1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
3 @c Free Software Foundation, Inc.
4 @c This is part of the GCC manual.
5 @c For copying conditions, see the file gcc.texi.
12 @c man begin COPYRIGHT
13 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
14 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
15 Free Software Foundation, Inc.
17 Permission is granted to copy, distribute and/or modify this document
18 under the terms of the GNU Free Documentation License, Version 1.2 or
19 any later version published by the Free Software Foundation; with the
20 Invariant Sections being ``GNU General Public License'' and ``Funding
21 Free Software'', the Front-Cover texts being (a) (see below), and with
22 the Back-Cover Texts being (b) (see below). A copy of the license is
23 included in the gfdl(7) man page.
25 (a) The FSF's Front-Cover Text is:
29 (b) The FSF's Back-Cover Text is:
31 You have freedom to copy and modify this GNU Manual, like GNU
32 software. Copies published by the Free Software Foundation raise
33 funds for GNU development.
35 @c Set file name and title for the man page.
37 @settitle GNU project C and C++ compiler
39 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
40 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
41 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
42 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
43 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
44 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
45 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
47 Only the most useful options are listed here; see below for the
48 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
51 gpl(7), gfdl(7), fsf-funding(7),
52 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
53 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
54 @file{ld}, @file{binutils} and @file{gdb}.
57 For instructions on reporting bugs, see
61 See the Info entry for @command{gcc}, or
62 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
63 for contributors to GCC@.
68 @chapter GCC Command Options
69 @cindex GCC command options
70 @cindex command options
71 @cindex options, GCC command
73 @c man begin DESCRIPTION
74 When you invoke GCC, it normally does preprocessing, compilation,
75 assembly and linking. The ``overall options'' allow you to stop this
76 process at an intermediate stage. For example, the @option{-c} option
77 says not to run the linker. Then the output consists of object files
78 output by the assembler.
80 Other options are passed on to one stage of processing. Some options
81 control the preprocessor and others the compiler itself. Yet other
82 options control the assembler and linker; most of these are not
83 documented here, since you rarely need to use any of them.
85 @cindex C compilation options
86 Most of the command line options that you can use with GCC are useful
87 for C programs; when an option is only useful with another language
88 (usually C++), the explanation says so explicitly. If the description
89 for a particular option does not mention a source language, you can use
90 that option with all supported languages.
92 @cindex C++ compilation options
93 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
94 options for compiling C++ programs.
96 @cindex grouping options
97 @cindex options, grouping
98 The @command{gcc} program accepts options and file names as operands. Many
99 options have multi-letter names; therefore multiple single-letter options
100 may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
103 @cindex order of options
104 @cindex options, order
105 You can mix options and other arguments. For the most part, the order
106 you use doesn't matter. Order does matter when you use several
107 options of the same kind; for example, if you specify @option{-L} more
108 than once, the directories are searched in the order specified. Also,
109 the placement of the @option{-l} option is significant.
111 Many options have long names starting with @samp{-f} or with
112 @samp{-W}---for example,
113 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
114 these have both positive and negative forms; the negative form of
115 @option{-ffoo} would be @option{-fno-foo}. This manual documents
116 only one of these two forms, whichever one is not the default.
120 @xref{Option Index}, for an index to GCC's options.
123 * Option Summary:: Brief list of all options, without explanations.
124 * Overall Options:: Controlling the kind of output:
125 an executable, object files, assembler files,
126 or preprocessed source.
127 * Invoking G++:: Compiling C++ programs.
128 * C Dialect Options:: Controlling the variant of C language compiled.
129 * C++ Dialect Options:: Variations on C++.
130 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
132 * Language Independent Options:: Controlling how diagnostics should be
134 * Warning Options:: How picky should the compiler be?
135 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
136 * Optimize Options:: How much optimization?
137 * Preprocessor Options:: Controlling header files and macro definitions.
138 Also, getting dependency information for Make.
139 * Assembler Options:: Passing options to the assembler.
140 * Link Options:: Specifying libraries and so on.
141 * Directory Options:: Where to find header files and libraries.
142 Where to find the compiler executable files.
143 * Spec Files:: How to pass switches to sub-processes.
144 * Target Options:: Running a cross-compiler, or an old version of GCC.
145 * Submodel Options:: Specifying minor hardware or convention variations,
146 such as 68010 vs 68020.
147 * Code Gen Options:: Specifying conventions for function calls, data layout
149 * Environment Variables:: Env vars that affect GCC.
150 * Precompiled Headers:: Compiling a header once, and using it many times.
151 * Running Protoize:: Automatically adding or removing function prototypes.
157 @section Option Summary
159 Here is a summary of all the options, grouped by type. Explanations are
160 in the following sections.
163 @item Overall Options
164 @xref{Overall Options,,Options Controlling the Kind of Output}.
165 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
166 -x @var{language} -v -### --help@r{[}=@var{class}@r{]} --target-help @gol
167 --version -wrapper@@@var{file}}
169 @item C Language Options
170 @xref{C Dialect Options,,Options Controlling C Dialect}.
171 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
172 -aux-info @var{filename} @gol
173 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
174 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
175 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
176 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
177 -fsigned-bitfields -fsigned-char @gol
178 -funsigned-bitfields -funsigned-char}
180 @item C++ Language Options
181 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
182 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
183 -fconserve-space -ffriend-injection @gol
184 -fno-elide-constructors @gol
185 -fno-enforce-eh-specs @gol
186 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
187 -fno-implicit-templates @gol
188 -fno-implicit-inline-templates @gol
189 -fno-implement-inlines -fms-extensions @gol
190 -fno-nonansi-builtins -fno-operator-names @gol
191 -fno-optional-diags -fpermissive @gol
192 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
193 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
194 -fno-default-inline -fvisibility-inlines-hidden @gol
195 -fvisibility-ms-compat @gol
196 -Wabi -Wctor-dtor-privacy @gol
197 -Wnon-virtual-dtor -Wreorder @gol
198 -Weffc++ -Wstrict-null-sentinel @gol
199 -Wno-non-template-friend -Wold-style-cast @gol
200 -Woverloaded-virtual -Wno-pmf-conversions @gol
203 @item Objective-C and Objective-C++ Language Options
204 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
205 Objective-C and Objective-C++ Dialects}.
206 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
207 -fgnu-runtime -fnext-runtime @gol
208 -fno-nil-receivers @gol
209 -fobjc-call-cxx-cdtors @gol
210 -fobjc-direct-dispatch @gol
211 -fobjc-exceptions @gol
213 -freplace-objc-classes @gol
216 -Wassign-intercept @gol
217 -Wno-protocol -Wselector @gol
218 -Wstrict-selector-match @gol
219 -Wundeclared-selector}
221 @item Language Independent Options
222 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
223 @gccoptlist{-fmessage-length=@var{n} @gol
224 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
225 -fdiagnostics-show-option}
227 @item Warning Options
228 @xref{Warning Options,,Options to Request or Suppress Warnings}.
229 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
230 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
231 -Wno-attributes -Wno-builtin-macro-redefined @gol
232 -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
233 -Wchar-subscripts -Wclobbered -Wcomment @gol
234 -Wconversion -Wcoverage-mismatch -Wno-deprecated @gol
235 -Wno-deprecated-declarations -Wdisabled-optimization @gol
236 -Wdisallowed-function-list=@var{sym},@var{sym},@dots{} @gol
237 -Wno-div-by-zero -Wempty-body -Wenum-compare -Wno-endif-labels @gol
238 -Werror -Werror=* @gol
239 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
240 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol
241 -Wformat-security -Wformat-y2k @gol
242 -Wframe-larger-than=@var{len} -Wignored-qualifiers @gol
243 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
244 -Winit-self -Winline @gol
245 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
246 -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol
247 -Wlogical-op -Wlong-long @gol
248 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
249 -Wmissing-format-attribute -Wmissing-include-dirs @gol
250 -Wmissing-noreturn -Wno-mudflap @gol
251 -Wno-multichar -Wnonnull -Wno-overflow @gol
252 -Woverlength-strings -Wpacked -Wpadded @gol
253 -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol
254 -Wpointer-arith -Wno-pointer-to-int-cast @gol
255 -Wredundant-decls @gol
256 -Wreturn-type -Wsequence-point -Wshadow @gol
257 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
258 -Wstrict-aliasing -Wstrict-aliasing=n @gol
259 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
260 -Wswitch -Wswitch-default -Wswitch-enum @gol
261 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
262 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
263 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
264 -Wunused-value -Wunused-variable @gol
265 -Wvariadic-macros -Wvla @gol
266 -Wvolatile-register-var -Wwrite-strings}
268 @item C and Objective-C-only Warning Options
269 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
270 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
271 -Wold-style-declaration -Wold-style-definition @gol
272 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
273 -Wdeclaration-after-statement -Wpointer-sign}
275 @item Debugging Options
276 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
277 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
278 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
279 -fdump-noaddr -fdump-unnumbered @gol
280 -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
281 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
282 -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
283 -fdump-statistics @gol
285 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
289 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
292 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
293 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
295 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
297 -fdump-tree-nrv -fdump-tree-vect @gol
298 -fdump-tree-sink @gol
299 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
300 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
301 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
302 -ftree-vectorizer-verbose=@var{n} @gol
303 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
304 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
305 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
306 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
307 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
308 -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
309 -ftest-coverage -ftime-report -fvar-tracking @gol
310 -g -g@var{level} -gcoff -gdwarf-2 @gol
311 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
312 -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
313 -fdebug-prefix-map=@var{old}=@var{new} @gol
314 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
315 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
316 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
317 -print-multi-directory -print-multi-lib @gol
318 -print-prog-name=@var{program} -print-search-dirs -Q @gol
319 -print-sysroot -print-sysroot-headers-suffix @gol
322 @item Optimization Options
323 @xref{Optimize Options,,Options that Control Optimization}.
325 -falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
326 -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol
327 -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol
328 -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol
329 -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping @gol
330 -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range @gol
331 -fdata-sections -fdce -fdce @gol
332 -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse @gol
333 -fearly-inlining -fexpensive-optimizations -ffast-math @gol
334 -ffinite-math-only -ffloat-store -fforward-propagate @gol
335 -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm @gol
336 -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
337 -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
338 -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-marix-reorg -fipa-pta @gol
339 -fipa-pure-const -fipa-reference -fipa-struct-reorg @gol
340 -fipa-type-escape -fira -fira-algorithm=@var{algorithm} @gol
341 -fira-coalesce -fno-ira-share-save-slots @gol
342 -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol
343 -fivopts -fkeep-inline-functions -fkeep-static-consts @gol
344 -floop-block -floop-interchange -floop-strip-mine @gol
345 -fmerge-all-constants -fmerge-constants -fmodulo-sched @gol
346 -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap @gol
347 -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline @gol
348 -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol
349 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
350 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol
351 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
352 -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol
353 -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays @gol
354 -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol
355 -fprofile-generate=@var{path} @gol
356 -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
357 -freciprocal-math -fregmove -frename-registers -freorder-blocks @gol
358 -freorder-blocks-and-partition -freorder-functions @gol
359 -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
360 -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks @gol
361 -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous @gol
362 -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
363 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
364 -fselective-scheduling -fselective-scheduling2 @gol
365 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
366 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
367 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
368 -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
369 -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
370 -ftree-copyrename -ftree-dce @gol
371 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
372 -ftree-loop-distribution @gol
373 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
374 -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-reassoc @gol
375 -ftree-sink -ftree-sra -ftree-switch-conversion @gol
376 -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol
377 -funit-at-a-time -funroll-all-loops -funroll-loops @gol
378 -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol
379 -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol
381 --param @var{name}=@var{value}
382 -O -O0 -O1 -O2 -O3 -Os}
384 @item Preprocessor Options
385 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
386 @gccoptlist{-A@var{question}=@var{answer} @gol
387 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
388 -C -dD -dI -dM -dN @gol
389 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
390 -idirafter @var{dir} @gol
391 -include @var{file} -imacros @var{file} @gol
392 -iprefix @var{file} -iwithprefix @var{dir} @gol
393 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
394 -imultilib @var{dir} -isysroot @var{dir} @gol
395 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
396 -P -fworking-directory -remap @gol
397 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
398 -Xpreprocessor @var{option}}
400 @item Assembler Option
401 @xref{Assembler Options,,Passing Options to the Assembler}.
402 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
405 @xref{Link Options,,Options for Linking}.
406 @gccoptlist{@var{object-file-name} -l@var{library} @gol
407 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
408 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
409 -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
412 @item Directory Options
413 @xref{Directory Options,,Options for Directory Search}.
414 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
415 -specs=@var{file} -I- --sysroot=@var{dir}}
418 @c I wrote this xref this way to avoid overfull hbox. -- rms
419 @xref{Target Options}.
420 @gccoptlist{-V @var{version} -b @var{machine}}
422 @item Machine Dependent Options
423 @xref{Submodel Options,,Hardware Models and Configurations}.
424 @c This list is ordered alphanumerically by subsection name.
425 @c Try and put the significant identifier (CPU or system) first,
426 @c so users have a clue at guessing where the ones they want will be.
