
15938 localization information that allow GCC to work with different
15939 national conventions. GCC inspects the locale categories
15940 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
15941 so. These locale categories can be set to any value supported by your
15942 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
15943 Kingdom encoded in UTF-8.
15945 The @env{LC_CTYPE} environment variable specifies character
15946 classification. GCC uses it to determine the character boundaries in
15947 a string; this is needed for some multibyte encodings that contain quote
15948 and escape characters that would otherwise be interpreted as a string
15951 The @env{LC_MESSAGES} environment variable specifies the language to
15952 use in diagnostic messages.
15954 If the @env{LC_ALL} environment variable is set, it overrides the value
15955 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
15956 and @env{LC_MESSAGES} default to the value of the @env{LANG}
15957 environment variable. If none of these variables are set, GCC
15958 defaults to traditional C English behavior.
15962 If @env{TMPDIR} is set, it specifies the directory to use for temporary
15963 files. GCC uses temporary files to hold the output of one stage of
15964 compilation which is to be used as input to the next stage: for example,
15965 the output of the preprocessor, which is the input to the compiler
15968 @item GCC_EXEC_PREFIX
15969 @findex GCC_EXEC_PREFIX
15970 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
15971 names of the subprograms executed by the compiler. No slash is added
15972 when this prefix is combined with the name of a subprogram, but you can
15973 specify a prefix that ends with a slash if you wish.
15975 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
15976 an appropriate prefix to use based on the pathname it was invoked with.
15978 If GCC cannot find the subprogram using the specified prefix, it
15979 tries looking in the usual places for the subprogram.
15981 The default value of @env{GCC_EXEC_PREFIX} is
15982 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
15983 the installed compiler. In many cases @var{prefix} is the value
15984 of @code{prefix} when you ran the @file{configure} script.
15986 Other prefixes specified with @option{-B} take precedence over this prefix.
15988 This prefix is also used for finding files such as @file{crt0.o} that are
15991 In addition, the prefix is used in an unusual way in finding the
15992 directories to search for header files. For each of the standard
15993 directories whose name normally begins with @samp{/usr/local/lib/gcc}
15994 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
15995 replacing that beginning with the specified prefix to produce an
15996 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
15997 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
15998 These alternate directories are searched first; the standard directories
15999 come next. If a standard directory begins with the configured
16000 @var{prefix} then the value of @var{prefix} is replaced by
16001 @env{GCC_EXEC_PREFIX} when looking for header files.
16003 @item COMPILER_PATH
16004 @findex COMPILER_PATH
16005 The value of @env{COMPILER_PATH} is a colon-separated list of
16006 directories, much like @env{PATH}. GCC tries the directories thus
16007 specified when searching for subprograms, if it can't find the
16008 subprograms using @env{GCC_EXEC_PREFIX}.
16011 @findex LIBRARY_PATH
16012 The value of @env{LIBRARY_PATH} is a colon-separated list of
16013 directories, much like @env{PATH}. When configured as a native compiler,
16014 GCC tries the directories thus specified when searching for special
16015 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
16016 using GCC also uses these directories when searching for ordinary
16017 libraries for the @option{-l} option (but directories specified with
16018 @option{-L} come first).
16022 @cindex locale definition
16023 This variable is used to pass locale information to the compiler. One way in
16024 which this information is used is to determine the character set to be used
16025 when character literals, string literals and comments are parsed in C and C++.
16026 When the compiler is configured to allow multibyte characters,
16027 the following values for @env{LANG} are recognized:
16031 Recognize JIS characters.
16033 Recognize SJIS characters.
16035 Recognize EUCJP characters.
16038 If @env{LANG} is not defined, or if it has some other value, then the
16039 compiler will use mblen and mbtowc as defined by the default locale to
16040 recognize and translate multibyte characters.
16044 Some additional environments variables affect the behavior of the
16047 @include cppenv.texi
16051 @node Precompiled Headers
16052 @section Using Precompiled Headers
16053 @cindex precompiled headers
16054 @cindex speed of compilation
16056 Often large projects have many header files that are included in every
16057 source file. The time the compiler takes to process these header files
16058 over and over again can account for nearly all of the time required to
16059 build the project. To make builds faster, GCC allows users to
16060 `precompile' a header file; then, if builds can use the precompiled
16061 header file they will be much faster.
16063 To create a precompiled header file, simply compile it as you would any
16064 other file, if necessary using the @option{-x} option to make the driver
16065 treat it as a C or C++ header file. You will probably want to use a
16066 tool like @command{make} to keep the precompiled header up-to-date when
16067 the headers it contains change.
