1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
156 @section Option Summary
158 Here is a summary of all the options, grouped by type. Explanations are
159 in the following sections.
162 @item Overall Options
163 @xref{Overall Options,,Options Controlling the Kind of Output}.
164 @gccoptlist{-c -S -E -o @var{file} -combine -no-canonical-prefixes @gol
165 -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol
167 --version -wrapper@@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg}}
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -fno-pretty-templates @gol
193 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
194 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
195 -fno-default-inline -fvisibility-inlines-hidden @gol
196 -fvisibility-ms-compat @gol
197 -Wabi -Wctor-dtor-privacy @gol
198 -Wnon-virtual-dtor -Wreorder @gol
199 -Weffc++ -Wstrict-null-sentinel @gol
200 -Wno-non-template-friend -Wold-style-cast @gol
201 -Woverloaded-virtual -Wno-pmf-conversions @gol
204 @item Objective-C and Objective-C++ Language Options
205 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
206 Objective-C and Objective-C++ Dialects}.
207 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
208 -fgnu-runtime -fnext-runtime @gol
209 -fno-nil-receivers @gol
210 -fobjc-call-cxx-cdtors @gol
211 -fobjc-direct-dispatch @gol
212 -fobjc-exceptions @gol
214 -freplace-objc-classes @gol
217 -Wassign-intercept @gol
218 -Wno-protocol -Wselector @gol
219 -Wstrict-selector-match @gol
220 -Wundeclared-selector}
222 @item Language Independent Options
223 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
224 @gccoptlist{-fmessage-length=@var{n} @gol
225 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
226 -fdiagnostics-show-option}
228 @item Warning Options
229 @xref{Warning Options,,Options to Request or Suppress Warnings}.
230 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
231 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
232 -Wno-attributes -Wno-builtin-macro-redefined @gol
233 -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
234 -Wchar-subscripts -Wclobbered -Wcomment @gol
235 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
236 -Wno-deprecated-declarations -Wdisabled-optimization @gol
237 -Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol
238 -Werror -Werror=* @gol
239 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
240 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
241 -Wformat-security -Wformat-y2k @gol
242 -Wframe-larger-than=@var{len} -Wjump-misses-init -Wignored-qualifiers @gol
243 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
244 -Winit-self -Winline @gol
245 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
246 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
247 -Wlogical-op -Wlong-long @gol
248 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
249 -Wmissing-format-attribute -Wmissing-include-dirs @gol
250 -Wmissing-noreturn -Wno-mudflap @gol
251 -Wno-multichar -Wnonnull -Wno-overflow @gol
252 -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol
253 -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
254 -Wpointer-arith -Wno-pointer-to-int-cast @gol
255 -Wredundant-decls @gol
256 -Wreturn-type -Wsequence-point -Wshadow @gol
257 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
258 -Wstrict-aliasing -Wstrict-aliasing=n @gol
259 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
260 -Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol
261 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
262 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
263 -Wunsuffixed-float-constants -Wunused -Wunused-function @gol
264 -Wunused-label -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable @gol
265 -Wvariadic-macros -Wvla @gol
266 -Wvolatile-register-var -Wwrite-strings}
268 @item C and Objective-C-only Warning Options
269 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
270 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
271 -Wold-style-declaration -Wold-style-definition @gol
272 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
273 -Wdeclaration-after-statement -Wpointer-sign}
275 @item Debugging Options
276 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
277 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
278 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
279 -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
280 -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
281 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
282 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
283 -fdump-statistics @gol
285 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
289 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
295 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
298 -fdump-tree-nrv -fdump-tree-vect @gol
299 -fdump-tree-sink @gol
300 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
301 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
302 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
303 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
304 -ftree-vectorizer-verbose=@var{n} @gol
305 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
306 -fdump-final-insns=@var{file} @gol
307 -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
308 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
309 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
310 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
311 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
312 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
313 -ftest-coverage -ftime-report -fvar-tracking @gol
314 -fvar-tracking-assigments -fvar-tracking-assignments-toggle @gol
315 -g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol
316 -ggdb -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
317 -gvms -gxcoff -gxcoff+ @gol
318 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
319 -fdebug-prefix-map=@var{old}=@var{new} @gol
320 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
321 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
322 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
323 -print-multi-directory -print-multi-lib @gol
324 -print-prog-name=@var{program} -print-search-dirs -Q @gol
325 -print-sysroot -print-sysroot-headers-suffix @gol
326 -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
328 @item Optimization Options
329 @xref{Optimize Options,,Options that Control Optimization}.
331 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
332 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
333 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
334 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
335 -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping @gol
336 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
337 -fdata-sections -fdce -fdce @gol
338 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
339 -fearly-inlining -fipa-sra -fexpensive-optimizations -ffast-math @gol
340 -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
341 -fforward-propagate -ffunction-sections @gol
342 -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
343 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
344 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
345 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta @gol
346 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
347 -fipa-type-escape -fira-algorithm=@var{algorithm} @gol
348 -fira-region=@var{region} -fira-coalesce -fno-ira-share-save-slots @gol
349 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
350 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
351 -floop-block -floop-interchange -floop-strip-mine -fgraphite-identity @gol
352 -floop-parallelize-all @gol
353 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
354 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
355 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
356 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
357 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
358 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
359 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
360 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
361 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
362 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
363 -fprofile-generate=@var{path} @gol
364 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
365 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
366 -freorder-blocks-and-partition -freorder-functions @gol
367 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
368 -frounding-math -fsched2-use-superblocks @gol
369 -fsched2-use-traces -fsched-pressure @gol
370 -fsched-spec-load -fsched-spec-load-dangerous @gol
371 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
372 -fsched-group-heuristic -fsched-critical-path-heuristic @gol
373 -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
374 -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
375 -fschedule-insns -fschedule-insns2 -fsection-anchors @gol
376 -fselective-scheduling -fselective-scheduling2 @gol
377 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
378 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
379 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
380 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
381 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
382 -ftree-copyrename -ftree-dce @gol
383 -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-loop-im @gol
384 -ftree-phiprop -ftree-loop-distribution @gol
385 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
386 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-pta -ftree-reassoc @gol
387 -ftree-sink -ftree-sra -ftree-switch-conversion @gol
388 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
389 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
390 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
391 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
393 --param @var{name}=@var{value}
394 -O -O0 -O1 -O2 -O3 -Os}
396 @item Preprocessor Options
397 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
398 @gccoptlist{-A@var{question}=@var{answer} @gol
399 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
400 -C -dD -dI -dM -dN @gol
401 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
402 -idirafter @var{dir} @gol
403 -include @var{file} -imacros @var{file} @gol
404 -iprefix @var{file} -iwithprefix @var{dir} @gol
405 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
406 -imultilib @var{dir} -isysroot @var{dir} @gol
407 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
408 -P -fworking-directory -remap @gol
409 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
410 -Xpreprocessor @var{option}}
412 @item Assembler Option
413 @xref{Assembler Options,,Passing Options to the Assembler}.
414 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
417 @xref{Link Options,,Options for Linking}.
418 @gccoptlist{@var{object-file-name} -l@var{library} @gol
419 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
420 -s -static -static-libgcc -static-libstdc++ -shared @gol
421 -shared-libgcc -symbolic @gol
422 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
425 @item Directory Options
426 @xref{Directory Options,,Options for Directory Search}.
427 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
428 -specs=@var{file} -I- --sysroot=@var{dir}}
431 @c I wrote this xref this way to avoid overfull hbox. -- rms
432 @xref{Target Options}.
433 @gccoptlist{-V @var{version} -b @var{machine}}
435 @item Machine Dependent Options
436 @xref{Submodel Options,,Hardware Models and Configurations}.
437 @c This list is ordered alphanumerically by subsection name.
438 @c Try and put the significant identifier (CPU or system) first,
439 @c so users have a clue at guessing where the ones they want will be.
442 @gccoptlist{-EB -EL @gol
443 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
444 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
447 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
448 -mabi=@var{name} @gol
449 -mapcs-stack-check -mno-apcs-stack-check @gol
450 -mapcs-float -mno-apcs-float @gol
451 -mapcs-reentrant -mno-apcs-reentrant @gol
452 -msched-prolog -mno-sched-prolog @gol
453 -mlittle-endian -mbig-endian -mwords-little-endian @gol
454 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
455 -mfp16-format=@var{name}
456 -mthumb-interwork -mno-thumb-interwork @gol
457 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
458 -mstructure-size-boundary=@var{n} @gol
459 -mabort-on-noreturn @gol
460 -mlong-calls -mno-long-calls @gol
461 -msingle-pic-base -mno-single-pic-base @gol
462 -mpic-register=@var{reg} @gol
463 -mnop-fun-dllimport @gol
464 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
465 -mpoke-function-name @gol
467 -mtpcs-frame -mtpcs-leaf-frame @gol
468 -mcaller-super-interworking -mcallee-super-interworking @gol
470 -mword-relocations @gol
471 -mfix-cortex-m3-ldrd}
474 @gccoptlist{-mmcu=@var{mcu} -msize -mno-interrupts @gol
475 -mcall-prologues -mtiny-stack -mint8}
477 @emph{Blackfin Options}
478 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
479 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
480 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
481 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
482 -mno-id-shared-library -mshared-library-id=@var{n} @gol
483 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
484 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
485 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
489 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
490 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
491 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
492 -mstack-align -mdata-align -mconst-align @gol
493 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
494 -melf -maout -melinux -mlinux -sim -sim2 @gol
495 -mmul-bug-workaround -mno-mul-bug-workaround}
498 @gccoptlist{-mmac -mpush-args}
500 @emph{Darwin Options}
501 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
502 -arch_only -bind_at_load -bundle -bundle_loader @gol
503 -client_name -compatibility_version -current_version @gol
505 -dependency-file -dylib_file -dylinker_install_name @gol
506 -dynamic -dynamiclib -exported_symbols_list @gol
507 -filelist -flat_namespace -force_cpusubtype_ALL @gol
508 -force_flat_namespace -headerpad_max_install_names @gol
510 -image_base -init -install_name -keep_private_externs @gol
511 -multi_module -multiply_defined -multiply_defined_unused @gol
512 -noall_load -no_dead_strip_inits_and_terms @gol
513 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
514 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
515 -private_bundle -read_only_relocs -sectalign @gol
516 -sectobjectsymbols -whyload -seg1addr @gol
517 -sectcreate -sectobjectsymbols -sectorder @gol
518 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
519 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
520 -segprot -segs_read_only_addr -segs_read_write_addr @gol
521 -single_module -static -sub_library -sub_umbrella @gol
522 -twolevel_namespace -umbrella -undefined @gol
523 -unexported_symbols_list -weak_reference_mismatches @gol
524 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
525 -mkernel -mone-byte-bool}
527 @emph{DEC Alpha Options}
528 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
529 -mieee -mieee-with-inexact -mieee-conformant @gol
530 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
531 -mtrap-precision=@var{mode} -mbuild-constants @gol
532 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
533 -mbwx -mmax -mfix -mcix @gol
534 -mfloat-vax -mfloat-ieee @gol
535 -mexplicit-relocs -msmall-data -mlarge-data @gol
536 -msmall-text -mlarge-text @gol
537 -mmemory-latency=@var{time}}
539 @emph{DEC Alpha/VMS Options}
540 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
543 @gccoptlist{-msmall-model -mno-lsim}
546 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
547 -mhard-float -msoft-float @gol
548 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
549 -mdouble -mno-double @gol
550 -mmedia -mno-media -mmuladd -mno-muladd @gol
551 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
552 -mlinked-fp -mlong-calls -malign-labels @gol
553 -mlibrary-pic -macc-4 -macc-8 @gol
554 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
555 -moptimize-membar -mno-optimize-membar @gol
556 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
557 -mvliw-branch -mno-vliw-branch @gol
558 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
559 -mno-nested-cond-exec -mtomcat-stats @gol
563 @emph{GNU/Linux Options}
564 @gccoptlist{-muclibc}
566 @emph{H8/300 Options}
567 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
570 @gccoptlist{-march=@var{architecture-type} @gol
571 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
572 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
573 -mfixed-range=@var{register-range} @gol
574 -mjump-in-delay -mlinker-opt -mlong-calls @gol
575 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
576 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
577 -mno-jump-in-delay -mno-long-load-store @gol
578 -mno-portable-runtime -mno-soft-float @gol
579 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
580 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
581 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
582 -munix=@var{unix-std} -nolibdld -static -threads}
584 @emph{i386 and x86-64 Options}
585 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
586 -mfpmath=@var{unit} @gol
587 -masm=@var{dialect} -mno-fancy-math-387 @gol
588 -mno-fp-ret-in-387 -msoft-float @gol
589 -mno-wide-multiply -mrtd -malign-double @gol
590 -mpreferred-stack-boundary=@var{num}
591 -mincoming-stack-boundary=@var{num}
592 -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip @gol
593 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
595 -msse4a -m3dnow -mpopcnt -mabm -mfma4 @gol
596 -mthreads -mno-align-stringops -minline-all-stringops @gol
597 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
598 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
599 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
600 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
601 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
602 -mcmodel=@var{code-model} -mabi=@var{name} @gol
603 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
607 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
608 -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
609 -mconstant-gp -mauto-pic -mfused-madd @gol
610 -minline-float-divide-min-latency @gol
611 -minline-float-divide-max-throughput @gol
612 -mno-inline-float-divide @gol
613 -minline-int-divide-min-latency @gol
614 -minline-int-divide-max-throughput @gol
615 -mno-inline-int-divide @gol
616 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
617 -mno-inline-sqrt @gol
618 -mdwarf2-asm -mearly-stop-bits @gol
619 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
620 -mtune=@var{cpu-type} -milp32 -mlp64 @gol
621 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
622 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
623 -msched-spec-ldc -msched-spec-control-ldc @gol
624 -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
625 -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
626 -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
627 -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
629 @emph{IA-64/VMS Options}
630 @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64}
632 @emph{M32R/D Options}
633 @gccoptlist{-m32r2 -m32rx -m32r @gol
635 -malign-loops -mno-align-loops @gol
636 -missue-rate=@var{number} @gol
637 -mbranch-cost=@var{number} @gol
638 -mmodel=@var{code-size-model-type} @gol
639 -msdata=@var{sdata-type} @gol
640 -mno-flush-func -mflush-func=@var{name} @gol
641 -mno-flush-trap -mflush-trap=@var{number} @gol
645 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
647 @emph{M680x0 Options}
648 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
649 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
650 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
651 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
652 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
653 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
654 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
655 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
658 @emph{M68hc1x Options}
659 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
660 -mauto-incdec -minmax -mlong-calls -mshort @gol
661 -msoft-reg-count=@var{count}}
664 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
665 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
666 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
667 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
668 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
671 @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
672 -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
673 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
674 -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
678 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
679 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
680 -mips64 -mips64r2 @gol
681 -mips16 -mno-mips16 -mflip-mips16 @gol
682 -minterlink-mips16 -mno-interlink-mips16 @gol
683 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
684 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
685 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
686 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
687 -mfpu=@var{fpu-type} @gol
688 -msmartmips -mno-smartmips @gol
689 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
690 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
691 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
692 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
693 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
694 -membedded-data -mno-embedded-data @gol
695 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
696 -mcode-readable=@var{setting} @gol
697 -msplit-addresses -mno-split-addresses @gol
698 -mexplicit-relocs -mno-explicit-relocs @gol
699 -mcheck-zero-division -mno-check-zero-division @gol
700 -mdivide-traps -mdivide-breaks @gol
701 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
702 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
703 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
704 -mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol
705 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
706 -mflush-func=@var{func} -mno-flush-func @gol
707 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
708 -mfp-exceptions -mno-fp-exceptions @gol
709 -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
710 -mrelax-pic-calls -mno-relax-pic-calls}
713 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
714 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
715 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
716 -mno-base-addresses -msingle-exit -mno-single-exit}
718 @emph{MN10300 Options}
719 @gccoptlist{-mmult-bug -mno-mult-bug @gol
720 -mam33 -mno-am33 @gol
721 -mam33-2 -mno-am33-2 @gol
722 -mreturn-pointer-on-d0 @gol
725 @emph{PDP-11 Options}
726 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
727 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
728 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
729 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
730 -mbranch-expensive -mbranch-cheap @gol
731 -msplit -mno-split -munix-asm -mdec-asm}
733 @emph{picoChip Options}
734 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N}
735 -msymbol-as-address -mno-inefficient-warnings}
737 @emph{PowerPC Options}
738 See RS/6000 and PowerPC Options.
740 @emph{RS/6000 and PowerPC Options}
741 @gccoptlist{-mcpu=@var{cpu-type} @gol
742 -mtune=@var{cpu-type} @gol
743 -mpower -mno-power -mpower2 -mno-power2 @gol
744 -mpowerpc -mpowerpc64 -mno-powerpc @gol
745 -maltivec -mno-altivec @gol
746 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
747 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
748 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
749 -mfprnd -mno-fprnd @gol
750 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
751 -mnew-mnemonics -mold-mnemonics @gol
752 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
753 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
754 -malign-power -malign-natural @gol
755 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
756 -msingle-float -mdouble-float -msimple-fpu @gol
757 -mstring -mno-string -mupdate -mno-update @gol
758 -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
759 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
760 -mstrict-align -mno-strict-align -mrelocatable @gol
761 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
762 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
763 -mdynamic-no-pic -maltivec -mswdiv @gol
764 -mprioritize-restricted-insns=@var{priority} @gol
765 -msched-costly-dep=@var{dependence_type} @gol
766 -minsert-sched-nops=@var{scheme} @gol
767 -mcall-sysv -mcall-netbsd @gol
768 -maix-struct-return -msvr4-struct-return @gol
769 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
770 -misel -mno-isel @gol
771 -misel=yes -misel=no @gol
773 -mspe=yes -mspe=no @gol
775 -mgen-cell-microcode -mwarn-cell-microcode @gol
776 -mvrsave -mno-vrsave @gol
777 -mmulhw -mno-mulhw @gol
778 -mdlmzb -mno-dlmzb @gol
779 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
780 -mprototype -mno-prototype @gol
781 -msim -mmvme -mads -myellowknife -memb -msdata @gol
782 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
784 @emph{S/390 and zSeries Options}
785 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
786 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
787 -mlong-double-64 -mlong-double-128 @gol
788 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
789 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
790 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
791 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
792 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
795 @gccoptlist{-meb -mel @gol
799 -mscore5 -mscore5u -mscore7 -mscore7d}
802 @gccoptlist{-m1 -m2 -m2e @gol
803 -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
805 -m4-nofpu -m4-single-only -m4-single -m4 @gol
806 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
807 -m5-64media -m5-64media-nofpu @gol
808 -m5-32media -m5-32media-nofpu @gol
809 -m5-compact -m5-compact-nofpu @gol
810 -mb -ml -mdalign -mrelax @gol
811 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
812 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
813 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
814 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
815 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
819 @gccoptlist{-mcpu=@var{cpu-type} @gol
820 -mtune=@var{cpu-type} @gol
821 -mcmodel=@var{code-model} @gol
822 -m32 -m64 -mapp-regs -mno-app-regs @gol
823 -mfaster-structs -mno-faster-structs @gol
824 -mfpu -mno-fpu -mhard-float -msoft-float @gol
825 -mhard-quad-float -msoft-quad-float @gol
826 -mimpure-text -mno-impure-text -mlittle-endian @gol
827 -mstack-bias -mno-stack-bias @gol
828 -munaligned-doubles -mno-unaligned-doubles @gol
829 -mv8plus -mno-v8plus -mvis -mno-vis
830 -threads -pthreads -pthread}
833 @gccoptlist{-mwarn-reloc -merror-reloc @gol
834 -msafe-dma -munsafe-dma @gol
836 -msmall-mem -mlarge-mem -mstdmain @gol
837 -mfixed-range=@var{register-range}}
839 @emph{System V Options}
840 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
843 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
844 -mprolog-function -mno-prolog-function -mspace @gol
845 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
846 -mapp-regs -mno-app-regs @gol
847 -mdisable-callt -mno-disable-callt @gol
853 @gccoptlist{-mg -mgnu -munix}
855 @emph{VxWorks Options}
856 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
857 -Xbind-lazy -Xbind-now}
859 @emph{x86-64 Options}
860 See i386 and x86-64 Options.
862 @emph{i386 and x86-64 Windows Options}
863 @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll
864 -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows}
866 @emph{Xstormy16 Options}
869 @emph{Xtensa Options}
870 @gccoptlist{-mconst16 -mno-const16 @gol
871 -mfused-madd -mno-fused-madd @gol
872 -mserialize-volatile -mno-serialize-volatile @gol
873 -mtext-section-literals -mno-text-section-literals @gol
874 -mtarget-align -mno-target-align @gol
875 -mlongcalls -mno-longcalls}
877 @emph{zSeries Options}
878 See S/390 and zSeries Options.
880 @item Code Generation Options
881 @xref{Code Gen Options,,Options for Code Generation Conventions}.
882 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
883 -ffixed-@var{reg} -fexceptions @gol
884 -fnon-call-exceptions -funwind-tables @gol
885 -fasynchronous-unwind-tables @gol
886 -finhibit-size-directive -finstrument-functions @gol
887 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
888 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
889 -fno-common -fno-ident @gol
890 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
891 -fno-jump-tables @gol
892 -frecord-gcc-switches @gol
893 -freg-struct-return -fshort-enums @gol
894 -fshort-double -fshort-wchar @gol
895 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
896 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
897 -fno-stack-limit -fargument-alias -fargument-noalias @gol
898 -fargument-noalias-global -fargument-noalias-anything @gol
899 -fleading-underscore -ftls-model=@var{model} @gol
900 -ftrapv -fwrapv -fbounds-check @gol
905 * Overall Options:: Controlling the kind of output:
906 an executable, object files, assembler files,
907 or preprocessed source.
908 * C Dialect Options:: Controlling the variant of C language compiled.
909 * C++ Dialect Options:: Variations on C++.
910 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
912 * Language Independent Options:: Controlling how diagnostics should be
914 * Warning Options:: How picky should the compiler be?
915 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
916 * Optimize Options:: How much optimization?
917 * Preprocessor Options:: Controlling header files and macro definitions.
918 Also, getting dependency information for Make.
919 * Assembler Options:: Passing options to the assembler.
920 * Link Options:: Specifying libraries and so on.
921 * Directory Options:: Where to find header files and libraries.
922 Where to find the compiler executable files.
923 * Spec Files:: How to pass switches to sub-processes.
924 * Target Options:: Running a cross-compiler, or an old version of GCC.
927 @node Overall Options
928 @section Options Controlling the Kind of Output
930 Compilation can involve up to four stages: preprocessing, compilation
931 proper, assembly and linking, always in that order. GCC is capable of
932 preprocessing and compiling several files either into several
933 assembler input files, or into one assembler input file; then each
934 assembler input file produces an object file, and linking combines all
935 the object files (those newly compiled, and those specified as input)
936 into an executable file.
938 @cindex file name suffix
939 For any given input file, the file name suffix determines what kind of
944 C source code which must be preprocessed.
947 C source code which should not be preprocessed.
950 C++ source code which should not be preprocessed.
953 Objective-C source code. Note that you must link with the @file{libobjc}
954 library to make an Objective-C program work.
957 Objective-C source code which should not be preprocessed.
961 Objective-C++ source code. Note that you must link with the @file{libobjc}
962 library to make an Objective-C++ program work. Note that @samp{.M} refers
963 to a literal capital M@.
966 Objective-C++ source code which should not be preprocessed.
969 C, C++, Objective-C or Objective-C++ header file to be turned into a
974 @itemx @var{file}.cxx
975 @itemx @var{file}.cpp
976 @itemx @var{file}.CPP
977 @itemx @var{file}.c++
979 C++ source code which must be preprocessed. Note that in @samp{.cxx},
980 the last two letters must both be literally @samp{x}. Likewise,
981 @samp{.C} refers to a literal capital C@.
985 Objective-C++ source code which must be preprocessed.
988 Objective-C++ source code which should not be preprocessed.
993 @itemx @var{file}.hxx
994 @itemx @var{file}.hpp
995 @itemx @var{file}.HPP
996 @itemx @var{file}.h++
997 @itemx @var{file}.tcc
998 C++ header file to be turned into a precompiled header.
1001 @itemx @var{file}.for
1002 @itemx @var{file}.ftn
1003 Fixed form Fortran source code which should not be preprocessed.
1006 @itemx @var{file}.FOR
1007 @itemx @var{file}.fpp
1008 @itemx @var{file}.FPP
1009 @itemx @var{file}.FTN
1010 Fixed form Fortran source code which must be preprocessed (with the traditional
1013 @item @var{file}.f90
1014 @itemx @var{file}.f95
1015 @itemx @var{file}.f03
1016 @itemx @var{file}.f08
1017 Free form Fortran source code which should not be preprocessed.
1019 @item @var{file}.F90
1020 @itemx @var{file}.F95
1021 @itemx @var{file}.F03
1022 @itemx @var{file}.F08
1023 Free form Fortran source code which must be preprocessed (with the
1024 traditional preprocessor).
1026 @c FIXME: Descriptions of Java file types.
1032 @item @var{file}.ads
1033 Ada source code file which contains a library unit declaration (a
1034 declaration of a package, subprogram, or generic, or a generic
1035 instantiation), or a library unit renaming declaration (a package,
1036 generic, or subprogram renaming declaration). Such files are also
1039 @item @var{file}.adb
1040 Ada source code file containing a library unit body (a subprogram or
1041 package body). Such files are also called @dfn{bodies}.
1043 @c GCC also knows about some suffixes for languages not yet included:
1054 @itemx @var{file}.sx
1055 Assembler code which must be preprocessed.
1058 An object file to be fed straight into linking.
1059 Any file name with no recognized suffix is treated this way.
1063 You can specify the input language explicitly with the @option{-x} option:
1066 @item -x @var{language}
1067 Specify explicitly the @var{language} for the following input files
1068 (rather than letting the compiler choose a default based on the file
1069 name suffix). This option applies to all following input files until
1070 the next @option{-x} option. Possible values for @var{language} are:
1072 c c-header c-cpp-output
1073 c++ c++-header c++-cpp-output
1074 objective-c objective-c-header objective-c-cpp-output
1075 objective-c++ objective-c++-header objective-c++-cpp-output
1076 assembler assembler-with-cpp
1078 f77 f77-cpp-input f95 f95-cpp-input
1083 Turn off any specification of a language, so that subsequent files are
1084 handled according to their file name suffixes (as they are if @option{-x}
1085 has not been used at all).
1087 @item -pass-exit-codes
1088 @opindex pass-exit-codes
1089 Normally the @command{gcc} program will exit with the code of 1 if any
1090 phase of the compiler returns a non-success return code. If you specify
1091 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1092 numerically highest error produced by any phase that returned an error
1093 indication. The C, C++, and Fortran frontends return 4, if an internal
1094 compiler error is encountered.
1097 If you only want some of the stages of compilation, you can use
1098 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1099 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1100 @command{gcc} is to stop. Note that some combinations (for example,
1101 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1106 Compile or assemble the source files, but do not link. The linking
1107 stage simply is not done. The ultimate output is in the form of an
1108 object file for each source file.
1110 By default, the object file name for a source file is made by replacing
1111 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1113 Unrecognized input files, not requiring compilation or assembly, are
1118 Stop after the stage of compilation proper; do not assemble. The output
1119 is in the form of an assembler code file for each non-assembler input
1122 By default, the assembler file name for a source file is made by
1123 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1125 Input files that don't require compilation are ignored.
1129 Stop after the preprocessing stage; do not run the compiler proper. The
1130 output is in the form of preprocessed source code, which is sent to the
1133 Input files which don't require preprocessing are ignored.
1135 @cindex output file option
1138 Place output in file @var{file}. This applies regardless to whatever
1139 sort of output is being produced, whether it be an executable file,
1140 an object file, an assembler file or preprocessed C code.
1142 If @option{-o} is not specified, the default is to put an executable
1143 file in @file{a.out}, the object file for
1144 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1145 assembler file in @file{@var{source}.s}, a precompiled header file in
1146 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1151 Print (on standard error output) the commands executed to run the stages
1152 of compilation. Also print the version number of the compiler driver
1153 program and of the preprocessor and the compiler proper.
1157 Like @option{-v} except the commands are not executed and all command
1158 arguments are quoted. This is useful for shell scripts to capture the
1159 driver-generated command lines.
1163 Use pipes rather than temporary files for communication between the
1164 various stages of compilation. This fails to work on some systems where
1165 the assembler is unable to read from a pipe; but the GNU assembler has
1170 If you are compiling multiple source files, this option tells the driver
1171 to pass all the source files to the compiler at once (for those
1172 languages for which the compiler can handle this). This will allow
1173 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1174 language for which this is supported is C@. If you pass source files for
1175 multiple languages to the driver, using this option, the driver will invoke
1176 the compiler(s) that support IMA once each, passing each compiler all the
1177 source files appropriate for it. For those languages that do not support
1178 IMA this option will be ignored, and the compiler will be invoked once for
1179 each source file in that language. If you use this option in conjunction
1180 with @option{-save-temps}, the compiler will generate multiple
1182 (one for each source file), but only one (combined) @file{.o} or
1187 Print (on the standard output) a description of the command line options
1188 understood by @command{gcc}. If the @option{-v} option is also specified
1189 then @option{--help} will also be passed on to the various processes
1190 invoked by @command{gcc}, so that they can display the command line options
1191 they accept. If the @option{-Wextra} option has also been specified
1192 (prior to the @option{--help} option), then command line options which
1193 have no documentation associated with them will also be displayed.
1196 @opindex target-help
1197 Print (on the standard output) a description of target-specific command
1198 line options for each tool. For some targets extra target-specific
1199 information may also be printed.
1201 @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
1202 Print (on the standard output) a description of the command line
1203 options understood by the compiler that fit into all specified classes
1204 and qualifiers. These are the supported classes:
1207 @item @samp{optimizers}
1208 This will display all of the optimization options supported by the
1211 @item @samp{warnings}
1212 This will display all of the options controlling warning messages
1213 produced by the compiler.
1216 This will display target-specific options. Unlike the
1217 @option{--target-help} option however, target-specific options of the
1218 linker and assembler will not be displayed. This is because those
1219 tools do not currently support the extended @option{--help=} syntax.
1222 This will display the values recognized by the @option{--param}
1225 @item @var{language}
1226 This will display the options supported for @var{language}, where
1227 @var{language} is the name of one of the languages supported in this
1231 This will display the options that are common to all languages.
1234 These are the supported qualifiers:
1237 @item @samp{undocumented}
1238 Display only those options which are undocumented.
1241 Display options which take an argument that appears after an equal
1242 sign in the same continuous piece of text, such as:
1243 @samp{--help=target}.
1245 @item @samp{separate}
1246 Display options which take an argument that appears as a separate word
1247 following the original option, such as: @samp{-o output-file}.
1250 Thus for example to display all the undocumented target-specific
1251 switches supported by the compiler the following can be used:
1254 --help=target,undocumented
1257 The sense of a qualifier can be inverted by prefixing it with the
1258 @samp{^} character, so for example to display all binary warning
1259 options (i.e., ones that are either on or off and that do not take an
1260 argument), which have a description the following can be used:
1263 --help=warnings,^joined,^undocumented
1266 The argument to @option{--help=} should not consist solely of inverted
1269 Combining several classes is possible, although this usually
1270 restricts the output by so much that there is nothing to display. One
1271 case where it does work however is when one of the classes is
1272 @var{target}. So for example to display all the target-specific
1273 optimization options the following can be used:
1276 --help=target,optimizers
1279 The @option{--help=} option can be repeated on the command line. Each
1280 successive use will display its requested class of options, skipping
1281 those that have already been displayed.
1283 If the @option{-Q} option appears on the command line before the
1284 @option{--help=} option, then the descriptive text displayed by
1285 @option{--help=} is changed. Instead of describing the displayed
1286 options, an indication is given as to whether the option is enabled,
1287 disabled or set to a specific value (assuming that the compiler
1288 knows this at the point where the @option{--help=} option is used).
1290 Here is a truncated example from the ARM port of @command{gcc}:
1293 % gcc -Q -mabi=2 --help=target -c
1294 The following options are target specific:
1296 -mabort-on-noreturn [disabled]
1300 The output is sensitive to the effects of previous command line
1301 options, so for example it is possible to find out which optimizations
1302 are enabled at @option{-O2} by using:
1305 -Q -O2 --help=optimizers
1308 Alternatively you can discover which binary optimizations are enabled
1309 by @option{-O3} by using:
1312 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1313 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1314 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1317 @item -no-canonical-prefixes
1318 @opindex no-canonical-prefixes
1319 Do not expand any symbolic links, resolve references to @samp{/../}
1320 or @samp{/./}, or make the path absolute when generating a relative
1325 Display the version number and copyrights of the invoked GCC@.
1329 Invoke all subcommands under a wrapper program. It takes a single
1330 comma separated list as an argument, which will be used to invoke
1334 gcc -c t.c -wrapper gdb,--args
1337 This will invoke all subprograms of gcc under "gdb --args",
1338 thus cc1 invocation will be "gdb --args cc1 ...".
1340 @item -fplugin=@var{name}.so
1341 Load the plugin code in file @var{name}.so, assumed to be a
1342 shared object to be dlopen'd by the compiler. The base name of
1343 the shared object file is used to identify the plugin for the
1344 purposes of argument parsing (See
1345 @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
1346 Each plugin should define the callback functions specified in the
1349 @item -fplugin-arg-@var{name}-@var{key}=@var{value}
1350 Define an argument called @var{key} with a value of @var{value}
1351 for the plugin called @var{name}.
1353 @include @value{srcdir}/../libiberty/at-file.texi
1357 @section Compiling C++ Programs
1359 @cindex suffixes for C++ source
1360 @cindex C++ source file suffixes
1361 C++ source files conventionally use one of the suffixes @samp{.C},
1362 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1363 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1364 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1365 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1366 files with these names and compiles them as C++ programs even if you
1367 call the compiler the same way as for compiling C programs (usually
1368 with the name @command{gcc}).
1372 However, the use of @command{gcc} does not add the C++ library.
1373 @command{g++} is a program that calls GCC and treats @samp{.c},
1374 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1375 files unless @option{-x} is used, and automatically specifies linking
1376 against the C++ library. This program is also useful when
1377 precompiling a C header file with a @samp{.h} extension for use in C++
1378 compilations. On many systems, @command{g++} is also installed with
1379 the name @command{c++}.
1381 @cindex invoking @command{g++}
1382 When you compile C++ programs, you may specify many of the same
1383 command-line options that you use for compiling programs in any
1384 language; or command-line options meaningful for C and related
1385 languages; or options that are meaningful only for C++ programs.
1386 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1387 explanations of options for languages related to C@.
1388 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1389 explanations of options that are meaningful only for C++ programs.
1391 @node C Dialect Options
1392 @section Options Controlling C Dialect
1393 @cindex dialect options
1394 @cindex language dialect options
1395 @cindex options, dialect
1397 The following options control the dialect of C (or languages derived
1398 from C, such as C++, Objective-C and Objective-C++) that the compiler
1402 @cindex ANSI support
1406 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1407 equivalent to @samp{-std=c++98}.
1409 This turns off certain features of GCC that are incompatible with ISO
1410 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1411 such as the @code{asm} and @code{typeof} keywords, and
1412 predefined macros such as @code{unix} and @code{vax} that identify the
1413 type of system you are using. It also enables the undesirable and
1414 rarely used ISO trigraph feature. For the C compiler,
1415 it disables recognition of C++ style @samp{//} comments as well as
1416 the @code{inline} keyword.
1418 The alternate keywords @code{__asm__}, @code{__extension__},
1419 @code{__inline__} and @code{__typeof__} continue to work despite
1420 @option{-ansi}. You would not want to use them in an ISO C program, of
1421 course, but it is useful to put them in header files that might be included
1422 in compilations done with @option{-ansi}. Alternate predefined macros
1423 such as @code{__unix__} and @code{__vax__} are also available, with or
1424 without @option{-ansi}.
1426 The @option{-ansi} option does not cause non-ISO programs to be
1427 rejected gratuitously. For that, @option{-pedantic} is required in
1428 addition to @option{-ansi}. @xref{Warning Options}.
1430 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1431 option is used. Some header files may notice this macro and refrain
1432 from declaring certain functions or defining certain macros that the
1433 ISO standard doesn't call for; this is to avoid interfering with any
1434 programs that might use these names for other things.
1436 Functions that would normally be built in but do not have semantics
1437 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1438 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1439 built-in functions provided by GCC}, for details of the functions
1444 Determine the language standard. @xref{Standards,,Language Standards
1445 Supported by GCC}, for details of these standard versions. This option
1446 is currently only supported when compiling C or C++.
1448 The compiler can accept several base standards, such as @samp{c89} or
1449 @samp{c++98}, and GNU dialects of those standards, such as
1450 @samp{gnu89} or @samp{gnu++98}. By specifying a base standard, the
1451 compiler will accept all programs following that standard and those
1452 using GNU extensions that do not contradict it. For example,
1453 @samp{-std=c89} turns off certain features of GCC that are
1454 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1455 keywords, but not other GNU extensions that do not have a meaning in
1456 ISO C90, such as omitting the middle term of a @code{?:}
1457 expression. On the other hand, by specifying a GNU dialect of a
1458 standard, all features the compiler support are enabled, even when
1459 those features change the meaning of the base standard and some
1460 strict-conforming programs may be rejected. The particular standard
1461 is used by @option{-pedantic} to identify which features are GNU
1462 extensions given that version of the standard. For example
1463 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1464 comments, while @samp{-std=gnu99 -pedantic} would not.
1466 A value for this option must be provided; possible values are
1471 Support all ISO C90 programs (certain GNU extensions that conflict
1472 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1474 @item iso9899:199409
1475 ISO C90 as modified in amendment 1.
1481 ISO C99. Note that this standard is not yet fully supported; see
1482 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1483 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1486 GNU dialect of ISO C90 (including some C99 features). This
1487 is the default for C code.
1491 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1492 this will become the default. The name @samp{gnu9x} is deprecated.
1495 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1499 GNU dialect of @option{-std=c++98}. This is the default for
1503 The working draft of the upcoming ISO C++0x standard. This option
1504 enables experimental features that are likely to be included in
1505 C++0x. The working draft is constantly changing, and any feature that is
1506 enabled by this flag may be removed from future versions of GCC if it is
1507 not part of the C++0x standard.
1510 GNU dialect of @option{-std=c++0x}. This option enables
1511 experimental features that may be removed in future versions of GCC.
1514 @item -fgnu89-inline
1515 @opindex fgnu89-inline
1516 The option @option{-fgnu89-inline} tells GCC to use the traditional
1517 GNU semantics for @code{inline} functions when in C99 mode.
1518 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1519 is accepted and ignored by GCC versions 4.1.3 up to but not including
1520 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1521 C99 mode. Using this option is roughly equivalent to adding the
1522 @code{gnu_inline} function attribute to all inline functions
1523 (@pxref{Function Attributes}).
1525 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1526 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1527 specifies the default behavior). This option was first supported in
1528 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1530 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1531 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1532 in effect for @code{inline} functions. @xref{Common Predefined
1533 Macros,,,cpp,The C Preprocessor}.
1535 @item -aux-info @var{filename}
1537 Output to the given filename prototyped declarations for all functions
1538 declared and/or defined in a translation unit, including those in header
1539 files. This option is silently ignored in any language other than C@.
1541 Besides declarations, the file indicates, in comments, the origin of
1542 each declaration (source file and line), whether the declaration was
1543 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1544 @samp{O} for old, respectively, in the first character after the line
1545 number and the colon), and whether it came from a declaration or a
1546 definition (@samp{C} or @samp{F}, respectively, in the following
1547 character). In the case of function definitions, a K&R-style list of
1548 arguments followed by their declarations is also provided, inside
1549 comments, after the declaration.
1553 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1554 keyword, so that code can use these words as identifiers. You can use
1555 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1556 instead. @option{-ansi} implies @option{-fno-asm}.
1558 In C++, this switch only affects the @code{typeof} keyword, since
1559 @code{asm} and @code{inline} are standard keywords. You may want to
1560 use the @option{-fno-gnu-keywords} flag instead, which has the same
1561 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1562 switch only affects the @code{asm} and @code{typeof} keywords, since
1563 @code{inline} is a standard keyword in ISO C99.
1566 @itemx -fno-builtin-@var{function}
1567 @opindex fno-builtin
1568 @cindex built-in functions
1569 Don't recognize built-in functions that do not begin with
1570 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1571 functions provided by GCC}, for details of the functions affected,
1572 including those which are not built-in functions when @option{-ansi} or
1573 @option{-std} options for strict ISO C conformance are used because they
1574 do not have an ISO standard meaning.
1576 GCC normally generates special code to handle certain built-in functions
1577 more efficiently; for instance, calls to @code{alloca} may become single
1578 instructions that adjust the stack directly, and calls to @code{memcpy}
1579 may become inline copy loops. The resulting code is often both smaller
1580 and faster, but since the function calls no longer appear as such, you
1581 cannot set a breakpoint on those calls, nor can you change the behavior
1582 of the functions by linking with a different library. In addition,
1583 when a function is recognized as a built-in function, GCC may use
1584 information about that function to warn about problems with calls to
1585 that function, or to generate more efficient code, even if the
1586 resulting code still contains calls to that function. For example,
1587 warnings are given with @option{-Wformat} for bad calls to
1588 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1589 known not to modify global memory.
1591 With the @option{-fno-builtin-@var{function}} option
1592 only the built-in function @var{function} is
1593 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1594 function is named that is not built-in in this version of GCC, this
1595 option is ignored. There is no corresponding
1596 @option{-fbuiltin-@var{function}} option; if you wish to enable
1597 built-in functions selectively when using @option{-fno-builtin} or
1598 @option{-ffreestanding}, you may define macros such as:
1601 #define abs(n) __builtin_abs ((n))
1602 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1607 @cindex hosted environment
1609 Assert that compilation takes place in a hosted environment. This implies
1610 @option{-fbuiltin}. A hosted environment is one in which the
1611 entire standard library is available, and in which @code{main} has a return
1612 type of @code{int}. Examples are nearly everything except a kernel.
1613 This is equivalent to @option{-fno-freestanding}.
1615 @item -ffreestanding
1616 @opindex ffreestanding
1617 @cindex hosted environment
1619 Assert that compilation takes place in a freestanding environment. This
1620 implies @option{-fno-builtin}. A freestanding environment
1621 is one in which the standard library may not exist, and program startup may
1622 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1623 This is equivalent to @option{-fno-hosted}.
1625 @xref{Standards,,Language Standards Supported by GCC}, for details of
1626 freestanding and hosted environments.
1630 @cindex openmp parallel
1631 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1632 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1633 compiler generates parallel code according to the OpenMP Application
1634 Program Interface v3.0 @w{@uref{http://www.openmp.org/}}. This option
1635 implies @option{-pthread}, and thus is only supported on targets that
1636 have support for @option{-pthread}.
1638 @item -fms-extensions
1639 @opindex fms-extensions
1640 Accept some non-standard constructs used in Microsoft header files.
1642 Some cases of unnamed fields in structures and unions are only
1643 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1644 fields within structs/unions}, for details.
1648 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1649 options for strict ISO C conformance) implies @option{-trigraphs}.
1651 @item -no-integrated-cpp
1652 @opindex no-integrated-cpp
1653 Performs a compilation in two passes: preprocessing and compiling. This
1654 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1655 @option{-B} option. The user supplied compilation step can then add in
1656 an additional preprocessing step after normal preprocessing but before
1657 compiling. The default is to use the integrated cpp (internal cpp)
1659 The semantics of this option will change if "cc1", "cc1plus", and
1660 "cc1obj" are merged.
1662 @cindex traditional C language
1663 @cindex C language, traditional
1665 @itemx -traditional-cpp
1666 @opindex traditional-cpp
1667 @opindex traditional
1668 Formerly, these options caused GCC to attempt to emulate a pre-standard
1669 C compiler. They are now only supported with the @option{-E} switch.
1670 The preprocessor continues to support a pre-standard mode. See the GNU
1671 CPP manual for details.
1673 @item -fcond-mismatch
1674 @opindex fcond-mismatch
1675 Allow conditional expressions with mismatched types in the second and
1676 third arguments. The value of such an expression is void. This option
1677 is not supported for C++.
1679 @item -flax-vector-conversions
1680 @opindex flax-vector-conversions
1681 Allow implicit conversions between vectors with differing numbers of
1682 elements and/or incompatible element types. This option should not be
1685 @item -funsigned-char
1686 @opindex funsigned-char
1687 Let the type @code{char} be unsigned, like @code{unsigned char}.
1689 Each kind of machine has a default for what @code{char} should
1690 be. It is either like @code{unsigned char} by default or like
1691 @code{signed char} by default.
1693 Ideally, a portable program should always use @code{signed char} or
1694 @code{unsigned char} when it depends on the signedness of an object.
1695 But many programs have been written to use plain @code{char} and
1696 expect it to be signed, or expect it to be unsigned, depending on the
1697 machines they were written for. This option, and its inverse, let you
1698 make such a program work with the opposite default.
1700 The type @code{char} is always a distinct type from each of
1701 @code{signed char} or @code{unsigned char}, even though its behavior
1702 is always just like one of those two.
1705 @opindex fsigned-char
1706 Let the type @code{char} be signed, like @code{signed char}.
1708 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1709 the negative form of @option{-funsigned-char}. Likewise, the option
1710 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1712 @item -fsigned-bitfields
1713 @itemx -funsigned-bitfields
1714 @itemx -fno-signed-bitfields
1715 @itemx -fno-unsigned-bitfields
1716 @opindex fsigned-bitfields
1717 @opindex funsigned-bitfields
1718 @opindex fno-signed-bitfields
1719 @opindex fno-unsigned-bitfields
1720 These options control whether a bit-field is signed or unsigned, when the
1721 declaration does not use either @code{signed} or @code{unsigned}. By
1722 default, such a bit-field is signed, because this is consistent: the
1723 basic integer types such as @code{int} are signed types.
1726 @node C++ Dialect Options
1727 @section Options Controlling C++ Dialect
1729 @cindex compiler options, C++
1730 @cindex C++ options, command line
1731 @cindex options, C++
1732 This section describes the command-line options that are only meaningful
1733 for C++ programs; but you can also use most of the GNU compiler options
1734 regardless of what language your program is in. For example, you
1735 might compile a file @code{firstClass.C} like this:
1738 g++ -g -frepo -O -c firstClass.C
1742 In this example, only @option{-frepo} is an option meant
1743 only for C++ programs; you can use the other options with any
1744 language supported by GCC@.
1746 Here is a list of options that are @emph{only} for compiling C++ programs:
1750 @item -fabi-version=@var{n}
1751 @opindex fabi-version
1752 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1753 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1754 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1755 the version that conforms most closely to the C++ ABI specification.
1756 Therefore, the ABI obtained using version 0 will change as ABI bugs
1759 The default is version 2.
1761 @item -fno-access-control
1762 @opindex fno-access-control
1763 Turn off all access checking. This switch is mainly useful for working
1764 around bugs in the access control code.
1768 Check that the pointer returned by @code{operator new} is non-null
1769 before attempting to modify the storage allocated. This check is
1770 normally unnecessary because the C++ standard specifies that
1771 @code{operator new} will only return @code{0} if it is declared
1772 @samp{throw()}, in which case the compiler will always check the
1773 return value even without this option. In all other cases, when
1774 @code{operator new} has a non-empty exception specification, memory
1775 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1776 @samp{new (nothrow)}.
1778 @item -fconserve-space
1779 @opindex fconserve-space
1780 Put uninitialized or runtime-initialized global variables into the
1781 common segment, as C does. This saves space in the executable at the
1782 cost of not diagnosing duplicate definitions. If you compile with this
1783 flag and your program mysteriously crashes after @code{main()} has
1784 completed, you may have an object that is being destroyed twice because
1785 two definitions were merged.
1787 This option is no longer useful on most targets, now that support has
1788 been added for putting variables into BSS without making them common.
1790 @item -fno-deduce-init-list
1791 @opindex fno-deduce-init-list
1792 Disable deduction of a template type parameter as
1793 std::initializer_list from a brace-enclosed initializer list, i.e.
1796 template <class T> auto forward(T t) -> decltype (realfn (t))
1803 forward(@{1,2@}); // call forward<std::initializer_list<int>>
1807 This option is present because this deduction is an extension to the
1808 current specification in the C++0x working draft, and there was
1809 some concern about potential overload resolution problems.
1811 @item -ffriend-injection
1812 @opindex ffriend-injection
1813 Inject friend functions into the enclosing namespace, so that they are
1814 visible outside the scope of the class in which they are declared.
1815 Friend functions were documented to work this way in the old Annotated
1816 C++ Reference Manual, and versions of G++ before 4.1 always worked
1817 that way. However, in ISO C++ a friend function which is not declared
1818 in an enclosing scope can only be found using argument dependent
1819 lookup. This option causes friends to be injected as they were in
1822 This option is for compatibility, and may be removed in a future
1825 @item -fno-elide-constructors
1826 @opindex fno-elide-constructors
1827 The C++ standard allows an implementation to omit creating a temporary
1828 which is only used to initialize another object of the same type.
1829 Specifying this option disables that optimization, and forces G++ to
1830 call the copy constructor in all cases.
1832 @item -fno-enforce-eh-specs
1833 @opindex fno-enforce-eh-specs
1834 Don't generate code to check for violation of exception specifications
1835 at runtime. This option violates the C++ standard, but may be useful
1836 for reducing code size in production builds, much like defining
1837 @samp{NDEBUG}. This does not give user code permission to throw
1838 exceptions in violation of the exception specifications; the compiler
1839 will still optimize based on the specifications, so throwing an
1840 unexpected exception will result in undefined behavior.
1843 @itemx -fno-for-scope
1845 @opindex fno-for-scope
1846 If @option{-ffor-scope} is specified, the scope of variables declared in
1847 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1848 as specified by the C++ standard.
1849 If @option{-fno-for-scope} is specified, the scope of variables declared in
1850 a @i{for-init-statement} extends to the end of the enclosing scope,
1851 as was the case in old versions of G++, and other (traditional)
1852 implementations of C++.
1854 The default if neither flag is given to follow the standard,
1855 but to allow and give a warning for old-style code that would
1856 otherwise be invalid, or have different behavior.
1858 @item -fno-gnu-keywords
1859 @opindex fno-gnu-keywords
1860 Do not recognize @code{typeof} as a keyword, so that code can use this
1861 word as an identifier. You can use the keyword @code{__typeof__} instead.
1862 @option{-ansi} implies @option{-fno-gnu-keywords}.
1864 @item -fno-implicit-templates
1865 @opindex fno-implicit-templates
1866 Never emit code for non-inline templates which are instantiated
1867 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1868 @xref{Template Instantiation}, for more information.
1870 @item -fno-implicit-inline-templates
1871 @opindex fno-implicit-inline-templates
1872 Don't emit code for implicit instantiations of inline templates, either.
1873 The default is to handle inlines differently so that compiles with and
1874 without optimization will need the same set of explicit instantiations.
1876 @item -fno-implement-inlines
1877 @opindex fno-implement-inlines
1878 To save space, do not emit out-of-line copies of inline functions
1879 controlled by @samp{#pragma implementation}. This will cause linker
1880 errors if these functions are not inlined everywhere they are called.
1882 @item -fms-extensions
1883 @opindex fms-extensions
1884 Disable pedantic warnings about constructs used in MFC, such as implicit
1885 int and getting a pointer to member function via non-standard syntax.
1887 @item -fno-nonansi-builtins
1888 @opindex fno-nonansi-builtins
1889 Disable built-in declarations of functions that are not mandated by
1890 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1891 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1893 @item -fno-operator-names
1894 @opindex fno-operator-names
1895 Do not treat the operator name keywords @code{and}, @code{bitand},
1896 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1897 synonyms as keywords.
1899 @item -fno-optional-diags
1900 @opindex fno-optional-diags
1901 Disable diagnostics that the standard says a compiler does not need to
1902 issue. Currently, the only such diagnostic issued by G++ is the one for
1903 a name having multiple meanings within a class.
1906 @opindex fpermissive
1907 Downgrade some diagnostics about nonconformant code from errors to
1908 warnings. Thus, using @option{-fpermissive} will allow some
1909 nonconforming code to compile.
1911 @item -fno-pretty-templates
1912 @opindex fno-pretty-templates
1913 When an error message refers to a specialization of a function
1914 template, the compiler will normally print the signature of the
1915 template followed by the template arguments and any typedefs or
1916 typenames in the signature (e.g. @code{void f(T) [with T = int]}
1917 rather than @code{void f(int)}) so that it's clear which template is
1918 involved. When an error message refers to a specialization of a class
1919 template, the compiler will omit any template arguments which match
1920 the default template arguments for that template. If either of these
1921 behaviors make it harder to understand the error message rather than
1922 easier, using @option{-fno-pretty-templates} will disable them.
1926 Enable automatic template instantiation at link time. This option also
1927 implies @option{-fno-implicit-templates}. @xref{Template
1928 Instantiation}, for more information.
1932 Disable generation of information about every class with virtual
1933 functions for use by the C++ runtime type identification features
1934 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1935 of the language, you can save some space by using this flag. Note that
1936 exception handling uses the same information, but it will generate it as
1937 needed. The @samp{dynamic_cast} operator can still be used for casts that
1938 do not require runtime type information, i.e.@: casts to @code{void *} or to
1939 unambiguous base classes.
1943 Emit statistics about front-end processing at the end of the compilation.
1944 This information is generally only useful to the G++ development team.
1946 @item -ftemplate-depth-@var{n}
1947 @opindex ftemplate-depth
1948 Set the maximum instantiation depth for template classes to @var{n}.
1949 A limit on the template instantiation depth is needed to detect
1950 endless recursions during template class instantiation. ANSI/ISO C++
1951 conforming programs must not rely on a maximum depth greater than 17
1952 (changed to 1024 in C++0x).
1954 @item -fno-threadsafe-statics
1955 @opindex fno-threadsafe-statics
1956 Do not emit the extra code to use the routines specified in the C++
1957 ABI for thread-safe initialization of local statics. You can use this
1958 option to reduce code size slightly in code that doesn't need to be
1961 @item -fuse-cxa-atexit
1962 @opindex fuse-cxa-atexit
1963 Register destructors for objects with static storage duration with the
1964 @code{__cxa_atexit} function rather than the @code{atexit} function.
1965 This option is required for fully standards-compliant handling of static
1966 destructors, but will only work if your C library supports
1967 @code{__cxa_atexit}.
1969 @item -fno-use-cxa-get-exception-ptr
1970 @opindex fno-use-cxa-get-exception-ptr
1971 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1972 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1973 if the runtime routine is not available.
1975 @item -fvisibility-inlines-hidden
1976 @opindex fvisibility-inlines-hidden
1977 This switch declares that the user does not attempt to compare
1978 pointers to inline methods where the addresses of the two functions
1979 were taken in different shared objects.
1981 The effect of this is that GCC may, effectively, mark inline methods with
1982 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1983 appear in the export table of a DSO and do not require a PLT indirection
1984 when used within the DSO@. Enabling this option can have a dramatic effect
1985 on load and link times of a DSO as it massively reduces the size of the
1986 dynamic export table when the library makes heavy use of templates.
1988 The behavior of this switch is not quite the same as marking the
1989 methods as hidden directly, because it does not affect static variables
1990 local to the function or cause the compiler to deduce that
1991 the function is defined in only one shared object.
1993 You may mark a method as having a visibility explicitly to negate the
1994 effect of the switch for that method. For example, if you do want to
1995 compare pointers to a particular inline method, you might mark it as
1996 having default visibility. Marking the enclosing class with explicit
1997 visibility will have no effect.
1999 Explicitly instantiated inline methods are unaffected by this option
2000 as their linkage might otherwise cross a shared library boundary.
2001 @xref{Template Instantiation}.
2003 @item -fvisibility-ms-compat
2004 @opindex fvisibility-ms-compat
2005 This flag attempts to use visibility settings to make GCC's C++
2006 linkage model compatible with that of Microsoft Visual Studio.
2008 The flag makes these changes to GCC's linkage model:
2012 It sets the default visibility to @code{hidden}, like
2013 @option{-fvisibility=hidden}.
2016 Types, but not their members, are not hidden by default.
2019 The One Definition Rule is relaxed for types without explicit
2020 visibility specifications which are defined in more than one different
2021 shared object: those declarations are permitted if they would have
2022 been permitted when this option was not used.
2025 In new code it is better to use @option{-fvisibility=hidden} and
2026 export those classes which are intended to be externally visible.
2027 Unfortunately it is possible for code to rely, perhaps accidentally,
2028 on the Visual Studio behavior.
2030 Among the consequences of these changes are that static data members
2031 of the same type with the same name but defined in different shared
2032 objects will be different, so changing one will not change the other;
2033 and that pointers to function members defined in different shared
2034 objects may not compare equal. When this flag is given, it is a
2035 violation of the ODR to define types with the same name differently.
2039 Do not use weak symbol support, even if it is provided by the linker.
2040 By default, G++ will use weak symbols if they are available. This
2041 option exists only for testing, and should not be used by end-users;
2042 it will result in inferior code and has no benefits. This option may
2043 be removed in a future release of G++.
2047 Do not search for header files in the standard directories specific to
2048 C++, but do still search the other standard directories. (This option
2049 is used when building the C++ library.)
2052 In addition, these optimization, warning, and code generation options
2053 have meanings only for C++ programs:
2056 @item -fno-default-inline
2057 @opindex fno-default-inline
2058 Do not assume @samp{inline} for functions defined inside a class scope.
2059 @xref{Optimize Options,,Options That Control Optimization}. Note that these
2060 functions will have linkage like inline functions; they just won't be
2063 @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
2066 Warn when G++ generates code that is probably not compatible with the
2067 vendor-neutral C++ ABI@. Although an effort has been made to warn about
2068 all such cases, there are probably some cases that are not warned about,
2069 even though G++ is generating incompatible code. There may also be
2070 cases where warnings are emitted even though the code that is generated
2073 You should rewrite your code to avoid these warnings if you are
2074 concerned about the fact that code generated by G++ may not be binary
2075 compatible with code generated by other compilers.
2077 The known incompatibilities at this point include:
2082 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
2083 pack data into the same byte as a base class. For example:
2086 struct A @{ virtual void f(); int f1 : 1; @};
2087 struct B : public A @{ int f2 : 1; @};
2091 In this case, G++ will place @code{B::f2} into the same byte
2092 as@code{A::f1}; other compilers will not. You can avoid this problem
2093 by explicitly padding @code{A} so that its size is a multiple of the
2094 byte size on your platform; that will cause G++ and other compilers to
2095 layout @code{B} identically.
2098 Incorrect handling of tail-padding for virtual bases. G++ does not use
2099 tail padding when laying out virtual bases. For example:
2102 struct A @{ virtual void f(); char c1; @};
2103 struct B @{ B(); char c2; @};
2104 struct C : public A, public virtual B @{@};
2108 In this case, G++ will not place @code{B} into the tail-padding for
2109 @code{A}; other compilers will. You can avoid this problem by
2110 explicitly padding @code{A} so that its size is a multiple of its
2111 alignment (ignoring virtual base classes); that will cause G++ and other
2112 compilers to layout @code{C} identically.
2115 Incorrect handling of bit-fields with declared widths greater than that
2116 of their underlying types, when the bit-fields appear in a union. For
2120 union U @{ int i : 4096; @};
2124 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2125 union too small by the number of bits in an @code{int}.
2128 Empty classes can be placed at incorrect offsets. For example:
2138 struct C : public B, public A @{@};
2142 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2143 it should be placed at offset zero. G++ mistakenly believes that the
2144 @code{A} data member of @code{B} is already at offset zero.
2147 Names of template functions whose types involve @code{typename} or
2148 template template parameters can be mangled incorrectly.
2151 template <typename Q>
2152 void f(typename Q::X) @{@}
2154 template <template <typename> class Q>
2155 void f(typename Q<int>::X) @{@}
2159 Instantiations of these templates may be mangled incorrectly.
2163 It also warns psABI related changes. The known psABI changes at this
2169 For SYSV/x86-64, when passing union with long double, it is changed to
2170 pass in memory as specified in psABI. For example:
2180 @code{union U} will always be passed in memory.
2184 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2185 @opindex Wctor-dtor-privacy
2186 @opindex Wno-ctor-dtor-privacy
2187 Warn when a class seems unusable because all the constructors or
2188 destructors in that class are private, and it has neither friends nor
2189 public static member functions.
2191 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2192 @opindex Wnon-virtual-dtor
2193 @opindex Wno-non-virtual-dtor
2194 Warn when a class has virtual functions and accessible non-virtual
2195 destructor, in which case it would be possible but unsafe to delete
2196 an instance of a derived class through a pointer to the base class.
2197 This warning is also enabled if -Weffc++ is specified.
2199 @item -Wreorder @r{(C++ and Objective-C++ only)}
2201 @opindex Wno-reorder
2202 @cindex reordering, warning
2203 @cindex warning for reordering of member initializers
2204 Warn when the order of member initializers given in the code does not
2205 match the order in which they must be executed. For instance:
2211 A(): j (0), i (1) @{ @}
2215 The compiler will rearrange the member initializers for @samp{i}
2216 and @samp{j} to match the declaration order of the members, emitting
2217 a warning to that effect. This warning is enabled by @option{-Wall}.
2220 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2223 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2226 Warn about violations of the following style guidelines from Scott Meyers'
2227 @cite{Effective C++} book:
2231 Item 11: Define a copy constructor and an assignment operator for classes
2232 with dynamically allocated memory.
2235 Item 12: Prefer initialization to assignment in constructors.
2238 Item 14: Make destructors virtual in base classes.
2241 Item 15: Have @code{operator=} return a reference to @code{*this}.
2244 Item 23: Don't try to return a reference when you must return an object.
2248 Also warn about violations of the following style guidelines from
2249 Scott Meyers' @cite{More Effective C++} book:
2253 Item 6: Distinguish between prefix and postfix forms of increment and
2254 decrement operators.
2257 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2261 When selecting this option, be aware that the standard library
2262 headers do not obey all of these guidelines; use @samp{grep -v}
2263 to filter out those warnings.
2265 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2266 @opindex Wstrict-null-sentinel
2267 @opindex Wno-strict-null-sentinel
2268 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2269 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2270 to @code{__null}. Although it is a null pointer constant not a null pointer,
2271 it is guaranteed to be of the same size as a pointer. But this use is
2272 not portable across different compilers.
2274 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2275 @opindex Wno-non-template-friend
2276 @opindex Wnon-template-friend
2277 Disable warnings when non-templatized friend functions are declared
2278 within a template. Since the advent of explicit template specification
2279 support in G++, if the name of the friend is an unqualified-id (i.e.,
2280 @samp{friend foo(int)}), the C++ language specification demands that the
2281 friend declare or define an ordinary, nontemplate function. (Section
2282 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2283 could be interpreted as a particular specialization of a templatized
2284 function. Because this non-conforming behavior is no longer the default
2285 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2286 check existing code for potential trouble spots and is on by default.
2287 This new compiler behavior can be turned off with
2288 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2289 but disables the helpful warning.
2291 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2292 @opindex Wold-style-cast
2293 @opindex Wno-old-style-cast
2294 Warn if an old-style (C-style) cast to a non-void type is used within
2295 a C++ program. The new-style casts (@samp{dynamic_cast},
2296 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2297 less vulnerable to unintended effects and much easier to search for.
2299 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2300 @opindex Woverloaded-virtual
2301 @opindex Wno-overloaded-virtual
2302 @cindex overloaded virtual fn, warning
2303 @cindex warning for overloaded virtual fn
2304 Warn when a function declaration hides virtual functions from a
2305 base class. For example, in:
2312 struct B: public A @{
2317 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2325 will fail to compile.
2327 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2328 @opindex Wno-pmf-conversions
2329 @opindex Wpmf-conversions
2330 Disable the diagnostic for converting a bound pointer to member function
2333 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2334 @opindex Wsign-promo
2335 @opindex Wno-sign-promo
2336 Warn when overload resolution chooses a promotion from unsigned or
2337 enumerated type to a signed type, over a conversion to an unsigned type of
2338 the same size. Previous versions of G++ would try to preserve
2339 unsignedness, but the standard mandates the current behavior.
2344 A& operator = (int);
2354 In this example, G++ will synthesize a default @samp{A& operator =
2355 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2358 @node Objective-C and Objective-C++ Dialect Options
2359 @section Options Controlling Objective-C and Objective-C++ Dialects
2361 @cindex compiler options, Objective-C and Objective-C++
2362 @cindex Objective-C and Objective-C++ options, command line
2363 @cindex options, Objective-C and Objective-C++
2364 (NOTE: This manual does not describe the Objective-C and Objective-C++
2365 languages themselves. See @xref{Standards,,Language Standards
2366 Supported by GCC}, for references.)
2368 This section describes the command-line options that are only meaningful
2369 for Objective-C and Objective-C++ programs, but you can also use most of
2370 the language-independent GNU compiler options.
2371 For example, you might compile a file @code{some_class.m} like this:
2374 gcc -g -fgnu-runtime -O -c some_class.m
2378 In this example, @option{-fgnu-runtime} is an option meant only for
2379 Objective-C and Objective-C++ programs; you can use the other options with
2380 any language supported by GCC@.
2382 Note that since Objective-C is an extension of the C language, Objective-C
2383 compilations may also use options specific to the C front-end (e.g.,
2384 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2385 C++-specific options (e.g., @option{-Wabi}).
2387 Here is a list of options that are @emph{only} for compiling Objective-C
2388 and Objective-C++ programs:
2391 @item -fconstant-string-class=@var{class-name}
2392 @opindex fconstant-string-class
2393 Use @var{class-name} as the name of the class to instantiate for each
2394 literal string specified with the syntax @code{@@"@dots{}"}. The default
2395 class name is @code{NXConstantString} if the GNU runtime is being used, and
2396 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2397 @option{-fconstant-cfstrings} option, if also present, will override the
2398 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2399 to be laid out as constant CoreFoundation strings.
2402 @opindex fgnu-runtime
2403 Generate object code compatible with the standard GNU Objective-C
2404 runtime. This is the default for most types of systems.
2406 @item -fnext-runtime
2407 @opindex fnext-runtime
2408 Generate output compatible with the NeXT runtime. This is the default
2409 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2410 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2413 @item -fno-nil-receivers
2414 @opindex fno-nil-receivers
2415 Assume that all Objective-C message dispatches (e.g.,
2416 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2417 is not @code{nil}. This allows for more efficient entry points in the runtime
2418 to be used. Currently, this option is only available in conjunction with
2419 the NeXT runtime on Mac OS X 10.3 and later.
2421 @item -fobjc-call-cxx-cdtors
2422 @opindex fobjc-call-cxx-cdtors
2423 For each Objective-C class, check if any of its instance variables is a
2424 C++ object with a non-trivial default constructor. If so, synthesize a
2425 special @code{- (id) .cxx_construct} instance method that will run
2426 non-trivial default constructors on any such instance variables, in order,
2427 and then return @code{self}. Similarly, check if any instance variable
2428 is a C++ object with a non-trivial destructor, and if so, synthesize a
2429 special @code{- (void) .cxx_destruct} method that will run
2430 all such default destructors, in reverse order.