429 @gccoptlist{-EB -EL @gol
430 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
431 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
434 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
435 -mabi=@var{name} @gol
436 -mapcs-stack-check -mno-apcs-stack-check @gol
437 -mapcs-float -mno-apcs-float @gol
438 -mapcs-reentrant -mno-apcs-reentrant @gol
439 -msched-prolog -mno-sched-prolog @gol
440 -mlittle-endian -mbig-endian -mwords-little-endian @gol
441 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
442 -mthumb-interwork -mno-thumb-interwork @gol
443 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
444 -mstructure-size-boundary=@var{n} @gol
445 -mabort-on-noreturn @gol
446 -mlong-calls -mno-long-calls @gol
447 -msingle-pic-base -mno-single-pic-base @gol
448 -mpic-register=@var{reg} @gol
449 -mnop-fun-dllimport @gol
450 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
451 -mpoke-function-name @gol
453 -mtpcs-frame -mtpcs-leaf-frame @gol
454 -mcaller-super-interworking -mcallee-super-interworking @gol
459 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
460 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
462 @emph{Blackfin Options}
463 @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
464 -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
465 -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
466 -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
467 -mno-id-shared-library -mshared-library-id=@var{n} @gol
468 -mleaf-id-shared-library -mno-leaf-id-shared-library @gol
469 -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
470 -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram}
473 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
474 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
475 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
476 -mstack-align -mdata-align -mconst-align @gol
477 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
478 -melf -maout -melinux -mlinux -sim -sim2 @gol
479 -mmul-bug-workaround -mno-mul-bug-workaround}
482 @gccoptlist{-mmac -mpush-args}
484 @emph{Darwin Options}
485 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
486 -arch_only -bind_at_load -bundle -bundle_loader @gol
487 -client_name -compatibility_version -current_version @gol
489 -dependency-file -dylib_file -dylinker_install_name @gol
490 -dynamic -dynamiclib -exported_symbols_list @gol
491 -filelist -flat_namespace -force_cpusubtype_ALL @gol
492 -force_flat_namespace -headerpad_max_install_names @gol
494 -image_base -init -install_name -keep_private_externs @gol
495 -multi_module -multiply_defined -multiply_defined_unused @gol
496 -noall_load -no_dead_strip_inits_and_terms @gol
497 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
498 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
499 -private_bundle -read_only_relocs -sectalign @gol
500 -sectobjectsymbols -whyload -seg1addr @gol
501 -sectcreate -sectobjectsymbols -sectorder @gol
502 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
503 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
504 -segprot -segs_read_only_addr -segs_read_write_addr @gol
505 -single_module -static -sub_library -sub_umbrella @gol
506 -twolevel_namespace -umbrella -undefined @gol
507 -unexported_symbols_list -weak_reference_mismatches @gol
508 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
509 -mkernel -mone-byte-bool}
511 @emph{DEC Alpha Options}
512 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
513 -mieee -mieee-with-inexact -mieee-conformant @gol
514 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
515 -mtrap-precision=@var{mode} -mbuild-constants @gol
516 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
517 -mbwx -mmax -mfix -mcix @gol
518 -mfloat-vax -mfloat-ieee @gol
519 -mexplicit-relocs -msmall-data -mlarge-data @gol
520 -msmall-text -mlarge-text @gol
521 -mmemory-latency=@var{time}}
523 @emph{DEC Alpha/VMS Options}
524 @gccoptlist{-mvms-return-codes}
527 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
528 -mhard-float -msoft-float @gol
529 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
530 -mdouble -mno-double @gol
531 -mmedia -mno-media -mmuladd -mno-muladd @gol
532 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
533 -mlinked-fp -mlong-calls -malign-labels @gol
534 -mlibrary-pic -macc-4 -macc-8 @gol
535 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
536 -moptimize-membar -mno-optimize-membar @gol
537 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
538 -mvliw-branch -mno-vliw-branch @gol
539 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
540 -mno-nested-cond-exec -mtomcat-stats @gol
544 @emph{GNU/Linux Options}
545 @gccoptlist{-muclibc}
547 @emph{H8/300 Options}
548 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
551 @gccoptlist{-march=@var{architecture-type} @gol
552 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
553 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
554 -mfixed-range=@var{register-range} @gol
555 -mjump-in-delay -mlinker-opt -mlong-calls @gol
556 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
557 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
558 -mno-jump-in-delay -mno-long-load-store @gol
559 -mno-portable-runtime -mno-soft-float @gol
560 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
561 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
562 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
563 -munix=@var{unix-std} -nolibdld -static -threads}
565 @emph{i386 and x86-64 Options}
566 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
567 -mfpmath=@var{unit} @gol
568 -masm=@var{dialect} -mno-fancy-math-387 @gol
569 -mno-fp-ret-in-387 -msoft-float @gol
570 -mno-wide-multiply -mrtd -malign-double @gol
571 -mpreferred-stack-boundary=@var{num}
572 -mincoming-stack-boundary=@var{num}
573 -mcld -mcx16 -msahf -mrecip @gol
574 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
576 -msse4a -m3dnow -mpopcnt -mabm -msse5 @gol
577 -mthreads -mno-align-stringops -minline-all-stringops @gol
578 -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
579 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
580 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
581 -mveclibabi=@var{type} -mpc32 -mpc64 -mpc80 -mstackrealign @gol
582 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
583 -mcmodel=@var{code-model} @gol
584 -m32 -m64 -mlarge-data-threshold=@var{num} @gol
585 -mfused-madd -mno-fused-madd -msse2avx}
588 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
589 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
590 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
591 -minline-float-divide-max-throughput @gol
592 -minline-int-divide-min-latency @gol
593 -minline-int-divide-max-throughput @gol
594 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
595 -mno-dwarf2-asm -mearly-stop-bits @gol
596 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
597 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
598 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
599 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
600 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
601 -mno-sched-prefer-non-data-spec-insns @gol
602 -mno-sched-prefer-non-control-spec-insns @gol
603 -mno-sched-count-spec-in-critical-path}
605 @emph{M32R/D Options}
606 @gccoptlist{-m32r2 -m32rx -m32r @gol
608 -malign-loops -mno-align-loops @gol
609 -missue-rate=@var{number} @gol
610 -mbranch-cost=@var{number} @gol
611 -mmodel=@var{code-size-model-type} @gol
612 -msdata=@var{sdata-type} @gol
613 -mno-flush-func -mflush-func=@var{name} @gol
614 -mno-flush-trap -mflush-trap=@var{number} @gol
618 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
620 @emph{M680x0 Options}
621 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
622 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
623 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
624 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
625 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
626 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
627 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
628 -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
631 @emph{M68hc1x Options}
632 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
633 -mauto-incdec -minmax -mlong-calls -mshort @gol
634 -msoft-reg-count=@var{count}}
637 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
638 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
639 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
640 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
641 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
644 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
645 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol
646 -mips64 -mips64r2 @gol
647 -mips16 -mno-mips16 -mflip-mips16 @gol
648 -minterlink-mips16 -mno-interlink-mips16 @gol
649 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
650 -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
651 -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol
652 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
653 -mfpu=@var{fpu-type} @gol
654 -msmartmips -mno-smartmips @gol
655 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
656 -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
657 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
658 -G@var{num} -mlocal-sdata -mno-local-sdata @gol
659 -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
660 -membedded-data -mno-embedded-data @gol
661 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
662 -mcode-readable=@var{setting} @gol
663 -msplit-addresses -mno-split-addresses @gol
664 -mexplicit-relocs -mno-explicit-relocs @gol
665 -mcheck-zero-division -mno-check-zero-division @gol
666 -mdivide-traps -mdivide-breaks @gol
667 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
668 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
669 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
670 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 @gol
671 -mfix-sb1 -mno-fix-sb1 @gol
672 -mflush-func=@var{func} -mno-flush-func @gol
673 -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
674 -mfp-exceptions -mno-fp-exceptions @gol
675 -mvr4130-align -mno-vr4130-align}
678 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
679 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
680 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
681 -mno-base-addresses -msingle-exit -mno-single-exit}
683 @emph{MN10300 Options}
684 @gccoptlist{-mmult-bug -mno-mult-bug @gol
685 -mam33 -mno-am33 @gol
686 -mam33-2 -mno-am33-2 @gol
687 -mreturn-pointer-on-d0 @gol
690 @emph{PDP-11 Options}
691 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
692 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
693 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
694 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
695 -mbranch-expensive -mbranch-cheap @gol
696 -msplit -mno-split -munix-asm -mdec-asm}
698 @emph{picoChip Options}
699 @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N}
700 -msymbol-as-address -mno-inefficient-warnings}
702 @emph{PowerPC Options}
703 See RS/6000 and PowerPC Options.
705 @emph{RS/6000 and PowerPC Options}
706 @gccoptlist{-mcpu=@var{cpu-type} @gol
707 -mtune=@var{cpu-type} @gol
708 -mpower -mno-power -mpower2 -mno-power2 @gol
709 -mpowerpc -mpowerpc64 -mno-powerpc @gol
710 -maltivec -mno-altivec @gol
711 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
712 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
713 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
714 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
715 -mnew-mnemonics -mold-mnemonics @gol
716 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
717 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
718 -malign-power -malign-natural @gol
719 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
720 -msingle-float -mdouble-float -msimple-fpu @gol
721 -mstring -mno-string -mupdate -mno-update @gol
722 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
723 -mstrict-align -mno-strict-align -mrelocatable @gol
724 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
725 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
726 -mdynamic-no-pic -maltivec -mswdiv @gol
727 -mprioritize-restricted-insns=@var{priority} @gol
728 -msched-costly-dep=@var{dependence_type} @gol
729 -minsert-sched-nops=@var{scheme} @gol
730 -mcall-sysv -mcall-netbsd @gol
731 -maix-struct-return -msvr4-struct-return @gol
732 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
733 -misel -mno-isel @gol
734 -misel=yes -misel=no @gol
736 -mspe=yes -mspe=no @gol
738 -mgen-cell-microcode -mwarn-cell-microcode @gol
739 -mvrsave -mno-vrsave @gol
740 -mmulhw -mno-mulhw @gol
741 -mdlmzb -mno-dlmzb @gol
742 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
743 -mprototype -mno-prototype @gol
744 -msim -mmvme -mads -myellowknife -memb -msdata @gol
745 -msdata=@var{opt} -mvxworks -G @var{num} -pthread}
747 @emph{S/390 and zSeries Options}
748 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
749 -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
750 -mlong-double-64 -mlong-double-128 @gol
751 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
752 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
753 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
754 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
755 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
758 @gccoptlist{-meb -mel @gol
762 -mscore5 -mscore5u -mscore7 -mscore7d}
765 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
766 -m4-nofpu -m4-single-only -m4-single -m4 @gol
767 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
768 -m5-64media -m5-64media-nofpu @gol
769 -m5-32media -m5-32media-nofpu @gol
770 -m5-compact -m5-compact-nofpu @gol
771 -mb -ml -mdalign -mrelax @gol
772 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
773 -mieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace @gol
774 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
775 -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
776 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
780 @gccoptlist{-mcpu=@var{cpu-type} @gol
781 -mtune=@var{cpu-type} @gol
782 -mcmodel=@var{code-model} @gol
783 -m32 -m64 -mapp-regs -mno-app-regs @gol
784 -mfaster-structs -mno-faster-structs @gol
785 -mfpu -mno-fpu -mhard-float -msoft-float @gol
786 -mhard-quad-float -msoft-quad-float @gol
787 -mimpure-text -mno-impure-text -mlittle-endian @gol
788 -mstack-bias -mno-stack-bias @gol
789 -munaligned-doubles -mno-unaligned-doubles @gol
790 -mv8plus -mno-v8plus -mvis -mno-vis
791 -threads -pthreads -pthread}
794 @gccoptlist{-mwarn-reloc -merror-reloc @gol
795 -msafe-dma -munsafe-dma @gol
797 -msmall-mem -mlarge-mem -mstdmain @gol
798 -mfixed-range=@var{register-range}}
800 @emph{System V Options}
801 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
804 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
805 -mprolog-function -mno-prolog-function -mspace @gol
806 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
807 -mapp-regs -mno-app-regs @gol
808 -mdisable-callt -mno-disable-callt @gol
814 @gccoptlist{-mg -mgnu -munix}
816 @emph{VxWorks Options}
817 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
818 -Xbind-lazy -Xbind-now}
820 @emph{x86-64 Options}
821 See i386 and x86-64 Options.
823 @emph{Xstormy16 Options}
826 @emph{Xtensa Options}
827 @gccoptlist{-mconst16 -mno-const16 @gol
828 -mfused-madd -mno-fused-madd @gol
829 -mserialize-volatile -mno-serialize-volatile @gol
830 -mtext-section-literals -mno-text-section-literals @gol
831 -mtarget-align -mno-target-align @gol
832 -mlongcalls -mno-longcalls}
834 @emph{zSeries Options}
835 See S/390 and zSeries Options.
837 @item Code Generation Options
838 @xref{Code Gen Options,,Options for Code Generation Conventions}.
839 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
840 -ffixed-@var{reg} -fexceptions @gol
841 -fnon-call-exceptions -funwind-tables @gol
842 -fasynchronous-unwind-tables @gol
843 -finhibit-size-directive -finstrument-functions @gol
844 -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
845 -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol
846 -fno-common -fno-ident @gol
847 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
848 -fno-jump-tables @gol
849 -frecord-gcc-switches @gol
850 -freg-struct-return -fshort-enums @gol
851 -fshort-double -fshort-wchar @gol
852 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
853 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
854 -fno-stack-limit -fargument-alias -fargument-noalias @gol
855 -fargument-noalias-global -fargument-noalias-anything @gol
856 -fleading-underscore -ftls-model=@var{model} @gol
857 -ftrapv -fwrapv -fbounds-check @gol
862 * Overall Options:: Controlling the kind of output:
863 an executable, object files, assembler files,
864 or preprocessed source.
865 * C Dialect Options:: Controlling the variant of C language compiled.
866 * C++ Dialect Options:: Variations on C++.
867 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
869 * Language Independent Options:: Controlling how diagnostics should be
871 * Warning Options:: How picky should the compiler be?
872 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
873 * Optimize Options:: How much optimization?
874 * Preprocessor Options:: Controlling header files and macro definitions.
875 Also, getting dependency information for Make.
876 * Assembler Options:: Passing options to the assembler.
877 * Link Options:: Specifying libraries and so on.
878 * Directory Options:: Where to find header files and libraries.
879 Where to find the compiler executable files.
880 * Spec Files:: How to pass switches to sub-processes.
881 * Target Options:: Running a cross-compiler, or an old version of GCC.
884 @node Overall Options
885 @section Options Controlling the Kind of Output
887 Compilation can involve up to four stages: preprocessing, compilation
888 proper, assembly and linking, always in that order. GCC is capable of
889 preprocessing and compiling several files either into several
890 assembler input files, or into one assembler input file; then each
891 assembler input file produces an object file, and linking combines all
892 the object files (those newly compiled, and those specified as input)
893 into an executable file.
895 @cindex file name suffix
896 For any given input file, the file name suffix determines what kind of
901 C source code which must be preprocessed.
904 C source code which should not be preprocessed.
907 C++ source code which should not be preprocessed.
910 Objective-C source code. Note that you must link with the @file{libobjc}
911 library to make an Objective-C program work.
914 Objective-C source code which should not be preprocessed.
918 Objective-C++ source code. Note that you must link with the @file{libobjc}
919 library to make an Objective-C++ program work. Note that @samp{.M} refers
920 to a literal capital M@.
923 Objective-C++ source code which should not be preprocessed.
926 C, C++, Objective-C or Objective-C++ header file to be turned into a
931 @itemx @var{file}.cxx
932 @itemx @var{file}.cpp
933 @itemx @var{file}.CPP
934 @itemx @var{file}.c++
936 C++ source code which must be preprocessed. Note that in @samp{.cxx},
937 the last two letters must both be literally @samp{x}. Likewise,
938 @samp{.C} refers to a literal capital C@.
942 Objective-C++ source code which must be preprocessed.
945 Objective-C++ source code which should not be preprocessed.
950 @itemx @var{file}.hxx
951 @itemx @var{file}.hpp
952 @itemx @var{file}.HPP
953 @itemx @var{file}.h++
954 @itemx @var{file}.tcc
955 C++ header file to be turned into a precompiled header.
958 @itemx @var{file}.for
959 @itemx @var{file}.ftn
960 Fixed form Fortran source code which should not be preprocessed.
963 @itemx @var{file}.FOR
964 @itemx @var{file}.fpp
965 @itemx @var{file}.FPP
966 @itemx @var{file}.FTN
967 Fixed form Fortran source code which must be preprocessed (with the traditional
971 @itemx @var{file}.f95
972 @itemx @var{file}.f03
973 @itemx @var{file}.f08
974 Free form Fortran source code which should not be preprocessed.
977 @itemx @var{file}.F95
978 @itemx @var{file}.F03
979 @itemx @var{file}.F08
980 Free form Fortran source code which must be preprocessed (with the
981 traditional preprocessor).
983 @c FIXME: Descriptions of Java file types.
990 Ada source code file which contains a library unit declaration (a
991 declaration of a package, subprogram, or generic, or a generic
992 instantiation), or a library unit renaming declaration (a package,
993 generic, or subprogram renaming declaration). Such files are also
997 Ada source code file containing a library unit body (a subprogram or
998 package body). Such files are also called @dfn{bodies}.
1000 @c GCC also knows about some suffixes for languages not yet included:
1011 @itemx @var{file}.sx
1012 Assembler code which must be preprocessed.
1015 An object file to be fed straight into linking.
1016 Any file name with no recognized suffix is treated this way.
1020 You can specify the input language explicitly with the @option{-x} option:
1023 @item -x @var{language}
1024 Specify explicitly the @var{language} for the following input files
1025 (rather than letting the compiler choose a default based on the file
1026 name suffix). This option applies to all following input files until
1027 the next @option{-x} option. Possible values for @var{language} are:
1029 c c-header c-cpp-output
1030 c++ c++-header c++-cpp-output
1031 objective-c objective-c-header objective-c-cpp-output
1032 objective-c++ objective-c++-header objective-c++-cpp-output
1033 assembler assembler-with-cpp
1035 f77 f77-cpp-input f95 f95-cpp-input
1040 Turn off any specification of a language, so that subsequent files are
1041 handled according to their file name suffixes (as they are if @option{-x}
1042 has not been used at all).
1044 @item -pass-exit-codes
1045 @opindex pass-exit-codes
1046 Normally the @command{gcc} program will exit with the code of 1 if any
1047 phase of the compiler returns a non-success return code. If you specify
1048 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1049 numerically highest error produced by any phase that returned an error
1050 indication. The C, C++, and Fortran frontends return 4, if an internal
1051 compiler error is encountered.
1054 If you only want some of the stages of compilation, you can use
1055 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1056 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1057 @command{gcc} is to stop. Note that some combinations (for example,
1058 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1063 Compile or assemble the source files, but do not link. The linking
1064 stage simply is not done. The ultimate output is in the form of an
1065 object file for each source file.
1067 By default, the object file name for a source file is made by replacing
1068 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1070 Unrecognized input files, not requiring compilation or assembly, are
1075 Stop after the stage of compilation proper; do not assemble. The output
1076 is in the form of an assembler code file for each non-assembler input
1079 By default, the assembler file name for a source file is made by
1080 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1082 Input files that don't require compilation are ignored.
1086 Stop after the preprocessing stage; do not run the compiler proper. The
1087 output is in the form of preprocessed source code, which is sent to the
1090 Input files which don't require preprocessing are ignored.
1092 @cindex output file option
1095 Place output in file @var{file}. This applies regardless to whatever
1096 sort of output is being produced, whether it be an executable file,
1097 an object file, an assembler file or preprocessed C code.
1099 If @option{-o} is not specified, the default is to put an executable
1100 file in @file{a.out}, the object file for
1101 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1102 assembler file in @file{@var{source}.s}, a precompiled header file in
1103 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1108 Print (on standard error output) the commands executed to run the stages
1109 of compilation. Also print the version number of the compiler driver
1110 program and of the preprocessor and the compiler proper.
1114 Like @option{-v} except the commands are not executed and all command
1115 arguments are quoted. This is useful for shell scripts to capture the
1116 driver-generated command lines.
1120 Use pipes rather than temporary files for communication between the
1121 various stages of compilation. This fails to work on some systems where
1122 the assembler is unable to read from a pipe; but the GNU assembler has
1127 If you are compiling multiple source files, this option tells the driver
1128 to pass all the source files to the compiler at once (for those
1129 languages for which the compiler can handle this). This will allow
1130 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1131 language for which this is supported is C@. If you pass source files for
1132 multiple languages to the driver, using this option, the driver will invoke
1133 the compiler(s) that support IMA once each, passing each compiler all the
1134 source files appropriate for it. For those languages that do not support
1135 IMA this option will be ignored, and the compiler will be invoked once for
1136 each source file in that language. If you use this option in conjunction
1137 with @option{-save-temps}, the compiler will generate multiple
1139 (one for each source file), but only one (combined) @file{.o} or
1144 Print (on the standard output) a description of the command line options
1145 understood by @command{gcc}. If the @option{-v} option is also specified
1146 then @option{--help} will also be passed on to the various processes
1147 invoked by @command{gcc}, so that they can display the command line options
1148 they accept. If the @option{-Wextra} option has also been specified
1149 (prior to the @option{--help} option), then command line options which
1150 have no documentation associated with them will also be displayed.
1153 @opindex target-help
1154 Print (on the standard output) a description of target-specific command
1155 line options for each tool. For some targets extra target-specific
1156 information may also be printed.
1158 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1159 Print (on the standard output) a description of the command line
1160 options understood by the compiler that fit into a specific class.
1161 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1162 @samp{params}, or @var{language}:
1165 @item @samp{optimizers}
1166 This will display all of the optimization options supported by the
1169 @item @samp{warnings}
1170 This will display all of the options controlling warning messages
1171 produced by the compiler.
1174 This will display target-specific options. Unlike the
1175 @option{--target-help} option however, target-specific options of the
1176 linker and assembler will not be displayed. This is because those
1177 tools do not currently support the extended @option{--help=} syntax.