16069 A precompiled header file will be searched for when @code{#include} is
16070 seen in the compilation. As it searches for the included file
16071 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
16072 compiler looks for a precompiled header in each directory just before it
16073 looks for the include file in that directory. The name searched for is
16074 the name specified in the @code{#include} with @samp{.gch} appended. If
16075 the precompiled header file can't be used, it is ignored.
16077 For instance, if you have @code{#include "all.h"}, and you have
16078 @file{all.h.gch} in the same directory as @file{all.h}, then the
16079 precompiled header file will be used if possible, and the original
16080 header will be used otherwise.
16082 Alternatively, you might decide to put the precompiled header file in a
16083 directory and use @option{-I} to ensure that directory is searched
16084 before (or instead of) the directory containing the original header.
16085 Then, if you want to check that the precompiled header file is always
16086 used, you can put a file of the same name as the original header in this
16087 directory containing an @code{#error} command.
16089 This also works with @option{-include}. So yet another way to use
16090 precompiled headers, good for projects not designed with precompiled
16091 header files in mind, is to simply take most of the header files used by
16092 a project, include them from another header file, precompile that header
16093 file, and @option{-include} the precompiled header. If the header files
16094 have guards against multiple inclusion, they will be skipped because
16095 they've already been included (in the precompiled header).
16097 If you need to precompile the same header file for different
16098 languages, targets, or compiler options, you can instead make a
16099 @emph{directory} named like @file{all.h.gch}, and put each precompiled
16100 header in the directory, perhaps using @option{-o}. It doesn't matter
16101 what you call the files in the directory, every precompiled header in
16102 the directory will be considered. The first precompiled header
16103 encountered in the directory that is valid for this compilation will
16104 be used; they're searched in no particular order.
16106 There are many other possibilities, limited only by your imagination,
16107 good sense, and the constraints of your build system.
16109 A precompiled header file can be used only when these conditions apply:
16113 Only one precompiled header can be used in a particular compilation.
16116 A precompiled header can't be used once the first C token is seen. You
16117 can have preprocessor directives before a precompiled header; you can
16118 even include a precompiled header from inside another header, so long as
16119 there are no C tokens before the @code{#include}.
16122 The precompiled header file must be produced for the same language as
16123 the current compilation. You can't use a C precompiled header for a C++
16127 The precompiled header file must have been produced by the same compiler
16128 binary as the current compilation is using.
16131 Any macros defined before the precompiled header is included must
16132 either be defined in the same way as when the precompiled header was
16133 generated, or must not affect the precompiled header, which usually
16134 means that they don't appear in the precompiled header at all.
16136 The @option{-D} option is one way to define a macro before a
16137 precompiled header is included; using a @code{#define} can also do it.
16138 There are also some options that define macros implicitly, like
16139 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
16142 @item If debugging information is output when using the precompiled
16143 header, using @option{-g} or similar, the same kind of debugging information
16144 must have been output when building the precompiled header. However,
16145 a precompiled header built using @option{-g} can be used in a compilation
16146 when no debugging information is being output.
16148 @item The same @option{-m} options must generally be used when building
16149 and using the precompiled header. @xref{Submodel Options},
16150 for any cases where this rule is relaxed.
16152 @item Each of the following options must be the same when building and using
16153 the precompiled header:
16155 @gccoptlist{-fexceptions}
16158 Some other command-line options starting with @option{-f},
16159 @option{-p}, or @option{-O} must be defined in the same way as when
16160 the precompiled header was generated. At present, it's not clear
16161 which options are safe to change and which are not; the safest choice
16162 is to use exactly the same options when generating and using the
16163 precompiled header. The following are known to be safe:
16165 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
16166 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
16167 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
16172 For all of these except the last, the compiler will automatically
16173 ignore the precompiled header if the conditions aren't met. If you
16174 find an option combination that doesn't work and doesn't cause the
16175 precompiled header to be ignored, please consider filing a bug report,
16178 If you do use differing options when generating and using the
16179 precompiled header, the actual behavior will be a mixture of the
16180 behavior for the options. For instance, if you use @option{-g} to
16181 generate the precompiled header but not when using it, you may or may
16182 not get debugging information for routines in the precompiled header.
16184 @node Running Protoize
16185 @section Running Protoize
16187 The program @code{protoize} is an optional part of GCC@. You can use
16188 it to add prototypes to a program, thus converting the program to ISO
16189 C in one respect. The companion program @code{unprotoize} does the
16190 reverse: it removes argument types from any prototypes that are found.
16192 When you run these programs, you must specify a set of source files as
16193 command line arguments. The conversion programs start out by compiling
16194 these files to see what functions they define. The information gathered
16195 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
16197 After scanning comes actual conversion. The specified files are all
16198 eligible to be converted; any files they include (whether sources or
16199 just headers) are eligible as well.