2432 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2433 thusly generated will only operate on instance variables declared in the
2434 current Objective-C class, and not those inherited from superclasses. It
2435 is the responsibility of the Objective-C runtime to invoke all such methods
2436 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2437 will be invoked by the runtime immediately after a new object
2438 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2439 be invoked immediately before the runtime deallocates an object instance.
2441 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2442 support for invoking the @code{- (id) .cxx_construct} and
2443 @code{- (void) .cxx_destruct} methods.
2445 @item -fobjc-direct-dispatch
2446 @opindex fobjc-direct-dispatch
2447 Allow fast jumps to the message dispatcher. On Darwin this is
2448 accomplished via the comm page.
2450 @item -fobjc-exceptions
2451 @opindex fobjc-exceptions
2452 Enable syntactic support for structured exception handling in Objective-C,
2453 similar to what is offered by C++ and Java. This option is
2454 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2463 @@catch (AnObjCClass *exc) @{
2470 @@catch (AnotherClass *exc) @{
2473 @@catch (id allOthers) @{
2483 The @code{@@throw} statement may appear anywhere in an Objective-C or
2484 Objective-C++ program; when used inside of a @code{@@catch} block, the
2485 @code{@@throw} may appear without an argument (as shown above), in which case
2486 the object caught by the @code{@@catch} will be rethrown.
2488 Note that only (pointers to) Objective-C objects may be thrown and
2489 caught using this scheme. When an object is thrown, it will be caught
2490 by the nearest @code{@@catch} clause capable of handling objects of that type,
2491 analogously to how @code{catch} blocks work in C++ and Java. A
2492 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2493 any and all Objective-C exceptions not caught by previous @code{@@catch}
2496 The @code{@@finally} clause, if present, will be executed upon exit from the
2497 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2498 regardless of whether any exceptions are thrown, caught or rethrown
2499 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2500 of the @code{finally} clause in Java.
2502 There are several caveats to using the new exception mechanism:
2506 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2507 idioms provided by the @code{NSException} class, the new
2508 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2509 systems, due to additional functionality needed in the (NeXT) Objective-C
2513 As mentioned above, the new exceptions do not support handling
2514 types other than Objective-C objects. Furthermore, when used from
2515 Objective-C++, the Objective-C exception model does not interoperate with C++
2516 exceptions at this time. This means you cannot @code{@@throw} an exception
2517 from Objective-C and @code{catch} it in C++, or vice versa
2518 (i.e., @code{throw @dots{} @@catch}).
2521 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2522 blocks for thread-safe execution:
2525 @@synchronized (ObjCClass *guard) @{
2530 Upon entering the @code{@@synchronized} block, a thread of execution shall
2531 first check whether a lock has been placed on the corresponding @code{guard}
2532 object by another thread. If it has, the current thread shall wait until
2533 the other thread relinquishes its lock. Once @code{guard} becomes available,
2534 the current thread will place its own lock on it, execute the code contained in
2535 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2536 making @code{guard} available to other threads).
2538 Unlike Java, Objective-C does not allow for entire methods to be marked
2539 @code{@@synchronized}. Note that throwing exceptions out of
2540 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2541 to be unlocked properly.
2545 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2547 @item -freplace-objc-classes
2548 @opindex freplace-objc-classes
2549 Emit a special marker instructing @command{ld(1)} not to statically link in
2550 the resulting object file, and allow @command{dyld(1)} to load it in at
2551 run time instead. This is used in conjunction with the Fix-and-Continue
2552 debugging mode, where the object file in question may be recompiled and
2553 dynamically reloaded in the course of program execution, without the need
2554 to restart the program itself. Currently, Fix-and-Continue functionality
2555 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2560 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2561 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2562 compile time) with static class references that get initialized at load time,
2563 which improves run-time performance. Specifying the @option{-fzero-link} flag
2564 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2565 to be retained. This is useful in Zero-Link debugging mode, since it allows
2566 for individual class implementations to be modified during program execution.
2570 Dump interface declarations for all classes seen in the source file to a
2571 file named @file{@var{sourcename}.decl}.
2573 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2574 @opindex Wassign-intercept
2575 @opindex Wno-assign-intercept
2576 Warn whenever an Objective-C assignment is being intercepted by the
2579 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2580 @opindex Wno-protocol
2582 If a class is declared to implement a protocol, a warning is issued for
2583 every method in the protocol that is not implemented by the class. The
2584 default behavior is to issue a warning for every method not explicitly
2585 implemented in the class, even if a method implementation is inherited
2586 from the superclass. If you use the @option{-Wno-protocol} option, then
2587 methods inherited from the superclass are considered to be implemented,
2588 and no warning is issued for them.
2590 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2592 @opindex Wno-selector
2593 Warn if multiple methods of different types for the same selector are
2594 found during compilation. The check is performed on the list of methods
2595 in the final stage of compilation. Additionally, a check is performed
2596 for each selector appearing in a @code{@@selector(@dots{})}
2597 expression, and a corresponding method for that selector has been found
2598 during compilation. Because these checks scan the method table only at
2599 the end of compilation, these warnings are not produced if the final
2600 stage of compilation is not reached, for example because an error is
2601 found during compilation, or because the @option{-fsyntax-only} option is
2604 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2605 @opindex Wstrict-selector-match
2606 @opindex Wno-strict-selector-match
2607 Warn if multiple methods with differing argument and/or return types are
2608 found for a given selector when attempting to send a message using this
2609 selector to a receiver of type @code{id} or @code{Class}. When this flag
2610 is off (which is the default behavior), the compiler will omit such warnings
2611 if any differences found are confined to types which share the same size
2614 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2615 @opindex Wundeclared-selector
2616 @opindex Wno-undeclared-selector
2617 Warn if a @code{@@selector(@dots{})} expression referring to an
2618 undeclared selector is found. A selector is considered undeclared if no
2619 method with that name has been declared before the
2620 @code{@@selector(@dots{})} expression, either explicitly in an
2621 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2622 an @code{@@implementation} section. This option always performs its
2623 checks as soon as a @code{@@selector(@dots{})} expression is found,
2624 while @option{-Wselector} only performs its checks in the final stage of
2625 compilation. This also enforces the coding style convention
2626 that methods and selectors must be declared before being used.
2628 @item -print-objc-runtime-info
2629 @opindex print-objc-runtime-info
2630 Generate C header describing the largest structure that is passed by
2635 @node Language Independent Options
2636 @section Options to Control Diagnostic Messages Formatting
2637 @cindex options to control diagnostics formatting
2638 @cindex diagnostic messages
2639 @cindex message formatting
2641 Traditionally, diagnostic messages have been formatted irrespective of
2642 the output device's aspect (e.g.@: its width, @dots{}). The options described
2643 below can be used to control the diagnostic messages formatting
2644 algorithm, e.g.@: how many characters per line, how often source location
2645 information should be reported. Right now, only the C++ front end can
2646 honor these options. However it is expected, in the near future, that
2647 the remaining front ends would be able to digest them correctly.
2650 @item -fmessage-length=@var{n}
2651 @opindex fmessage-length
2652 Try to format error messages so that they fit on lines of about @var{n}
2653 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2654 the front ends supported by GCC@. If @var{n} is zero, then no
2655 line-wrapping will be done; each error message will appear on a single
2658 @opindex fdiagnostics-show-location
2659 @item -fdiagnostics-show-location=once
2660 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2661 reporter to emit @emph{once} source location information; that is, in
2662 case the message is too long to fit on a single physical line and has to
2663 be wrapped, the source location won't be emitted (as prefix) again,
2664 over and over, in subsequent continuation lines. This is the default
2667 @item -fdiagnostics-show-location=every-line
2668 Only meaningful in line-wrapping mode. Instructs the diagnostic
2669 messages reporter to emit the same source location information (as
2670 prefix) for physical lines that result from the process of breaking
2671 a message which is too long to fit on a single line.
2673 @item -fdiagnostics-show-option
2674 @opindex fdiagnostics-show-option
2675 This option instructs the diagnostic machinery to add text to each
2676 diagnostic emitted, which indicates which command line option directly
2677 controls that diagnostic, when such an option is known to the
2678 diagnostic machinery.
2680 @item -Wcoverage-mismatch
2681 @opindex Wcoverage-mismatch
2682 Warn if feedback profiles do not match when using the
2683 @option{-fprofile-use} option.
2684 If a source file was changed between @option{-fprofile-gen} and
2685 @option{-fprofile-use}, the files with the profile feedback can fail
2686 to match the source file and GCC can not use the profile feedback
2687 information. By default, GCC emits an error message in this case.
2688 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2689 error. GCC does not use appropriate feedback profiles, so using this
2690 option can result in poorly optimized code. This option is useful
2691 only in the case of very minor changes such as bug fixes to an
2696 @node Warning Options
2697 @section Options to Request or Suppress Warnings
2698 @cindex options to control warnings
2699 @cindex warning messages
2700 @cindex messages, warning
2701 @cindex suppressing warnings
2703 Warnings are diagnostic messages that report constructions which
2704 are not inherently erroneous but which are risky or suggest there
2705 may have been an error.
2707 The following language-independent options do not enable specific
2708 warnings but control the kinds of diagnostics produced by GCC.
2711 @cindex syntax checking
2713 @opindex fsyntax-only
2714 Check the code for syntax errors, but don't do anything beyond that.
2718 Inhibit all warning messages.
2723 Make all warnings into errors.
2728 Make the specified warning into an error. The specifier for a warning
2729 is appended, for example @option{-Werror=switch} turns the warnings
2730 controlled by @option{-Wswitch} into errors. This switch takes a
2731 negative form, to be used to negate @option{-Werror} for specific
2732 warnings, for example @option{-Wno-error=switch} makes
2733 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2734 is in effect. You can use the @option{-fdiagnostics-show-option}
2735 option to have each controllable warning amended with the option which
2736 controls it, to determine what to use with this option.
2738 Note that specifying @option{-Werror=}@var{foo} automatically implies
2739 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2742 @item -Wfatal-errors
2743 @opindex Wfatal-errors
2744 @opindex Wno-fatal-errors
2745 This option causes the compiler to abort compilation on the first error
2746 occurred rather than trying to keep going and printing further error
2751 You can request many specific warnings with options beginning
2752 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2753 implicit declarations. Each of these specific warning options also
2754 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2755 example, @option{-Wno-implicit}. This manual lists only one of the
2756 two forms, whichever is not the default. For further,
2757 language-specific options also refer to @ref{C++ Dialect Options} and
2758 @ref{Objective-C and Objective-C++ Dialect Options}.
2763 Issue all the warnings demanded by strict ISO C and ISO C++;
2764 reject all programs that use forbidden extensions, and some other
2765 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2766 version of the ISO C standard specified by any @option{-std} option used.
2768 Valid ISO C and ISO C++ programs should compile properly with or without
2769 this option (though a rare few will require @option{-ansi} or a
2770 @option{-std} option specifying the required version of ISO C)@. However,
2771 without this option, certain GNU extensions and traditional C and C++
2772 features are supported as well. With this option, they are rejected.
2774 @option{-pedantic} does not cause warning messages for use of the
2775 alternate keywords whose names begin and end with @samp{__}. Pedantic
2776 warnings are also disabled in the expression that follows
2777 @code{__extension__}. However, only system header files should use
2778 these escape routes; application programs should avoid them.
2779 @xref{Alternate Keywords}.
2781 Some users try to use @option{-pedantic} to check programs for strict ISO
2782 C conformance. They soon find that it does not do quite what they want:
2783 it finds some non-ISO practices, but not all---only those for which
2784 ISO C @emph{requires} a diagnostic, and some others for which
2785 diagnostics have been added.
2787 A feature to report any failure to conform to ISO C might be useful in
2788 some instances, but would require considerable additional work and would
2789 be quite different from @option{-pedantic}. We don't have plans to
2790 support such a feature in the near future.
2792 Where the standard specified with @option{-std} represents a GNU
2793 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2794 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2795 extended dialect is based. Warnings from @option{-pedantic} are given
2796 where they are required by the base standard. (It would not make sense
2797 for such warnings to be given only for features not in the specified GNU
2798 C dialect, since by definition the GNU dialects of C include all
2799 features the compiler supports with the given option, and there would be
2800 nothing to warn about.)
2802 @item -pedantic-errors
2803 @opindex pedantic-errors
2804 Like @option{-pedantic}, except that errors are produced rather than
2810 This enables all the warnings about constructions that some users
2811 consider questionable, and that are easy to avoid (or modify to
2812 prevent the warning), even in conjunction with macros. This also
2813 enables some language-specific warnings described in @ref{C++ Dialect
2814 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2816 @option{-Wall} turns on the following warning flags:
2818 @gccoptlist{-Waddress @gol
2819 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2821 -Wchar-subscripts @gol
2822 -Wenum-compare @r{(in C/Objc; this is on by default in C++)} @gol
2824 -Wimplicit-function-declaration @gol
2827 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2828 -Wmissing-braces @gol
2834 -Wsequence-point @gol
2835 -Wsign-compare @r{(only in C++)} @gol
2836 -Wstrict-aliasing @gol
2837 -Wstrict-overflow=1 @gol
2840 -Wuninitialized @gol
2841 -Wunknown-pragmas @gol
2842 -Wunused-function @gol
2845 -Wunused-variable @gol
2846 -Wvolatile-register-var @gol
2849 Note that some warning flags are not implied by @option{-Wall}. Some of
2850 them warn about constructions that users generally do not consider
2851 questionable, but which occasionally you might wish to check for;
2852 others warn about constructions that are necessary or hard to avoid in
2853 some cases, and there is no simple way to modify the code to suppress
2854 the warning. Some of them are enabled by @option{-Wextra} but many of
2855 them must be enabled individually.
2861 This enables some extra warning flags that are not enabled by
2862 @option{-Wall}. (This option used to be called @option{-W}. The older
2863 name is still supported, but the newer name is more descriptive.)
2865 @gccoptlist{-Wclobbered @gol
2867 -Wignored-qualifiers @gol
2868 -Wmissing-field-initializers @gol
2869 -Wmissing-parameter-type @r{(C only)} @gol
2870 -Wold-style-declaration @r{(C only)} @gol
2871 -Woverride-init @gol
2874 -Wuninitialized @gol
2875 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2878 The option @option{-Wextra} also prints warning messages for the
2884 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2885 @samp{>}, or @samp{>=}.
2888 (C++ only) An enumerator and a non-enumerator both appear in a
2889 conditional expression.
2892 (C++ only) Ambiguous virtual bases.
2895 (C++ only) Subscripting an array which has been declared @samp{register}.
2898 (C++ only) Taking the address of a variable which has been declared
2902 (C++ only) A base class is not initialized in a derived class' copy
2907 @item -Wchar-subscripts
2908 @opindex Wchar-subscripts
2909 @opindex Wno-char-subscripts
2910 Warn if an array subscript has type @code{char}. This is a common cause
2911 of error, as programmers often forget that this type is signed on some
2913 This warning is enabled by @option{-Wall}.
2917 @opindex Wno-comment
2918 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2919 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2920 This warning is enabled by @option{-Wall}.
2925 @opindex ffreestanding
2926 @opindex fno-builtin
2927 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2928 the arguments supplied have types appropriate to the format string
2929 specified, and that the conversions specified in the format string make
2930 sense. This includes standard functions, and others specified by format
2931 attributes (@pxref{Function Attributes}), in the @code{printf},
2932 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2933 not in the C standard) families (or other target-specific families).
2934 Which functions are checked without format attributes having been
2935 specified depends on the standard version selected, and such checks of
2936 functions without the attribute specified are disabled by
2937 @option{-ffreestanding} or @option{-fno-builtin}.
2939 The formats are checked against the format features supported by GNU
2940 libc version 2.2. These include all ISO C90 and C99 features, as well
2941 as features from the Single Unix Specification and some BSD and GNU
2942 extensions. Other library implementations may not support all these
2943 features; GCC does not support warning about features that go beyond a
2944 particular library's limitations. However, if @option{-pedantic} is used
2945 with @option{-Wformat}, warnings will be given about format features not
2946 in the selected standard version (but not for @code{strfmon} formats,
2947 since those are not in any version of the C standard). @xref{C Dialect
2948 Options,,Options Controlling C Dialect}.
2950 Since @option{-Wformat} also checks for null format arguments for
2951 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2953 @option{-Wformat} is included in @option{-Wall}. For more control over some
2954 aspects of format checking, the options @option{-Wformat-y2k},
2955 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2956 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2957 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2960 @opindex Wformat-y2k
2961 @opindex Wno-format-y2k
2962 If @option{-Wformat} is specified, also warn about @code{strftime}
2963 formats which may yield only a two-digit year.
2965 @item -Wno-format-contains-nul
2966 @opindex Wno-format-contains-nul
2967 @opindex Wformat-contains-nul
2968 If @option{-Wformat} is specified, do not warn about format strings that
2971 @item -Wno-format-extra-args
2972 @opindex Wno-format-extra-args
2973 @opindex Wformat-extra-args
2974 If @option{-Wformat} is specified, do not warn about excess arguments to a
2975 @code{printf} or @code{scanf} format function. The C standard specifies
2976 that such arguments are ignored.
2978 Where the unused arguments lie between used arguments that are
2979 specified with @samp{$} operand number specifications, normally
2980 warnings are still given, since the implementation could not know what
2981 type to pass to @code{va_arg} to skip the unused arguments. However,
2982 in the case of @code{scanf} formats, this option will suppress the
2983 warning if the unused arguments are all pointers, since the Single
2984 Unix Specification says that such unused arguments are allowed.
2986 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2987 @opindex Wno-format-zero-length
2988 @opindex Wformat-zero-length
2989 If @option{-Wformat} is specified, do not warn about zero-length formats.
2990 The C standard specifies that zero-length formats are allowed.
2992 @item -Wformat-nonliteral
2993 @opindex Wformat-nonliteral
2994 @opindex Wno-format-nonliteral
2995 If @option{-Wformat} is specified, also warn if the format string is not a
2996 string literal and so cannot be checked, unless the format function
2997 takes its format arguments as a @code{va_list}.
2999 @item -Wformat-security
3000 @opindex Wformat-security
3001 @opindex Wno-format-security
3002 If @option{-Wformat} is specified, also warn about uses of format
3003 functions that represent possible security problems. At present, this
3004 warns about calls to @code{printf} and @code{scanf} functions where the
3005 format string is not a string literal and there are no format arguments,
3006 as in @code{printf (foo);}. This may be a security hole if the format
3007 string came from untrusted input and contains @samp{%n}. (This is
3008 currently a subset of what @option{-Wformat-nonliteral} warns about, but
3009 in future warnings may be added to @option{-Wformat-security} that are not
3010 included in @option{-Wformat-nonliteral}.)
3014 @opindex Wno-format=2
3015 Enable @option{-Wformat} plus format checks not included in
3016 @option{-Wformat}. Currently equivalent to @samp{-Wformat
3017 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
3019 @item -Wnonnull @r{(C and Objective-C only)}
3021 @opindex Wno-nonnull
3022 Warn about passing a null pointer for arguments marked as
3023 requiring a non-null value by the @code{nonnull} function attribute.
3025 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
3026 can be disabled with the @option{-Wno-nonnull} option.
3028 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
3030 @opindex Wno-init-self
3031 Warn about uninitialized variables which are initialized with themselves.
3032 Note this option can only be used with the @option{-Wuninitialized} option.
3034 For example, GCC will warn about @code{i} being uninitialized in the
3035 following snippet only when @option{-Winit-self} has been specified:
3046 @item -Wimplicit-int @r{(C and Objective-C only)}
3047 @opindex Wimplicit-int
3048 @opindex Wno-implicit-int
3049 Warn when a declaration does not specify a type.
3050 This warning is enabled by @option{-Wall}.
3052 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
3053 @opindex Wimplicit-function-declaration
3054 @opindex Wno-implicit-function-declaration
3055 Give a warning whenever a function is used before being declared. In
3056 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
3057 enabled by default and it is made into an error by
3058 @option{-pedantic-errors}. This warning is also enabled by
3063 @opindex Wno-implicit
3064 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
3065 This warning is enabled by @option{-Wall}.
3067 @item -Wignored-qualifiers @r{(C and C++ only)}
3068 @opindex Wignored-qualifiers
3069 @opindex Wno-ignored-qualifiers
3070 Warn if the return type of a function has a type qualifier
3071 such as @code{const}. For ISO C such a type qualifier has no effect,
3072 since the value returned by a function is not an lvalue.
3073 For C++, the warning is only emitted for scalar types or @code{void}.
3074 ISO C prohibits qualified @code{void} return types on function
3075 definitions, so such return types always receive a warning
3076 even without this option.
3078 This warning is also enabled by @option{-Wextra}.
3083 Warn if the type of @samp{main} is suspicious. @samp{main} should be
3084 a function with external linkage, returning int, taking either zero
3085 arguments, two, or three arguments of appropriate types. This warning
3086 is enabled by default in C++ and is enabled by either @option{-Wall}
3087 or @option{-pedantic}.
3089 @item -Wmissing-braces
3090 @opindex Wmissing-braces
3091 @opindex Wno-missing-braces
3092 Warn if an aggregate or union initializer is not fully bracketed. In
3093 the following example, the initializer for @samp{a} is not fully
3094 bracketed, but that for @samp{b} is fully bracketed.
3097 int a[2][2] = @{ 0, 1, 2, 3 @};
3098 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
3101 This warning is enabled by @option{-Wall}.
3103 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
3104 @opindex Wmissing-include-dirs
3105 @opindex Wno-missing-include-dirs
3106 Warn if a user-supplied include directory does not exist.
3109 @opindex Wparentheses
3110 @opindex Wno-parentheses
3111 Warn if parentheses are omitted in certain contexts, such
3112 as when there is an assignment in a context where a truth value
3113 is expected, or when operators are nested whose precedence people
3114 often get confused about.
3116 Also warn if a comparison like @samp{x<=y<=z} appears; this is
3117 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
3118 interpretation from that of ordinary mathematical notation.
3120 Also warn about constructions where there may be confusion to which
3121 @code{if} statement an @code{else} branch belongs. Here is an example of
3136 In C/C++, every @code{else} branch belongs to the innermost possible
3137 @code{if} statement, which in this example is @code{if (b)}. This is
3138 often not what the programmer expected, as illustrated in the above
3139 example by indentation the programmer chose. When there is the
3140 potential for this confusion, GCC will issue a warning when this flag
3141 is specified. To eliminate the warning, add explicit braces around
3142 the innermost @code{if} statement so there is no way the @code{else}
3143 could belong to the enclosing @code{if}. The resulting code would
3160 This warning is enabled by @option{-Wall}.
3162 @item -Wsequence-point
3163 @opindex Wsequence-point
3164 @opindex Wno-sequence-point
3165 Warn about code that may have undefined semantics because of violations
3166 of sequence point rules in the C and C++ standards.
3168 The C and C++ standards defines the order in which expressions in a C/C++
3169 program are evaluated in terms of @dfn{sequence points}, which represent
3170 a partial ordering between the execution of parts of the program: those
3171 executed before the sequence point, and those executed after it. These
3172 occur after the evaluation of a full expression (one which is not part
3173 of a larger expression), after the evaluation of the first operand of a
3174 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3175 function is called (but after the evaluation of its arguments and the
3176 expression denoting the called function), and in certain other places.
3177 Other than as expressed by the sequence point rules, the order of
3178 evaluation of subexpressions of an expression is not specified. All
3179 these rules describe only a partial order rather than a total order,
3180 since, for example, if two functions are called within one expression
3181 with no sequence point between them, the order in which the functions
3182 are called is not specified. However, the standards committee have
3183 ruled that function calls do not overlap.
3185 It is not specified when between sequence points modifications to the
3186 values of objects take effect. Programs whose behavior depends on this
3187 have undefined behavior; the C and C++ standards specify that ``Between
3188 the previous and next sequence point an object shall have its stored
3189 value modified at most once by the evaluation of an expression.
3190 Furthermore, the prior value shall be read only to determine the value
3191 to be stored.''. If a program breaks these rules, the results on any
3192 particular implementation are entirely unpredictable.
3194 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3195 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3196 diagnosed by this option, and it may give an occasional false positive
3197 result, but in general it has been found fairly effective at detecting
3198 this sort of problem in programs.
3200 The standard is worded confusingly, therefore there is some debate
3201 over the precise meaning of the sequence point rules in subtle cases.
3202 Links to discussions of the problem, including proposed formal
3203 definitions, may be found on the GCC readings page, at
3204 @w{@uref{http://gcc.gnu.org/readings.html}}.
3206 This warning is enabled by @option{-Wall} for C and C++.
3209 @opindex Wreturn-type
3210 @opindex Wno-return-type
3211 Warn whenever a function is defined with a return-type that defaults
3212 to @code{int}. Also warn about any @code{return} statement with no
3213 return-value in a function whose return-type is not @code{void}
3214 (falling off the end of the function body is considered returning
3215 without a value), and about a @code{return} statement with an
3216 expression in a function whose return-type is @code{void}.
3218 For C++, a function without return type always produces a diagnostic
3219 message, even when @option{-Wno-return-type} is specified. The only
3220 exceptions are @samp{main} and functions defined in system headers.
3222 This warning is enabled by @option{-Wall}.
3227 Warn whenever a @code{switch} statement has an index of enumerated type
3228 and lacks a @code{case} for one or more of the named codes of that
3229 enumeration. (The presence of a @code{default} label prevents this
3230 warning.) @code{case} labels outside the enumeration range also
3231 provoke warnings when this option is used (even if there is a
3232 @code{default} label).
3233 This warning is enabled by @option{-Wall}.
3235 @item -Wswitch-default
3236 @opindex Wswitch-default
3237 @opindex Wno-switch-default
3238 Warn whenever a @code{switch} statement does not have a @code{default}
3242 @opindex Wswitch-enum
3243 @opindex Wno-switch-enum
3244 Warn whenever a @code{switch} statement has an index of enumerated type
3245 and lacks a @code{case} for one or more of the named codes of that
3246 enumeration. @code{case} labels outside the enumeration range also
3247 provoke warnings when this option is used. The only difference
3248 between @option{-Wswitch} and this option is that this option gives a
3249 warning about an omitted enumeration code even if there is a
3250 @code{default} label.
3252 @item -Wsync-nand @r{(C and C++ only)}
3254 @opindex Wno-sync-nand
3255 Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
3256 built-in functions are used. These functions changed semantics in GCC 4.4.
3260 @opindex Wno-trigraphs
3261 Warn if any trigraphs are encountered that might change the meaning of
3262 the program (trigraphs within comments are not warned about).
3263 This warning is enabled by @option{-Wall}.
3265 @item -Wunused-function
3266 @opindex Wunused-function
3267 @opindex Wno-unused-function
3268 Warn whenever a static function is declared but not defined or a
3269 non-inline static function is unused.
3270 This warning is enabled by @option{-Wall}.
3272 @item -Wunused-label
3273 @opindex Wunused-label
3274 @opindex Wno-unused-label
3275 Warn whenever a label is declared but not used.
3276 This warning is enabled by @option{-Wall}.
3278 To suppress this warning use the @samp{unused} attribute
3279 (@pxref{Variable Attributes}).
3281 @item -Wunused-parameter
3282 @opindex Wunused-parameter
3283 @opindex Wno-unused-parameter
3284 Warn whenever a function parameter is unused aside from its declaration.
3286 To suppress this warning use the @samp{unused} attribute
3287 (@pxref{Variable Attributes}).
3289 @item -Wno-unused-result
3290 @opindex Wunused-result
3291 @opindex Wno-unused-result
3292 Do not warn if a caller of a function marked with attribute
3293 @code{warn_unused_result} (@pxref{Variable Attributes}) does not use
3294 its return value. The default is @option{-Wunused-result}.
3296 @item -Wunused-variable
3297 @opindex Wunused-variable
3298 @opindex Wno-unused-variable
3299 Warn whenever a local variable or non-constant static variable is unused
3300 aside from its declaration.
3301 This warning is enabled by @option{-Wall}.
3303 To suppress this warning use the @samp{unused} attribute
3304 (@pxref{Variable Attributes}).
3306 @item -Wunused-value
3307 @opindex Wunused-value
3308 @opindex Wno-unused-value
3309 Warn whenever a statement computes a result that is explicitly not
3310 used. To suppress this warning cast the unused expression to
3311 @samp{void}. This includes an expression-statement or the left-hand
3312 side of a comma expression that contains no side effects. For example,
3313 an expression such as @samp{x[i,j]} will cause a warning, while
3314 @samp{x[(void)i,j]} will not.
3316 This warning is enabled by @option{-Wall}.
3321 All the above @option{-Wunused} options combined.
3323 In order to get a warning about an unused function parameter, you must
3324 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3325 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3327 @item -Wuninitialized
3328 @opindex Wuninitialized
3329 @opindex Wno-uninitialized
3330 Warn if an automatic variable is used without first being initialized
3331 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3332 warn if a non-static reference or non-static @samp{const} member
3333 appears in a class without constructors.
3335 If you want to warn about code which uses the uninitialized value of the
3336 variable in its own initializer, use the @option{-Winit-self} option.
3338 These warnings occur for individual uninitialized or clobbered
3339 elements of structure, union or array variables as well as for
3340 variables which are uninitialized or clobbered as a whole. They do
3341 not occur for variables or elements declared @code{volatile}. Because
3342 these warnings depend on optimization, the exact variables or elements
3343 for which there are warnings will depend on the precise optimization
3344 options and version of GCC used.
3346 Note that there may be no warning about a variable that is used only
3347 to compute a value that itself is never used, because such
3348 computations may be deleted by data flow analysis before the warnings
3351 These warnings are made optional because GCC is not smart
3352 enough to see all the reasons why the code might be correct
3353 despite appearing to have an error. Here is one example of how
3374 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3375 always initialized, but GCC doesn't know this. Here is
3376 another common case:
3381 if (change_y) save_y = y, y = new_y;
3383 if (change_y) y = save_y;
3388 This has no bug because @code{save_y} is used only if it is set.
3390 @cindex @code{longjmp} warnings
3391 This option also warns when a non-volatile automatic variable might be
3392 changed by a call to @code{longjmp}. These warnings as well are possible
3393 only in optimizing compilation.
3395 The compiler sees only the calls to @code{setjmp}. It cannot know
3396 where @code{longjmp} will be called; in fact, a signal handler could
3397 call it at any point in the code. As a result, you may get a warning
3398 even when there is in fact no problem because @code{longjmp} cannot
3399 in fact be called at the place which would cause a problem.
3401 Some spurious warnings can be avoided if you declare all the functions
3402 you use that never return as @code{noreturn}. @xref{Function
3405 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3407 @item -Wunknown-pragmas
3408 @opindex Wunknown-pragmas
3409 @opindex Wno-unknown-pragmas
3410 @cindex warning for unknown pragmas
3411 @cindex unknown pragmas, warning
3412 @cindex pragmas, warning of unknown
3413 Warn when a #pragma directive is encountered which is not understood by
3414 GCC@. If this command line option is used, warnings will even be issued
3415 for unknown pragmas in system header files. This is not the case if
3416 the warnings were only enabled by the @option{-Wall} command line option.
3419 @opindex Wno-pragmas
3421 Do not warn about misuses of pragmas, such as incorrect parameters,
3422 invalid syntax, or conflicts between pragmas. See also
3423 @samp{-Wunknown-pragmas}.
3425 @item -Wstrict-aliasing
3426 @opindex Wstrict-aliasing
3427 @opindex Wno-strict-aliasing
3428 This option is only active when @option{-fstrict-aliasing} is active.
3429 It warns about code which might break the strict aliasing rules that the
3430 compiler is using for optimization. The warning does not catch all
3431 cases, but does attempt to catch the more common pitfalls. It is
3432 included in @option{-Wall}.
3433 It is equivalent to @option{-Wstrict-aliasing=3}
3435 @item -Wstrict-aliasing=n
3436 @opindex Wstrict-aliasing=n
3437 @opindex Wno-strict-aliasing=n
3438 This option is only active when @option{-fstrict-aliasing} is active.
3439 It warns about code which might break the strict aliasing rules that the
3440 compiler is using for optimization.
3441 Higher levels correspond to higher accuracy (fewer false positives).
3442 Higher levels also correspond to more effort, similar to the way -O works.
3443 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3446 Level 1: Most aggressive, quick, least accurate.
3447 Possibly useful when higher levels
3448 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3449 false negatives. However, it has many false positives.
3450 Warns for all pointer conversions between possibly incompatible types,
3451 even if never dereferenced. Runs in the frontend only.
3453 Level 2: Aggressive, quick, not too precise.
3454 May still have many false positives (not as many as level 1 though),
3455 and few false negatives (but possibly more than level 1).
3456 Unlike level 1, it only warns when an address is taken. Warns about
3457 incomplete types. Runs in the frontend only.
3459 Level 3 (default for @option{-Wstrict-aliasing}):
3460 Should have very few false positives and few false
3461 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3462 Takes care of the common punn+dereference pattern in the frontend:
3463 @code{*(int*)&some_float}.
3464 If optimization is enabled, it also runs in the backend, where it deals
3465 with multiple statement cases using flow-sensitive points-to information.
3466 Only warns when the converted pointer is dereferenced.
3467 Does not warn about incomplete types.
3469 @item -Wstrict-overflow
3470 @itemx -Wstrict-overflow=@var{n}
3471 @opindex Wstrict-overflow
3472 @opindex Wno-strict-overflow
3473 This option is only active when @option{-fstrict-overflow} is active.
3474 It warns about cases where the compiler optimizes based on the
3475 assumption that signed overflow does not occur. Note that it does not
3476 warn about all cases where the code might overflow: it only warns
3477 about cases where the compiler implements some optimization. Thus
3478 this warning depends on the optimization level.
3480 An optimization which assumes that signed overflow does not occur is
3481 perfectly safe if the values of the variables involved are such that
3482 overflow never does, in fact, occur. Therefore this warning can
3483 easily give a false positive: a warning about code which is not
3484 actually a problem. To help focus on important issues, several
3485 warning levels are defined. No warnings are issued for the use of
3486 undefined signed overflow when estimating how many iterations a loop
3487 will require, in particular when determining whether a loop will be
3491 @item -Wstrict-overflow=1
3492 Warn about cases which are both questionable and easy to avoid. For
3493 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3494 compiler will simplify this to @code{1}. This level of
3495 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3496 are not, and must be explicitly requested.
3498 @item -Wstrict-overflow=2
3499 Also warn about other cases where a comparison is simplified to a
3500 constant. For example: @code{abs (x) >= 0}. This can only be
3501 simplified when @option{-fstrict-overflow} is in effect, because
3502 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3503 zero. @option{-Wstrict-overflow} (with no level) is the same as
3504 @option{-Wstrict-overflow=2}.
3506 @item -Wstrict-overflow=3
3507 Also warn about other cases where a comparison is simplified. For
3508 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3510 @item -Wstrict-overflow=4
3511 Also warn about other simplifications not covered by the above cases.
3512 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3514 @item -Wstrict-overflow=5
3515 Also warn about cases where the compiler reduces the magnitude of a
3516 constant involved in a comparison. For example: @code{x + 2 > y} will
3517 be simplified to @code{x + 1 >= y}. This is reported only at the
3518 highest warning level because this simplification applies to many
3519 comparisons, so this warning level will give a very large number of
3523 @item -Warray-bounds
3524 @opindex Wno-array-bounds
3525 @opindex Warray-bounds
3526 This option is only active when @option{-ftree-vrp} is active
3527 (default for -O2 and above). It warns about subscripts to arrays
3528 that are always out of bounds. This warning is enabled by @option{-Wall}.
3530 @item -Wno-div-by-zero
3531 @opindex Wno-div-by-zero
3532 @opindex Wdiv-by-zero
3533 Do not warn about compile-time integer division by zero. Floating point
3534 division by zero is not warned about, as it can be a legitimate way of
3535 obtaining infinities and NaNs.
3537 @item -Wsystem-headers
3538 @opindex Wsystem-headers
3539 @opindex Wno-system-headers
3540 @cindex warnings from system headers
3541 @cindex system headers, warnings from
3542 Print warning messages for constructs found in system header files.
3543 Warnings from system headers are normally suppressed, on the assumption
3544 that they usually do not indicate real problems and would only make the
3545 compiler output harder to read. Using this command line option tells
3546 GCC to emit warnings from system headers as if they occurred in user
3547 code. However, note that using @option{-Wall} in conjunction with this
3548 option will @emph{not} warn about unknown pragmas in system
3549 headers---for that, @option{-Wunknown-pragmas} must also be used.
3552 @opindex Wfloat-equal
3553 @opindex Wno-float-equal
3554 Warn if floating point values are used in equality comparisons.
3556 The idea behind this is that sometimes it is convenient (for the
3557 programmer) to consider floating-point values as approximations to
3558 infinitely precise real numbers. If you are doing this, then you need
3559 to compute (by analyzing the code, or in some other way) the maximum or
3560 likely maximum error that the computation introduces, and allow for it
3561 when performing comparisons (and when producing output, but that's a
3562 different problem). In particular, instead of testing for equality, you
3563 would check to see whether the two values have ranges that overlap; and
3564 this is done with the relational operators, so equality comparisons are
3567 @item -Wtraditional @r{(C and Objective-C only)}
3568 @opindex Wtraditional
3569 @opindex Wno-traditional
3570 Warn about certain constructs that behave differently in traditional and
3571 ISO C@. Also warn about ISO C constructs that have no traditional C
3572 equivalent, and/or problematic constructs which should be avoided.
3576 Macro parameters that appear within string literals in the macro body.
3577 In traditional C macro replacement takes place within string literals,
3578 but does not in ISO C@.
3581 In traditional C, some preprocessor directives did not exist.
3582 Traditional preprocessors would only consider a line to be a directive
3583 if the @samp{#} appeared in column 1 on the line. Therefore
3584 @option{-Wtraditional} warns about directives that traditional C
3585 understands but would ignore because the @samp{#} does not appear as the
3586 first character on the line. It also suggests you hide directives like
3587 @samp{#pragma} not understood by traditional C by indenting them. Some
3588 traditional implementations would not recognize @samp{#elif}, so it
3589 suggests avoiding it altogether.
3592 A function-like macro that appears without arguments.
3595 The unary plus operator.
3598 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3599 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3600 constants.) Note, these suffixes appear in macros defined in the system
3601 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3602 Use of these macros in user code might normally lead to spurious
3603 warnings, however GCC's integrated preprocessor has enough context to
3604 avoid warning in these cases.
3607 A function declared external in one block and then used after the end of
3611 A @code{switch} statement has an operand of type @code{long}.
3614 A non-@code{static} function declaration follows a @code{static} one.
3615 This construct is not accepted by some traditional C compilers.
3618 The ISO type of an integer constant has a different width or
3619 signedness from its traditional type. This warning is only issued if
3620 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3621 typically represent bit patterns, are not warned about.
3624 Usage of ISO string concatenation is detected.
3627 Initialization of automatic aggregates.
3630 Identifier conflicts with labels. Traditional C lacks a separate
3631 namespace for labels.
3634 Initialization of unions. If the initializer is zero, the warning is
3635 omitted. This is done under the assumption that the zero initializer in
3636 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3637 initializer warnings and relies on default initialization to zero in the
3641 Conversions by prototypes between fixed/floating point values and vice
3642 versa. The absence of these prototypes when compiling with traditional
3643 C would cause serious problems. This is a subset of the possible
3644 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3647 Use of ISO C style function definitions. This warning intentionally is
3648 @emph{not} issued for prototype declarations or variadic functions
3649 because these ISO C features will appear in your code when using
3650 libiberty's traditional C compatibility macros, @code{PARAMS} and
3651 @code{VPARAMS}. This warning is also bypassed for nested functions
3652 because that feature is already a GCC extension and thus not relevant to
3653 traditional C compatibility.
3656 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3657 @opindex Wtraditional-conversion
3658 @opindex Wno-traditional-conversion
3659 Warn if a prototype causes a type conversion that is different from what
3660 would happen to the same argument in the absence of a prototype. This
3661 includes conversions of fixed point to floating and vice versa, and
3662 conversions changing the width or signedness of a fixed point argument
3663 except when the same as the default promotion.
3665 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3666 @opindex Wdeclaration-after-statement
3667 @opindex Wno-declaration-after-statement
3668 Warn when a declaration is found after a statement in a block. This
3669 construct, known from C++, was introduced with ISO C99 and is by default
3670 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3671 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3676 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3678 @item -Wno-endif-labels
3679 @opindex Wno-endif-labels
3680 @opindex Wendif-labels
3681 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3686 Warn whenever a local variable shadows another local variable, parameter or
3687 global variable or whenever a built-in function is shadowed.
3689 @item -Wlarger-than=@var{len}
3690 @opindex Wlarger-than=@var{len}
3691 @opindex Wlarger-than-@var{len}
3692 Warn whenever an object of larger than @var{len} bytes is defined.
3694 @item -Wframe-larger-than=@var{len}
3695 @opindex Wframe-larger-than
3696 Warn if the size of a function frame is larger than @var{len} bytes.
3697 The computation done to determine the stack frame size is approximate
3698 and not conservative.
3699 The actual requirements may be somewhat greater than @var{len}
3700 even if you do not get a warning. In addition, any space allocated
3701 via @code{alloca}, variable-length arrays, or related constructs
3702 is not included by the compiler when determining
3703 whether or not to issue a warning.
3705 @item -Wunsafe-loop-optimizations
3706 @opindex Wunsafe-loop-optimizations
3707 @opindex Wno-unsafe-loop-optimizations
3708 Warn if the loop cannot be optimized because the compiler could not
3709 assume anything on the bounds of the loop indices. With
3710 @option{-funsafe-loop-optimizations} warn if the compiler made
3713 @item -Wno-pedantic-ms-format @r{(MinGW targets only)}
3714 @opindex Wno-pedantic-ms-format
3715 @opindex Wpedantic-ms-format
3716 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3717 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3718 depending on the MS runtime, when you are using the options @option{-Wformat}
3719 and @option{-pedantic} without gnu-extensions.
3721 @item -Wpointer-arith
3722 @opindex Wpointer-arith
3723 @opindex Wno-pointer-arith
3724 Warn about anything that depends on the ``size of'' a function type or
3725 of @code{void}. GNU C assigns these types a size of 1, for
3726 convenience in calculations with @code{void *} pointers and pointers
3727 to functions. In C++, warn also when an arithmetic operation involves
3728 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3731 @opindex Wtype-limits
3732 @opindex Wno-type-limits
3733 Warn if a comparison is always true or always false due to the limited
3734 range of the data type, but do not warn for constant expressions. For
3735 example, warn if an unsigned variable is compared against zero with
3736 @samp{<} or @samp{>=}. This warning is also enabled by
3739 @item -Wbad-function-cast @r{(C and Objective-C only)}
3740 @opindex Wbad-function-cast
3741 @opindex Wno-bad-function-cast
3742 Warn whenever a function call is cast to a non-matching type.
3743 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3745 @item -Wc++-compat @r{(C and Objective-C only)}
3746 Warn about ISO C constructs that are outside of the common subset of
3747 ISO C and ISO C++, e.g.@: request for implicit conversion from
3748 @code{void *} to a pointer to non-@code{void} type.
3750 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3751 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3752 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3753 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3757 @opindex Wno-cast-qual
3758 Warn whenever a pointer is cast so as to remove a type qualifier from
3759 the target type. For example, warn if a @code{const char *} is cast
3760 to an ordinary @code{char *}.
3762 Also warn when making a cast which introduces a type qualifier in an
3763 unsafe way. For example, casting @code{char **} to @code{const char **}
3764 is unsafe, as in this example:
3767 /* p is char ** value. */
3768 const char **q = (const char **) p;
3769 /* Assignment of readonly string to const char * is OK. */
3771 /* Now char** pointer points to read-only memory. */
3776 @opindex Wcast-align
3777 @opindex Wno-cast-align
3778 Warn whenever a pointer is cast such that the required alignment of the
3779 target is increased. For example, warn if a @code{char *} is cast to
3780 an @code{int *} on machines where integers can only be accessed at
3781 two- or four-byte boundaries.
3783 @item -Wwrite-strings
3784 @opindex Wwrite-strings
3785 @opindex Wno-write-strings
3786 When compiling C, give string constants the type @code{const
3787 char[@var{length}]} so that copying the address of one into a
3788 non-@code{const} @code{char *} pointer will get a warning. These
3789 warnings will help you find at compile time code that can try to write
3790 into a string constant, but only if you have been very careful about
3791 using @code{const} in declarations and prototypes. Otherwise, it will
3792 just be a nuisance. This is why we did not make @option{-Wall} request
3795 When compiling C++, warn about the deprecated conversion from string
3796 literals to @code{char *}. This warning is enabled by default for C++
3801 @opindex Wno-clobbered
3802 Warn for variables that might be changed by @samp{longjmp} or
3803 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3806 @opindex Wconversion
3807 @opindex Wno-conversion
3808 Warn for implicit conversions that may alter a value. This includes
3809 conversions between real and integer, like @code{abs (x)} when
3810 @code{x} is @code{double}; conversions between signed and unsigned,
3811 like @code{unsigned ui = -1}; and conversions to smaller types, like
3812 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3813 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3814 changed by the conversion like in @code{abs (2.0)}. Warnings about
3815 conversions between signed and unsigned integers can be disabled by
3816 using @option{-Wno-sign-conversion}.
3818 For C++, also warn for conversions between @code{NULL} and non-pointer
3819 types; confusing overload resolution for user-defined conversions; and
3820 conversions that will never use a type conversion operator:
3821 conversions to @code{void}, the same type, a base class or a reference
3822 to them. Warnings about conversions between signed and unsigned
3823 integers are disabled by default in C++ unless
3824 @option{-Wsign-conversion} is explicitly enabled.
3827 @opindex Wempty-body
3828 @opindex Wno-empty-body
3829 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3830 while} statement. This warning is also enabled by @option{-Wextra}.
3832 @item -Wenum-compare
3833 @opindex Wenum-compare
3834 @opindex Wno-enum-compare
3835 Warn about a comparison between values of different enum types. In C++
3836 this warning is enabled by default. In C this warning is enabled by
3839 @item -Wjump-misses-init @r{(C, Objective-C only)}
3840 @opindex Wjump-misses-init
3841 @opindex Wno-jump-misses-init
3842 Warn if a @code{goto} statement or a @code{switch} statement jumps
3843 forward across the initialization of a variable, or jumps backward to a
3844 label after the variable has been initialized. This only warns about
3845 variables which are initialized when they are declared. This warning is
3846 only supported for C and Objective C; in C++ this sort of branch is an
3849 @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
3850 can be disabled with the @option{-Wno-jump-misses-init} option.
3852 @item -Wsign-compare
3853 @opindex Wsign-compare
3854 @opindex Wno-sign-compare
3855 @cindex warning for comparison of signed and unsigned values
3856 @cindex comparison of signed and unsigned values, warning
3857 @cindex signed and unsigned values, comparison warning
3858 Warn when a comparison between signed and unsigned values could produce
3859 an incorrect result when the signed value is converted to unsigned.
3860 This warning is also enabled by @option{-Wextra}; to get the other warnings
3861 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3863 @item -Wsign-conversion
3864 @opindex Wsign-conversion
3865 @opindex Wno-sign-conversion
3866 Warn for implicit conversions that may change the sign of an integer
3867 value, like assigning a signed integer expression to an unsigned
3868 integer variable. An explicit cast silences the warning. In C, this
3869 option is enabled also by @option{-Wconversion}.
3873 @opindex Wno-address
3874 Warn about suspicious uses of memory addresses. These include using
3875 the address of a function in a conditional expression, such as
3876 @code{void func(void); if (func)}, and comparisons against the memory
3877 address of a string literal, such as @code{if (x == "abc")}. Such
3878 uses typically indicate a programmer error: the address of a function
3879 always evaluates to true, so their use in a conditional usually
3880 indicate that the programmer forgot the parentheses in a function
3881 call; and comparisons against string literals result in unspecified
3882 behavior and are not portable in C, so they usually indicate that the
3883 programmer intended to use @code{strcmp}. This warning is enabled by
3887 @opindex Wlogical-op
3888 @opindex Wno-logical-op
3889 Warn about suspicious uses of logical operators in expressions.
3890 This includes using logical operators in contexts where a
3891 bit-wise operator is likely to be expected.
3893 @item -Waggregate-return
3894 @opindex Waggregate-return
3895 @opindex Wno-aggregate-return
3896 Warn if any functions that return structures or unions are defined or
3897 called. (In languages where you can return an array, this also elicits
3900 @item -Wno-attributes
3901 @opindex Wno-attributes
3902 @opindex Wattributes
3903 Do not warn if an unexpected @code{__attribute__} is used, such as
3904 unrecognized attributes, function attributes applied to variables,
3905 etc. This will not stop errors for incorrect use of supported
3908 @item -Wno-builtin-macro-redefined
3909 @opindex Wno-builtin-macro-redefined
3910 @opindex Wbuiltin-macro-redefined
3911 Do not warn if certain built-in macros are redefined. This suppresses
3912 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
3913 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
3915 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3916 @opindex Wstrict-prototypes
3917 @opindex Wno-strict-prototypes
3918 Warn if a function is declared or defined without specifying the
3919 argument types. (An old-style function definition is permitted without
3920 a warning if preceded by a declaration which specifies the argument
3923 @item -Wold-style-declaration @r{(C and Objective-C only)}
3924 @opindex Wold-style-declaration
3925 @opindex Wno-old-style-declaration
3926 Warn for obsolescent usages, according to the C Standard, in a
3927 declaration. For example, warn if storage-class specifiers like
3928 @code{static} are not the first things in a declaration. This warning
3929 is also enabled by @option{-Wextra}.
3931 @item -Wold-style-definition @r{(C and Objective-C only)}
3932 @opindex Wold-style-definition
3933 @opindex Wno-old-style-definition
3934 Warn if an old-style function definition is used. A warning is given
3935 even if there is a previous prototype.
3937 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3938 @opindex Wmissing-parameter-type
3939 @opindex Wno-missing-parameter-type
3940 A function parameter is declared without a type specifier in K&R-style
3947 This warning is also enabled by @option{-Wextra}.
3949 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3950 @opindex Wmissing-prototypes
3951 @opindex Wno-missing-prototypes
3952 Warn if a global function is defined without a previous prototype
3953 declaration. This warning is issued even if the definition itself
3954 provides a prototype. The aim is to detect global functions that fail
3955 to be declared in header files.
3957 @item -Wmissing-declarations
3958 @opindex Wmissing-declarations
3959 @opindex Wno-missing-declarations
3960 Warn if a global function is defined without a previous declaration.
3961 Do so even if the definition itself provides a prototype.
3962 Use this option to detect global functions that are not declared in
3963 header files. In C++, no warnings are issued for function templates,
3964 or for inline functions, or for functions in anonymous namespaces.
3966 @item -Wmissing-field-initializers
3967 @opindex Wmissing-field-initializers
3968 @opindex Wno-missing-field-initializers
3972 Warn if a structure's initializer has some fields missing. For
3973 example, the following code would cause such a warning, because
3974 @code{x.h} is implicitly zero:
3977 struct s @{ int f, g, h; @};
3978 struct s x = @{ 3, 4 @};
3981 This option does not warn about designated initializers, so the following
3982 modification would not trigger a warning:
3985 struct s @{ int f, g, h; @};
3986 struct s x = @{ .f = 3, .g = 4 @};
3989 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3990 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3992 @item -Wmissing-noreturn
3993 @opindex Wmissing-noreturn
3994 @opindex Wno-missing-noreturn
3995 Warn about functions which might be candidates for attribute @code{noreturn}.
3996 Note these are only possible candidates, not absolute ones. Care should
3997 be taken to manually verify functions actually do not ever return before
3998 adding the @code{noreturn} attribute, otherwise subtle code generation
3999 bugs could be introduced. You will not get a warning for @code{main} in
4000 hosted C environments.
4002 @item -Wmissing-format-attribute
4003 @opindex Wmissing-format-attribute
4004 @opindex Wno-missing-format-attribute
4007 Warn about function pointers which might be candidates for @code{format}
4008 attributes. Note these are only possible candidates, not absolute ones.
4009 GCC will guess that function pointers with @code{format} attributes that
4010 are used in assignment, initialization, parameter passing or return
4011 statements should have a corresponding @code{format} attribute in the
4012 resulting type. I.e.@: the left-hand side of the assignment or
4013 initialization, the type of the parameter variable, or the return type
4014 of the containing function respectively should also have a @code{format}
4015 attribute to avoid the warning.
4017 GCC will also warn about function definitions which might be
4018 candidates for @code{format} attributes. Again, these are only
4019 possible candidates. GCC will guess that @code{format} attributes
4020 might be appropriate for any function that calls a function like
4021 @code{vprintf} or @code{vscanf}, but this might not always be the
4022 case, and some functions for which @code{format} attributes are
4023 appropriate may not be detected.
4025 @item -Wno-multichar
4026 @opindex Wno-multichar
4028 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
4029 Usually they indicate a typo in the user's code, as they have
4030 implementation-defined values, and should not be used in portable code.
4032 @item -Wnormalized=<none|id|nfc|nfkc>
4033 @opindex Wnormalized=
4036 @cindex character set, input normalization
4037 In ISO C and ISO C++, two identifiers are different if they are
4038 different sequences of characters. However, sometimes when characters
4039 outside the basic ASCII character set are used, you can have two
4040 different character sequences that look the same. To avoid confusion,
4041 the ISO 10646 standard sets out some @dfn{normalization rules} which
4042 when applied ensure that two sequences that look the same are turned into
4043 the same sequence. GCC can warn you if you are using identifiers which
4044 have not been normalized; this option controls that warning.
4046 There are four levels of warning that GCC supports. The default is
4047 @option{-Wnormalized=nfc}, which warns about any identifier which is
4048 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
4049 recommended form for most uses.
4051 Unfortunately, there are some characters which ISO C and ISO C++ allow
4052 in identifiers that when turned into NFC aren't allowable as
4053 identifiers. That is, there's no way to use these symbols in portable
4054 ISO C or C++ and have all your identifiers in NFC@.
4055 @option{-Wnormalized=id} suppresses the warning for these characters.
4056 It is hoped that future versions of the standards involved will correct
4057 this, which is why this option is not the default.
4059 You can switch the warning off for all characters by writing
4060 @option{-Wnormalized=none}. You would only want to do this if you
4061 were using some other normalization scheme (like ``D''), because
4062 otherwise you can easily create bugs that are literally impossible to see.
4064 Some characters in ISO 10646 have distinct meanings but look identical
4065 in some fonts or display methodologies, especially once formatting has
4066 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
4067 LETTER N'', will display just like a regular @code{n} which has been
4068 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
4069 normalization scheme to convert all these into a standard form as
4070 well, and GCC will warn if your code is not in NFKC if you use
4071 @option{-Wnormalized=nfkc}. This warning is comparable to warning
4072 about every identifier that contains the letter O because it might be
4073 confused with the digit 0, and so is not the default, but may be
4074 useful as a local coding convention if the programming environment is
4075 unable to be fixed to display these characters distinctly.
4077 @item -Wno-deprecated
4078 @opindex Wno-deprecated
4079 @opindex Wdeprecated
4080 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
4082 @item -Wno-deprecated-declarations
4083 @opindex Wno-deprecated-declarations
4084 @opindex Wdeprecated-declarations
4085 Do not warn about uses of functions (@pxref{Function Attributes}),
4086 variables (@pxref{Variable Attributes}), and types (@pxref{Type
4087 Attributes}) marked as deprecated by using the @code{deprecated}
4091 @opindex Wno-overflow
4093 Do not warn about compile-time overflow in constant expressions.
4095 @item -Woverride-init @r{(C and Objective-C only)}
4096 @opindex Woverride-init
4097 @opindex Wno-override-init
4101 Warn if an initialized field without side effects is overridden when
4102 using designated initializers (@pxref{Designated Inits, , Designated
4105 This warning is included in @option{-Wextra}. To get other
4106 @option{-Wextra} warnings without this one, use @samp{-Wextra
4107 -Wno-override-init}.
4112 Warn if a structure is given the packed attribute, but the packed
4113 attribute has no effect on the layout or size of the structure.
4114 Such structures may be mis-aligned for little benefit. For
4115 instance, in this code, the variable @code{f.x} in @code{struct bar}
4116 will be misaligned even though @code{struct bar} does not itself
4117 have the packed attribute:
4124 @} __attribute__((packed));
4132 @item -Wpacked-bitfield-compat
4133 @opindex Wpacked-bitfield-compat
4134 @opindex Wno-packed-bitfield-compat
4135 The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
4136 on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
4137 the change can lead to differences in the structure layout. GCC
4138 informs you when the offset of such a field has changed in GCC 4.4.
4139 For example there is no longer a 4-bit padding between field @code{a}
4140 and @code{b} in this structure:
4147 @} __attribute__ ((packed));
4150 This warning is enabled by default. Use
4151 @option{-Wno-packed-bitfield-compat} to disable this warning.
4156 Warn if padding is included in a structure, either to align an element
4157 of the structure or to align the whole structure. Sometimes when this
4158 happens it is possible to rearrange the fields of the structure to
4159 reduce the padding and so make the structure smaller.
4161 @item -Wredundant-decls
4162 @opindex Wredundant-decls
4163 @opindex Wno-redundant-decls
4164 Warn if anything is declared more than once in the same scope, even in
4165 cases where multiple declaration is valid and changes nothing.
4167 @item -Wnested-externs @r{(C and Objective-C only)}
4168 @opindex Wnested-externs
4169 @opindex Wno-nested-externs
4170 Warn if an @code{extern} declaration is encountered within a function.
4172 @item -Wunreachable-code
4173 @opindex Wunreachable-code
4174 @opindex Wno-unreachable-code
4175 Warn if the compiler detects that code will never be executed.
4177 This option is intended to warn when the compiler detects that at
4178 least a whole line of source code will never be executed, because
4179 some condition is never satisfied or because it is after a
4180 procedure that never returns.
4182 It is possible for this option to produce a warning even though there
4183 are circumstances under which part of the affected line can be executed,
4184 so care should be taken when removing apparently-unreachable code.
4186 For instance, when a function is inlined, a warning may mean that the
4187 line is unreachable in only one inlined copy of the function.
4189 This option is not made part of @option{-Wall} because in a debugging
4190 version of a program there is often substantial code which checks
4191 correct functioning of the program and is, hopefully, unreachable
4192 because the program does work. Another common use of unreachable
4193 code is to provide behavior which is selectable at compile-time.
4198 Warn if a function can not be inlined and it was declared as inline.
4199 Even with this option, the compiler will not warn about failures to
4200 inline functions declared in system headers.
4202 The compiler uses a variety of heuristics to determine whether or not
4203 to inline a function. For example, the compiler takes into account
4204 the size of the function being inlined and the amount of inlining
4205 that has already been done in the current function. Therefore,
4206 seemingly insignificant changes in the source program can cause the
4207 warnings produced by @option{-Winline} to appear or disappear.
4209 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4210 @opindex Wno-invalid-offsetof
4211 @opindex Winvalid-offsetof
4212 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4213 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4214 to a non-POD type is undefined. In existing C++ implementations,
4215 however, @samp{offsetof} typically gives meaningful results even when
4216 applied to certain kinds of non-POD types. (Such as a simple
4217 @samp{struct} that fails to be a POD type only by virtue of having a
4218 constructor.) This flag is for users who are aware that they are
4219 writing nonportable code and who have deliberately chosen to ignore the
4222 The restrictions on @samp{offsetof} may be relaxed in a future version
4223 of the C++ standard.
4225 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4226 @opindex Wno-int-to-pointer-cast
4227 @opindex Wint-to-pointer-cast
4228 Suppress warnings from casts to pointer type of an integer of a
4231 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4232 @opindex Wno-pointer-to-int-cast
4233 @opindex Wpointer-to-int-cast
4234 Suppress warnings from casts from a pointer to an integer type of a
4238 @opindex Winvalid-pch
4239 @opindex Wno-invalid-pch
4240 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4241 the search path but can't be used.
4245 @opindex Wno-long-long
4246 Warn if @samp{long long} type is used. This is enabled by either
4247 @option{-pedantic} or @option{-Wtraditional} in ISO C90 and C++98
4248 modes. To inhibit the warning messages, use @option{-Wno-long-long}.
4250 @item -Wvariadic-macros
4251 @opindex Wvariadic-macros
4252 @opindex Wno-variadic-macros
4253 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4254 alternate syntax when in pedantic ISO C99 mode. This is default.
4255 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4260 Warn if variable length array is used in the code.
4261 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4262 the variable length array.
4264 @item -Wvolatile-register-var
4265 @opindex Wvolatile-register-var
4266 @opindex Wno-volatile-register-var
4267 Warn if a register variable is declared volatile. The volatile
4268 modifier does not inhibit all optimizations that may eliminate reads
4269 and/or writes to register variables. This warning is enabled by
4272 @item -Wdisabled-optimization
4273 @opindex Wdisabled-optimization
4274 @opindex Wno-disabled-optimization
4275 Warn if a requested optimization pass is disabled. This warning does
4276 not generally indicate that there is anything wrong with your code; it
4277 merely indicates that GCC's optimizers were unable to handle the code
4278 effectively. Often, the problem is that your code is too big or too
4279 complex; GCC will refuse to optimize programs when the optimization
4280 itself is likely to take inordinate amounts of time.
4282 @item -Wpointer-sign @r{(C and Objective-C only)}
4283 @opindex Wpointer-sign
4284 @opindex Wno-pointer-sign
4285 Warn for pointer argument passing or assignment with different signedness.
4286 This option is only supported for C and Objective-C@. It is implied by
4287 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4288 @option{-Wno-pointer-sign}.
4290 @item -Wstack-protector
4291 @opindex Wstack-protector
4292 @opindex Wno-stack-protector
4293 This option is only active when @option{-fstack-protector} is active. It
4294 warns about functions that will not be protected against stack smashing.
4297 @opindex Wno-mudflap
4298 Suppress warnings about constructs that cannot be instrumented by
4301 @item -Woverlength-strings
4302 @opindex Woverlength-strings
4303 @opindex Wno-overlength-strings
4304 Warn about string constants which are longer than the ``minimum
4305 maximum'' length specified in the C standard. Modern compilers
4306 generally allow string constants which are much longer than the
4307 standard's minimum limit, but very portable programs should avoid
4308 using longer strings.
4310 The limit applies @emph{after} string constant concatenation, and does
4311 not count the trailing NUL@. In C89, the limit was 509 characters; in
4312 C99, it was raised to 4095. C++98 does not specify a normative
4313 minimum maximum, so we do not diagnose overlength strings in C++@.
4315 This option is implied by @option{-pedantic}, and can be disabled with
4316 @option{-Wno-overlength-strings}.
4318 @item -Wunsuffixed-float-constants
4319 @opindex Wunsuffixed-float-constants
4321 GCC will issue a warning for any floating constant that does not have
4322 a suffix. When used together with @option{-Wsystem-headers} it will
4323 warn about such constants in system header files. This can be useful
4324 when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
4325 from the decimal floating-point extension to C99.
4328 @node Debugging Options
4329 @section Options for Debugging Your Program or GCC
4330 @cindex options, debugging
4331 @cindex debugging information options
4333 GCC has various special options that are used for debugging
4334 either your program or GCC:
4339 Produce debugging information in the operating system's native format
4340 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4343 On most systems that use stabs format, @option{-g} enables use of extra
4344 debugging information that only GDB can use; this extra information
4345 makes debugging work better in GDB but will probably make other debuggers
4347 refuse to read the program. If you want to control for certain whether
4348 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4349 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4351 GCC allows you to use @option{-g} with
4352 @option{-O}. The shortcuts taken by optimized code may occasionally
4353 produce surprising results: some variables you declared may not exist
4354 at all; flow of control may briefly move where you did not expect it;
4355 some statements may not be executed because they compute constant
4356 results or their values were already at hand; some statements may
4357 execute in different places because they were moved out of loops.
4359 Nevertheless it proves possible to debug optimized output. This makes
4360 it reasonable to use the optimizer for programs that might have bugs.
4362 The following options are useful when GCC is generated with the
4363 capability for more than one debugging format.
4367 Produce debugging information for use by GDB@. This means to use the
4368 most expressive format available (DWARF 2, stabs, or the native format
4369 if neither of those are supported), including GDB extensions if at all
4374 Produce debugging information in stabs format (if that is supported),
4375 without GDB extensions. This is the format used by DBX on most BSD
4376 systems. On MIPS, Alpha and System V Release 4 systems this option
4377 produces stabs debugging output which is not understood by DBX or SDB@.
4378 On System V Release 4 systems this option requires the GNU assembler.
4380 @item -feliminate-unused-debug-symbols
4381 @opindex feliminate-unused-debug-symbols
4382 Produce debugging information in stabs format (if that is supported),
4383 for only symbols that are actually used.
4385 @item -femit-class-debug-always
4386 Instead of emitting debugging information for a C++ class in only one
4387 object file, emit it in all object files using the class. This option
4388 should be used only with debuggers that are unable to handle the way GCC
4389 normally emits debugging information for classes because using this
4390 option will increase the size of debugging information by as much as a
4395 Produce debugging information in stabs format (if that is supported),
4396 using GNU extensions understood only by the GNU debugger (GDB)@. The
4397 use of these extensions is likely to make other debuggers crash or
4398 refuse to read the program.
4402 Produce debugging information in COFF format (if that is supported).
4403 This is the format used by SDB on most System V systems prior to
4408 Produce debugging information in XCOFF format (if that is supported).
4409 This is the format used by the DBX debugger on IBM RS/6000 systems.
4413 Produce debugging information in XCOFF format (if that is supported),
4414 using GNU extensions understood only by the GNU debugger (GDB)@. The
4415 use of these extensions is likely to make other debuggers crash or
4416 refuse to read the program, and may cause assemblers other than the GNU
4417 assembler (GAS) to fail with an error.
4419 @item -gdwarf-@var{version}
4420 @opindex gdwarf-@var{version}
4421 Produce debugging information in DWARF format (if that is
4422 supported). This is the format used by DBX on IRIX 6. The value
4423 of @var{version} may be either 2, 3 or 4; the default version is 2.
4425 Note that with DWARF version 2 some ports require, and will always
4426 use, some non-conflicting DWARF 3 extensions in the unwind tables.
4428 Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
4429 for maximum benefit.
4431 @item -gstrict-dwarf
4432 @opindex gstrict-dwarf
4433 Disallow using extensions of later DWARF standard version than selected
4434 with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
4435 DWARF extensions from later standard versions is allowed.
4437 @item -gno-strict-dwarf
4438 @opindex gno-strict-dwarf
4439 Allow using extensions of later DWARF standard version than selected with
4440 @option{-gdwarf-@var{version}}.
4444 Produce debugging information in VMS debug format (if that is
4445 supported). This is the format used by DEBUG on VMS systems.
4448 @itemx -ggdb@var{level}
4449 @itemx -gstabs@var{level}
4450 @itemx -gcoff@var{level}
4451 @itemx -gxcoff@var{level}
4452 @itemx -gvms@var{level}
4453 Request debugging information and also use @var{level} to specify how
4454 much information. The default level is 2.
4456 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4459 Level 1 produces minimal information, enough for making backtraces in
4460 parts of the program that you don't plan to debug. This includes
4461 descriptions of functions and external variables, but no information
4462 about local variables and no line numbers.
4464 Level 3 includes extra information, such as all the macro definitions
4465 present in the program. Some debuggers support macro expansion when
4466 you use @option{-g3}.