1180 This will display the values recognized by the @option{--param}
1183 @item @var{language}
1184 This will display the options supported for @var{language}, where
1185 @var{language} is the name of one of the languages supported in this
1189 This will display the options that are common to all languages.
1192 It is possible to further refine the output of the @option{--help=}
1193 option by adding a comma separated list of qualifiers after the
1194 class. These can be any from the following list:
1197 @item @samp{undocumented}
1198 Display only those options which are undocumented.
1201 Display options which take an argument that appears after an equal
1202 sign in the same continuous piece of text, such as:
1203 @samp{--help=target}.
1205 @item @samp{separate}
1206 Display options which take an argument that appears as a separate word
1207 following the original option, such as: @samp{-o output-file}.
1210 Thus for example to display all the undocumented target-specific
1211 switches supported by the compiler the following can be used:
1214 --help=target,undocumented
1217 The sense of a qualifier can be inverted by prefixing it with the
1218 @var{^} character, so for example to display all binary warning
1219 options (i.e., ones that are either on or off and that do not take an
1220 argument), which have a description the following can be used:
1223 --help=warnings,^joined,^undocumented
1226 A class can also be used as a qualifier, although this usually
1227 restricts the output by so much that there is nothing to display. One
1228 case where it does work however is when one of the classes is
1229 @var{target}. So for example to display all the target-specific
1230 optimization options the following can be used:
1233 --help=target,optimizers
1236 The @option{--help=} option can be repeated on the command line. Each
1237 successive use will display its requested class of options, skipping
1238 those that have already been displayed.
1240 If the @option{-Q} option appears on the command line before the
1241 @option{--help=} option, then the descriptive text displayed by
1242 @option{--help=} is changed. Instead of describing the displayed
1243 options, an indication is given as to whether the option is enabled,
1244 disabled or set to a specific value (assuming that the compiler
1245 knows this at the point where the @option{--help=} option is used).
1247 Here is a truncated example from the ARM port of @command{gcc}:
1250 % gcc -Q -mabi=2 --help=target -c
1251 The following options are target specific:
1253 -mabort-on-noreturn [disabled]
1257 The output is sensitive to the effects of previous command line
1258 options, so for example it is possible to find out which optimizations
1259 are enabled at @option{-O2} by using:
1262 -O2 --help=optimizers
1265 Alternatively you can discover which binary optimizations are enabled
1266 by @option{-O3} by using:
1269 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1270 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1271 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1276 Display the version number and copyrights of the invoked GCC@.
1280 Invoke all subcommands under a wrapper program. It takes a single
1281 comma separated list as an argument, which will be used to invoke
1285 gcc -c t.c -wrapper gdb,--args
1288 This will invoke all subprograms of gcc under "gdb --args",
1289 thus cc1 invocation will be "gdb --args cc1 ...".
1291 @include @value{srcdir}/../libiberty/at-file.texi
1295 @section Compiling C++ Programs
1297 @cindex suffixes for C++ source
1298 @cindex C++ source file suffixes
1299 C++ source files conventionally use one of the suffixes @samp{.C},
1300 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1301 @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
1302 @samp{.H}, or (for shared template code) @samp{.tcc}; and
1303 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1304 files with these names and compiles them as C++ programs even if you
1305 call the compiler the same way as for compiling C programs (usually
1306 with the name @command{gcc}).
1310 However, the use of @command{gcc} does not add the C++ library.
1311 @command{g++} is a program that calls GCC and treats @samp{.c},
1312 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1313 files unless @option{-x} is used, and automatically specifies linking
1314 against the C++ library. This program is also useful when
1315 precompiling a C header file with a @samp{.h} extension for use in C++
1316 compilations. On many systems, @command{g++} is also installed with
1317 the name @command{c++}.
1319 @cindex invoking @command{g++}
1320 When you compile C++ programs, you may specify many of the same
1321 command-line options that you use for compiling programs in any
1322 language; or command-line options meaningful for C and related
1323 languages; or options that are meaningful only for C++ programs.
1324 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1325 explanations of options for languages related to C@.
1326 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1327 explanations of options that are meaningful only for C++ programs.
1329 @node C Dialect Options
1330 @section Options Controlling C Dialect
1331 @cindex dialect options
1332 @cindex language dialect options
1333 @cindex options, dialect
1335 The following options control the dialect of C (or languages derived
1336 from C, such as C++, Objective-C and Objective-C++) that the compiler
1340 @cindex ANSI support
1344 In C mode, this is equivalent to @samp{-std=c89}. In C++ mode, it is
1345 equivalent to @samp{-std=c++98}.
1347 This turns off certain features of GCC that are incompatible with ISO
1348 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1349 such as the @code{asm} and @code{typeof} keywords, and
1350 predefined macros such as @code{unix} and @code{vax} that identify the
1351 type of system you are using. It also enables the undesirable and
1352 rarely used ISO trigraph feature. For the C compiler,
1353 it disables recognition of C++ style @samp{//} comments as well as
1354 the @code{inline} keyword.
1356 The alternate keywords @code{__asm__}, @code{__extension__},
1357 @code{__inline__} and @code{__typeof__} continue to work despite
1358 @option{-ansi}. You would not want to use them in an ISO C program, of
1359 course, but it is useful to put them in header files that might be included
1360 in compilations done with @option{-ansi}. Alternate predefined macros
1361 such as @code{__unix__} and @code{__vax__} are also available, with or
1362 without @option{-ansi}.
1364 The @option{-ansi} option does not cause non-ISO programs to be
1365 rejected gratuitously. For that, @option{-pedantic} is required in
1366 addition to @option{-ansi}. @xref{Warning Options}.
1368 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1369 option is used. Some header files may notice this macro and refrain
1370 from declaring certain functions or defining certain macros that the
1371 ISO standard doesn't call for; this is to avoid interfering with any
1372 programs that might use these names for other things.
1374 Functions that would normally be built in but do not have semantics
1375 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1376 functions when @option{-ansi} is used. @xref{Other Builtins,,Other
1377 built-in functions provided by GCC}, for details of the functions
1382 Determine the language standard. @xref{Standards,,Language Standards
1383 Supported by GCC}, for details of these standard versions. This option
1384 is currently only supported when compiling C or C++.
1386 The compiler can accept several base standards, such as @samp{c89} or
1387 @samp{c++98}, and GNU dialects of those standards, such as
1388 @samp{gnu89} or @samp{gnu++98}. By specifing a base standard, the
1389 compiler will accept all programs following that standard and those
1390 using GNU extensions that do not contradict it. For example,
1391 @samp{-std=c89} turns off certain features of GCC that are
1392 incompatible with ISO C90, such as the @code{asm} and @code{typeof}
1393 keywords, but not other GNU extensions that do not have a meaning in
1394 ISO C90, such as omitting the middle term of a @code{?:}
1395 expression. On the other hand, by specifing a GNU dialect of a
1396 standard, all features the compiler support are enabled, even when
1397 those features change the meaning of the base standard and some
1398 strict-conforming programs may be rejected. The particular standard
1399 is used by @option{-pedantic} to identify which features are GNU
1400 extensions given that version of the standard. For example
1401 @samp{-std=gnu89 -pedantic} would warn about C++ style @samp{//}
1402 comments, while @samp{-std=gnu99 -pedantic} would not.
1404 A value for this option must be provided; possible values are
1409 Support all ISO C90 programs (certain GNU extensions that conflict
1410 with ISO C90 are disabled). Same as @option{-ansi} for C code.
1412 @item iso9899:199409
1413 ISO C90 as modified in amendment 1.
1419 ISO C99. Note that this standard is not yet fully supported; see
1420 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1421 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1424 GNU dialect of ISO C90 (including some C99 features). This
1425 is the default for C code.
1429 GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC,
1430 this will become the default. The name @samp{gnu9x} is deprecated.
1433 The 1998 ISO C++ standard plus amendments. Same as @option{-ansi} for
1437 GNU dialect of @option{-std=c++98}. This is the default for
1441 The working draft of the upcoming ISO C++0x standard. This option
1442 enables experimental features that are likely to be included in
1443 C++0x. The working draft is constantly changing, and any feature that is
1444 enabled by this flag may be removed from future versions of GCC if it is
1445 not part of the C++0x standard.
1448 GNU dialect of @option{-std=c++0x}. This option enables
1449 experimental features that may be removed in future versions of GCC.
1452 @item -fgnu89-inline
1453 @opindex fgnu89-inline
1454 The option @option{-fgnu89-inline} tells GCC to use the traditional
1455 GNU semantics for @code{inline} functions when in C99 mode.
1456 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1457 is accepted and ignored by GCC versions 4.1.3 up to but not including
1458 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1459 C99 mode. Using this option is roughly equivalent to adding the
1460 @code{gnu_inline} function attribute to all inline functions
1461 (@pxref{Function Attributes}).
1463 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1464 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1465 specifies the default behavior). This option was first supported in
1466 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1468 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1469 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1470 in effect for @code{inline} functions. @xref{Common Predefined
1471 Macros,,,cpp,The C Preprocessor}.
1473 @item -aux-info @var{filename}
1475 Output to the given filename prototyped declarations for all functions
1476 declared and/or defined in a translation unit, including those in header
1477 files. This option is silently ignored in any language other than C@.
1479 Besides declarations, the file indicates, in comments, the origin of
1480 each declaration (source file and line), whether the declaration was
1481 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1482 @samp{O} for old, respectively, in the first character after the line
1483 number and the colon), and whether it came from a declaration or a
1484 definition (@samp{C} or @samp{F}, respectively, in the following
1485 character). In the case of function definitions, a K&R-style list of
1486 arguments followed by their declarations is also provided, inside
1487 comments, after the declaration.
1491 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1492 keyword, so that code can use these words as identifiers. You can use
1493 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1494 instead. @option{-ansi} implies @option{-fno-asm}.
1496 In C++, this switch only affects the @code{typeof} keyword, since
1497 @code{asm} and @code{inline} are standard keywords. You may want to
1498 use the @option{-fno-gnu-keywords} flag instead, which has the same
1499 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1500 switch only affects the @code{asm} and @code{typeof} keywords, since
1501 @code{inline} is a standard keyword in ISO C99.
1504 @itemx -fno-builtin-@var{function}
1505 @opindex fno-builtin
1506 @cindex built-in functions
1507 Don't recognize built-in functions that do not begin with
1508 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1509 functions provided by GCC}, for details of the functions affected,
1510 including those which are not built-in functions when @option{-ansi} or
1511 @option{-std} options for strict ISO C conformance are used because they
1512 do not have an ISO standard meaning.
1514 GCC normally generates special code to handle certain built-in functions
1515 more efficiently; for instance, calls to @code{alloca} may become single
1516 instructions that adjust the stack directly, and calls to @code{memcpy}
1517 may become inline copy loops. The resulting code is often both smaller
1518 and faster, but since the function calls no longer appear as such, you
1519 cannot set a breakpoint on those calls, nor can you change the behavior
1520 of the functions by linking with a different library. In addition,
1521 when a function is recognized as a built-in function, GCC may use
1522 information about that function to warn about problems with calls to
1523 that function, or to generate more efficient code, even if the
1524 resulting code still contains calls to that function. For example,
1525 warnings are given with @option{-Wformat} for bad calls to
1526 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1527 known not to modify global memory.
1529 With the @option{-fno-builtin-@var{function}} option
1530 only the built-in function @var{function} is
1531 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1532 function is named that is not built-in in this version of GCC, this
1533 option is ignored. There is no corresponding
1534 @option{-fbuiltin-@var{function}} option; if you wish to enable
1535 built-in functions selectively when using @option{-fno-builtin} or
1536 @option{-ffreestanding}, you may define macros such as:
1539 #define abs(n) __builtin_abs ((n))
1540 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1545 @cindex hosted environment
1547 Assert that compilation takes place in a hosted environment. This implies
1548 @option{-fbuiltin}. A hosted environment is one in which the
1549 entire standard library is available, and in which @code{main} has a return
1550 type of @code{int}. Examples are nearly everything except a kernel.
1551 This is equivalent to @option{-fno-freestanding}.
1553 @item -ffreestanding
1554 @opindex ffreestanding
1555 @cindex hosted environment
1557 Assert that compilation takes place in a freestanding environment. This
1558 implies @option{-fno-builtin}. A freestanding environment
1559 is one in which the standard library may not exist, and program startup may
1560 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1561 This is equivalent to @option{-fno-hosted}.
1563 @xref{Standards,,Language Standards Supported by GCC}, for details of
1564 freestanding and hosted environments.
1568 @cindex openmp parallel
1569 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1570 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1571 compiler generates parallel code according to the OpenMP Application
1572 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}. This option
1573 implies @option{-pthread}, and thus is only supported on targets that
1574 have support for @option{-pthread}.
1576 @item -fms-extensions
1577 @opindex fms-extensions
1578 Accept some non-standard constructs used in Microsoft header files.
1580 Some cases of unnamed fields in structures and unions are only
1581 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1582 fields within structs/unions}, for details.
1586 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1587 options for strict ISO C conformance) implies @option{-trigraphs}.
1589 @item -no-integrated-cpp
1590 @opindex no-integrated-cpp
1591 Performs a compilation in two passes: preprocessing and compiling. This
1592 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1593 @option{-B} option. The user supplied compilation step can then add in
1594 an additional preprocessing step after normal preprocessing but before
1595 compiling. The default is to use the integrated cpp (internal cpp)
1597 The semantics of this option will change if "cc1", "cc1plus", and
1598 "cc1obj" are merged.
1600 @cindex traditional C language
1601 @cindex C language, traditional
1603 @itemx -traditional-cpp
1604 @opindex traditional-cpp
1605 @opindex traditional
1606 Formerly, these options caused GCC to attempt to emulate a pre-standard
1607 C compiler. They are now only supported with the @option{-E} switch.
1608 The preprocessor continues to support a pre-standard mode. See the GNU
1609 CPP manual for details.
1611 @item -fcond-mismatch
1612 @opindex fcond-mismatch
1613 Allow conditional expressions with mismatched types in the second and
1614 third arguments. The value of such an expression is void. This option
1615 is not supported for C++.
1617 @item -flax-vector-conversions
1618 @opindex flax-vector-conversions
1619 Allow implicit conversions between vectors with differing numbers of
1620 elements and/or incompatible element types. This option should not be
1623 @item -funsigned-char
1624 @opindex funsigned-char
1625 Let the type @code{char} be unsigned, like @code{unsigned char}.
1627 Each kind of machine has a default for what @code{char} should
1628 be. It is either like @code{unsigned char} by default or like
1629 @code{signed char} by default.
1631 Ideally, a portable program should always use @code{signed char} or
1632 @code{unsigned char} when it depends on the signedness of an object.
1633 But many programs have been written to use plain @code{char} and
1634 expect it to be signed, or expect it to be unsigned, depending on the
1635 machines they were written for. This option, and its inverse, let you
1636 make such a program work with the opposite default.
1638 The type @code{char} is always a distinct type from each of
1639 @code{signed char} or @code{unsigned char}, even though its behavior
1640 is always just like one of those two.
1643 @opindex fsigned-char
1644 Let the type @code{char} be signed, like @code{signed char}.
1646 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1647 the negative form of @option{-funsigned-char}. Likewise, the option
1648 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1650 @item -fsigned-bitfields
1651 @itemx -funsigned-bitfields
1652 @itemx -fno-signed-bitfields
1653 @itemx -fno-unsigned-bitfields
1654 @opindex fsigned-bitfields
1655 @opindex funsigned-bitfields
1656 @opindex fno-signed-bitfields
1657 @opindex fno-unsigned-bitfields
1658 These options control whether a bit-field is signed or unsigned, when the
1659 declaration does not use either @code{signed} or @code{unsigned}. By
1660 default, such a bit-field is signed, because this is consistent: the
1661 basic integer types such as @code{int} are signed types.
1664 @node C++ Dialect Options
1665 @section Options Controlling C++ Dialect
1667 @cindex compiler options, C++
1668 @cindex C++ options, command line
1669 @cindex options, C++
1670 This section describes the command-line options that are only meaningful
1671 for C++ programs; but you can also use most of the GNU compiler options
1672 regardless of what language your program is in. For example, you
1673 might compile a file @code{firstClass.C} like this:
1676 g++ -g -frepo -O -c firstClass.C
1680 In this example, only @option{-frepo} is an option meant
1681 only for C++ programs; you can use the other options with any
1682 language supported by GCC@.
1684 Here is a list of options that are @emph{only} for compiling C++ programs:
1688 @item -fabi-version=@var{n}
1689 @opindex fabi-version
1690 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1691 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1692 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1693 the version that conforms most closely to the C++ ABI specification.
1694 Therefore, the ABI obtained using version 0 will change as ABI bugs
1697 The default is version 2.
1699 @item -fno-access-control
1700 @opindex fno-access-control
1701 Turn off all access checking. This switch is mainly useful for working
1702 around bugs in the access control code.
1706 Check that the pointer returned by @code{operator new} is non-null
1707 before attempting to modify the storage allocated. This check is
1708 normally unnecessary because the C++ standard specifies that
1709 @code{operator new} will only return @code{0} if it is declared
1710 @samp{throw()}, in which case the compiler will always check the
1711 return value even without this option. In all other cases, when
1712 @code{operator new} has a non-empty exception specification, memory
1713 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1714 @samp{new (nothrow)}.
1716 @item -fconserve-space
1717 @opindex fconserve-space
1718 Put uninitialized or runtime-initialized global variables into the
1719 common segment, as C does. This saves space in the executable at the
1720 cost of not diagnosing duplicate definitions. If you compile with this
1721 flag and your program mysteriously crashes after @code{main()} has
1722 completed, you may have an object that is being destroyed twice because
1723 two definitions were merged.
1725 This option is no longer useful on most targets, now that support has
1726 been added for putting variables into BSS without making them common.