16201 But not all the eligible files are converted. By default,
16202 @code{protoize} and @code{unprotoize} convert only source and header
16203 files in the current directory. You can specify additional directories
16204 whose files should be converted with the @option{-d @var{directory}}
16205 option. You can also specify particular files to exclude with the
16206 @option{-x @var{file}} option. A file is converted if it is eligible, its
16207 directory name matches one of the specified directory names, and its
16208 name within the directory has not been excluded.
16210 Basic conversion with @code{protoize} consists of rewriting most
16211 function definitions and function declarations to specify the types of
16212 the arguments. The only ones not rewritten are those for varargs
16215 @code{protoize} optionally inserts prototype declarations at the
16216 beginning of the source file, to make them available for any calls that
16217 precede the function's definition. Or it can insert prototype
16218 declarations with block scope in the blocks where undeclared functions
16221 Basic conversion with @code{unprotoize} consists of rewriting most
16222 function declarations to remove any argument types, and rewriting
16223 function definitions to the old-style pre-ISO form.
16225 Both conversion programs print a warning for any function declaration or
16226 definition that they can't convert. You can suppress these warnings
16229 The output from @code{protoize} or @code{unprotoize} replaces the
16230 original source file. The original file is renamed to a name ending
16231 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
16232 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
16233 for DOS) file already exists, then the source file is simply discarded.
16235 @code{protoize} and @code{unprotoize} both depend on GCC itself to
16236 scan the program and collect information about the functions it uses.
16237 So neither of these programs will work until GCC is installed.
16239 Here is a table of the options you can use with @code{protoize} and
16240 @code{unprotoize}. Each option works with both programs unless
16244 @item -B @var{directory}
16245 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
16246 usual directory (normally @file{/usr/local/lib}). This file contains
16247 prototype information about standard system functions. This option
16248 applies only to @code{protoize}.
16250 @item -c @var{compilation-options}
16251 Use @var{compilation-options} as the options when running @command{gcc} to
16252 produce the @samp{.X} files. The special option @option{-aux-info} is
16253 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
16255 Note that the compilation options must be given as a single argument to
16256 @code{protoize} or @code{unprotoize}. If you want to specify several
16257 @command{gcc} options, you must quote the entire set of compilation options
16258 to make them a single word in the shell.
16260 There are certain @command{gcc} arguments that you cannot use, because they
16261 would produce the wrong kind of output. These include @option{-g},
16262 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
16263 the @var{compilation-options}, they are ignored.
16266 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
16267 systems) instead of @samp{.c}. This is convenient if you are converting
16268 a C program to C++. This option applies only to @code{protoize}.
16271 Add explicit global declarations. This means inserting explicit
16272 declarations at the beginning of each source file for each function
16273 that is called in the file and was not declared. These declarations
16274 precede the first function definition that contains a call to an
16275 undeclared function. This option applies only to @code{protoize}.
16277 @item -i @var{string}
16278 Indent old-style parameter declarations with the string @var{string}.
16279 This option applies only to @code{protoize}.
16281 @code{unprotoize} converts prototyped function definitions to old-style
16282 function definitions, where the arguments are declared between the
16283 argument list and the initial @samp{@{}. By default, @code{unprotoize}
16284 uses five spaces as the indentation. If you want to indent with just
16285 one space instead, use @option{-i " "}.
16288 Keep the @samp{.X} files. Normally, they are deleted after conversion
16292 Add explicit local declarations. @code{protoize} with @option{-l} inserts
16293 a prototype declaration for each function in each block which calls the
16294 function without any declaration. This option applies only to
16298 Make no real changes. This mode just prints information about the conversions
16299 that would have been done without @option{-n}.
16302 Make no @samp{.save} files. The original files are simply deleted.
16303 Use this option with caution.
16305 @item -p @var{program}
16306 Use the program @var{program} as the compiler. Normally, the name
16307 @file{gcc} is used.
16310 Work quietly. Most warnings are suppressed.
16313 Print the version number, just like @option{-v} for @command{gcc}.
16316 If you need special compiler options to compile one of your program's
16317 source files, then you should generate that file's @samp{.X} file
16318 specially, by running @command{gcc} on that source file with the
16319 appropriate options and the option @option{-aux-info}. Then run
16320 @code{protoize} on the entire set of files. @code{protoize} will use
16321 the existing @samp{.X} file because it is newer than the source file.
16325 gcc -Dfoo=bar file1.c -aux-info file1.X
16330 You need to include the special files along with the rest in the
16331 @code{protoize} command, even though their @samp{.X} files already
16332 exist, because otherwise they won't get converted.
16334 @xref{Protoize Caveats}, for more information on how to use
16335 @code{protoize} successfully.