4468 @option{-gdwarf-2} does not accept a concatenated debug level, because
4469 GCC used to support an option @option{-gdwarf} that meant to generate
4470 debug information in version 1 of the DWARF format (which is very
4471 different from version 2), and it would have been too confusing. That
4472 debug format is long obsolete, but the option cannot be changed now.
4473 Instead use an additional @option{-g@var{level}} option to change the
4474 debug level for DWARF.
4478 Turn off generation of debug info, if leaving out this option would have
4479 generated it, or turn it on at level 2 otherwise. The position of this
4480 argument in the command line does not matter, it takes effect after all
4481 other options are processed, and it does so only once, no matter how
4482 many times it is given. This is mainly intended to be used with
4483 @option{-fcompare-debug}.
4485 @item -fdump-final-insns@r{[}=@var{file}@r{]}
4486 @opindex fdump-final-insns
4487 Dump the final internal representation (RTL) to @var{file}. If the
4488 optional argument is omitted (or if @var{file} is @code{.}), the name
4489 of the dump file will be determined by appending @code{.gkd} to the
4490 compilation output file name.
4492 @item -fcompare-debug@r{[}=@var{opts}@r{]}
4493 @opindex fcompare-debug
4494 @opindex fno-compare-debug
4495 If no error occurs during compilation, run the compiler a second time,
4496 adding @var{opts} and @option{-fcompare-debug-second} to the arguments
4497 passed to the second compilation. Dump the final internal
4498 representation in both compilations, and print an error if they differ.
4500 If the equal sign is omitted, the default @option{-gtoggle} is used.
4502 The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
4503 and nonzero, implicitly enables @option{-fcompare-debug}. If
4504 @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
4505 then it is used for @var{opts}, otherwise the default @option{-gtoggle}
4508 @option{-fcompare-debug=}, with the equal sign but without @var{opts},
4509 is equivalent to @option{-fno-compare-debug}, which disables the dumping
4510 of the final representation and the second compilation, preventing even
4511 @env{GCC_COMPARE_DEBUG} from taking effect.
4513 To verify full coverage during @option{-fcompare-debug} testing, set
4514 @env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden},
4515 which GCC will reject as an invalid option in any actual compilation
4516 (rather than preprocessing, assembly or linking). To get just a
4517 warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
4518 not overridden} will do.
4520 @item -fcompare-debug-second
4521 @opindex fcompare-debug-second
4522 This option is implicitly passed to the compiler for the second
4523 compilation requested by @option{-fcompare-debug}, along with options to
4524 silence warnings, and omitting other options that would cause
4525 side-effect compiler outputs to files or to the standard output. Dump
4526 files and preserved temporary files are renamed so as to contain the
4527 @code{.gk} additional extension during the second compilation, to avoid
4528 overwriting those generated by the first.
4530 When this option is passed to the compiler driver, it causes the
4531 @emph{first} compilation to be skipped, which makes it useful for little
4532 other than debugging the compiler proper.
4534 @item -feliminate-dwarf2-dups
4535 @opindex feliminate-dwarf2-dups
4536 Compress DWARF2 debugging information by eliminating duplicated
4537 information about each symbol. This option only makes sense when
4538 generating DWARF2 debugging information with @option{-gdwarf-2}.
4540 @item -femit-struct-debug-baseonly
4541 Emit debug information for struct-like types
4542 only when the base name of the compilation source file
4543 matches the base name of file in which the struct was defined.
4545 This option substantially reduces the size of debugging information,
4546 but at significant potential loss in type information to the debugger.
4547 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4548 See @option{-femit-struct-debug-detailed} for more detailed control.
4550 This option works only with DWARF 2.
4552 @item -femit-struct-debug-reduced
4553 Emit debug information for struct-like types
4554 only when the base name of the compilation source file
4555 matches the base name of file in which the type was defined,
4556 unless the struct is a template or defined in a system header.
4558 This option significantly reduces the size of debugging information,
4559 with some potential loss in type information to the debugger.
4560 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4561 See @option{-femit-struct-debug-detailed} for more detailed control.
4563 This option works only with DWARF 2.
4565 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4566 Specify the struct-like types
4567 for which the compiler will generate debug information.
4568 The intent is to reduce duplicate struct debug information
4569 between different object files within the same program.
4571 This option is a detailed version of
4572 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4573 which will serve for most needs.
4575 A specification has the syntax
4576 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4578 The optional first word limits the specification to
4579 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4580 A struct type is used directly when it is the type of a variable, member.
4581 Indirect uses arise through pointers to structs.
4582 That is, when use of an incomplete struct would be legal, the use is indirect.
4584 @samp{struct one direct; struct two * indirect;}.
4586 The optional second word limits the specification to
4587 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4588 Generic structs are a bit complicated to explain.
4589 For C++, these are non-explicit specializations of template classes,
4590 or non-template classes within the above.
4591 Other programming languages have generics,
4592 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4594 The third word specifies the source files for those
4595 structs for which the compiler will emit debug information.
4596 The values @samp{none} and @samp{any} have the normal meaning.
4597 The value @samp{base} means that
4598 the base of name of the file in which the type declaration appears
4599 must match the base of the name of the main compilation file.
4600 In practice, this means that
4601 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4602 but types declared in other header will not.
4603 The value @samp{sys} means those types satisfying @samp{base}
4604 or declared in system or compiler headers.
4606 You may need to experiment to determine the best settings for your application.
4608 The default is @samp{-femit-struct-debug-detailed=all}.
4610 This option works only with DWARF 2.
4612 @item -fno-merge-debug-strings
4613 @opindex fmerge-debug-strings
4614 @opindex fno-merge-debug-strings
4615 Direct the linker to not merge together strings in the debugging
4616 information which are identical in different object files. Merging is
4617 not supported by all assemblers or linkers. Merging decreases the size
4618 of the debug information in the output file at the cost of increasing
4619 link processing time. Merging is enabled by default.
4621 @item -fdebug-prefix-map=@var{old}=@var{new}
4622 @opindex fdebug-prefix-map
4623 When compiling files in directory @file{@var{old}}, record debugging
4624 information describing them as in @file{@var{new}} instead.
4626 @item -fno-dwarf2-cfi-asm
4627 @opindex fdwarf2-cfi-asm
4628 @opindex fno-dwarf2-cfi-asm
4629 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4630 instead of using GAS @code{.cfi_*} directives.
4632 @cindex @command{prof}
4635 Generate extra code to write profile information suitable for the
4636 analysis program @command{prof}. You must use this option when compiling
4637 the source files you want data about, and you must also use it when
4640 @cindex @command{gprof}
4643 Generate extra code to write profile information suitable for the
4644 analysis program @command{gprof}. You must use this option when compiling
4645 the source files you want data about, and you must also use it when
4650 Makes the compiler print out each function name as it is compiled, and
4651 print some statistics about each pass when it finishes.
4654 @opindex ftime-report
4655 Makes the compiler print some statistics about the time consumed by each
4656 pass when it finishes.
4659 @opindex fmem-report
4660 Makes the compiler print some statistics about permanent memory
4661 allocation when it finishes.
4663 @item -fpre-ipa-mem-report
4664 @opindex fpre-ipa-mem-report
4665 @item -fpost-ipa-mem-report
4666 @opindex fpost-ipa-mem-report
4667 Makes the compiler print some statistics about permanent memory
4668 allocation before or after interprocedural optimization.
4670 @item -fprofile-arcs
4671 @opindex fprofile-arcs
4672 Add code so that program flow @dfn{arcs} are instrumented. During
4673 execution the program records how many times each branch and call is
4674 executed and how many times it is taken or returns. When the compiled
4675 program exits it saves this data to a file called
4676 @file{@var{auxname}.gcda} for each source file. The data may be used for
4677 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4678 test coverage analysis (@option{-ftest-coverage}). Each object file's
4679 @var{auxname} is generated from the name of the output file, if
4680 explicitly specified and it is not the final executable, otherwise it is
4681 the basename of the source file. In both cases any suffix is removed
4682 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4683 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4684 @xref{Cross-profiling}.
4686 @cindex @command{gcov}
4690 This option is used to compile and link code instrumented for coverage
4691 analysis. The option is a synonym for @option{-fprofile-arcs}
4692 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4693 linking). See the documentation for those options for more details.
4698 Compile the source files with @option{-fprofile-arcs} plus optimization
4699 and code generation options. For test coverage analysis, use the
4700 additional @option{-ftest-coverage} option. You do not need to profile
4701 every source file in a program.
4704 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4705 (the latter implies the former).
4708 Run the program on a representative workload to generate the arc profile
4709 information. This may be repeated any number of times. You can run
4710 concurrent instances of your program, and provided that the file system
4711 supports locking, the data files will be correctly updated. Also
4712 @code{fork} calls are detected and correctly handled (double counting
4716 For profile-directed optimizations, compile the source files again with
4717 the same optimization and code generation options plus
4718 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4719 Control Optimization}).
4722 For test coverage analysis, use @command{gcov} to produce human readable
4723 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4724 @command{gcov} documentation for further information.
4728 With @option{-fprofile-arcs}, for each function of your program GCC
4729 creates a program flow graph, then finds a spanning tree for the graph.
4730 Only arcs that are not on the spanning tree have to be instrumented: the
4731 compiler adds code to count the number of times that these arcs are
4732 executed. When an arc is the only exit or only entrance to a block, the
4733 instrumentation code can be added to the block; otherwise, a new basic
4734 block must be created to hold the instrumentation code.
4737 @item -ftest-coverage
4738 @opindex ftest-coverage
4739 Produce a notes file that the @command{gcov} code-coverage utility
4740 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4741 show program coverage. Each source file's note file is called
4742 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4743 above for a description of @var{auxname} and instructions on how to
4744 generate test coverage data. Coverage data will match the source files
4745 more closely, if you do not optimize.
4747 @item -fdbg-cnt-list
4748 @opindex fdbg-cnt-list
4749 Print the name and the counter upperbound for all debug counters.
4751 @item -fdbg-cnt=@var{counter-value-list}
4753 Set the internal debug counter upperbound. @var{counter-value-list}
4754 is a comma-separated list of @var{name}:@var{value} pairs
4755 which sets the upperbound of each debug counter @var{name} to @var{value}.
4756 All debug counters have the initial upperbound of @var{UINT_MAX},
4757 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4758 e.g. With -fdbg-cnt=dce:10,tail_call:0
4759 dbg_cnt(dce) will return true only for first 10 invocations
4760 and dbg_cnt(tail_call) will return false always.
4762 @item -d@var{letters}
4763 @itemx -fdump-rtl-@var{pass}
4765 Says to make debugging dumps during compilation at times specified by
4766 @var{letters}. This is used for debugging the RTL-based passes of the
4767 compiler. The file names for most of the dumps are made by appending
4768 a pass number and a word to the @var{dumpname}, and the files are
4769 created in the directory of the output file. @var{dumpname} is
4770 generated from the name of the output file, if explicitly specified
4771 and it is not an executable, otherwise it is the basename of the
4772 source file. These switches may have different effects when
4773 @option{-E} is used for preprocessing.
4775 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
4776 @option{-d} option @var{letters}. Here are the possible
4777 letters for use in @var{pass} and @var{letters}, and their meanings:
4781 @item -fdump-rtl-alignments
4782 @opindex fdump-rtl-alignments
4783 Dump after branch alignments have been computed.
4785 @item -fdump-rtl-asmcons
4786 @opindex fdump-rtl-asmcons
4787 Dump after fixing rtl statements that have unsatisfied in/out constraints.
4789 @item -fdump-rtl-auto_inc_dec
4790 @opindex fdump-rtl-auto_inc_dec
4791 Dump after auto-inc-dec discovery. This pass is only run on
4792 architectures that have auto inc or auto dec instructions.
4794 @item -fdump-rtl-barriers
4795 @opindex fdump-rtl-barriers
4796 Dump after cleaning up the barrier instructions.
4798 @item -fdump-rtl-bbpart
4799 @opindex fdump-rtl-bbpart
4800 Dump after partitioning hot and cold basic blocks.
4802 @item -fdump-rtl-bbro
4803 @opindex fdump-rtl-bbro
4804 Dump after block reordering.
4806 @item -fdump-rtl-btl1
4807 @itemx -fdump-rtl-btl2
4808 @opindex fdump-rtl-btl2
4809 @opindex fdump-rtl-btl2
4810 @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
4811 after the two branch
4812 target load optimization passes.
4814 @item -fdump-rtl-bypass
4815 @opindex fdump-rtl-bypass
4816 Dump after jump bypassing and control flow optimizations.
4818 @item -fdump-rtl-combine
4819 @opindex fdump-rtl-combine
4820 Dump after the RTL instruction combination pass.
4822 @item -fdump-rtl-compgotos
4823 @opindex fdump-rtl-compgotos
4824 Dump after duplicating the computed gotos.
4826 @item -fdump-rtl-ce1
4827 @itemx -fdump-rtl-ce2
4828 @itemx -fdump-rtl-ce3
4829 @opindex fdump-rtl-ce1
4830 @opindex fdump-rtl-ce2
4831 @opindex fdump-rtl-ce3
4832 @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
4833 @option{-fdump-rtl-ce3} enable dumping after the three
4834 if conversion passes.
4836 @itemx -fdump-rtl-cprop_hardreg
4837 @opindex fdump-rtl-cprop_hardreg
4838 Dump after hard register copy propagation.
4840 @itemx -fdump-rtl-csa
4841 @opindex fdump-rtl-csa
4842 Dump after combining stack adjustments.
4844 @item -fdump-rtl-cse1
4845 @itemx -fdump-rtl-cse2
4846 @opindex fdump-rtl-cse1
4847 @opindex fdump-rtl-cse2
4848 @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
4849 the two common sub-expression elimination passes.
4851 @itemx -fdump-rtl-dce
4852 @opindex fdump-rtl-dce
4853 Dump after the standalone dead code elimination passes.
4855 @itemx -fdump-rtl-dbr
4856 @opindex fdump-rtl-dbr
4857 Dump after delayed branch scheduling.
4859 @item -fdump-rtl-dce1
4860 @itemx -fdump-rtl-dce2
4861 @opindex fdump-rtl-dce1
4862 @opindex fdump-rtl-dce2
4863 @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
4864 the two dead store elimination passes.
4867 @opindex fdump-rtl-eh
4868 Dump after finalization of EH handling code.
4870 @item -fdump-rtl-eh_ranges
4871 @opindex fdump-rtl-eh_ranges
4872 Dump after conversion of EH handling range regions.
4874 @item -fdump-rtl-expand
4875 @opindex fdump-rtl-expand
4876 Dump after RTL generation.
4878 @item -fdump-rtl-fwprop1
4879 @itemx -fdump-rtl-fwprop2
4880 @opindex fdump-rtl-fwprop1
4881 @opindex fdump-rtl-fwprop2
4882 @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
4883 dumping after the two forward propagation passes.
4885 @item -fdump-rtl-gcse1
4886 @itemx -fdump-rtl-gcse2
4887 @opindex fdump-rtl-gcse1
4888 @opindex fdump-rtl-gcse2
4889 @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
4890 after global common subexpression elimination.
4892 @item -fdump-rtl-init-regs
4893 @opindex fdump-rtl-init-regs
4894 Dump after the initialization of the registers.
4896 @item -fdump-rtl-initvals
4897 @opindex fdump-rtl-initvals
4898 Dump after the computation of the initial value sets.
4900 @itemx -fdump-rtl-into_cfglayout
4901 @opindex fdump-rtl-into_cfglayout
4902 Dump after converting to cfglayout mode.
4904 @item -fdump-rtl-ira
4905 @opindex fdump-rtl-ira
4906 Dump after iterated register allocation.
4908 @item -fdump-rtl-jump
4909 @opindex fdump-rtl-jump
4910 Dump after the second jump optimization.
4912 @item -fdump-rtl-loop2
4913 @opindex fdump-rtl-loop2
4914 @option{-fdump-rtl-loop2} enables dumping after the rtl
4915 loop optimization passes.
4917 @item -fdump-rtl-mach
4918 @opindex fdump-rtl-mach
4919 Dump after performing the machine dependent reorganization pass, if that
4922 @item -fdump-rtl-mode_sw
4923 @opindex fdump-rtl-mode_sw
4924 Dump after removing redundant mode switches.
4926 @item -fdump-rtl-rnreg
4927 @opindex fdump-rtl-rnreg
4928 Dump after register renumbering.
4930 @itemx -fdump-rtl-outof_cfglayout
4931 @opindex fdump-rtl-outof_cfglayout
4932 Dump after converting from cfglayout mode.
4934 @item -fdump-rtl-peephole2
4935 @opindex fdump-rtl-peephole2
4936 Dump after the peephole pass.
4938 @item -fdump-rtl-postreload
4939 @opindex fdump-rtl-postreload
4940 Dump after post-reload optimizations.
4942 @itemx -fdump-rtl-pro_and_epilogue
4943 @opindex fdump-rtl-pro_and_epilogue
4944 Dump after generating the function pro and epilogues.
4946 @item -fdump-rtl-regmove
4947 @opindex fdump-rtl-regmove
4948 Dump after the register move pass.
4950 @item -fdump-rtl-sched1
4951 @itemx -fdump-rtl-sched2
4952 @opindex fdump-rtl-sched1
4953 @opindex fdump-rtl-sched2
4954 @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
4955 after the basic block scheduling passes.
4957 @item -fdump-rtl-see
4958 @opindex fdump-rtl-see
4959 Dump after sign extension elimination.
4961 @item -fdump-rtl-seqabstr
4962 @opindex fdump-rtl-seqabstr
4963 Dump after common sequence discovery.
4965 @item -fdump-rtl-shorten
4966 @opindex fdump-rtl-shorten
4967 Dump after shortening branches.
4969 @item -fdump-rtl-sibling
4970 @opindex fdump-rtl-sibling
4971 Dump after sibling call optimizations.
4973 @item -fdump-rtl-split1
4974 @itemx -fdump-rtl-split2
4975 @itemx -fdump-rtl-split3
4976 @itemx -fdump-rtl-split4
4977 @itemx -fdump-rtl-split5
4978 @opindex fdump-rtl-split1
4979 @opindex fdump-rtl-split2
4980 @opindex fdump-rtl-split3
4981 @opindex fdump-rtl-split4
4982 @opindex fdump-rtl-split5
4983 @option{-fdump-rtl-split1}, @option{-fdump-rtl-split2},
4984 @option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and
4985 @option{-fdump-rtl-split5} enable dumping after five rounds of
4986 instruction splitting.
4988 @item -fdump-rtl-sms
4989 @opindex fdump-rtl-sms
4990 Dump after modulo scheduling. This pass is only run on some
4993 @item -fdump-rtl-stack
4994 @opindex fdump-rtl-stack
4995 Dump after conversion from GCC's "flat register file" registers to the
4996 x87's stack-like registers. This pass is only run on x86 variants.
4998 @item -fdump-rtl-subreg1
4999 @itemx -fdump-rtl-subreg2
5000 @opindex fdump-rtl-subreg1
5001 @opindex fdump-rtl-subreg2
5002 @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
5003 the two subreg expansion passes.
5005 @item -fdump-rtl-unshare
5006 @opindex fdump-rtl-unshare
5007 Dump after all rtl has been unshared.
5009 @item -fdump-rtl-vartrack
5010 @opindex fdump-rtl-vartrack
5011 Dump after variable tracking.
5013 @item -fdump-rtl-vregs
5014 @opindex fdump-rtl-vregs
5015 Dump after converting virtual registers to hard registers.
5017 @item -fdump-rtl-web
5018 @opindex fdump-rtl-web
5019 Dump after live range splitting.
5021 @item -fdump-rtl-regclass
5022 @itemx -fdump-rtl-subregs_of_mode_init
5023 @itemx -fdump-rtl-subregs_of_mode_finish
5024 @itemx -fdump-rtl-dfinit
5025 @itemx -fdump-rtl-dfinish
5026 @opindex fdump-rtl-regclass
5027 @opindex fdump-rtl-subregs_of_mode_init
5028 @opindex fdump-rtl-subregs_of_mode_finish
5029 @opindex fdump-rtl-dfinit
5030 @opindex fdump-rtl-dfinish
5031 These dumps are defined but always produce empty files.
5033 @item -fdump-rtl-all
5034 @opindex fdump-rtl-all
5035 Produce all the dumps listed above.
5039 Annotate the assembler output with miscellaneous debugging information.
5043 Dump all macro definitions, at the end of preprocessing, in addition to
5048 Produce a core dump whenever an error occurs.
5052 Print statistics on memory usage, at the end of the run, to
5057 Annotate the assembler output with a comment indicating which
5058 pattern and alternative was used. The length of each instruction is
5063 Dump the RTL in the assembler output as a comment before each instruction.
5064 Also turns on @option{-dp} annotation.
5068 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
5069 dump a representation of the control flow graph suitable for viewing with VCG
5070 to @file{@var{file}.@var{pass}.vcg}.
5074 Just generate RTL for a function instead of compiling it. Usually used
5075 with @option{-fdump-rtl-expand}.
5079 Dump debugging information during parsing, to standard error.
5083 @opindex fdump-noaddr
5084 When doing debugging dumps, suppress address output. This makes it more
5085 feasible to use diff on debugging dumps for compiler invocations with
5086 different compiler binaries and/or different
5087 text / bss / data / heap / stack / dso start locations.
5089 @item -fdump-unnumbered
5090 @opindex fdump-unnumbered
5091 When doing debugging dumps, suppress instruction numbers and address output.
5092 This makes it more feasible to use diff on debugging dumps for compiler
5093 invocations with different options, in particular with and without
5096 @item -fdump-unnumbered-links
5097 @opindex fdump-unnumbered-links
5098 When doing debugging dumps (see @option{-d} option above), suppress
5099 instruction numbers for the links to the previous and next instructions
5102 @item -fdump-translation-unit @r{(C++ only)}
5103 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
5104 @opindex fdump-translation-unit
5105 Dump a representation of the tree structure for the entire translation
5106 unit to a file. The file name is made by appending @file{.tu} to the
5107 source file name, and the file is created in the same directory as the
5108 output file. If the @samp{-@var{options}} form is used, @var{options}
5109 controls the details of the dump as described for the
5110 @option{-fdump-tree} options.
5112 @item -fdump-class-hierarchy @r{(C++ only)}
5113 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
5114 @opindex fdump-class-hierarchy
5115 Dump a representation of each class's hierarchy and virtual function
5116 table layout to a file. The file name is made by appending
5117 @file{.class} to the source file name, and the file is created in the
5118 same directory as the output file. If the @samp{-@var{options}} form
5119 is used, @var{options} controls the details of the dump as described
5120 for the @option{-fdump-tree} options.
5122 @item -fdump-ipa-@var{switch}
5124 Control the dumping at various stages of inter-procedural analysis
5125 language tree to a file. The file name is generated by appending a
5126 switch specific suffix to the source file name, and the file is created
5127 in the same directory as the output file. The following dumps are
5132 Enables all inter-procedural analysis dumps.
5135 Dumps information about call-graph optimization, unused function removal,
5136 and inlining decisions.
5139 Dump after function inlining.
5143 @item -fdump-statistics-@var{option}
5144 @opindex fdump-statistics
5145 Enable and control dumping of pass statistics in a separate file. The
5146 file name is generated by appending a suffix ending in
5147 @samp{.statistics} to the source file name, and the file is created in
5148 the same directory as the output file. If the @samp{-@var{option}}
5149 form is used, @samp{-stats} will cause counters to be summed over the
5150 whole compilation unit while @samp{-details} will dump every event as
5151 the passes generate them. The default with no option is to sum
5152 counters for each function compiled.
5154 @item -fdump-tree-@var{switch}
5155 @itemx -fdump-tree-@var{switch}-@var{options}
5157 Control the dumping at various stages of processing the intermediate
5158 language tree to a file. The file name is generated by appending a
5159 switch specific suffix to the source file name, and the file is
5160 created in the same directory as the output file. If the
5161 @samp{-@var{options}} form is used, @var{options} is a list of
5162 @samp{-} separated options that control the details of the dump. Not
5163 all options are applicable to all dumps, those which are not
5164 meaningful will be ignored. The following options are available
5168 Print the address of each node. Usually this is not meaningful as it
5169 changes according to the environment and source file. Its primary use
5170 is for tying up a dump file with a debug environment.
5172 If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
5173 in the dump instead of @code{DECL_NAME}. Its primary use is ease of
5174 use working backward from mangled names in the assembly file.
5176 Inhibit dumping of members of a scope or body of a function merely
5177 because that scope has been reached. Only dump such items when they
5178 are directly reachable by some other path. When dumping pretty-printed
5179 trees, this option inhibits dumping the bodies of control structures.
5181 Print a raw representation of the tree. By default, trees are
5182 pretty-printed into a C-like representation.
5184 Enable more detailed dumps (not honored by every dump option).
5186 Enable dumping various statistics about the pass (not honored by every dump
5189 Enable showing basic block boundaries (disabled in raw dumps).
5191 Enable showing virtual operands for every statement.
5193 Enable showing line numbers for statements.
5195 Enable showing the unique ID (@code{DECL_UID}) for each variable.
5197 Enable showing the tree dump for each statement.
5199 Enable showing the EH region number holding each statement.
5201 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
5202 and @option{lineno}.
5205 The following tree dumps are possible:
5209 @opindex fdump-tree-original
5210 Dump before any tree based optimization, to @file{@var{file}.original}.
5213 @opindex fdump-tree-optimized
5214 Dump after all tree based optimization, to @file{@var{file}.optimized}.
5217 @opindex fdump-tree-gimple
5218 Dump each function before and after the gimplification pass to a file. The
5219 file name is made by appending @file{.gimple} to the source file name.
5222 @opindex fdump-tree-cfg
5223 Dump the control flow graph of each function to a file. The file name is
5224 made by appending @file{.cfg} to the source file name.
5227 @opindex fdump-tree-vcg
5228 Dump the control flow graph of each function to a file in VCG format. The
5229 file name is made by appending @file{.vcg} to the source file name. Note
5230 that if the file contains more than one function, the generated file cannot
5231 be used directly by VCG@. You will need to cut and paste each function's
5232 graph into its own separate file first.
5235 @opindex fdump-tree-ch
5236 Dump each function after copying loop headers. The file name is made by
5237 appending @file{.ch} to the source file name.
5240 @opindex fdump-tree-ssa
5241 Dump SSA related information to a file. The file name is made by appending
5242 @file{.ssa} to the source file name.
5245 @opindex fdump-tree-alias
5246 Dump aliasing information for each function. The file name is made by
5247 appending @file{.alias} to the source file name.
5250 @opindex fdump-tree-ccp
5251 Dump each function after CCP@. The file name is made by appending
5252 @file{.ccp} to the source file name.
5255 @opindex fdump-tree-storeccp
5256 Dump each function after STORE-CCP@. The file name is made by appending
5257 @file{.storeccp} to the source file name.
5260 @opindex fdump-tree-pre
5261 Dump trees after partial redundancy elimination. The file name is made
5262 by appending @file{.pre} to the source file name.
5265 @opindex fdump-tree-fre
5266 Dump trees after full redundancy elimination. The file name is made
5267 by appending @file{.fre} to the source file name.
5270 @opindex fdump-tree-copyprop
5271 Dump trees after copy propagation. The file name is made
5272 by appending @file{.copyprop} to the source file name.
5274 @item store_copyprop
5275 @opindex fdump-tree-store_copyprop
5276 Dump trees after store copy-propagation. The file name is made
5277 by appending @file{.store_copyprop} to the source file name.
5280 @opindex fdump-tree-dce
5281 Dump each function after dead code elimination. The file name is made by
5282 appending @file{.dce} to the source file name.
5285 @opindex fdump-tree-mudflap
5286 Dump each function after adding mudflap instrumentation. The file name is
5287 made by appending @file{.mudflap} to the source file name.
5290 @opindex fdump-tree-sra
5291 Dump each function after performing scalar replacement of aggregates. The
5292 file name is made by appending @file{.sra} to the source file name.
5295 @opindex fdump-tree-sink
5296 Dump each function after performing code sinking. The file name is made
5297 by appending @file{.sink} to the source file name.
5300 @opindex fdump-tree-dom
5301 Dump each function after applying dominator tree optimizations. The file
5302 name is made by appending @file{.dom} to the source file name.
5305 @opindex fdump-tree-dse
5306 Dump each function after applying dead store elimination. The file
5307 name is made by appending @file{.dse} to the source file name.
5310 @opindex fdump-tree-phiopt
5311 Dump each function after optimizing PHI nodes into straightline code. The file
5312 name is made by appending @file{.phiopt} to the source file name.
5315 @opindex fdump-tree-forwprop
5316 Dump each function after forward propagating single use variables. The file
5317 name is made by appending @file{.forwprop} to the source file name.
5320 @opindex fdump-tree-copyrename
5321 Dump each function after applying the copy rename optimization. The file
5322 name is made by appending @file{.copyrename} to the source file name.
5325 @opindex fdump-tree-nrv
5326 Dump each function after applying the named return value optimization on
5327 generic trees. The file name is made by appending @file{.nrv} to the source
5331 @opindex fdump-tree-vect
5332 Dump each function after applying vectorization of loops. The file name is
5333 made by appending @file{.vect} to the source file name.
5336 @opindex fdump-tree-vrp
5337 Dump each function after Value Range Propagation (VRP). The file name
5338 is made by appending @file{.vrp} to the source file name.
5341 @opindex fdump-tree-all
5342 Enable all the available tree dumps with the flags provided in this option.
5345 @item -ftree-vectorizer-verbose=@var{n}
5346 @opindex ftree-vectorizer-verbose
5347 This option controls the amount of debugging output the vectorizer prints.
5348 This information is written to standard error, unless
5349 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
5350 in which case it is output to the usual dump listing file, @file{.vect}.
5351 For @var{n}=0 no diagnostic information is reported.
5352 If @var{n}=1 the vectorizer reports each loop that got vectorized,
5353 and the total number of loops that got vectorized.
5354 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
5355 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
5356 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
5357 level that @option{-fdump-tree-vect-stats} uses.
5358 Higher verbosity levels mean either more information dumped for each
5359 reported loop, or same amount of information reported for more loops:
5360 If @var{n}=3, alignment related information is added to the reports.
5361 If @var{n}=4, data-references related information (e.g.@: memory dependences,
5362 memory access-patterns) is added to the reports.
5363 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
5364 that did not pass the first analysis phase (i.e., may not be countable, or
5365 may have complicated control-flow).
5366 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
5367 For @var{n}=7, all the information the vectorizer generates during its
5368 analysis and transformation is reported. This is the same verbosity level
5369 that @option{-fdump-tree-vect-details} uses.
5371 @item -frandom-seed=@var{string}
5372 @opindex frandom-seed
5373 This option provides a seed that GCC uses when it would otherwise use
5374 random numbers. It is used to generate certain symbol names
5375 that have to be different in every compiled file. It is also used to
5376 place unique stamps in coverage data files and the object files that
5377 produce them. You can use the @option{-frandom-seed} option to produce
5378 reproducibly identical object files.
5380 The @var{string} should be different for every file you compile.
5382 @item -fsched-verbose=@var{n}
5383 @opindex fsched-verbose
5384 On targets that use instruction scheduling, this option controls the
5385 amount of debugging output the scheduler prints. This information is
5386 written to standard error, unless @option{-fdump-rtl-sched1} or
5387 @option{-fdump-rtl-sched2} is specified, in which case it is output
5388 to the usual dump listing file, @file{.sched} or @file{.sched2}
5389 respectively. However for @var{n} greater than nine, the output is
5390 always printed to standard error.
5392 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5393 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5394 For @var{n} greater than one, it also output basic block probabilities,
5395 detailed ready list information and unit/insn info. For @var{n} greater
5396 than two, it includes RTL at abort point, control-flow and regions info.
5397 And for @var{n} over four, @option{-fsched-verbose} also includes
5401 @itemx -save-temps=cwd
5403 Store the usual ``temporary'' intermediate files permanently; place them
5404 in the current directory and name them based on the source file. Thus,
5405 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5406 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5407 preprocessed @file{foo.i} output file even though the compiler now
5408 normally uses an integrated preprocessor.
5410 When used in combination with the @option{-x} command line option,
5411 @option{-save-temps} is sensible enough to avoid over writing an
5412 input source file with the same extension as an intermediate file.
5413 The corresponding intermediate file may be obtained by renaming the
5414 source file before using @option{-save-temps}.
5416 If you invoke GCC in parallel, compiling several different source
5417 files that share a common base name in different subdirectories or the
5418 same source file compiled for multiple output destinations, it is
5419 likely that the different parallel compilers will interfere with each
5420 other, and overwrite the temporary files. For instance:
5423 gcc -save-temps -o outdir1/foo.o indir1/foo.c&
5424 gcc -save-temps -o outdir2/foo.o indir2/foo.c&
5427 may result in @file{foo.i} and @file{foo.o} being written to
5428 simultaneously by both compilers.
5430 @item -save-temps=obj
5431 @opindex save-temps=obj
5432 Store the usual ``temporary'' intermediate files permanently. If the
5433 @option{-o} option is used, the temporary files are based on the
5434 object file. If the @option{-o} option is not used, the
5435 @option{-save-temps=obj} switch behaves like @option{-save-temps}.
5440 gcc -save-temps=obj -c foo.c
5441 gcc -save-temps=obj -c bar.c -o dir/xbar.o
5442 gcc -save-temps=obj foobar.c -o dir2/yfoobar
5445 would create @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
5446 @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
5447 @file{dir2/yfoobar.o}.
5449 @item -time@r{[}=@var{file}@r{]}
5451 Report the CPU time taken by each subprocess in the compilation
5452 sequence. For C source files, this is the compiler proper and assembler
5453 (plus the linker if linking is done).
5455 Without the specification of an output file, the output looks like this:
5462 The first number on each line is the ``user time'', that is time spent
5463 executing the program itself. The second number is ``system time'',
5464 time spent executing operating system routines on behalf of the program.
5465 Both numbers are in seconds.
5467 With the specification of an output file, the output is appended to the
5468 named file, and it looks like this:
5471 0.12 0.01 cc1 @var{options}
5472 0.00 0.01 as @var{options}
5475 The ``user time'' and the ``system time'' are moved before the program
5476 name, and the options passed to the program are displayed, so that one
5477 can later tell what file was being compiled, and with which options.
5479 @item -fvar-tracking
5480 @opindex fvar-tracking
5481 Run variable tracking pass. It computes where variables are stored at each
5482 position in code. Better debugging information is then generated
5483 (if the debugging information format supports this information).
5485 It is enabled by default when compiling with optimization (@option{-Os},
5486 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5487 the debug info format supports it.
5489 @item -fvar-tracking-assignments
5490 @opindex fvar-tracking-assignments
5491 @opindex fno-var-tracking-assignments
5492 Annotate assignments to user variables early in the compilation and
5493 attempt to carry the annotations over throughout the compilation all the
5494 way to the end, in an attempt to improve debug information while
5495 optimizing. Use of @option{-gdwarf-4} is recommended along with it.
5497 It can be enabled even if var-tracking is disabled, in which case
5498 annotations will be created and maintained, but discarded at the end.
5500 @item -fvar-tracking-assignments-toggle
5501 @opindex fvar-tracking-assignments-toggle
5502 @opindex fno-var-tracking-assignments-toggle
5503 Toggle @option{-fvar-tracking-assignments}, in the same way that
5504 @option{-gtoggle} toggles @option{-g}.
5506 @item -print-file-name=@var{library}
5507 @opindex print-file-name
5508 Print the full absolute name of the library file @var{library} that
5509 would be used when linking---and don't do anything else. With this
5510 option, GCC does not compile or link anything; it just prints the
5513 @item -print-multi-directory
5514 @opindex print-multi-directory
5515 Print the directory name corresponding to the multilib selected by any
5516 other switches present in the command line. This directory is supposed
5517 to exist in @env{GCC_EXEC_PREFIX}.
5519 @item -print-multi-lib
5520 @opindex print-multi-lib
5521 Print the mapping from multilib directory names to compiler switches
5522 that enable them. The directory name is separated from the switches by
5523 @samp{;}, and each switch starts with an @samp{@@} instead of the
5524 @samp{-}, without spaces between multiple switches. This is supposed to
5525 ease shell-processing.
5527 @item -print-prog-name=@var{program}
5528 @opindex print-prog-name
5529 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5531 @item -print-libgcc-file-name
5532 @opindex print-libgcc-file-name
5533 Same as @option{-print-file-name=libgcc.a}.
5535 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5536 but you do want to link with @file{libgcc.a}. You can do
5539 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5542 @item -print-search-dirs
5543 @opindex print-search-dirs
5544 Print the name of the configured installation directory and a list of
5545 program and library directories @command{gcc} will search---and don't do anything else.
5547 This is useful when @command{gcc} prints the error message
5548 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5549 To resolve this you either need to put @file{cpp0} and the other compiler
5550 components where @command{gcc} expects to find them, or you can set the environment
5551 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5552 Don't forget the trailing @samp{/}.
5553 @xref{Environment Variables}.
5555 @item -print-sysroot
5556 @opindex print-sysroot
5557 Print the target sysroot directory that will be used during
5558 compilation. This is the target sysroot specified either at configure
5559 time or using the @option{--sysroot} option, possibly with an extra
5560 suffix that depends on compilation options. If no target sysroot is
5561 specified, the option prints nothing.
5563 @item -print-sysroot-headers-suffix
5564 @opindex print-sysroot-headers-suffix
5565 Print the suffix added to the target sysroot when searching for
5566 headers, or give an error if the compiler is not configured with such
5567 a suffix---and don't do anything else.
5570 @opindex dumpmachine
5571 Print the compiler's target machine (for example,
5572 @samp{i686-pc-linux-gnu})---and don't do anything else.
5575 @opindex dumpversion
5576 Print the compiler version (for example, @samp{3.0})---and don't do
5581 Print the compiler's built-in specs---and don't do anything else. (This
5582 is used when GCC itself is being built.) @xref{Spec Files}.
5584 @item -feliminate-unused-debug-types
5585 @opindex feliminate-unused-debug-types
5586 Normally, when producing DWARF2 output, GCC will emit debugging
5587 information for all types declared in a compilation
5588 unit, regardless of whether or not they are actually used
5589 in that compilation unit. Sometimes this is useful, such as
5590 if, in the debugger, you want to cast a value to a type that is
5591 not actually used in your program (but is declared). More often,
5592 however, this results in a significant amount of wasted space.
5593 With this option, GCC will avoid producing debug symbol output
5594 for types that are nowhere used in the source file being compiled.
5597 @node Optimize Options
5598 @section Options That Control Optimization
5599 @cindex optimize options
5600 @cindex options, optimization
5602 These options control various sorts of optimizations.
5604 Without any optimization option, the compiler's goal is to reduce the
5605 cost of compilation and to make debugging produce the expected
5606 results. Statements are independent: if you stop the program with a
5607 breakpoint between statements, you can then assign a new value to any
5608 variable or change the program counter to any other statement in the
5609 function and get exactly the results you would expect from the source
5612 Turning on optimization flags makes the compiler attempt to improve
5613 the performance and/or code size at the expense of compilation time
5614 and possibly the ability to debug the program.
5616 The compiler performs optimization based on the knowledge it has of the
5617 program. Compiling multiple files at once to a single output file mode allows
5618 the compiler to use information gained from all of the files when compiling
5621 Not all optimizations are controlled directly by a flag. Only
5622 optimizations that have a flag are listed in this section.
5624 Depending on the target and how GCC was configured, a slightly different
5625 set of optimizations may be enabled at each @option{-O} level than
5626 those listed here. You can invoke GCC with @samp{-Q --help=optimizers}
5627 to find out the exact set of optimizations that are enabled at each level.
5628 @xref{Overall Options}, for examples.
5635 Optimize. Optimizing compilation takes somewhat more time, and a lot
5636 more memory for a large function.
5638 With @option{-O}, the compiler tries to reduce code size and execution
5639 time, without performing any optimizations that take a great deal of
5642 @option{-O} turns on the following optimization flags:
5645 -fcprop-registers @gol
5648 -fdelayed-branch @gol
5650 -fguess-branch-probability @gol
5651 -fif-conversion2 @gol
5652 -fif-conversion @gol
5653 -fipa-pure-const @gol
5654 -fipa-reference @gol
5656 -fsplit-wide-types @gol
5657 -ftree-builtin-call-dce @gol
5660 -ftree-copyrename @gol
5662 -ftree-dominator-opts @gol
5664 -ftree-forwprop @gol
5672 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5673 where doing so does not interfere with debugging.
5677 Optimize even more. GCC performs nearly all supported optimizations
5678 that do not involve a space-speed tradeoff.
5679 As compared to @option{-O}, this option increases both compilation time
5680 and the performance of the generated code.
5682 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5683 also turns on the following optimization flags:
5684 @gccoptlist{-fthread-jumps @gol
5685 -falign-functions -falign-jumps @gol
5686 -falign-loops -falign-labels @gol
5689 -fcse-follow-jumps -fcse-skip-blocks @gol
5690 -fdelete-null-pointer-checks @gol
5691 -fexpensive-optimizations @gol
5692 -fgcse -fgcse-lm @gol
5693 -finline-small-functions @gol
5694 -findirect-inlining @gol
5696 -foptimize-sibling-calls @gol
5699 -freorder-blocks -freorder-functions @gol
5700 -frerun-cse-after-loop @gol
5701 -fsched-interblock -fsched-spec @gol
5702 -fschedule-insns -fschedule-insns2 @gol
5703 -fstrict-aliasing -fstrict-overflow @gol
5704 -ftree-switch-conversion @gol
5708 Please note the warning under @option{-fgcse} about
5709 invoking @option{-O2} on programs that use computed gotos.
5713 Optimize yet more. @option{-O3} turns on all optimizations specified
5714 by @option{-O2} and also turns on the @option{-finline-functions},
5715 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5716 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5720 Reduce compilation time and make debugging produce the expected
5721 results. This is the default.
5725 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5726 do not typically increase code size. It also performs further
5727 optimizations designed to reduce code size.
5729 @option{-Os} disables the following optimization flags:
5730 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5731 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5732 -fprefetch-loop-arrays -ftree-vect-loop-version}
5734 If you use multiple @option{-O} options, with or without level numbers,
5735 the last such option is the one that is effective.
5738 Options of the form @option{-f@var{flag}} specify machine-independent
5739 flags. Most flags have both positive and negative forms; the negative
5740 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5741 below, only one of the forms is listed---the one you typically will
5742 use. You can figure out the other form by either removing @samp{no-}
5745 The following options control specific optimizations. They are either
5746 activated by @option{-O} options or are related to ones that are. You
5747 can use the following flags in the rare cases when ``fine-tuning'' of
5748 optimizations to be performed is desired.
5751 @item -fno-default-inline
5752 @opindex fno-default-inline
5753 Do not make member functions inline by default merely because they are
5754 defined inside the class scope (C++ only). Otherwise, when you specify
5755 @w{@option{-O}}, member functions defined inside class scope are compiled
5756 inline by default; i.e., you don't need to add @samp{inline} in front of
5757 the member function name.
5759 @item -fno-defer-pop
5760 @opindex fno-defer-pop
5761 Always pop the arguments to each function call as soon as that function
5762 returns. For machines which must pop arguments after a function call,
5763 the compiler normally lets arguments accumulate on the stack for several
5764 function calls and pops them all at once.
5766 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5768 @item -fforward-propagate
5769 @opindex fforward-propagate
5770 Perform a forward propagation pass on RTL@. The pass tries to combine two
5771 instructions and checks if the result can be simplified. If loop unrolling
5772 is active, two passes are performed and the second is scheduled after
5775 This option is enabled by default at optimization levels @option{-O},
5776 @option{-O2}, @option{-O3}, @option{-Os}.
5778 @item -fomit-frame-pointer
5779 @opindex fomit-frame-pointer
5780 Don't keep the frame pointer in a register for functions that
5781 don't need one. This avoids the instructions to save, set up and
5782 restore frame pointers; it also makes an extra register available
5783 in many functions. @strong{It also makes debugging impossible on
5786 On some machines, such as the VAX, this flag has no effect, because
5787 the standard calling sequence automatically handles the frame pointer
5788 and nothing is saved by pretending it doesn't exist. The
5789 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5790 whether a target machine supports this flag. @xref{Registers,,Register
5791 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5793 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5795 @item -foptimize-sibling-calls
5796 @opindex foptimize-sibling-calls
5797 Optimize sibling and tail recursive calls.
5799 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5803 Don't pay attention to the @code{inline} keyword. Normally this option
5804 is used to keep the compiler from expanding any functions inline.
5805 Note that if you are not optimizing, no functions can be expanded inline.
5807 @item -finline-small-functions
5808 @opindex finline-small-functions
5809 Integrate functions into their callers when their body is smaller than expected
5810 function call code (so overall size of program gets smaller). The compiler
5811 heuristically decides which functions are simple enough to be worth integrating
5814 Enabled at level @option{-O2}.
5816 @item -findirect-inlining
5817 @opindex findirect-inlining
5818 Inline also indirect calls that are discovered to be known at compile
5819 time thanks to previous inlining. This option has any effect only
5820 when inlining itself is turned on by the @option{-finline-functions}
5821 or @option{-finline-small-functions} options.
5823 Enabled at level @option{-O2}.
5825 @item -finline-functions
5826 @opindex finline-functions
5827 Integrate all simple functions into their callers. The compiler
5828 heuristically decides which functions are simple enough to be worth
5829 integrating in this way.
5831 If all calls to a given function are integrated, and the function is
5832 declared @code{static}, then the function is normally not output as
5833 assembler code in its own right.
5835 Enabled at level @option{-O3}.
5837 @item -finline-functions-called-once
5838 @opindex finline-functions-called-once
5839 Consider all @code{static} functions called once for inlining into their
5840 caller even if they are not marked @code{inline}. If a call to a given
5841 function is integrated, then the function is not output as assembler code
5844 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5846 @item -fearly-inlining
5847 @opindex fearly-inlining
5848 Inline functions marked by @code{always_inline} and functions whose body seems
5849 smaller than the function call overhead early before doing
5850 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5851 makes profiling significantly cheaper and usually inlining faster on programs
5852 having large chains of nested wrapper functions.
5858 Perform interprocedural scalar replacement of aggregates, removal of
5859 unused parameters and replacement of parameters passed by reference
5860 by parameters passed by value.
5862 Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
5864 @item -finline-limit=@var{n}
5865 @opindex finline-limit
5866 By default, GCC limits the size of functions that can be inlined. This flag
5867 allows coarse control of this limit. @var{n} is the size of functions that
5868 can be inlined in number of pseudo instructions.
5870 Inlining is actually controlled by a number of parameters, which may be
5871 specified individually by using @option{--param @var{name}=@var{value}}.
5872 The @option{-finline-limit=@var{n}} option sets some of these parameters
5876 @item max-inline-insns-single
5877 is set to @var{n}/2.
5878 @item max-inline-insns-auto
5879 is set to @var{n}/2.
5882 See below for a documentation of the individual
5883 parameters controlling inlining and for the defaults of these parameters.
5885 @emph{Note:} there may be no value to @option{-finline-limit} that results
5886 in default behavior.
5888 @emph{Note:} pseudo instruction represents, in this particular context, an
5889 abstract measurement of function's size. In no way does it represent a count
5890 of assembly instructions and as such its exact meaning might change from one
5891 release to an another.
5893 @item -fkeep-inline-functions
5894 @opindex fkeep-inline-functions
5895 In C, emit @code{static} functions that are declared @code{inline}
5896 into the object file, even if the function has been inlined into all
5897 of its callers. This switch does not affect functions using the
5898 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5899 inline functions into the object file.
5901 @item -fkeep-static-consts
5902 @opindex fkeep-static-consts
5903 Emit variables declared @code{static const} when optimization isn't turned
5904 on, even if the variables aren't referenced.
5906 GCC enables this option by default. If you want to force the compiler to
5907 check if the variable was referenced, regardless of whether or not
5908 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5910 @item -fmerge-constants
5911 @opindex fmerge-constants
5912 Attempt to merge identical constants (string constants and floating point
5913 constants) across compilation units.
5915 This option is the default for optimized compilation if the assembler and
5916 linker support it. Use @option{-fno-merge-constants} to inhibit this
5919 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5921 @item -fmerge-all-constants
5922 @opindex fmerge-all-constants
5923 Attempt to merge identical constants and identical variables.
5925 This option implies @option{-fmerge-constants}. In addition to
5926 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5927 arrays or initialized constant variables with integral or floating point
5928 types. Languages like C or C++ require each variable, including multiple
5929 instances of the same variable in recursive calls, to have distinct locations,
5930 so using this option will result in non-conforming
5933 @item -fmodulo-sched
5934 @opindex fmodulo-sched
5935 Perform swing modulo scheduling immediately before the first scheduling
5936 pass. This pass looks at innermost loops and reorders their
5937 instructions by overlapping different iterations.
5939 @item -fmodulo-sched-allow-regmoves
5940 @opindex fmodulo-sched-allow-regmoves
5941 Perform more aggressive SMS based modulo scheduling with register moves
5942 allowed. By setting this flag certain anti-dependences edges will be
5943 deleted which will trigger the generation of reg-moves based on the
5944 life-range analysis. This option is effective only with
5945 @option{-fmodulo-sched} enabled.
5947 @item -fno-branch-count-reg
5948 @opindex fno-branch-count-reg
5949 Do not use ``decrement and branch'' instructions on a count register,
5950 but instead generate a sequence of instructions that decrement a
5951 register, compare it against zero, then branch based upon the result.
5952 This option is only meaningful on architectures that support such
5953 instructions, which include x86, PowerPC, IA-64 and S/390.
5955 The default is @option{-fbranch-count-reg}.
5957 @item -fno-function-cse
5958 @opindex fno-function-cse
5959 Do not put function addresses in registers; make each instruction that
5960 calls a constant function contain the function's address explicitly.
5962 This option results in less efficient code, but some strange hacks
5963 that alter the assembler output may be confused by the optimizations
5964 performed when this option is not used.
5966 The default is @option{-ffunction-cse}
5968 @item -fno-zero-initialized-in-bss
5969 @opindex fno-zero-initialized-in-bss
5970 If the target supports a BSS section, GCC by default puts variables that
5971 are initialized to zero into BSS@. This can save space in the resulting
5974 This option turns off this behavior because some programs explicitly
5975 rely on variables going to the data section. E.g., so that the
5976 resulting executable can find the beginning of that section and/or make
5977 assumptions based on that.
5979 The default is @option{-fzero-initialized-in-bss}.
5981 @item -fmudflap -fmudflapth -fmudflapir
5985 @cindex bounds checking
5987 For front-ends that support it (C and C++), instrument all risky
5988 pointer/array dereferencing operations, some standard library
5989 string/heap functions, and some other associated constructs with
5990 range/validity tests. Modules so instrumented should be immune to
5991 buffer overflows, invalid heap use, and some other classes of C/C++
5992 programming errors. The instrumentation relies on a separate runtime
5993 library (@file{libmudflap}), which will be linked into a program if
5994 @option{-fmudflap} is given at link time. Run-time behavior of the
5995 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5996 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5999 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
6000 link if your program is multi-threaded. Use @option{-fmudflapir}, in
6001 addition to @option{-fmudflap} or @option{-fmudflapth}, if
6002 instrumentation should ignore pointer reads. This produces less
6003 instrumentation (and therefore faster execution) and still provides
6004 some protection against outright memory corrupting writes, but allows
6005 erroneously read data to propagate within a program.
6007 @item -fthread-jumps
6008 @opindex fthread-jumps
6009 Perform optimizations where we check to see if a jump branches to a
6010 location where another comparison subsumed by the first is found. If
6011 so, the first branch is redirected to either the destination of the
6012 second branch or a point immediately following it, depending on whether
6013 the condition is known to be true or false.
6015 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6017 @item -fsplit-wide-types
6018 @opindex fsplit-wide-types
6019 When using a type that occupies multiple registers, such as @code{long
6020 long} on a 32-bit system, split the registers apart and allocate them
6021 independently. This normally generates better code for those types,
6022 but may make debugging more difficult.
6024 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
6027 @item -fcse-follow-jumps
6028 @opindex fcse-follow-jumps
6029 In common subexpression elimination (CSE), scan through jump instructions
6030 when the target of the jump is not reached by any other path. For
6031 example, when CSE encounters an @code{if} statement with an
6032 @code{else} clause, CSE will follow the jump when the condition
6035 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6037 @item -fcse-skip-blocks
6038 @opindex fcse-skip-blocks
6039 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
6040 follow jumps which conditionally skip over blocks. When CSE
6041 encounters a simple @code{if} statement with no else clause,
6042 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
6043 body of the @code{if}.
6045 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6047 @item -frerun-cse-after-loop
6048 @opindex frerun-cse-after-loop
6049 Re-run common subexpression elimination after loop optimizations has been
6052 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6056 Perform a global common subexpression elimination pass.
6057 This pass also performs global constant and copy propagation.
6059 @emph{Note:} When compiling a program using computed gotos, a GCC
6060 extension, you may get better runtime performance if you disable
6061 the global common subexpression elimination pass by adding
6062 @option{-fno-gcse} to the command line.
6064 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6068 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
6069 attempt to move loads which are only killed by stores into themselves. This
6070 allows a loop containing a load/store sequence to be changed to a load outside
6071 the loop, and a copy/store within the loop.
6073 Enabled by default when gcse is enabled.
6077 When @option{-fgcse-sm} is enabled, a store motion pass is run after
6078 global common subexpression elimination. This pass will attempt to move
6079 stores out of loops. When used in conjunction with @option{-fgcse-lm},
6080 loops containing a load/store sequence can be changed to a load before
6081 the loop and a store after the loop.
6083 Not enabled at any optimization level.
6087 When @option{-fgcse-las} is enabled, the global common subexpression
6088 elimination pass eliminates redundant loads that come after stores to the
6089 same memory location (both partial and full redundancies).
6091 Not enabled at any optimization level.
6093 @item -fgcse-after-reload
6094 @opindex fgcse-after-reload
6095 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
6096 pass is performed after reload. The purpose of this pass is to cleanup
6099 @item -funsafe-loop-optimizations
6100 @opindex funsafe-loop-optimizations
6101 If given, the loop optimizer will assume that loop indices do not
6102 overflow, and that the loops with nontrivial exit condition are not
6103 infinite. This enables a wider range of loop optimizations even if
6104 the loop optimizer itself cannot prove that these assumptions are valid.
6105 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
6106 if it finds this kind of loop.
6108 @item -fcrossjumping
6109 @opindex fcrossjumping
6110 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
6111 resulting code may or may not perform better than without cross-jumping.
6113 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6115 @item -fauto-inc-dec
6116 @opindex fauto-inc-dec
6117 Combine increments or decrements of addresses with memory accesses.
6118 This pass is always skipped on architectures that do not have
6119 instructions to support this. Enabled by default at @option{-O} and
6120 higher on architectures that support this.
6124 Perform dead code elimination (DCE) on RTL@.
6125 Enabled by default at @option{-O} and higher.
6129 Perform dead store elimination (DSE) on RTL@.
6130 Enabled by default at @option{-O} and higher.
6132 @item -fif-conversion
6133 @opindex fif-conversion
6134 Attempt to transform conditional jumps into branch-less equivalents. This
6135 include use of conditional moves, min, max, set flags and abs instructions, and
6136 some tricks doable by standard arithmetics. The use of conditional execution
6137 on chips where it is available is controlled by @code{if-conversion2}.
6139 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6141 @item -fif-conversion2
6142 @opindex fif-conversion2
6143 Use conditional execution (where available) to transform conditional jumps into
6144 branch-less equivalents.
6146 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6148 @item -fdelete-null-pointer-checks
6149 @opindex fdelete-null-pointer-checks
6150 Assume that programs cannot safely dereference null pointers, and that
6151 no code or data element resides there. This enables simple constant
6152 folding optimizations at all optimization levels. In addition, other
6153 optimization passes in GCC use this flag to control global dataflow
6154 analyses that eliminate useless checks for null pointers; these assume
6155 that if a pointer is checked after it has already been dereferenced,
6158 Note however that in some environments this assumption is not true.
6159 Use @option{-fno-delete-null-pointer-checks} to disable this optimization
6160 for programs which depend on that behavior.
6162 Some targets, especially embedded ones, disable this option at all levels.
6163 Otherwise it is enabled at all levels: @option{-O0}, @option{-O1},
6164 @option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information
6165 are enabled independently at different optimization levels.
6167 @item -fexpensive-optimizations
6168 @opindex fexpensive-optimizations
6169 Perform a number of minor optimizations that are relatively expensive.
6171 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6173 @item -foptimize-register-move
6175 @opindex foptimize-register-move
6177 Attempt to reassign register numbers in move instructions and as
6178 operands of other simple instructions in order to maximize the amount of
6179 register tying. This is especially helpful on machines with two-operand
6182 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
6185 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6187 @item -fira-algorithm=@var{algorithm}
6188 Use specified coloring algorithm for the integrated register
6189 allocator. The @var{algorithm} argument should be @code{priority} or
6190 @code{CB}. The first algorithm specifies Chow's priority coloring,
6191 the second one specifies Chaitin-Briggs coloring. The second
6192 algorithm can be unimplemented for some architectures. If it is
6193 implemented, it is the default because Chaitin-Briggs coloring as a
6194 rule generates a better code.
6196 @item -fira-region=@var{region}
6197 Use specified regions for the integrated register allocator. The
6198 @var{region} argument should be one of @code{all}, @code{mixed}, or
6199 @code{one}. The first value means using all loops as register
6200 allocation regions, the second value which is the default means using
6201 all loops except for loops with small register pressure as the
6202 regions, and third one means using all function as a single region.
6203 The first value can give best result for machines with small size and
6204 irregular register set, the third one results in faster and generates
6205 decent code and the smallest size code, and the default value usually
6206 give the best results in most cases and for most architectures.
6208 @item -fira-coalesce
6209 @opindex fira-coalesce
6210 Do optimistic register coalescing. This option might be profitable for
6211 architectures with big regular register files.
6213 @item -fno-ira-share-save-slots
6214 @opindex fno-ira-share-save-slots
6215 Switch off sharing stack slots used for saving call used hard
6216 registers living through a call. Each hard register will get a
6217 separate stack slot and as a result function stack frame will be
6220 @item -fno-ira-share-spill-slots
6221 @opindex fno-ira-share-spill-slots
6222 Switch off sharing stack slots allocated for pseudo-registers. Each
6223 pseudo-register which did not get a hard register will get a separate
6224 stack slot and as a result function stack frame will be bigger.
6226 @item -fira-verbose=@var{n}
6227 @opindex fira-verbose
6228 Set up how verbose dump file for the integrated register allocator
6229 will be. Default value is 5. If the value is greater or equal to 10,
6230 the dump file will be stderr as if the value were @var{n} minus 10.
6232 @item -fdelayed-branch
6233 @opindex fdelayed-branch
6234 If supported for the target machine, attempt to reorder instructions
6235 to exploit instruction slots available after delayed branch
6238 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6240 @item -fschedule-insns
6241 @opindex fschedule-insns
6242 If supported for the target machine, attempt to reorder instructions to
6243 eliminate execution stalls due to required data being unavailable. This
6244 helps machines that have slow floating point or memory load instructions
6245 by allowing other instructions to be issued until the result of the load
6246 or floating point instruction is required.
6248 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6250 @item -fschedule-insns2
6251 @opindex fschedule-insns2
6252 Similar to @option{-fschedule-insns}, but requests an additional pass of
6253 instruction scheduling after register allocation has been done. This is
6254 especially useful on machines with a relatively small number of
6255 registers and where memory load instructions take more than one cycle.
6257 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6259 @item -fno-sched-interblock
6260 @opindex fno-sched-interblock
6261 Don't schedule instructions across basic blocks. This is normally
6262 enabled by default when scheduling before register allocation, i.e.@:
6263 with @option{-fschedule-insns} or at @option{-O2} or higher.
6265 @item -fno-sched-spec
6266 @opindex fno-sched-spec
6267 Don't allow speculative motion of non-load instructions. This is normally
6268 enabled by default when scheduling before register allocation, i.e.@:
6269 with @option{-fschedule-insns} or at @option{-O2} or higher.
6271 @item -fsched-pressure
6272 @opindex fsched-pressure
6273 Enable register pressure sensitive insn scheduling before the register
6274 allocation. This only makes sense when scheduling before register
6275 allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
6276 @option{-O2} or higher. Usage of this option can improve the
6277 generated code and decrease its size by preventing register pressure
6278 increase above the number of available hard registers and as a
6279 consequence register spills in the register allocation.
6281 @item -fsched-spec-load
6282 @opindex fsched-spec-load
6283 Allow speculative motion of some load instructions. This only makes
6284 sense when scheduling before register allocation, i.e.@: with
6285 @option{-fschedule-insns} or at @option{-O2} or higher.
6287 @item -fsched-spec-load-dangerous
6288 @opindex fsched-spec-load-dangerous
6289 Allow speculative motion of more load instructions. This only makes
6290 sense when scheduling before register allocation, i.e.@: with
6291 @option{-fschedule-insns} or at @option{-O2} or higher.
6293 @item -fsched-stalled-insns
6294 @itemx -fsched-stalled-insns=@var{n}
6295 @opindex fsched-stalled-insns
6296 Define how many insns (if any) can be moved prematurely from the queue
6297 of stalled insns into the ready list, during the second scheduling pass.
6298 @option{-fno-sched-stalled-insns} means that no insns will be moved
6299 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
6300 on how many queued insns can be moved prematurely.
6301 @option{-fsched-stalled-insns} without a value is equivalent to
6302 @option{-fsched-stalled-insns=1}.
6304 @item -fsched-stalled-insns-dep
6305 @itemx -fsched-stalled-insns-dep=@var{n}
6306 @opindex fsched-stalled-insns-dep
6307 Define how many insn groups (cycles) will be examined for a dependency
6308 on a stalled insn that is candidate for premature removal from the queue
6309 of stalled insns. This has an effect only during the second scheduling pass,
6310 and only if @option{-fsched-stalled-insns} is used.
6311 @option{-fno-sched-stalled-insns-dep} is equivalent to
6312 @option{-fsched-stalled-insns-dep=0}.
6313 @option{-fsched-stalled-insns-dep} without a value is equivalent to
6314 @option{-fsched-stalled-insns-dep=1}.
6316 @item -fsched2-use-superblocks
6317 @opindex fsched2-use-superblocks
6318 When scheduling after register allocation, do use superblock scheduling
6319 algorithm. Superblock scheduling allows motion across basic block boundaries
6320 resulting on faster schedules. This option is experimental, as not all machine
6321 descriptions used by GCC model the CPU closely enough to avoid unreliable
6322 results from the algorithm.
6324 This only makes sense when scheduling after register allocation, i.e.@: with
6325 @option{-fschedule-insns2} or at @option{-O2} or higher.
6327 @item -fsched-group-heuristic
6328 @opindex fsched-group-heuristic
6329 Enable the group heuristic in the scheduler. This heuristic favors
6330 the instruction that belongs to a schedule group. This is enabled
6331 by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
6332 or @option{-fschedule-insns2} or at @option{-O2} or higher.
6334 @item -fsched-critical-path-heuristic
6335 @opindex fsched-critical-path-heuristic
6336 Enable the critical-path heuristic in the scheduler. This heuristic favors
6337 instructions on the critical path. This is enabled by default when
6338 scheduling is enabled, i.e.@: with @option{-fschedule-insns}
6339 or @option{-fschedule-insns2} or at @option{-O2} or higher.
6341 @item -fsched-spec-insn-heuristic
6342 @opindex fsched-spec-insn-heuristic
6343 Enable the speculative instruction heuristic in the scheduler. This
6344 heuristic favors speculative instructions with greater dependency weakness.
6345 This is enabled by default when scheduling is enabled, i.e.@:
6346 with @option{-fschedule-insns} or @option{-fschedule-insns2}
6347 or at @option{-O2} or higher.
6349 @item -fsched-rank-heuristic
6350 @opindex fsched-rank-heuristic
6351 Enable the rank heuristic in the scheduler. This heuristic favors
6352 the instruction belonging to a basic block with greater size or frequency.
6353 This is enabled by default when scheduling is enabled, i.e.@:
6354 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6355 at @option{-O2} or higher.
6357 @item -fsched-last-insn-heuristic
6358 @opindex fsched-last-insn-heuristic
6359 Enable the last-instruction heuristic in the scheduler. This heuristic
6360 favors the instruction that is less dependent on the last instruction
6361 scheduled. This is enabled by default when scheduling is enabled,
6362 i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6363 at @option{-O2} or higher.
6365 @item -fsched-dep-count-heuristic
6366 @opindex fsched-dep-count-heuristic
6367 Enable the dependent-count heuristic in the scheduler. This heuristic
6368 favors the instruction that has more instructions depending on it.
6369 This is enabled by default when scheduling is enabled, i.e.@:
6370 with @option{-fschedule-insns} or @option{-fschedule-insns2} or
6371 at @option{-O2} or higher.
6373 @item -fsched2-use-traces
6374 @opindex fsched2-use-traces
6375 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
6376 allocation and additionally perform code duplication in order to increase the
6377 size of superblocks using tracer pass. See @option{-ftracer} for details on
6380 This mode should produce faster but significantly longer programs. Also
6381 without @option{-fbranch-probabilities} the traces constructed may not
6382 match the reality and hurt the performance. This only makes
6383 sense when scheduling after register allocation, i.e.@: with
6384 @option{-fschedule-insns2} or at @option{-O2} or higher.
6386 @item -freschedule-modulo-scheduled-loops
6387 @opindex freschedule-modulo-scheduled-loops
6388 The modulo scheduling comes before the traditional scheduling, if a loop
6389 was modulo scheduled we may want to prevent the later scheduling passes
6390 from changing its schedule, we use this option to control that.
6392 @item -fselective-scheduling
6393 @opindex fselective-scheduling
6394 Schedule instructions using selective scheduling algorithm. Selective
6395 scheduling runs instead of the first scheduler pass.
6397 @item -fselective-scheduling2
6398 @opindex fselective-scheduling2
6399 Schedule instructions using selective scheduling algorithm. Selective
6400 scheduling runs instead of the second scheduler pass.
6402 @item -fsel-sched-pipelining
6403 @opindex fsel-sched-pipelining
6404 Enable software pipelining of innermost loops during selective scheduling.
6405 This option has no effect until one of @option{-fselective-scheduling} or
6406 @option{-fselective-scheduling2} is turned on.
6408 @item -fsel-sched-pipelining-outer-loops
6409 @opindex fsel-sched-pipelining-outer-loops
6410 When pipelining loops during selective scheduling, also pipeline outer loops.
6411 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
6413 @item -fcaller-saves
6414 @opindex fcaller-saves
6415 Enable values to be allocated in registers that will be clobbered by
6416 function calls, by emitting extra instructions to save and restore the
6417 registers around such calls. Such allocation is done only when it
6418 seems to result in better code than would otherwise be produced.
6420 This option is always enabled by default on certain machines, usually
6421 those which have no call-preserved registers to use instead.
6423 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6425 @item -fconserve-stack
6426 @opindex fconserve-stack
6427 Attempt to minimize stack usage. The compiler will attempt to use less
6428 stack space, even if that makes the program slower. This option
6429 implies setting the @option{large-stack-frame} parameter to 100
6430 and the @option{large-stack-frame-growth} parameter to 400.
6432 @item -ftree-reassoc
6433 @opindex ftree-reassoc
6434 Perform reassociation on trees. This flag is enabled by default
6435 at @option{-O} and higher.