1728 @item -ffriend-injection
1729 @opindex ffriend-injection
1730 Inject friend functions into the enclosing namespace, so that they are
1731 visible outside the scope of the class in which they are declared.
1732 Friend functions were documented to work this way in the old Annotated
1733 C++ Reference Manual, and versions of G++ before 4.1 always worked
1734 that way. However, in ISO C++ a friend function which is not declared
1735 in an enclosing scope can only be found using argument dependent
1736 lookup. This option causes friends to be injected as they were in
1739 This option is for compatibility, and may be removed in a future
1742 @item -fno-elide-constructors
1743 @opindex fno-elide-constructors
1744 The C++ standard allows an implementation to omit creating a temporary
1745 which is only used to initialize another object of the same type.
1746 Specifying this option disables that optimization, and forces G++ to
1747 call the copy constructor in all cases.
1749 @item -fno-enforce-eh-specs
1750 @opindex fno-enforce-eh-specs
1751 Don't generate code to check for violation of exception specifications
1752 at runtime. This option violates the C++ standard, but may be useful
1753 for reducing code size in production builds, much like defining
1754 @samp{NDEBUG}. This does not give user code permission to throw
1755 exceptions in violation of the exception specifications; the compiler
1756 will still optimize based on the specifications, so throwing an
1757 unexpected exception will result in undefined behavior.
1760 @itemx -fno-for-scope
1762 @opindex fno-for-scope
1763 If @option{-ffor-scope} is specified, the scope of variables declared in
1764 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1765 as specified by the C++ standard.
1766 If @option{-fno-for-scope} is specified, the scope of variables declared in
1767 a @i{for-init-statement} extends to the end of the enclosing scope,
1768 as was the case in old versions of G++, and other (traditional)
1769 implementations of C++.
1771 The default if neither flag is given to follow the standard,
1772 but to allow and give a warning for old-style code that would
1773 otherwise be invalid, or have different behavior.
1775 @item -fno-gnu-keywords
1776 @opindex fno-gnu-keywords
1777 Do not recognize @code{typeof} as a keyword, so that code can use this
1778 word as an identifier. You can use the keyword @code{__typeof__} instead.
1779 @option{-ansi} implies @option{-fno-gnu-keywords}.
1781 @item -fno-implicit-templates
1782 @opindex fno-implicit-templates
1783 Never emit code for non-inline templates which are instantiated
1784 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1785 @xref{Template Instantiation}, for more information.
1787 @item -fno-implicit-inline-templates
1788 @opindex fno-implicit-inline-templates
1789 Don't emit code for implicit instantiations of inline templates, either.
1790 The default is to handle inlines differently so that compiles with and
1791 without optimization will need the same set of explicit instantiations.
1793 @item -fno-implement-inlines
1794 @opindex fno-implement-inlines
1795 To save space, do not emit out-of-line copies of inline functions
1796 controlled by @samp{#pragma implementation}. This will cause linker
1797 errors if these functions are not inlined everywhere they are called.
1799 @item -fms-extensions
1800 @opindex fms-extensions
1801 Disable pedantic warnings about constructs used in MFC, such as implicit
1802 int and getting a pointer to member function via non-standard syntax.
1804 @item -fno-nonansi-builtins
1805 @opindex fno-nonansi-builtins
1806 Disable built-in declarations of functions that are not mandated by
1807 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1808 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1810 @item -fno-operator-names
1811 @opindex fno-operator-names
1812 Do not treat the operator name keywords @code{and}, @code{bitand},
1813 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1814 synonyms as keywords.
1816 @item -fno-optional-diags
1817 @opindex fno-optional-diags
1818 Disable diagnostics that the standard says a compiler does not need to
1819 issue. Currently, the only such diagnostic issued by G++ is the one for
1820 a name having multiple meanings within a class.
1823 @opindex fpermissive
1824 Downgrade some diagnostics about nonconformant code from errors to
1825 warnings. Thus, using @option{-fpermissive} will allow some
1826 nonconforming code to compile.
1830 Enable automatic template instantiation at link time. This option also
1831 implies @option{-fno-implicit-templates}. @xref{Template
1832 Instantiation}, for more information.
1836 Disable generation of information about every class with virtual
1837 functions for use by the C++ runtime type identification features
1838 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1839 of the language, you can save some space by using this flag. Note that
1840 exception handling uses the same information, but it will generate it as
1841 needed. The @samp{dynamic_cast} operator can still be used for casts that
1842 do not require runtime type information, i.e.@: casts to @code{void *} or to
1843 unambiguous base classes.
1847 Emit statistics about front-end processing at the end of the compilation.
1848 This information is generally only useful to the G++ development team.
1850 @item -ftemplate-depth-@var{n}
1851 @opindex ftemplate-depth
1852 Set the maximum instantiation depth for template classes to @var{n}.
1853 A limit on the template instantiation depth is needed to detect
1854 endless recursions during template class instantiation. ANSI/ISO C++
1855 conforming programs must not rely on a maximum depth greater than 17.
1857 @item -fno-threadsafe-statics
1858 @opindex fno-threadsafe-statics
1859 Do not emit the extra code to use the routines specified in the C++
1860 ABI for thread-safe initialization of local statics. You can use this
1861 option to reduce code size slightly in code that doesn't need to be
1864 @item -fuse-cxa-atexit
1865 @opindex fuse-cxa-atexit
1866 Register destructors for objects with static storage duration with the
1867 @code{__cxa_atexit} function rather than the @code{atexit} function.
1868 This option is required for fully standards-compliant handling of static
1869 destructors, but will only work if your C library supports
1870 @code{__cxa_atexit}.
1872 @item -fno-use-cxa-get-exception-ptr
1873 @opindex fno-use-cxa-get-exception-ptr
1874 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1875 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1876 if the runtime routine is not available.
1878 @item -fvisibility-inlines-hidden
1879 @opindex fvisibility-inlines-hidden
1880 This switch declares that the user does not attempt to compare
1881 pointers to inline methods where the addresses of the two functions
1882 were taken in different shared objects.
1884 The effect of this is that GCC may, effectively, mark inline methods with
1885 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1886 appear in the export table of a DSO and do not require a PLT indirection
1887 when used within the DSO@. Enabling this option can have a dramatic effect
1888 on load and link times of a DSO as it massively reduces the size of the
1889 dynamic export table when the library makes heavy use of templates.
1891 The behavior of this switch is not quite the same as marking the
1892 methods as hidden directly, because it does not affect static variables
1893 local to the function or cause the compiler to deduce that
1894 the function is defined in only one shared object.
1896 You may mark a method as having a visibility explicitly to negate the
1897 effect of the switch for that method. For example, if you do want to
1898 compare pointers to a particular inline method, you might mark it as
1899 having default visibility. Marking the enclosing class with explicit
1900 visibility will have no effect.
1902 Explicitly instantiated inline methods are unaffected by this option
1903 as their linkage might otherwise cross a shared library boundary.
1904 @xref{Template Instantiation}.
1906 @item -fvisibility-ms-compat
1907 @opindex fvisibility-ms-compat
1908 This flag attempts to use visibility settings to make GCC's C++
1909 linkage model compatible with that of Microsoft Visual Studio.
1911 The flag makes these changes to GCC's linkage model:
1915 It sets the default visibility to @code{hidden}, like
1916 @option{-fvisibility=hidden}.
1919 Types, but not their members, are not hidden by default.
1922 The One Definition Rule is relaxed for types without explicit
1923 visibility specifications which are defined in more than one different
1924 shared object: those declarations are permitted if they would have
1925 been permitted when this option was not used.
1928 In new code it is better to use @option{-fvisibility=hidden} and
1929 export those classes which are intended to be externally visible.
1930 Unfortunately it is possible for code to rely, perhaps accidentally,
1931 on the Visual Studio behavior.
1933 Among the consequences of these changes are that static data members
1934 of the same type with the same name but defined in different shared
1935 objects will be different, so changing one will not change the other;
1936 and that pointers to function members defined in different shared
1937 objects may not compare equal. When this flag is given, it is a
1938 violation of the ODR to define types with the same name differently.
1942 Do not use weak symbol support, even if it is provided by the linker.
1943 By default, G++ will use weak symbols if they are available. This
1944 option exists only for testing, and should not be used by end-users;
1945 it will result in inferior code and has no benefits. This option may
1946 be removed in a future release of G++.
1950 Do not search for header files in the standard directories specific to
1951 C++, but do still search the other standard directories. (This option
1952 is used when building the C++ library.)
1955 In addition, these optimization, warning, and code generation options
1956 have meanings only for C++ programs:
1959 @item -fno-default-inline
1960 @opindex fno-default-inline
1961 Do not assume @samp{inline} for functions defined inside a class scope.
1962 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1963 functions will have linkage like inline functions; they just won't be
1966 @item -Wabi @r{(C++ and Objective-C++ only)}
1969 Warn when G++ generates code that is probably not compatible with the
1970 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1971 all such cases, there are probably some cases that are not warned about,
1972 even though G++ is generating incompatible code. There may also be
1973 cases where warnings are emitted even though the code that is generated
1976 You should rewrite your code to avoid these warnings if you are
1977 concerned about the fact that code generated by G++ may not be binary
1978 compatible with code generated by other compilers.
1980 The known incompatibilities at this point include:
1985 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1986 pack data into the same byte as a base class. For example:
1989 struct A @{ virtual void f(); int f1 : 1; @};
1990 struct B : public A @{ int f2 : 1; @};
1994 In this case, G++ will place @code{B::f2} into the same byte
1995 as@code{A::f1}; other compilers will not. You can avoid this problem
1996 by explicitly padding @code{A} so that its size is a multiple of the
1997 byte size on your platform; that will cause G++ and other compilers to
1998 layout @code{B} identically.
2001 Incorrect handling of tail-padding for virtual bases. G++ does not use
2002 tail padding when laying out virtual bases. For example:
2005 struct A @{ virtual void f(); char c1; @};
2006 struct B @{ B(); char c2; @};
2007 struct C : public A, public virtual B @{@};
2011 In this case, G++ will not place @code{B} into the tail-padding for
2012 @code{A}; other compilers will. You can avoid this problem by
2013 explicitly padding @code{A} so that its size is a multiple of its
2014 alignment (ignoring virtual base classes); that will cause G++ and other
2015 compilers to layout @code{C} identically.
2018 Incorrect handling of bit-fields with declared widths greater than that
2019 of their underlying types, when the bit-fields appear in a union. For
2023 union U @{ int i : 4096; @};
2027 Assuming that an @code{int} does not have 4096 bits, G++ will make the
2028 union too small by the number of bits in an @code{int}.
2031 Empty classes can be placed at incorrect offsets. For example:
2041 struct C : public B, public A @{@};
2045 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
2046 it should be placed at offset zero. G++ mistakenly believes that the
2047 @code{A} data member of @code{B} is already at offset zero.
2050 Names of template functions whose types involve @code{typename} or
2051 template template parameters can be mangled incorrectly.
2054 template <typename Q>
2055 void f(typename Q::X) @{@}
2057 template <template <typename> class Q>
2058 void f(typename Q<int>::X) @{@}
2062 Instantiations of these templates may be mangled incorrectly.
2066 @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
2067 @opindex Wctor-dtor-privacy
2068 @opindex Wno-ctor-dtor-privacy
2069 Warn when a class seems unusable because all the constructors or
2070 destructors in that class are private, and it has neither friends nor
2071 public static member functions.
2073 @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
2074 @opindex Wnon-virtual-dtor
2075 @opindex Wno-non-virtual-dtor
2076 Warn when a class has virtual functions and accessible non-virtual
2077 destructor, in which case it would be possible but unsafe to delete
2078 an instance of a derived class through a pointer to the base class.
2079 This warning is also enabled if -Weffc++ is specified.
2081 @item -Wreorder @r{(C++ and Objective-C++ only)}
2083 @opindex Wno-reorder
2084 @cindex reordering, warning
2085 @cindex warning for reordering of member initializers
2086 Warn when the order of member initializers given in the code does not
2087 match the order in which they must be executed. For instance:
2093 A(): j (0), i (1) @{ @}
2097 The compiler will rearrange the member initializers for @samp{i}
2098 and @samp{j} to match the declaration order of the members, emitting
2099 a warning to that effect. This warning is enabled by @option{-Wall}.
2102 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2105 @item -Weffc++ @r{(C++ and Objective-C++ only)}
2108 Warn about violations of the following style guidelines from Scott Meyers'
2109 @cite{Effective C++} book:
2113 Item 11: Define a copy constructor and an assignment operator for classes
2114 with dynamically allocated memory.
2117 Item 12: Prefer initialization to assignment in constructors.
2120 Item 14: Make destructors virtual in base classes.
2123 Item 15: Have @code{operator=} return a reference to @code{*this}.
2126 Item 23: Don't try to return a reference when you must return an object.
2130 Also warn about violations of the following style guidelines from
2131 Scott Meyers' @cite{More Effective C++} book:
2135 Item 6: Distinguish between prefix and postfix forms of increment and
2136 decrement operators.
2139 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2143 When selecting this option, be aware that the standard library
2144 headers do not obey all of these guidelines; use @samp{grep -v}
2145 to filter out those warnings.
2147 @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
2148 @opindex Wstrict-null-sentinel
2149 @opindex Wno-strict-null-sentinel
2150 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2151 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2152 to @code{__null}. Although it is a null pointer constant not a null pointer,
2153 it is guaranteed to of the same size as a pointer. But this use is
2154 not portable across different compilers.
2156 @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
2157 @opindex Wno-non-template-friend
2158 @opindex Wnon-template-friend
2159 Disable warnings when non-templatized friend functions are declared
2160 within a template. Since the advent of explicit template specification
2161 support in G++, if the name of the friend is an unqualified-id (i.e.,
2162 @samp{friend foo(int)}), the C++ language specification demands that the
2163 friend declare or define an ordinary, nontemplate function. (Section
2164 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2165 could be interpreted as a particular specialization of a templatized
2166 function. Because this non-conforming behavior is no longer the default
2167 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2168 check existing code for potential trouble spots and is on by default.
2169 This new compiler behavior can be turned off with
2170 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2171 but disables the helpful warning.
2173 @item -Wold-style-cast @r{(C++ and Objective-C++ only)}
2174 @opindex Wold-style-cast
2175 @opindex Wno-old-style-cast
2176 Warn if an old-style (C-style) cast to a non-void type is used within
2177 a C++ program. The new-style casts (@samp{dynamic_cast},
2178 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2179 less vulnerable to unintended effects and much easier to search for.
2181 @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
2182 @opindex Woverloaded-virtual
2183 @opindex Wno-overloaded-virtual
2184 @cindex overloaded virtual fn, warning
2185 @cindex warning for overloaded virtual fn
2186 Warn when a function declaration hides virtual functions from a
2187 base class. For example, in:
2194 struct B: public A @{
2199 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2207 will fail to compile.
2209 @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
2210 @opindex Wno-pmf-conversions
2211 @opindex Wpmf-conversions
2212 Disable the diagnostic for converting a bound pointer to member function
2215 @item -Wsign-promo @r{(C++ and Objective-C++ only)}
2216 @opindex Wsign-promo
2217 @opindex Wno-sign-promo
2218 Warn when overload resolution chooses a promotion from unsigned or
2219 enumerated type to a signed type, over a conversion to an unsigned type of
2220 the same size. Previous versions of G++ would try to preserve
2221 unsignedness, but the standard mandates the current behavior.
2226 A& operator = (int);
2236 In this example, G++ will synthesize a default @samp{A& operator =
2237 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2240 @node Objective-C and Objective-C++ Dialect Options
2241 @section Options Controlling Objective-C and Objective-C++ Dialects
2243 @cindex compiler options, Objective-C and Objective-C++
2244 @cindex Objective-C and Objective-C++ options, command line
2245 @cindex options, Objective-C and Objective-C++
2246 (NOTE: This manual does not describe the Objective-C and Objective-C++
2247 languages themselves. See @xref{Standards,,Language Standards
2248 Supported by GCC}, for references.)
2250 This section describes the command-line options that are only meaningful
2251 for Objective-C and Objective-C++ programs, but you can also use most of
2252 the language-independent GNU compiler options.
2253 For example, you might compile a file @code{some_class.m} like this:
2256 gcc -g -fgnu-runtime -O -c some_class.m
2260 In this example, @option{-fgnu-runtime} is an option meant only for
2261 Objective-C and Objective-C++ programs; you can use the other options with
2262 any language supported by GCC@.
2264 Note that since Objective-C is an extension of the C language, Objective-C
2265 compilations may also use options specific to the C front-end (e.g.,
2266 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2267 C++-specific options (e.g., @option{-Wabi}).
2269 Here is a list of options that are @emph{only} for compiling Objective-C
2270 and Objective-C++ programs:
2273 @item -fconstant-string-class=@var{class-name}
2274 @opindex fconstant-string-class
2275 Use @var{class-name} as the name of the class to instantiate for each
2276 literal string specified with the syntax @code{@@"@dots{}"}. The default
2277 class name is @code{NXConstantString} if the GNU runtime is being used, and
2278 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2279 @option{-fconstant-cfstrings} option, if also present, will override the
2280 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2281 to be laid out as constant CoreFoundation strings.
2284 @opindex fgnu-runtime
2285 Generate object code compatible with the standard GNU Objective-C
2286 runtime. This is the default for most types of systems.
2288 @item -fnext-runtime
2289 @opindex fnext-runtime
2290 Generate output compatible with the NeXT runtime. This is the default
2291 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2292 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2295 @item -fno-nil-receivers
2296 @opindex fno-nil-receivers
2297 Assume that all Objective-C message dispatches (e.g.,
2298 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2299 is not @code{nil}. This allows for more efficient entry points in the runtime
2300 to be used. Currently, this option is only available in conjunction with
2301 the NeXT runtime on Mac OS X 10.3 and later.