6439 Perform partial redundancy elimination (PRE) on trees. This flag is
6440 enabled by default at @option{-O2} and @option{-O3}.
6442 @item -ftree-forwprop
6443 @opindex ftree-forwprop
6444 Perform forward propagation on trees. This flag is enabled by default
6445 at @option{-O} and higher.
6449 Perform full redundancy elimination (FRE) on trees. The difference
6450 between FRE and PRE is that FRE only considers expressions
6451 that are computed on all paths leading to the redundant computation.
6452 This analysis is faster than PRE, though it exposes fewer redundancies.
6453 This flag is enabled by default at @option{-O} and higher.
6455 @item -ftree-phiprop
6456 @opindex ftree-phiprop
6457 Perform hoisting of loads from conditional pointers on trees. This
6458 pass is enabled by default at @option{-O} and higher.
6460 @item -ftree-copy-prop
6461 @opindex ftree-copy-prop
6462 Perform copy propagation on trees. This pass eliminates unnecessary
6463 copy operations. This flag is enabled by default at @option{-O} and
6466 @item -fipa-pure-const
6467 @opindex fipa-pure-const
6468 Discover which functions are pure or constant.
6469 Enabled by default at @option{-O} and higher.
6471 @item -fipa-reference
6472 @opindex fipa-reference
6473 Discover which static variables do not escape cannot escape the
6475 Enabled by default at @option{-O} and higher.
6477 @item -fipa-struct-reorg
6478 @opindex fipa-struct-reorg
6479 Perform structure reorganization optimization, that change C-like structures
6480 layout in order to better utilize spatial locality. This transformation is
6481 affective for programs containing arrays of structures. Available in two
6482 compilation modes: profile-based (enabled with @option{-fprofile-generate})
6483 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
6484 to provide the safety of this transformation. It works only in whole program
6485 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
6486 enabled. Structures considered @samp{cold} by this transformation are not
6487 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
6489 With this flag, the program debug info reflects a new structure layout.
6493 Perform interprocedural pointer analysis. This option is experimental
6494 and does not affect generated code.
6498 Perform interprocedural constant propagation.
6499 This optimization analyzes the program to determine when values passed
6500 to functions are constants and then optimizes accordingly.
6501 This optimization can substantially increase performance
6502 if the application has constants passed to functions.
6503 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
6505 @item -fipa-cp-clone
6506 @opindex fipa-cp-clone
6507 Perform function cloning to make interprocedural constant propagation stronger.
6508 When enabled, interprocedural constant propagation will perform function cloning
6509 when externally visible function can be called with constant arguments.
6510 Because this optimization can create multiple copies of functions,
6511 it may significantly increase code size
6512 (see @option{--param ipcp-unit-growth=@var{value}}).
6513 This flag is enabled by default at @option{-O3}.
6515 @item -fipa-matrix-reorg
6516 @opindex fipa-matrix-reorg
6517 Perform matrix flattening and transposing.
6518 Matrix flattening tries to replace an @math{m}-dimensional matrix
6519 with its equivalent @math{n}-dimensional matrix, where @math{n < m}.
6520 This reduces the level of indirection needed for accessing the elements
6521 of the matrix. The second optimization is matrix transposing that
6522 attempts to change the order of the matrix's dimensions in order to
6523 improve cache locality.
6524 Both optimizations need the @option{-fwhole-program} flag.
6525 Transposing is enabled only if profiling information is available.
6529 Perform forward store motion on trees. This flag is
6530 enabled by default at @option{-O} and higher.
6534 Perform sparse conditional constant propagation (CCP) on trees. This
6535 pass only operates on local scalar variables and is enabled by default
6536 at @option{-O} and higher.
6538 @item -ftree-switch-conversion
6539 Perform conversion of simple initializations in a switch to
6540 initializations from a scalar array. This flag is enabled by default
6541 at @option{-O2} and higher.
6545 Perform dead code elimination (DCE) on trees. This flag is enabled by
6546 default at @option{-O} and higher.
6548 @item -ftree-builtin-call-dce
6549 @opindex ftree-builtin-call-dce
6550 Perform conditional dead code elimination (DCE) for calls to builtin functions
6551 that may set @code{errno} but are otherwise side-effect free. This flag is
6552 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6555 @item -ftree-dominator-opts
6556 @opindex ftree-dominator-opts
6557 Perform a variety of simple scalar cleanups (constant/copy
6558 propagation, redundancy elimination, range propagation and expression
6559 simplification) based on a dominator tree traversal. This also
6560 performs jump threading (to reduce jumps to jumps). This flag is
6561 enabled by default at @option{-O} and higher.
6565 Perform dead store elimination (DSE) on trees. A dead store is a store into
6566 a memory location which will later be overwritten by another store without
6567 any intervening loads. In this case the earlier store can be deleted. This
6568 flag is enabled by default at @option{-O} and higher.
6572 Perform loop header copying on trees. This is beneficial since it increases
6573 effectiveness of code motion optimizations. It also saves one jump. This flag
6574 is enabled by default at @option{-O} and higher. It is not enabled
6575 for @option{-Os}, since it usually increases code size.
6577 @item -ftree-loop-optimize
6578 @opindex ftree-loop-optimize
6579 Perform loop optimizations on trees. This flag is enabled by default
6580 at @option{-O} and higher.
6582 @item -ftree-loop-linear
6583 @opindex ftree-loop-linear
6584 Perform linear loop transformations on tree. This flag can improve cache
6585 performance and allow further loop optimizations to take place.
6587 @item -floop-interchange
6588 Perform loop interchange transformations on loops. Interchanging two
6589 nested loops switches the inner and outer loops. For example, given a
6594 A(J, I) = A(J, I) * C
6598 loop interchange will transform the loop as if the user had written:
6602 A(J, I) = A(J, I) * C
6606 which can be beneficial when @code{N} is larger than the caches,
6607 because in Fortran, the elements of an array are stored in memory
6608 contiguously by column, and the original loop iterates over rows,
6609 potentially creating at each access a cache miss. This optimization
6610 applies to all the languages supported by GCC and is not limited to
6611 Fortran. To use this code transformation, GCC has to be configured
6612 with @option{--with-ppl} and @option{--with-cloog} to enable the
6613 Graphite loop transformation infrastructure.
6615 @item -floop-strip-mine
6616 Perform loop strip mining transformations on loops. Strip mining
6617 splits a loop into two nested loops. The outer loop has strides
6618 equal to the strip size and the inner loop has strides of the
6619 original loop within a strip. For example, given a loop like:
6625 loop strip mining will transform the loop as if the user had written:
6628 DO I = II, min (II + 3, N)
6633 This optimization applies to all the languages supported by GCC and is
6634 not limited to Fortran. To use this code transformation, GCC has to
6635 be configured with @option{--with-ppl} and @option{--with-cloog} to
6636 enable the Graphite loop transformation infrastructure.
6639 Perform loop blocking transformations on loops. Blocking strip mines
6640 each loop in the loop nest such that the memory accesses of the
6641 element loops fit inside caches. For example, given a loop like:
6645 A(J, I) = B(I) + C(J)
6649 loop blocking will transform the loop as if the user had written:
6653 DO I = II, min (II + 63, N)
6654 DO J = JJ, min (JJ + 63, M)
6655 A(J, I) = B(I) + C(J)
6661 which can be beneficial when @code{M} is larger than the caches,
6662 because the innermost loop will iterate over a smaller amount of data
6663 that can be kept in the caches. This optimization applies to all the
6664 languages supported by GCC and is not limited to Fortran. To use this
6665 code transformation, GCC has to be configured with @option{--with-ppl}
6666 and @option{--with-cloog} to enable the Graphite loop transformation
6669 @item -fgraphite-identity
6670 @opindex fgraphite-identity
6671 Enable the identity transformation for graphite. For every SCoP we generate
6672 the polyhedral representation and transform it back to gimple. Using
6673 @option{-fgraphite-identity} we can check the costs or benefits of the
6674 GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
6675 are also performed by the code generator CLooG, like index splitting and
6676 dead code elimination in loops.
6678 @item -floop-parallelize-all
6679 Use the Graphite data dependence analysis to identify loops that can
6680 be parallelized. Parallelize all the loops that can be analyzed to
6681 not contain loop carried dependences without checking that it is
6682 profitable to parallelize the loops.
6684 @item -fcheck-data-deps
6685 @opindex fcheck-data-deps
6686 Compare the results of several data dependence analyzers. This option
6687 is used for debugging the data dependence analyzers.
6689 @item -ftree-loop-distribution
6690 Perform loop distribution. This flag can improve cache performance on
6691 big loop bodies and allow further loop optimizations, like
6692 parallelization or vectorization, to take place. For example, the loop
6709 @item -ftree-loop-im
6710 @opindex ftree-loop-im
6711 Perform loop invariant motion on trees. This pass moves only invariants that
6712 would be hard to handle at RTL level (function calls, operations that expand to
6713 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
6714 operands of conditions that are invariant out of the loop, so that we can use
6715 just trivial invariantness analysis in loop unswitching. The pass also includes
6718 @item -ftree-loop-ivcanon
6719 @opindex ftree-loop-ivcanon
6720 Create a canonical counter for number of iterations in the loop for that
6721 determining number of iterations requires complicated analysis. Later
6722 optimizations then may determine the number easily. Useful especially
6723 in connection with unrolling.
6727 Perform induction variable optimizations (strength reduction, induction
6728 variable merging and induction variable elimination) on trees.
6730 @item -ftree-parallelize-loops=n
6731 @opindex ftree-parallelize-loops
6732 Parallelize loops, i.e., split their iteration space to run in n threads.
6733 This is only possible for loops whose iterations are independent
6734 and can be arbitrarily reordered. The optimization is only
6735 profitable on multiprocessor machines, for loops that are CPU-intensive,
6736 rather than constrained e.g.@: by memory bandwidth. This option
6737 implies @option{-pthread}, and thus is only supported on targets
6738 that have support for @option{-pthread}.
6742 Perform function-local points-to analysis on trees. This flag is
6743 enabled by default at @option{-O} and higher.
6747 Perform scalar replacement of aggregates. This pass replaces structure
6748 references with scalars to prevent committing structures to memory too
6749 early. This flag is enabled by default at @option{-O} and higher.
6751 @item -ftree-copyrename
6752 @opindex ftree-copyrename
6753 Perform copy renaming on trees. This pass attempts to rename compiler
6754 temporaries to other variables at copy locations, usually resulting in
6755 variable names which more closely resemble the original variables. This flag
6756 is enabled by default at @option{-O} and higher.
6760 Perform temporary expression replacement during the SSA->normal phase. Single
6761 use/single def temporaries are replaced at their use location with their
6762 defining expression. This results in non-GIMPLE code, but gives the expanders
6763 much more complex trees to work on resulting in better RTL generation. This is
6764 enabled by default at @option{-O} and higher.
6766 @item -ftree-vectorize
6767 @opindex ftree-vectorize
6768 Perform loop vectorization on trees. This flag is enabled by default at
6771 @item -ftree-vect-loop-version
6772 @opindex ftree-vect-loop-version
6773 Perform loop versioning when doing loop vectorization on trees. When a loop
6774 appears to be vectorizable except that data alignment or data dependence cannot
6775 be determined at compile time then vectorized and non-vectorized versions of
6776 the loop are generated along with runtime checks for alignment or dependence
6777 to control which version is executed. This option is enabled by default
6778 except at level @option{-Os} where it is disabled.
6780 @item -fvect-cost-model
6781 @opindex fvect-cost-model
6782 Enable cost model for vectorization.
6786 Perform Value Range Propagation on trees. This is similar to the
6787 constant propagation pass, but instead of values, ranges of values are
6788 propagated. This allows the optimizers to remove unnecessary range
6789 checks like array bound checks and null pointer checks. This is
6790 enabled by default at @option{-O2} and higher. Null pointer check
6791 elimination is only done if @option{-fdelete-null-pointer-checks} is
6796 Perform tail duplication to enlarge superblock size. This transformation
6797 simplifies the control flow of the function allowing other optimizations to do
6800 @item -funroll-loops
6801 @opindex funroll-loops
6802 Unroll loops whose number of iterations can be determined at compile
6803 time or upon entry to the loop. @option{-funroll-loops} implies
6804 @option{-frerun-cse-after-loop}. This option makes code larger,
6805 and may or may not make it run faster.
6807 @item -funroll-all-loops
6808 @opindex funroll-all-loops
6809 Unroll all loops, even if their number of iterations is uncertain when
6810 the loop is entered. This usually makes programs run more slowly.
6811 @option{-funroll-all-loops} implies the same options as
6812 @option{-funroll-loops},
6814 @item -fsplit-ivs-in-unroller
6815 @opindex fsplit-ivs-in-unroller
6816 Enables expressing of values of induction variables in later iterations
6817 of the unrolled loop using the value in the first iteration. This breaks
6818 long dependency chains, thus improving efficiency of the scheduling passes.
6820 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6821 same effect. However in cases the loop body is more complicated than
6822 a single basic block, this is not reliable. It also does not work at all
6823 on some of the architectures due to restrictions in the CSE pass.
6825 This optimization is enabled by default.
6827 @item -fvariable-expansion-in-unroller
6828 @opindex fvariable-expansion-in-unroller
6829 With this option, the compiler will create multiple copies of some
6830 local variables when unrolling a loop which can result in superior code.
6832 @item -fpredictive-commoning
6833 @opindex fpredictive-commoning
6834 Perform predictive commoning optimization, i.e., reusing computations
6835 (especially memory loads and stores) performed in previous
6836 iterations of loops.
6838 This option is enabled at level @option{-O3}.
6840 @item -fprefetch-loop-arrays
6841 @opindex fprefetch-loop-arrays
6842 If supported by the target machine, generate instructions to prefetch
6843 memory to improve the performance of loops that access large arrays.
6845 This option may generate better or worse code; results are highly
6846 dependent on the structure of loops within the source code.
6848 Disabled at level @option{-Os}.
6851 @itemx -fno-peephole2
6852 @opindex fno-peephole
6853 @opindex fno-peephole2
6854 Disable any machine-specific peephole optimizations. The difference
6855 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6856 are implemented in the compiler; some targets use one, some use the
6857 other, a few use both.
6859 @option{-fpeephole} is enabled by default.
6860 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6862 @item -fno-guess-branch-probability
6863 @opindex fno-guess-branch-probability
6864 Do not guess branch probabilities using heuristics.
6866 GCC will use heuristics to guess branch probabilities if they are
6867 not provided by profiling feedback (@option{-fprofile-arcs}). These
6868 heuristics are based on the control flow graph. If some branch probabilities
6869 are specified by @samp{__builtin_expect}, then the heuristics will be
6870 used to guess branch probabilities for the rest of the control flow graph,
6871 taking the @samp{__builtin_expect} info into account. The interactions
6872 between the heuristics and @samp{__builtin_expect} can be complex, and in
6873 some cases, it may be useful to disable the heuristics so that the effects
6874 of @samp{__builtin_expect} are easier to understand.
6876 The default is @option{-fguess-branch-probability} at levels
6877 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6879 @item -freorder-blocks
6880 @opindex freorder-blocks
6881 Reorder basic blocks in the compiled function in order to reduce number of
6882 taken branches and improve code locality.
6884 Enabled at levels @option{-O2}, @option{-O3}.
6886 @item -freorder-blocks-and-partition
6887 @opindex freorder-blocks-and-partition
6888 In addition to reordering basic blocks in the compiled function, in order
6889 to reduce number of taken branches, partitions hot and cold basic blocks
6890 into separate sections of the assembly and .o files, to improve
6891 paging and cache locality performance.
6893 This optimization is automatically turned off in the presence of
6894 exception handling, for linkonce sections, for functions with a user-defined
6895 section attribute and on any architecture that does not support named
6898 @item -freorder-functions
6899 @opindex freorder-functions
6900 Reorder functions in the object file in order to
6901 improve code locality. This is implemented by using special
6902 subsections @code{.text.hot} for most frequently executed functions and
6903 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6904 the linker so object file format must support named sections and linker must
6905 place them in a reasonable way.
6907 Also profile feedback must be available in to make this option effective. See
6908 @option{-fprofile-arcs} for details.
6910 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6912 @item -fstrict-aliasing
6913 @opindex fstrict-aliasing
6914 Allow the compiler to assume the strictest aliasing rules applicable to
6915 the language being compiled. For C (and C++), this activates
6916 optimizations based on the type of expressions. In particular, an
6917 object of one type is assumed never to reside at the same address as an
6918 object of a different type, unless the types are almost the same. For
6919 example, an @code{unsigned int} can alias an @code{int}, but not a
6920 @code{void*} or a @code{double}. A character type may alias any other
6923 @anchor{Type-punning}Pay special attention to code like this:
6936 The practice of reading from a different union member than the one most
6937 recently written to (called ``type-punning'') is common. Even with
6938 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6939 is accessed through the union type. So, the code above will work as
6940 expected. @xref{Structures unions enumerations and bit-fields
6941 implementation}. However, this code might not:
6952 Similarly, access by taking the address, casting the resulting pointer
6953 and dereferencing the result has undefined behavior, even if the cast
6954 uses a union type, e.g.:
6958 return ((union a_union *) &d)->i;
6962 The @option{-fstrict-aliasing} option is enabled at levels
6963 @option{-O2}, @option{-O3}, @option{-Os}.
6965 @item -fstrict-overflow
6966 @opindex fstrict-overflow
6967 Allow the compiler to assume strict signed overflow rules, depending
6968 on the language being compiled. For C (and C++) this means that
6969 overflow when doing arithmetic with signed numbers is undefined, which
6970 means that the compiler may assume that it will not happen. This
6971 permits various optimizations. For example, the compiler will assume
6972 that an expression like @code{i + 10 > i} will always be true for
6973 signed @code{i}. This assumption is only valid if signed overflow is
6974 undefined, as the expression is false if @code{i + 10} overflows when
6975 using twos complement arithmetic. When this option is in effect any
6976 attempt to determine whether an operation on signed numbers will
6977 overflow must be written carefully to not actually involve overflow.
6979 This option also allows the compiler to assume strict pointer
6980 semantics: given a pointer to an object, if adding an offset to that
6981 pointer does not produce a pointer to the same object, the addition is
6982 undefined. This permits the compiler to conclude that @code{p + u >
6983 p} is always true for a pointer @code{p} and unsigned integer
6984 @code{u}. This assumption is only valid because pointer wraparound is
6985 undefined, as the expression is false if @code{p + u} overflows using
6986 twos complement arithmetic.
6988 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6989 that integer signed overflow is fully defined: it wraps. When
6990 @option{-fwrapv} is used, there is no difference between
6991 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6992 integers. With @option{-fwrapv} certain types of overflow are
6993 permitted. For example, if the compiler gets an overflow when doing
6994 arithmetic on constants, the overflowed value can still be used with
6995 @option{-fwrapv}, but not otherwise.
6997 The @option{-fstrict-overflow} option is enabled at levels
6998 @option{-O2}, @option{-O3}, @option{-Os}.
7000 @item -falign-functions
7001 @itemx -falign-functions=@var{n}
7002 @opindex falign-functions
7003 Align the start of functions to the next power-of-two greater than
7004 @var{n}, skipping up to @var{n} bytes. For instance,
7005 @option{-falign-functions=32} aligns functions to the next 32-byte
7006 boundary, but @option{-falign-functions=24} would align to the next
7007 32-byte boundary only if this can be done by skipping 23 bytes or less.
7009 @option{-fno-align-functions} and @option{-falign-functions=1} are
7010 equivalent and mean that functions will not be aligned.
7012 Some assemblers only support this flag when @var{n} is a power of two;
7013 in that case, it is rounded up.
7015 If @var{n} is not specified or is zero, use a machine-dependent default.
7017 Enabled at levels @option{-O2}, @option{-O3}.
7019 @item -falign-labels
7020 @itemx -falign-labels=@var{n}
7021 @opindex falign-labels
7022 Align all branch targets to a power-of-two boundary, skipping up to
7023 @var{n} bytes like @option{-falign-functions}. This option can easily
7024 make code slower, because it must insert dummy operations for when the
7025 branch target is reached in the usual flow of the code.
7027 @option{-fno-align-labels} and @option{-falign-labels=1} are
7028 equivalent and mean that labels will not be aligned.
7030 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
7031 are greater than this value, then their values are used instead.
7033 If @var{n} is not specified or is zero, use a machine-dependent default
7034 which is very likely to be @samp{1}, meaning no alignment.
7036 Enabled at levels @option{-O2}, @option{-O3}.
7039 @itemx -falign-loops=@var{n}
7040 @opindex falign-loops
7041 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
7042 like @option{-falign-functions}. The hope is that the loop will be
7043 executed many times, which will make up for any execution of the dummy
7046 @option{-fno-align-loops} and @option{-falign-loops=1} are
7047 equivalent and mean that loops will not be aligned.
7049 If @var{n} is not specified or is zero, use a machine-dependent default.
7051 Enabled at levels @option{-O2}, @option{-O3}.
7054 @itemx -falign-jumps=@var{n}
7055 @opindex falign-jumps
7056 Align branch targets to a power-of-two boundary, for branch targets
7057 where the targets can only be reached by jumping, skipping up to @var{n}
7058 bytes like @option{-falign-functions}. In this case, no dummy operations
7061 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
7062 equivalent and mean that loops will not be aligned.
7064 If @var{n} is not specified or is zero, use a machine-dependent default.
7066 Enabled at levels @option{-O2}, @option{-O3}.
7068 @item -funit-at-a-time
7069 @opindex funit-at-a-time
7070 This option is left for compatibility reasons. @option{-funit-at-a-time}
7071 has no effect, while @option{-fno-unit-at-a-time} implies
7072 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
7076 @item -fno-toplevel-reorder
7077 @opindex fno-toplevel-reorder
7078 Do not reorder top-level functions, variables, and @code{asm}
7079 statements. Output them in the same order that they appear in the
7080 input file. When this option is used, unreferenced static variables
7081 will not be removed. This option is intended to support existing code
7082 which relies on a particular ordering. For new code, it is better to
7085 Enabled at level @option{-O0}. When disabled explicitly, it also imply
7086 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
7091 Constructs webs as commonly used for register allocation purposes and assign
7092 each web individual pseudo register. This allows the register allocation pass
7093 to operate on pseudos directly, but also strengthens several other optimization
7094 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
7095 however, make debugging impossible, since variables will no longer stay in a
7098 Enabled by default with @option{-funroll-loops}.
7100 @item -fwhole-program
7101 @opindex fwhole-program
7102 Assume that the current compilation unit represents the whole program being
7103 compiled. All public functions and variables with the exception of @code{main}
7104 and those merged by attribute @code{externally_visible} become static functions
7105 and in effect are optimized more aggressively by interprocedural optimizers.
7106 While this option is equivalent to proper use of the @code{static} keyword for
7107 programs consisting of a single file, in combination with option
7108 @option{--combine} this flag can be used to compile many smaller scale C
7109 programs since the functions and variables become local for the whole combined
7110 compilation unit, not for the single source file itself.
7112 This option implies @option{-fwhole-file} for Fortran programs.
7114 @item -fcprop-registers
7115 @opindex fcprop-registers
7116 After register allocation and post-register allocation instruction splitting,
7117 we perform a copy-propagation pass to try to reduce scheduling dependencies
7118 and occasionally eliminate the copy.
7120 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
7122 @item -fprofile-correction
7123 @opindex fprofile-correction
7124 Profiles collected using an instrumented binary for multi-threaded programs may
7125 be inconsistent due to missed counter updates. When this option is specified,
7126 GCC will use heuristics to correct or smooth out such inconsistencies. By
7127 default, GCC will emit an error message when an inconsistent profile is detected.
7129 @item -fprofile-dir=@var{path}
7130 @opindex fprofile-dir
7132 Set the directory to search the profile data files in to @var{path}.
7133 This option affects only the profile data generated by
7134 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
7135 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
7136 and its related options.
7137 By default, GCC will use the current directory as @var{path}
7138 thus the profile data file will appear in the same directory as the object file.
7140 @item -fprofile-generate
7141 @itemx -fprofile-generate=@var{path}
7142 @opindex fprofile-generate
7144 Enable options usually used for instrumenting application to produce
7145 profile useful for later recompilation with profile feedback based
7146 optimization. You must use @option{-fprofile-generate} both when
7147 compiling and when linking your program.
7149 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
7151 If @var{path} is specified, GCC will look at the @var{path} to find
7152 the profile feedback data files. See @option{-fprofile-dir}.
7155 @itemx -fprofile-use=@var{path}
7156 @opindex fprofile-use
7157 Enable profile feedback directed optimizations, and optimizations
7158 generally profitable only with profile feedback available.
7160 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
7161 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
7163 By default, GCC emits an error message if the feedback profiles do not
7164 match the source code. This error can be turned into a warning by using
7165 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
7168 If @var{path} is specified, GCC will look at the @var{path} to find
7169 the profile feedback data files. See @option{-fprofile-dir}.
7172 The following options control compiler behavior regarding floating
7173 point arithmetic. These options trade off between speed and
7174 correctness. All must be specifically enabled.
7178 @opindex ffloat-store
7179 Do not store floating point variables in registers, and inhibit other
7180 options that might change whether a floating point value is taken from a
7183 @cindex floating point precision
7184 This option prevents undesirable excess precision on machines such as
7185 the 68000 where the floating registers (of the 68881) keep more
7186 precision than a @code{double} is supposed to have. Similarly for the
7187 x86 architecture. For most programs, the excess precision does only
7188 good, but a few programs rely on the precise definition of IEEE floating
7189 point. Use @option{-ffloat-store} for such programs, after modifying
7190 them to store all pertinent intermediate computations into variables.
7192 @item -fexcess-precision=@var{style}
7193 @opindex fexcess-precision
7194 This option allows further control over excess precision on machines
7195 where floating-point registers have more precision than the IEEE
7196 @code{float} and @code{double} types and the processor does not
7197 support operations rounding to those types. By default,
7198 @option{-fexcess-precision=fast} is in effect; this means that
7199 operations are carried out in the precision of the registers and that
7200 it is unpredictable when rounding to the types specified in the source
7201 code takes place. When compiling C, if
7202 @option{-fexcess-precision=standard} is specified then excess
7203 precision will follow the rules specified in ISO C99; in particular,
7204 both casts and assignments cause values to be rounded to their
7205 semantic types (whereas @option{-ffloat-store} only affects
7206 assignments). This option is enabled by default for C if a strict
7207 conformance option such as @option{-std=c99} is used.
7210 @option{-fexcess-precision=standard} is not implemented for languages
7211 other than C, and has no effect if
7212 @option{-funsafe-math-optimizations} or @option{-ffast-math} is
7213 specified. On the x86, it also has no effect if @option{-mfpmath=sse}
7214 or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
7215 semantics apply without excess precision, and in the latter, rounding
7220 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
7221 @option{-ffinite-math-only}, @option{-fno-rounding-math},
7222 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
7224 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
7226 This option is not turned on by any @option{-O} option since
7227 it can result in incorrect output for programs which depend on
7228 an exact implementation of IEEE or ISO rules/specifications for
7229 math functions. It may, however, yield faster code for programs
7230 that do not require the guarantees of these specifications.
7232 @item -fno-math-errno
7233 @opindex fno-math-errno
7234 Do not set ERRNO after calling math functions that are executed
7235 with a single instruction, e.g., sqrt. A program that relies on
7236 IEEE exceptions for math error handling may want to use this flag
7237 for speed while maintaining IEEE arithmetic compatibility.
7239 This option is not turned on by any @option{-O} option since
7240 it can result in incorrect output for programs which depend on
7241 an exact implementation of IEEE or ISO rules/specifications for
7242 math functions. It may, however, yield faster code for programs
7243 that do not require the guarantees of these specifications.
7245 The default is @option{-fmath-errno}.
7247 On Darwin systems, the math library never sets @code{errno}. There is
7248 therefore no reason for the compiler to consider the possibility that
7249 it might, and @option{-fno-math-errno} is the default.
7251 @item -funsafe-math-optimizations
7252 @opindex funsafe-math-optimizations
7254 Allow optimizations for floating-point arithmetic that (a) assume
7255 that arguments and results are valid and (b) may violate IEEE or
7256 ANSI standards. When used at link-time, it may include libraries
7257 or startup files that change the default FPU control word or other
7258 similar optimizations.
7260 This option is not turned on by any @option{-O} option since
7261 it can result in incorrect output for programs which depend on
7262 an exact implementation of IEEE or ISO rules/specifications for
7263 math functions. It may, however, yield faster code for programs
7264 that do not require the guarantees of these specifications.
7265 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
7266 @option{-fassociative-math} and @option{-freciprocal-math}.
7268 The default is @option{-fno-unsafe-math-optimizations}.
7270 @item -fassociative-math
7271 @opindex fassociative-math
7273 Allow re-association of operands in series of floating-point operations.
7274 This violates the ISO C and C++ language standard by possibly changing
7275 computation result. NOTE: re-ordering may change the sign of zero as
7276 well as ignore NaNs and inhibit or create underflow or overflow (and
7277 thus cannot be used on a code which relies on rounding behavior like
7278 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
7279 and thus may not be used when ordered comparisons are required.
7280 This option requires that both @option{-fno-signed-zeros} and
7281 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
7282 much sense with @option{-frounding-math}.
7284 The default is @option{-fno-associative-math}.
7286 @item -freciprocal-math
7287 @opindex freciprocal-math
7289 Allow the reciprocal of a value to be used instead of dividing by
7290 the value if this enables optimizations. For example @code{x / y}
7291 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
7292 is subject to common subexpression elimination. Note that this loses
7293 precision and increases the number of flops operating on the value.
7295 The default is @option{-fno-reciprocal-math}.
7297 @item -ffinite-math-only
7298 @opindex ffinite-math-only
7299 Allow optimizations for floating-point arithmetic that assume
7300 that arguments and results are not NaNs or +-Infs.
7302 This option is not turned on by any @option{-O} option since
7303 it can result in incorrect output for programs which depend on
7304 an exact implementation of IEEE or ISO rules/specifications for
7305 math functions. It may, however, yield faster code for programs
7306 that do not require the guarantees of these specifications.
7308 The default is @option{-fno-finite-math-only}.
7310 @item -fno-signed-zeros
7311 @opindex fno-signed-zeros
7312 Allow optimizations for floating point arithmetic that ignore the
7313 signedness of zero. IEEE arithmetic specifies the behavior of
7314 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
7315 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
7316 This option implies that the sign of a zero result isn't significant.
7318 The default is @option{-fsigned-zeros}.
7320 @item -fno-trapping-math
7321 @opindex fno-trapping-math
7322 Compile code assuming that floating-point operations cannot generate
7323 user-visible traps. These traps include division by zero, overflow,
7324 underflow, inexact result and invalid operation. This option requires
7325 that @option{-fno-signaling-nans} be in effect. Setting this option may
7326 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
7328 This option should never be turned on by any @option{-O} option since
7329 it can result in incorrect output for programs which depend on
7330 an exact implementation of IEEE or ISO rules/specifications for
7333 The default is @option{-ftrapping-math}.
7335 @item -frounding-math
7336 @opindex frounding-math
7337 Disable transformations and optimizations that assume default floating
7338 point rounding behavior. This is round-to-zero for all floating point
7339 to integer conversions, and round-to-nearest for all other arithmetic
7340 truncations. This option should be specified for programs that change
7341 the FP rounding mode dynamically, or that may be executed with a
7342 non-default rounding mode. This option disables constant folding of
7343 floating point expressions at compile-time (which may be affected by
7344 rounding mode) and arithmetic transformations that are unsafe in the
7345 presence of sign-dependent rounding modes.
7347 The default is @option{-fno-rounding-math}.
7349 This option is experimental and does not currently guarantee to
7350 disable all GCC optimizations that are affected by rounding mode.
7351 Future versions of GCC may provide finer control of this setting
7352 using C99's @code{FENV_ACCESS} pragma. This command line option
7353 will be used to specify the default state for @code{FENV_ACCESS}.
7355 @item -fsignaling-nans
7356 @opindex fsignaling-nans
7357 Compile code assuming that IEEE signaling NaNs may generate user-visible
7358 traps during floating-point operations. Setting this option disables
7359 optimizations that may change the number of exceptions visible with
7360 signaling NaNs. This option implies @option{-ftrapping-math}.
7362 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
7365 The default is @option{-fno-signaling-nans}.
7367 This option is experimental and does not currently guarantee to
7368 disable all GCC optimizations that affect signaling NaN behavior.
7370 @item -fsingle-precision-constant
7371 @opindex fsingle-precision-constant
7372 Treat floating point constant as single precision constant instead of
7373 implicitly converting it to double precision constant.
7375 @item -fcx-limited-range
7376 @opindex fcx-limited-range
7377 When enabled, this option states that a range reduction step is not
7378 needed when performing complex division. Also, there is no checking
7379 whether the result of a complex multiplication or division is @code{NaN
7380 + I*NaN}, with an attempt to rescue the situation in that case. The
7381 default is @option{-fno-cx-limited-range}, but is enabled by
7382 @option{-ffast-math}.
7384 This option controls the default setting of the ISO C99
7385 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
7388 @item -fcx-fortran-rules
7389 @opindex fcx-fortran-rules
7390 Complex multiplication and division follow Fortran rules. Range
7391 reduction is done as part of complex division, but there is no checking
7392 whether the result of a complex multiplication or division is @code{NaN
7393 + I*NaN}, with an attempt to rescue the situation in that case.
7395 The default is @option{-fno-cx-fortran-rules}.
7399 The following options control optimizations that may improve
7400 performance, but are not enabled by any @option{-O} options. This
7401 section includes experimental options that may produce broken code.
7404 @item -fbranch-probabilities
7405 @opindex fbranch-probabilities
7406 After running a program compiled with @option{-fprofile-arcs}
7407 (@pxref{Debugging Options,, Options for Debugging Your Program or
7408 @command{gcc}}), you can compile it a second time using
7409 @option{-fbranch-probabilities}, to improve optimizations based on
7410 the number of times each branch was taken. When the program
7411 compiled with @option{-fprofile-arcs} exits it saves arc execution
7412 counts to a file called @file{@var{sourcename}.gcda} for each source
7413 file. The information in this data file is very dependent on the
7414 structure of the generated code, so you must use the same source code
7415 and the same optimization options for both compilations.
7417 With @option{-fbranch-probabilities}, GCC puts a
7418 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
7419 These can be used to improve optimization. Currently, they are only
7420 used in one place: in @file{reorg.c}, instead of guessing which path a
7421 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
7422 exactly determine which path is taken more often.
7424 @item -fprofile-values
7425 @opindex fprofile-values
7426 If combined with @option{-fprofile-arcs}, it adds code so that some
7427 data about values of expressions in the program is gathered.
7429 With @option{-fbranch-probabilities}, it reads back the data gathered
7430 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
7431 notes to instructions for their later usage in optimizations.
7433 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
7437 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
7438 a code to gather information about values of expressions.
7440 With @option{-fbranch-probabilities}, it reads back the data gathered
7441 and actually performs the optimizations based on them.
7442 Currently the optimizations include specialization of division operation
7443 using the knowledge about the value of the denominator.
7445 @item -frename-registers
7446 @opindex frename-registers
7447 Attempt to avoid false dependencies in scheduled code by making use
7448 of registers left over after register allocation. This optimization
7449 will most benefit processors with lots of registers. Depending on the
7450 debug information format adopted by the target, however, it can
7451 make debugging impossible, since variables will no longer stay in
7452 a ``home register''.
7454 Enabled by default with @option{-funroll-loops}.
7458 Perform tail duplication to enlarge superblock size. This transformation
7459 simplifies the control flow of the function allowing other optimizations to do
7462 Enabled with @option{-fprofile-use}.
7464 @item -funroll-loops
7465 @opindex funroll-loops
7466 Unroll loops whose number of iterations can be determined at compile time or
7467 upon entry to the loop. @option{-funroll-loops} implies
7468 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
7469 It also turns on complete loop peeling (i.e.@: complete removal of loops with
7470 small constant number of iterations). This option makes code larger, and may
7471 or may not make it run faster.
7473 Enabled with @option{-fprofile-use}.
7475 @item -funroll-all-loops
7476 @opindex funroll-all-loops
7477 Unroll all loops, even if their number of iterations is uncertain when
7478 the loop is entered. This usually makes programs run more slowly.
7479 @option{-funroll-all-loops} implies the same options as
7480 @option{-funroll-loops}.
7483 @opindex fpeel-loops
7484 Peels the loops for that there is enough information that they do not
7485 roll much (from profile feedback). It also turns on complete loop peeling
7486 (i.e.@: complete removal of loops with small constant number of iterations).
7488 Enabled with @option{-fprofile-use}.
7490 @item -fmove-loop-invariants
7491 @opindex fmove-loop-invariants
7492 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
7493 at level @option{-O1}
7495 @item -funswitch-loops
7496 @opindex funswitch-loops
7497 Move branches with loop invariant conditions out of the loop, with duplicates
7498 of the loop on both branches (modified according to result of the condition).
7500 @item -ffunction-sections
7501 @itemx -fdata-sections
7502 @opindex ffunction-sections
7503 @opindex fdata-sections
7504 Place each function or data item into its own section in the output
7505 file if the target supports arbitrary sections. The name of the
7506 function or the name of the data item determines the section's name
7509 Use these options on systems where the linker can perform optimizations
7510 to improve locality of reference in the instruction space. Most systems
7511 using the ELF object format and SPARC processors running Solaris 2 have
7512 linkers with such optimizations. AIX may have these optimizations in
7515 Only use these options when there are significant benefits from doing
7516 so. When you specify these options, the assembler and linker will
7517 create larger object and executable files and will also be slower.
7518 You will not be able to use @code{gprof} on all systems if you
7519 specify this option and you may have problems with debugging if
7520 you specify both this option and @option{-g}.
7522 @item -fbranch-target-load-optimize
7523 @opindex fbranch-target-load-optimize
7524 Perform branch target register load optimization before prologue / epilogue
7526 The use of target registers can typically be exposed only during reload,
7527 thus hoisting loads out of loops and doing inter-block scheduling needs
7528 a separate optimization pass.
7530 @item -fbranch-target-load-optimize2
7531 @opindex fbranch-target-load-optimize2
7532 Perform branch target register load optimization after prologue / epilogue
7535 @item -fbtr-bb-exclusive
7536 @opindex fbtr-bb-exclusive
7537 When performing branch target register load optimization, don't reuse
7538 branch target registers in within any basic block.
7540 @item -fstack-protector
7541 @opindex fstack-protector
7542 Emit extra code to check for buffer overflows, such as stack smashing
7543 attacks. This is done by adding a guard variable to functions with
7544 vulnerable objects. This includes functions that call alloca, and
7545 functions with buffers larger than 8 bytes. The guards are initialized
7546 when a function is entered and then checked when the function exits.
7547 If a guard check fails, an error message is printed and the program exits.
7549 @item -fstack-protector-all
7550 @opindex fstack-protector-all
7551 Like @option{-fstack-protector} except that all functions are protected.
7553 @item -fsection-anchors
7554 @opindex fsection-anchors
7555 Try to reduce the number of symbolic address calculations by using
7556 shared ``anchor'' symbols to address nearby objects. This transformation
7557 can help to reduce the number of GOT entries and GOT accesses on some
7560 For example, the implementation of the following function @code{foo}:
7564 int foo (void) @{ return a + b + c; @}
7567 would usually calculate the addresses of all three variables, but if you
7568 compile it with @option{-fsection-anchors}, it will access the variables
7569 from a common anchor point instead. The effect is similar to the
7570 following pseudocode (which isn't valid C):
7575 register int *xr = &x;
7576 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
7580 Not all targets support this option.
7582 @item --param @var{name}=@var{value}
7584 In some places, GCC uses various constants to control the amount of
7585 optimization that is done. For example, GCC will not inline functions
7586 that contain more that a certain number of instructions. You can
7587 control some of these constants on the command-line using the
7588 @option{--param} option.
7590 The names of specific parameters, and the meaning of the values, are
7591 tied to the internals of the compiler, and are subject to change
7592 without notice in future releases.
7594 In each case, the @var{value} is an integer. The allowable choices for
7595 @var{name} are given in the following table:
7598 @item struct-reorg-cold-struct-ratio
7599 The threshold ratio (as a percentage) between a structure frequency
7600 and the frequency of the hottest structure in the program. This parameter
7601 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
7602 We say that if the ratio of a structure frequency, calculated by profiling,
7603 to the hottest structure frequency in the program is less than this
7604 parameter, then structure reorganization is not applied to this structure.
7607 @item predictable-branch-cost-outcome
7608 When branch is predicted to be taken with probability lower than this threshold
7609 (in percent), then it is considered well predictable. The default is 10.
7611 @item max-crossjump-edges
7612 The maximum number of incoming edges to consider for crossjumping.
7613 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
7614 the number of edges incoming to each block. Increasing values mean
7615 more aggressive optimization, making the compile time increase with
7616 probably small improvement in executable size.
7618 @item min-crossjump-insns
7619 The minimum number of instructions which must be matched at the end
7620 of two blocks before crossjumping will be performed on them. This
7621 value is ignored in the case where all instructions in the block being
7622 crossjumped from are matched. The default value is 5.
7624 @item max-grow-copy-bb-insns
7625 The maximum code size expansion factor when copying basic blocks
7626 instead of jumping. The expansion is relative to a jump instruction.
7627 The default value is 8.
7629 @item max-goto-duplication-insns
7630 The maximum number of instructions to duplicate to a block that jumps
7631 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
7632 passes, GCC factors computed gotos early in the compilation process,
7633 and unfactors them as late as possible. Only computed jumps at the
7634 end of a basic blocks with no more than max-goto-duplication-insns are
7635 unfactored. The default value is 8.
7637 @item max-delay-slot-insn-search
7638 The maximum number of instructions to consider when looking for an
7639 instruction to fill a delay slot. If more than this arbitrary number of
7640 instructions is searched, the time savings from filling the delay slot
7641 will be minimal so stop searching. Increasing values mean more
7642 aggressive optimization, making the compile time increase with probably
7643 small improvement in executable run time.
7645 @item max-delay-slot-live-search
7646 When trying to fill delay slots, the maximum number of instructions to
7647 consider when searching for a block with valid live register
7648 information. Increasing this arbitrarily chosen value means more
7649 aggressive optimization, increasing the compile time. This parameter
7650 should be removed when the delay slot code is rewritten to maintain the
7653 @item max-gcse-memory
7654 The approximate maximum amount of memory that will be allocated in
7655 order to perform the global common subexpression elimination
7656 optimization. If more memory than specified is required, the
7657 optimization will not be done.
7659 @item max-pending-list-length
7660 The maximum number of pending dependencies scheduling will allow
7661 before flushing the current state and starting over. Large functions
7662 with few branches or calls can create excessively large lists which
7663 needlessly consume memory and resources.
7665 @item max-inline-insns-single
7666 Several parameters control the tree inliner used in gcc.
7667 This number sets the maximum number of instructions (counted in GCC's
7668 internal representation) in a single function that the tree inliner
7669 will consider for inlining. This only affects functions declared
7670 inline and methods implemented in a class declaration (C++).
7671 The default value is 300.
7673 @item max-inline-insns-auto
7674 When you use @option{-finline-functions} (included in @option{-O3}),
7675 a lot of functions that would otherwise not be considered for inlining
7676 by the compiler will be investigated. To those functions, a different
7677 (more restrictive) limit compared to functions declared inline can
7679 The default value is 50.
7681 @item large-function-insns
7682 The limit specifying really large functions. For functions larger than this
7683 limit after inlining, inlining is constrained by
7684 @option{--param large-function-growth}. This parameter is useful primarily
7685 to avoid extreme compilation time caused by non-linear algorithms used by the
7687 The default value is 2700.
7689 @item large-function-growth
7690 Specifies maximal growth of large function caused by inlining in percents.
7691 The default value is 100 which limits large function growth to 2.0 times
7694 @item large-unit-insns
7695 The limit specifying large translation unit. Growth caused by inlining of
7696 units larger than this limit is limited by @option{--param inline-unit-growth}.
7697 For small units this might be too tight (consider unit consisting of function A
7698 that is inline and B that just calls A three time. If B is small relative to
7699 A, the growth of unit is 300\% and yet such inlining is very sane. For very
7700 large units consisting of small inlineable functions however the overall unit
7701 growth limit is needed to avoid exponential explosion of code size. Thus for
7702 smaller units, the size is increased to @option{--param large-unit-insns}
7703 before applying @option{--param inline-unit-growth}. The default is 10000
7705 @item inline-unit-growth
7706 Specifies maximal overall growth of the compilation unit caused by inlining.
7707 The default value is 30 which limits unit growth to 1.3 times the original
7710 @item ipcp-unit-growth
7711 Specifies maximal overall growth of the compilation unit caused by
7712 interprocedural constant propagation. The default value is 10 which limits
7713 unit growth to 1.1 times the original size.
7715 @item large-stack-frame
7716 The limit specifying large stack frames. While inlining the algorithm is trying
7717 to not grow past this limit too much. Default value is 256 bytes.
7719 @item large-stack-frame-growth
7720 Specifies maximal growth of large stack frames caused by inlining in percents.
7721 The default value is 1000 which limits large stack frame growth to 11 times
7724 @item max-inline-insns-recursive
7725 @itemx max-inline-insns-recursive-auto
7726 Specifies maximum number of instructions out-of-line copy of self recursive inline
7727 function can grow into by performing recursive inlining.
7729 For functions declared inline @option{--param max-inline-insns-recursive} is
7730 taken into account. For function not declared inline, recursive inlining
7731 happens only when @option{-finline-functions} (included in @option{-O3}) is
7732 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
7733 default value is 450.
7735 @item max-inline-recursive-depth
7736 @itemx max-inline-recursive-depth-auto
7737 Specifies maximum recursion depth used by the recursive inlining.
7739 For functions declared inline @option{--param max-inline-recursive-depth} is
7740 taken into account. For function not declared inline, recursive inlining
7741 happens only when @option{-finline-functions} (included in @option{-O3}) is
7742 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
7745 @item min-inline-recursive-probability
7746 Recursive inlining is profitable only for function having deep recursion
7747 in average and can hurt for function having little recursion depth by
7748 increasing the prologue size or complexity of function body to other
7751 When profile feedback is available (see @option{-fprofile-generate}) the actual
7752 recursion depth can be guessed from probability that function will recurse via
7753 given call expression. This parameter limits inlining only to call expression
7754 whose probability exceeds given threshold (in percents). The default value is
7757 @item early-inlining-insns
7758 Specify growth that early inliner can make. In effect it increases amount of
7759 inlining for code having large abstraction penalty. The default value is 8.
7761 @item max-early-inliner-iterations
7762 @itemx max-early-inliner-iterations
7763 Limit of iterations of early inliner. This basically bounds number of nested
7764 indirect calls early inliner can resolve. Deeper chains are still handled by
7767 @item min-vect-loop-bound
7768 The minimum number of iterations under which a loop will not get vectorized
7769 when @option{-ftree-vectorize} is used. The number of iterations after
7770 vectorization needs to be greater than the value specified by this option
7771 to allow vectorization. The default value is 0.
7773 @item max-unrolled-insns
7774 The maximum number of instructions that a loop should have if that loop
7775 is unrolled, and if the loop is unrolled, it determines how many times
7776 the loop code is unrolled.
7778 @item max-average-unrolled-insns
7779 The maximum number of instructions biased by probabilities of their execution
7780 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7781 it determines how many times the loop code is unrolled.
7783 @item max-unroll-times
7784 The maximum number of unrollings of a single loop.
7786 @item max-peeled-insns
7787 The maximum number of instructions that a loop should have if that loop
7788 is peeled, and if the loop is peeled, it determines how many times
7789 the loop code is peeled.
7791 @item max-peel-times
7792 The maximum number of peelings of a single loop.
7794 @item max-completely-peeled-insns
7795 The maximum number of insns of a completely peeled loop.
7797 @item max-completely-peel-times
7798 The maximum number of iterations of a loop to be suitable for complete peeling.
7800 @item max-unswitch-insns
7801 The maximum number of insns of an unswitched loop.
7803 @item max-unswitch-level
7804 The maximum number of branches unswitched in a single loop.
7807 The minimum cost of an expensive expression in the loop invariant motion.
7809 @item iv-consider-all-candidates-bound
7810 Bound on number of candidates for induction variables below that
7811 all candidates are considered for each use in induction variable
7812 optimizations. Only the most relevant candidates are considered
7813 if there are more candidates, to avoid quadratic time complexity.
7815 @item iv-max-considered-uses
7816 The induction variable optimizations give up on loops that contain more
7817 induction variable uses.
7819 @item iv-always-prune-cand-set-bound
7820 If number of candidates in the set is smaller than this value,
7821 we always try to remove unnecessary ivs from the set during its
7822 optimization when a new iv is added to the set.
7824 @item scev-max-expr-size
7825 Bound on size of expressions used in the scalar evolutions analyzer.
7826 Large expressions slow the analyzer.
7828 @item omega-max-vars
7829 The maximum number of variables in an Omega constraint system.
7830 The default value is 128.
7832 @item omega-max-geqs
7833 The maximum number of inequalities in an Omega constraint system.
7834 The default value is 256.
7837 The maximum number of equalities in an Omega constraint system.
7838 The default value is 128.
7840 @item omega-max-wild-cards
7841 The maximum number of wildcard variables that the Omega solver will
7842 be able to insert. The default value is 18.
7844 @item omega-hash-table-size
7845 The size of the hash table in the Omega solver. The default value is
7848 @item omega-max-keys
7849 The maximal number of keys used by the Omega solver. The default
7852 @item omega-eliminate-redundant-constraints
7853 When set to 1, use expensive methods to eliminate all redundant
7854 constraints. The default value is 0.
7856 @item vect-max-version-for-alignment-checks
7857 The maximum number of runtime checks that can be performed when
7858 doing loop versioning for alignment in the vectorizer. See option
7859 ftree-vect-loop-version for more information.
7861 @item vect-max-version-for-alias-checks
7862 The maximum number of runtime checks that can be performed when
7863 doing loop versioning for alias in the vectorizer. See option
7864 ftree-vect-loop-version for more information.
7866 @item max-iterations-to-track
7868 The maximum number of iterations of a loop the brute force algorithm
7869 for analysis of # of iterations of the loop tries to evaluate.
7871 @item hot-bb-count-fraction
7872 Select fraction of the maximal count of repetitions of basic block in program
7873 given basic block needs to have to be considered hot.
7875 @item hot-bb-frequency-fraction
7876 Select fraction of the maximal frequency of executions of basic block in
7877 function given basic block needs to have to be considered hot
7879 @item max-predicted-iterations
7880 The maximum number of loop iterations we predict statically. This is useful
7881 in cases where function contain single loop with known bound and other loop
7882 with unknown. We predict the known number of iterations correctly, while
7883 the unknown number of iterations average to roughly 10. This means that the
7884 loop without bounds would appear artificially cold relative to the other one.
7886 @item align-threshold
7888 Select fraction of the maximal frequency of executions of basic block in
7889 function given basic block will get aligned.
7891 @item align-loop-iterations
7893 A loop expected to iterate at lest the selected number of iterations will get
7896 @item tracer-dynamic-coverage
7897 @itemx tracer-dynamic-coverage-feedback
7899 This value is used to limit superblock formation once the given percentage of
7900 executed instructions is covered. This limits unnecessary code size
7903 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7904 feedback is available. The real profiles (as opposed to statically estimated
7905 ones) are much less balanced allowing the threshold to be larger value.
7907 @item tracer-max-code-growth
7908 Stop tail duplication once code growth has reached given percentage. This is
7909 rather hokey argument, as most of the duplicates will be eliminated later in
7910 cross jumping, so it may be set to much higher values than is the desired code
7913 @item tracer-min-branch-ratio
7915 Stop reverse growth when the reverse probability of best edge is less than this
7916 threshold (in percent).
7918 @item tracer-min-branch-ratio
7919 @itemx tracer-min-branch-ratio-feedback
7921 Stop forward growth if the best edge do have probability lower than this
7924 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7925 compilation for profile feedback and one for compilation without. The value
7926 for compilation with profile feedback needs to be more conservative (higher) in
7927 order to make tracer effective.
7929 @item max-cse-path-length
7931 Maximum number of basic blocks on path that cse considers. The default is 10.
7934 The maximum instructions CSE process before flushing. The default is 1000.
7936 @item ggc-min-expand
7938 GCC uses a garbage collector to manage its own memory allocation. This
7939 parameter specifies the minimum percentage by which the garbage
7940 collector's heap should be allowed to expand between collections.
7941 Tuning this may improve compilation speed; it has no effect on code
7944 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7945 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7946 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7947 GCC is not able to calculate RAM on a particular platform, the lower
7948 bound of 30% is used. Setting this parameter and
7949 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7950 every opportunity. This is extremely slow, but can be useful for
7953 @item ggc-min-heapsize
7955 Minimum size of the garbage collector's heap before it begins bothering
7956 to collect garbage. The first collection occurs after the heap expands
7957 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7958 tuning this may improve compilation speed, and has no effect on code
7961 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7962 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7963 with a lower bound of 4096 (four megabytes) and an upper bound of
7964 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7965 particular platform, the lower bound is used. Setting this parameter
7966 very large effectively disables garbage collection. Setting this
7967 parameter and @option{ggc-min-expand} to zero causes a full collection
7968 to occur at every opportunity.
7970 @item max-reload-search-insns
7971 The maximum number of instruction reload should look backward for equivalent
7972 register. Increasing values mean more aggressive optimization, making the
7973 compile time increase with probably slightly better performance. The default
7976 @item max-cselib-memory-locations
7977 The maximum number of memory locations cselib should take into account.
7978 Increasing values mean more aggressive optimization, making the compile time
7979 increase with probably slightly better performance. The default value is 500.
7981 @item reorder-blocks-duplicate
7982 @itemx reorder-blocks-duplicate-feedback
7984 Used by basic block reordering pass to decide whether to use unconditional
7985 branch or duplicate the code on its destination. Code is duplicated when its
7986 estimated size is smaller than this value multiplied by the estimated size of
7987 unconditional jump in the hot spots of the program.
7989 The @option{reorder-block-duplicate-feedback} is used only when profile
7990 feedback is available and may be set to higher values than
7991 @option{reorder-block-duplicate} since information about the hot spots is more
7994 @item max-sched-ready-insns
7995 The maximum number of instructions ready to be issued the scheduler should
7996 consider at any given time during the first scheduling pass. Increasing
7997 values mean more thorough searches, making the compilation time increase
7998 with probably little benefit. The default value is 100.
8000 @item max-sched-region-blocks
8001 The maximum number of blocks in a region to be considered for
8002 interblock scheduling. The default value is 10.
8004 @item max-pipeline-region-blocks
8005 The maximum number of blocks in a region to be considered for
8006 pipelining in the selective scheduler. The default value is 15.
8008 @item max-sched-region-insns
8009 The maximum number of insns in a region to be considered for
8010 interblock scheduling. The default value is 100.
8012 @item max-pipeline-region-insns
8013 The maximum number of insns in a region to be considered for
8014 pipelining in the selective scheduler. The default value is 200.
8017 The minimum probability (in percents) of reaching a source block
8018 for interblock speculative scheduling. The default value is 40.
8020 @item max-sched-extend-regions-iters
8021 The maximum number of iterations through CFG to extend regions.
8022 0 - disable region extension,
8023 N - do at most N iterations.
8024 The default value is 0.
8026 @item max-sched-insn-conflict-delay
8027 The maximum conflict delay for an insn to be considered for speculative motion.
8028 The default value is 3.
8030 @item sched-spec-prob-cutoff
8031 The minimal probability of speculation success (in percents), so that
8032 speculative insn will be scheduled.
8033 The default value is 40.
8035 @item sched-mem-true-dep-cost
8036 Minimal distance (in CPU cycles) between store and load targeting same
8037 memory locations. The default value is 1.
8039 @item selsched-max-lookahead
8040 The maximum size of the lookahead window of selective scheduling. It is a
8041 depth of search for available instructions.
8042 The default value is 50.
8044 @item selsched-max-sched-times
8045 The maximum number of times that an instruction will be scheduled during
8046 selective scheduling. This is the limit on the number of iterations
8047 through which the instruction may be pipelined. The default value is 2.
8049 @item selsched-max-insns-to-rename
8050 The maximum number of best instructions in the ready list that are considered
8051 for renaming in the selective scheduler. The default value is 2.
8053 @item max-last-value-rtl
8054 The maximum size measured as number of RTLs that can be recorded in an expression
8055 in combiner for a pseudo register as last known value of that register. The default
8058 @item integer-share-limit
8059 Small integer constants can use a shared data structure, reducing the
8060 compiler's memory usage and increasing its speed. This sets the maximum
8061 value of a shared integer constant. The default value is 256.
8063 @item min-virtual-mappings
8064 Specifies the minimum number of virtual mappings in the incremental
8065 SSA updater that should be registered to trigger the virtual mappings
8066 heuristic defined by virtual-mappings-ratio. The default value is
8069 @item virtual-mappings-ratio
8070 If the number of virtual mappings is virtual-mappings-ratio bigger
8071 than the number of virtual symbols to be updated, then the incremental
8072 SSA updater switches to a full update for those symbols. The default
8075 @item ssp-buffer-size
8076 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
8077 protection when @option{-fstack-protection} is used.
8079 @item max-jump-thread-duplication-stmts
8080 Maximum number of statements allowed in a block that needs to be
8081 duplicated when threading jumps.
8083 @item max-fields-for-field-sensitive
8084 Maximum number of fields in a structure we will treat in
8085 a field sensitive manner during pointer analysis. The default is zero
8086 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
8088 @item prefetch-latency
8089 Estimate on average number of instructions that are executed before
8090 prefetch finishes. The distance we prefetch ahead is proportional
8091 to this constant. Increasing this number may also lead to less
8092 streams being prefetched (see @option{simultaneous-prefetches}).
8094 @item simultaneous-prefetches
8095 Maximum number of prefetches that can run at the same time.
8097 @item l1-cache-line-size
8098 The size of cache line in L1 cache, in bytes.
8101 The size of L1 cache, in kilobytes.
8104 The size of L2 cache, in kilobytes.
8106 @item min-insn-to-prefetch-ratio
8107 The minimum ratio between the number of instructions and the
8108 number of prefetches to enable prefetching in a loop with an
8111 @item prefetch-min-insn-to-mem-ratio
8112 The minimum ratio between the number of instructions and the
8113 number of memory references to enable prefetching in a loop.
8115 @item use-canonical-types
8116 Whether the compiler should use the ``canonical'' type system. By
8117 default, this should always be 1, which uses a more efficient internal
8118 mechanism for comparing types in C++ and Objective-C++. However, if
8119 bugs in the canonical type system are causing compilation failures,
8120 set this value to 0 to disable canonical types.
8122 @item switch-conversion-max-branch-ratio
8123 Switch initialization conversion will refuse to create arrays that are
8124 bigger than @option{switch-conversion-max-branch-ratio} times the number of
8125 branches in the switch.
8127 @item max-partial-antic-length
8128 Maximum length of the partial antic set computed during the tree
8129 partial redundancy elimination optimization (@option{-ftree-pre}) when
8130 optimizing at @option{-O3} and above. For some sorts of source code
8131 the enhanced partial redundancy elimination optimization can run away,
8132 consuming all of the memory available on the host machine. This
8133 parameter sets a limit on the length of the sets that are computed,
8134 which prevents the runaway behavior. Setting a value of 0 for
8135 this parameter will allow an unlimited set length.
8137 @item sccvn-max-scc-size
8138 Maximum size of a strongly connected component (SCC) during SCCVN
8139 processing. If this limit is hit, SCCVN processing for the whole
8140 function will not be done and optimizations depending on it will
8141 be disabled. The default maximum SCC size is 10000.
8143 @item ira-max-loops-num
8144 IRA uses a regional register allocation by default. If a function
8145 contains loops more than number given by the parameter, only at most
8146 given number of the most frequently executed loops will form regions
8147 for the regional register allocation. The default value of the
8150 @item ira-max-conflict-table-size
8151 Although IRA uses a sophisticated algorithm of compression conflict
8152 table, the table can be still big for huge functions. If the conflict
8153 table for a function could be more than size in MB given by the
8154 parameter, the conflict table is not built and faster, simpler, and
8155 lower quality register allocation algorithm will be used. The
8156 algorithm do not use pseudo-register conflicts. The default value of
8157 the parameter is 2000.
8159 @item loop-invariant-max-bbs-in-loop
8160 Loop invariant motion can be very expensive, both in compile time and
8161 in amount of needed compile time memory, with very large loops. Loops
8162 with more basic blocks than this parameter won't have loop invariant
8163 motion optimization performed on them. The default value of the
8164 parameter is 1000 for -O1 and 10000 for -O2 and above.
8166 @item min-nondebug-insn-uid
8167 Use uids starting at this parameter for nondebug insns. The range below
8168 the parameter is reserved exclusively for debug insns created by
8169 @option{-fvar-tracking-assignments}, but debug insns may get
8170 (non-overlapping) uids above it if the reserved range is exhausted.
8172 @item ipa-sra-ptr-growth-factor
8173 IPA-SRA will replace a pointer to an aggregate with one or more new
8174 parameters only when their cumulative size is less or equal to
8175 @option{ipa-sra-ptr-growth-factor} times the size of the original
8181 @node Preprocessor Options
8182 @section Options Controlling the Preprocessor
8183 @cindex preprocessor options
8184 @cindex options, preprocessor
8186 These options control the C preprocessor, which is run on each C source
8187 file before actual compilation.
8189 If you use the @option{-E} option, nothing is done except preprocessing.
8190 Some of these options make sense only together with @option{-E} because
8191 they cause the preprocessor output to be unsuitable for actual
8195 @item -Wp,@var{option}
8197 You can use @option{-Wp,@var{option}} to bypass the compiler driver
8198 and pass @var{option} directly through to the preprocessor. If
8199 @var{option} contains commas, it is split into multiple options at the
8200 commas. However, many options are modified, translated or interpreted
8201 by the compiler driver before being passed to the preprocessor, and
8202 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
8203 interface is undocumented and subject to change, so whenever possible
8204 you should avoid using @option{-Wp} and let the driver handle the
8207 @item -Xpreprocessor @var{option}
8208 @opindex Xpreprocessor
8209 Pass @var{option} as an option to the preprocessor. You can use this to
8210 supply system-specific preprocessor options which GCC does not know how to
8213 If you want to pass an option that takes an argument, you must use
8214 @option{-Xpreprocessor} twice, once for the option and once for the argument.
8217 @include cppopts.texi
8219 @node Assembler Options
8220 @section Passing Options to the Assembler
8222 @c prevent bad page break with this line
8223 You can pass options to the assembler.
8226 @item -Wa,@var{option}
8228 Pass @var{option} as an option to the assembler. If @var{option}
8229 contains commas, it is split into multiple options at the commas.
8231 @item -Xassembler @var{option}
8233 Pass @var{option} as an option to the assembler. You can use this to
8234 supply system-specific assembler options which GCC does not know how to
8237 If you want to pass an option that takes an argument, you must use
8238 @option{-Xassembler} twice, once for the option and once for the argument.
8243 @section Options for Linking
8244 @cindex link options
8245 @cindex options, linking
8247 These options come into play when the compiler links object files into
8248 an executable output file. They are meaningless if the compiler is
8249 not doing a link step.
8253 @item @var{object-file-name}
8254 A file name that does not end in a special recognized suffix is
8255 considered to name an object file or library. (Object files are
8256 distinguished from libraries by the linker according to the file
8257 contents.) If linking is done, these object files are used as input
8266 If any of these options is used, then the linker is not run, and
8267 object file names should not be used as arguments. @xref{Overall
8271 @item -l@var{library}
8272 @itemx -l @var{library}
8274 Search the library named @var{library} when linking. (The second
8275 alternative with the library as a separate argument is only for
8276 POSIX compliance and is not recommended.)
8278 It makes a difference where in the command you write this option; the
8279 linker searches and processes libraries and object files in the order they
8280 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
8281 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
8282 to functions in @samp{z}, those functions may not be loaded.
8284 The linker searches a standard list of directories for the library,
8285 which is actually a file named @file{lib@var{library}.a}. The linker
8286 then uses this file as if it had been specified precisely by name.
8288 The directories searched include several standard system directories
8289 plus any that you specify with @option{-L}.
8291 Normally the files found this way are library files---archive files
8292 whose members are object files. The linker handles an archive file by
8293 scanning through it for members which define symbols that have so far
8294 been referenced but not defined. But if the file that is found is an
8295 ordinary object file, it is linked in the usual fashion. The only
8296 difference between using an @option{-l} option and specifying a file name
8297 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
8298 and searches several directories.
8302 You need this special case of the @option{-l} option in order to
8303 link an Objective-C or Objective-C++ program.
8306 @opindex nostartfiles
8307 Do not use the standard system startup files when linking.
8308 The standard system libraries are used normally, unless @option{-nostdlib}
8309 or @option{-nodefaultlibs} is used.
8311 @item -nodefaultlibs
8312 @opindex nodefaultlibs
8313 Do not use the standard system libraries when linking.
8314 Only the libraries you specify will be passed to the linker, options
8315 specifying linkage of the system libraries, such as @code{-static-libgcc}
8316 or @code{-shared-libgcc}, will be ignored.
8317 The standard startup files are used normally, unless @option{-nostartfiles}
8318 is used. The compiler may generate calls to @code{memcmp},
8319 @code{memset}, @code{memcpy} and @code{memmove}.
8320 These entries are usually resolved by entries in
8321 libc. These entry points should be supplied through some other
8322 mechanism when this option is specified.
8326 Do not use the standard system startup files or libraries when linking.
8327 No startup files and only the libraries you specify will be passed to
8328 the linker, options specifying linkage of the system libraries, such as
8329 @code{-static-libgcc} or @code{-shared-libgcc}, will be ignored.
8330 The compiler may generate calls to @code{memcmp}, @code{memset},
8331 @code{memcpy} and @code{memmove}.
8332 These entries are usually resolved by entries in
8333 libc. These entry points should be supplied through some other
8334 mechanism when this option is specified.
8336 @cindex @option{-lgcc}, use with @option{-nostdlib}
8337 @cindex @option{-nostdlib} and unresolved references
8338 @cindex unresolved references and @option{-nostdlib}
8339 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
8340 @cindex @option{-nodefaultlibs} and unresolved references
8341 @cindex unresolved references and @option{-nodefaultlibs}
8342 One of the standard libraries bypassed by @option{-nostdlib} and
8343 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
8344 that GCC uses to overcome shortcomings of particular machines, or special
8345 needs for some languages.
8346 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
8347 Collection (GCC) Internals},
8348 for more discussion of @file{libgcc.a}.)
8349 In most cases, you need @file{libgcc.a} even when you want to avoid
8350 other standard libraries. In other words, when you specify @option{-nostdlib}
8351 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
8352 This ensures that you have no unresolved references to internal GCC
8353 library subroutines. (For example, @samp{__main}, used to ensure C++
8354 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
8355 GNU Compiler Collection (GCC) Internals}.)
8359 Produce a position independent executable on targets which support it.
8360 For predictable results, you must also specify the same set of options
8361 that were used to generate code (@option{-fpie}, @option{-fPIE},
8362 or model suboptions) when you specify this option.
8366 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
8367 that support it. This instructs the linker to add all symbols, not
8368 only used ones, to the dynamic symbol table. This option is needed
8369 for some uses of @code{dlopen} or to allow obtaining backtraces
8370 from within a program.
8374 Remove all symbol table and relocation information from the executable.
8378 On systems that support dynamic linking, this prevents linking with the shared
8379 libraries. On other systems, this option has no effect.
8383 Produce a shared object which can then be linked with other objects to
8384 form an executable. Not all systems support this option. For predictable
8385 results, you must also specify the same set of options that were used to
8386 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
8387 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
8388 needs to build supplementary stub code for constructors to work. On
8389 multi-libbed systems, @samp{gcc -shared} must select the correct support
8390 libraries to link against. Failing to supply the correct flags may lead
8391 to subtle defects. Supplying them in cases where they are not necessary
8394 @item -shared-libgcc
8395 @itemx -static-libgcc
8396 @opindex shared-libgcc
8397 @opindex static-libgcc
8398 On systems that provide @file{libgcc} as a shared library, these options
8399 force the use of either the shared or static version respectively.
8400 If no shared version of @file{libgcc} was built when the compiler was
8401 configured, these options have no effect.
8403 There are several situations in which an application should use the
8404 shared @file{libgcc} instead of the static version. The most common
8405 of these is when the application wishes to throw and catch exceptions
8406 across different shared libraries. In that case, each of the libraries
8407 as well as the application itself should use the shared @file{libgcc}.
8409 Therefore, the G++ and GCJ drivers automatically add
8410 @option{-shared-libgcc} whenever you build a shared library or a main
8411 executable, because C++ and Java programs typically use exceptions, so
8412 this is the right thing to do.
8414 If, instead, you use the GCC driver to create shared libraries, you may
8415 find that they will not always be linked with the shared @file{libgcc}.
8416 If GCC finds, at its configuration time, that you have a non-GNU linker
8417 or a GNU linker that does not support option @option{--eh-frame-hdr},
8418 it will link the shared version of @file{libgcc} into shared libraries
8419 by default. Otherwise, it will take advantage of the linker and optimize
8420 away the linking with the shared version of @file{libgcc}, linking with
8421 the static version of libgcc by default. This allows exceptions to
8422 propagate through such shared libraries, without incurring relocation
8423 costs at library load time.
8425 However, if a library or main executable is supposed to throw or catch
8426 exceptions, you must link it using the G++ or GCJ driver, as appropriate
8427 for the languages used in the program, or using the option
8428 @option{-shared-libgcc}, such that it is linked with the shared
8431 @item -static-libstdc++
8432 When the @command{g++} program is used to link a C++ program, it will
8433 normally automatically link against @option{libstdc++}. If
8434 @file{libstdc++} is available as a shared library, and the
8435 @option{-static} option is not used, then this will link against the
8436 shared version of @file{libstdc++}. That is normally fine. However, it
8437 is sometimes useful to freeze the version of @file{libstdc++} used by
8438 the program without going all the way to a fully static link. The
8439 @option{-static-libstdc++} option directs the @command{g++} driver to
8440 link @file{libstdc++} statically, without necessarily linking other
8441 libraries statically.
8445 Bind references to global symbols when building a shared object. Warn
8446 about any unresolved references (unless overridden by the link editor
8447 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
8450 @item -T @var{script}
8452 @cindex linker script
8453 Use @var{script} as the linker script. This option is supported by most
8454 systems using the GNU linker. On some targets, such as bare-board
8455 targets without an operating system, the @option{-T} option may be required
8456 when linking to avoid references to undefined symbols.
8458 @item -Xlinker @var{option}
8460 Pass @var{option} as an option to the linker. You can use this to
8461 supply system-specific linker options which GCC does not know how to
8464 If you want to pass an option that takes a separate argument, you must use
8465 @option{-Xlinker} twice, once for the option and once for the argument.
8466 For example, to pass @option{-assert definitions}, you must write
8467 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
8468 @option{-Xlinker "-assert definitions"}, because this passes the entire
8469 string as a single argument, which is not what the linker expects.
8471 When using the GNU linker, it is usually more convenient to pass
8472 arguments to linker options using the @option{@var{option}=@var{value}}
8473 syntax than as separate arguments. For example, you can specify
8474 @samp{-Xlinker -Map=output.map} rather than
8475 @samp{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
8476 this syntax for command-line options.
8478 @item -Wl,@var{option}
8480 Pass @var{option} as an option to the linker. If @var{option} contains
8481 commas, it is split into multiple options at the commas. You can use this
8482 syntax to pass an argument to the option.
8483 For example, @samp{-Wl,-Map,output.map} passes @samp{-Map output.map} to the
8484 linker. When using the GNU linker, you can also get the same effect with
8485 @samp{-Wl,-Map=output.map}.
8487 @item -u @var{symbol}
8489 Pretend the symbol @var{symbol} is undefined, to force linking of
8490 library modules to define it. You can use @option{-u} multiple times with
8491 different symbols to force loading of additional library modules.
8494 @node Directory Options
8495 @section Options for Directory Search
8496 @cindex directory options
8497 @cindex options, directory search
8500 These options specify directories to search for header files, for
8501 libraries and for parts of the compiler:
8506 Add the directory @var{dir} to the head of the list of directories to be
8507 searched for header files. This can be used to override a system header
8508 file, substituting your own version, since these directories are
8509 searched before the system header file directories. However, you should
8510 not use this option to add directories that contain vendor-supplied
8511 system header files (use @option{-isystem} for that). If you use more than
8512 one @option{-I} option, the directories are scanned in left-to-right
8513 order; the standard system directories come after.
8515 If a standard system include directory, or a directory specified with
8516 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
8517 option will be ignored. The directory will still be searched but as a
8518 system directory at its normal position in the system include chain.
8519 This is to ensure that GCC's procedure to fix buggy system headers and
8520 the ordering for the include_next directive are not inadvertently changed.
8521 If you really need to change the search order for system directories,
8522 use the @option{-nostdinc} and/or @option{-isystem} options.
8524 @item -iquote@var{dir}
8526 Add the directory @var{dir} to the head of the list of directories to
8527 be searched for header files only for the case of @samp{#include
8528 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
8529 otherwise just like @option{-I}.
8533 Add directory @var{dir} to the list of directories to be searched
8536 @item -B@var{prefix}
8538 This option specifies where to find the executables, libraries,
8539 include files, and data files of the compiler itself.
8541 The compiler driver program runs one or more of the subprograms
8542 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
8543 @var{prefix} as a prefix for each program it tries to run, both with and
8544 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
8546 For each subprogram to be run, the compiler driver first tries the
8547 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
8548 was not specified, the driver tries two standard prefixes, which are
8549 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
8550 those results in a file name that is found, the unmodified program
8551 name is searched for using the directories specified in your
8552 @env{PATH} environment variable.
8554 The compiler will check to see if the path provided by the @option{-B}
8555 refers to a directory, and if necessary it will add a directory
8556 separator character at the end of the path.
8558 @option{-B} prefixes that effectively specify directory names also apply
8559 to libraries in the linker, because the compiler translates these
8560 options into @option{-L} options for the linker. They also apply to
8561 includes files in the preprocessor, because the compiler translates these
8562 options into @option{-isystem} options for the preprocessor. In this case,
8563 the compiler appends @samp{include} to the prefix.
8565 The run-time support file @file{libgcc.a} can also be searched for using
8566 the @option{-B} prefix, if needed. If it is not found there, the two
8567 standard prefixes above are tried, and that is all. The file is left
8568 out of the link if it is not found by those means.
8570 Another way to specify a prefix much like the @option{-B} prefix is to use
8571 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
8574 As a special kludge, if the path provided by @option{-B} is
8575 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
8576 9, then it will be replaced by @file{[dir/]include}. This is to help
8577 with boot-strapping the compiler.
8579 @item -specs=@var{file}
8581 Process @var{file} after the compiler reads in the standard @file{specs}
8582 file, in order to override the defaults that the @file{gcc} driver
8583 program uses when determining what switches to pass to @file{cc1},
8584 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
8585 @option{-specs=@var{file}} can be specified on the command line, and they
8586 are processed in order, from left to right.
8588 @item --sysroot=@var{dir}
8590 Use @var{dir} as the logical root directory for headers and libraries.
8591 For example, if the compiler would normally search for headers in
8592 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
8593 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
8595 If you use both this option and the @option{-isysroot} option, then
8596 the @option{--sysroot} option will apply to libraries, but the
8597 @option{-isysroot} option will apply to header files.
8599 The GNU linker (beginning with version 2.16) has the necessary support
8600 for this option. If your linker does not support this option, the
8601 header file aspect of @option{--sysroot} will still work, but the
8602 library aspect will not.
8606 This option has been deprecated. Please use @option{-iquote} instead for
8607 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
8608 Any directories you specify with @option{-I} options before the @option{-I-}
8609 option are searched only for the case of @samp{#include "@var{file}"};
8610 they are not searched for @samp{#include <@var{file}>}.
8612 If additional directories are specified with @option{-I} options after
8613 the @option{-I-}, these directories are searched for all @samp{#include}
8614 directives. (Ordinarily @emph{all} @option{-I} directories are used
8617 In addition, the @option{-I-} option inhibits the use of the current
8618 directory (where the current input file came from) as the first search
8619 directory for @samp{#include "@var{file}"}. There is no way to
8620 override this effect of @option{-I-}. With @option{-I.} you can specify
8621 searching the directory which was current when the compiler was
8622 invoked. That is not exactly the same as what the preprocessor does
8623 by default, but it is often satisfactory.
8625 @option{-I-} does not inhibit the use of the standard system directories
8626 for header files. Thus, @option{-I-} and @option{-nostdinc} are
8633 @section Specifying subprocesses and the switches to pass to them
8636 @command{gcc} is a driver program. It performs its job by invoking a
8637 sequence of other programs to do the work of compiling, assembling and
8638 linking. GCC interprets its command-line parameters and uses these to
8639 deduce which programs it should invoke, and which command-line options
8640 it ought to place on their command lines. This behavior is controlled
8641 by @dfn{spec strings}. In most cases there is one spec string for each
8642 program that GCC can invoke, but a few programs have multiple spec
8643 strings to control their behavior. The spec strings built into GCC can
8644 be overridden by using the @option{-specs=} command-line switch to specify
8647 @dfn{Spec files} are plaintext files that are used to construct spec
8648 strings. They consist of a sequence of directives separated by blank
8649 lines. The type of directive is determined by the first non-whitespace
8650 character on the line and it can be one of the following:
8653 @item %@var{command}
8654 Issues a @var{command} to the spec file processor. The commands that can
8658 @item %include <@var{file}>
8660 Search for @var{file} and insert its text at the current point in the
8663 @item %include_noerr <@var{file}>
8664 @cindex %include_noerr
8665 Just like @samp{%include}, but do not generate an error message if the include
8666 file cannot be found.
8668 @item %rename @var{old_name} @var{new_name}
8670 Rename the spec string @var{old_name} to @var{new_name}.
8674 @item *[@var{spec_name}]:
8675 This tells the compiler to create, override or delete the named spec
8676 string. All lines after this directive up to the next directive or
8677 blank line are considered to be the text for the spec string. If this
8678 results in an empty string then the spec will be deleted. (Or, if the
8679 spec did not exist, then nothing will happened.) Otherwise, if the spec
8680 does not currently exist a new spec will be created. If the spec does
8681 exist then its contents will be overridden by the text of this
8682 directive, unless the first character of that text is the @samp{+}
8683 character, in which case the text will be appended to the spec.
8685 @item [@var{suffix}]:
8686 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
8687 and up to the next directive or blank line are considered to make up the
8688 spec string for the indicated suffix. When the compiler encounters an
8689 input file with the named suffix, it will processes the spec string in
8690 order to work out how to compile that file. For example:
8697 This says that any input file whose name ends in @samp{.ZZ} should be
8698 passed to the program @samp{z-compile}, which should be invoked with the
8699 command-line switch @option{-input} and with the result of performing the
8700 @samp{%i} substitution. (See below.)
8702 As an alternative to providing a spec string, the text that follows a
8703 suffix directive can be one of the following:
8706 @item @@@var{language}
8707 This says that the suffix is an alias for a known @var{language}. This is
8708 similar to using the @option{-x} command-line switch to GCC to specify a
8709 language explicitly. For example:
8716 Says that .ZZ files are, in fact, C++ source files.
8719 This causes an error messages saying:
8722 @var{name} compiler not installed on this system.
8726 GCC already has an extensive list of suffixes built into it.
8727 This directive will add an entry to the end of the list of suffixes, but
8728 since the list is searched from the end backwards, it is effectively
8729 possible to override earlier entries using this technique.
8733 GCC has the following spec strings built into it. Spec files can
8734 override these strings or create their own. Note that individual
8735 targets can also add their own spec strings to this list.
8738 asm Options to pass to the assembler
8739 asm_final Options to pass to the assembler post-processor
8740 cpp Options to pass to the C preprocessor
8741 cc1 Options to pass to the C compiler
8742 cc1plus Options to pass to the C++ compiler
8743 endfile Object files to include at the end of the link
8744 link Options to pass to the linker
8745 lib Libraries to include on the command line to the linker
8746 libgcc Decides which GCC support library to pass to the linker
8747 linker Sets the name of the linker
8748 predefines Defines to be passed to the C preprocessor
8749 signed_char Defines to pass to CPP to say whether @code{char} is signed
8751 startfile Object files to include at the start of the link
8754 Here is a small example of a spec file:
8760 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
8763 This example renames the spec called @samp{lib} to @samp{old_lib} and
8764 then overrides the previous definition of @samp{lib} with a new one.
8765 The new definition adds in some extra command-line options before
8766 including the text of the old definition.
8768 @dfn{Spec strings} are a list of command-line options to be passed to their
8769 corresponding program. In addition, the spec strings can contain
8770 @samp{%}-prefixed sequences to substitute variable text or to
8771 conditionally insert text into the command line. Using these constructs
8772 it is possible to generate quite complex command lines.
8774 Here is a table of all defined @samp{%}-sequences for spec
8775 strings. Note that spaces are not generated automatically around the
8776 results of expanding these sequences. Therefore you can concatenate them
8777 together or combine them with constant text in a single argument.
8781 Substitute one @samp{%} into the program name or argument.
8784 Substitute the name of the input file being processed.
8787 Substitute the basename of the input file being processed.
8788 This is the substring up to (and not including) the last period
8789 and not including the directory.
8792 This is the same as @samp{%b}, but include the file suffix (text after
8796 Marks the argument containing or following the @samp{%d} as a
8797 temporary file name, so that that file will be deleted if GCC exits
8798 successfully. Unlike @samp{%g}, this contributes no text to the
8801 @item %g@var{suffix}
8802 Substitute a file name that has suffix @var{suffix} and is chosen
8803 once per compilation, and mark the argument in the same way as
8804 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
8805 name is now chosen in a way that is hard to predict even when previously
8806 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
8807 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
8808 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
8809 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
8810 was simply substituted with a file name chosen once per compilation,
8811 without regard to any appended suffix (which was therefore treated
8812 just like ordinary text), making such attacks more likely to succeed.
8814 @item %u@var{suffix}
8815 Like @samp{%g}, but generates a new temporary file name even if
8816 @samp{%u@var{suffix}} was already seen.
8818 @item %U@var{suffix}
8819 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
8820 new one if there is no such last file name. In the absence of any
8821 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
8822 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
8823 would involve the generation of two distinct file names, one
8824 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
8825 simply substituted with a file name chosen for the previous @samp{%u},
8826 without regard to any appended suffix.
8828 @item %j@var{suffix}
8829 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
8830 writable, and if save-temps is off; otherwise, substitute the name
8831 of a temporary file, just like @samp{%u}. This temporary file is not
8832 meant for communication between processes, but rather as a junk
8835 @item %|@var{suffix}
8836 @itemx %m@var{suffix}
8837 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
8838 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
8839 all. These are the two most common ways to instruct a program that it
8840 should read from standard input or write to standard output. If you
8841 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
8842 construct: see for example @file{f/lang-specs.h}.
8844 @item %.@var{SUFFIX}
8845 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
8846 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
8847 terminated by the next space or %.
8850 Marks the argument containing or following the @samp{%w} as the
8851 designated output file of this compilation. This puts the argument
8852 into the sequence of arguments that @samp{%o} will substitute later.
8855 Substitutes the names of all the output files, with spaces
8856 automatically placed around them. You should write spaces
8857 around the @samp{%o} as well or the results are undefined.
8858 @samp{%o} is for use in the specs for running the linker.
8859 Input files whose names have no recognized suffix are not compiled
8860 at all, but they are included among the output files, so they will
8864 Substitutes the suffix for object files. Note that this is
8865 handled specially when it immediately follows @samp{%g, %u, or %U},
8866 because of the need for those to form complete file names. The
8867 handling is such that @samp{%O} is treated exactly as if it had already
8868 been substituted, except that @samp{%g, %u, and %U} do not currently
8869 support additional @var{suffix} characters following @samp{%O} as they would
8870 following, for example, @samp{.o}.
8873 Substitutes the standard macro predefinitions for the
8874 current target machine. Use this when running @code{cpp}.
8877 Like @samp{%p}, but puts @samp{__} before and after the name of each
8878 predefined macro, except for macros that start with @samp{__} or with
8879 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8883 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8884 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8885 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8886 and @option{-imultilib} as necessary.
8889 Current argument is the name of a library or startup file of some sort.
8890 Search for that file in a standard list of directories and substitute
8891 the full name found. The current working directory is included in the
8892 list of directories scanned.
8895 Current argument is the name of a linker script. Search for that file
8896 in the current list of directories to scan for libraries. If the file
8897 is located insert a @option{--script} option into the command line
8898 followed by the full path name found. If the file is not found then
8899 generate an error message. Note: the current working directory is not
8903 Print @var{str} as an error message. @var{str} is terminated by a newline.
8904 Use this when inconsistent options are detected.
8907 Substitute the contents of spec string @var{name} at this point.
8910 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8912 @item %x@{@var{option}@}
8913 Accumulate an option for @samp{%X}.
8916 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8920 Output the accumulated assembler options specified by @option{-Wa}.
8923 Output the accumulated preprocessor options specified by @option{-Wp}.
8926 Process the @code{asm} spec. This is used to compute the
8927 switches to be passed to the assembler.
8930 Process the @code{asm_final} spec. This is a spec string for
8931 passing switches to an assembler post-processor, if such a program is
8935 Process the @code{link} spec. This is the spec for computing the
8936 command line passed to the linker. Typically it will make use of the
8937 @samp{%L %G %S %D and %E} sequences.
8940 Dump out a @option{-L} option for each directory that GCC believes might
8941 contain startup files. If the target supports multilibs then the
8942 current multilib directory will be prepended to each of these paths.
8945 Process the @code{lib} spec. This is a spec string for deciding which
8946 libraries should be included on the command line to the linker.
8949 Process the @code{libgcc} spec. This is a spec string for deciding
8950 which GCC support library should be included on the command line to the linker.
8953 Process the @code{startfile} spec. This is a spec for deciding which
8954 object files should be the first ones passed to the linker. Typically
8955 this might be a file named @file{crt0.o}.
8958 Process the @code{endfile} spec. This is a spec string that specifies
8959 the last object files that will be passed to the linker.
8962 Process the @code{cpp} spec. This is used to construct the arguments
8963 to be passed to the C preprocessor.
8966 Process the @code{cc1} spec. This is used to construct the options to be
8967 passed to the actual C compiler (@samp{cc1}).
8970 Process the @code{cc1plus} spec. This is used to construct the options to be
8971 passed to the actual C++ compiler (@samp{cc1plus}).
8974 Substitute the variable part of a matched option. See below.
8975 Note that each comma in the substituted string is replaced by
8979 Remove all occurrences of @code{-S} from the command line. Note---this
8980 command is position dependent. @samp{%} commands in the spec string
8981 before this one will see @code{-S}, @samp{%} commands in the spec string
8982 after this one will not.
8984 @item %:@var{function}(@var{args})
8985 Call the named function @var{function}, passing it @var{args}.
8986 @var{args} is first processed as a nested spec string, then split
8987 into an argument vector in the usual fashion. The function returns
8988 a string which is processed as if it had appeared literally as part
8989 of the current spec.
8991 The following built-in spec functions are provided:
8995 The @code{getenv} spec function takes two arguments: an environment
8996 variable name and a string. If the environment variable is not
8997 defined, a fatal error is issued. Otherwise, the return value is the
8998 value of the environment variable concatenated with the string. For
8999 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
9002 %:getenv(TOPDIR /include)
9005 expands to @file{/path/to/top/include}.
9007 @item @code{if-exists}
9008 The @code{if-exists} spec function takes one argument, an absolute
9009 pathname to a file. If the file exists, @code{if-exists} returns the
9010 pathname. Here is a small example of its usage:
9014 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
9017 @item @code{if-exists-else}
9018 The @code{if-exists-else} spec function is similar to the @code{if-exists}
9019 spec function, except that it takes two arguments. The first argument is
9020 an absolute pathname to a file. If the file exists, @code{if-exists-else}
9021 returns the pathname. If it does not exist, it returns the second argument.
9022 This way, @code{if-exists-else} can be used to select one file or another,
9023 based on the existence of the first. Here is a small example of its usage:
9027 crt0%O%s %:if-exists(crti%O%s) \
9028 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
9031 @item @code{replace-outfile}
9032 The @code{replace-outfile} spec function takes two arguments. It looks for the
9033 first argument in the outfiles array and replaces it with the second argument. Here
9034 is a small example of its usage:
9037 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
9040 @item @code{print-asm-header}
9041 The @code{print-asm-header} function takes no arguments and simply
9042 prints a banner like:
9048 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
9051 It is used to separate compiler options from assembler options
9052 in the @option{--target-help} output.
9056 Substitutes the @code{-S} switch, if that switch was given to GCC@.
9057 If that switch was not specified, this substitutes nothing. Note that
9058 the leading dash is omitted when specifying this option, and it is
9059 automatically inserted if the substitution is performed. Thus the spec
9060 string @samp{%@{foo@}} would match the command-line option @option{-foo}
9061 and would output the command line option @option{-foo}.
9063 @item %W@{@code{S}@}
9064 Like %@{@code{S}@} but mark last argument supplied within as a file to be
9067 @item %@{@code{S}*@}
9068 Substitutes all the switches specified to GCC whose names start
9069 with @code{-S}, but which also take an argument. This is used for
9070 switches like @option{-o}, @option{-D}, @option{-I}, etc.
9071 GCC considers @option{-o foo} as being
9072 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
9073 text, including the space. Thus two arguments would be generated.
9075 @item %@{@code{S}*&@code{T}*@}
9076 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
9077 (the order of @code{S} and @code{T} in the spec is not significant).
9078 There can be any number of ampersand-separated variables; for each the
9079 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
9081 @item %@{@code{S}:@code{X}@}
9082 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
9084 @item %@{!@code{S}:@code{X}@}
9085 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
9087 @item %@{@code{S}*:@code{X}@}
9088 Substitutes @code{X} if one or more switches whose names start with
9089 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
9090 once, no matter how many such switches appeared. However, if @code{%*}
9091 appears somewhere in @code{X}, then @code{X} will be substituted once
9092 for each matching switch, with the @code{%*} replaced by the part of
9093 that switch that matched the @code{*}.
9095 @item %@{.@code{S}:@code{X}@}
9096 Substitutes @code{X}, if processing a file with suffix @code{S}.
9098 @item %@{!.@code{S}:@code{X}@}
9099 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
9101 @item %@{,@code{S}:@code{X}@}
9102 Substitutes @code{X}, if processing a file for language @code{S}.
9104 @item %@{!,@code{S}:@code{X}@}
9105 Substitutes @code{X}, if not processing a file for language @code{S}.
9107 @item %@{@code{S}|@code{P}:@code{X}@}
9108 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
9109 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
9110 @code{*} sequences as well, although they have a stronger binding than
9111 the @samp{|}. If @code{%*} appears in @code{X}, all of the
9112 alternatives must be starred, and only the first matching alternative
9115 For example, a spec string like this:
9118 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
9121 will output the following command-line options from the following input
9122 command-line options:
9127 -d fred.c -foo -baz -boggle
9128 -d jim.d -bar -baz -boggle
9131 @item %@{S:X; T:Y; :D@}
9133 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
9134 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
9135 be as many clauses as you need. This may be combined with @code{.},
9136 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
9141 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
9142 construct may contain other nested @samp{%} constructs or spaces, or
9143 even newlines. They are processed as usual, as described above.
9144 Trailing white space in @code{X} is ignored. White space may also
9145 appear anywhere on the left side of the colon in these constructs,
9146 except between @code{.} or @code{*} and the corresponding word.
9148 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
9149 handled specifically in these constructs. If another value of
9150 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
9151 @option{-W} switch is found later in the command line, the earlier
9152 switch value is ignored, except with @{@code{S}*@} where @code{S} is
9153 just one letter, which passes all matching options.
9155 The character @samp{|} at the beginning of the predicate text is used to
9156 indicate that a command should be piped to the following command, but
9157 only if @option{-pipe} is specified.
9159 It is built into GCC which switches take arguments and which do not.
9160 (You might think it would be useful to generalize this to allow each
9161 compiler's spec to say which switches take arguments. But this cannot
9162 be done in a consistent fashion. GCC cannot even decide which input
9163 files have been specified without knowing which switches take arguments,
9164 and it must know which input files to compile in order to tell which
9167 GCC also knows implicitly that arguments starting in @option{-l} are to be
9168 treated as compiler output files, and passed to the linker in their
9169 proper position among the other output files.
9171 @c man begin OPTIONS
9173 @node Target Options
9174 @section Specifying Target Machine and Compiler Version
9175 @cindex target options
9176 @cindex cross compiling
9177 @cindex specifying machine version
9178 @cindex specifying compiler version and target machine
9179 @cindex compiler version, specifying
9180 @cindex target machine, specifying
9182 The usual way to run GCC is to run the executable called @file{gcc}, or
9183 @file{<machine>-gcc} when cross-compiling, or
9184 @file{<machine>-gcc-<version>} to run a version other than the one that
9185 was installed last. Sometimes this is inconvenient, so GCC provides
9186 options that will switch to another cross-compiler or version.
9189 @item -b @var{machine}
9191 The argument @var{machine} specifies the target machine for compilation.
9193 The value to use for @var{machine} is the same as was specified as the
9194 machine type when configuring GCC as a cross-compiler. For
9195 example, if a cross-compiler was configured with @samp{configure
9196 arm-elf}, meaning to compile for an arm processor with elf binaries,
9197 then you would specify @option{-b arm-elf} to run that cross compiler.
9198 Because there are other options beginning with @option{-b}, the
9199 configuration must contain a hyphen, or @option{-b} alone should be one
9200 argument followed by the configuration in the next argument.
9202 @item -V @var{version}
9204 The argument @var{version} specifies which version of GCC to run.
9205 This is useful when multiple versions are installed. For example,
9206 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
9209 The @option{-V} and @option{-b} options work by running the
9210 @file{<machine>-gcc-<version>} executable, so there's no real reason to
9211 use them if you can just run that directly.
9213 @node Submodel Options
9214 @section Hardware Models and Configurations
9215 @cindex submodel options
9216 @cindex specifying hardware config
9217 @cindex hardware models and configurations, specifying
9218 @cindex machine dependent options
9220 Earlier we discussed the standard option @option{-b} which chooses among
9221 different installed compilers for completely different target
9222 machines, such as VAX vs.@: 68000 vs.@: 80386.
9224 In addition, each of these target machine types can have its own
9225 special options, starting with @samp{-m}, to choose among various
9226 hardware models or configurations---for example, 68010 vs 68020,
9227 floating coprocessor or none. A single installed version of the
9228 compiler can compile for any model or configuration, according to the
9231 Some configurations of the compiler also support additional special
9232 options, usually for compatibility with other compilers on the same
9235 @c This list is ordered alphanumerically by subsection name.
9236 @c It should be the same order and spelling as these options are listed
9237 @c in Machine Dependent Options
9243 * Blackfin Options::
9247 * DEC Alpha Options::
9248 * DEC Alpha/VMS Options::
9251 * GNU/Linux Options::
9254 * i386 and x86-64 Options::
9255 * i386 and x86-64 Windows Options::
9257 * IA-64/VMS Options::
9268 * picoChip Options::
9270 * RS/6000 and PowerPC Options::
9271 * S/390 and zSeries Options::
9276 * System V Options::
9281 * Xstormy16 Options::
9287 @subsection ARC Options
9290 These options are defined for ARC implementations:
9295 Compile code for little endian mode. This is the default.
9299 Compile code for big endian mode.
9302 @opindex mmangle-cpu
9303 Prepend the name of the cpu to all public symbol names.
9304 In multiple-processor systems, there are many ARC variants with different
9305 instruction and register set characteristics. This flag prevents code
9306 compiled for one cpu to be linked with code compiled for another.
9307 No facility exists for handling variants that are ``almost identical''.
9308 This is an all or nothing option.
9310 @item -mcpu=@var{cpu}
9312 Compile code for ARC variant @var{cpu}.
9313 Which variants are supported depend on the configuration.
9314 All variants support @option{-mcpu=base}, this is the default.
9316 @item -mtext=@var{text-section}
9317 @itemx -mdata=@var{data-section}
9318 @itemx -mrodata=@var{readonly-data-section}
9322 Put functions, data, and readonly data in @var{text-section},
9323 @var{data-section}, and @var{readonly-data-section} respectively
9324 by default. This can be overridden with the @code{section} attribute.
9325 @xref{Variable Attributes}.
9327 @item -mfix-cortex-m3-ldrd
9328 @opindex mfix-cortex-m3-ldrd
9329 Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
9330 with overlapping destination and base registers are used. This option avoids
9331 generating these instructions. This option is enabled by default when
9332 @option{-mcpu=cortex-m3} is specified.
9337 @subsection ARM Options
9340 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
9344 @item -mabi=@var{name}
9346 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
9347 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
9350 @opindex mapcs-frame
9351 Generate a stack frame that is compliant with the ARM Procedure Call
9352 Standard for all functions, even if this is not strictly necessary for
9353 correct execution of the code. Specifying @option{-fomit-frame-pointer}
9354 with this option will cause the stack frames not to be generated for
9355 leaf functions. The default is @option{-mno-apcs-frame}.
9359 This is a synonym for @option{-mapcs-frame}.
9362 @c not currently implemented
9363 @item -mapcs-stack-check
9364 @opindex mapcs-stack-check
9365 Generate code to check the amount of stack space available upon entry to
9366 every function (that actually uses some stack space). If there is
9367 insufficient space available then either the function
9368 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
9369 called, depending upon the amount of stack space required. The run time
9370 system is required to provide these functions. The default is
9371 @option{-mno-apcs-stack-check}, since this produces smaller code.
9373 @c not currently implemented
9375 @opindex mapcs-float
9376 Pass floating point arguments using the float point registers. This is
9377 one of the variants of the APCS@. This option is recommended if the
9378 target hardware has a floating point unit or if a lot of floating point
9379 arithmetic is going to be performed by the code. The default is
9380 @option{-mno-apcs-float}, since integer only code is slightly increased in
9381 size if @option{-mapcs-float} is used.
9383 @c not currently implemented
9384 @item -mapcs-reentrant
9385 @opindex mapcs-reentrant
9386 Generate reentrant, position independent code. The default is
9387 @option{-mno-apcs-reentrant}.
9390 @item -mthumb-interwork
9391 @opindex mthumb-interwork
9392 Generate code which supports calling between the ARM and Thumb
9393 instruction sets. Without this option the two instruction sets cannot
9394 be reliably used inside one program. The default is
9395 @option{-mno-thumb-interwork}, since slightly larger code is generated
9396 when @option{-mthumb-interwork} is specified.
9398 @item -mno-sched-prolog
9399 @opindex mno-sched-prolog
9400 Prevent the reordering of instructions in the function prolog, or the
9401 merging of those instruction with the instructions in the function's
9402 body. This means that all functions will start with a recognizable set
9403 of instructions (or in fact one of a choice from a small set of
9404 different function prologues), and this information can be used to
9405 locate the start if functions inside an executable piece of code. The
9406 default is @option{-msched-prolog}.
9408 @item -mfloat-abi=@var{name}
9410 Specifies which floating-point ABI to use. Permissible values
9411 are: @samp{soft}, @samp{softfp} and @samp{hard}.
9413 Specifying @samp{soft} causes GCC to generate output containing
9414 library calls for floating-point operations.
9415 @samp{softfp} allows the generation of code using hardware floating-point
9416 instructions, but still uses the soft-float calling conventions.
9417 @samp{hard} allows generation of floating-point instructions
9418 and uses FPU-specific calling conventions.
9420 The default depends on the specific target configuration. Note that
9421 the hard-float and soft-float ABIs are not link-compatible; you must
9422 compile your entire program with the same ABI, and link with a
9423 compatible set of libraries.
9426 @opindex mhard-float
9427 Equivalent to @option{-mfloat-abi=hard}.
9430 @opindex msoft-float
9431 Equivalent to @option{-mfloat-abi=soft}.
9433 @item -mlittle-endian
9434 @opindex mlittle-endian
9435 Generate code for a processor running in little-endian mode. This is
9436 the default for all standard configurations.
9439 @opindex mbig-endian
9440 Generate code for a processor running in big-endian mode; the default is
9441 to compile code for a little-endian processor.
9443 @item -mwords-little-endian
9444 @opindex mwords-little-endian
9445 This option only applies when generating code for big-endian processors.
9446 Generate code for a little-endian word order but a big-endian byte
9447 order. That is, a byte order of the form @samp{32107654}. Note: this
9448 option should only be used if you require compatibility with code for
9449 big-endian ARM processors generated by versions of the compiler prior to
9452 @item -mcpu=@var{name}
9454 This specifies the name of the target ARM processor. GCC uses this name
9455 to determine what kind of instructions it can emit when generating
9456 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
9457 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
9458 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
9459 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
9460 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
9462 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
9463 @samp{arm710t}, @samp{arm720t}, @samp{arm740t},
9464 @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
9465 @samp{strongarm1110},
9466 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
9467 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
9468 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
9469 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
9470 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
9471 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
9472 @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
9473 @samp{cortex-a8}, @samp{cortex-a9},
9474 @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
9477 @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
9479 @item -mtune=@var{name}
9481 This option is very similar to the @option{-mcpu=} option, except that
9482 instead of specifying the actual target processor type, and hence
9483 restricting which instructions can be used, it specifies that GCC should
9484 tune the performance of the code as if the target were of the type
9485 specified in this option, but still choosing the instructions that it
9486 will generate based on the cpu specified by a @option{-mcpu=} option.
9487 For some ARM implementations better performance can be obtained by using
9490 @item -march=@var{name}
9492 This specifies the name of the target ARM architecture. GCC uses this
9493 name to determine what kind of instructions it can emit when generating
9494 assembly code. This option can be used in conjunction with or instead
9495 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
9496 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
9497 @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
9498 @samp{armv6}, @samp{armv6j},
9499 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
9500 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
9501 @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
9503 @item -mfpu=@var{name}
9504 @itemx -mfpe=@var{number}
9505 @itemx -mfp=@var{number}
9509 This specifies what floating point hardware (or hardware emulation) is
9510 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
9511 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16},
9512 @samp{neon}, and @samp{neon-fp16}. @option{-mfp} and @option{-mfpe}
9513 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
9514 with older versions of GCC@.
9516 If @option{-msoft-float} is specified this specifies the format of
9517 floating point values.
9519 @item -mfp16-format=@var{name}
9520 @opindex mfp16-format
9521 Specify the format of the @code{__fp16} half-precision floating-point type.
9522 Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
9523 the default is @samp{none}, in which case the @code{__fp16} type is not
9524 defined. @xref{Half-Precision}, for more information.
9526 @item -mstructure-size-boundary=@var{n}
9527 @opindex mstructure-size-boundary
9528 The size of all structures and unions will be rounded up to a multiple
9529 of the number of bits set by this option. Permissible values are 8, 32
9530 and 64. The default value varies for different toolchains. For the COFF
9531 targeted toolchain the default value is 8. A value of 64 is only allowed
9532 if the underlying ABI supports it.
9534 Specifying the larger number can produce faster, more efficient code, but
9535 can also increase the size of the program. Different values are potentially
9536 incompatible. Code compiled with one value cannot necessarily expect to
9537 work with code or libraries compiled with another value, if they exchange
9538 information using structures or unions.
9540 @item -mabort-on-noreturn
9541 @opindex mabort-on-noreturn
9542 Generate a call to the function @code{abort} at the end of a
9543 @code{noreturn} function. It will be executed if the function tries to
9547 @itemx -mno-long-calls
9548 @opindex mlong-calls
9549 @opindex mno-long-calls
9550 Tells the compiler to perform function calls by first loading the
9551 address of the function into a register and then performing a subroutine
9552 call on this register. This switch is needed if the target function
9553 will lie outside of the 64 megabyte addressing range of the offset based
9554 version of subroutine call instruction.
9556 Even if this switch is enabled, not all function calls will be turned
9557 into long calls. The heuristic is that static functions, functions
9558 which have the @samp{short-call} attribute, functions that are inside
9559 the scope of a @samp{#pragma no_long_calls} directive and functions whose
9560 definitions have already been compiled within the current compilation
9561 unit, will not be turned into long calls. The exception to this rule is
9562 that weak function definitions, functions with the @samp{long-call}
9563 attribute or the @samp{section} attribute, and functions that are within
9564 the scope of a @samp{#pragma long_calls} directive, will always be
9565 turned into long calls.
9567 This feature is not enabled by default. Specifying
9568 @option{-mno-long-calls} will restore the default behavior, as will
9569 placing the function calls within the scope of a @samp{#pragma
9570 long_calls_off} directive. Note these switches have no effect on how
9571 the compiler generates code to handle function calls via function
9574 @item -msingle-pic-base
9575 @opindex msingle-pic-base
9576 Treat the register used for PIC addressing as read-only, rather than
9577 loading it in the prologue for each function. The run-time system is
9578 responsible for initializing this register with an appropriate value
9579 before execution begins.
9581 @item -mpic-register=@var{reg}
9582 @opindex mpic-register
9583 Specify the register to be used for PIC addressing. The default is R10
9584 unless stack-checking is enabled, when R9 is used.
9586 @item -mcirrus-fix-invalid-insns
9587 @opindex mcirrus-fix-invalid-insns
9588 @opindex mno-cirrus-fix-invalid-insns
9589 Insert NOPs into the instruction stream to in order to work around
9590 problems with invalid Maverick instruction combinations. This option
9591 is only valid if the @option{-mcpu=ep9312} option has been used to
9592 enable generation of instructions for the Cirrus Maverick floating
9593 point co-processor. This option is not enabled by default, since the
9594 problem is only present in older Maverick implementations. The default
9595 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
9598 @item -mpoke-function-name
9599 @opindex mpoke-function-name
9600 Write the name of each function into the text section, directly
9601 preceding the function prologue. The generated code is similar to this:
9605 .ascii "arm_poke_function_name", 0
9608 .word 0xff000000 + (t1 - t0)
9609 arm_poke_function_name
9611 stmfd sp!, @{fp, ip, lr, pc@}
9615 When performing a stack backtrace, code can inspect the value of
9616 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
9617 location @code{pc - 12} and the top 8 bits are set, then we know that
9618 there is a function name embedded immediately preceding this location
9619 and has length @code{((pc[-3]) & 0xff000000)}.
9623 Generate code for the Thumb instruction set. The default is to
9624 use the 32-bit ARM instruction set.
9625 This option automatically enables either 16-bit Thumb-1 or
9626 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
9627 and @option{-march=@var{name}} options. This option is not passed to the
9628 assembler. If you want to force assembler files to be interpreted as Thumb code,
9629 either add a @samp{.thumb} directive to the source or pass the @option{-mthumb}
9630 option directly to the assembler by prefixing it with @option{-Wa}.
9633 @opindex mtpcs-frame
9634 Generate a stack frame that is compliant with the Thumb Procedure Call
9635 Standard for all non-leaf functions. (A leaf function is one that does
9636 not call any other functions.) The default is @option{-mno-tpcs-frame}.
9638 @item -mtpcs-leaf-frame
9639 @opindex mtpcs-leaf-frame
9640 Generate a stack frame that is compliant with the Thumb Procedure Call
9641 Standard for all leaf functions. (A leaf function is one that does
9642 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
9644 @item -mcallee-super-interworking
9645 @opindex mcallee-super-interworking
9646 Gives all externally visible functions in the file being compiled an ARM
9647 instruction set header which switches to Thumb mode before executing the
9648 rest of the function. This allows these functions to be called from
9649 non-interworking code. This option is not valid in AAPCS configurations
9650 because interworking is enabled by default.
9652 @item -mcaller-super-interworking
9653 @opindex mcaller-super-interworking
9654 Allows calls via function pointers (including virtual functions) to
9655 execute correctly regardless of whether the target code has been
9656 compiled for interworking or not. There is a small overhead in the cost
9657 of executing a function pointer if this option is enabled. This option
9658 is not valid in AAPCS configurations because interworking is enabled
9661 @item -mtp=@var{name}
9663 Specify the access model for the thread local storage pointer. The valid
9664 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
9665 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
9666 (supported in the arm6k architecture), and @option{auto}, which uses the
9667 best available method for the selected processor. The default setting is
9670 @item -mword-relocations
9671 @opindex mword-relocations
9672 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
9673 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
9674 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
9680 @subsection AVR Options
9683 These options are defined for AVR implementations:
9686 @item -mmcu=@var{mcu}
9688 Specify ATMEL AVR instruction set or MCU type.
9690 Instruction set avr1 is for the minimal AVR core, not supported by the C
9691 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9692 attiny11, attiny12, attiny15, attiny28).
9694 Instruction set avr2 (default) is for the classic AVR core with up to
9695 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9696 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9697 at90c8534, at90s8535).
9699 Instruction set avr3 is for the classic AVR core with up to 128K program
9700 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9702 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9703 memory space (MCU types: atmega8, atmega83, atmega85).
9705 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9706 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9707 atmega64, atmega128, at43usb355, at94k).
9711 Output instruction sizes to the asm file.
9713 @item -mno-interrupts
9714 @opindex mno-interrupts
9715 Generated code is not compatible with hardware interrupts.
9716 Code size will be smaller.
9718 @item -mcall-prologues
9719 @opindex mcall-prologues
9720 Functions prologues/epilogues expanded as call to appropriate
9721 subroutines. Code size will be smaller.
9724 @opindex mtiny-stack
9725 Change only the low 8 bits of the stack pointer.
9729 Assume int to be 8 bit integer. This affects the sizes of all types: A
9730 char will be 1 byte, an int will be 1 byte, a long will be 2 bytes
9731 and long long will be 4 bytes. Please note that this option does not
9732 comply to the C standards, but it will provide you with smaller code
9736 @node Blackfin Options
9737 @subsection Blackfin Options
9738 @cindex Blackfin Options
9741 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
9743 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
9744 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
9745 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
9746 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
9747 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
9748 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
9749 @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
9751 The optional @var{sirevision} specifies the silicon revision of the target
9752 Blackfin processor. Any workarounds available for the targeted silicon revision
9753 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
9754 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
9755 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
9756 hexadecimal digits representing the major and minor numbers in the silicon
9757 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
9758 is not defined. If @var{sirevision} is @samp{any}, the
9759 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
9760 If this optional @var{sirevision} is not used, GCC assumes the latest known
9761 silicon revision of the targeted Blackfin processor.
9763 Support for @samp{bf561} is incomplete. For @samp{bf561},
9764 Only the processor macro is defined.
9765 Without this option, @samp{bf532} is used as the processor by default.
9766 The corresponding predefined processor macros for @var{cpu} is to
9767 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
9768 provided by libgloss to be linked in if @option{-msim} is not given.
9772 Specifies that the program will be run on the simulator. This causes
9773 the simulator BSP provided by libgloss to be linked in. This option
9774 has effect only for @samp{bfin-elf} toolchain.
9775 Certain other options, such as @option{-mid-shared-library} and
9776 @option{-mfdpic}, imply @option{-msim}.
9778 @item -momit-leaf-frame-pointer
9779 @opindex momit-leaf-frame-pointer
9780 Don't keep the frame pointer in a register for leaf functions. This
9781 avoids the instructions to save, set up and restore frame pointers and
9782 makes an extra register available in leaf functions. The option
9783 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9784 which might make debugging harder.
9786 @item -mspecld-anomaly
9787 @opindex mspecld-anomaly
9788 When enabled, the compiler will ensure that the generated code does not
9789 contain speculative loads after jump instructions. If this option is used,
9790 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
9792 @item -mno-specld-anomaly
9793 @opindex mno-specld-anomaly
9794 Don't generate extra code to prevent speculative loads from occurring.
9796 @item -mcsync-anomaly
9797 @opindex mcsync-anomaly
9798 When enabled, the compiler will ensure that the generated code does not
9799 contain CSYNC or SSYNC instructions too soon after conditional branches.
9800 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
9802 @item -mno-csync-anomaly
9803 @opindex mno-csync-anomaly
9804 Don't generate extra code to prevent CSYNC or SSYNC instructions from
9805 occurring too soon after a conditional branch.
9809 When enabled, the compiler is free to take advantage of the knowledge that
9810 the entire program fits into the low 64k of memory.
9813 @opindex mno-low-64k
9814 Assume that the program is arbitrarily large. This is the default.
9816 @item -mstack-check-l1
9817 @opindex mstack-check-l1
9818 Do stack checking using information placed into L1 scratchpad memory by the
9821 @item -mid-shared-library
9822 @opindex mid-shared-library
9823 Generate code that supports shared libraries via the library ID method.
9824 This allows for execute in place and shared libraries in an environment
9825 without virtual memory management. This option implies @option{-fPIC}.
9826 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9828 @item -mno-id-shared-library
9829 @opindex mno-id-shared-library
9830 Generate code that doesn't assume ID based shared libraries are being used.
9831 This is the default.
9833 @item -mleaf-id-shared-library
9834 @opindex mleaf-id-shared-library
9835 Generate code that supports shared libraries via the library ID method,
9836 but assumes that this library or executable won't link against any other
9837 ID shared libraries. That allows the compiler to use faster code for jumps
9840 @item -mno-leaf-id-shared-library
9841 @opindex mno-leaf-id-shared-library
9842 Do not assume that the code being compiled won't link against any ID shared
9843 libraries. Slower code will be generated for jump and call insns.
9845 @item -mshared-library-id=n
9846 @opindex mshared-library-id
9847 Specified the identification number of the ID based shared library being
9848 compiled. Specifying a value of 0 will generate more compact code, specifying
9849 other values will force the allocation of that number to the current
9850 library but is no more space or time efficient than omitting this option.
9854 Generate code that allows the data segment to be located in a different
9855 area of memory from the text segment. This allows for execute in place in
9856 an environment without virtual memory management by eliminating relocations
9857 against the text section.
9860 @opindex mno-sep-data
9861 Generate code that assumes that the data segment follows the text segment.
9862 This is the default.
9865 @itemx -mno-long-calls
9866 @opindex mlong-calls
9867 @opindex mno-long-calls
9868 Tells the compiler to perform function calls by first loading the
9869 address of the function into a register and then performing a subroutine
9870 call on this register. This switch is needed if the target function
9871 will lie outside of the 24 bit addressing range of the offset based
9872 version of subroutine call instruction.
9874 This feature is not enabled by default. Specifying
9875 @option{-mno-long-calls} will restore the default behavior. Note these
9876 switches have no effect on how the compiler generates code to handle
9877 function calls via function pointers.
9881 Link with the fast floating-point library. This library relaxes some of
9882 the IEEE floating-point standard's rules for checking inputs against
9883 Not-a-Number (NAN), in the interest of performance.
9886 @opindex minline-plt
9887 Enable inlining of PLT entries in function calls to functions that are
9888 not known to bind locally. It has no effect without @option{-mfdpic}.
9892 Build standalone application for multicore Blackfin processor. Proper
9893 start files and link scripts will be used to support multicore.
9894 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9895 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9896 @option{-mcorea} or @option{-mcoreb}. If it's used without
9897 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9898 programming model is used. In this model, the main function of Core B
9899 should be named as coreb_main. If it's used with @option{-mcorea} or
9900 @option{-mcoreb}, one application per core programming model is used.
9901 If this option is not used, single core application programming
9906 Build standalone application for Core A of BF561 when using
9907 one application per core programming model. Proper start files
9908 and link scripts will be used to support Core A. This option
9909 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9913 Build standalone application for Core B of BF561 when using
9914 one application per core programming model. Proper start files
9915 and link scripts will be used to support Core B. This option
9916 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9917 should be used instead of main. It must be used with
9918 @option{-mmulticore}.
9922 Build standalone application for SDRAM. Proper start files and
9923 link scripts will be used to put the application into SDRAM.
9924 Loader should initialize SDRAM before loading the application
9925 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9929 Assume that ICPLBs are enabled at runtime. This has an effect on certain
9930 anomaly workarounds. For Linux targets, the default is to assume ICPLBs
9931 are enabled; for standalone applications the default is off.
9935 @subsection CRIS Options
9936 @cindex CRIS Options
9938 These options are defined specifically for the CRIS ports.
9941 @item -march=@var{architecture-type}
9942 @itemx -mcpu=@var{architecture-type}
9945 Generate code for the specified architecture. The choices for
9946 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9947 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9948 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9951 @item -mtune=@var{architecture-type}
9953 Tune to @var{architecture-type} everything applicable about the generated
9954 code, except for the ABI and the set of available instructions. The
9955 choices for @var{architecture-type} are the same as for
9956 @option{-march=@var{architecture-type}}.
9958 @item -mmax-stack-frame=@var{n}
9959 @opindex mmax-stack-frame
9960 Warn when the stack frame of a function exceeds @var{n} bytes.
9966 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9967 @option{-march=v3} and @option{-march=v8} respectively.
9969 @item -mmul-bug-workaround
9970 @itemx -mno-mul-bug-workaround
9971 @opindex mmul-bug-workaround
9972 @opindex mno-mul-bug-workaround
9973 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9974 models where it applies. This option is active by default.
9978 Enable CRIS-specific verbose debug-related information in the assembly
9979 code. This option also has the effect to turn off the @samp{#NO_APP}
9980 formatted-code indicator to the assembler at the beginning of the
9985 Do not use condition-code results from previous instruction; always emit
9986 compare and test instructions before use of condition codes.
9988 @item -mno-side-effects
9989 @opindex mno-side-effects
9990 Do not emit instructions with side-effects in addressing modes other than
9994 @itemx -mno-stack-align
9996 @itemx -mno-data-align
9997 @itemx -mconst-align
9998 @itemx -mno-const-align
9999 @opindex mstack-align
10000 @opindex mno-stack-align
10001 @opindex mdata-align
10002 @opindex mno-data-align
10003 @opindex mconst-align
10004 @opindex mno-const-align
10005 These options (no-options) arranges (eliminate arrangements) for the
10006 stack-frame, individual data and constants to be aligned for the maximum
10007 single data access size for the chosen CPU model. The default is to
10008 arrange for 32-bit alignment. ABI details such as structure layout are
10009 not affected by these options.
10017 Similar to the stack- data- and const-align options above, these options
10018 arrange for stack-frame, writable data and constants to all be 32-bit,
10019 16-bit or 8-bit aligned. The default is 32-bit alignment.
10021 @item -mno-prologue-epilogue
10022 @itemx -mprologue-epilogue
10023 @opindex mno-prologue-epilogue
10024 @opindex mprologue-epilogue
10025 With @option{-mno-prologue-epilogue}, the normal function prologue and
10026 epilogue that sets up the stack-frame are omitted and no return
10027 instructions or return sequences are generated in the code. Use this
10028 option only together with visual inspection of the compiled code: no
10029 warnings or errors are generated when call-saved registers must be saved,
10030 or storage for local variable needs to be allocated.
10034 @opindex mno-gotplt
10036 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
10037 instruction sequences that load addresses for functions from the PLT part
10038 of the GOT rather than (traditional on other architectures) calls to the
10039 PLT@. The default is @option{-mgotplt}.
10043 Legacy no-op option only recognized with the cris-axis-elf and
10044 cris-axis-linux-gnu targets.
10048 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
10052 This option, recognized for the cris-axis-elf arranges
10053 to link with input-output functions from a simulator library. Code,
10054 initialized data and zero-initialized data are allocated consecutively.
10058 Like @option{-sim}, but pass linker options to locate initialized data at
10059 0x40000000 and zero-initialized data at 0x80000000.
10063 @subsection CRX Options
10064 @cindex CRX Options
10066 These options are defined specifically for the CRX ports.
10072 Enable the use of multiply-accumulate instructions. Disabled by default.
10075 @opindex mpush-args
10076 Push instructions will be used to pass outgoing arguments when functions
10077 are called. Enabled by default.
10080 @node Darwin Options
10081 @subsection Darwin Options
10082 @cindex Darwin options
10084 These options are defined for all architectures running the Darwin operating
10087 FSF GCC on Darwin does not create ``fat'' object files; it will create
10088 an object file for the single architecture that it was built to
10089 target. Apple's GCC on Darwin does create ``fat'' files if multiple
10090 @option{-arch} options are used; it does so by running the compiler or
10091 linker multiple times and joining the results together with
10094 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
10095 @samp{i686}) is determined by the flags that specify the ISA
10096 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
10097 @option{-force_cpusubtype_ALL} option can be used to override this.
10099 The Darwin tools vary in their behavior when presented with an ISA
10100 mismatch. The assembler, @file{as}, will only permit instructions to
10101 be used that are valid for the subtype of the file it is generating,
10102 so you cannot put 64-bit instructions in a @samp{ppc750} object file.
10103 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
10104 and print an error if asked to create a shared library with a less
10105 restrictive subtype than its input files (for instance, trying to put
10106 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
10107 for executables, @file{ld}, will quietly give the executable the most
10108 restrictive subtype of any of its input files.
10113 Add the framework directory @var{dir} to the head of the list of
10114 directories to be searched for header files. These directories are
10115 interleaved with those specified by @option{-I} options and are
10116 scanned in a left-to-right order.
10118 A framework directory is a directory with frameworks in it. A
10119 framework is a directory with a @samp{"Headers"} and/or
10120 @samp{"PrivateHeaders"} directory contained directly in it that ends
10121 in @samp{".framework"}. The name of a framework is the name of this
10122 directory excluding the @samp{".framework"}. Headers associated with
10123 the framework are found in one of those two directories, with
10124 @samp{"Headers"} being searched first. A subframework is a framework
10125 directory that is in a framework's @samp{"Frameworks"} directory.
10126 Includes of subframework headers can only appear in a header of a
10127 framework that contains the subframework, or in a sibling subframework
10128 header. Two subframeworks are siblings if they occur in the same
10129 framework. A subframework should not have the same name as a
10130 framework, a warning will be issued if this is violated. Currently a
10131 subframework cannot have subframeworks, in the future, the mechanism
10132 may be extended to support this. The standard frameworks can be found
10133 in @samp{"/System/Library/Frameworks"} and
10134 @samp{"/Library/Frameworks"}. An example include looks like
10135 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
10136 the name of the framework and header.h is found in the
10137 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
10139 @item -iframework@var{dir}
10140 @opindex iframework
10141 Like @option{-F} except the directory is a treated as a system
10142 directory. The main difference between this @option{-iframework} and
10143 @option{-F} is that with @option{-iframework} the compiler does not
10144 warn about constructs contained within header files found via
10145 @var{dir}. This option is valid only for the C family of languages.
10149 Emit debugging information for symbols that are used. For STABS
10150 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
10151 This is by default ON@.
10155 Emit debugging information for all symbols and types.
10157 @item -mmacosx-version-min=@var{version}
10158 The earliest version of MacOS X that this executable will run on
10159 is @var{version}. Typical values of @var{version} include @code{10.1},
10160 @code{10.2}, and @code{10.3.9}.
10162 If the compiler was built to use the system's headers by default,
10163 then the default for this option is the system version on which the
10164 compiler is running, otherwise the default is to make choices which
10165 are compatible with as many systems and code bases as possible.
10169 Enable kernel development mode. The @option{-mkernel} option sets
10170 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
10171 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
10172 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
10173 applicable. This mode also sets @option{-mno-altivec},
10174 @option{-msoft-float}, @option{-fno-builtin} and
10175 @option{-mlong-branch} for PowerPC targets.
10177 @item -mone-byte-bool
10178 @opindex mone-byte-bool
10179 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
10180 By default @samp{sizeof(bool)} is @samp{4} when compiling for
10181 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
10182 option has no effect on x86.
10184 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
10185 to generate code that is not binary compatible with code generated
10186 without that switch. Using this switch may require recompiling all
10187 other modules in a program, including system libraries. Use this
10188 switch to conform to a non-default data model.
10190 @item -mfix-and-continue
10191 @itemx -ffix-and-continue
10192 @itemx -findirect-data
10193 @opindex mfix-and-continue
10194 @opindex ffix-and-continue
10195 @opindex findirect-data
10196 Generate code suitable for fast turn around development. Needed to
10197 enable gdb to dynamically load @code{.o} files into already running
10198 programs. @option{-findirect-data} and @option{-ffix-and-continue}
10199 are provided for backwards compatibility.
10203 Loads all members of static archive libraries.
10204 See man ld(1) for more information.
10206 @item -arch_errors_fatal
10207 @opindex arch_errors_fatal
10208 Cause the errors having to do with files that have the wrong architecture
10211 @item -bind_at_load
10212 @opindex bind_at_load
10213 Causes the output file to be marked such that the dynamic linker will
10214 bind all undefined references when the file is loaded or launched.
10218 Produce a Mach-o bundle format file.
10219 See man ld(1) for more information.
10221 @item -bundle_loader @var{executable}
10222 @opindex bundle_loader
10223 This option specifies the @var{executable} that will be loading the build
10224 output file being linked. See man ld(1) for more information.
10227 @opindex dynamiclib
10228 When passed this option, GCC will produce a dynamic library instead of
10229 an executable when linking, using the Darwin @file{libtool} command.
10231 @item -force_cpusubtype_ALL
10232 @opindex force_cpusubtype_ALL
10233 This causes GCC's output file to have the @var{ALL} subtype, instead of
10234 one controlled by the @option{-mcpu} or @option{-march} option.
10236 @item -allowable_client @var{client_name}
10237 @itemx -client_name
10238 @itemx -compatibility_version
10239 @itemx -current_version
10241 @itemx -dependency-file
10243 @itemx -dylinker_install_name
10245 @itemx -exported_symbols_list
10247 @itemx -flat_namespace
10248 @itemx -force_flat_namespace
10249 @itemx -headerpad_max_install_names
10252 @itemx -install_name
10253 @itemx -keep_private_externs
10254 @itemx -multi_module
10255 @itemx -multiply_defined
10256 @itemx -multiply_defined_unused
10258 @itemx -no_dead_strip_inits_and_terms
10259 @itemx -nofixprebinding
10260 @itemx -nomultidefs
10262 @itemx -noseglinkedit
10263 @itemx -pagezero_size
10265 @itemx -prebind_all_twolevel_modules
10266 @itemx -private_bundle
10267 @itemx -read_only_relocs
10269 @itemx -sectobjectsymbols
10273 @itemx -sectobjectsymbols
10276 @itemx -segs_read_only_addr
10277 @itemx -segs_read_write_addr
10278 @itemx -seg_addr_table
10279 @itemx -seg_addr_table_filename
10280 @itemx -seglinkedit
10282 @itemx -segs_read_only_addr
10283 @itemx -segs_read_write_addr
10284 @itemx -single_module
10286 @itemx -sub_library
10287 @itemx -sub_umbrella
10288 @itemx -twolevel_namespace
10291 @itemx -unexported_symbols_list
10292 @itemx -weak_reference_mismatches
10293 @itemx -whatsloaded
10294 @opindex allowable_client
10295 @opindex client_name
10296 @opindex compatibility_version
10297 @opindex current_version
10298 @opindex dead_strip
10299 @opindex dependency-file
10300 @opindex dylib_file
10301 @opindex dylinker_install_name
10303 @opindex exported_symbols_list
10305 @opindex flat_namespace
10306 @opindex force_flat_namespace
10307 @opindex headerpad_max_install_names
10308 @opindex image_base
10310 @opindex install_name
10311 @opindex keep_private_externs
10312 @opindex multi_module
10313 @opindex multiply_defined
10314 @opindex multiply_defined_unused
10315 @opindex noall_load
10316 @opindex no_dead_strip_inits_and_terms
10317 @opindex nofixprebinding
10318 @opindex nomultidefs
10320 @opindex noseglinkedit
10321 @opindex pagezero_size
10323 @opindex prebind_all_twolevel_modules
10324 @opindex private_bundle
10325 @opindex read_only_relocs
10327 @opindex sectobjectsymbols
10330 @opindex sectcreate
10331 @opindex sectobjectsymbols
10334 @opindex segs_read_only_addr
10335 @opindex segs_read_write_addr
10336 @opindex seg_addr_table
10337 @opindex seg_addr_table_filename
10338 @opindex seglinkedit
10340 @opindex segs_read_only_addr
10341 @opindex segs_read_write_addr
10342 @opindex single_module
10344 @opindex sub_library
10345 @opindex sub_umbrella
10346 @opindex twolevel_namespace
10349 @opindex unexported_symbols_list
10350 @opindex weak_reference_mismatches
10351 @opindex whatsloaded
10352 These options are passed to the Darwin linker. The Darwin linker man page
10353 describes them in detail.
10356 @node DEC Alpha Options
10357 @subsection DEC Alpha Options
10359 These @samp{-m} options are defined for the DEC Alpha implementations:
10362 @item -mno-soft-float
10363 @itemx -msoft-float
10364 @opindex mno-soft-float
10365 @opindex msoft-float
10366 Use (do not use) the hardware floating-point instructions for
10367 floating-point operations. When @option{-msoft-float} is specified,
10368 functions in @file{libgcc.a} will be used to perform floating-point
10369 operations. Unless they are replaced by routines that emulate the
10370 floating-point operations, or compiled in such a way as to call such
10371 emulations routines, these routines will issue floating-point
10372 operations. If you are compiling for an Alpha without floating-point
10373 operations, you must ensure that the library is built so as not to call
10376 Note that Alpha implementations without floating-point operations are
10377 required to have floating-point registers.
10380 @itemx -mno-fp-regs
10382 @opindex mno-fp-regs
10383 Generate code that uses (does not use) the floating-point register set.
10384 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
10385 register set is not used, floating point operands are passed in integer
10386 registers as if they were integers and floating-point results are passed
10387 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
10388 so any function with a floating-point argument or return value called by code
10389 compiled with @option{-mno-fp-regs} must also be compiled with that
10392 A typical use of this option is building a kernel that does not use,
10393 and hence need not save and restore, any floating-point registers.
10397 The Alpha architecture implements floating-point hardware optimized for
10398 maximum performance. It is mostly compliant with the IEEE floating
10399 point standard. However, for full compliance, software assistance is
10400 required. This option generates code fully IEEE compliant code
10401 @emph{except} that the @var{inexact-flag} is not maintained (see below).
10402 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
10403 defined during compilation. The resulting code is less efficient but is
10404 able to correctly support denormalized numbers and exceptional IEEE
10405 values such as not-a-number and plus/minus infinity. Other Alpha
10406 compilers call this option @option{-ieee_with_no_inexact}.
10408 @item -mieee-with-inexact
10409 @opindex mieee-with-inexact
10410 This is like @option{-mieee} except the generated code also maintains
10411 the IEEE @var{inexact-flag}. Turning on this option causes the
10412 generated code to implement fully-compliant IEEE math. In addition to
10413 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
10414 macro. On some Alpha implementations the resulting code may execute
10415 significantly slower than the code generated by default. Since there is
10416 very little code that depends on the @var{inexact-flag}, you should
10417 normally not specify this option. Other Alpha compilers call this
10418 option @option{-ieee_with_inexact}.
10420 @item -mfp-trap-mode=@var{trap-mode}
10421 @opindex mfp-trap-mode
10422 This option controls what floating-point related traps are enabled.
10423 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
10424 The trap mode can be set to one of four values:
10428 This is the default (normal) setting. The only traps that are enabled
10429 are the ones that cannot be disabled in software (e.g., division by zero
10433 In addition to the traps enabled by @samp{n}, underflow traps are enabled
10437 Like @samp{u}, but the instructions are marked to be safe for software
10438 completion (see Alpha architecture manual for details).
10441 Like @samp{su}, but inexact traps are enabled as well.
10444 @item -mfp-rounding-mode=@var{rounding-mode}
10445 @opindex mfp-rounding-mode
10446 Selects the IEEE rounding mode. Other Alpha compilers call this option
10447 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
10452 Normal IEEE rounding mode. Floating point numbers are rounded towards
10453 the nearest machine number or towards the even machine number in case
10457 Round towards minus infinity.
10460 Chopped rounding mode. Floating point numbers are rounded towards zero.
10463 Dynamic rounding mode. A field in the floating point control register
10464 (@var{fpcr}, see Alpha architecture reference manual) controls the
10465 rounding mode in effect. The C library initializes this register for
10466 rounding towards plus infinity. Thus, unless your program modifies the
10467 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
10470 @item -mtrap-precision=@var{trap-precision}
10471 @opindex mtrap-precision
10472 In the Alpha architecture, floating point traps are imprecise. This
10473 means without software assistance it is impossible to recover from a
10474 floating trap and program execution normally needs to be terminated.
10475 GCC can generate code that can assist operating system trap handlers
10476 in determining the exact location that caused a floating point trap.
10477 Depending on the requirements of an application, different levels of
10478 precisions can be selected:
10482 Program precision. This option is the default and means a trap handler
10483 can only identify which program caused a floating point exception.
10486 Function precision. The trap handler can determine the function that
10487 caused a floating point exception.
10490 Instruction precision. The trap handler can determine the exact
10491 instruction that caused a floating point exception.
10494 Other Alpha compilers provide the equivalent options called
10495 @option{-scope_safe} and @option{-resumption_safe}.
10497 @item -mieee-conformant
10498 @opindex mieee-conformant
10499 This option marks the generated code as IEEE conformant. You must not
10500 use this option unless you also specify @option{-mtrap-precision=i} and either
10501 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
10502 is to emit the line @samp{.eflag 48} in the function prologue of the
10503 generated assembly file. Under DEC Unix, this has the effect that
10504 IEEE-conformant math library routines will be linked in.
10506 @item -mbuild-constants
10507 @opindex mbuild-constants
10508 Normally GCC examines a 32- or 64-bit integer constant to
10509 see if it can construct it from smaller constants in two or three
10510 instructions. If it cannot, it will output the constant as a literal and
10511 generate code to load it from the data segment at runtime.
10513 Use this option to require GCC to construct @emph{all} integer constants
10514 using code, even if it takes more instructions (the maximum is six).
10516 You would typically use this option to build a shared library dynamic
10517 loader. Itself a shared library, it must relocate itself in memory
10518 before it can find the variables and constants in its own data segment.
10524 Select whether to generate code to be assembled by the vendor-supplied
10525 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
10543 Indicate whether GCC should generate code to use the optional BWX,
10544 CIX, FIX and MAX instruction sets. The default is to use the instruction
10545 sets supported by the CPU type specified via @option{-mcpu=} option or that
10546 of the CPU on which GCC was built if none was specified.
10549 @itemx -mfloat-ieee
10550 @opindex mfloat-vax
10551 @opindex mfloat-ieee
10552 Generate code that uses (does not use) VAX F and G floating point
10553 arithmetic instead of IEEE single and double precision.