2303 @item -fobjc-call-cxx-cdtors
2304 @opindex fobjc-call-cxx-cdtors
2305 For each Objective-C class, check if any of its instance variables is a
2306 C++ object with a non-trivial default constructor. If so, synthesize a
2307 special @code{- (id) .cxx_construct} instance method that will run
2308 non-trivial default constructors on any such instance variables, in order,
2309 and then return @code{self}. Similarly, check if any instance variable
2310 is a C++ object with a non-trivial destructor, and if so, synthesize a
2311 special @code{- (void) .cxx_destruct} method that will run
2312 all such default destructors, in reverse order.
2314 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2315 thusly generated will only operate on instance variables declared in the
2316 current Objective-C class, and not those inherited from superclasses. It
2317 is the responsibility of the Objective-C runtime to invoke all such methods
2318 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2319 will be invoked by the runtime immediately after a new object
2320 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2321 be invoked immediately before the runtime deallocates an object instance.
2323 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2324 support for invoking the @code{- (id) .cxx_construct} and
2325 @code{- (void) .cxx_destruct} methods.
2327 @item -fobjc-direct-dispatch
2328 @opindex fobjc-direct-dispatch
2329 Allow fast jumps to the message dispatcher. On Darwin this is
2330 accomplished via the comm page.
2332 @item -fobjc-exceptions
2333 @opindex fobjc-exceptions
2334 Enable syntactic support for structured exception handling in Objective-C,
2335 similar to what is offered by C++ and Java. This option is
2336 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2345 @@catch (AnObjCClass *exc) @{
2352 @@catch (AnotherClass *exc) @{
2355 @@catch (id allOthers) @{
2365 The @code{@@throw} statement may appear anywhere in an Objective-C or
2366 Objective-C++ program; when used inside of a @code{@@catch} block, the
2367 @code{@@throw} may appear without an argument (as shown above), in which case
2368 the object caught by the @code{@@catch} will be rethrown.
2370 Note that only (pointers to) Objective-C objects may be thrown and
2371 caught using this scheme. When an object is thrown, it will be caught
2372 by the nearest @code{@@catch} clause capable of handling objects of that type,
2373 analogously to how @code{catch} blocks work in C++ and Java. A
2374 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2375 any and all Objective-C exceptions not caught by previous @code{@@catch}
2378 The @code{@@finally} clause, if present, will be executed upon exit from the
2379 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2380 regardless of whether any exceptions are thrown, caught or rethrown
2381 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2382 of the @code{finally} clause in Java.
2384 There are several caveats to using the new exception mechanism:
2388 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2389 idioms provided by the @code{NSException} class, the new
2390 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2391 systems, due to additional functionality needed in the (NeXT) Objective-C
2395 As mentioned above, the new exceptions do not support handling
2396 types other than Objective-C objects. Furthermore, when used from
2397 Objective-C++, the Objective-C exception model does not interoperate with C++
2398 exceptions at this time. This means you cannot @code{@@throw} an exception
2399 from Objective-C and @code{catch} it in C++, or vice versa
2400 (i.e., @code{throw @dots{} @@catch}).
2403 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2404 blocks for thread-safe execution:
2407 @@synchronized (ObjCClass *guard) @{
2412 Upon entering the @code{@@synchronized} block, a thread of execution shall
2413 first check whether a lock has been placed on the corresponding @code{guard}
2414 object by another thread. If it has, the current thread shall wait until
2415 the other thread relinquishes its lock. Once @code{guard} becomes available,
2416 the current thread will place its own lock on it, execute the code contained in
2417 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2418 making @code{guard} available to other threads).
2420 Unlike Java, Objective-C does not allow for entire methods to be marked
2421 @code{@@synchronized}. Note that throwing exceptions out of
2422 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2423 to be unlocked properly.
2427 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2429 @item -freplace-objc-classes
2430 @opindex freplace-objc-classes
2431 Emit a special marker instructing @command{ld(1)} not to statically link in
2432 the resulting object file, and allow @command{dyld(1)} to load it in at
2433 run time instead. This is used in conjunction with the Fix-and-Continue
2434 debugging mode, where the object file in question may be recompiled and
2435 dynamically reloaded in the course of program execution, without the need
2436 to restart the program itself. Currently, Fix-and-Continue functionality
2437 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2442 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2443 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2444 compile time) with static class references that get initialized at load time,
2445 which improves run-time performance. Specifying the @option{-fzero-link} flag
2446 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2447 to be retained. This is useful in Zero-Link debugging mode, since it allows
2448 for individual class implementations to be modified during program execution.
2452 Dump interface declarations for all classes seen in the source file to a
2453 file named @file{@var{sourcename}.decl}.
2455 @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
2456 @opindex Wassign-intercept
2457 @opindex Wno-assign-intercept
2458 Warn whenever an Objective-C assignment is being intercepted by the
2461 @item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
2462 @opindex Wno-protocol
2464 If a class is declared to implement a protocol, a warning is issued for
2465 every method in the protocol that is not implemented by the class. The
2466 default behavior is to issue a warning for every method not explicitly
2467 implemented in the class, even if a method implementation is inherited
2468 from the superclass. If you use the @option{-Wno-protocol} option, then
2469 methods inherited from the superclass are considered to be implemented,
2470 and no warning is issued for them.
2472 @item -Wselector @r{(Objective-C and Objective-C++ only)}
2474 @opindex Wno-selector
2475 Warn if multiple methods of different types for the same selector are
2476 found during compilation. The check is performed on the list of methods
2477 in the final stage of compilation. Additionally, a check is performed
2478 for each selector appearing in a @code{@@selector(@dots{})}
2479 expression, and a corresponding method for that selector has been found
2480 during compilation. Because these checks scan the method table only at
2481 the end of compilation, these warnings are not produced if the final
2482 stage of compilation is not reached, for example because an error is
2483 found during compilation, or because the @option{-fsyntax-only} option is
2486 @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
2487 @opindex Wstrict-selector-match
2488 @opindex Wno-strict-selector-match
2489 Warn if multiple methods with differing argument and/or return types are
2490 found for a given selector when attempting to send a message using this
2491 selector to a receiver of type @code{id} or @code{Class}. When this flag
2492 is off (which is the default behavior), the compiler will omit such warnings
2493 if any differences found are confined to types which share the same size
2496 @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
2497 @opindex Wundeclared-selector
2498 @opindex Wno-undeclared-selector
2499 Warn if a @code{@@selector(@dots{})} expression referring to an
2500 undeclared selector is found. A selector is considered undeclared if no
2501 method with that name has been declared before the
2502 @code{@@selector(@dots{})} expression, either explicitly in an
2503 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2504 an @code{@@implementation} section. This option always performs its
2505 checks as soon as a @code{@@selector(@dots{})} expression is found,
2506 while @option{-Wselector} only performs its checks in the final stage of
2507 compilation. This also enforces the coding style convention
2508 that methods and selectors must be declared before being used.
2510 @item -print-objc-runtime-info
2511 @opindex print-objc-runtime-info
2512 Generate C header describing the largest structure that is passed by
2517 @node Language Independent Options
2518 @section Options to Control Diagnostic Messages Formatting
2519 @cindex options to control diagnostics formatting
2520 @cindex diagnostic messages
2521 @cindex message formatting
2523 Traditionally, diagnostic messages have been formatted irrespective of
2524 the output device's aspect (e.g.@: its width, @dots{}). The options described
2525 below can be used to control the diagnostic messages formatting
2526 algorithm, e.g.@: how many characters per line, how often source location
2527 information should be reported. Right now, only the C++ front end can
2528 honor these options. However it is expected, in the near future, that
2529 the remaining front ends would be able to digest them correctly.
2532 @item -fmessage-length=@var{n}
2533 @opindex fmessage-length
2534 Try to format error messages so that they fit on lines of about @var{n}
2535 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2536 the front ends supported by GCC@. If @var{n} is zero, then no
2537 line-wrapping will be done; each error message will appear on a single
2540 @opindex fdiagnostics-show-location
2541 @item -fdiagnostics-show-location=once
2542 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2543 reporter to emit @emph{once} source location information; that is, in
2544 case the message is too long to fit on a single physical line and has to
2545 be wrapped, the source location won't be emitted (as prefix) again,
2546 over and over, in subsequent continuation lines. This is the default
2549 @item -fdiagnostics-show-location=every-line
2550 Only meaningful in line-wrapping mode. Instructs the diagnostic
2551 messages reporter to emit the same source location information (as
2552 prefix) for physical lines that result from the process of breaking
2553 a message which is too long to fit on a single line.
2555 @item -fdiagnostics-show-option
2556 @opindex fdiagnostics-show-option
2557 This option instructs the diagnostic machinery to add text to each
2558 diagnostic emitted, which indicates which command line option directly
2559 controls that diagnostic, when such an option is known to the
2560 diagnostic machinery.
2562 @item -Wcoverage-mismatch
2563 @opindex Wcoverage-mismatch
2564 Warn if feedback profiles do not match when using the
2565 @option{-fprofile-use} option.
2566 If a source file was changed between @option{-fprofile-gen} and
2567 @option{-fprofile-use}, the files with the profile feedback can fail
2568 to match the source file and GCC can not use the profile feedback
2569 information. By default, GCC emits an error message in this case.
2570 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2571 error. GCC does not use appropriate feedback profiles, so using this
2572 option can result in poorly optimized code. This option is useful
2573 only in the case of very minor changes such as bug fixes to an
2578 @node Warning Options
2579 @section Options to Request or Suppress Warnings
2580 @cindex options to control warnings
2581 @cindex warning messages
2582 @cindex messages, warning
2583 @cindex suppressing warnings
2585 Warnings are diagnostic messages that report constructions which
2586 are not inherently erroneous but which are risky or suggest there
2587 may have been an error.
2589 The following language-independent options do not enable specific
2590 warnings but control the kinds of diagnostics produced by GCC.
2593 @cindex syntax checking
2595 @opindex fsyntax-only
2596 Check the code for syntax errors, but don't do anything beyond that.
2600 Inhibit all warning messages.
2605 Make all warnings into errors.
2610 Make the specified warning into an error. The specifier for a warning
2611 is appended, for example @option{-Werror=switch} turns the warnings
2612 controlled by @option{-Wswitch} into errors. This switch takes a
2613 negative form, to be used to negate @option{-Werror} for specific
2614 warnings, for example @option{-Wno-error=switch} makes
2615 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
2616 is in effect. You can use the @option{-fdiagnostics-show-option}
2617 option to have each controllable warning amended with the option which
2618 controls it, to determine what to use with this option.
2620 Note that specifying @option{-Werror=}@var{foo} automatically implies
2621 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
2624 @item -Wfatal-errors
2625 @opindex Wfatal-errors
2626 @opindex Wno-fatal-errors
2627 This option causes the compiler to abort compilation on the first error
2628 occurred rather than trying to keep going and printing further error
2633 You can request many specific warnings with options beginning
2634 @samp{-W}, for example @option{-Wimplicit} to request warnings on
2635 implicit declarations. Each of these specific warning options also
2636 has a negative form beginning @samp{-Wno-} to turn off warnings; for
2637 example, @option{-Wno-implicit}. This manual lists only one of the
2638 two forms, whichever is not the default. For further,
2639 language-specific options also refer to @ref{C++ Dialect Options} and
2640 @ref{Objective-C and Objective-C++ Dialect Options}.
2645 Issue all the warnings demanded by strict ISO C and ISO C++;
2646 reject all programs that use forbidden extensions, and some other
2647 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2648 version of the ISO C standard specified by any @option{-std} option used.
2650 Valid ISO C and ISO C++ programs should compile properly with or without
2651 this option (though a rare few will require @option{-ansi} or a
2652 @option{-std} option specifying the required version of ISO C)@. However,
2653 without this option, certain GNU extensions and traditional C and C++
2654 features are supported as well. With this option, they are rejected.
2656 @option{-pedantic} does not cause warning messages for use of the
2657 alternate keywords whose names begin and end with @samp{__}. Pedantic
2658 warnings are also disabled in the expression that follows
2659 @code{__extension__}. However, only system header files should use
2660 these escape routes; application programs should avoid them.
2661 @xref{Alternate Keywords}.
2663 Some users try to use @option{-pedantic} to check programs for strict ISO
2664 C conformance. They soon find that it does not do quite what they want:
2665 it finds some non-ISO practices, but not all---only those for which
2666 ISO C @emph{requires} a diagnostic, and some others for which
2667 diagnostics have been added.
2669 A feature to report any failure to conform to ISO C might be useful in
2670 some instances, but would require considerable additional work and would
2671 be quite different from @option{-pedantic}. We don't have plans to
2672 support such a feature in the near future.
2674 Where the standard specified with @option{-std} represents a GNU
2675 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2676 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2677 extended dialect is based. Warnings from @option{-pedantic} are given
2678 where they are required by the base standard. (It would not make sense
2679 for such warnings to be given only for features not in the specified GNU
2680 C dialect, since by definition the GNU dialects of C include all
2681 features the compiler supports with the given option, and there would be
2682 nothing to warn about.)
2684 @item -pedantic-errors
2685 @opindex pedantic-errors
2686 Like @option{-pedantic}, except that errors are produced rather than
2692 This enables all the warnings about constructions that some users
2693 consider questionable, and that are easy to avoid (or modify to
2694 prevent the warning), even in conjunction with macros. This also
2695 enables some language-specific warnings described in @ref{C++ Dialect
2696 Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
2698 @option{-Wall} turns on the following warning flags:
2700 @gccoptlist{-Waddress @gol
2701 -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol
2703 -Wchar-subscripts @gol
2705 -Wimplicit-function-declaration @gol
2708 -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
2709 -Wmissing-braces @gol
2715 -Wsequence-point @gol
2716 -Wsign-compare @r{(only in C++)} @gol
2717 -Wstrict-aliasing @gol
2718 -Wstrict-overflow=1 @gol
2721 -Wuninitialized @gol
2722 -Wunknown-pragmas @gol
2723 -Wunused-function @gol
2726 -Wunused-variable @gol
2727 -Wvolatile-register-var @gol
2730 Note that some warning flags are not implied by @option{-Wall}. Some of
2731 them warn about constructions that users generally do not consider
2732 questionable, but which occasionally you might wish to check for;
2733 others warn about constructions that are necessary or hard to avoid in
2734 some cases, and there is no simple way to modify the code to suppress
2735 the warning. Some of them are enabled by @option{-Wextra} but many of
2736 them must be enabled individually.
2742 This enables some extra warning flags that are not enabled by
2743 @option{-Wall}. (This option used to be called @option{-W}. The older
2744 name is still supported, but the newer name is more descriptive.)
2746 @gccoptlist{-Wclobbered @gol
2748 -Wignored-qualifiers @gol
2749 -Wmissing-field-initializers @gol
2750 -Wmissing-parameter-type @r{(C only)} @gol
2751 -Wold-style-declaration @r{(C only)} @gol
2752 -Woverride-init @gol
2755 -Wuninitialized @gol
2756 -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
2759 The option @option{-Wextra} also prints warning messages for the
2765 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2766 @samp{>}, or @samp{>=}.
2769 (C++ only) An enumerator and a non-enumerator both appear in a
2770 conditional expression.
2773 (C++ only) Ambiguous virtual bases.
2776 (C++ only) Subscripting an array which has been declared @samp{register}.
2779 (C++ only) Taking the address of a variable which has been declared
2783 (C++ only) A base class is not initialized in a derived class' copy
2788 @item -Wchar-subscripts
2789 @opindex Wchar-subscripts
2790 @opindex Wno-char-subscripts
2791 Warn if an array subscript has type @code{char}. This is a common cause
2792 of error, as programmers often forget that this type is signed on some
2794 This warning is enabled by @option{-Wall}.
2798 @opindex Wno-comment
2799 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2800 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2801 This warning is enabled by @option{-Wall}.
2806 @opindex ffreestanding
2807 @opindex fno-builtin
2808 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2809 the arguments supplied have types appropriate to the format string
2810 specified, and that the conversions specified in the format string make
2811 sense. This includes standard functions, and others specified by format
2812 attributes (@pxref{Function Attributes}), in the @code{printf},
2813 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2814 not in the C standard) families (or other target-specific families).
2815 Which functions are checked without format attributes having been
2816 specified depends on the standard version selected, and such checks of
2817 functions without the attribute specified are disabled by
2818 @option{-ffreestanding} or @option{-fno-builtin}.
2820 The formats are checked against the format features supported by GNU
2821 libc version 2.2. These include all ISO C90 and C99 features, as well
2822 as features from the Single Unix Specification and some BSD and GNU
2823 extensions. Other library implementations may not support all these
2824 features; GCC does not support warning about features that go beyond a
2825 particular library's limitations. However, if @option{-pedantic} is used
2826 with @option{-Wformat}, warnings will be given about format features not
2827 in the selected standard version (but not for @code{strfmon} formats,
2828 since those are not in any version of the C standard). @xref{C Dialect
2829 Options,,Options Controlling C Dialect}.
2831 Since @option{-Wformat} also checks for null format arguments for
2832 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2834 @option{-Wformat} is included in @option{-Wall}. For more control over some
2835 aspects of format checking, the options @option{-Wformat-y2k},
2836 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2837 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2838 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2841 @opindex Wformat-y2k
2842 @opindex Wno-format-y2k
2843 If @option{-Wformat} is specified, also warn about @code{strftime}
2844 formats which may yield only a two-digit year.
2846 @item -Wno-format-contains-nul
2847 @opindex Wno-format-contains-nul
2848 @opindex Wformat-contains-nul
2849 If @option{-Wformat} is specified, do not warn about format strings that
2852 @item -Wno-format-extra-args
2853 @opindex Wno-format-extra-args
2854 @opindex Wformat-extra-args
2855 If @option{-Wformat} is specified, do not warn about excess arguments to a
2856 @code{printf} or @code{scanf} format function. The C standard specifies
2857 that such arguments are ignored.