10555 @item -mexplicit-relocs
10556 @itemx -mno-explicit-relocs
10557 @opindex mexplicit-relocs
10558 @opindex mno-explicit-relocs
10559 Older Alpha assemblers provided no way to generate symbol relocations
10560 except via assembler macros. Use of these macros does not allow
10561 optimal instruction scheduling. GNU binutils as of version 2.12
10562 supports a new syntax that allows the compiler to explicitly mark
10563 which relocations should apply to which instructions. This option
10564 is mostly useful for debugging, as GCC detects the capabilities of
10565 the assembler when it is built and sets the default accordingly.
10568 @itemx -mlarge-data
10569 @opindex msmall-data
10570 @opindex mlarge-data
10571 When @option{-mexplicit-relocs} is in effect, static data is
10572 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
10573 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
10574 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
10575 16-bit relocations off of the @code{$gp} register. This limits the
10576 size of the small data area to 64KB, but allows the variables to be
10577 directly accessed via a single instruction.
10579 The default is @option{-mlarge-data}. With this option the data area
10580 is limited to just below 2GB@. Programs that require more than 2GB of
10581 data must use @code{malloc} or @code{mmap} to allocate the data in the
10582 heap instead of in the program's data segment.
10584 When generating code for shared libraries, @option{-fpic} implies
10585 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
10588 @itemx -mlarge-text
10589 @opindex msmall-text
10590 @opindex mlarge-text
10591 When @option{-msmall-text} is used, the compiler assumes that the
10592 code of the entire program (or shared library) fits in 4MB, and is
10593 thus reachable with a branch instruction. When @option{-msmall-data}
10594 is used, the compiler can assume that all local symbols share the
10595 same @code{$gp} value, and thus reduce the number of instructions
10596 required for a function call from 4 to 1.
10598 The default is @option{-mlarge-text}.
10600 @item -mcpu=@var{cpu_type}
10602 Set the instruction set and instruction scheduling parameters for
10603 machine type @var{cpu_type}. You can specify either the @samp{EV}
10604 style name or the corresponding chip number. GCC supports scheduling
10605 parameters for the EV4, EV5 and EV6 family of processors and will
10606 choose the default values for the instruction set from the processor
10607 you specify. If you do not specify a processor type, GCC will default
10608 to the processor on which the compiler was built.
10610 Supported values for @var{cpu_type} are
10616 Schedules as an EV4 and has no instruction set extensions.
10620 Schedules as an EV5 and has no instruction set extensions.
10624 Schedules as an EV5 and supports the BWX extension.
10629 Schedules as an EV5 and supports the BWX and MAX extensions.
10633 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
10637 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
10640 Native Linux/GNU toolchains also support the value @samp{native},
10641 which selects the best architecture option for the host processor.
10642 @option{-mcpu=native} has no effect if GCC does not recognize
10645 @item -mtune=@var{cpu_type}
10647 Set only the instruction scheduling parameters for machine type
10648 @var{cpu_type}. The instruction set is not changed.
10650 Native Linux/GNU toolchains also support the value @samp{native},
10651 which selects the best architecture option for the host processor.
10652 @option{-mtune=native} has no effect if GCC does not recognize
10655 @item -mmemory-latency=@var{time}
10656 @opindex mmemory-latency
10657 Sets the latency the scheduler should assume for typical memory
10658 references as seen by the application. This number is highly
10659 dependent on the memory access patterns used by the application
10660 and the size of the external cache on the machine.
10662 Valid options for @var{time} are
10666 A decimal number representing clock cycles.
10672 The compiler contains estimates of the number of clock cycles for
10673 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
10674 (also called Dcache, Scache, and Bcache), as well as to main memory.
10675 Note that L3 is only valid for EV5.
10680 @node DEC Alpha/VMS Options
10681 @subsection DEC Alpha/VMS Options
10683 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
10686 @item -mvms-return-codes
10687 @opindex mvms-return-codes
10688 Return VMS condition codes from main. The default is to return POSIX
10689 style condition (e.g.@: error) codes.
10691 @item -mdebug-main=@var{prefix}
10692 @opindex mdebug-main=@var{prefix}
10693 Flag the first routine whose name starts with @var{prefix} as the main
10694 routine for the debugger.
10698 Default to 64bit memory allocation routines.
10702 @subsection FR30 Options
10703 @cindex FR30 Options
10705 These options are defined specifically for the FR30 port.
10709 @item -msmall-model
10710 @opindex msmall-model
10711 Use the small address space model. This can produce smaller code, but
10712 it does assume that all symbolic values and addresses will fit into a
10717 Assume that run-time support has been provided and so there is no need
10718 to include the simulator library (@file{libsim.a}) on the linker
10724 @subsection FRV Options
10725 @cindex FRV Options
10731 Only use the first 32 general purpose registers.
10736 Use all 64 general purpose registers.
10741 Use only the first 32 floating point registers.
10746 Use all 64 floating point registers
10749 @opindex mhard-float
10751 Use hardware instructions for floating point operations.
10754 @opindex msoft-float
10756 Use library routines for floating point operations.
10761 Dynamically allocate condition code registers.
10766 Do not try to dynamically allocate condition code registers, only
10767 use @code{icc0} and @code{fcc0}.
10772 Change ABI to use double word insns.
10777 Do not use double word instructions.
10782 Use floating point double instructions.
10785 @opindex mno-double
10787 Do not use floating point double instructions.
10792 Use media instructions.
10797 Do not use media instructions.
10802 Use multiply and add/subtract instructions.
10805 @opindex mno-muladd
10807 Do not use multiply and add/subtract instructions.
10812 Select the FDPIC ABI, that uses function descriptors to represent
10813 pointers to functions. Without any PIC/PIE-related options, it
10814 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
10815 assumes GOT entries and small data are within a 12-bit range from the
10816 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
10817 are computed with 32 bits.
10818 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10821 @opindex minline-plt
10823 Enable inlining of PLT entries in function calls to functions that are
10824 not known to bind locally. It has no effect without @option{-mfdpic}.
10825 It's enabled by default if optimizing for speed and compiling for
10826 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
10827 optimization option such as @option{-O3} or above is present in the
10833 Assume a large TLS segment when generating thread-local code.
10838 Do not assume a large TLS segment when generating thread-local code.
10843 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
10844 that is known to be in read-only sections. It's enabled by default,
10845 except for @option{-fpic} or @option{-fpie}: even though it may help
10846 make the global offset table smaller, it trades 1 instruction for 4.
10847 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
10848 one of which may be shared by multiple symbols, and it avoids the need
10849 for a GOT entry for the referenced symbol, so it's more likely to be a
10850 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
10852 @item -multilib-library-pic
10853 @opindex multilib-library-pic
10855 Link with the (library, not FD) pic libraries. It's implied by
10856 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
10857 @option{-fpic} without @option{-mfdpic}. You should never have to use
10861 @opindex mlinked-fp
10863 Follow the EABI requirement of always creating a frame pointer whenever
10864 a stack frame is allocated. This option is enabled by default and can
10865 be disabled with @option{-mno-linked-fp}.
10868 @opindex mlong-calls
10870 Use indirect addressing to call functions outside the current
10871 compilation unit. This allows the functions to be placed anywhere
10872 within the 32-bit address space.
10874 @item -malign-labels
10875 @opindex malign-labels
10877 Try to align labels to an 8-byte boundary by inserting nops into the
10878 previous packet. This option only has an effect when VLIW packing
10879 is enabled. It doesn't create new packets; it merely adds nops to
10882 @item -mlibrary-pic
10883 @opindex mlibrary-pic
10885 Generate position-independent EABI code.
10890 Use only the first four media accumulator registers.
10895 Use all eight media accumulator registers.
10900 Pack VLIW instructions.
10905 Do not pack VLIW instructions.
10908 @opindex mno-eflags
10910 Do not mark ABI switches in e_flags.
10913 @opindex mcond-move
10915 Enable the use of conditional-move instructions (default).
10917 This switch is mainly for debugging the compiler and will likely be removed
10918 in a future version.
10920 @item -mno-cond-move
10921 @opindex mno-cond-move
10923 Disable the use of conditional-move instructions.
10925 This switch is mainly for debugging the compiler and will likely be removed
10926 in a future version.
10931 Enable the use of conditional set instructions (default).
10933 This switch is mainly for debugging the compiler and will likely be removed
10934 in a future version.
10939 Disable the use of conditional set instructions.
10941 This switch is mainly for debugging the compiler and will likely be removed
10942 in a future version.
10945 @opindex mcond-exec
10947 Enable the use of conditional execution (default).
10949 This switch is mainly for debugging the compiler and will likely be removed
10950 in a future version.
10952 @item -mno-cond-exec
10953 @opindex mno-cond-exec
10955 Disable the use of conditional execution.
10957 This switch is mainly for debugging the compiler and will likely be removed
10958 in a future version.
10960 @item -mvliw-branch
10961 @opindex mvliw-branch
10963 Run a pass to pack branches into VLIW instructions (default).
10965 This switch is mainly for debugging the compiler and will likely be removed
10966 in a future version.
10968 @item -mno-vliw-branch
10969 @opindex mno-vliw-branch
10971 Do not run a pass to pack branches into VLIW instructions.
10973 This switch is mainly for debugging the compiler and will likely be removed
10974 in a future version.
10976 @item -mmulti-cond-exec
10977 @opindex mmulti-cond-exec
10979 Enable optimization of @code{&&} and @code{||} in conditional execution
10982 This switch is mainly for debugging the compiler and will likely be removed
10983 in a future version.
10985 @item -mno-multi-cond-exec
10986 @opindex mno-multi-cond-exec
10988 Disable optimization of @code{&&} and @code{||} in conditional execution.
10990 This switch is mainly for debugging the compiler and will likely be removed
10991 in a future version.
10993 @item -mnested-cond-exec
10994 @opindex mnested-cond-exec
10996 Enable nested conditional execution optimizations (default).
10998 This switch is mainly for debugging the compiler and will likely be removed
10999 in a future version.
11001 @item -mno-nested-cond-exec
11002 @opindex mno-nested-cond-exec
11004 Disable nested conditional execution optimizations.
11006 This switch is mainly for debugging the compiler and will likely be removed
11007 in a future version.
11009 @item -moptimize-membar
11010 @opindex moptimize-membar
11012 This switch removes redundant @code{membar} instructions from the
11013 compiler generated code. It is enabled by default.
11015 @item -mno-optimize-membar
11016 @opindex mno-optimize-membar
11018 This switch disables the automatic removal of redundant @code{membar}
11019 instructions from the generated code.
11021 @item -mtomcat-stats
11022 @opindex mtomcat-stats
11024 Cause gas to print out tomcat statistics.
11026 @item -mcpu=@var{cpu}
11029 Select the processor type for which to generate code. Possible values are
11030 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
11031 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
11035 @node GNU/Linux Options
11036 @subsection GNU/Linux Options
11038 These @samp{-m} options are defined for GNU/Linux targets:
11043 Use the GNU C library instead of uClibc. This is the default except
11044 on @samp{*-*-linux-*uclibc*} targets.
11048 Use uClibc instead of the GNU C library. This is the default on
11049 @samp{*-*-linux-*uclibc*} targets.
11052 @node H8/300 Options
11053 @subsection H8/300 Options
11055 These @samp{-m} options are defined for the H8/300 implementations:
11060 Shorten some address references at link time, when possible; uses the
11061 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
11062 ld, Using ld}, for a fuller description.
11066 Generate code for the H8/300H@.
11070 Generate code for the H8S@.
11074 Generate code for the H8S and H8/300H in the normal mode. This switch
11075 must be used either with @option{-mh} or @option{-ms}.
11079 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
11083 Make @code{int} data 32 bits by default.
11086 @opindex malign-300
11087 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
11088 The default for the H8/300H and H8S is to align longs and floats on 4
11090 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
11091 This option has no effect on the H8/300.
11095 @subsection HPPA Options
11096 @cindex HPPA Options
11098 These @samp{-m} options are defined for the HPPA family of computers:
11101 @item -march=@var{architecture-type}
11103 Generate code for the specified architecture. The choices for
11104 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
11105 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
11106 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
11107 architecture option for your machine. Code compiled for lower numbered
11108 architectures will run on higher numbered architectures, but not the
11111 @item -mpa-risc-1-0
11112 @itemx -mpa-risc-1-1
11113 @itemx -mpa-risc-2-0
11114 @opindex mpa-risc-1-0
11115 @opindex mpa-risc-1-1
11116 @opindex mpa-risc-2-0
11117 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
11120 @opindex mbig-switch
11121 Generate code suitable for big switch tables. Use this option only if
11122 the assembler/linker complain about out of range branches within a switch
11125 @item -mjump-in-delay
11126 @opindex mjump-in-delay
11127 Fill delay slots of function calls with unconditional jump instructions
11128 by modifying the return pointer for the function call to be the target
11129 of the conditional jump.
11131 @item -mdisable-fpregs
11132 @opindex mdisable-fpregs
11133 Prevent floating point registers from being used in any manner. This is
11134 necessary for compiling kernels which perform lazy context switching of
11135 floating point registers. If you use this option and attempt to perform
11136 floating point operations, the compiler will abort.
11138 @item -mdisable-indexing
11139 @opindex mdisable-indexing
11140 Prevent the compiler from using indexing address modes. This avoids some
11141 rather obscure problems when compiling MIG generated code under MACH@.
11143 @item -mno-space-regs
11144 @opindex mno-space-regs
11145 Generate code that assumes the target has no space registers. This allows
11146 GCC to generate faster indirect calls and use unscaled index address modes.
11148 Such code is suitable for level 0 PA systems and kernels.
11150 @item -mfast-indirect-calls
11151 @opindex mfast-indirect-calls
11152 Generate code that assumes calls never cross space boundaries. This
11153 allows GCC to emit code which performs faster indirect calls.
11155 This option will not work in the presence of shared libraries or nested
11158 @item -mfixed-range=@var{register-range}
11159 @opindex mfixed-range
11160 Generate code treating the given register range as fixed registers.
11161 A fixed register is one that the register allocator can not use. This is
11162 useful when compiling kernel code. A register range is specified as
11163 two registers separated by a dash. Multiple register ranges can be
11164 specified separated by a comma.
11166 @item -mlong-load-store
11167 @opindex mlong-load-store
11168 Generate 3-instruction load and store sequences as sometimes required by
11169 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
11172 @item -mportable-runtime
11173 @opindex mportable-runtime
11174 Use the portable calling conventions proposed by HP for ELF systems.
11178 Enable the use of assembler directives only GAS understands.
11180 @item -mschedule=@var{cpu-type}
11182 Schedule code according to the constraints for the machine type
11183 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
11184 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
11185 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
11186 proper scheduling option for your machine. The default scheduling is
11190 @opindex mlinker-opt
11191 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
11192 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
11193 linkers in which they give bogus error messages when linking some programs.
11196 @opindex msoft-float
11197 Generate output containing library calls for floating point.
11198 @strong{Warning:} the requisite libraries are not available for all HPPA
11199 targets. Normally the facilities of the machine's usual C compiler are
11200 used, but this cannot be done directly in cross-compilation. You must make
11201 your own arrangements to provide suitable library functions for
11204 @option{-msoft-float} changes the calling convention in the output file;
11205 therefore, it is only useful if you compile @emph{all} of a program with
11206 this option. In particular, you need to compile @file{libgcc.a}, the
11207 library that comes with GCC, with @option{-msoft-float} in order for
11212 Generate the predefine, @code{_SIO}, for server IO@. The default is
11213 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
11214 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
11215 options are available under HP-UX and HI-UX@.
11219 Use GNU ld specific options. This passes @option{-shared} to ld when
11220 building a shared library. It is the default when GCC is configured,
11221 explicitly or implicitly, with the GNU linker. This option does not
11222 have any affect on which ld is called, it only changes what parameters
11223 are passed to that ld. The ld that is called is determined by the
11224 @option{--with-ld} configure option, GCC's program search path, and
11225 finally by the user's @env{PATH}. The linker used by GCC can be printed
11226 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
11227 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
11231 Use HP ld specific options. This passes @option{-b} to ld when building
11232 a shared library and passes @option{+Accept TypeMismatch} to ld on all
11233 links. It is the default when GCC is configured, explicitly or
11234 implicitly, with the HP linker. This option does not have any affect on
11235 which ld is called, it only changes what parameters are passed to that
11236 ld. The ld that is called is determined by the @option{--with-ld}
11237 configure option, GCC's program search path, and finally by the user's
11238 @env{PATH}. The linker used by GCC can be printed using @samp{which
11239 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
11240 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
11243 @opindex mno-long-calls
11244 Generate code that uses long call sequences. This ensures that a call
11245 is always able to reach linker generated stubs. The default is to generate
11246 long calls only when the distance from the call site to the beginning
11247 of the function or translation unit, as the case may be, exceeds a
11248 predefined limit set by the branch type being used. The limits for
11249 normal calls are 7,600,000 and 240,000 bytes, respectively for the
11250 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
11253 Distances are measured from the beginning of functions when using the
11254 @option{-ffunction-sections} option, or when using the @option{-mgas}
11255 and @option{-mno-portable-runtime} options together under HP-UX with
11258 It is normally not desirable to use this option as it will degrade
11259 performance. However, it may be useful in large applications,
11260 particularly when partial linking is used to build the application.
11262 The types of long calls used depends on the capabilities of the
11263 assembler and linker, and the type of code being generated. The
11264 impact on systems that support long absolute calls, and long pic
11265 symbol-difference or pc-relative calls should be relatively small.
11266 However, an indirect call is used on 32-bit ELF systems in pic code
11267 and it is quite long.
11269 @item -munix=@var{unix-std}
11271 Generate compiler predefines and select a startfile for the specified
11272 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
11273 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
11274 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
11275 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
11276 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
11279 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
11280 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
11281 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
11282 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
11283 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
11284 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
11286 It is @emph{important} to note that this option changes the interfaces
11287 for various library routines. It also affects the operational behavior
11288 of the C library. Thus, @emph{extreme} care is needed in using this
11291 Library code that is intended to operate with more than one UNIX
11292 standard must test, set and restore the variable @var{__xpg4_extended_mask}
11293 as appropriate. Most GNU software doesn't provide this capability.
11297 Suppress the generation of link options to search libdld.sl when the
11298 @option{-static} option is specified on HP-UX 10 and later.
11302 The HP-UX implementation of setlocale in libc has a dependency on
11303 libdld.sl. There isn't an archive version of libdld.sl. Thus,
11304 when the @option{-static} option is specified, special link options
11305 are needed to resolve this dependency.
11307 On HP-UX 10 and later, the GCC driver adds the necessary options to
11308 link with libdld.sl when the @option{-static} option is specified.
11309 This causes the resulting binary to be dynamic. On the 64-bit port,
11310 the linkers generate dynamic binaries by default in any case. The
11311 @option{-nolibdld} option can be used to prevent the GCC driver from
11312 adding these link options.
11316 Add support for multithreading with the @dfn{dce thread} library
11317 under HP-UX@. This option sets flags for both the preprocessor and
11321 @node i386 and x86-64 Options
11322 @subsection Intel 386 and AMD x86-64 Options
11323 @cindex i386 Options
11324 @cindex x86-64 Options
11325 @cindex Intel 386 Options
11326 @cindex AMD x86-64 Options
11328 These @samp{-m} options are defined for the i386 and x86-64 family of
11332 @item -mtune=@var{cpu-type}
11334 Tune to @var{cpu-type} everything applicable about the generated code, except
11335 for the ABI and the set of available instructions. The choices for
11336 @var{cpu-type} are:
11339 Produce code optimized for the most common IA32/AMD64/EM64T processors.
11340 If you know the CPU on which your code will run, then you should use
11341 the corresponding @option{-mtune} option instead of
11342 @option{-mtune=generic}. But, if you do not know exactly what CPU users
11343 of your application will have, then you should use this option.
11345 As new processors are deployed in the marketplace, the behavior of this
11346 option will change. Therefore, if you upgrade to a newer version of
11347 GCC, the code generated option will change to reflect the processors
11348 that were most common when that version of GCC was released.
11350 There is no @option{-march=generic} option because @option{-march}
11351 indicates the instruction set the compiler can use, and there is no
11352 generic instruction set applicable to all processors. In contrast,
11353 @option{-mtune} indicates the processor (or, in this case, collection of
11354 processors) for which the code is optimized.
11356 This selects the CPU to tune for at compilation time by determining
11357 the processor type of the compiling machine. Using @option{-mtune=native}
11358 will produce code optimized for the local machine under the constraints
11359 of the selected instruction set. Using @option{-march=native} will
11360 enable all instruction subsets supported by the local machine (hence
11361 the result might not run on different machines).
11363 Original Intel's i386 CPU@.
11365 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
11366 @item i586, pentium
11367 Intel Pentium CPU with no MMX support.
11369 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
11371 Intel PentiumPro CPU@.
11373 Same as @code{generic}, but when used as @code{march} option, PentiumPro
11374 instruction set will be used, so the code will run on all i686 family chips.
11376 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
11377 @item pentium3, pentium3m
11378 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
11381 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
11382 support. Used by Centrino notebooks.
11383 @item pentium4, pentium4m
11384 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
11386 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
11389 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
11390 SSE2 and SSE3 instruction set support.
11392 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
11393 instruction set support.
11395 Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
11396 instruction set support.
11398 AMD K6 CPU with MMX instruction set support.
11400 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
11401 @item athlon, athlon-tbird
11402 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
11404 @item athlon-4, athlon-xp, athlon-mp
11405 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
11406 instruction set support.
11407 @item k8, opteron, athlon64, athlon-fx
11408 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
11409 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
11410 @item k8-sse3, opteron-sse3, athlon64-sse3
11411 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
11412 @item amdfam10, barcelona
11413 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
11414 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
11415 instruction set extensions.)
11417 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
11420 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
11421 instruction set support.
11423 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
11424 implemented for this chip.)
11426 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
11427 implemented for this chip.)
11429 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
11432 While picking a specific @var{cpu-type} will schedule things appropriately
11433 for that particular chip, the compiler will not generate any code that
11434 does not run on the i386 without the @option{-march=@var{cpu-type}} option
11437 @item -march=@var{cpu-type}
11439 Generate instructions for the machine type @var{cpu-type}. The choices
11440 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
11441 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
11443 @item -mcpu=@var{cpu-type}
11445 A deprecated synonym for @option{-mtune}.
11447 @item -mfpmath=@var{unit}
11449 Generate floating point arithmetics for selected unit @var{unit}. The choices
11450 for @var{unit} are:
11454 Use the standard 387 floating point coprocessor present majority of chips and
11455 emulated otherwise. Code compiled with this option will run almost everywhere.
11456 The temporary results are computed in 80bit precision instead of precision
11457 specified by the type resulting in slightly different results compared to most
11458 of other chips. See @option{-ffloat-store} for more detailed description.
11460 This is the default choice for i386 compiler.
11463 Use scalar floating point instructions present in the SSE instruction set.
11464 This instruction set is supported by Pentium3 and newer chips, in the AMD line
11465 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
11466 instruction set supports only single precision arithmetics, thus the double and
11467 extended precision arithmetics is still done using 387. Later version, present
11468 only in Pentium4 and the future AMD x86-64 chips supports double precision
11471 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
11472 or @option{-msse2} switches to enable SSE extensions and make this option
11473 effective. For the x86-64 compiler, these extensions are enabled by default.
11475 The resulting code should be considerably faster in the majority of cases and avoid
11476 the numerical instability problems of 387 code, but may break some existing
11477 code that expects temporaries to be 80bit.
11479 This is the default choice for the x86-64 compiler.
11484 Attempt to utilize both instruction sets at once. This effectively double the
11485 amount of available registers and on chips with separate execution units for
11486 387 and SSE the execution resources too. Use this option with care, as it is
11487 still experimental, because the GCC register allocator does not model separate
11488 functional units well resulting in instable performance.
11491 @item -masm=@var{dialect}
11492 @opindex masm=@var{dialect}
11493 Output asm instructions using selected @var{dialect}. Supported
11494 choices are @samp{intel} or @samp{att} (the default one). Darwin does
11495 not support @samp{intel}.
11498 @itemx -mno-ieee-fp
11500 @opindex mno-ieee-fp
11501 Control whether or not the compiler uses IEEE floating point
11502 comparisons. These handle correctly the case where the result of a
11503 comparison is unordered.
11506 @opindex msoft-float
11507 Generate output containing library calls for floating point.
11508 @strong{Warning:} the requisite libraries are not part of GCC@.
11509 Normally the facilities of the machine's usual C compiler are used, but
11510 this can't be done directly in cross-compilation. You must make your
11511 own arrangements to provide suitable library functions for
11514 On machines where a function returns floating point results in the 80387
11515 register stack, some floating point opcodes may be emitted even if
11516 @option{-msoft-float} is used.
11518 @item -mno-fp-ret-in-387
11519 @opindex mno-fp-ret-in-387
11520 Do not use the FPU registers for return values of functions.
11522 The usual calling convention has functions return values of types
11523 @code{float} and @code{double} in an FPU register, even if there
11524 is no FPU@. The idea is that the operating system should emulate
11527 The option @option{-mno-fp-ret-in-387} causes such values to be returned
11528 in ordinary CPU registers instead.
11530 @item -mno-fancy-math-387
11531 @opindex mno-fancy-math-387
11532 Some 387 emulators do not support the @code{sin}, @code{cos} and
11533 @code{sqrt} instructions for the 387. Specify this option to avoid
11534 generating those instructions. This option is the default on FreeBSD,
11535 OpenBSD and NetBSD@. This option is overridden when @option{-march}
11536 indicates that the target cpu will always have an FPU and so the
11537 instruction will not need emulation. As of revision 2.6.1, these
11538 instructions are not generated unless you also use the
11539 @option{-funsafe-math-optimizations} switch.
11541 @item -malign-double
11542 @itemx -mno-align-double
11543 @opindex malign-double
11544 @opindex mno-align-double
11545 Control whether GCC aligns @code{double}, @code{long double}, and
11546 @code{long long} variables on a two word boundary or a one word
11547 boundary. Aligning @code{double} variables on a two word boundary will
11548 produce code that runs somewhat faster on a @samp{Pentium} at the
11549 expense of more memory.
11551 On x86-64, @option{-malign-double} is enabled by default.
11553 @strong{Warning:} if you use the @option{-malign-double} switch,
11554 structures containing the above types will be aligned differently than
11555 the published application binary interface specifications for the 386
11556 and will not be binary compatible with structures in code compiled
11557 without that switch.
11559 @item -m96bit-long-double
11560 @itemx -m128bit-long-double
11561 @opindex m96bit-long-double
11562 @opindex m128bit-long-double
11563 These switches control the size of @code{long double} type. The i386
11564 application binary interface specifies the size to be 96 bits,
11565 so @option{-m96bit-long-double} is the default in 32 bit mode.
11567 Modern architectures (Pentium and newer) would prefer @code{long double}
11568 to be aligned to an 8 or 16 byte boundary. In arrays or structures
11569 conforming to the ABI, this would not be possible. So specifying a
11570 @option{-m128bit-long-double} will align @code{long double}
11571 to a 16 byte boundary by padding the @code{long double} with an additional
11574 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
11575 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
11577 Notice that neither of these options enable any extra precision over the x87
11578 standard of 80 bits for a @code{long double}.
11580 @strong{Warning:} if you override the default value for your target ABI, the
11581 structures and arrays containing @code{long double} variables will change
11582 their size as well as function calling convention for function taking
11583 @code{long double} will be modified. Hence they will not be binary
11584 compatible with arrays or structures in code compiled without that switch.
11586 @item -mlarge-data-threshold=@var{number}
11587 @opindex mlarge-data-threshold=@var{number}
11588 When @option{-mcmodel=medium} is specified, the data greater than
11589 @var{threshold} are placed in large data section. This value must be the
11590 same across all object linked into the binary and defaults to 65535.
11594 Use a different function-calling convention, in which functions that
11595 take a fixed number of arguments return with the @code{ret} @var{num}
11596 instruction, which pops their arguments while returning. This saves one
11597 instruction in the caller since there is no need to pop the arguments
11600 You can specify that an individual function is called with this calling
11601 sequence with the function attribute @samp{stdcall}. You can also
11602 override the @option{-mrtd} option by using the function attribute
11603 @samp{cdecl}. @xref{Function Attributes}.
11605 @strong{Warning:} this calling convention is incompatible with the one
11606 normally used on Unix, so you cannot use it if you need to call
11607 libraries compiled with the Unix compiler.
11609 Also, you must provide function prototypes for all functions that
11610 take variable numbers of arguments (including @code{printf});
11611 otherwise incorrect code will be generated for calls to those
11614 In addition, seriously incorrect code will result if you call a
11615 function with too many arguments. (Normally, extra arguments are
11616 harmlessly ignored.)
11618 @item -mregparm=@var{num}
11620 Control how many registers are used to pass integer arguments. By
11621 default, no registers are used to pass arguments, and at most 3
11622 registers can be used. You can control this behavior for a specific
11623 function by using the function attribute @samp{regparm}.
11624 @xref{Function Attributes}.
11626 @strong{Warning:} if you use this switch, and
11627 @var{num} is nonzero, then you must build all modules with the same
11628 value, including any libraries. This includes the system libraries and
11632 @opindex msseregparm
11633 Use SSE register passing conventions for float and double arguments
11634 and return values. You can control this behavior for a specific
11635 function by using the function attribute @samp{sseregparm}.
11636 @xref{Function Attributes}.
11638 @strong{Warning:} if you use this switch then you must build all
11639 modules with the same value, including any libraries. This includes
11640 the system libraries and startup modules.
11649 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
11650 is specified, the significands of results of floating-point operations are
11651 rounded to 24 bits (single precision); @option{-mpc64} rounds the
11652 significands of results of floating-point operations to 53 bits (double
11653 precision) and @option{-mpc80} rounds the significands of results of
11654 floating-point operations to 64 bits (extended double precision), which is
11655 the default. When this option is used, floating-point operations in higher
11656 precisions are not available to the programmer without setting the FPU
11657 control word explicitly.
11659 Setting the rounding of floating-point operations to less than the default
11660 80 bits can speed some programs by 2% or more. Note that some mathematical
11661 libraries assume that extended precision (80 bit) floating-point operations
11662 are enabled by default; routines in such libraries could suffer significant
11663 loss of accuracy, typically through so-called "catastrophic cancellation",
11664 when this option is used to set the precision to less than extended precision.
11666 @item -mstackrealign
11667 @opindex mstackrealign
11668 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
11669 option will generate an alternate prologue and epilogue that realigns the
11670 runtime stack if necessary. This supports mixing legacy codes that keep
11671 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
11672 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
11673 applicable to individual functions.
11675 @item -mpreferred-stack-boundary=@var{num}
11676 @opindex mpreferred-stack-boundary
11677 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
11678 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
11679 the default is 4 (16 bytes or 128 bits).
11681 @item -mincoming-stack-boundary=@var{num}
11682 @opindex mincoming-stack-boundary
11683 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
11684 boundary. If @option{-mincoming-stack-boundary} is not specified,
11685 the one specified by @option{-mpreferred-stack-boundary} will be used.
11687 On Pentium and PentiumPro, @code{double} and @code{long double} values
11688 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
11689 suffer significant run time performance penalties. On Pentium III, the
11690 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
11691 properly if it is not 16 byte aligned.
11693 To ensure proper alignment of this values on the stack, the stack boundary
11694 must be as aligned as that required by any value stored on the stack.
11695 Further, every function must be generated such that it keeps the stack
11696 aligned. Thus calling a function compiled with a higher preferred
11697 stack boundary from a function compiled with a lower preferred stack
11698 boundary will most likely misalign the stack. It is recommended that
11699 libraries that use callbacks always use the default setting.
11701 This extra alignment does consume extra stack space, and generally
11702 increases code size. Code that is sensitive to stack space usage, such
11703 as embedded systems and operating system kernels, may want to reduce the
11704 preferred alignment to @option{-mpreferred-stack-boundary=2}.
11744 These switches enable or disable the use of instructions in the MMX,
11745 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, FMA4, ABM or
11746 3DNow!@: extended instruction sets.
11747 These extensions are also available as built-in functions: see
11748 @ref{X86 Built-in Functions}, for details of the functions enabled and
11749 disabled by these switches.
11751 To have SSE/SSE2 instructions generated automatically from floating-point
11752 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
11754 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
11755 generates new AVX instructions or AVX equivalence for all SSEx instructions
11758 These options will enable GCC to use these extended instructions in
11759 generated code, even without @option{-mfpmath=sse}. Applications which
11760 perform runtime CPU detection must compile separate files for each
11761 supported architecture, using the appropriate flags. In particular,
11762 the file containing the CPU detection code should be compiled without
11767 This option instructs GCC to emit a @code{cld} instruction in the prologue
11768 of functions that use string instructions. String instructions depend on
11769 the DF flag to select between autoincrement or autodecrement mode. While the
11770 ABI specifies the DF flag to be cleared on function entry, some operating
11771 systems violate this specification by not clearing the DF flag in their
11772 exception dispatchers. The exception handler can be invoked with the DF flag
11773 set which leads to wrong direction mode, when string instructions are used.
11774 This option can be enabled by default on 32-bit x86 targets by configuring
11775 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
11776 instructions can be suppressed with the @option{-mno-cld} compiler option
11781 This option will enable GCC to use CMPXCHG16B instruction in generated code.
11782 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
11783 data types. This is useful for high resolution counters that could be updated
11784 by multiple processors (or cores). This instruction is generated as part of
11785 atomic built-in functions: see @ref{Atomic Builtins} for details.
11789 This option will enable GCC to use SAHF instruction in generated 64-bit code.
11790 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
11791 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
11792 SAHF are load and store instructions, respectively, for certain status flags.
11793 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
11794 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
11798 This option will enable GCC to use movbe instruction to implement
11799 @code{__builtin_bswap32} and @code{__builtin_bswap64}.
11803 This option will enable built-in functions, @code{__builtin_ia32_crc32qi},
11804 @code{__builtin_ia32_crc32hi}. @code{__builtin_ia32_crc32si} and
11805 @code{__builtin_ia32_crc32di} to generate the crc32 machine instruction.
11809 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
11810 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Raphson step
11811 to increase precision instead of DIVSS and SQRTSS (and their vectorized
11812 variants) for single precision floating point arguments. These instructions
11813 are generated only when @option{-funsafe-math-optimizations} is enabled
11814 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
11815 Note that while the throughput of the sequence is higher than the throughput
11816 of the non-reciprocal instruction, the precision of the sequence can be
11817 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
11819 @item -mveclibabi=@var{type}
11820 @opindex mveclibabi
11821 Specifies the ABI type to use for vectorizing intrinsics using an
11822 external library. Supported types are @code{svml} for the Intel short
11823 vector math library and @code{acml} for the AMD math core library style
11824 of interfacing. GCC will currently emit calls to @code{vmldExp2},
11825 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
11826 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
11827 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
11828 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
11829 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
11830 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
11831 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
11832 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
11833 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
11834 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
11835 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
11836 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
11837 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
11838 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
11839 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
11840 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
11841 compatible library will have to be specified at link time.
11843 @item -mabi=@var{name}
11845 Generate code for the specified calling convention. Permissible values
11846 are: @samp{sysv} for the ABI used on GNU/Linux and other systems and
11847 @samp{ms} for the Microsoft ABI. The default is to use the Microsoft
11848 ABI when targeting Windows. On all other systems, the default is the
11849 SYSV ABI. You can control this behavior for a specific function by
11850 using the function attribute @samp{ms_abi}/@samp{sysv_abi}.
11851 @xref{Function Attributes}.
11854 @itemx -mno-push-args
11855 @opindex mpush-args
11856 @opindex mno-push-args
11857 Use PUSH operations to store outgoing parameters. This method is shorter
11858 and usually equally fast as method using SUB/MOV operations and is enabled
11859 by default. In some cases disabling it may improve performance because of
11860 improved scheduling and reduced dependencies.
11862 @item -maccumulate-outgoing-args
11863 @opindex maccumulate-outgoing-args
11864 If enabled, the maximum amount of space required for outgoing arguments will be
11865 computed in the function prologue. This is faster on most modern CPUs
11866 because of reduced dependencies, improved scheduling and reduced stack usage
11867 when preferred stack boundary is not equal to 2. The drawback is a notable
11868 increase in code size. This switch implies @option{-mno-push-args}.
11872 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
11873 on thread-safe exception handling must compile and link all code with the
11874 @option{-mthreads} option. When compiling, @option{-mthreads} defines
11875 @option{-D_MT}; when linking, it links in a special thread helper library
11876 @option{-lmingwthrd} which cleans up per thread exception handling data.
11878 @item -mno-align-stringops
11879 @opindex mno-align-stringops
11880 Do not align destination of inlined string operations. This switch reduces
11881 code size and improves performance in case the destination is already aligned,
11882 but GCC doesn't know about it.
11884 @item -minline-all-stringops
11885 @opindex minline-all-stringops
11886 By default GCC inlines string operations only when destination is known to be
11887 aligned at least to 4 byte boundary. This enables more inlining, increase code
11888 size, but may improve performance of code that depends on fast memcpy, strlen
11889 and memset for short lengths.
11891 @item -minline-stringops-dynamically
11892 @opindex minline-stringops-dynamically
11893 For string operation of unknown size, inline runtime checks so for small
11894 blocks inline code is used, while for large blocks library call is used.
11896 @item -mstringop-strategy=@var{alg}
11897 @opindex mstringop-strategy=@var{alg}
11898 Overwrite internal decision heuristic about particular algorithm to inline
11899 string operation with. The allowed values are @code{rep_byte},
11900 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
11901 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
11902 expanding inline loop, @code{libcall} for always expanding library call.
11904 @item -momit-leaf-frame-pointer
11905 @opindex momit-leaf-frame-pointer
11906 Don't keep the frame pointer in a register for leaf functions. This
11907 avoids the instructions to save, set up and restore frame pointers and
11908 makes an extra register available in leaf functions. The option
11909 @option{-fomit-frame-pointer} removes the frame pointer for all functions
11910 which might make debugging harder.
11912 @item -mtls-direct-seg-refs
11913 @itemx -mno-tls-direct-seg-refs
11914 @opindex mtls-direct-seg-refs
11915 Controls whether TLS variables may be accessed with offsets from the
11916 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
11917 or whether the thread base pointer must be added. Whether or not this
11918 is legal depends on the operating system, and whether it maps the
11919 segment to cover the entire TLS area.
11921 For systems that use GNU libc, the default is on.
11924 @itemx -mno-sse2avx
11926 Specify that the assembler should encode SSE instructions with VEX
11927 prefix. The option @option{-mavx} turns this on by default.
11930 These @samp{-m} switches are supported in addition to the above
11931 on AMD x86-64 processors in 64-bit environments.
11938 Generate code for a 32-bit or 64-bit environment.
11939 The 32-bit environment sets int, long and pointer to 32 bits and
11940 generates code that runs on any i386 system.
11941 The 64-bit environment sets int to 32 bits and long and pointer
11942 to 64 bits and generates code for AMD's x86-64 architecture. For
11943 darwin only the -m64 option turns off the @option{-fno-pic} and
11944 @option{-mdynamic-no-pic} options.
11946 @item -mno-red-zone
11947 @opindex mno-red-zone
11948 Do not use a so called red zone for x86-64 code. The red zone is mandated
11949 by the x86-64 ABI, it is a 128-byte area beyond the location of the
11950 stack pointer that will not be modified by signal or interrupt handlers
11951 and therefore can be used for temporary data without adjusting the stack
11952 pointer. The flag @option{-mno-red-zone} disables this red zone.
11954 @item -mcmodel=small
11955 @opindex mcmodel=small
11956 Generate code for the small code model: the program and its symbols must
11957 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11958 Programs can be statically or dynamically linked. This is the default
11961 @item -mcmodel=kernel
11962 @opindex mcmodel=kernel
11963 Generate code for the kernel code model. The kernel runs in the
11964 negative 2 GB of the address space.
11965 This model has to be used for Linux kernel code.
11967 @item -mcmodel=medium
11968 @opindex mcmodel=medium
11969 Generate code for the medium model: The program is linked in the lower 2
11970 GB of the address space. Small symbols are also placed there. Symbols
11971 with sizes larger than @option{-mlarge-data-threshold} are put into
11972 large data or bss sections and can be located above 2GB. Programs can
11973 be statically or dynamically linked.
11975 @item -mcmodel=large
11976 @opindex mcmodel=large
11977 Generate code for the large model: This model makes no assumptions
11978 about addresses and sizes of sections.
11981 @node IA-64 Options
11982 @subsection IA-64 Options
11983 @cindex IA-64 Options
11985 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11989 @opindex mbig-endian
11990 Generate code for a big endian target. This is the default for HP-UX@.
11992 @item -mlittle-endian
11993 @opindex mlittle-endian
11994 Generate code for a little endian target. This is the default for AIX5
12000 @opindex mno-gnu-as
12001 Generate (or don't) code for the GNU assembler. This is the default.
12002 @c Also, this is the default if the configure option @option{--with-gnu-as}
12008 @opindex mno-gnu-ld
12009 Generate (or don't) code for the GNU linker. This is the default.
12010 @c Also, this is the default if the configure option @option{--with-gnu-ld}
12015 Generate code that does not use a global pointer register. The result
12016 is not position independent code, and violates the IA-64 ABI@.
12018 @item -mvolatile-asm-stop
12019 @itemx -mno-volatile-asm-stop
12020 @opindex mvolatile-asm-stop
12021 @opindex mno-volatile-asm-stop
12022 Generate (or don't) a stop bit immediately before and after volatile asm
12025 @item -mregister-names
12026 @itemx -mno-register-names
12027 @opindex mregister-names
12028 @opindex mno-register-names
12029 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
12030 the stacked registers. This may make assembler output more readable.
12036 Disable (or enable) optimizations that use the small data section. This may
12037 be useful for working around optimizer bugs.
12039 @item -mconstant-gp
12040 @opindex mconstant-gp
12041 Generate code that uses a single constant global pointer value. This is
12042 useful when compiling kernel code.
12046 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
12047 This is useful when compiling firmware code.
12049 @item -minline-float-divide-min-latency
12050 @opindex minline-float-divide-min-latency
12051 Generate code for inline divides of floating point values
12052 using the minimum latency algorithm.
12054 @item -minline-float-divide-max-throughput
12055 @opindex minline-float-divide-max-throughput
12056 Generate code for inline divides of floating point values
12057 using the maximum throughput algorithm.
12059 @item -mno-inline-float-divide
12060 @opindex mno-inline-float-divide
12061 Do not generate inline code for divides of floating point values.
12063 @item -minline-int-divide-min-latency
12064 @opindex minline-int-divide-min-latency
12065 Generate code for inline divides of integer values
12066 using the minimum latency algorithm.
12068 @item -minline-int-divide-max-throughput
12069 @opindex minline-int-divide-max-throughput
12070 Generate code for inline divides of integer values
12071 using the maximum throughput algorithm.
12073 @item -mno-inline-int-divide
12074 @opindex mno-inline-int-divide
12075 Do not generate inline code for divides of integer values.
12077 @item -minline-sqrt-min-latency
12078 @opindex minline-sqrt-min-latency
12079 Generate code for inline square roots
12080 using the minimum latency algorithm.
12082 @item -minline-sqrt-max-throughput
12083 @opindex minline-sqrt-max-throughput
12084 Generate code for inline square roots
12085 using the maximum throughput algorithm.
12087 @item -mno-inline-sqrt
12088 @opindex mno-inline-sqrt
12089 Do not generate inline code for sqrt.
12092 @itemx -mno-fused-madd
12093 @opindex mfused-madd
12094 @opindex mno-fused-madd
12095 Do (don't) generate code that uses the fused multiply/add or multiply/subtract
12096 instructions. The default is to use these instructions.
12098 @item -mno-dwarf2-asm
12099 @itemx -mdwarf2-asm
12100 @opindex mno-dwarf2-asm
12101 @opindex mdwarf2-asm
12102 Don't (or do) generate assembler code for the DWARF2 line number debugging
12103 info. This may be useful when not using the GNU assembler.
12105 @item -mearly-stop-bits
12106 @itemx -mno-early-stop-bits
12107 @opindex mearly-stop-bits
12108 @opindex mno-early-stop-bits
12109 Allow stop bits to be placed earlier than immediately preceding the
12110 instruction that triggered the stop bit. This can improve instruction
12111 scheduling, but does not always do so.
12113 @item -mfixed-range=@var{register-range}
12114 @opindex mfixed-range
12115 Generate code treating the given register range as fixed registers.
12116 A fixed register is one that the register allocator can not use. This is
12117 useful when compiling kernel code. A register range is specified as
12118 two registers separated by a dash. Multiple register ranges can be
12119 specified separated by a comma.
12121 @item -mtls-size=@var{tls-size}
12123 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
12126 @item -mtune=@var{cpu-type}
12128 Tune the instruction scheduling for a particular CPU, Valid values are
12129 itanium, itanium1, merced, itanium2, and mckinley.
12135 Generate code for a 32-bit or 64-bit environment.
12136 The 32-bit environment sets int, long and pointer to 32 bits.
12137 The 64-bit environment sets int to 32 bits and long and pointer
12138 to 64 bits. These are HP-UX specific flags.
12140 @item -mno-sched-br-data-spec
12141 @itemx -msched-br-data-spec
12142 @opindex mno-sched-br-data-spec
12143 @opindex msched-br-data-spec
12144 (Dis/En)able data speculative scheduling before reload.
12145 This will result in generation of the ld.a instructions and
12146 the corresponding check instructions (ld.c / chk.a).
12147 The default is 'disable'.
12149 @item -msched-ar-data-spec
12150 @itemx -mno-sched-ar-data-spec
12151 @opindex msched-ar-data-spec
12152 @opindex mno-sched-ar-data-spec
12153 (En/Dis)able data speculative scheduling after reload.
12154 This will result in generation of the ld.a instructions and
12155 the corresponding check instructions (ld.c / chk.a).
12156 The default is 'enable'.
12158 @item -mno-sched-control-spec
12159 @itemx -msched-control-spec
12160 @opindex mno-sched-control-spec
12161 @opindex msched-control-spec
12162 (Dis/En)able control speculative scheduling. This feature is
12163 available only during region scheduling (i.e.@: before reload).
12164 This will result in generation of the ld.s instructions and
12165 the corresponding check instructions chk.s .
12166 The default is 'disable'.
12168 @item -msched-br-in-data-spec
12169 @itemx -mno-sched-br-in-data-spec
12170 @opindex msched-br-in-data-spec
12171 @opindex mno-sched-br-in-data-spec
12172 (En/Dis)able speculative scheduling of the instructions that
12173 are dependent on the data speculative loads before reload.
12174 This is effective only with @option{-msched-br-data-spec} enabled.
12175 The default is 'enable'.
12177 @item -msched-ar-in-data-spec
12178 @itemx -mno-sched-ar-in-data-spec
12179 @opindex msched-ar-in-data-spec
12180 @opindex mno-sched-ar-in-data-spec
12181 (En/Dis)able speculative scheduling of the instructions that
12182 are dependent on the data speculative loads after reload.
12183 This is effective only with @option{-msched-ar-data-spec} enabled.
12184 The default is 'enable'.
12186 @item -msched-in-control-spec
12187 @itemx -mno-sched-in-control-spec
12188 @opindex msched-in-control-spec
12189 @opindex mno-sched-in-control-spec
12190 (En/Dis)able speculative scheduling of the instructions that
12191 are dependent on the control speculative loads.
12192 This is effective only with @option{-msched-control-spec} enabled.
12193 The default is 'enable'.
12195 @item -mno-sched-prefer-non-data-spec-insns
12196 @itemx -msched-prefer-non-data-spec-insns
12197 @opindex mno-sched-prefer-non-data-spec-insns
12198 @opindex msched-prefer-non-data-spec-insns
12199 If enabled, data speculative instructions will be chosen for schedule
12200 only if there are no other choices at the moment. This will make
12201 the use of the data speculation much more conservative.
12202 The default is 'disable'.
12204 @item -mno-sched-prefer-non-control-spec-insns
12205 @itemx -msched-prefer-non-control-spec-insns
12206 @opindex mno-sched-prefer-non-control-spec-insns
12207 @opindex msched-prefer-non-control-spec-insns
12208 If enabled, control speculative instructions will be chosen for schedule
12209 only if there are no other choices at the moment. This will make
12210 the use of the control speculation much more conservative.
12211 The default is 'disable'.
12213 @item -mno-sched-count-spec-in-critical-path
12214 @itemx -msched-count-spec-in-critical-path
12215 @opindex mno-sched-count-spec-in-critical-path
12216 @opindex msched-count-spec-in-critical-path
12217 If enabled, speculative dependencies will be considered during
12218 computation of the instructions priorities. This will make the use of the
12219 speculation a bit more conservative.
12220 The default is 'disable'.
12222 @item -msched-spec-ldc
12223 @opindex msched-spec-ldc
12224 Use a simple data speculation check. This option is on by default.
12226 @item -msched-control-spec-ldc
12227 @opindex msched-spec-ldc
12228 Use a simple check for control speculation. This option is on by default.
12230 @item -msched-stop-bits-after-every-cycle
12231 @opindex msched-stop-bits-after-every-cycle
12232 Place a stop bit after every cycle when scheduling. This option is on
12235 @item -msched-fp-mem-deps-zero-cost
12236 @opindex msched-fp-mem-deps-zero-cost
12237 Assume that floating-point stores and loads are not likely to cause a conflict
12238 when placed into the same instruction group. This option is disabled by
12241 @item -msel-sched-dont-check-control-spec
12242 @opindex msel-sched-dont-check-control-spec
12243 Generate checks for control speculation in selective scheduling.
12244 This flag is disabled by default.
12246 @item -msched-max-memory-insns=@var{max-insns}
12247 @opindex msched-max-memory-insns
12248 Limit on the number of memory insns per instruction group, giving lower
12249 priority to subsequent memory insns attempting to schedule in the same
12250 instruction group. Frequently useful to prevent cache bank conflicts.
12251 The default value is 1.
12253 @item -msched-max-memory-insns-hard-limit
12254 @opindex msched-max-memory-insns-hard-limit
12255 Disallow more than `msched-max-memory-insns' in instruction group.
12256 Otherwise, limit is `soft' meaning that we would prefer non-memory operations
12257 when limit is reached but may still schedule memory operations.
12261 @node IA-64/VMS Options
12262 @subsection IA-64/VMS Options
12264 These @samp{-m} options are defined for the IA-64/VMS implementations:
12267 @item -mvms-return-codes
12268 @opindex mvms-return-codes
12269 Return VMS condition codes from main. The default is to return POSIX
12270 style condition (e.g.@ error) codes.
12272 @item -mdebug-main=@var{prefix}
12273 @opindex mdebug-main=@var{prefix}
12274 Flag the first routine whose name starts with @var{prefix} as the main
12275 routine for the debugger.
12279 Default to 64bit memory allocation routines.
12283 @subsection M32C Options
12284 @cindex M32C options
12287 @item -mcpu=@var{name}
12289 Select the CPU for which code is generated. @var{name} may be one of
12290 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
12291 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
12292 the M32C/80 series.
12296 Specifies that the program will be run on the simulator. This causes
12297 an alternate runtime library to be linked in which supports, for
12298 example, file I/O@. You must not use this option when generating
12299 programs that will run on real hardware; you must provide your own
12300 runtime library for whatever I/O functions are needed.
12302 @item -memregs=@var{number}
12304 Specifies the number of memory-based pseudo-registers GCC will use
12305 during code generation. These pseudo-registers will be used like real
12306 registers, so there is a tradeoff between GCC's ability to fit the
12307 code into available registers, and the performance penalty of using
12308 memory instead of registers. Note that all modules in a program must
12309 be compiled with the same value for this option. Because of that, you
12310 must not use this option with the default runtime libraries gcc
12315 @node M32R/D Options
12316 @subsection M32R/D Options
12317 @cindex M32R/D options
12319 These @option{-m} options are defined for Renesas M32R/D architectures:
12324 Generate code for the M32R/2@.
12328 Generate code for the M32R/X@.
12332 Generate code for the M32R@. This is the default.
12334 @item -mmodel=small
12335 @opindex mmodel=small
12336 Assume all objects live in the lower 16MB of memory (so that their addresses
12337 can be loaded with the @code{ld24} instruction), and assume all subroutines
12338 are reachable with the @code{bl} instruction.
12339 This is the default.
12341 The addressability of a particular object can be set with the
12342 @code{model} attribute.
12344 @item -mmodel=medium
12345 @opindex mmodel=medium
12346 Assume objects may be anywhere in the 32-bit address space (the compiler
12347 will generate @code{seth/add3} instructions to load their addresses), and
12348 assume all subroutines are reachable with the @code{bl} instruction.
12350 @item -mmodel=large
12351 @opindex mmodel=large
12352 Assume objects may be anywhere in the 32-bit address space (the compiler
12353 will generate @code{seth/add3} instructions to load their addresses), and
12354 assume subroutines may not be reachable with the @code{bl} instruction
12355 (the compiler will generate the much slower @code{seth/add3/jl}
12356 instruction sequence).
12359 @opindex msdata=none
12360 Disable use of the small data area. Variables will be put into
12361 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
12362 @code{section} attribute has been specified).
12363 This is the default.
12365 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
12366 Objects may be explicitly put in the small data area with the
12367 @code{section} attribute using one of these sections.
12369 @item -msdata=sdata
12370 @opindex msdata=sdata
12371 Put small global and static data in the small data area, but do not
12372 generate special code to reference them.
12375 @opindex msdata=use
12376 Put small global and static data in the small data area, and generate
12377 special instructions to reference them.
12381 @cindex smaller data references
12382 Put global and static objects less than or equal to @var{num} bytes
12383 into the small data or bss sections instead of the normal data or bss
12384 sections. The default value of @var{num} is 8.
12385 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
12386 for this option to have any effect.
12388 All modules should be compiled with the same @option{-G @var{num}} value.
12389 Compiling with different values of @var{num} may or may not work; if it
12390 doesn't the linker will give an error message---incorrect code will not be
12395 Makes the M32R specific code in the compiler display some statistics
12396 that might help in debugging programs.
12398 @item -malign-loops
12399 @opindex malign-loops
12400 Align all loops to a 32-byte boundary.
12402 @item -mno-align-loops
12403 @opindex mno-align-loops
12404 Do not enforce a 32-byte alignment for loops. This is the default.
12406 @item -missue-rate=@var{number}
12407 @opindex missue-rate=@var{number}
12408 Issue @var{number} instructions per cycle. @var{number} can only be 1
12411 @item -mbranch-cost=@var{number}
12412 @opindex mbranch-cost=@var{number}
12413 @var{number} can only be 1 or 2. If it is 1 then branches will be
12414 preferred over conditional code, if it is 2, then the opposite will
12417 @item -mflush-trap=@var{number}
12418 @opindex mflush-trap=@var{number}
12419 Specifies the trap number to use to flush the cache. The default is
12420 12. Valid numbers are between 0 and 15 inclusive.
12422 @item -mno-flush-trap
12423 @opindex mno-flush-trap
12424 Specifies that the cache cannot be flushed by using a trap.
12426 @item -mflush-func=@var{name}
12427 @opindex mflush-func=@var{name}
12428 Specifies the name of the operating system function to call to flush
12429 the cache. The default is @emph{_flush_cache}, but a function call
12430 will only be used if a trap is not available.
12432 @item -mno-flush-func
12433 @opindex mno-flush-func
12434 Indicates that there is no OS function for flushing the cache.
12438 @node M680x0 Options
12439 @subsection M680x0 Options
12440 @cindex M680x0 options
12442 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
12443 The default settings depend on which architecture was selected when
12444 the compiler was configured; the defaults for the most common choices
12448 @item -march=@var{arch}
12450 Generate code for a specific M680x0 or ColdFire instruction set
12451 architecture. Permissible values of @var{arch} for M680x0
12452 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
12453 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
12454 architectures are selected according to Freescale's ISA classification
12455 and the permissible values are: @samp{isaa}, @samp{isaaplus},
12456 @samp{isab} and @samp{isac}.
12458 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
12459 code for a ColdFire target. The @var{arch} in this macro is one of the
12460 @option{-march} arguments given above.
12462 When used together, @option{-march} and @option{-mtune} select code
12463 that runs on a family of similar processors but that is optimized
12464 for a particular microarchitecture.
12466 @item -mcpu=@var{cpu}
12468 Generate code for a specific M680x0 or ColdFire processor.
12469 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
12470 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
12471 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
12472 below, which also classifies the CPUs into families:
12474 @multitable @columnfractions 0.20 0.80
12475 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
12476 @item @samp{51} @tab @samp{51} @samp{51ac} @samp{51cn} @samp{51em} @samp{51qe}
12477 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
12478 @item @samp{5206e} @tab @samp{5206e}
12479 @item @samp{5208} @tab @samp{5207} @samp{5208}
12480 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
12481 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
12482 @item @samp{5216} @tab @samp{5214} @samp{5216}
12483 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
12484 @item @samp{5225} @tab @samp{5224} @samp{5225}
12485 @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259}
12486 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
12487 @item @samp{5249} @tab @samp{5249}
12488 @item @samp{5250} @tab @samp{5250}
12489 @item @samp{5271} @tab @samp{5270} @samp{5271}
12490 @item @samp{5272} @tab @samp{5272}
12491 @item @samp{5275} @tab @samp{5274} @samp{5275}
12492 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
12493 @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017}
12494 @item @samp{5307} @tab @samp{5307}
12495 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
12496 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
12497 @item @samp{5407} @tab @samp{5407}
12498 @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}
12501 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
12502 @var{arch} is compatible with @var{cpu}. Other combinations of
12503 @option{-mcpu} and @option{-march} are rejected.
12505 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
12506 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
12507 where the value of @var{family} is given by the table above.
12509 @item -mtune=@var{tune}
12511 Tune the code for a particular microarchitecture, within the
12512 constraints set by @option{-march} and @option{-mcpu}.
12513 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
12514 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
12515 and @samp{cpu32}. The ColdFire microarchitectures
12516 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
12518 You can also use @option{-mtune=68020-40} for code that needs
12519 to run relatively well on 68020, 68030 and 68040 targets.
12520 @option{-mtune=68020-60} is similar but includes 68060 targets
12521 as well. These two options select the same tuning decisions as
12522 @option{-m68020-40} and @option{-m68020-60} respectively.
12524 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
12525 when tuning for 680x0 architecture @var{arch}. It also defines
12526 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
12527 option is used. If gcc is tuning for a range of architectures,
12528 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
12529 it defines the macros for every architecture in the range.
12531 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
12532 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
12533 of the arguments given above.
12539 Generate output for a 68000. This is the default
12540 when the compiler is configured for 68000-based systems.
12541 It is equivalent to @option{-march=68000}.
12543 Use this option for microcontrollers with a 68000 or EC000 core,
12544 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
12548 Generate output for a 68010. This is the default
12549 when the compiler is configured for 68010-based systems.
12550 It is equivalent to @option{-march=68010}.
12556 Generate output for a 68020. This is the default
12557 when the compiler is configured for 68020-based systems.
12558 It is equivalent to @option{-march=68020}.
12562 Generate output for a 68030. This is the default when the compiler is
12563 configured for 68030-based systems. It is equivalent to
12564 @option{-march=68030}.
12568 Generate output for a 68040. This is the default when the compiler is
12569 configured for 68040-based systems. It is equivalent to
12570 @option{-march=68040}.
12572 This option inhibits the use of 68881/68882 instructions that have to be
12573 emulated by software on the 68040. Use this option if your 68040 does not
12574 have code to emulate those instructions.
12578 Generate output for a 68060. This is the default when the compiler is
12579 configured for 68060-based systems. It is equivalent to
12580 @option{-march=68060}.
12582 This option inhibits the use of 68020 and 68881/68882 instructions that
12583 have to be emulated by software on the 68060. Use this option if your 68060
12584 does not have code to emulate those instructions.
12588 Generate output for a CPU32. This is the default
12589 when the compiler is configured for CPU32-based systems.
12590 It is equivalent to @option{-march=cpu32}.
12592 Use this option for microcontrollers with a
12593 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
12594 68336, 68340, 68341, 68349 and 68360.
12598 Generate output for a 520X ColdFire CPU@. This is the default
12599 when the compiler is configured for 520X-based systems.
12600 It is equivalent to @option{-mcpu=5206}, and is now deprecated
12601 in favor of that option.
12603 Use this option for microcontroller with a 5200 core, including
12604 the MCF5202, MCF5203, MCF5204 and MCF5206.
12608 Generate output for a 5206e ColdFire CPU@. The option is now
12609 deprecated in favor of the equivalent @option{-mcpu=5206e}.
12613 Generate output for a member of the ColdFire 528X family.
12614 The option is now deprecated in favor of the equivalent
12615 @option{-mcpu=528x}.
12619 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
12620 in favor of the equivalent @option{-mcpu=5307}.
12624 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
12625 in favor of the equivalent @option{-mcpu=5407}.
12629 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
12630 This includes use of hardware floating point instructions.
12631 The option is equivalent to @option{-mcpu=547x}, and is now
12632 deprecated in favor of that option.
12636 Generate output for a 68040, without using any of the new instructions.
12637 This results in code which can run relatively efficiently on either a
12638 68020/68881 or a 68030 or a 68040. The generated code does use the
12639 68881 instructions that are emulated on the 68040.
12641 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
12645 Generate output for a 68060, without using any of the new instructions.
12646 This results in code which can run relatively efficiently on either a
12647 68020/68881 or a 68030 or a 68040. The generated code does use the
12648 68881 instructions that are emulated on the 68060.
12650 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
12654 @opindex mhard-float
12656 Generate floating-point instructions. This is the default for 68020
12657 and above, and for ColdFire devices that have an FPU@. It defines the
12658 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
12659 on ColdFire targets.
12662 @opindex msoft-float
12663 Do not generate floating-point instructions; use library calls instead.
12664 This is the default for 68000, 68010, and 68832 targets. It is also
12665 the default for ColdFire devices that have no FPU.
12671 Generate (do not generate) ColdFire hardware divide and remainder
12672 instructions. If @option{-march} is used without @option{-mcpu},
12673 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
12674 architectures. Otherwise, the default is taken from the target CPU
12675 (either the default CPU, or the one specified by @option{-mcpu}). For
12676 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
12677 @option{-mcpu=5206e}.
12679 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
12683 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12684 Additionally, parameters passed on the stack are also aligned to a
12685 16-bit boundary even on targets whose API mandates promotion to 32-bit.
12689 Do not consider type @code{int} to be 16 bits wide. This is the default.
12692 @itemx -mno-bitfield
12693 @opindex mnobitfield
12694 @opindex mno-bitfield
12695 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
12696 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
12700 Do use the bit-field instructions. The @option{-m68020} option implies
12701 @option{-mbitfield}. This is the default if you use a configuration
12702 designed for a 68020.
12706 Use a different function-calling convention, in which functions
12707 that take a fixed number of arguments return with the @code{rtd}
12708 instruction, which pops their arguments while returning. This
12709 saves one instruction in the caller since there is no need to pop
12710 the arguments there.
12712 This calling convention is incompatible with the one normally
12713 used on Unix, so you cannot use it if you need to call libraries
12714 compiled with the Unix compiler.
12716 Also, you must provide function prototypes for all functions that
12717 take variable numbers of arguments (including @code{printf});
12718 otherwise incorrect code will be generated for calls to those
12721 In addition, seriously incorrect code will result if you call a
12722 function with too many arguments. (Normally, extra arguments are
12723 harmlessly ignored.)
12725 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
12726 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
12730 Do not use the calling conventions selected by @option{-mrtd}.
12731 This is the default.
12734 @itemx -mno-align-int
12735 @opindex malign-int
12736 @opindex mno-align-int
12737 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
12738 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
12739 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
12740 Aligning variables on 32-bit boundaries produces code that runs somewhat
12741 faster on processors with 32-bit busses at the expense of more memory.
12743 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
12744 align structures containing the above types differently than
12745 most published application binary interface specifications for the m68k.
12749 Use the pc-relative addressing mode of the 68000 directly, instead of
12750 using a global offset table. At present, this option implies @option{-fpic},
12751 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
12752 not presently supported with @option{-mpcrel}, though this could be supported for
12753 68020 and higher processors.
12755 @item -mno-strict-align
12756 @itemx -mstrict-align
12757 @opindex mno-strict-align
12758 @opindex mstrict-align
12759 Do not (do) assume that unaligned memory references will be handled by
12763 Generate code that allows the data segment to be located in a different
12764 area of memory from the text segment. This allows for execute in place in
12765 an environment without virtual memory management. This option implies
12768 @item -mno-sep-data
12769 Generate code that assumes that the data segment follows the text segment.
12770 This is the default.
12772 @item -mid-shared-library
12773 Generate code that supports shared libraries via the library ID method.
12774 This allows for execute in place and shared libraries in an environment
12775 without virtual memory management. This option implies @option{-fPIC}.
12777 @item -mno-id-shared-library
12778 Generate code that doesn't assume ID based shared libraries are being used.
12779 This is the default.
12781 @item -mshared-library-id=n
12782 Specified the identification number of the ID based shared library being
12783 compiled. Specifying a value of 0 will generate more compact code, specifying
12784 other values will force the allocation of that number to the current
12785 library but is no more space or time efficient than omitting this option.
12791 When generating position-independent code for ColdFire, generate code
12792 that works if the GOT has more than 8192 entries. This code is
12793 larger and slower than code generated without this option. On M680x0
12794 processors, this option is not needed; @option{-fPIC} suffices.
12796 GCC normally uses a single instruction to load values from the GOT@.
12797 While this is relatively efficient, it only works if the GOT
12798 is smaller than about 64k. Anything larger causes the linker
12799 to report an error such as:
12801 @cindex relocation truncated to fit (ColdFire)
12803 relocation truncated to fit: R_68K_GOT16O foobar
12806 If this happens, you should recompile your code with @option{-mxgot}.
12807 It should then work with very large GOTs. However, code generated with
12808 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
12809 the value of a global symbol.
12811 Note that some linkers, including newer versions of the GNU linker,
12812 can create multiple GOTs and sort GOT entries. If you have such a linker,
12813 you should only need to use @option{-mxgot} when compiling a single
12814 object file that accesses more than 8192 GOT entries. Very few do.
12816 These options have no effect unless GCC is generating
12817 position-independent code.
12821 @node M68hc1x Options
12822 @subsection M68hc1x Options
12823 @cindex M68hc1x options
12825 These are the @samp{-m} options defined for the 68hc11 and 68hc12
12826 microcontrollers. The default values for these options depends on
12827 which style of microcontroller was selected when the compiler was configured;
12828 the defaults for the most common choices are given below.
12835 Generate output for a 68HC11. This is the default
12836 when the compiler is configured for 68HC11-based systems.
12842 Generate output for a 68HC12. This is the default
12843 when the compiler is configured for 68HC12-based systems.
12849 Generate output for a 68HCS12.
12851 @item -mauto-incdec
12852 @opindex mauto-incdec
12853 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
12860 Enable the use of 68HC12 min and max instructions.
12863 @itemx -mno-long-calls
12864 @opindex mlong-calls
12865 @opindex mno-long-calls
12866 Treat all calls as being far away (near). If calls are assumed to be
12867 far away, the compiler will use the @code{call} instruction to
12868 call a function and the @code{rtc} instruction for returning.
12872 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12874 @item -msoft-reg-count=@var{count}
12875 @opindex msoft-reg-count
12876 Specify the number of pseudo-soft registers which are used for the
12877 code generation. The maximum number is 32. Using more pseudo-soft
12878 register may or may not result in better code depending on the program.
12879 The default is 4 for 68HC11 and 2 for 68HC12.
12883 @node MCore Options
12884 @subsection MCore Options
12885 @cindex MCore options
12887 These are the @samp{-m} options defined for the Motorola M*Core
12893 @itemx -mno-hardlit
12895 @opindex mno-hardlit
12896 Inline constants into the code stream if it can be done in two
12897 instructions or less.
12903 Use the divide instruction. (Enabled by default).
12905 @item -mrelax-immediate
12906 @itemx -mno-relax-immediate
12907 @opindex mrelax-immediate
12908 @opindex mno-relax-immediate
12909 Allow arbitrary sized immediates in bit operations.
12911 @item -mwide-bitfields
12912 @itemx -mno-wide-bitfields
12913 @opindex mwide-bitfields
12914 @opindex mno-wide-bitfields
12915 Always treat bit-fields as int-sized.
12917 @item -m4byte-functions
12918 @itemx -mno-4byte-functions
12919 @opindex m4byte-functions
12920 @opindex mno-4byte-functions
12921 Force all functions to be aligned to a four byte boundary.
12923 @item -mcallgraph-data
12924 @itemx -mno-callgraph-data
12925 @opindex mcallgraph-data
12926 @opindex mno-callgraph-data
12927 Emit callgraph information.
12930 @itemx -mno-slow-bytes
12931 @opindex mslow-bytes
12932 @opindex mno-slow-bytes
12933 Prefer word access when reading byte quantities.
12935 @item -mlittle-endian
12936 @itemx -mbig-endian
12937 @opindex mlittle-endian
12938 @opindex mbig-endian
12939 Generate code for a little endian target.
12945 Generate code for the 210 processor.
12949 Assume that run-time support has been provided and so omit the
12950 simulator library (@file{libsim.a)} from the linker command line.
12952 @item -mstack-increment=@var{size}
12953 @opindex mstack-increment
12954 Set the maximum amount for a single stack increment operation. Large
12955 values can increase the speed of programs which contain functions
12956 that need a large amount of stack space, but they can also trigger a
12957 segmentation fault if the stack is extended too much. The default
12963 @subsection MeP Options
12964 @cindex MeP options
12970 Enables the @code{abs} instruction, which is the absolute difference
12971 between two registers.
12975 Enables all the optional instructions - average, multiply, divide, bit
12976 operations, leading zero, absolute difference, min/max, clip, and
12982 Enables the @code{ave} instruction, which computes the average of two
12985 @item -mbased=@var{n}
12987 Variables of size @var{n} bytes or smaller will be placed in the
12988 @code{.based} section by default. Based variables use the @code{$tp}
12989 register as a base register, and there is a 128 byte limit to the
12990 @code{.based} section.
12994 Enables the bit operation instructions - bit test (@code{btstm}), set
12995 (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
12996 test-and-set (@code{tas}).
12998 @item -mc=@var{name}
13000 Selects which section constant data will be placed in. @var{name} may
13001 be @code{tiny}, @code{near}, or @code{far}.
13005 Enables the @code{clip} instruction. Note that @code{-mclip} is not
13006 useful unless you also provide @code{-mminmax}.
13008 @item -mconfig=@var{name}
13010 Selects one of the build-in core configurations. Each MeP chip has
13011 one or more modules in it; each module has a core CPU and a variety of
13012 coprocessors, optional instructions, and peripherals. The
13013 @code{MeP-Integrator} tool, not part of GCC, provides these
13014 configurations through this option; using this option is the same as
13015 using all the corresponding command line options. The default
13016 configuration is @code{default}.
13020 Enables the coprocessor instructions. By default, this is a 32-bit
13021 coprocessor. Note that the coprocessor is normally enabled via the
13022 @code{-mconfig=} option.
13026 Enables the 32-bit coprocessor's instructions.
13030 Enables the 64-bit coprocessor's instructions.
13034 Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
13038 Causes constant variables to be placed in the @code{.near} section.
13042 Enables the @code{div} and @code{divu} instructions.
13046 Generate big-endian code.
13050 Generate little-endian code.
13052 @item -mio-volatile
13053 @opindex mio-volatile
13054 Tells the compiler that any variable marked with the @code{io}
13055 attribute is to be considered volatile.
13059 Causes variables to be assigned to the @code{.far} section by default.
13063 Enables the @code{leadz} (leading zero) instruction.
13067 Causes variables to be assigned to the @code{.near} section by default.
13071 Enables the @code{min} and @code{max} instructions.
13075 Enables the multiplication and multiply-accumulate instructions.
13079 Disables all the optional instructions enabled by @code{-mall-opts}.
13083 Enables the @code{repeat} and @code{erepeat} instructions, used for
13084 low-overhead looping.
13088 Causes all variables to default to the @code{.tiny} section. Note
13089 that there is a 65536 byte limit to this section. Accesses to these
13090 variables use the @code{%gp} base register.
13094 Enables the saturation instructions. Note that the compiler does not
13095 currently generate these itself, but this option is included for
13096 compatibility with other tools, like @code{as}.
13100 Link the SDRAM-based runtime instead of the default ROM-based runtime.
13104 Link the simulator runtime libraries.
13108 Link the simulator runtime libraries, excluding built-in support
13109 for reset and exception vectors and tables.
13113 Causes all functions to default to the @code{.far} section. Without
13114 this option, functions default to the @code{.near} section.
13116 @item -mtiny=@var{n}
13118 Variables that are @var{n} bytes or smaller will be allocated to the
13119 @code{.tiny} section. These variables use the @code{$gp} base
13120 register. The default for this option is 4, but note that there's a
13121 65536 byte limit to the @code{.tiny} section.
13126 @subsection MIPS Options
13127 @cindex MIPS options
13133 Generate big-endian code.
13137 Generate little-endian code. This is the default for @samp{mips*el-*-*}
13140 @item -march=@var{arch}
13142 Generate code that will run on @var{arch}, which can be the name of a
13143 generic MIPS ISA, or the name of a particular processor.
13145 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
13146 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
13147 The processor names are:
13148 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
13149 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
13150 @samp{5kc}, @samp{5kf},
13152 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
13153 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
13154 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
13155 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
13156 @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
13157 @samp{loongson2e}, @samp{loongson2f},
13161 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
13162 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
13163 @samp{rm7000}, @samp{rm9000},
13164 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
13167 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
13168 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
13170 The special value @samp{from-abi} selects the
13171 most compatible architecture for the selected ABI (that is,
13172 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
13174 Native Linux/GNU toolchains also support the value @samp{native},
13175 which selects the best architecture option for the host processor.
13176 @option{-march=native} has no effect if GCC does not recognize
13179 In processor names, a final @samp{000} can be abbreviated as @samp{k}
13180 (for example, @samp{-march=r2k}). Prefixes are optional, and
13181 @samp{vr} may be written @samp{r}.
13183 Names of the form @samp{@var{n}f2_1} refer to processors with
13184 FPUs clocked at half the rate of the core, names of the form
13185 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
13186 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
13187 processors with FPUs clocked a ratio of 3:2 with respect to the core.
13188 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
13189 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
13190 accepted as synonyms for @samp{@var{n}f1_1}.
13192 GCC defines two macros based on the value of this option. The first
13193 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
13194 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
13195 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
13196 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
13197 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
13199 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
13200 above. In other words, it will have the full prefix and will not
13201 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
13202 the macro names the resolved architecture (either @samp{"mips1"} or
13203 @samp{"mips3"}). It names the default architecture when no
13204 @option{-march} option is given.
13206 @item -mtune=@var{arch}
13208 Optimize for @var{arch}. Among other things, this option controls
13209 the way instructions are scheduled, and the perceived cost of arithmetic
13210 operations. The list of @var{arch} values is the same as for
13213 When this option is not used, GCC will optimize for the processor
13214 specified by @option{-march}. By using @option{-march} and
13215 @option{-mtune} together, it is possible to generate code that will
13216 run on a family of processors, but optimize the code for one
13217 particular member of that family.
13219 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
13220 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
13221 @samp{-march} ones described above.
13225 Equivalent to @samp{-march=mips1}.
13229 Equivalent to @samp{-march=mips2}.
13233 Equivalent to @samp{-march=mips3}.
13237 Equivalent to @samp{-march=mips4}.
13241 Equivalent to @samp{-march=mips32}.
13245 Equivalent to @samp{-march=mips32r2}.
13249 Equivalent to @samp{-march=mips64}.
13253 Equivalent to @samp{-march=mips64r2}.
13258 @opindex mno-mips16
13259 Generate (do not generate) MIPS16 code. If GCC is targetting a
13260 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
13262 MIPS16 code generation can also be controlled on a per-function basis
13263 by means of @code{mips16} and @code{nomips16} attributes.
13264 @xref{Function Attributes}, for more information.
13266 @item -mflip-mips16
13267 @opindex mflip-mips16
13268 Generate MIPS16 code on alternating functions. This option is provided
13269 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
13270 not intended for ordinary use in compiling user code.
13272 @item -minterlink-mips16
13273 @itemx -mno-interlink-mips16
13274 @opindex minterlink-mips16
13275 @opindex mno-interlink-mips16
13276 Require (do not require) that non-MIPS16 code be link-compatible with
13279 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
13280 it must either use a call or an indirect jump. @option{-minterlink-mips16}
13281 therefore disables direct jumps unless GCC knows that the target of the
13282 jump is not MIPS16.
13294 Generate code for the given ABI@.
13296 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
13297 generates 64-bit code when you select a 64-bit architecture, but you
13298 can use @option{-mgp32} to get 32-bit code instead.
13300 For information about the O64 ABI, see
13301 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
13303 GCC supports a variant of the o32 ABI in which floating-point registers
13304 are 64 rather than 32 bits wide. You can select this combination with
13305 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
13306 and @samp{mfhc1} instructions and is therefore only supported for
13307 MIPS32R2 processors.
13309 The register assignments for arguments and return values remain the
13310 same, but each scalar value is passed in a single 64-bit register
13311 rather than a pair of 32-bit registers. For example, scalar
13312 floating-point values are returned in @samp{$f0} only, not a
13313 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
13314 remains the same, but all 64 bits are saved.
13317 @itemx -mno-abicalls
13319 @opindex mno-abicalls
13320 Generate (do not generate) code that is suitable for SVR4-style
13321 dynamic objects. @option{-mabicalls} is the default for SVR4-based
13326 Generate (do not generate) code that is fully position-independent,
13327 and that can therefore be linked into shared libraries. This option
13328 only affects @option{-mabicalls}.
13330 All @option{-mabicalls} code has traditionally been position-independent,
13331 regardless of options like @option{-fPIC} and @option{-fpic}. However,
13332 as an extension, the GNU toolchain allows executables to use absolute
13333 accesses for locally-binding symbols. It can also use shorter GP
13334 initialization sequences and generate direct calls to locally-defined
13335 functions. This mode is selected by @option{-mno-shared}.
13337 @option{-mno-shared} depends on binutils 2.16 or higher and generates
13338 objects that can only be linked by the GNU linker. However, the option
13339 does not affect the ABI of the final executable; it only affects the ABI
13340 of relocatable objects. Using @option{-mno-shared} will generally make
13341 executables both smaller and quicker.
13343 @option{-mshared} is the default.
13349 Assume (do not assume) that the static and dynamic linkers
13350 support PLTs and copy relocations. This option only affects
13351 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
13352 has no effect without @samp{-msym32}.
13354 You can make @option{-mplt} the default by configuring
13355 GCC with @option{--with-mips-plt}. The default is
13356 @option{-mno-plt} otherwise.
13362 Lift (do not lift) the usual restrictions on the size of the global
13365 GCC normally uses a single instruction to load values from the GOT@.
13366 While this is relatively efficient, it will only work if the GOT
13367 is smaller than about 64k. Anything larger will cause the linker
13368 to report an error such as:
13370 @cindex relocation truncated to fit (MIPS)
13372 relocation truncated to fit: R_MIPS_GOT16 foobar
13375 If this happens, you should recompile your code with @option{-mxgot}.
13376 It should then work with very large GOTs, although it will also be
13377 less efficient, since it will take three instructions to fetch the
13378 value of a global symbol.
13380 Note that some linkers can create multiple GOTs. If you have such a
13381 linker, you should only need to use @option{-mxgot} when a single object
13382 file accesses more than 64k's worth of GOT entries. Very few do.
13384 These options have no effect unless GCC is generating position
13389 Assume that general-purpose registers are 32 bits wide.
13393 Assume that general-purpose registers are 64 bits wide.
13397 Assume that floating-point registers are 32 bits wide.
13401 Assume that floating-point registers are 64 bits wide.
13404 @opindex mhard-float
13405 Use floating-point coprocessor instructions.
13408 @opindex msoft-float
13409 Do not use floating-point coprocessor instructions. Implement
13410 floating-point calculations using library calls instead.
13412 @item -msingle-float
13413 @opindex msingle-float
13414 Assume that the floating-point coprocessor only supports single-precision
13417 @item -mdouble-float
13418 @opindex mdouble-float
13419 Assume that the floating-point coprocessor supports double-precision
13420 operations. This is the default.
13426 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
13427 implement atomic memory built-in functions. When neither option is
13428 specified, GCC will use the instructions if the target architecture
13431 @option{-mllsc} is useful if the runtime environment can emulate the
13432 instructions and @option{-mno-llsc} can be useful when compiling for
13433 nonstandard ISAs. You can make either option the default by
13434 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
13435 respectively. @option{--with-llsc} is the default for some
13436 configurations; see the installation documentation for details.
13442 Use (do not use) revision 1 of the MIPS DSP ASE@.
13443 @xref{MIPS DSP Built-in Functions}. This option defines the
13444 preprocessor macro @samp{__mips_dsp}. It also defines
13445 @samp{__mips_dsp_rev} to 1.
13451 Use (do not use) revision 2 of the MIPS DSP ASE@.
13452 @xref{MIPS DSP Built-in Functions}. This option defines the
13453 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
13454 It also defines @samp{__mips_dsp_rev} to 2.
13457 @itemx -mno-smartmips
13458 @opindex msmartmips
13459 @opindex mno-smartmips
13460 Use (do not use) the MIPS SmartMIPS ASE.
13462 @item -mpaired-single
13463 @itemx -mno-paired-single
13464 @opindex mpaired-single
13465 @opindex mno-paired-single
13466 Use (do not use) paired-single floating-point instructions.
13467 @xref{MIPS Paired-Single Support}. This option requires
13468 hardware floating-point support to be enabled.
13474 Use (do not use) MIPS Digital Media Extension instructions.
13475 This option can only be used when generating 64-bit code and requires
13476 hardware floating-point support to be enabled.
13481 @opindex mno-mips3d
13482 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
13483 The option @option{-mips3d} implies @option{-mpaired-single}.
13489 Use (do not use) MT Multithreading instructions.
13493 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
13494 an explanation of the default and the way that the pointer size is
13499 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
13501 The default size of @code{int}s, @code{long}s and pointers depends on
13502 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
13503 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
13504 32-bit @code{long}s. Pointers are the same size as @code{long}s,
13505 or the same size as integer registers, whichever is smaller.
13511 Assume (do not assume) that all symbols have 32-bit values, regardless
13512 of the selected ABI@. This option is useful in combination with
13513 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
13514 to generate shorter and faster references to symbolic addresses.
13518 Put definitions of externally-visible data in a small data section
13519 if that data is no bigger than @var{num} bytes. GCC can then access
13520 the data more efficiently; see @option{-mgpopt} for details.
13522 The default @option{-G} option depends on the configuration.
13524 @item -mlocal-sdata
13525 @itemx -mno-local-sdata
13526 @opindex mlocal-sdata
13527 @opindex mno-local-sdata
13528 Extend (do not extend) the @option{-G} behavior to local data too,
13529 such as to static variables in C@. @option{-mlocal-sdata} is the
13530 default for all configurations.
13532 If the linker complains that an application is using too much small data,
13533 you might want to try rebuilding the less performance-critical parts with
13534 @option{-mno-local-sdata}. You might also want to build large
13535 libraries with @option{-mno-local-sdata}, so that the libraries leave
13536 more room for the main program.
13538 @item -mextern-sdata
13539 @itemx -mno-extern-sdata
13540 @opindex mextern-sdata
13541 @opindex mno-extern-sdata
13542 Assume (do not assume) that externally-defined data will be in
13543 a small data section if that data is within the @option{-G} limit.
13544 @option{-mextern-sdata} is the default for all configurations.
13546 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
13547 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
13548 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
13549 is placed in a small data section. If @var{Var} is defined by another
13550 module, you must either compile that module with a high-enough
13551 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
13552 definition. If @var{Var} is common, you must link the application
13553 with a high-enough @option{-G} setting.
13555 The easiest way of satisfying these restrictions is to compile
13556 and link every module with the same @option{-G} option. However,
13557 you may wish to build a library that supports several different
13558 small data limits. You can do this by compiling the library with
13559 the highest supported @option{-G} setting and additionally using
13560 @option{-mno-extern-sdata} to stop the library from making assumptions
13561 about externally-defined data.
13567 Use (do not use) GP-relative accesses for symbols that are known to be
13568 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
13569 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
13572 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
13573 might not hold the value of @code{_gp}. For example, if the code is
13574 part of a library that might be used in a boot monitor, programs that
13575 call boot monitor routines will pass an unknown value in @code{$gp}.
13576 (In such situations, the boot monitor itself would usually be compiled
13577 with @option{-G0}.)
13579 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
13580 @option{-mno-extern-sdata}.
13582 @item -membedded-data
13583 @itemx -mno-embedded-data
13584 @opindex membedded-data
13585 @opindex mno-embedded-data
13586 Allocate variables to the read-only data section first if possible, then
13587 next in the small data section if possible, otherwise in data. This gives
13588 slightly slower code than the default, but reduces the amount of RAM required
13589 when executing, and thus may be preferred for some embedded systems.
13591 @item -muninit-const-in-rodata
13592 @itemx -mno-uninit-const-in-rodata
13593 @opindex muninit-const-in-rodata
13594 @opindex mno-uninit-const-in-rodata
13595 Put uninitialized @code{const} variables in the read-only data section.
13596 This option is only meaningful in conjunction with @option{-membedded-data}.
13598 @item -mcode-readable=@var{setting}
13599 @opindex mcode-readable
13600 Specify whether GCC may generate code that reads from executable sections.
13601 There are three possible settings:
13604 @item -mcode-readable=yes
13605 Instructions may freely access executable sections. This is the
13608 @item -mcode-readable=pcrel
13609 MIPS16 PC-relative load instructions can access executable sections,
13610 but other instructions must not do so. This option is useful on 4KSc
13611 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
13612 It is also useful on processors that can be configured to have a dual
13613 instruction/data SRAM interface and that, like the M4K, automatically
13614 redirect PC-relative loads to the instruction RAM.
13616 @item -mcode-readable=no
13617 Instructions must not access executable sections. This option can be
13618 useful on targets that are configured to have a dual instruction/data
13619 SRAM interface but that (unlike the M4K) do not automatically redirect
13620 PC-relative loads to the instruction RAM.
13623 @item -msplit-addresses
13624 @itemx -mno-split-addresses
13625 @opindex msplit-addresses
13626 @opindex mno-split-addresses
13627 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
13628 relocation operators. This option has been superseded by
13629 @option{-mexplicit-relocs} but is retained for backwards compatibility.
13631 @item -mexplicit-relocs
13632 @itemx -mno-explicit-relocs
13633 @opindex mexplicit-relocs
13634 @opindex mno-explicit-relocs
13635 Use (do not use) assembler relocation operators when dealing with symbolic
13636 addresses. The alternative, selected by @option{-mno-explicit-relocs},
13637 is to use assembler macros instead.
13639 @option{-mexplicit-relocs} is the default if GCC was configured
13640 to use an assembler that supports relocation operators.
13642 @item -mcheck-zero-division
13643 @itemx -mno-check-zero-division
13644 @opindex mcheck-zero-division
13645 @opindex mno-check-zero-division
13646 Trap (do not trap) on integer division by zero.
13648 The default is @option{-mcheck-zero-division}.
13650 @item -mdivide-traps
13651 @itemx -mdivide-breaks
13652 @opindex mdivide-traps
13653 @opindex mdivide-breaks
13654 MIPS systems check for division by zero by generating either a
13655 conditional trap or a break instruction. Using traps results in
13656 smaller code, but is only supported on MIPS II and later. Also, some
13657 versions of the Linux kernel have a bug that prevents trap from
13658 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
13659 allow conditional traps on architectures that support them and
13660 @option{-mdivide-breaks} to force the use of breaks.
13662 The default is usually @option{-mdivide-traps}, but this can be
13663 overridden at configure time using @option{--with-divide=breaks}.
13664 Divide-by-zero checks can be completely disabled using
13665 @option{-mno-check-zero-division}.
13670 @opindex mno-memcpy
13671 Force (do not force) the use of @code{memcpy()} for non-trivial block
13672 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
13673 most constant-sized copies.
13676 @itemx -mno-long-calls
13677 @opindex mlong-calls
13678 @opindex mno-long-calls
13679 Disable (do not disable) use of the @code{jal} instruction. Calling
13680 functions using @code{jal} is more efficient but requires the caller
13681 and callee to be in the same 256 megabyte segment.
13683 This option has no effect on abicalls code. The default is
13684 @option{-mno-long-calls}.
13690 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
13691 instructions, as provided by the R4650 ISA@.
13694 @itemx -mno-fused-madd
13695 @opindex mfused-madd
13696 @opindex mno-fused-madd
13697 Enable (disable) use of the floating point multiply-accumulate
13698 instructions, when they are available. The default is
13699 @option{-mfused-madd}.
13701 When multiply-accumulate instructions are used, the intermediate
13702 product is calculated to infinite precision and is not subject to
13703 the FCSR Flush to Zero bit. This may be undesirable in some
13708 Tell the MIPS assembler to not run its preprocessor over user
13709 assembler files (with a @samp{.s} suffix) when assembling them.
13712 @itemx -mno-fix-r4000
13713 @opindex mfix-r4000
13714 @opindex mno-fix-r4000
13715 Work around certain R4000 CPU errata:
13718 A double-word or a variable shift may give an incorrect result if executed
13719 immediately after starting an integer division.
13721 A double-word or a variable shift may give an incorrect result if executed
13722 while an integer multiplication is in progress.
13724 An integer division may give an incorrect result if started in a delay slot
13725 of a taken branch or a jump.
13729 @itemx -mno-fix-r4400
13730 @opindex mfix-r4400
13731 @opindex mno-fix-r4400
13732 Work around certain R4400 CPU errata:
13735 A double-word or a variable shift may give an incorrect result if executed
13736 immediately after starting an integer division.
13740 @itemx -mno-fix-r10000
13741 @opindex mfix-r10000
13742 @opindex mno-fix-r10000
13743 Work around certain R10000 errata:
13746 @code{ll}/@code{sc} sequences may not behave atomically on revisions
13747 prior to 3.0. They may deadlock on revisions 2.6 and earlier.
13750 This option can only be used if the target architecture supports
13751 branch-likely instructions. @option{-mfix-r10000} is the default when
13752 @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
13756 @itemx -mno-fix-vr4120
13757 @opindex mfix-vr4120
13758 Work around certain VR4120 errata:
13761 @code{dmultu} does not always produce the correct result.
13763 @code{div} and @code{ddiv} do not always produce the correct result if one
13764 of the operands is negative.
13766 The workarounds for the division errata rely on special functions in
13767 @file{libgcc.a}. At present, these functions are only provided by
13768 the @code{mips64vr*-elf} configurations.
13770 Other VR4120 errata require a nop to be inserted between certain pairs of
13771 instructions. These errata are handled by the assembler, not by GCC itself.
13774 @opindex mfix-vr4130
13775 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
13776 workarounds are implemented by the assembler rather than by GCC,
13777 although GCC will avoid using @code{mflo} and @code{mfhi} if the
13778 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
13779 instructions are available instead.
13782 @itemx -mno-fix-sb1
13784 Work around certain SB-1 CPU core errata.
13785 (This flag currently works around the SB-1 revision 2
13786 ``F1'' and ``F2'' floating point errata.)
13788 @item -mr10k-cache-barrier=@var{setting}
13789 @opindex mr10k-cache-barrier
13790 Specify whether GCC should insert cache barriers to avoid the
13791 side-effects of speculation on R10K processors.
13793 In common with many processors, the R10K tries to predict the outcome
13794 of a conditional branch and speculatively executes instructions from
13795 the ``taken'' branch. It later aborts these instructions if the
13796 predicted outcome was wrong. However, on the R10K, even aborted
13797 instructions can have side effects.
13799 This problem only affects kernel stores and, depending on the system,
13800 kernel loads. As an example, a speculatively-executed store may load
13801 the target memory into cache and mark the cache line as dirty, even if
13802 the store itself is later aborted. If a DMA operation writes to the
13803 same area of memory before the ``dirty'' line is flushed, the cached
13804 data will overwrite the DMA-ed data. See the R10K processor manual
13805 for a full description, including other potential problems.
13807 One workaround is to insert cache barrier instructions before every memory
13808 access that might be speculatively executed and that might have side
13809 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
13810 controls GCC's implementation of this workaround. It assumes that
13811 aborted accesses to any byte in the following regions will not have
13816 the memory occupied by the current function's stack frame;
13819 the memory occupied by an incoming stack argument;
13822 the memory occupied by an object with a link-time-constant address.
13825 It is the kernel's responsibility to ensure that speculative
13826 accesses to these regions are indeed safe.
13828 If the input program contains a function declaration such as:
13834 then the implementation of @code{foo} must allow @code{j foo} and
13835 @code{jal foo} to be executed speculatively. GCC honors this
13836 restriction for functions it compiles itself. It expects non-GCC
13837 functions (such as hand-written assembly code) to do the same.
13839 The option has three forms:
13842 @item -mr10k-cache-barrier=load-store
13843 Insert a cache barrier before a load or store that might be
13844 speculatively executed and that might have side effects even
13847 @item -mr10k-cache-barrier=store
13848 Insert a cache barrier before a store that might be speculatively
13849 executed and that might have side effects even if aborted.
13851 @item -mr10k-cache-barrier=none
13852 Disable the insertion of cache barriers. This is the default setting.
13855 @item -mflush-func=@var{func}
13856 @itemx -mno-flush-func
13857 @opindex mflush-func
13858 Specifies the function to call to flush the I and D caches, or to not
13859 call any such function. If called, the function must take the same
13860 arguments as the common @code{_flush_func()}, that is, the address of the
13861 memory range for which the cache is being flushed, the size of the
13862 memory range, and the number 3 (to flush both caches). The default
13863 depends on the target GCC was configured for, but commonly is either
13864 @samp{_flush_func} or @samp{__cpu_flush}.
13866 @item mbranch-cost=@var{num}
13867 @opindex mbranch-cost
13868 Set the cost of branches to roughly @var{num} ``simple'' instructions.
13869 This cost is only a heuristic and is not guaranteed to produce
13870 consistent results across releases. A zero cost redundantly selects
13871 the default, which is based on the @option{-mtune} setting.
13873 @item -mbranch-likely
13874 @itemx -mno-branch-likely
13875 @opindex mbranch-likely
13876 @opindex mno-branch-likely
13877 Enable or disable use of Branch Likely instructions, regardless of the
13878 default for the selected architecture. By default, Branch Likely
13879 instructions may be generated if they are supported by the selected
13880 architecture. An exception is for the MIPS32 and MIPS64 architectures
13881 and processors which implement those architectures; for those, Branch
13882 Likely instructions will not be generated by default because the MIPS32
13883 and MIPS64 architectures specifically deprecate their use.
13885 @item -mfp-exceptions
13886 @itemx -mno-fp-exceptions
13887 @opindex mfp-exceptions
13888 Specifies whether FP exceptions are enabled. This affects how we schedule
13889 FP instructions for some processors. The default is that FP exceptions are
13892 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
13893 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
13896 @item -mvr4130-align
13897 @itemx -mno-vr4130-align
13898 @opindex mvr4130-align
13899 The VR4130 pipeline is two-way superscalar, but can only issue two
13900 instructions together if the first one is 8-byte aligned. When this
13901 option is enabled, GCC will align pairs of instructions that it
13902 thinks should execute in parallel.
13904 This option only has an effect when optimizing for the VR4130.
13905 It normally makes code faster, but at the expense of making it bigger.
13906 It is enabled by default at optimization level @option{-O3}.
13911 Enable (disable) generation of @code{synci} instructions on
13912 architectures that support it. The @code{synci} instructions (if
13913 enabled) will be generated when @code{__builtin___clear_cache()} is
13916 This option defaults to @code{-mno-synci}, but the default can be
13917 overridden by configuring with @code{--with-synci}.
13919 When compiling code for single processor systems, it is generally safe
13920 to use @code{synci}. However, on many multi-core (SMP) systems, it
13921 will not invalidate the instruction caches on all cores and may lead
13922 to undefined behavior.
13924 @item -mrelax-pic-calls
13925 @itemx -mno-relax-pic-calls
13926 @opindex mrelax-pic-calls
13927 Try to turn PIC calls that are normally dispatched via register
13928 @code{$25} into direct calls. This is only possible if the linker can
13929 resolve the destination at link-time and if the destination is within
13930 range for a direct call.
13932 @option{-mrelax-pic-calls} is the default if GCC was configured to use
13933 an assembler and a linker that supports the @code{.reloc} assembly
13934 directive and @code{-mexplicit-relocs} is in effect. With
13935 @code{-mno-explicit-relocs}, this optimization can be performed by the
13936 assembler and the linker alone without help from the compiler.
13940 @subsection MMIX Options
13941 @cindex MMIX Options
13943 These options are defined for the MMIX:
13947 @itemx -mno-libfuncs
13949 @opindex mno-libfuncs
13950 Specify that intrinsic library functions are being compiled, passing all
13951 values in registers, no matter the size.
13954 @itemx -mno-epsilon
13956 @opindex mno-epsilon
13957 Generate floating-point comparison instructions that compare with respect
13958 to the @code{rE} epsilon register.
13960 @item -mabi=mmixware
13962 @opindex mabi=mmixware
13964 Generate code that passes function parameters and return values that (in
13965 the called function) are seen as registers @code{$0} and up, as opposed to
13966 the GNU ABI which uses global registers @code{$231} and up.
13968 @item -mzero-extend
13969 @itemx -mno-zero-extend
13970 @opindex mzero-extend
13971 @opindex mno-zero-extend
13972 When reading data from memory in sizes shorter than 64 bits, use (do not
13973 use) zero-extending load instructions by default, rather than
13974 sign-extending ones.
13977 @itemx -mno-knuthdiv
13979 @opindex mno-knuthdiv
13980 Make the result of a division yielding a remainder have the same sign as
13981 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
13982 remainder follows the sign of the dividend. Both methods are
13983 arithmetically valid, the latter being almost exclusively used.
13985 @item -mtoplevel-symbols
13986 @itemx -mno-toplevel-symbols
13987 @opindex mtoplevel-symbols
13988 @opindex mno-toplevel-symbols
13989 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
13990 code can be used with the @code{PREFIX} assembly directive.
13994 Generate an executable in the ELF format, rather than the default
13995 @samp{mmo} format used by the @command{mmix} simulator.
13997 @item -mbranch-predict
13998 @itemx -mno-branch-predict
13999 @opindex mbranch-predict
14000 @opindex mno-branch-predict
14001 Use (do not use) the probable-branch instructions, when static branch
14002 prediction indicates a probable branch.
14004 @item -mbase-addresses
14005 @itemx -mno-base-addresses
14006 @opindex mbase-addresses
14007 @opindex mno-base-addresses
14008 Generate (do not generate) code that uses @emph{base addresses}. Using a
14009 base address automatically generates a request (handled by the assembler
14010 and the linker) for a constant to be set up in a global register. The
14011 register is used for one or more base address requests within the range 0
14012 to 255 from the value held in the register. The generally leads to short
14013 and fast code, but the number of different data items that can be
14014 addressed is limited. This means that a program that uses lots of static
14015 data may require @option{-mno-base-addresses}.
14017 @item -msingle-exit
14018 @itemx -mno-single-exit
14019 @opindex msingle-exit
14020 @opindex mno-single-exit
14021 Force (do not force) generated code to have a single exit point in each
14025 @node MN10300 Options
14026 @subsection MN10300 Options
14027 @cindex MN10300 options
14029 These @option{-m} options are defined for Matsushita MN10300 architectures:
14034 Generate code to avoid bugs in the multiply instructions for the MN10300
14035 processors. This is the default.
14037 @item -mno-mult-bug
14038 @opindex mno-mult-bug
14039 Do not generate code to avoid bugs in the multiply instructions for the
14040 MN10300 processors.
14044 Generate code which uses features specific to the AM33 processor.
14048 Do not generate code which uses features specific to the AM33 processor. This
14051 @item -mreturn-pointer-on-d0
14052 @opindex mreturn-pointer-on-d0
14053 When generating a function which returns a pointer, return the pointer
14054 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
14055 only in a0, and attempts to call such functions without a prototype
14056 would result in errors. Note that this option is on by default; use
14057 @option{-mno-return-pointer-on-d0} to disable it.
14061 Do not link in the C run-time initialization object file.
14065 Indicate to the linker that it should perform a relaxation optimization pass
14066 to shorten branches, calls and absolute memory addresses. This option only
14067 has an effect when used on the command line for the final link step.
14069 This option makes symbolic debugging impossible.
14072 @node PDP-11 Options
14073 @subsection PDP-11 Options
14074 @cindex PDP-11 Options
14076 These options are defined for the PDP-11:
14081 Use hardware FPP floating point. This is the default. (FIS floating
14082 point on the PDP-11/40 is not supported.)
14085 @opindex msoft-float
14086 Do not use hardware floating point.
14090 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
14094 Return floating-point results in memory. This is the default.
14098 Generate code for a PDP-11/40.
14102 Generate code for a PDP-11/45. This is the default.
14106 Generate code for a PDP-11/10.
14108 @item -mbcopy-builtin
14109 @opindex mbcopy-builtin
14110 Use inline @code{movmemhi} patterns for copying memory. This is the
14115 Do not use inline @code{movmemhi} patterns for copying memory.
14121 Use 16-bit @code{int}. This is the default.
14127 Use 32-bit @code{int}.
14130 @itemx -mno-float32
14132 @opindex mno-float32
14133 Use 64-bit @code{float}. This is the default.
14136 @itemx -mno-float64
14138 @opindex mno-float64
14139 Use 32-bit @code{float}.
14143 Use @code{abshi2} pattern. This is the default.
14147 Do not use @code{abshi2} pattern.
14149 @item -mbranch-expensive
14150 @opindex mbranch-expensive
14151 Pretend that branches are expensive. This is for experimenting with
14152 code generation only.
14154 @item -mbranch-cheap
14155 @opindex mbranch-cheap
14156 Do not pretend that branches are expensive. This is the default.
14160 Generate code for a system with split I&D@.
14164 Generate code for a system without split I&D@. This is the default.
14168 Use Unix assembler syntax. This is the default when configured for
14169 @samp{pdp11-*-bsd}.
14173 Use DEC assembler syntax. This is the default when configured for any
14174 PDP-11 target other than @samp{pdp11-*-bsd}.
14177 @node picoChip Options
14178 @subsection picoChip Options
14179 @cindex picoChip options
14181 These @samp{-m} options are defined for picoChip implementations:
14185 @item -mae=@var{ae_type}
14187 Set the instruction set, register set, and instruction scheduling
14188 parameters for array element type @var{ae_type}. Supported values
14189 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
14191 @option{-mae=ANY} selects a completely generic AE type. Code
14192 generated with this option will run on any of the other AE types. The
14193 code will not be as efficient as it would be if compiled for a specific
14194 AE type, and some types of operation (e.g., multiplication) will not
14195 work properly on all types of AE.
14197 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
14198 for compiled code, and is the default.
14200 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
14201 option may suffer from poor performance of byte (char) manipulation,
14202 since the DSP AE does not provide hardware support for byte load/stores.
14204 @item -msymbol-as-address
14205 Enable the compiler to directly use a symbol name as an address in a
14206 load/store instruction, without first loading it into a
14207 register. Typically, the use of this option will generate larger
14208 programs, which run faster than when the option isn't used. However, the
14209 results vary from program to program, so it is left as a user option,
14210 rather than being permanently enabled.
14212 @item -mno-inefficient-warnings
14213 Disables warnings about the generation of inefficient code. These
14214 warnings can be generated, for example, when compiling code which
14215 performs byte-level memory operations on the MAC AE type. The MAC AE has
14216 no hardware support for byte-level memory operations, so all byte
14217 load/stores must be synthesized from word load/store operations. This is
14218 inefficient and a warning will be generated indicating to the programmer
14219 that they should rewrite the code to avoid byte operations, or to target
14220 an AE type which has the necessary hardware support. This option enables
14221 the warning to be turned off.
14225 @node PowerPC Options
14226 @subsection PowerPC Options
14227 @cindex PowerPC options
14229 These are listed under @xref{RS/6000 and PowerPC Options}.
14231 @node RS/6000 and PowerPC Options
14232 @subsection IBM RS/6000 and PowerPC Options
14233 @cindex RS/6000 and PowerPC Options
14234 @cindex IBM RS/6000 and PowerPC Options
14236 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
14243 @itemx -mno-powerpc
14244 @itemx -mpowerpc-gpopt
14245 @itemx -mno-powerpc-gpopt
14246 @itemx -mpowerpc-gfxopt
14247 @itemx -mno-powerpc-gfxopt
14249 @itemx -mno-powerpc64
14253 @itemx -mno-popcntb
14255 @itemx -mno-popcntd
14263 @itemx -mno-hard-dfp
14267 @opindex mno-power2
14269 @opindex mno-powerpc
14270 @opindex mpowerpc-gpopt
14271 @opindex mno-powerpc-gpopt
14272 @opindex mpowerpc-gfxopt
14273 @opindex mno-powerpc-gfxopt
14274 @opindex mpowerpc64
14275 @opindex mno-powerpc64
14279 @opindex mno-popcntb
14281 @opindex mno-popcntd
14287 @opindex mno-mfpgpr
14289 @opindex mno-hard-dfp
14290 GCC supports two related instruction set architectures for the
14291 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
14292 instructions supported by the @samp{rios} chip set used in the original
14293 RS/6000 systems and the @dfn{PowerPC} instruction set is the
14294 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
14295 the IBM 4xx, 6xx, and follow-on microprocessors.
14297 Neither architecture is a subset of the other. However there is a
14298 large common subset of instructions supported by both. An MQ
14299 register is included in processors supporting the POWER architecture.
14301 You use these options to specify which instructions are available on the
14302 processor you are using. The default value of these options is
14303 determined when configuring GCC@. Specifying the
14304 @option{-mcpu=@var{cpu_type}} overrides the specification of these
14305 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
14306 rather than the options listed above.
14308 The @option{-mpower} option allows GCC to generate instructions that
14309 are found only in the POWER architecture and to use the MQ register.
14310 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
14311 to generate instructions that are present in the POWER2 architecture but
14312 not the original POWER architecture.
14314 The @option{-mpowerpc} option allows GCC to generate instructions that
14315 are found only in the 32-bit subset of the PowerPC architecture.
14316 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
14317 GCC to use the optional PowerPC architecture instructions in the
14318 General Purpose group, including floating-point square root. Specifying
14319 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
14320 use the optional PowerPC architecture instructions in the Graphics
14321 group, including floating-point select.
14323 The @option{-mmfcrf} option allows GCC to generate the move from
14324 condition register field instruction implemented on the POWER4
14325 processor and other processors that support the PowerPC V2.01
14327 The @option{-mpopcntb} option allows GCC to generate the popcount and
14328 double precision FP reciprocal estimate instruction implemented on the
14329 POWER5 processor and other processors that support the PowerPC V2.02
14331 The @option{-mpopcntd} option allows GCC to generate the popcount
14332 instruction implemented on the POWER7 processor and other processors
14333 that support the PowerPC V2.06 architecture.
14334 The @option{-mfprnd} option allows GCC to generate the FP round to
14335 integer instructions implemented on the POWER5+ processor and other
14336 processors that support the PowerPC V2.03 architecture.
14337 The @option{-mcmpb} option allows GCC to generate the compare bytes
14338 instruction implemented on the POWER6 processor and other processors
14339 that support the PowerPC V2.05 architecture.
14340 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
14341 general purpose register instructions implemented on the POWER6X
14342 processor and other processors that support the extended PowerPC V2.05
14344 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
14345 point instructions implemented on some POWER processors.
14347 The @option{-mpowerpc64} option allows GCC to generate the additional
14348 64-bit instructions that are found in the full PowerPC64 architecture
14349 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
14350 @option{-mno-powerpc64}.
14352 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
14353 will use only the instructions in the common subset of both
14354 architectures plus some special AIX common-mode calls, and will not use
14355 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
14356 permits GCC to use any instruction from either architecture and to
14357 allow use of the MQ register; specify this for the Motorola MPC601.
14359 @item -mnew-mnemonics
14360 @itemx -mold-mnemonics
14361 @opindex mnew-mnemonics
14362 @opindex mold-mnemonics
14363 Select which mnemonics to use in the generated assembler code. With
14364 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
14365 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
14366 assembler mnemonics defined for the POWER architecture. Instructions
14367 defined in only one architecture have only one mnemonic; GCC uses that
14368 mnemonic irrespective of which of these options is specified.
14370 GCC defaults to the mnemonics appropriate for the architecture in
14371 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
14372 value of these option. Unless you are building a cross-compiler, you
14373 should normally not specify either @option{-mnew-mnemonics} or
14374 @option{-mold-mnemonics}, but should instead accept the default.
14376 @item -mcpu=@var{cpu_type}
14378 Set architecture type, register usage, choice of mnemonics, and
14379 instruction scheduling parameters for machine type @var{cpu_type}.
14380 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
14381 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
14382 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
14383 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
14384 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
14385 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
14386 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
14387 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
14388 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7},
14389 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
14390 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
14392 @option{-mcpu=common} selects a completely generic processor. Code
14393 generated under this option will run on any POWER or PowerPC processor.
14394 GCC will use only the instructions in the common subset of both
14395 architectures, and will not use the MQ register. GCC assumes a generic
14396 processor model for scheduling purposes.
14398 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
14399 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
14400 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
14401 types, with an appropriate, generic processor model assumed for
14402 scheduling purposes.
14404 The other options specify a specific processor. Code generated under
14405 those options will run best on that processor, and may not run at all on
14408 The @option{-mcpu} options automatically enable or disable the
14411 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
14412 -mnew-mnemonics -mpopcntb -mpopcntd -mpower -mpower2 -mpowerpc64 @gol
14413 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
14414 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx}
14416 The particular options set for any particular CPU will vary between
14417 compiler versions, depending on what setting seems to produce optimal
14418 code for that CPU; it doesn't necessarily reflect the actual hardware's
14419 capabilities. If you wish to set an individual option to a particular
14420 value, you may specify it after the @option{-mcpu} option, like
14421 @samp{-mcpu=970 -mno-altivec}.
14423 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
14424 not enabled or disabled by the @option{-mcpu} option at present because
14425 AIX does not have full support for these options. You may still
14426 enable or disable them individually if you're sure it'll work in your
14429 @item -mtune=@var{cpu_type}
14431 Set the instruction scheduling parameters for machine type
14432 @var{cpu_type}, but do not set the architecture type, register usage, or
14433 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
14434 values for @var{cpu_type} are used for @option{-mtune} as for
14435 @option{-mcpu}. If both are specified, the code generated will use the
14436 architecture, registers, and mnemonics set by @option{-mcpu}, but the
14437 scheduling parameters set by @option{-mtune}.
14443 Generate code to compute division as reciprocal estimate and iterative
14444 refinement, creating opportunities for increased throughput. This
14445 feature requires: optional PowerPC Graphics instruction set for single
14446 precision and FRE instruction for double precision, assuming divides
14447 cannot generate user-visible traps, and the domain values not include
14448 Infinities, denormals or zero denominator.
14451 @itemx -mno-altivec
14453 @opindex mno-altivec
14454 Generate code that uses (does not use) AltiVec instructions, and also
14455 enable the use of built-in functions that allow more direct access to
14456 the AltiVec instruction set. You may also need to set
14457 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
14463 @opindex mno-vrsave
14464 Generate VRSAVE instructions when generating AltiVec code.
14466 @item -mgen-cell-microcode
14467 @opindex mgen-cell-microcode
14468 Generate Cell microcode instructions
14470 @item -mwarn-cell-microcode
14471 @opindex mwarn-cell-microcode
14472 Warning when a Cell microcode instruction is going to emitted. An example
14473 of a Cell microcode instruction is a variable shift.
14476 @opindex msecure-plt
14477 Generate code that allows ld and ld.so to build executables and shared
14478 libraries with non-exec .plt and .got sections. This is a PowerPC
14479 32-bit SYSV ABI option.
14483 Generate code that uses a BSS .plt section that ld.so fills in, and
14484 requires .plt and .got sections that are both writable and executable.
14485 This is a PowerPC 32-bit SYSV ABI option.
14491 This switch enables or disables the generation of ISEL instructions.
14493 @item -misel=@var{yes/no}
14494 This switch has been deprecated. Use @option{-misel} and
14495 @option{-mno-isel} instead.
14501 This switch enables or disables the generation of SPE simd
14507 @opindex mno-paired
14508 This switch enables or disables the generation of PAIRED simd
14511 @item -mspe=@var{yes/no}
14512 This option has been deprecated. Use @option{-mspe} and
14513 @option{-mno-spe} instead.
14519 Generate code that uses (does not use) vector/scalar (VSX)
14520 instructions, and also enable the use of built-in functions that allow
14521 more direct access to the VSX instruction set.
14523 @item -mfloat-gprs=@var{yes/single/double/no}
14524 @itemx -mfloat-gprs
14525 @opindex mfloat-gprs
14526 This switch enables or disables the generation of floating point
14527 operations on the general purpose registers for architectures that
14530 The argument @var{yes} or @var{single} enables the use of
14531 single-precision floating point operations.
14533 The argument @var{double} enables the use of single and
14534 double-precision floating point operations.
14536 The argument @var{no} disables floating point operations on the
14537 general purpose registers.
14539 This option is currently only available on the MPC854x.
14545 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
14546 targets (including GNU/Linux). The 32-bit environment sets int, long
14547 and pointer to 32 bits and generates code that runs on any PowerPC
14548 variant. The 64-bit environment sets int to 32 bits and long and
14549 pointer to 64 bits, and generates code for PowerPC64, as for
14550 @option{-mpowerpc64}.
14553 @itemx -mno-fp-in-toc
14554 @itemx -mno-sum-in-toc
14555 @itemx -mminimal-toc
14557 @opindex mno-fp-in-toc
14558 @opindex mno-sum-in-toc
14559 @opindex mminimal-toc
14560 Modify generation of the TOC (Table Of Contents), which is created for
14561 every executable file. The @option{-mfull-toc} option is selected by
14562 default. In that case, GCC will allocate at least one TOC entry for
14563 each unique non-automatic variable reference in your program. GCC
14564 will also place floating-point constants in the TOC@. However, only
14565 16,384 entries are available in the TOC@.
14567 If you receive a linker error message that saying you have overflowed
14568 the available TOC space, you can reduce the amount of TOC space used
14569 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
14570 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
14571 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
14572 generate code to calculate the sum of an address and a constant at
14573 run-time instead of putting that sum into the TOC@. You may specify one
14574 or both of these options. Each causes GCC to produce very slightly
14575 slower and larger code at the expense of conserving TOC space.
14577 If you still run out of space in the TOC even when you specify both of
14578 these options, specify @option{-mminimal-toc} instead. This option causes
14579 GCC to make only one TOC entry for every file. When you specify this
14580 option, GCC will produce code that is slower and larger but which
14581 uses extremely little TOC space. You may wish to use this option
14582 only on files that contain less frequently executed code.
14588 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
14589 @code{long} type, and the infrastructure needed to support them.
14590 Specifying @option{-maix64} implies @option{-mpowerpc64} and
14591 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
14592 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
14595 @itemx -mno-xl-compat
14596 @opindex mxl-compat
14597 @opindex mno-xl-compat
14598 Produce code that conforms more closely to IBM XL compiler semantics
14599 when using AIX-compatible ABI@. Pass floating-point arguments to
14600 prototyped functions beyond the register save area (RSA) on the stack
14601 in addition to argument FPRs. Do not assume that most significant
14602 double in 128-bit long double value is properly rounded when comparing
14603 values and converting to double. Use XL symbol names for long double
14606 The AIX calling convention was extended but not initially documented to
14607 handle an obscure K&R C case of calling a function that takes the
14608 address of its arguments with fewer arguments than declared. IBM XL
14609 compilers access floating point arguments which do not fit in the
14610 RSA from the stack when a subroutine is compiled without
14611 optimization. Because always storing floating-point arguments on the
14612 stack is inefficient and rarely needed, this option is not enabled by
14613 default and only is necessary when calling subroutines compiled by IBM
14614 XL compilers without optimization.
14618 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
14619 application written to use message passing with special startup code to
14620 enable the application to run. The system must have PE installed in the
14621 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
14622 must be overridden with the @option{-specs=} option to specify the
14623 appropriate directory location. The Parallel Environment does not
14624 support threads, so the @option{-mpe} option and the @option{-pthread}
14625 option are incompatible.
14627 @item -malign-natural
14628 @itemx -malign-power
14629 @opindex malign-natural
14630 @opindex malign-power
14631 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
14632 @option{-malign-natural} overrides the ABI-defined alignment of larger
14633 types, such as floating-point doubles, on their natural size-based boundary.
14634 The option @option{-malign-power} instructs GCC to follow the ABI-specified
14635 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
14637 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
14641 @itemx -mhard-float
14642 @opindex msoft-float
14643 @opindex mhard-float
14644 Generate code that does not use (uses) the floating-point register set.
14645 Software floating point emulation is provided if you use the
14646 @option{-msoft-float} option, and pass the option to GCC when linking.
14648 @item -msingle-float
14649 @itemx -mdouble-float
14650 @opindex msingle-float
14651 @opindex mdouble-float
14652 Generate code for single or double-precision floating point operations.
14653 @option{-mdouble-float} implies @option{-msingle-float}.
14656 @opindex msimple-fpu
14657 Do not generate sqrt and div instructions for hardware floating point unit.
14661 Specify type of floating point unit. Valid values are @var{sp_lite}
14662 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
14663 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
14664 and @var{dp_full} (equivalent to -mdouble-float).
14667 @opindex mxilinx-fpu
14668 Perform optimizations for floating point unit on Xilinx PPC 405/440.
14671 @itemx -mno-multiple
14673 @opindex mno-multiple
14674 Generate code that uses (does not use) the load multiple word
14675 instructions and the store multiple word instructions. These
14676 instructions are generated by default on POWER systems, and not
14677 generated on PowerPC systems. Do not use @option{-mmultiple} on little
14678 endian PowerPC systems, since those instructions do not work when the
14679 processor is in little endian mode. The exceptions are PPC740 and
14680 PPC750 which permit the instructions usage in little endian mode.
14685 @opindex mno-string
14686 Generate code that uses (does not use) the load string instructions
14687 and the store string word instructions to save multiple registers and
14688 do small block moves. These instructions are generated by default on
14689 POWER systems, and not generated on PowerPC systems. Do not use
14690 @option{-mstring} on little endian PowerPC systems, since those
14691 instructions do not work when the processor is in little endian mode.
14692 The exceptions are PPC740 and PPC750 which permit the instructions
14693 usage in little endian mode.
14698 @opindex mno-update
14699 Generate code that uses (does not use) the load or store instructions
14700 that update the base register to the address of the calculated memory
14701 location. These instructions are generated by default. If you use
14702 @option{-mno-update}, there is a small window between the time that the
14703 stack pointer is updated and the address of the previous frame is
14704 stored, which means code that walks the stack frame across interrupts or
14705 signals may get corrupted data.
14707 @item -mavoid-indexed-addresses
14708 @item -mno-avoid-indexed-addresses
14709 @opindex mavoid-indexed-addresses
14710 @opindex mno-avoid-indexed-addresses
14711 Generate code that tries to avoid (not avoid) the use of indexed load
14712 or store instructions. These instructions can incur a performance
14713 penalty on Power6 processors in certain situations, such as when
14714 stepping through large arrays that cross a 16M boundary. This option
14715 is enabled by default when targetting Power6 and disabled otherwise.
14718 @itemx -mno-fused-madd
14719 @opindex mfused-madd
14720 @opindex mno-fused-madd
14721 Generate code that uses (does not use) the floating point multiply and
14722 accumulate instructions. These instructions are generated by default if
14723 hardware floating is used.
14729 Generate code that uses (does not use) the half-word multiply and
14730 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
14731 These instructions are generated by default when targetting those
14738 Generate code that uses (does not use) the string-search @samp{dlmzb}
14739 instruction on the IBM 405, 440 and 464 processors. This instruction is
14740 generated by default when targetting those processors.
14742 @item -mno-bit-align
14744 @opindex mno-bit-align
14745 @opindex mbit-align
14746 On System V.4 and embedded PowerPC systems do not (do) force structures
14747 and unions that contain bit-fields to be aligned to the base type of the
14750 For example, by default a structure containing nothing but 8
14751 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
14752 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
14753 the structure would be aligned to a 1 byte boundary and be one byte in
14756 @item -mno-strict-align
14757 @itemx -mstrict-align
14758 @opindex mno-strict-align
14759 @opindex mstrict-align
14760 On System V.4 and embedded PowerPC systems do not (do) assume that
14761 unaligned memory references will be handled by the system.
14763 @item -mrelocatable
14764 @itemx -mno-relocatable
14765 @opindex mrelocatable
14766 @opindex mno-relocatable
14767 On embedded PowerPC systems generate code that allows (does not allow)
14768 the program to be relocated to a different address at runtime. If you
14769 use @option{-mrelocatable} on any module, all objects linked together must
14770 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
14772 @item -mrelocatable-lib
14773 @itemx -mno-relocatable-lib
14774 @opindex mrelocatable-lib
14775 @opindex mno-relocatable-lib
14776 On embedded PowerPC systems generate code that allows (does not allow)
14777 the program to be relocated to a different address at runtime. Modules
14778 compiled with @option{-mrelocatable-lib} can be linked with either modules
14779 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
14780 with modules compiled with the @option{-mrelocatable} options.
14786 On System V.4 and embedded PowerPC systems do not (do) assume that
14787 register 2 contains a pointer to a global area pointing to the addresses
14788 used in the program.
14791 @itemx -mlittle-endian
14793 @opindex mlittle-endian
14794 On System V.4 and embedded PowerPC systems compile code for the
14795 processor in little endian mode. The @option{-mlittle-endian} option is
14796 the same as @option{-mlittle}.
14799 @itemx -mbig-endian
14801 @opindex mbig-endian
14802 On System V.4 and embedded PowerPC systems compile code for the
14803 processor in big endian mode. The @option{-mbig-endian} option is
14804 the same as @option{-mbig}.
14806 @item -mdynamic-no-pic
14807 @opindex mdynamic-no-pic
14808 On Darwin and Mac OS X systems, compile code so that it is not
14809 relocatable, but that its external references are relocatable. The
14810 resulting code is suitable for applications, but not shared
14813 @item -mprioritize-restricted-insns=@var{priority}
14814 @opindex mprioritize-restricted-insns
14815 This option controls the priority that is assigned to
14816 dispatch-slot restricted instructions during the second scheduling
14817 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
14818 @var{no/highest/second-highest} priority to dispatch slot restricted
14821 @item -msched-costly-dep=@var{dependence_type}
14822 @opindex msched-costly-dep
14823 This option controls which dependences are considered costly
14824 by the target during instruction scheduling. The argument
14825 @var{dependence_type} takes one of the following values:
14826 @var{no}: no dependence is costly,
14827 @var{all}: all dependences are costly,
14828 @var{true_store_to_load}: a true dependence from store to load is costly,
14829 @var{store_to_load}: any dependence from store to load is costly,
14830 @var{number}: any dependence which latency >= @var{number} is costly.
14832 @item -minsert-sched-nops=@var{scheme}
14833 @opindex minsert-sched-nops
14834 This option controls which nop insertion scheme will be used during
14835 the second scheduling pass. The argument @var{scheme} takes one of the
14837 @var{no}: Don't insert nops.
14838 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
14839 according to the scheduler's grouping.
14840 @var{regroup_exact}: Insert nops to force costly dependent insns into
14841 separate groups. Insert exactly as many nops as needed to force an insn
14842 to a new group, according to the estimated processor grouping.
14843 @var{number}: Insert nops to force costly dependent insns into
14844 separate groups. Insert @var{number} nops to force an insn to a new group.
14847 @opindex mcall-sysv
14848 On System V.4 and embedded PowerPC systems compile code using calling
14849 conventions that adheres to the March 1995 draft of the System V
14850 Application Binary Interface, PowerPC processor supplement. This is the
14851 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
14853 @item -mcall-sysv-eabi
14855 @opindex mcall-sysv-eabi
14856 @opindex mcall-eabi
14857 Specify both @option{-mcall-sysv} and @option{-meabi} options.
14859 @item -mcall-sysv-noeabi
14860 @opindex mcall-sysv-noeabi
14861 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
14863 @item -mcall-aixdesc
14865 On System V.4 and embedded PowerPC systems compile code for the AIX
14869 @opindex mcall-linux
14870 On System V.4 and embedded PowerPC systems compile code for the
14871 Linux-based GNU system.
14875 On System V.4 and embedded PowerPC systems compile code for the
14876 Hurd-based GNU system.
14878 @item -mcall-freebsd
14879 @opindex mcall-freebsd
14880 On System V.4 and embedded PowerPC systems compile code for the
14881 FreeBSD operating system.
14883 @item -mcall-netbsd
14884 @opindex mcall-netbsd
14885 On System V.4 and embedded PowerPC systems compile code for the
14886 NetBSD operating system.
14888 @item -mcall-openbsd
14889 @opindex mcall-netbsd
14890 On System V.4 and embedded PowerPC systems compile code for the
14891 OpenBSD operating system.
14893 @item -maix-struct-return
14894 @opindex maix-struct-return
14895 Return all structures in memory (as specified by the AIX ABI)@.
14897 @item -msvr4-struct-return
14898 @opindex msvr4-struct-return
14899 Return structures smaller than 8 bytes in registers (as specified by the
14902 @item -mabi=@var{abi-type}
14904 Extend the current ABI with a particular extension, or remove such extension.
14905 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
14906 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
14910 Extend the current ABI with SPE ABI extensions. This does not change
14911 the default ABI, instead it adds the SPE ABI extensions to the current
14915 @opindex mabi=no-spe
14916 Disable Booke SPE ABI extensions for the current ABI@.
14918 @item -mabi=ibmlongdouble
14919 @opindex mabi=ibmlongdouble
14920 Change the current ABI to use IBM extended precision long double.
14921 This is a PowerPC 32-bit SYSV ABI option.
14923 @item -mabi=ieeelongdouble
14924 @opindex mabi=ieeelongdouble
14925 Change the current ABI to use IEEE extended precision long double.
14926 This is a PowerPC 32-bit Linux ABI option.
14929 @itemx -mno-prototype
14930 @opindex mprototype
14931 @opindex mno-prototype
14932 On System V.4 and embedded PowerPC systems assume that all calls to
14933 variable argument functions are properly prototyped. Otherwise, the
14934 compiler must insert an instruction before every non prototyped call to
14935 set or clear bit 6 of the condition code register (@var{CR}) to
14936 indicate whether floating point values were passed in the floating point
14937 registers in case the function takes a variable arguments. With
14938 @option{-mprototype}, only calls to prototyped variable argument functions
14939 will set or clear the bit.
14943 On embedded PowerPC systems, assume that the startup module is called
14944 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
14945 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
14950 On embedded PowerPC systems, assume that the startup module is called
14951 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
14956 On embedded PowerPC systems, assume that the startup module is called
14957 @file{crt0.o} and the standard C libraries are @file{libads.a} and
14960 @item -myellowknife
14961 @opindex myellowknife
14962 On embedded PowerPC systems, assume that the startup module is called
14963 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
14968 On System V.4 and embedded PowerPC systems, specify that you are
14969 compiling for a VxWorks system.
14973 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
14974 header to indicate that @samp{eabi} extended relocations are used.
14980 On System V.4 and embedded PowerPC systems do (do not) adhere to the
14981 Embedded Applications Binary Interface (eabi) which is a set of
14982 modifications to the System V.4 specifications. Selecting @option{-meabi}
14983 means that the stack is aligned to an 8 byte boundary, a function
14984 @code{__eabi} is called to from @code{main} to set up the eabi
14985 environment, and the @option{-msdata} option can use both @code{r2} and
14986 @code{r13} to point to two separate small data areas. Selecting
14987 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
14988 do not call an initialization function from @code{main}, and the
14989 @option{-msdata} option will only use @code{r13} to point to a single
14990 small data area. The @option{-meabi} option is on by default if you
14991 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
14994 @opindex msdata=eabi
14995 On System V.4 and embedded PowerPC systems, put small initialized
14996 @code{const} global and static data in the @samp{.sdata2} section, which
14997 is pointed to by register @code{r2}. Put small initialized
14998 non-@code{const} global and static data in the @samp{.sdata} section,
14999 which is pointed to by register @code{r13}. Put small uninitialized
15000 global and static data in the @samp{.sbss} section, which is adjacent to
15001 the @samp{.sdata} section. The @option{-msdata=eabi} option is
15002 incompatible with the @option{-mrelocatable} option. The
15003 @option{-msdata=eabi} option also sets the @option{-memb} option.
15006 @opindex msdata=sysv
15007 On System V.4 and embedded PowerPC systems, put small global and static
15008 data in the @samp{.sdata} section, which is pointed to by register
15009 @code{r13}. Put small uninitialized global and static data in the
15010 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
15011 The @option{-msdata=sysv} option is incompatible with the
15012 @option{-mrelocatable} option.
15014 @item -msdata=default
15016 @opindex msdata=default
15018 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
15019 compile code the same as @option{-msdata=eabi}, otherwise compile code the
15020 same as @option{-msdata=sysv}.
15023 @opindex msdata=data
15024 On System V.4 and embedded PowerPC systems, put small global
15025 data in the @samp{.sdata} section. Put small uninitialized global
15026 data in the @samp{.sbss} section. Do not use register @code{r13}
15027 to address small data however. This is the default behavior unless
15028 other @option{-msdata} options are used.
15032 @opindex msdata=none
15034 On embedded PowerPC systems, put all initialized global and static data
15035 in the @samp{.data} section, and all uninitialized data in the
15036 @samp{.bss} section.
15040 @cindex smaller data references (PowerPC)
15041 @cindex .sdata/.sdata2 references (PowerPC)
15042 On embedded PowerPC systems, put global and static items less than or
15043 equal to @var{num} bytes into the small data or bss sections instead of
15044 the normal data or bss section. By default, @var{num} is 8. The
15045 @option{-G @var{num}} switch is also passed to the linker.
15046 All modules should be compiled with the same @option{-G @var{num}} value.
15049 @itemx -mno-regnames
15051 @opindex mno-regnames
15052 On System V.4 and embedded PowerPC systems do (do not) emit register
15053 names in the assembly language output using symbolic forms.
15056 @itemx -mno-longcall
15058 @opindex mno-longcall
15059 By default assume that all calls are far away so that a longer more
15060 expensive calling sequence is required. This is required for calls
15061 further than 32 megabytes (33,554,432 bytes) from the current location.
15062 A short call will be generated if the compiler knows
15063 the call cannot be that far away. This setting can be overridden by
15064 the @code{shortcall} function attribute, or by @code{#pragma
15067 Some linkers are capable of detecting out-of-range calls and generating
15068 glue code on the fly. On these systems, long calls are unnecessary and
15069 generate slower code. As of this writing, the AIX linker can do this,
15070 as can the GNU linker for PowerPC/64. It is planned to add this feature
15071 to the GNU linker for 32-bit PowerPC systems as well.
15073 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
15074 callee, L42'', plus a ``branch island'' (glue code). The two target
15075 addresses represent the callee and the ``branch island''. The
15076 Darwin/PPC linker will prefer the first address and generate a ``bl
15077 callee'' if the PPC ``bl'' instruction will reach the callee directly;
15078 otherwise, the linker will generate ``bl L42'' to call the ``branch
15079 island''. The ``branch island'' is appended to the body of the
15080 calling function; it computes the full 32-bit address of the callee
15083 On Mach-O (Darwin) systems, this option directs the compiler emit to
15084 the glue for every direct call, and the Darwin linker decides whether
15085 to use or discard it.
15087 In the future, we may cause GCC to ignore all longcall specifications
15088 when the linker is known to generate glue.
15090 @item -mtls-markers
15091 @itemx -mno-tls-markers
15092 @opindex mtls-markers
15093 @opindex mno-tls-markers
15094 Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
15095 specifying the function argument. The relocation allows ld to
15096 reliably associate function call with argument setup instructions for
15097 TLS optimization, which in turn allows gcc to better schedule the
15102 Adds support for multithreading with the @dfn{pthreads} library.
15103 This option sets flags for both the preprocessor and linker.
15107 @node S/390 and zSeries Options
15108 @subsection S/390 and zSeries Options
15109 @cindex S/390 and zSeries Options
15111 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
15115 @itemx -msoft-float
15116 @opindex mhard-float
15117 @opindex msoft-float
15118 Use (do not use) the hardware floating-point instructions and registers
15119 for floating-point operations. When @option{-msoft-float} is specified,
15120 functions in @file{libgcc.a} will be used to perform floating-point
15121 operations. When @option{-mhard-float} is specified, the compiler
15122 generates IEEE floating-point instructions. This is the default.
15125 @itemx -mno-hard-dfp
15127 @opindex mno-hard-dfp
15128 Use (do not use) the hardware decimal-floating-point instructions for
15129 decimal-floating-point operations. When @option{-mno-hard-dfp} is
15130 specified, functions in @file{libgcc.a} will be used to perform
15131 decimal-floating-point operations. When @option{-mhard-dfp} is
15132 specified, the compiler generates decimal-floating-point hardware
15133 instructions. This is the default for @option{-march=z9-ec} or higher.
15135 @item -mlong-double-64
15136 @itemx -mlong-double-128
15137 @opindex mlong-double-64
15138 @opindex mlong-double-128
15139 These switches control the size of @code{long double} type. A size
15140 of 64bit makes the @code{long double} type equivalent to the @code{double}
15141 type. This is the default.
15144 @itemx -mno-backchain
15145 @opindex mbackchain
15146 @opindex mno-backchain
15147 Store (do not store) the address of the caller's frame as backchain pointer
15148 into the callee's stack frame.
15149 A backchain may be needed to allow debugging using tools that do not understand
15150 DWARF-2 call frame information.
15151 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
15152 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
15153 the backchain is placed into the topmost word of the 96/160 byte register
15156 In general, code compiled with @option{-mbackchain} is call-compatible with
15157 code compiled with @option{-mmo-backchain}; however, use of the backchain
15158 for debugging purposes usually requires that the whole binary is built with
15159 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
15160 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
15161 to build a linux kernel use @option{-msoft-float}.