2859 Where the unused arguments lie between used arguments that are
2860 specified with @samp{$} operand number specifications, normally
2861 warnings are still given, since the implementation could not know what
2862 type to pass to @code{va_arg} to skip the unused arguments. However,
2863 in the case of @code{scanf} formats, this option will suppress the
2864 warning if the unused arguments are all pointers, since the Single
2865 Unix Specification says that such unused arguments are allowed.
2867 @item -Wno-format-zero-length @r{(C and Objective-C only)}
2868 @opindex Wno-format-zero-length
2869 @opindex Wformat-zero-length
2870 If @option{-Wformat} is specified, do not warn about zero-length formats.
2871 The C standard specifies that zero-length formats are allowed.
2873 @item -Wformat-nonliteral
2874 @opindex Wformat-nonliteral
2875 @opindex Wno-format-nonliteral
2876 If @option{-Wformat} is specified, also warn if the format string is not a
2877 string literal and so cannot be checked, unless the format function
2878 takes its format arguments as a @code{va_list}.
2880 @item -Wformat-security
2881 @opindex Wformat-security
2882 @opindex Wno-format-security
2883 If @option{-Wformat} is specified, also warn about uses of format
2884 functions that represent possible security problems. At present, this
2885 warns about calls to @code{printf} and @code{scanf} functions where the
2886 format string is not a string literal and there are no format arguments,
2887 as in @code{printf (foo);}. This may be a security hole if the format
2888 string came from untrusted input and contains @samp{%n}. (This is
2889 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2890 in future warnings may be added to @option{-Wformat-security} that are not
2891 included in @option{-Wformat-nonliteral}.)
2895 @opindex Wno-format=2
2896 Enable @option{-Wformat} plus format checks not included in
2897 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2898 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2900 @item -Wnonnull @r{(C and Objective-C only)}
2902 @opindex Wno-nonnull
2903 Warn about passing a null pointer for arguments marked as
2904 requiring a non-null value by the @code{nonnull} function attribute.
2906 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2907 can be disabled with the @option{-Wno-nonnull} option.
2909 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2911 @opindex Wno-init-self
2912 Warn about uninitialized variables which are initialized with themselves.
2913 Note this option can only be used with the @option{-Wuninitialized} option.
2915 For example, GCC will warn about @code{i} being uninitialized in the
2916 following snippet only when @option{-Winit-self} has been specified:
2927 @item -Wimplicit-int @r{(C and Objective-C only)}
2928 @opindex Wimplicit-int
2929 @opindex Wno-implicit-int
2930 Warn when a declaration does not specify a type.
2931 This warning is enabled by @option{-Wall}.
2933 @item -Wimplicit-function-declaration @r{(C and Objective-C only)}
2934 @opindex Wimplicit-function-declaration
2935 @opindex Wno-implicit-function-declaration
2936 Give a warning whenever a function is used before being declared. In
2937 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2938 enabled by default and it is made into an error by
2939 @option{-pedantic-errors}. This warning is also enabled by
2944 @opindex Wno-implicit
2945 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2946 This warning is enabled by @option{-Wall}.
2948 @item -Wignored-qualifiers @r{(C and C++ only)}
2949 @opindex Wignored-qualifiers
2950 @opindex Wno-ignored-qualifiers
2951 Warn if the return type of a function has a type qualifier
2952 such as @code{const}. For ISO C such a type qualifier has no effect,
2953 since the value returned by a function is not an lvalue.
2954 For C++, the warning is only emitted for scalar types or @code{void}.
2955 ISO C prohibits qualified @code{void} return types on function
2956 definitions, so such return types always receive a warning
2957 even without this option.
2959 This warning is also enabled by @option{-Wextra}.
2964 Warn if the type of @samp{main} is suspicious. @samp{main} should be
2965 a function with external linkage, returning int, taking either zero
2966 arguments, two, or three arguments of appropriate types. This warning
2967 is enabled by default in C++ and is enabled by either @option{-Wall}
2968 or @option{-pedantic}.
2970 @item -Wmissing-braces
2971 @opindex Wmissing-braces
2972 @opindex Wno-missing-braces
2973 Warn if an aggregate or union initializer is not fully bracketed. In
2974 the following example, the initializer for @samp{a} is not fully
2975 bracketed, but that for @samp{b} is fully bracketed.
2978 int a[2][2] = @{ 0, 1, 2, 3 @};
2979 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2982 This warning is enabled by @option{-Wall}.
2984 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2985 @opindex Wmissing-include-dirs
2986 @opindex Wno-missing-include-dirs
2987 Warn if a user-supplied include directory does not exist.
2990 @opindex Wparentheses
2991 @opindex Wno-parentheses
2992 Warn if parentheses are omitted in certain contexts, such
2993 as when there is an assignment in a context where a truth value
2994 is expected, or when operators are nested whose precedence people
2995 often get confused about.
2997 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2998 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2999 interpretation from that of ordinary mathematical notation.
3001 Also warn about constructions where there may be confusion to which
3002 @code{if} statement an @code{else} branch belongs. Here is an example of
3017 In C/C++, every @code{else} branch belongs to the innermost possible
3018 @code{if} statement, which in this example is @code{if (b)}. This is
3019 often not what the programmer expected, as illustrated in the above
3020 example by indentation the programmer chose. When there is the
3021 potential for this confusion, GCC will issue a warning when this flag
3022 is specified. To eliminate the warning, add explicit braces around
3023 the innermost @code{if} statement so there is no way the @code{else}
3024 could belong to the enclosing @code{if}. The resulting code would
3041 This warning is enabled by @option{-Wall}.
3043 @item -Wsequence-point
3044 @opindex Wsequence-point
3045 @opindex Wno-sequence-point
3046 Warn about code that may have undefined semantics because of violations
3047 of sequence point rules in the C and C++ standards.
3049 The C and C++ standards defines the order in which expressions in a C/C++
3050 program are evaluated in terms of @dfn{sequence points}, which represent
3051 a partial ordering between the execution of parts of the program: those
3052 executed before the sequence point, and those executed after it. These
3053 occur after the evaluation of a full expression (one which is not part
3054 of a larger expression), after the evaluation of the first operand of a
3055 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
3056 function is called (but after the evaluation of its arguments and the
3057 expression denoting the called function), and in certain other places.
3058 Other than as expressed by the sequence point rules, the order of
3059 evaluation of subexpressions of an expression is not specified. All
3060 these rules describe only a partial order rather than a total order,
3061 since, for example, if two functions are called within one expression
3062 with no sequence point between them, the order in which the functions
3063 are called is not specified. However, the standards committee have
3064 ruled that function calls do not overlap.
3066 It is not specified when between sequence points modifications to the
3067 values of objects take effect. Programs whose behavior depends on this
3068 have undefined behavior; the C and C++ standards specify that ``Between
3069 the previous and next sequence point an object shall have its stored
3070 value modified at most once by the evaluation of an expression.
3071 Furthermore, the prior value shall be read only to determine the value
3072 to be stored.''. If a program breaks these rules, the results on any
3073 particular implementation are entirely unpredictable.
3075 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
3076 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
3077 diagnosed by this option, and it may give an occasional false positive
3078 result, but in general it has been found fairly effective at detecting
3079 this sort of problem in programs.
3081 The standard is worded confusingly, therefore there is some debate
3082 over the precise meaning of the sequence point rules in subtle cases.
3083 Links to discussions of the problem, including proposed formal
3084 definitions, may be found on the GCC readings page, at
3085 @w{@uref{http://gcc.gnu.org/readings.html}}.
3087 This warning is enabled by @option{-Wall} for C and C++.
3090 @opindex Wreturn-type
3091 @opindex Wno-return-type
3092 Warn whenever a function is defined with a return-type that defaults
3093 to @code{int}. Also warn about any @code{return} statement with no
3094 return-value in a function whose return-type is not @code{void}
3095 (falling off the end of the function body is considered returning
3096 without a value), and about a @code{return} statement with a
3097 expression in a function whose return-type is @code{void}.
3099 For C++, a function without return type always produces a diagnostic
3100 message, even when @option{-Wno-return-type} is specified. The only
3101 exceptions are @samp{main} and functions defined in system headers.
3103 This warning is enabled by @option{-Wall}.
3108 Warn whenever a @code{switch} statement has an index of enumerated type
3109 and lacks a @code{case} for one or more of the named codes of that
3110 enumeration. (The presence of a @code{default} label prevents this
3111 warning.) @code{case} labels outside the enumeration range also
3112 provoke warnings when this option is used.
3113 This warning is enabled by @option{-Wall}.
3115 @item -Wswitch-default
3116 @opindex Wswitch-default
3117 @opindex Wno-switch-default
3118 Warn whenever a @code{switch} statement does not have a @code{default}
3122 @opindex Wswitch-enum
3123 @opindex Wno-switch-enum
3124 Warn whenever a @code{switch} statement has an index of enumerated type
3125 and lacks a @code{case} for one or more of the named codes of that
3126 enumeration. @code{case} labels outside the enumeration range also
3127 provoke warnings when this option is used.
3131 @opindex Wno-trigraphs
3132 Warn if any trigraphs are encountered that might change the meaning of
3133 the program (trigraphs within comments are not warned about).
3134 This warning is enabled by @option{-Wall}.
3136 @item -Wunused-function
3137 @opindex Wunused-function
3138 @opindex Wno-unused-function
3139 Warn whenever a static function is declared but not defined or a
3140 non-inline static function is unused.
3141 This warning is enabled by @option{-Wall}.
3143 @item -Wunused-label
3144 @opindex Wunused-label
3145 @opindex Wno-unused-label
3146 Warn whenever a label is declared but not used.
3147 This warning is enabled by @option{-Wall}.
3149 To suppress this warning use the @samp{unused} attribute
3150 (@pxref{Variable Attributes}).
3152 @item -Wunused-parameter
3153 @opindex Wunused-parameter
3154 @opindex Wno-unused-parameter
3155 Warn whenever a function parameter is unused aside from its declaration.
3157 To suppress this warning use the @samp{unused} attribute
3158 (@pxref{Variable Attributes}).
3160 @item -Wunused-variable
3161 @opindex Wunused-variable
3162 @opindex Wno-unused-variable
3163 Warn whenever a local variable or non-constant static variable is unused
3164 aside from its declaration.
3165 This warning is enabled by @option{-Wall}.
3167 To suppress this warning use the @samp{unused} attribute
3168 (@pxref{Variable Attributes}).
3170 @item -Wunused-value
3171 @opindex Wunused-value
3172 @opindex Wno-unused-value
3173 Warn whenever a statement computes a result that is explicitly not
3174 used. To suppress this warning cast the unused expression to
3175 @samp{void}. This includes an expression-statement or the left-hand
3176 side of a comma expression that contains no side effects. For example,
3177 an expression such as @samp{x[i,j]} will cause a warning, while
3178 @samp{x[(void)i,j]} will not.
3180 This warning is enabled by @option{-Wall}.
3185 All the above @option{-Wunused} options combined.
3187 In order to get a warning about an unused function parameter, you must
3188 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
3189 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
3191 @item -Wuninitialized
3192 @opindex Wuninitialized
3193 @opindex Wno-uninitialized
3194 Warn if an automatic variable is used without first being initialized
3195 or if a variable may be clobbered by a @code{setjmp} call. In C++,
3196 warn if a non-static reference or non-static @samp{const} member
3197 appears in a class without constructors.
3199 If you want to warn about code which uses the uninitialized value of the
3200 variable in its own initializer, use the @option{-Winit-self} option.
3202 These warnings occur for individual uninitialized or clobbered
3203 elements of structure, union or array variables as well as for
3204 variables which are uninitialized or clobbered as a whole. They do
3205 not occur for variables or elements declared @code{volatile}. Because
3206 these warnings depend on optimization, the exact variables or elements
3207 for which there are warnings will depend on the precise optimization
3208 options and version of GCC used.
3210 Note that there may be no warning about a variable that is used only
3211 to compute a value that itself is never used, because such
3212 computations may be deleted by data flow analysis before the warnings
3215 These warnings are made optional because GCC is not smart
3216 enough to see all the reasons why the code might be correct
3217 despite appearing to have an error. Here is one example of how
3238 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
3239 always initialized, but GCC doesn't know this. Here is
3240 another common case:
3245 if (change_y) save_y = y, y = new_y;
3247 if (change_y) y = save_y;
3252 This has no bug because @code{save_y} is used only if it is set.
3254 @cindex @code{longjmp} warnings
3255 This option also warns when a non-volatile automatic variable might be
3256 changed by a call to @code{longjmp}. These warnings as well are possible
3257 only in optimizing compilation.
3259 The compiler sees only the calls to @code{setjmp}. It cannot know
3260 where @code{longjmp} will be called; in fact, a signal handler could
3261 call it at any point in the code. As a result, you may get a warning
3262 even when there is in fact no problem because @code{longjmp} cannot
3263 in fact be called at the place which would cause a problem.
3265 Some spurious warnings can be avoided if you declare all the functions
3266 you use that never return as @code{noreturn}. @xref{Function
3269 This warning is enabled by @option{-Wall} or @option{-Wextra}.
3271 @item -Wunknown-pragmas
3272 @opindex Wunknown-pragmas
3273 @opindex Wno-unknown-pragmas
3274 @cindex warning for unknown pragmas
3275 @cindex unknown pragmas, warning
3276 @cindex pragmas, warning of unknown
3277 Warn when a #pragma directive is encountered which is not understood by
3278 GCC@. If this command line option is used, warnings will even be issued
3279 for unknown pragmas in system header files. This is not the case if
3280 the warnings were only enabled by the @option{-Wall} command line option.
3283 @opindex Wno-pragmas
3285 Do not warn about misuses of pragmas, such as incorrect parameters,
3286 invalid syntax, or conflicts between pragmas. See also
3287 @samp{-Wunknown-pragmas}.
3289 @item -Wstrict-aliasing
3290 @opindex Wstrict-aliasing
3291 @opindex Wno-strict-aliasing
3292 This option is only active when @option{-fstrict-aliasing} is active.
3293 It warns about code which might break the strict aliasing rules that the
3294 compiler is using for optimization. The warning does not catch all
3295 cases, but does attempt to catch the more common pitfalls. It is
3296 included in @option{-Wall}.
3297 It is equivalent to @option{-Wstrict-aliasing=3}
3299 @item -Wstrict-aliasing=n
3300 @opindex Wstrict-aliasing=n
3301 @opindex Wno-strict-aliasing=n
3302 This option is only active when @option{-fstrict-aliasing} is active.
3303 It warns about code which might break the strict aliasing rules that the
3304 compiler is using for optimization.
3305 Higher levels correspond to higher accuracy (fewer false positives).
3306 Higher levels also correspond to more effort, similar to the way -O works.
3307 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3310 Level 1: Most aggressive, quick, least accurate.
3311 Possibly useful when higher levels
3312 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3313 false negatives. However, it has many false positives.
3314 Warns for all pointer conversions between possibly incompatible types,
3315 even if never dereferenced. Runs in the frontend only.
3317 Level 2: Aggressive, quick, not too precise.
3318 May still have many false positives (not as many as level 1 though),
3319 and few false negatives (but possibly more than level 1).
3320 Unlike level 1, it only warns when an address is taken. Warns about
3321 incomplete types. Runs in the frontend only.
3323 Level 3 (default for @option{-Wstrict-aliasing}):
3324 Should have very few false positives and few false
3325 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3326 Takes care of the common punn+dereference pattern in the frontend:
3327 @code{*(int*)&some_float}.
3328 If optimization is enabled, it also runs in the backend, where it deals
3329 with multiple statement cases using flow-sensitive points-to information.
3330 Only warns when the converted pointer is dereferenced.
3331 Does not warn about incomplete types.
3333 @item -Wstrict-overflow
3334 @itemx -Wstrict-overflow=@var{n}
3335 @opindex Wstrict-overflow
3336 @opindex Wno-strict-overflow
3337 This option is only active when @option{-fstrict-overflow} is active.
3338 It warns about cases where the compiler optimizes based on the
3339 assumption that signed overflow does not occur. Note that it does not
3340 warn about all cases where the code might overflow: it only warns
3341 about cases where the compiler implements some optimization. Thus
3342 this warning depends on the optimization level.
3344 An optimization which assumes that signed overflow does not occur is
3345 perfectly safe if the values of the variables involved are such that
3346 overflow never does, in fact, occur. Therefore this warning can
3347 easily give a false positive: a warning about code which is not
3348 actually a problem. To help focus on important issues, several
3349 warning levels are defined. No warnings are issued for the use of
3350 undefined signed overflow when estimating how many iterations a loop
3351 will require, in particular when determining whether a loop will be
3355 @item -Wstrict-overflow=1
3356 Warn about cases which are both questionable and easy to avoid. For
3357 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3358 compiler will simplify this to @code{1}. This level of
3359 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3360 are not, and must be explicitly requested.
3362 @item -Wstrict-overflow=2
3363 Also warn about other cases where a comparison is simplified to a
3364 constant. For example: @code{abs (x) >= 0}. This can only be
3365 simplified when @option{-fstrict-overflow} is in effect, because
3366 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3367 zero. @option{-Wstrict-overflow} (with no level) is the same as
3368 @option{-Wstrict-overflow=2}.