15163 The default is to not maintain the backchain.
15165 @item -mpacked-stack
15166 @itemx -mno-packed-stack
15167 @opindex mpacked-stack
15168 @opindex mno-packed-stack
15169 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
15170 specified, the compiler uses the all fields of the 96/160 byte register save
15171 area only for their default purpose; unused fields still take up stack space.
15172 When @option{-mpacked-stack} is specified, register save slots are densely
15173 packed at the top of the register save area; unused space is reused for other
15174 purposes, allowing for more efficient use of the available stack space.
15175 However, when @option{-mbackchain} is also in effect, the topmost word of
15176 the save area is always used to store the backchain, and the return address
15177 register is always saved two words below the backchain.
15179 As long as the stack frame backchain is not used, code generated with
15180 @option{-mpacked-stack} is call-compatible with code generated with
15181 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
15182 S/390 or zSeries generated code that uses the stack frame backchain at run
15183 time, not just for debugging purposes. Such code is not call-compatible
15184 with code compiled with @option{-mpacked-stack}. Also, note that the
15185 combination of @option{-mbackchain},
15186 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
15187 to build a linux kernel use @option{-msoft-float}.
15189 The default is to not use the packed stack layout.
15192 @itemx -mno-small-exec
15193 @opindex msmall-exec
15194 @opindex mno-small-exec
15195 Generate (or do not generate) code using the @code{bras} instruction
15196 to do subroutine calls.
15197 This only works reliably if the total executable size does not
15198 exceed 64k. The default is to use the @code{basr} instruction instead,
15199 which does not have this limitation.
15205 When @option{-m31} is specified, generate code compliant to the
15206 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
15207 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
15208 particular to generate 64-bit instructions. For the @samp{s390}
15209 targets, the default is @option{-m31}, while the @samp{s390x}
15210 targets default to @option{-m64}.
15216 When @option{-mzarch} is specified, generate code using the
15217 instructions available on z/Architecture.
15218 When @option{-mesa} is specified, generate code using the
15219 instructions available on ESA/390. Note that @option{-mesa} is
15220 not possible with @option{-m64}.
15221 When generating code compliant to the GNU/Linux for S/390 ABI,
15222 the default is @option{-mesa}. When generating code compliant
15223 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
15229 Generate (or do not generate) code using the @code{mvcle} instruction
15230 to perform block moves. When @option{-mno-mvcle} is specified,
15231 use a @code{mvc} loop instead. This is the default unless optimizing for
15238 Print (or do not print) additional debug information when compiling.
15239 The default is to not print debug information.
15241 @item -march=@var{cpu-type}
15243 Generate code that will run on @var{cpu-type}, which is the name of a system
15244 representing a certain processor type. Possible values for
15245 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
15246 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
15247 When generating code using the instructions available on z/Architecture,
15248 the default is @option{-march=z900}. Otherwise, the default is
15249 @option{-march=g5}.
15251 @item -mtune=@var{cpu-type}
15253 Tune to @var{cpu-type} everything applicable about the generated code,
15254 except for the ABI and the set of available instructions.
15255 The list of @var{cpu-type} values is the same as for @option{-march}.
15256 The default is the value used for @option{-march}.
15259 @itemx -mno-tpf-trace
15260 @opindex mtpf-trace
15261 @opindex mno-tpf-trace
15262 Generate code that adds (does not add) in TPF OS specific branches to trace
15263 routines in the operating system. This option is off by default, even
15264 when compiling for the TPF OS@.
15267 @itemx -mno-fused-madd
15268 @opindex mfused-madd
15269 @opindex mno-fused-madd
15270 Generate code that uses (does not use) the floating point multiply and
15271 accumulate instructions. These instructions are generated by default if
15272 hardware floating point is used.
15274 @item -mwarn-framesize=@var{framesize}
15275 @opindex mwarn-framesize
15276 Emit a warning if the current function exceeds the given frame size. Because
15277 this is a compile time check it doesn't need to be a real problem when the program
15278 runs. It is intended to identify functions which most probably cause
15279 a stack overflow. It is useful to be used in an environment with limited stack
15280 size e.g.@: the linux kernel.
15282 @item -mwarn-dynamicstack
15283 @opindex mwarn-dynamicstack
15284 Emit a warning if the function calls alloca or uses dynamically
15285 sized arrays. This is generally a bad idea with a limited stack size.
15287 @item -mstack-guard=@var{stack-guard}
15288 @itemx -mstack-size=@var{stack-size}
15289 @opindex mstack-guard
15290 @opindex mstack-size
15291 If these options are provided the s390 back end emits additional instructions in
15292 the function prologue which trigger a trap if the stack size is @var{stack-guard}
15293 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
15294 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
15295 the frame size of the compiled function is chosen.
15296 These options are intended to be used to help debugging stack overflow problems.
15297 The additionally emitted code causes only little overhead and hence can also be
15298 used in production like systems without greater performance degradation. The given
15299 values have to be exact powers of 2 and @var{stack-size} has to be greater than
15300 @var{stack-guard} without exceeding 64k.
15301 In order to be efficient the extra code makes the assumption that the stack starts
15302 at an address aligned to the value given by @var{stack-size}.
15303 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
15306 @node Score Options
15307 @subsection Score Options
15308 @cindex Score Options
15310 These options are defined for Score implementations:
15315 Compile code for big endian mode. This is the default.
15319 Compile code for little endian mode.
15323 Disable generate bcnz instruction.
15327 Enable generate unaligned load and store instruction.
15331 Enable the use of multiply-accumulate instructions. Disabled by default.
15335 Specify the SCORE5 as the target architecture.
15339 Specify the SCORE5U of the target architecture.
15343 Specify the SCORE7 as the target architecture. This is the default.
15347 Specify the SCORE7D as the target architecture.
15351 @subsection SH Options
15353 These @samp{-m} options are defined for the SH implementations:
15358 Generate code for the SH1.
15362 Generate code for the SH2.
15365 Generate code for the SH2e.
15369 Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
15370 that the floating-point unit is not used.
15372 @item -m2a-single-only
15373 @opindex m2a-single-only
15374 Generate code for the SH2a-FPU, in such a way that no double-precision
15375 floating point operations are used.
15378 @opindex m2a-single
15379 Generate code for the SH2a-FPU assuming the floating-point unit is in
15380 single-precision mode by default.
15384 Generate code for the SH2a-FPU assuming the floating-point unit is in
15385 double-precision mode by default.
15389 Generate code for the SH3.
15393 Generate code for the SH3e.
15397 Generate code for the SH4 without a floating-point unit.
15399 @item -m4-single-only
15400 @opindex m4-single-only
15401 Generate code for the SH4 with a floating-point unit that only
15402 supports single-precision arithmetic.
15406 Generate code for the SH4 assuming the floating-point unit is in
15407 single-precision mode by default.
15411 Generate code for the SH4.
15415 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
15416 floating-point unit is not used.
15418 @item -m4a-single-only
15419 @opindex m4a-single-only
15420 Generate code for the SH4a, in such a way that no double-precision
15421 floating point operations are used.
15424 @opindex m4a-single
15425 Generate code for the SH4a assuming the floating-point unit is in
15426 single-precision mode by default.
15430 Generate code for the SH4a.
15434 Same as @option{-m4a-nofpu}, except that it implicitly passes
15435 @option{-dsp} to the assembler. GCC doesn't generate any DSP
15436 instructions at the moment.
15440 Compile code for the processor in big endian mode.
15444 Compile code for the processor in little endian mode.
15448 Align doubles at 64-bit boundaries. Note that this changes the calling
15449 conventions, and thus some functions from the standard C library will
15450 not work unless you recompile it first with @option{-mdalign}.
15454 Shorten some address references at link time, when possible; uses the
15455 linker option @option{-relax}.
15459 Use 32-bit offsets in @code{switch} tables. The default is to use
15464 Enable the use of bit manipulation instructions on SH2A.
15468 Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
15469 alignment constraints.
15473 Comply with the calling conventions defined by Renesas.
15477 Comply with the calling conventions defined by Renesas.
15481 Comply with the calling conventions defined for GCC before the Renesas
15482 conventions were available. This option is the default for all
15483 targets of the SH toolchain except for @samp{sh-symbianelf}.
15486 @opindex mnomacsave
15487 Mark the @code{MAC} register as call-clobbered, even if
15488 @option{-mhitachi} is given.
15492 Increase IEEE-compliance of floating-point code.
15493 At the moment, this is equivalent to @option{-fno-finite-math-only}.
15494 When generating 16 bit SH opcodes, getting IEEE-conforming results for
15495 comparisons of NANs / infinities incurs extra overhead in every
15496 floating point comparison, therefore the default is set to
15497 @option{-ffinite-math-only}.
15499 @item -minline-ic_invalidate
15500 @opindex minline-ic_invalidate
15501 Inline code to invalidate instruction cache entries after setting up
15502 nested function trampolines.
15503 This option has no effect if -musermode is in effect and the selected
15504 code generation option (e.g. -m4) does not allow the use of the icbi
15506 If the selected code generation option does not allow the use of the icbi
15507 instruction, and -musermode is not in effect, the inlined code will
15508 manipulate the instruction cache address array directly with an associative
15509 write. This not only requires privileged mode, but it will also
15510 fail if the cache line had been mapped via the TLB and has become unmapped.
15514 Dump instruction size and location in the assembly code.
15517 @opindex mpadstruct
15518 This option is deprecated. It pads structures to multiple of 4 bytes,
15519 which is incompatible with the SH ABI@.
15523 Optimize for space instead of speed. Implied by @option{-Os}.
15526 @opindex mprefergot
15527 When generating position-independent code, emit function calls using
15528 the Global Offset Table instead of the Procedure Linkage Table.
15532 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
15533 if the inlined code would not work in user mode.
15534 This is the default when the target is @code{sh-*-linux*}.
15536 @item -multcost=@var{number}
15537 @opindex multcost=@var{number}
15538 Set the cost to assume for a multiply insn.
15540 @item -mdiv=@var{strategy}
15541 @opindex mdiv=@var{strategy}
15542 Set the division strategy to use for SHmedia code. @var{strategy} must be
15543 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
15544 inv:call2, inv:fp .
15545 "fp" performs the operation in floating point. This has a very high latency,
15546 but needs only a few instructions, so it might be a good choice if
15547 your code has enough easily exploitable ILP to allow the compiler to
15548 schedule the floating point instructions together with other instructions.
15549 Division by zero causes a floating point exception.
15550 "inv" uses integer operations to calculate the inverse of the divisor,
15551 and then multiplies the dividend with the inverse. This strategy allows
15552 cse and hoisting of the inverse calculation. Division by zero calculates
15553 an unspecified result, but does not trap.
15554 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
15555 have been found, or if the entire operation has been hoisted to the same
15556 place, the last stages of the inverse calculation are intertwined with the
15557 final multiply to reduce the overall latency, at the expense of using a few
15558 more instructions, and thus offering fewer scheduling opportunities with
15560 "call" calls a library function that usually implements the inv:minlat
15562 This gives high code density for m5-*media-nofpu compilations.
15563 "call2" uses a different entry point of the same library function, where it
15564 assumes that a pointer to a lookup table has already been set up, which
15565 exposes the pointer load to cse / code hoisting optimizations.
15566 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
15567 code generation, but if the code stays unoptimized, revert to the "call",
15568 "call2", or "fp" strategies, respectively. Note that the
15569 potentially-trapping side effect of division by zero is carried by a
15570 separate instruction, so it is possible that all the integer instructions
15571 are hoisted out, but the marker for the side effect stays where it is.
15572 A recombination to fp operations or a call is not possible in that case.
15573 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
15574 that the inverse calculation was nor separated from the multiply, they speed
15575 up division where the dividend fits into 20 bits (plus sign where applicable),
15576 by inserting a test to skip a number of operations in this case; this test
15577 slows down the case of larger dividends. inv20u assumes the case of a such
15578 a small dividend to be unlikely, and inv20l assumes it to be likely.
15580 @item -mdivsi3_libfunc=@var{name}
15581 @opindex mdivsi3_libfunc=@var{name}
15582 Set the name of the library function used for 32 bit signed division to
15583 @var{name}. This only affect the name used in the call and inv:call
15584 division strategies, and the compiler will still expect the same
15585 sets of input/output/clobbered registers as if this option was not present.
15587 @item -mfixed-range=@var{register-range}
15588 @opindex mfixed-range
15589 Generate code treating the given register range as fixed registers.
15590 A fixed register is one that the register allocator can not use. This is
15591 useful when compiling kernel code. A register range is specified as
15592 two registers separated by a dash. Multiple register ranges can be
15593 specified separated by a comma.
15595 @item -madjust-unroll
15596 @opindex madjust-unroll
15597 Throttle unrolling to avoid thrashing target registers.
15598 This option only has an effect if the gcc code base supports the
15599 TARGET_ADJUST_UNROLL_MAX target hook.
15601 @item -mindexed-addressing
15602 @opindex mindexed-addressing
15603 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
15604 This is only safe if the hardware and/or OS implement 32 bit wrap-around
15605 semantics for the indexed addressing mode. The architecture allows the
15606 implementation of processors with 64 bit MMU, which the OS could use to
15607 get 32 bit addressing, but since no current hardware implementation supports
15608 this or any other way to make the indexed addressing mode safe to use in
15609 the 32 bit ABI, the default is -mno-indexed-addressing.
15611 @item -mgettrcost=@var{number}
15612 @opindex mgettrcost=@var{number}
15613 Set the cost assumed for the gettr instruction to @var{number}.
15614 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
15618 Assume pt* instructions won't trap. This will generally generate better
15619 scheduled code, but is unsafe on current hardware. The current architecture
15620 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
15621 This has the unintentional effect of making it unsafe to schedule ptabs /
15622 ptrel before a branch, or hoist it out of a loop. For example,
15623 __do_global_ctors, a part of libgcc that runs constructors at program
15624 startup, calls functions in a list which is delimited by @minus{}1. With the
15625 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
15626 That means that all the constructors will be run a bit quicker, but when
15627 the loop comes to the end of the list, the program crashes because ptabs
15628 loads @minus{}1 into a target register. Since this option is unsafe for any
15629 hardware implementing the current architecture specification, the default
15630 is -mno-pt-fixed. Unless the user specifies a specific cost with
15631 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
15632 this deters register allocation using target registers for storing
15635 @item -minvalid-symbols
15636 @opindex minvalid-symbols
15637 Assume symbols might be invalid. Ordinary function symbols generated by
15638 the compiler will always be valid to load with movi/shori/ptabs or
15639 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
15640 to generate symbols that will cause ptabs / ptrel to trap.
15641 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
15642 It will then prevent cross-basic-block cse, hoisting and most scheduling
15643 of symbol loads. The default is @option{-mno-invalid-symbols}.
15646 @node SPARC Options
15647 @subsection SPARC Options
15648 @cindex SPARC options
15650 These @samp{-m} options are supported on the SPARC:
15653 @item -mno-app-regs
15655 @opindex mno-app-regs
15657 Specify @option{-mapp-regs} to generate output using the global registers
15658 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
15661 To be fully SVR4 ABI compliant at the cost of some performance loss,
15662 specify @option{-mno-app-regs}. You should compile libraries and system
15663 software with this option.
15666 @itemx -mhard-float
15668 @opindex mhard-float
15669 Generate output containing floating point instructions. This is the
15673 @itemx -msoft-float
15675 @opindex msoft-float
15676 Generate output containing library calls for floating point.
15677 @strong{Warning:} the requisite libraries are not available for all SPARC
15678 targets. Normally the facilities of the machine's usual C compiler are
15679 used, but this cannot be done directly in cross-compilation. You must make
15680 your own arrangements to provide suitable library functions for
15681 cross-compilation. The embedded targets @samp{sparc-*-aout} and
15682 @samp{sparclite-*-*} do provide software floating point support.
15684 @option{-msoft-float} changes the calling convention in the output file;
15685 therefore, it is only useful if you compile @emph{all} of a program with
15686 this option. In particular, you need to compile @file{libgcc.a}, the
15687 library that comes with GCC, with @option{-msoft-float} in order for
15690 @item -mhard-quad-float
15691 @opindex mhard-quad-float
15692 Generate output containing quad-word (long double) floating point
15695 @item -msoft-quad-float
15696 @opindex msoft-quad-float
15697 Generate output containing library calls for quad-word (long double)
15698 floating point instructions. The functions called are those specified
15699 in the SPARC ABI@. This is the default.
15701 As of this writing, there are no SPARC implementations that have hardware
15702 support for the quad-word floating point instructions. They all invoke
15703 a trap handler for one of these instructions, and then the trap handler
15704 emulates the effect of the instruction. Because of the trap handler overhead,
15705 this is much slower than calling the ABI library routines. Thus the
15706 @option{-msoft-quad-float} option is the default.
15708 @item -mno-unaligned-doubles
15709 @itemx -munaligned-doubles
15710 @opindex mno-unaligned-doubles
15711 @opindex munaligned-doubles
15712 Assume that doubles have 8 byte alignment. This is the default.
15714 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
15715 alignment only if they are contained in another type, or if they have an
15716 absolute address. Otherwise, it assumes they have 4 byte alignment.
15717 Specifying this option avoids some rare compatibility problems with code
15718 generated by other compilers. It is not the default because it results
15719 in a performance loss, especially for floating point code.
15721 @item -mno-faster-structs
15722 @itemx -mfaster-structs
15723 @opindex mno-faster-structs
15724 @opindex mfaster-structs
15725 With @option{-mfaster-structs}, the compiler assumes that structures
15726 should have 8 byte alignment. This enables the use of pairs of
15727 @code{ldd} and @code{std} instructions for copies in structure
15728 assignment, in place of twice as many @code{ld} and @code{st} pairs.
15729 However, the use of this changed alignment directly violates the SPARC
15730 ABI@. Thus, it's intended only for use on targets where the developer
15731 acknowledges that their resulting code will not be directly in line with
15732 the rules of the ABI@.
15734 @item -mimpure-text
15735 @opindex mimpure-text
15736 @option{-mimpure-text}, used in addition to @option{-shared}, tells
15737 the compiler to not pass @option{-z text} to the linker when linking a
15738 shared object. Using this option, you can link position-dependent
15739 code into a shared object.
15741 @option{-mimpure-text} suppresses the ``relocations remain against
15742 allocatable but non-writable sections'' linker error message.
15743 However, the necessary relocations will trigger copy-on-write, and the
15744 shared object is not actually shared across processes. Instead of
15745 using @option{-mimpure-text}, you should compile all source code with
15746 @option{-fpic} or @option{-fPIC}.
15748 This option is only available on SunOS and Solaris.
15750 @item -mcpu=@var{cpu_type}
15752 Set the instruction set, register set, and instruction scheduling parameters
15753 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
15754 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
15755 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
15756 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
15757 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
15759 Default instruction scheduling parameters are used for values that select
15760 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
15761 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
15763 Here is a list of each supported architecture and their supported
15768 v8: supersparc, hypersparc
15769 sparclite: f930, f934, sparclite86x
15771 v9: ultrasparc, ultrasparc3, niagara, niagara2
15774 By default (unless configured otherwise), GCC generates code for the V7
15775 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
15776 additionally optimizes it for the Cypress CY7C602 chip, as used in the
15777 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
15778 SPARCStation 1, 2, IPX etc.
15780 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
15781 architecture. The only difference from V7 code is that the compiler emits
15782 the integer multiply and integer divide instructions which exist in SPARC-V8
15783 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
15784 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
15787 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
15788 the SPARC architecture. This adds the integer multiply, integer divide step
15789 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
15790 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
15791 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
15792 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
15793 MB86934 chip, which is the more recent SPARClite with FPU@.
15795 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
15796 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
15797 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
15798 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
15799 optimizes it for the TEMIC SPARClet chip.
15801 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
15802 architecture. This adds 64-bit integer and floating-point move instructions,
15803 3 additional floating-point condition code registers and conditional move
15804 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
15805 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
15806 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
15807 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
15808 @option{-mcpu=niagara}, the compiler additionally optimizes it for
15809 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
15810 additionally optimizes it for Sun UltraSPARC T2 chips.
15812 @item -mtune=@var{cpu_type}
15814 Set the instruction scheduling parameters for machine type
15815 @var{cpu_type}, but do not set the instruction set or register set that the
15816 option @option{-mcpu=@var{cpu_type}} would.
15818 The same values for @option{-mcpu=@var{cpu_type}} can be used for
15819 @option{-mtune=@var{cpu_type}}, but the only useful values are those
15820 that select a particular cpu implementation. Those are @samp{cypress},
15821 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
15822 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
15823 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
15828 @opindex mno-v8plus
15829 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
15830 difference from the V8 ABI is that the global and out registers are
15831 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
15832 mode for all SPARC-V9 processors.
15838 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
15839 Visual Instruction Set extensions. The default is @option{-mno-vis}.
15842 These @samp{-m} options are supported in addition to the above
15843 on SPARC-V9 processors in 64-bit environments:
15846 @item -mlittle-endian
15847 @opindex mlittle-endian
15848 Generate code for a processor running in little-endian mode. It is only
15849 available for a few configurations and most notably not on Solaris and Linux.
15855 Generate code for a 32-bit or 64-bit environment.
15856 The 32-bit environment sets int, long and pointer to 32 bits.
15857 The 64-bit environment sets int to 32 bits and long and pointer
15860 @item -mcmodel=medlow
15861 @opindex mcmodel=medlow
15862 Generate code for the Medium/Low code model: 64-bit addresses, programs
15863 must be linked in the low 32 bits of memory. Programs can be statically
15864 or dynamically linked.
15866 @item -mcmodel=medmid
15867 @opindex mcmodel=medmid
15868 Generate code for the Medium/Middle code model: 64-bit addresses, programs
15869 must be linked in the low 44 bits of memory, the text and data segments must
15870 be less than 2GB in size and the data segment must be located within 2GB of
15873 @item -mcmodel=medany
15874 @opindex mcmodel=medany
15875 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
15876 may be linked anywhere in memory, the text and data segments must be less
15877 than 2GB in size and the data segment must be located within 2GB of the
15880 @item -mcmodel=embmedany
15881 @opindex mcmodel=embmedany
15882 Generate code for the Medium/Anywhere code model for embedded systems:
15883 64-bit addresses, the text and data segments must be less than 2GB in
15884 size, both starting anywhere in memory (determined at link time). The
15885 global register %g4 points to the base of the data segment. Programs
15886 are statically linked and PIC is not supported.
15889 @itemx -mno-stack-bias
15890 @opindex mstack-bias
15891 @opindex mno-stack-bias
15892 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
15893 frame pointer if present, are offset by @minus{}2047 which must be added back
15894 when making stack frame references. This is the default in 64-bit mode.
15895 Otherwise, assume no such offset is present.
15898 These switches are supported in addition to the above on Solaris:
15903 Add support for multithreading using the Solaris threads library. This
15904 option sets flags for both the preprocessor and linker. This option does
15905 not affect the thread safety of object code produced by the compiler or
15906 that of libraries supplied with it.
15910 Add support for multithreading using the POSIX threads library. This
15911 option sets flags for both the preprocessor and linker. This option does
15912 not affect the thread safety of object code produced by the compiler or
15913 that of libraries supplied with it.
15917 This is a synonym for @option{-pthreads}.
15921 @subsection SPU Options
15922 @cindex SPU options
15924 These @samp{-m} options are supported on the SPU:
15928 @itemx -merror-reloc
15929 @opindex mwarn-reloc
15930 @opindex merror-reloc
15932 The loader for SPU does not handle dynamic relocations. By default, GCC
15933 will give an error when it generates code that requires a dynamic
15934 relocation. @option{-mno-error-reloc} disables the error,
15935 @option{-mwarn-reloc} will generate a warning instead.
15938 @itemx -munsafe-dma
15940 @opindex munsafe-dma
15942 Instructions which initiate or test completion of DMA must not be
15943 reordered with respect to loads and stores of the memory which is being
15944 accessed. Users typically address this problem using the volatile
15945 keyword, but that can lead to inefficient code in places where the
15946 memory is known to not change. Rather than mark the memory as volatile
15947 we treat the DMA instructions as potentially effecting all memory. With
15948 @option{-munsafe-dma} users must use the volatile keyword to protect
15951 @item -mbranch-hints
15952 @opindex mbranch-hints
15954 By default, GCC will generate a branch hint instruction to avoid
15955 pipeline stalls for always taken or probably taken branches. A hint
15956 will not be generated closer than 8 instructions away from its branch.
15957 There is little reason to disable them, except for debugging purposes,
15958 or to make an object a little bit smaller.
15962 @opindex msmall-mem
15963 @opindex mlarge-mem
15965 By default, GCC generates code assuming that addresses are never larger
15966 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
15967 a full 32 bit address.
15972 By default, GCC links against startup code that assumes the SPU-style
15973 main function interface (which has an unconventional parameter list).
15974 With @option{-mstdmain}, GCC will link your program against startup
15975 code that assumes a C99-style interface to @code{main}, including a
15976 local copy of @code{argv} strings.
15978 @item -mfixed-range=@var{register-range}
15979 @opindex mfixed-range
15980 Generate code treating the given register range as fixed registers.
15981 A fixed register is one that the register allocator can not use. This is
15982 useful when compiling kernel code. A register range is specified as
15983 two registers separated by a dash. Multiple register ranges can be
15984 specified separated by a comma.
15987 @itemx -mdual-nops=@var{n}
15988 @opindex mdual-nops
15989 By default, GCC will insert nops to increase dual issue when it expects
15990 it to increase performance. @var{n} can be a value from 0 to 10. A
15991 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
15992 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
15994 @item -mhint-max-nops=@var{n}
15995 @opindex mhint-max-nops
15996 Maximum number of nops to insert for a branch hint. A branch hint must
15997 be at least 8 instructions away from the branch it is effecting. GCC
15998 will insert up to @var{n} nops to enforce this, otherwise it will not
15999 generate the branch hint.
16001 @item -mhint-max-distance=@var{n}
16002 @opindex mhint-max-distance
16003 The encoding of the branch hint instruction limits the hint to be within
16004 256 instructions of the branch it is effecting. By default, GCC makes
16005 sure it is within 125.
16008 @opindex msafe-hints
16009 Work around a hardware bug which causes the SPU to stall indefinitely.
16010 By default, GCC will insert the @code{hbrp} instruction to make sure
16011 this stall won't happen.
16015 @node System V Options
16016 @subsection Options for System V
16018 These additional options are available on System V Release 4 for
16019 compatibility with other compilers on those systems:
16024 Create a shared object.
16025 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
16029 Identify the versions of each tool used by the compiler, in a
16030 @code{.ident} assembler directive in the output.
16034 Refrain from adding @code{.ident} directives to the output file (this is
16037 @item -YP,@var{dirs}
16039 Search the directories @var{dirs}, and no others, for libraries
16040 specified with @option{-l}.
16042 @item -Ym,@var{dir}
16044 Look in the directory @var{dir} to find the M4 preprocessor.
16045 The assembler uses this option.
16046 @c This is supposed to go with a -Yd for predefined M4 macro files, but
16047 @c the generic assembler that comes with Solaris takes just -Ym.
16051 @subsection V850 Options
16052 @cindex V850 Options
16054 These @samp{-m} options are defined for V850 implementations:
16058 @itemx -mno-long-calls
16059 @opindex mlong-calls
16060 @opindex mno-long-calls
16061 Treat all calls as being far away (near). If calls are assumed to be
16062 far away, the compiler will always load the functions address up into a
16063 register, and call indirect through the pointer.
16069 Do not optimize (do optimize) basic blocks that use the same index
16070 pointer 4 or more times to copy pointer into the @code{ep} register, and
16071 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
16072 option is on by default if you optimize.
16074 @item -mno-prolog-function
16075 @itemx -mprolog-function
16076 @opindex mno-prolog-function
16077 @opindex mprolog-function
16078 Do not use (do use) external functions to save and restore registers
16079 at the prologue and epilogue of a function. The external functions
16080 are slower, but use less code space if more than one function saves
16081 the same number of registers. The @option{-mprolog-function} option
16082 is on by default if you optimize.
16086 Try to make the code as small as possible. At present, this just turns
16087 on the @option{-mep} and @option{-mprolog-function} options.
16089 @item -mtda=@var{n}
16091 Put static or global variables whose size is @var{n} bytes or less into
16092 the tiny data area that register @code{ep} points to. The tiny data
16093 area can hold up to 256 bytes in total (128 bytes for byte references).
16095 @item -msda=@var{n}
16097 Put static or global variables whose size is @var{n} bytes or less into
16098 the small data area that register @code{gp} points to. The small data
16099 area can hold up to 64 kilobytes.
16101 @item -mzda=@var{n}
16103 Put static or global variables whose size is @var{n} bytes or less into
16104 the first 32 kilobytes of memory.
16108 Specify that the target processor is the V850.
16111 @opindex mbig-switch
16112 Generate code suitable for big switch tables. Use this option only if
16113 the assembler/linker complain about out of range branches within a switch
16118 This option will cause r2 and r5 to be used in the code generated by
16119 the compiler. This setting is the default.
16121 @item -mno-app-regs
16122 @opindex mno-app-regs
16123 This option will cause r2 and r5 to be treated as fixed registers.
16127 Specify that the target processor is the V850E1. The preprocessor
16128 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
16129 this option is used.
16133 Specify that the target processor is the V850E@. The preprocessor
16134 constant @samp{__v850e__} will be defined if this option is used.
16136 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
16137 are defined then a default target processor will be chosen and the
16138 relevant @samp{__v850*__} preprocessor constant will be defined.
16140 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
16141 defined, regardless of which processor variant is the target.
16143 @item -mdisable-callt
16144 @opindex mdisable-callt
16145 This option will suppress generation of the CALLT instruction for the
16146 v850e and v850e1 flavors of the v850 architecture. The default is
16147 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
16152 @subsection VAX Options
16153 @cindex VAX options
16155 These @samp{-m} options are defined for the VAX:
16160 Do not output certain jump instructions (@code{aobleq} and so on)
16161 that the Unix assembler for the VAX cannot handle across long
16166 Do output those jump instructions, on the assumption that you
16167 will assemble with the GNU assembler.
16171 Output code for g-format floating point numbers instead of d-format.
16174 @node VxWorks Options
16175 @subsection VxWorks Options
16176 @cindex VxWorks Options
16178 The options in this section are defined for all VxWorks targets.
16179 Options specific to the target hardware are listed with the other
16180 options for that target.
16185 GCC can generate code for both VxWorks kernels and real time processes
16186 (RTPs). This option switches from the former to the latter. It also
16187 defines the preprocessor macro @code{__RTP__}.
16190 @opindex non-static
16191 Link an RTP executable against shared libraries rather than static
16192 libraries. The options @option{-static} and @option{-shared} can
16193 also be used for RTPs (@pxref{Link Options}); @option{-static}
16200 These options are passed down to the linker. They are defined for
16201 compatibility with Diab.
16204 @opindex Xbind-lazy
16205 Enable lazy binding of function calls. This option is equivalent to
16206 @option{-Wl,-z,now} and is defined for compatibility with Diab.
16210 Disable lazy binding of function calls. This option is the default and
16211 is defined for compatibility with Diab.
16214 @node x86-64 Options
16215 @subsection x86-64 Options
16216 @cindex x86-64 options
16218 These are listed under @xref{i386 and x86-64 Options}.
16220 @node i386 and x86-64 Windows Options
16221 @subsection i386 and x86-64 Windows Options
16222 @cindex i386 and x86-64 Windows Options
16224 These additional options are available for Windows targets:
16229 This option is available for Cygwin and MinGW targets. It
16230 specifies that a console application is to be generated, by
16231 instructing the linker to set the PE header subsystem type
16232 required for console applications.
16233 This is the default behavior for Cygwin and MinGW targets.
16237 This option is available for Cygwin targets. It specifies that
16238 the Cygwin internal interface is to be used for predefined
16239 preprocessor macros, C runtime libraries and related linker
16240 paths and options. For Cygwin targets this is the default behavior.
16241 This option is deprecated and will be removed in a future release.
16244 @opindex mno-cygwin
16245 This option is available for Cygwin targets. It specifies that
16246 the MinGW internal interface is to be used instead of Cygwin's, by
16247 setting MinGW-related predefined macros and linker paths and default
16249 This option is deprecated and will be removed in a future release.
16253 This option is available for Cygwin and MinGW targets. It
16254 specifies that a DLL - a dynamic link library - is to be
16255 generated, enabling the selection of the required runtime
16256 startup object and entry point.
16258 @item -mnop-fun-dllimport
16259 @opindex mnop-fun-dllimport
16260 This option is available for Cygwin and MinGW targets. It
16261 specifies that the dllimport attribute should be ignored.
16265 This option is available for MinGW targets. It specifies
16266 that MinGW-specific thread support is to be used.
16270 This option is available for mingw-w64 targets. It specifies
16271 that the UNICODE macro is getting pre-defined and that the
16272 unicode capable runtime startup code is choosen.
16276 This option is available for Cygwin and MinGW targets. It
16277 specifies that the typical Windows pre-defined macros are to
16278 be set in the pre-processor, but does not influence the choice
16279 of runtime library/startup code.
16283 This option is available for Cygwin and MinGW targets. It
16284 specifies that a GUI application is to be generated by
16285 instructing the linker to set the PE header subsystem type
16288 @item -mpe-aligned-commons
16289 @opindex mpe-aligned-commons
16290 This option is available for Cygwin and MinGW targets. It
16291 specifies that the GNU extension to the PE file format that
16292 permits the correct alignment of COMMON variables should be
16293 used when generating code. It will be enabled by default if
16294 GCC detects that the target assembler found during configuration
16295 supports the feature.
16298 See also under @ref{i386 and x86-64 Options} for standard options.
16300 @node Xstormy16 Options
16301 @subsection Xstormy16 Options
16302 @cindex Xstormy16 Options
16304 These options are defined for Xstormy16:
16309 Choose startup files and linker script suitable for the simulator.
16312 @node Xtensa Options
16313 @subsection Xtensa Options
16314 @cindex Xtensa Options
16316 These options are supported for Xtensa targets:
16320 @itemx -mno-const16
16322 @opindex mno-const16
16323 Enable or disable use of @code{CONST16} instructions for loading
16324 constant values. The @code{CONST16} instruction is currently not a
16325 standard option from Tensilica. When enabled, @code{CONST16}
16326 instructions are always used in place of the standard @code{L32R}
16327 instructions. The use of @code{CONST16} is enabled by default only if
16328 the @code{L32R} instruction is not available.
16331 @itemx -mno-fused-madd
16332 @opindex mfused-madd
16333 @opindex mno-fused-madd
16334 Enable or disable use of fused multiply/add and multiply/subtract
16335 instructions in the floating-point option. This has no effect if the
16336 floating-point option is not also enabled. Disabling fused multiply/add
16337 and multiply/subtract instructions forces the compiler to use separate
16338 instructions for the multiply and add/subtract operations. This may be
16339 desirable in some cases where strict IEEE 754-compliant results are
16340 required: the fused multiply add/subtract instructions do not round the
16341 intermediate result, thereby producing results with @emph{more} bits of
16342 precision than specified by the IEEE standard. Disabling fused multiply
16343 add/subtract instructions also ensures that the program output is not
16344 sensitive to the compiler's ability to combine multiply and add/subtract
16347 @item -mserialize-volatile
16348 @itemx -mno-serialize-volatile
16349 @opindex mserialize-volatile
16350 @opindex mno-serialize-volatile
16351 When this option is enabled, GCC inserts @code{MEMW} instructions before
16352 @code{volatile} memory references to guarantee sequential consistency.
16353 The default is @option{-mserialize-volatile}. Use
16354 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
16356 @item -mtext-section-literals
16357 @itemx -mno-text-section-literals
16358 @opindex mtext-section-literals
16359 @opindex mno-text-section-literals
16360 Control the treatment of literal pools. The default is
16361 @option{-mno-text-section-literals}, which places literals in a separate
16362 section in the output file. This allows the literal pool to be placed
16363 in a data RAM/ROM, and it also allows the linker to combine literal
16364 pools from separate object files to remove redundant literals and
16365 improve code size. With @option{-mtext-section-literals}, the literals
16366 are interspersed in the text section in order to keep them as close as
16367 possible to their references. This may be necessary for large assembly
16370 @item -mtarget-align
16371 @itemx -mno-target-align
16372 @opindex mtarget-align
16373 @opindex mno-target-align
16374 When this option is enabled, GCC instructs the assembler to
16375 automatically align instructions to reduce branch penalties at the
16376 expense of some code density. The assembler attempts to widen density
16377 instructions to align branch targets and the instructions following call
16378 instructions. If there are not enough preceding safe density
16379 instructions to align a target, no widening will be performed. The
16380 default is @option{-mtarget-align}. These options do not affect the
16381 treatment of auto-aligned instructions like @code{LOOP}, which the
16382 assembler will always align, either by widening density instructions or
16383 by inserting no-op instructions.
16386 @itemx -mno-longcalls
16387 @opindex mlongcalls
16388 @opindex mno-longcalls
16389 When this option is enabled, GCC instructs the assembler to translate
16390 direct calls to indirect calls unless it can determine that the target
16391 of a direct call is in the range allowed by the call instruction. This
16392 translation typically occurs for calls to functions in other source
16393 files. Specifically, the assembler translates a direct @code{CALL}
16394 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
16395 The default is @option{-mno-longcalls}. This option should be used in
16396 programs where the call target can potentially be out of range. This
16397 option is implemented in the assembler, not the compiler, so the
16398 assembly code generated by GCC will still show direct call
16399 instructions---look at the disassembled object code to see the actual
16400 instructions. Note that the assembler will use an indirect call for
16401 every cross-file call, not just those that really will be out of range.
16404 @node zSeries Options
16405 @subsection zSeries Options
16406 @cindex zSeries options
16408 These are listed under @xref{S/390 and zSeries Options}.
16410 @node Code Gen Options
16411 @section Options for Code Generation Conventions
16412 @cindex code generation conventions
16413 @cindex options, code generation
16414 @cindex run-time options
16416 These machine-independent options control the interface conventions
16417 used in code generation.
16419 Most of them have both positive and negative forms; the negative form
16420 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
16421 one of the forms is listed---the one which is not the default. You
16422 can figure out the other form by either removing @samp{no-} or adding
16426 @item -fbounds-check
16427 @opindex fbounds-check
16428 For front-ends that support it, generate additional code to check that
16429 indices used to access arrays are within the declared range. This is
16430 currently only supported by the Java and Fortran front-ends, where
16431 this option defaults to true and false respectively.
16435 This option generates traps for signed overflow on addition, subtraction,
16436 multiplication operations.
16440 This option instructs the compiler to assume that signed arithmetic
16441 overflow of addition, subtraction and multiplication wraps around
16442 using twos-complement representation. This flag enables some optimizations
16443 and disables others. This option is enabled by default for the Java
16444 front-end, as required by the Java language specification.
16447 @opindex fexceptions
16448 Enable exception handling. Generates extra code needed to propagate
16449 exceptions. For some targets, this implies GCC will generate frame
16450 unwind information for all functions, which can produce significant data
16451 size overhead, although it does not affect execution. If you do not
16452 specify this option, GCC will enable it by default for languages like
16453 C++ which normally require exception handling, and disable it for
16454 languages like C that do not normally require it. However, you may need
16455 to enable this option when compiling C code that needs to interoperate
16456 properly with exception handlers written in C++. You may also wish to
16457 disable this option if you are compiling older C++ programs that don't
16458 use exception handling.
16460 @item -fnon-call-exceptions
16461 @opindex fnon-call-exceptions
16462 Generate code that allows trapping instructions to throw exceptions.
16463 Note that this requires platform-specific runtime support that does
16464 not exist everywhere. Moreover, it only allows @emph{trapping}
16465 instructions to throw exceptions, i.e.@: memory references or floating
16466 point instructions. It does not allow exceptions to be thrown from
16467 arbitrary signal handlers such as @code{SIGALRM}.
16469 @item -funwind-tables
16470 @opindex funwind-tables
16471 Similar to @option{-fexceptions}, except that it will just generate any needed
16472 static data, but will not affect the generated code in any other way.
16473 You will normally not enable this option; instead, a language processor
16474 that needs this handling would enable it on your behalf.
16476 @item -fasynchronous-unwind-tables
16477 @opindex fasynchronous-unwind-tables
16478 Generate unwind table in dwarf2 format, if supported by target machine. The
16479 table is exact at each instruction boundary, so it can be used for stack
16480 unwinding from asynchronous events (such as debugger or garbage collector).
16482 @item -fpcc-struct-return
16483 @opindex fpcc-struct-return
16484 Return ``short'' @code{struct} and @code{union} values in memory like
16485 longer ones, rather than in registers. This convention is less
16486 efficient, but it has the advantage of allowing intercallability between
16487 GCC-compiled files and files compiled with other compilers, particularly
16488 the Portable C Compiler (pcc).
16490 The precise convention for returning structures in memory depends
16491 on the target configuration macros.
16493 Short structures and unions are those whose size and alignment match
16494 that of some integer type.
16496 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
16497 switch is not binary compatible with code compiled with the
16498 @option{-freg-struct-return} switch.
16499 Use it to conform to a non-default application binary interface.
16501 @item -freg-struct-return
16502 @opindex freg-struct-return
16503 Return @code{struct} and @code{union} values in registers when possible.
16504 This is more efficient for small structures than
16505 @option{-fpcc-struct-return}.
16507 If you specify neither @option{-fpcc-struct-return} nor
16508 @option{-freg-struct-return}, GCC defaults to whichever convention is
16509 standard for the target. If there is no standard convention, GCC
16510 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
16511 the principal compiler. In those cases, we can choose the standard, and
16512 we chose the more efficient register return alternative.
16514 @strong{Warning:} code compiled with the @option{-freg-struct-return}
16515 switch is not binary compatible with code compiled with the
16516 @option{-fpcc-struct-return} switch.
16517 Use it to conform to a non-default application binary interface.
16519 @item -fshort-enums
16520 @opindex fshort-enums
16521 Allocate to an @code{enum} type only as many bytes as it needs for the
16522 declared range of possible values. Specifically, the @code{enum} type
16523 will be equivalent to the smallest integer type which has enough room.
16525 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
16526 code that is not binary compatible with code generated without that switch.
16527 Use it to conform to a non-default application binary interface.
16529 @item -fshort-double
16530 @opindex fshort-double
16531 Use the same size for @code{double} as for @code{float}.
16533 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
16534 code that is not binary compatible with code generated without that switch.
16535 Use it to conform to a non-default application binary interface.
16537 @item -fshort-wchar
16538 @opindex fshort-wchar
16539 Override the underlying type for @samp{wchar_t} to be @samp{short
16540 unsigned int} instead of the default for the target. This option is
16541 useful for building programs to run under WINE@.
16543 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
16544 code that is not binary compatible with code generated without that switch.
16545 Use it to conform to a non-default application binary interface.
16548 @opindex fno-common
16549 In C code, controls the placement of uninitialized global variables.
16550 Unix C compilers have traditionally permitted multiple definitions of
16551 such variables in different compilation units by placing the variables
16553 This is the behavior specified by @option{-fcommon}, and is the default
16554 for GCC on most targets.
16555 On the other hand, this behavior is not required by ISO C, and on some
16556 targets may carry a speed or code size penalty on variable references.
16557 The @option{-fno-common} option specifies that the compiler should place
16558 uninitialized global variables in the data section of the object file,
16559 rather than generating them as common blocks.
16560 This has the effect that if the same variable is declared
16561 (without @code{extern}) in two different compilations,
16562 you will get a multiple-definition error when you link them.
16563 In this case, you must compile with @option{-fcommon} instead.
16564 Compiling with @option{-fno-common} is useful on targets for which
16565 it provides better performance, or if you wish to verify that the
16566 program will work on other systems which always treat uninitialized
16567 variable declarations this way.
16571 Ignore the @samp{#ident} directive.
16573 @item -finhibit-size-directive
16574 @opindex finhibit-size-directive
16575 Don't output a @code{.size} assembler directive, or anything else that
16576 would cause trouble if the function is split in the middle, and the
16577 two halves are placed at locations far apart in memory. This option is
16578 used when compiling @file{crtstuff.c}; you should not need to use it
16581 @item -fverbose-asm
16582 @opindex fverbose-asm
16583 Put extra commentary information in the generated assembly code to
16584 make it more readable. This option is generally only of use to those
16585 who actually need to read the generated assembly code (perhaps while
16586 debugging the compiler itself).
16588 @option{-fno-verbose-asm}, the default, causes the
16589 extra information to be omitted and is useful when comparing two assembler
16592 @item -frecord-gcc-switches
16593 @opindex frecord-gcc-switches
16594 This switch causes the command line that was used to invoke the
16595 compiler to be recorded into the object file that is being created.
16596 This switch is only implemented on some targets and the exact format
16597 of the recording is target and binary file format dependent, but it
16598 usually takes the form of a section containing ASCII text. This
16599 switch is related to the @option{-fverbose-asm} switch, but that
16600 switch only records information in the assembler output file as
16601 comments, so it never reaches the object file.
16605 @cindex global offset table
16607 Generate position-independent code (PIC) suitable for use in a shared
16608 library, if supported for the target machine. Such code accesses all
16609 constant addresses through a global offset table (GOT)@. The dynamic
16610 loader resolves the GOT entries when the program starts (the dynamic
16611 loader is not part of GCC; it is part of the operating system). If
16612 the GOT size for the linked executable exceeds a machine-specific
16613 maximum size, you get an error message from the linker indicating that
16614 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
16615 instead. (These maximums are 8k on the SPARC and 32k
16616 on the m68k and RS/6000. The 386 has no such limit.)
16618 Position-independent code requires special support, and therefore works
16619 only on certain machines. For the 386, GCC supports PIC for System V
16620 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
16621 position-independent.
16623 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
16628 If supported for the target machine, emit position-independent code,
16629 suitable for dynamic linking and avoiding any limit on the size of the
16630 global offset table. This option makes a difference on the m68k,
16631 PowerPC and SPARC@.
16633 Position-independent code requires special support, and therefore works
16634 only on certain machines.
16636 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
16643 These options are similar to @option{-fpic} and @option{-fPIC}, but
16644 generated position independent code can be only linked into executables.
16645 Usually these options are used when @option{-pie} GCC option will be
16646 used during linking.
16648 @option{-fpie} and @option{-fPIE} both define the macros
16649 @code{__pie__} and @code{__PIE__}. The macros have the value 1
16650 for @option{-fpie} and 2 for @option{-fPIE}.
16652 @item -fno-jump-tables
16653 @opindex fno-jump-tables
16654 Do not use jump tables for switch statements even where it would be
16655 more efficient than other code generation strategies. This option is
16656 of use in conjunction with @option{-fpic} or @option{-fPIC} for
16657 building code which forms part of a dynamic linker and cannot
16658 reference the address of a jump table. On some targets, jump tables
16659 do not require a GOT and this option is not needed.
16661 @item -ffixed-@var{reg}
16663 Treat the register named @var{reg} as a fixed register; generated code
16664 should never refer to it (except perhaps as a stack pointer, frame
16665 pointer or in some other fixed role).
16667 @var{reg} must be the name of a register. The register names accepted
16668 are machine-specific and are defined in the @code{REGISTER_NAMES}
16669 macro in the machine description macro file.
16671 This flag does not have a negative form, because it specifies a
16674 @item -fcall-used-@var{reg}
16675 @opindex fcall-used
16676 Treat the register named @var{reg} as an allocable register that is
16677 clobbered by function calls. It may be allocated for temporaries or
16678 variables that do not live across a call. Functions compiled this way
16679 will not save and restore the register @var{reg}.
16681 It is an error to used this flag with the frame pointer or stack pointer.
16682 Use of this flag for other registers that have fixed pervasive roles in
16683 the machine's execution model will produce disastrous results.
16685 This flag does not have a negative form, because it specifies a
16688 @item -fcall-saved-@var{reg}
16689 @opindex fcall-saved
16690 Treat the register named @var{reg} as an allocable register saved by
16691 functions. It may be allocated even for temporaries or variables that
16692 live across a call. Functions compiled this way will save and restore
16693 the register @var{reg} if they use it.
16695 It is an error to used this flag with the frame pointer or stack pointer.
16696 Use of this flag for other registers that have fixed pervasive roles in
16697 the machine's execution model will produce disastrous results.
16699 A different sort of disaster will result from the use of this flag for
16700 a register in which function values may be returned.
16702 This flag does not have a negative form, because it specifies a
16705 @item -fpack-struct[=@var{n}]
16706 @opindex fpack-struct
16707 Without a value specified, pack all structure members together without
16708 holes. When a value is specified (which must be a small power of two), pack
16709 structure members according to this value, representing the maximum
16710 alignment (that is, objects with default alignment requirements larger than
16711 this will be output potentially unaligned at the next fitting location.
16713 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
16714 code that is not binary compatible with code generated without that switch.
16715 Additionally, it makes the code suboptimal.
16716 Use it to conform to a non-default application binary interface.
16718 @item -finstrument-functions
16719 @opindex finstrument-functions
16720 Generate instrumentation calls for entry and exit to functions. Just
16721 after function entry and just before function exit, the following
16722 profiling functions will be called with the address of the current
16723 function and its call site. (On some platforms,
16724 @code{__builtin_return_address} does not work beyond the current
16725 function, so the call site information may not be available to the
16726 profiling functions otherwise.)
16729 void __cyg_profile_func_enter (void *this_fn,
16731 void __cyg_profile_func_exit (void *this_fn,
16735 The first argument is the address of the start of the current function,
16736 which may be looked up exactly in the symbol table.
16738 This instrumentation is also done for functions expanded inline in other
16739 functions. The profiling calls will indicate where, conceptually, the
16740 inline function is entered and exited. This means that addressable
16741 versions of such functions must be available. If all your uses of a
16742 function are expanded inline, this may mean an additional expansion of
16743 code size. If you use @samp{extern inline} in your C code, an
16744 addressable version of such functions must be provided. (This is
16745 normally the case anyways, but if you get lucky and the optimizer always
16746 expands the functions inline, you might have gotten away without
16747 providing static copies.)
16749 A function may be given the attribute @code{no_instrument_function}, in
16750 which case this instrumentation will not be done. This can be used, for
16751 example, for the profiling functions listed above, high-priority
16752 interrupt routines, and any functions from which the profiling functions
16753 cannot safely be called (perhaps signal handlers, if the profiling
16754 routines generate output or allocate memory).
16756 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
16757 @opindex finstrument-functions-exclude-file-list
16759 Set the list of functions that are excluded from instrumentation (see
16760 the description of @code{-finstrument-functions}). If the file that
16761 contains a function definition matches with one of @var{file}, then
16762 that function is not instrumented. The match is done on substrings:
16763 if the @var{file} parameter is a substring of the file name, it is
16764 considered to be a match.
16767 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
16768 will exclude any inline function defined in files whose pathnames
16769 contain @code{/bits/stl} or @code{include/sys}.
16771 If, for some reason, you want to include letter @code{','} in one of
16772 @var{sym}, write @code{'\,'}. For example,
16773 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
16774 (note the single quote surrounding the option).
16776 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
16777 @opindex finstrument-functions-exclude-function-list
16779 This is similar to @code{-finstrument-functions-exclude-file-list},
16780 but this option sets the list of function names to be excluded from
16781 instrumentation. The function name to be matched is its user-visible
16782 name, such as @code{vector<int> blah(const vector<int> &)}, not the
16783 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
16784 match is done on substrings: if the @var{sym} parameter is a substring
16785 of the function name, it is considered to be a match. For C99 and C++
16786 extended identifiers, the function name must be given in UTF-8, not
16787 using universal character names.
16789 @item -fstack-check
16790 @opindex fstack-check
16791 Generate code to verify that you do not go beyond the boundary of the
16792 stack. You should specify this flag if you are running in an
16793 environment with multiple threads, but only rarely need to specify it in
16794 a single-threaded environment since stack overflow is automatically
16795 detected on nearly all systems if there is only one stack.
16797 Note that this switch does not actually cause checking to be done; the
16798 operating system or the language runtime must do that. The switch causes
16799 generation of code to ensure that they see the stack being extended.
16801 You can additionally specify a string parameter: @code{no} means no
16802 checking, @code{generic} means force the use of old-style checking,
16803 @code{specific} means use the best checking method and is equivalent
16804 to bare @option{-fstack-check}.
16806 Old-style checking is a generic mechanism that requires no specific
16807 target support in the compiler but comes with the following drawbacks:
16811 Modified allocation strategy for large objects: they will always be
16812 allocated dynamically if their size exceeds a fixed threshold.
16815 Fixed limit on the size of the static frame of functions: when it is
16816 topped by a particular function, stack checking is not reliable and
16817 a warning is issued by the compiler.
16820 Inefficiency: because of both the modified allocation strategy and the
16821 generic implementation, the performances of the code are hampered.
16824 Note that old-style stack checking is also the fallback method for
16825 @code{specific} if no target support has been added in the compiler.
16827 @item -fstack-limit-register=@var{reg}
16828 @itemx -fstack-limit-symbol=@var{sym}
16829 @itemx -fno-stack-limit
16830 @opindex fstack-limit-register
16831 @opindex fstack-limit-symbol
16832 @opindex fno-stack-limit
16833 Generate code to ensure that the stack does not grow beyond a certain value,
16834 either the value of a register or the address of a symbol. If the stack
16835 would grow beyond the value, a signal is raised. For most targets,
16836 the signal is raised before the stack overruns the boundary, so
16837 it is possible to catch the signal without taking special precautions.
16839 For instance, if the stack starts at absolute address @samp{0x80000000}
16840 and grows downwards, you can use the flags
16841 @option{-fstack-limit-symbol=__stack_limit} and
16842 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
16843 of 128KB@. Note that this may only work with the GNU linker.
16845 @cindex aliasing of parameters
16846 @cindex parameters, aliased
16847 @item -fargument-alias
16848 @itemx -fargument-noalias
16849 @itemx -fargument-noalias-global
16850 @itemx -fargument-noalias-anything
16851 @opindex fargument-alias
16852 @opindex fargument-noalias
16853 @opindex fargument-noalias-global
16854 @opindex fargument-noalias-anything
16855 Specify the possible relationships among parameters and between
16856 parameters and global data.
16858 @option{-fargument-alias} specifies that arguments (parameters) may
16859 alias each other and may alias global storage.@*
16860 @option{-fargument-noalias} specifies that arguments do not alias
16861 each other, but may alias global storage.@*
16862 @option{-fargument-noalias-global} specifies that arguments do not
16863 alias each other and do not alias global storage.
16864 @option{-fargument-noalias-anything} specifies that arguments do not
16865 alias any other storage.
16867 Each language will automatically use whatever option is required by
16868 the language standard. You should not need to use these options yourself.
16870 @item -fleading-underscore
16871 @opindex fleading-underscore
16872 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
16873 change the way C symbols are represented in the object file. One use
16874 is to help link with legacy assembly code.
16876 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
16877 generate code that is not binary compatible with code generated without that
16878 switch. Use it to conform to a non-default application binary interface.
16879 Not all targets provide complete support for this switch.
16881 @item -ftls-model=@var{model}
16882 @opindex ftls-model
16883 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
16884 The @var{model} argument should be one of @code{global-dynamic},
16885 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
16887 The default without @option{-fpic} is @code{initial-exec}; with
16888 @option{-fpic} the default is @code{global-dynamic}.
16890 @item -fvisibility=@var{default|internal|hidden|protected}
16891 @opindex fvisibility
16892 Set the default ELF image symbol visibility to the specified option---all
16893 symbols will be marked with this unless overridden within the code.
16894 Using this feature can very substantially improve linking and
16895 load times of shared object libraries, produce more optimized
16896 code, provide near-perfect API export and prevent symbol clashes.
16897 It is @strong{strongly} recommended that you use this in any shared objects
16900 Despite the nomenclature, @code{default} always means public ie;
16901 available to be linked against from outside the shared object.
16902 @code{protected} and @code{internal} are pretty useless in real-world
16903 usage so the only other commonly used option will be @code{hidden}.
16904 The default if @option{-fvisibility} isn't specified is
16905 @code{default}, i.e., make every
16906 symbol public---this causes the same behavior as previous versions of
16909 A good explanation of the benefits offered by ensuring ELF
16910 symbols have the correct visibility is given by ``How To Write
16911 Shared Libraries'' by Ulrich Drepper (which can be found at
16912 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
16913 solution made possible by this option to marking things hidden when
16914 the default is public is to make the default hidden and mark things
16915 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
16916 and @code{__attribute__ ((visibility("default")))} instead of
16917 @code{__declspec(dllexport)} you get almost identical semantics with
16918 identical syntax. This is a great boon to those working with
16919 cross-platform projects.
16921 For those adding visibility support to existing code, you may find
16922 @samp{#pragma GCC visibility} of use. This works by you enclosing
16923 the declarations you wish to set visibility for with (for example)
16924 @samp{#pragma GCC visibility push(hidden)} and
16925 @samp{#pragma GCC visibility pop}.
16926 Bear in mind that symbol visibility should be viewed @strong{as
16927 part of the API interface contract} and thus all new code should
16928 always specify visibility when it is not the default ie; declarations
16929 only for use within the local DSO should @strong{always} be marked explicitly
16930 as hidden as so to avoid PLT indirection overheads---making this
16931 abundantly clear also aids readability and self-documentation of the code.
16932 Note that due to ISO C++ specification requirements, operator new and
16933 operator delete must always be of default visibility.
16935 Be aware that headers from outside your project, in particular system
16936 headers and headers from any other library you use, may not be
16937 expecting to be compiled with visibility other than the default. You
16938 may need to explicitly say @samp{#pragma GCC visibility push(default)}
16939 before including any such headers.
16941 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
16942 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
16943 no modifications. However, this means that calls to @samp{extern}
16944 functions with no explicit visibility will use the PLT, so it is more
16945 effective to use @samp{__attribute ((visibility))} and/or
16946 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
16947 declarations should be treated as hidden.
16949 Note that @samp{-fvisibility} does affect C++ vague linkage
16950 entities. This means that, for instance, an exception class that will
16951 be thrown between DSOs must be explicitly marked with default
16952 visibility so that the @samp{type_info} nodes will be unified between
16955 An overview of these techniques, their benefits and how to use them
16956 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
16962 @node Environment Variables
16963 @section Environment Variables Affecting GCC
16964 @cindex environment variables
16966 @c man begin ENVIRONMENT
16967 This section describes several environment variables that affect how GCC
16968 operates. Some of them work by specifying directories or prefixes to use
16969 when searching for various kinds of files. Some are used to specify other
16970 aspects of the compilation environment.
16972 Note that you can also specify places to search using options such as
16973 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
16974 take precedence over places specified using environment variables, which
16975 in turn take precedence over those specified by the configuration of GCC@.
16976 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
16977 GNU Compiler Collection (GCC) Internals}.
16982 @c @itemx LC_COLLATE
16984 @c @itemx LC_MONETARY
16985 @c @itemx LC_NUMERIC
16990 @c @findex LC_COLLATE
16991 @findex LC_MESSAGES
16992 @c @findex LC_MONETARY
16993 @c @findex LC_NUMERIC
16997 These environment variables control the way that GCC uses
16998 localization information that allow GCC to work with different
16999 national conventions. GCC inspects the locale categories
17000 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
17001 so. These locale categories can be set to any value supported by your
17002 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
17003 Kingdom encoded in UTF-8.
17005 The @env{LC_CTYPE} environment variable specifies character
17006 classification. GCC uses it to determine the character boundaries in
17007 a string; this is needed for some multibyte encodings that contain quote
17008 and escape characters that would otherwise be interpreted as a string
17011 The @env{LC_MESSAGES} environment variable specifies the language to
17012 use in diagnostic messages.
17014 If the @env{LC_ALL} environment variable is set, it overrides the value
17015 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
17016 and @env{LC_MESSAGES} default to the value of the @env{LANG}
17017 environment variable. If none of these variables are set, GCC
17018 defaults to traditional C English behavior.
17022 If @env{TMPDIR} is set, it specifies the directory to use for temporary
17023 files. GCC uses temporary files to hold the output of one stage of
17024 compilation which is to be used as input to the next stage: for example,
17025 the output of the preprocessor, which is the input to the compiler
17028 @item GCC_EXEC_PREFIX
17029 @findex GCC_EXEC_PREFIX
17030 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
17031 names of the subprograms executed by the compiler. No slash is added
17032 when this prefix is combined with the name of a subprogram, but you can
17033 specify a prefix that ends with a slash if you wish.
17035 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
17036 an appropriate prefix to use based on the pathname it was invoked with.
17038 If GCC cannot find the subprogram using the specified prefix, it
17039 tries looking in the usual places for the subprogram.
17041 The default value of @env{GCC_EXEC_PREFIX} is
17042 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
17043 the installed compiler. In many cases @var{prefix} is the value
17044 of @code{prefix} when you ran the @file{configure} script.
17046 Other prefixes specified with @option{-B} take precedence over this prefix.
17048 This prefix is also used for finding files such as @file{crt0.o} that are
17051 In addition, the prefix is used in an unusual way in finding the
17052 directories to search for header files. For each of the standard
17053 directories whose name normally begins with @samp{/usr/local/lib/gcc}
17054 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
17055 replacing that beginning with the specified prefix to produce an
17056 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
17057 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
17058 These alternate directories are searched first; the standard directories
17059 come next. If a standard directory begins with the configured
17060 @var{prefix} then the value of @var{prefix} is replaced by
17061 @env{GCC_EXEC_PREFIX} when looking for header files.
17063 @item COMPILER_PATH
17064 @findex COMPILER_PATH
17065 The value of @env{COMPILER_PATH} is a colon-separated list of
17066 directories, much like @env{PATH}. GCC tries the directories thus
17067 specified when searching for subprograms, if it can't find the
17068 subprograms using @env{GCC_EXEC_PREFIX}.
17071 @findex LIBRARY_PATH
17072 The value of @env{LIBRARY_PATH} is a colon-separated list of
17073 directories, much like @env{PATH}. When configured as a native compiler,
17074 GCC tries the directories thus specified when searching for special
17075 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
17076 using GCC also uses these directories when searching for ordinary
17077 libraries for the @option{-l} option (but directories specified with
17078 @option{-L} come first).
17082 @cindex locale definition
17083 This variable is used to pass locale information to the compiler. One way in
17084 which this information is used is to determine the character set to be used
17085 when character literals, string literals and comments are parsed in C and C++.
17086 When the compiler is configured to allow multibyte characters,
17087 the following values for @env{LANG} are recognized:
17091 Recognize JIS characters.
17093 Recognize SJIS characters.
17095 Recognize EUCJP characters.
17098 If @env{LANG} is not defined, or if it has some other value, then the
17099 compiler will use mblen and mbtowc as defined by the default locale to
17100 recognize and translate multibyte characters.
17104 Some additional environments variables affect the behavior of the
17107 @include cppenv.texi
17111 @node Precompiled Headers
17112 @section Using Precompiled Headers
17113 @cindex precompiled headers
17114 @cindex speed of compilation
17116 Often large projects have many header files that are included in every
17117 source file. The time the compiler takes to process these header files
17118 over and over again can account for nearly all of the time required to
17119 build the project. To make builds faster, GCC allows users to
17120 `precompile' a header file; then, if builds can use the precompiled
17121 header file they will be much faster.
17123 To create a precompiled header file, simply compile it as you would any
17124 other file, if necessary using the @option{-x} option to make the driver
17125 treat it as a C or C++ header file. You will probably want to use a
17126 tool like @command{make} to keep the precompiled header up-to-date when
17127 the headers it contains change.
17129 A precompiled header file will be searched for when @code{#include} is
17130 seen in the compilation. As it searches for the included file
17131 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
17132 compiler looks for a precompiled header in each directory just before it
17133 looks for the include file in that directory. The name searched for is
17134 the name specified in the @code{#include} with @samp{.gch} appended. If
17135 the precompiled header file can't be used, it is ignored.
17137 For instance, if you have @code{#include "all.h"}, and you have
17138 @file{all.h.gch} in the same directory as @file{all.h}, then the
17139 precompiled header file will be used if possible, and the original
17140 header will be used otherwise.
17142 Alternatively, you might decide to put the precompiled header file in a
17143 directory and use @option{-I} to ensure that directory is searched
17144 before (or instead of) the directory containing the original header.
17145 Then, if you want to check that the precompiled header file is always
17146 used, you can put a file of the same name as the original header in this
17147 directory containing an @code{#error} command.
17149 This also works with @option{-include}. So yet another way to use
17150 precompiled headers, good for projects not designed with precompiled
17151 header files in mind, is to simply take most of the header files used by
17152 a project, include them from another header file, precompile that header
17153 file, and @option{-include} the precompiled header. If the header files
17154 have guards against multiple inclusion, they will be skipped because
17155 they've already been included (in the precompiled header).
17157 If you need to precompile the same header file for different
17158 languages, targets, or compiler options, you can instead make a
17159 @emph{directory} named like @file{all.h.gch}, and put each precompiled
17160 header in the directory, perhaps using @option{-o}. It doesn't matter
17161 what you call the files in the directory, every precompiled header in
17162 the directory will be considered. The first precompiled header
17163 encountered in the directory that is valid for this compilation will
17164 be used; they're searched in no particular order.
17166 There are many other possibilities, limited only by your imagination,
17167 good sense, and the constraints of your build system.
17169 A precompiled header file can be used only when these conditions apply:
17173 Only one precompiled header can be used in a particular compilation.
17176 A precompiled header can't be used once the first C token is seen. You
17177 can have preprocessor directives before a precompiled header; you can
17178 even include a precompiled header from inside another header, so long as
17179 there are no C tokens before the @code{#include}.
17182 The precompiled header file must be produced for the same language as
17183 the current compilation. You can't use a C precompiled header for a C++
17187 The precompiled header file must have been produced by the same compiler
17188 binary as the current compilation is using.
17191 Any macros defined before the precompiled header is included must
17192 either be defined in the same way as when the precompiled header was
17193 generated, or must not affect the precompiled header, which usually
17194 means that they don't appear in the precompiled header at all.
17196 The @option{-D} option is one way to define a macro before a
17197 precompiled header is included; using a @code{#define} can also do it.
17198 There are also some options that define macros implicitly, like
17199 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
17202 @item If debugging information is output when using the precompiled
17203 header, using @option{-g} or similar, the same kind of debugging information
17204 must have been output when building the precompiled header. However,
17205 a precompiled header built using @option{-g} can be used in a compilation
17206 when no debugging information is being output.
17208 @item The same @option{-m} options must generally be used when building
17209 and using the precompiled header. @xref{Submodel Options},
17210 for any cases where this rule is relaxed.
17212 @item Each of the following options must be the same when building and using
17213 the precompiled header:
17215 @gccoptlist{-fexceptions}
17218 Some other command-line options starting with @option{-f},
17219 @option{-p}, or @option{-O} must be defined in the same way as when
17220 the precompiled header was generated. At present, it's not clear
17221 which options are safe to change and which are not; the safest choice
17222 is to use exactly the same options when generating and using the
17223 precompiled header. The following are known to be safe:
17225 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
17226 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
17227 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
17232 For all of these except the last, the compiler will automatically
17233 ignore the precompiled header if the conditions aren't met. If you
17234 find an option combination that doesn't work and doesn't cause the
17235 precompiled header to be ignored, please consider filing a bug report,
17238 If you do use differing options when generating and using the
17239 precompiled header, the actual behavior will be a mixture of the
17240 behavior for the options. For instance, if you use @option{-g} to
17241 generate the precompiled header but not when using it, you may or may
17242 not get debugging information for routines in the precompiled header.