3370 @item -Wstrict-overflow=3
3371 Also warn about other cases where a comparison is simplified. For
3372 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3374 @item -Wstrict-overflow=4
3375 Also warn about other simplifications not covered by the above cases.
3376 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3378 @item -Wstrict-overflow=5
3379 Also warn about cases where the compiler reduces the magnitude of a
3380 constant involved in a comparison. For example: @code{x + 2 > y} will
3381 be simplified to @code{x + 1 >= y}. This is reported only at the
3382 highest warning level because this simplification applies to many
3383 comparisons, so this warning level will give a very large number of
3387 @item -Warray-bounds
3388 @opindex Wno-array-bounds
3389 @opindex Warray-bounds
3390 This option is only active when @option{-ftree-vrp} is active
3391 (default for -O2 and above). It warns about subscripts to arrays
3392 that are always out of bounds. This warning is enabled by @option{-Wall}.
3394 @item -Wno-div-by-zero
3395 @opindex Wno-div-by-zero
3396 @opindex Wdiv-by-zero
3397 Do not warn about compile-time integer division by zero. Floating point
3398 division by zero is not warned about, as it can be a legitimate way of
3399 obtaining infinities and NaNs.
3401 @item -Wsystem-headers
3402 @opindex Wsystem-headers
3403 @opindex Wno-system-headers
3404 @cindex warnings from system headers
3405 @cindex system headers, warnings from
3406 Print warning messages for constructs found in system header files.
3407 Warnings from system headers are normally suppressed, on the assumption
3408 that they usually do not indicate real problems and would only make the
3409 compiler output harder to read. Using this command line option tells
3410 GCC to emit warnings from system headers as if they occurred in user
3411 code. However, note that using @option{-Wall} in conjunction with this
3412 option will @emph{not} warn about unknown pragmas in system
3413 headers---for that, @option{-Wunknown-pragmas} must also be used.
3416 @opindex Wfloat-equal
3417 @opindex Wno-float-equal
3418 Warn if floating point values are used in equality comparisons.
3420 The idea behind this is that sometimes it is convenient (for the
3421 programmer) to consider floating-point values as approximations to
3422 infinitely precise real numbers. If you are doing this, then you need
3423 to compute (by analyzing the code, or in some other way) the maximum or
3424 likely maximum error that the computation introduces, and allow for it
3425 when performing comparisons (and when producing output, but that's a
3426 different problem). In particular, instead of testing for equality, you
3427 would check to see whether the two values have ranges that overlap; and
3428 this is done with the relational operators, so equality comparisons are
3431 @item -Wtraditional @r{(C and Objective-C only)}
3432 @opindex Wtraditional
3433 @opindex Wno-traditional
3434 Warn about certain constructs that behave differently in traditional and
3435 ISO C@. Also warn about ISO C constructs that have no traditional C
3436 equivalent, and/or problematic constructs which should be avoided.
3440 Macro parameters that appear within string literals in the macro body.
3441 In traditional C macro replacement takes place within string literals,
3442 but does not in ISO C@.
3445 In traditional C, some preprocessor directives did not exist.
3446 Traditional preprocessors would only consider a line to be a directive
3447 if the @samp{#} appeared in column 1 on the line. Therefore
3448 @option{-Wtraditional} warns about directives that traditional C
3449 understands but would ignore because the @samp{#} does not appear as the
3450 first character on the line. It also suggests you hide directives like
3451 @samp{#pragma} not understood by traditional C by indenting them. Some
3452 traditional implementations would not recognize @samp{#elif}, so it
3453 suggests avoiding it altogether.
3456 A function-like macro that appears without arguments.
3459 The unary plus operator.
3462 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3463 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3464 constants.) Note, these suffixes appear in macros defined in the system
3465 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3466 Use of these macros in user code might normally lead to spurious
3467 warnings, however GCC's integrated preprocessor has enough context to
3468 avoid warning in these cases.
3471 A function declared external in one block and then used after the end of
3475 A @code{switch} statement has an operand of type @code{long}.
3478 A non-@code{static} function declaration follows a @code{static} one.
3479 This construct is not accepted by some traditional C compilers.
3482 The ISO type of an integer constant has a different width or
3483 signedness from its traditional type. This warning is only issued if
3484 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3485 typically represent bit patterns, are not warned about.
3488 Usage of ISO string concatenation is detected.
3491 Initialization of automatic aggregates.
3494 Identifier conflicts with labels. Traditional C lacks a separate
3495 namespace for labels.
3498 Initialization of unions. If the initializer is zero, the warning is
3499 omitted. This is done under the assumption that the zero initializer in
3500 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3501 initializer warnings and relies on default initialization to zero in the
3505 Conversions by prototypes between fixed/floating point values and vice
3506 versa. The absence of these prototypes when compiling with traditional
3507 C would cause serious problems. This is a subset of the possible
3508 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3511 Use of ISO C style function definitions. This warning intentionally is
3512 @emph{not} issued for prototype declarations or variadic functions
3513 because these ISO C features will appear in your code when using
3514 libiberty's traditional C compatibility macros, @code{PARAMS} and
3515 @code{VPARAMS}. This warning is also bypassed for nested functions
3516 because that feature is already a GCC extension and thus not relevant to
3517 traditional C compatibility.
3520 @item -Wtraditional-conversion @r{(C and Objective-C only)}
3521 @opindex Wtraditional-conversion
3522 @opindex Wno-traditional-conversion
3523 Warn if a prototype causes a type conversion that is different from what
3524 would happen to the same argument in the absence of a prototype. This
3525 includes conversions of fixed point to floating and vice versa, and
3526 conversions changing the width or signedness of a fixed point argument
3527 except when the same as the default promotion.
3529 @item -Wdeclaration-after-statement @r{(C and Objective-C only)}
3530 @opindex Wdeclaration-after-statement
3531 @opindex Wno-declaration-after-statement
3532 Warn when a declaration is found after a statement in a block. This
3533 construct, known from C++, was introduced with ISO C99 and is by default
3534 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3535 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3540 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3542 @item -Wno-endif-labels
3543 @opindex Wno-endif-labels
3544 @opindex Wendif-labels
3545 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3550 Warn whenever a local variable shadows another local variable, parameter or
3551 global variable or whenever a built-in function is shadowed.
3553 @item -Wlarger-than=@var{len}
3554 @opindex Wlarger-than=@var{len}
3555 @opindex Wlarger-than-@var{len}
3556 Warn whenever an object of larger than @var{len} bytes is defined.
3558 @item -Wframe-larger-than=@var{len}
3559 @opindex Wframe-larger-than
3560 Warn if the size of a function frame is larger than @var{len} bytes.
3561 The computation done to determine the stack frame size is approximate
3562 and not conservative.
3563 The actual requirements may be somewhat greater than @var{len}
3564 even if you do not get a warning. In addition, any space allocated
3565 via @code{alloca}, variable-length arrays, or related constructs
3566 is not included by the compiler when determining
3567 whether or not to issue a warning.
3569 @item -Wunsafe-loop-optimizations
3570 @opindex Wunsafe-loop-optimizations
3571 @opindex Wno-unsafe-loop-optimizations
3572 Warn if the loop cannot be optimized because the compiler could not
3573 assume anything on the bounds of the loop indices. With
3574 @option{-funsafe-loop-optimizations} warn if the compiler made
3577 @item -Wno-pedantic-ms-format
3578 @opindex Wno-pedantic-ms-format
3579 @opindex Wpedantic-ms-format
3580 Disables the warnings about non-ISO @code{printf} / @code{scanf} format
3581 width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets
3582 depending on the MS runtime, when you are using the options @option{-Wformat}
3583 and @option{-pedantic} without gnu-extensions.
3585 @item -Wpointer-arith
3586 @opindex Wpointer-arith
3587 @opindex Wno-pointer-arith
3588 Warn about anything that depends on the ``size of'' a function type or
3589 of @code{void}. GNU C assigns these types a size of 1, for
3590 convenience in calculations with @code{void *} pointers and pointers
3591 to functions. In C++, warn also when an arithmetic operation involves
3592 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3595 @opindex Wtype-limits
3596 @opindex Wno-type-limits
3597 Warn if a comparison is always true or always false due to the limited
3598 range of the data type, but do not warn for constant expressions. For
3599 example, warn if an unsigned variable is compared against zero with
3600 @samp{<} or @samp{>=}. This warning is also enabled by
3603 @item -Wbad-function-cast @r{(C and Objective-C only)}
3604 @opindex Wbad-function-cast
3605 @opindex Wno-bad-function-cast
3606 Warn whenever a function call is cast to a non-matching type.
3607 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3609 @item -Wc++-compat @r{(C and Objective-C only)}
3610 Warn about ISO C constructs that are outside of the common subset of
3611 ISO C and ISO C++, e.g.@: request for implicit conversion from
3612 @code{void *} to a pointer to non-@code{void} type.
3614 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3615 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3616 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3617 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3621 @opindex Wno-cast-qual
3622 Warn whenever a pointer is cast so as to remove a type qualifier from
3623 the target type. For example, warn if a @code{const char *} is cast
3624 to an ordinary @code{char *}.
3627 @opindex Wcast-align
3628 @opindex Wno-cast-align
3629 Warn whenever a pointer is cast such that the required alignment of the
3630 target is increased. For example, warn if a @code{char *} is cast to
3631 an @code{int *} on machines where integers can only be accessed at
3632 two- or four-byte boundaries.
3634 @item -Wwrite-strings
3635 @opindex Wwrite-strings
3636 @opindex Wno-write-strings
3637 When compiling C, give string constants the type @code{const
3638 char[@var{length}]} so that copying the address of one into a
3639 non-@code{const} @code{char *} pointer will get a warning. These
3640 warnings will help you find at compile time code that can try to write
3641 into a string constant, but only if you have been very careful about
3642 using @code{const} in declarations and prototypes. Otherwise, it will
3643 just be a nuisance. This is why we did not make @option{-Wall} request
3646 When compiling C++, warn about the deprecated conversion from string
3647 literals to @code{char *}. This warning is enabled by default for C++
3652 @opindex Wno-clobbered
3653 Warn for variables that might be changed by @samp{longjmp} or
3654 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3657 @opindex Wconversion
3658 @opindex Wno-conversion
3659 Warn for implicit conversions that may alter a value. This includes
3660 conversions between real and integer, like @code{abs (x)} when
3661 @code{x} is @code{double}; conversions between signed and unsigned,
3662 like @code{unsigned ui = -1}; and conversions to smaller types, like
3663 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3664 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3665 changed by the conversion like in @code{abs (2.0)}. Warnings about
3666 conversions between signed and unsigned integers can be disabled by
3667 using @option{-Wno-sign-conversion}.
3669 For C++, also warn for conversions between @code{NULL} and non-pointer
3670 types; confusing overload resolution for user-defined conversions; and
3671 conversions that will never use a type conversion operator:
3672 conversions to @code{void}, the same type, a base class or a reference
3673 to them. Warnings about conversions between signed and unsigned
3674 integers are disabled by default in C++ unless
3675 @option{-Wsign-conversion} is explicitly enabled.
3678 @opindex Wempty-body
3679 @opindex Wno-empty-body
3680 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3681 while} statement. This warning is also enabled by @option{-Wextra}.
3683 @item -Wenum-compare @r{(C++ and Objective-C++ only)}
3684 @opindex Wenum-compare
3685 @opindex Wno-enum-compare
3686 Warn about a comparison between values of different enum types. This
3687 warning is enabled by default.
3689 @item -Wsign-compare
3690 @opindex Wsign-compare
3691 @opindex Wno-sign-compare
3692 @cindex warning for comparison of signed and unsigned values
3693 @cindex comparison of signed and unsigned values, warning
3694 @cindex signed and unsigned values, comparison warning
3695 Warn when a comparison between signed and unsigned values could produce
3696 an incorrect result when the signed value is converted to unsigned.
3697 This warning is also enabled by @option{-Wextra}; to get the other warnings
3698 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3700 @item -Wsign-conversion
3701 @opindex Wsign-conversion
3702 @opindex Wno-sign-conversion
3703 Warn for implicit conversions that may change the sign of an integer
3704 value, like assigning a signed integer expression to an unsigned
3705 integer variable. An explicit cast silences the warning. In C, this
3706 option is enabled also by @option{-Wconversion}.
3710 @opindex Wno-address
3711 Warn about suspicious uses of memory addresses. These include using
3712 the address of a function in a conditional expression, such as
3713 @code{void func(void); if (func)}, and comparisons against the memory
3714 address of a string literal, such as @code{if (x == "abc")}. Such
3715 uses typically indicate a programmer error: the address of a function
3716 always evaluates to true, so their use in a conditional usually
3717 indicate that the programmer forgot the parentheses in a function
3718 call; and comparisons against string literals result in unspecified
3719 behavior and are not portable in C, so they usually indicate that the
3720 programmer intended to use @code{strcmp}. This warning is enabled by
3724 @opindex Wlogical-op
3725 @opindex Wno-logical-op
3726 Warn about suspicious uses of logical operators in expressions.
3727 This includes using logical operators in contexts where a
3728 bit-wise operator is likely to be expected.
3730 @item -Waggregate-return
3731 @opindex Waggregate-return
3732 @opindex Wno-aggregate-return
3733 Warn if any functions that return structures or unions are defined or
3734 called. (In languages where you can return an array, this also elicits
3737 @item -Wno-attributes
3738 @opindex Wno-attributes
3739 @opindex Wattributes
3740 Do not warn if an unexpected @code{__attribute__} is used, such as
3741 unrecognized attributes, function attributes applied to variables,
3742 etc. This will not stop errors for incorrect use of supported
3745 @item -Wno-builtin-macro-redefined
3746 @opindex Wno-builtin-macro-redefined
3747 @opindex Wbuiltin-macro-redefined
3748 Do not warn if certain built-in macros are redefined. This suppresses
3749 warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
3750 @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
3752 @item -Wstrict-prototypes @r{(C and Objective-C only)}
3753 @opindex Wstrict-prototypes
3754 @opindex Wno-strict-prototypes
3755 Warn if a function is declared or defined without specifying the
3756 argument types. (An old-style function definition is permitted without
3757 a warning if preceded by a declaration which specifies the argument
3760 @item -Wold-style-declaration @r{(C and Objective-C only)}
3761 @opindex Wold-style-declaration
3762 @opindex Wno-old-style-declaration
3763 Warn for obsolescent usages, according to the C Standard, in a
3764 declaration. For example, warn if storage-class specifiers like
3765 @code{static} are not the first things in a declaration. This warning
3766 is also enabled by @option{-Wextra}.
3768 @item -Wold-style-definition @r{(C and Objective-C only)}
3769 @opindex Wold-style-definition
3770 @opindex Wno-old-style-definition
3771 Warn if an old-style function definition is used. A warning is given
3772 even if there is a previous prototype.
3774 @item -Wmissing-parameter-type @r{(C and Objective-C only)}
3775 @opindex Wmissing-parameter-type
3776 @opindex Wno-missing-parameter-type
3777 A function parameter is declared without a type specifier in K&R-style
3784 This warning is also enabled by @option{-Wextra}.
3786 @item -Wmissing-prototypes @r{(C and Objective-C only)}
3787 @opindex Wmissing-prototypes
3788 @opindex Wno-missing-prototypes
3789 Warn if a global function is defined without a previous prototype
3790 declaration. This warning is issued even if the definition itself
3791 provides a prototype. The aim is to detect global functions that fail
3792 to be declared in header files.
3794 @item -Wmissing-declarations
3795 @opindex Wmissing-declarations
3796 @opindex Wno-missing-declarations
3797 Warn if a global function is defined without a previous declaration.
3798 Do so even if the definition itself provides a prototype.
3799 Use this option to detect global functions that are not declared in
3800 header files. In C++, no warnings are issued for function templates,
3801 or for inline functions, or for functions in anonymous namespaces.
3803 @item -Wmissing-field-initializers
3804 @opindex Wmissing-field-initializers
3805 @opindex Wno-missing-field-initializers
3809 Warn if a structure's initializer has some fields missing. For
3810 example, the following code would cause such a warning, because
3811 @code{x.h} is implicitly zero:
3814 struct s @{ int f, g, h; @};
3815 struct s x = @{ 3, 4 @};
3818 This option does not warn about designated initializers, so the following
3819 modification would not trigger a warning:
3822 struct s @{ int f, g, h; @};
3823 struct s x = @{ .f = 3, .g = 4 @};
3826 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3827 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3829 @item -Wmissing-noreturn
3830 @opindex Wmissing-noreturn
3831 @opindex Wno-missing-noreturn
3832 Warn about functions which might be candidates for attribute @code{noreturn}.
3833 Note these are only possible candidates, not absolute ones. Care should
3834 be taken to manually verify functions actually do not ever return before
3835 adding the @code{noreturn} attribute, otherwise subtle code generation
3836 bugs could be introduced. You will not get a warning for @code{main} in
3837 hosted C environments.
3839 @item -Wmissing-format-attribute
3840 @opindex Wmissing-format-attribute
3841 @opindex Wno-missing-format-attribute
3844 Warn about function pointers which might be candidates for @code{format}
3845 attributes. Note these are only possible candidates, not absolute ones.
3846 GCC will guess that function pointers with @code{format} attributes that
3847 are used in assignment, initialization, parameter passing or return
3848 statements should have a corresponding @code{format} attribute in the
3849 resulting type. I.e.@: the left-hand side of the assignment or
3850 initialization, the type of the parameter variable, or the return type
3851 of the containing function respectively should also have a @code{format}
3852 attribute to avoid the warning.
3854 GCC will also warn about function definitions which might be
3855 candidates for @code{format} attributes. Again, these are only
3856 possible candidates. GCC will guess that @code{format} attributes
3857 might be appropriate for any function that calls a function like
3858 @code{vprintf} or @code{vscanf}, but this might not always be the
3859 case, and some functions for which @code{format} attributes are
3860 appropriate may not be detected.
3862 @item -Wno-multichar
3863 @opindex Wno-multichar
3865 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3866 Usually they indicate a typo in the user's code, as they have
3867 implementation-defined values, and should not be used in portable code.
3869 @item -Wnormalized=<none|id|nfc|nfkc>
3870 @opindex Wnormalized=
3873 @cindex character set, input normalization
3874 In ISO C and ISO C++, two identifiers are different if they are
3875 different sequences of characters. However, sometimes when characters
3876 outside the basic ASCII character set are used, you can have two
3877 different character sequences that look the same. To avoid confusion,
3878 the ISO 10646 standard sets out some @dfn{normalization rules} which
3879 when applied ensure that two sequences that look the same are turned into
3880 the same sequence. GCC can warn you if you are using identifiers which
3881 have not been normalized; this option controls that warning.
3883 There are four levels of warning that GCC supports. The default is
3884 @option{-Wnormalized=nfc}, which warns about any identifier which is
3885 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3886 recommended form for most uses.
3888 Unfortunately, there are some characters which ISO C and ISO C++ allow
3889 in identifiers that when turned into NFC aren't allowable as
3890 identifiers. That is, there's no way to use these symbols in portable
3891 ISO C or C++ and have all your identifiers in NFC@.
3892 @option{-Wnormalized=id} suppresses the warning for these characters.
3893 It is hoped that future versions of the standards involved will correct
3894 this, which is why this option is not the default.
3896 You can switch the warning off for all characters by writing
3897 @option{-Wnormalized=none}. You would only want to do this if you
3898 were using some other normalization scheme (like ``D''), because
3899 otherwise you can easily create bugs that are literally impossible to see.
3901 Some characters in ISO 10646 have distinct meanings but look identical
3902 in some fonts or display methodologies, especially once formatting has
3903 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3904 LETTER N'', will display just like a regular @code{n} which has been
3905 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3906 normalization scheme to convert all these into a standard form as
3907 well, and GCC will warn if your code is not in NFKC if you use
3908 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3909 about every identifier that contains the letter O because it might be
3910 confused with the digit 0, and so is not the default, but may be
3911 useful as a local coding convention if the programming environment is
3912 unable to be fixed to display these characters distinctly.
3914 @item -Wno-deprecated
3915 @opindex Wno-deprecated
3916 @opindex Wdeprecated
3917 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
3919 @item -Wno-deprecated-declarations
3920 @opindex Wno-deprecated-declarations
3921 @opindex Wdeprecated-declarations
3922 Do not warn about uses of functions (@pxref{Function Attributes}),
3923 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3924 Attributes}) marked as deprecated by using the @code{deprecated}
3928 @opindex Wno-overflow
3930 Do not warn about compile-time overflow in constant expressions.
3932 @item -Woverride-init @r{(C and Objective-C only)}
3933 @opindex Woverride-init
3934 @opindex Wno-override-init
3938 Warn if an initialized field without side effects is overridden when
3939 using designated initializers (@pxref{Designated Inits, , Designated
3942 This warning is included in @option{-Wextra}. To get other
3943 @option{-Wextra} warnings without this one, use @samp{-Wextra
3944 -Wno-override-init}.
3949 Warn if a structure is given the packed attribute, but the packed
3950 attribute has no effect on the layout or size of the structure.
3951 Such structures may be mis-aligned for little benefit. For
3952 instance, in this code, the variable @code{f.x} in @code{struct bar}
3953 will be misaligned even though @code{struct bar} does not itself
3954 have the packed attribute:
3961 @} __attribute__((packed));
3972 Warn if padding is included in a structure, either to align an element
3973 of the structure or to align the whole structure. Sometimes when this
3974 happens it is possible to rearrange the fields of the structure to
3975 reduce the padding and so make the structure smaller.
3977 @item -Wredundant-decls
3978 @opindex Wredundant-decls
3979 @opindex Wno-redundant-decls
3980 Warn if anything is declared more than once in the same scope, even in
3981 cases where multiple declaration is valid and changes nothing.
3983 @item -Wnested-externs @r{(C and Objective-C only)}
3984 @opindex Wnested-externs
3985 @opindex Wno-nested-externs
3986 Warn if an @code{extern} declaration is encountered within a function.
3988 @item -Wunreachable-code
3989 @opindex Wunreachable-code
3990 @opindex Wno-unreachable-code
3991 Warn if the compiler detects that code will never be executed.
3993 This option is intended to warn when the compiler detects that at
3994 least a whole line of source code will never be executed, because
3995 some condition is never satisfied or because it is after a
3996 procedure that never returns.
3998 It is possible for this option to produce a warning even though there
3999 are circumstances under which part of the affected line can be executed,
4000 so care should be taken when removing apparently-unreachable code.
4002 For instance, when a function is inlined, a warning may mean that the
4003 line is unreachable in only one inlined copy of the function.
4005 This option is not made part of @option{-Wall} because in a debugging
4006 version of a program there is often substantial code which checks
4007 correct functioning of the program and is, hopefully, unreachable
4008 because the program does work. Another common use of unreachable
4009 code is to provide behavior which is selectable at compile-time.
4014 Warn if a function can not be inlined and it was declared as inline.
4015 Even with this option, the compiler will not warn about failures to
4016 inline functions declared in system headers.
4018 The compiler uses a variety of heuristics to determine whether or not
4019 to inline a function. For example, the compiler takes into account
4020 the size of the function being inlined and the amount of inlining
4021 that has already been done in the current function. Therefore,
4022 seemingly insignificant changes in the source program can cause the
4023 warnings produced by @option{-Winline} to appear or disappear.
4025 @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
4026 @opindex Wno-invalid-offsetof
4027 @opindex Winvalid-offsetof
4028 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
4029 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
4030 to a non-POD type is undefined. In existing C++ implementations,
4031 however, @samp{offsetof} typically gives meaningful results even when
4032 applied to certain kinds of non-POD types. (Such as a simple
4033 @samp{struct} that fails to be a POD type only by virtue of having a
4034 constructor.) This flag is for users who are aware that they are
4035 writing nonportable code and who have deliberately chosen to ignore the
4038 The restrictions on @samp{offsetof} may be relaxed in a future version
4039 of the C++ standard.
4041 @item -Wno-int-to-pointer-cast @r{(C and Objective-C only)}
4042 @opindex Wno-int-to-pointer-cast
4043 @opindex Wint-to-pointer-cast
4044 Suppress warnings from casts to pointer type of an integer of a
4047 @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
4048 @opindex Wno-pointer-to-int-cast
4049 @opindex Wpointer-to-int-cast
4050 Suppress warnings from casts from a pointer to an integer type of a
4054 @opindex Winvalid-pch
4055 @opindex Wno-invalid-pch
4056 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
4057 the search path but can't be used.
4061 @opindex Wno-long-long
4062 Warn if @samp{long long} type is used. This is default. To inhibit
4063 the warning messages, use @option{-Wno-long-long}. Flags
4064 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
4065 only when @option{-pedantic} flag is used.
4067 @item -Wvariadic-macros
4068 @opindex Wvariadic-macros
4069 @opindex Wno-variadic-macros
4070 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
4071 alternate syntax when in pedantic ISO C99 mode. This is default.
4072 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
4077 Warn if variable length array is used in the code.
4078 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
4079 the variable length array.
4081 @item -Wvolatile-register-var
4082 @opindex Wvolatile-register-var
4083 @opindex Wno-volatile-register-var
4084 Warn if a register variable is declared volatile. The volatile
4085 modifier does not inhibit all optimizations that may eliminate reads
4086 and/or writes to register variables. This warning is enabled by
4089 @item -Wdisabled-optimization
4090 @opindex Wdisabled-optimization
4091 @opindex Wno-disabled-optimization
4092 Warn if a requested optimization pass is disabled. This warning does
4093 not generally indicate that there is anything wrong with your code; it
4094 merely indicates that GCC's optimizers were unable to handle the code
4095 effectively. Often, the problem is that your code is too big or too
4096 complex; GCC will refuse to optimize programs when the optimization
4097 itself is likely to take inordinate amounts of time.
4099 @item -Wpointer-sign @r{(C and Objective-C only)}
4100 @opindex Wpointer-sign
4101 @opindex Wno-pointer-sign
4102 Warn for pointer argument passing or assignment with different signedness.
4103 This option is only supported for C and Objective-C@. It is implied by
4104 @option{-Wall} and by @option{-pedantic}, which can be disabled with
4105 @option{-Wno-pointer-sign}.
4107 @item -Wstack-protector
4108 @opindex Wstack-protector
4109 @opindex Wno-stack-protector
4110 This option is only active when @option{-fstack-protector} is active. It
4111 warns about functions that will not be protected against stack smashing.
4114 @opindex Wno-mudflap
4115 Suppress warnings about constructs that cannot be instrumented by
4118 @item -Woverlength-strings
4119 @opindex Woverlength-strings
4120 @opindex Wno-overlength-strings
4121 Warn about string constants which are longer than the ``minimum
4122 maximum'' length specified in the C standard. Modern compilers
4123 generally allow string constants which are much longer than the
4124 standard's minimum limit, but very portable programs should avoid
4125 using longer strings.
4127 The limit applies @emph{after} string constant concatenation, and does
4128 not count the trailing NUL@. In C89, the limit was 509 characters; in
4129 C99, it was raised to 4095. C++98 does not specify a normative
4130 minimum maximum, so we do not diagnose overlength strings in C++@.
4132 This option is implied by @option{-pedantic}, and can be disabled with
4133 @option{-Wno-overlength-strings}.
4135 @item -Wdisallowed-function-list=@var{sym},@var{sym},@dots{}
4136 @opindex Wdisallowed-function-list
4138 If any of @var{sym} is called, GCC will issue a warning. This can be useful
4139 in enforcing coding conventions that ban calls to certain functions, for
4140 example, @code{alloca}, @code{malloc}, etc.
4143 @node Debugging Options
4144 @section Options for Debugging Your Program or GCC
4145 @cindex options, debugging
4146 @cindex debugging information options
4148 GCC has various special options that are used for debugging
4149 either your program or GCC:
4154 Produce debugging information in the operating system's native format
4155 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
4158 On most systems that use stabs format, @option{-g} enables use of extra
4159 debugging information that only GDB can use; this extra information
4160 makes debugging work better in GDB but will probably make other debuggers
4162 refuse to read the program. If you want to control for certain whether
4163 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
4164 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
4166 GCC allows you to use @option{-g} with
4167 @option{-O}. The shortcuts taken by optimized code may occasionally
4168 produce surprising results: some variables you declared may not exist
4169 at all; flow of control may briefly move where you did not expect it;
4170 some statements may not be executed because they compute constant
4171 results or their values were already at hand; some statements may
4172 execute in different places because they were moved out of loops.
4174 Nevertheless it proves possible to debug optimized output. This makes
4175 it reasonable to use the optimizer for programs that might have bugs.
4177 The following options are useful when GCC is generated with the
4178 capability for more than one debugging format.
4182 Produce debugging information for use by GDB@. This means to use the
4183 most expressive format available (DWARF 2, stabs, or the native format
4184 if neither of those are supported), including GDB extensions if at all
4189 Produce debugging information in stabs format (if that is supported),
4190 without GDB extensions. This is the format used by DBX on most BSD
4191 systems. On MIPS, Alpha and System V Release 4 systems this option
4192 produces stabs debugging output which is not understood by DBX or SDB@.
4193 On System V Release 4 systems this option requires the GNU assembler.
4195 @item -feliminate-unused-debug-symbols
4196 @opindex feliminate-unused-debug-symbols
4197 Produce debugging information in stabs format (if that is supported),
4198 for only symbols that are actually used.
4200 @item -femit-class-debug-always
4201 Instead of emitting debugging information for a C++ class in only one
4202 object file, emit it in all object files using the class. This option
4203 should be used only with debuggers that are unable to handle the way GCC
4204 normally emits debugging information for classes because using this
4205 option will increase the size of debugging information by as much as a
4210 Produce debugging information in stabs format (if that is supported),
4211 using GNU extensions understood only by the GNU debugger (GDB)@. The
4212 use of these extensions is likely to make other debuggers crash or
4213 refuse to read the program.
4217 Produce debugging information in COFF format (if that is supported).
4218 This is the format used by SDB on most System V systems prior to
4223 Produce debugging information in XCOFF format (if that is supported).
4224 This is the format used by the DBX debugger on IBM RS/6000 systems.
4228 Produce debugging information in XCOFF format (if that is supported),
4229 using GNU extensions understood only by the GNU debugger (GDB)@. The
4230 use of these extensions is likely to make other debuggers crash or
4231 refuse to read the program, and may cause assemblers other than the GNU
4232 assembler (GAS) to fail with an error.
4236 Produce debugging information in DWARF version 2 format (if that is
4237 supported). This is the format used by DBX on IRIX 6. With this
4238 option, GCC uses features of DWARF version 3 when they are useful;
4239 version 3 is upward compatible with version 2, but may still cause
4240 problems for older debuggers.
4244 Produce debugging information in VMS debug format (if that is
4245 supported). This is the format used by DEBUG on VMS systems.
4248 @itemx -ggdb@var{level}
4249 @itemx -gstabs@var{level}
4250 @itemx -gcoff@var{level}
4251 @itemx -gxcoff@var{level}
4252 @itemx -gvms@var{level}
4253 Request debugging information and also use @var{level} to specify how
4254 much information. The default level is 2.
4256 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4259 Level 1 produces minimal information, enough for making backtraces in
4260 parts of the program that you don't plan to debug. This includes
4261 descriptions of functions and external variables, but no information
4262 about local variables and no line numbers.
4264 Level 3 includes extra information, such as all the macro definitions
4265 present in the program. Some debuggers support macro expansion when
4266 you use @option{-g3}.
4268 @option{-gdwarf-2} does not accept a concatenated debug level, because
4269 GCC used to support an option @option{-gdwarf} that meant to generate
4270 debug information in version 1 of the DWARF format (which is very
4271 different from version 2), and it would have been too confusing. That
4272 debug format is long obsolete, but the option cannot be changed now.
4273 Instead use an additional @option{-g@var{level}} option to change the
4274 debug level for DWARF2.
4276 @item -feliminate-dwarf2-dups
4277 @opindex feliminate-dwarf2-dups
4278 Compress DWARF2 debugging information by eliminating duplicated
4279 information about each symbol. This option only makes sense when
4280 generating DWARF2 debugging information with @option{-gdwarf-2}.
4282 @item -femit-struct-debug-baseonly
4283 Emit debug information for struct-like types
4284 only when the base name of the compilation source file
4285 matches the base name of file in which the struct was defined.
4287 This option substantially reduces the size of debugging information,
4288 but at significant potential loss in type information to the debugger.
4289 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4290 See @option{-femit-struct-debug-detailed} for more detailed control.
4292 This option works only with DWARF 2.
4294 @item -femit-struct-debug-reduced
4295 Emit debug information for struct-like types
4296 only when the base name of the compilation source file
4297 matches the base name of file in which the type was defined,
4298 unless the struct is a template or defined in a system header.
4300 This option significantly reduces the size of debugging information,
4301 with some potential loss in type information to the debugger.
4302 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4303 See @option{-femit-struct-debug-detailed} for more detailed control.
4305 This option works only with DWARF 2.
4307 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4308 Specify the struct-like types
4309 for which the compiler will generate debug information.
4310 The intent is to reduce duplicate struct debug information
4311 between different object files within the same program.
4313 This option is a detailed version of
4314 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4315 which will serve for most needs.
4317 A specification has the syntax
4318 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4320 The optional first word limits the specification to
4321 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4322 A struct type is used directly when it is the type of a variable, member.
4323 Indirect uses arise through pointers to structs.
4324 That is, when use of an incomplete struct would be legal, the use is indirect.
4326 @samp{struct one direct; struct two * indirect;}.
4328 The optional second word limits the specification to
4329 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4330 Generic structs are a bit complicated to explain.
4331 For C++, these are non-explicit specializations of template classes,
4332 or non-template classes within the above.
4333 Other programming languages have generics,
4334 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4336 The third word specifies the source files for those
4337 structs for which the compiler will emit debug information.
4338 The values @samp{none} and @samp{any} have the normal meaning.
4339 The value @samp{base} means that
4340 the base of name of the file in which the type declaration appears
4341 must match the base of the name of the main compilation file.
4342 In practice, this means that
4343 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4344 but types declared in other header will not.
4345 The value @samp{sys} means those types satisfying @samp{base}
4346 or declared in system or compiler headers.
4348 You may need to experiment to determine the best settings for your application.
4350 The default is @samp{-femit-struct-debug-detailed=all}.
4352 This option works only with DWARF 2.
4354 @item -fno-merge-debug-strings
4355 @opindex fmerge-debug-strings
4356 @opindex fno-merge-debug-strings
4357 Direct the linker to merge together strings which are identical in
4358 different object files. This is not supported by all assemblers or
4359 linker. This decreases the size of the debug information in the
4360 output file at the cost of increasing link processing time. This is
4363 @item -fdebug-prefix-map=@var{old}=@var{new}
4364 @opindex fdebug-prefix-map
4365 When compiling files in directory @file{@var{old}}, record debugging
4366 information describing them as in @file{@var{new}} instead.
4368 @item -fno-dwarf2-cfi-asm
4369 @opindex fdwarf2-cfi-asm
4370 @opindex fno-dwarf2-cfi-asm
4371 Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section
4372 instead of using GAS @code{.cfi_*} directives.
4374 @cindex @command{prof}
4377 Generate extra code to write profile information suitable for the
4378 analysis program @command{prof}. You must use this option when compiling
4379 the source files you want data about, and you must also use it when
4382 @cindex @command{gprof}
4385 Generate extra code to write profile information suitable for the
4386 analysis program @command{gprof}. You must use this option when compiling
4387 the source files you want data about, and you must also use it when
4392 Makes the compiler print out each function name as it is compiled, and
4393 print some statistics about each pass when it finishes.
4396 @opindex ftime-report
4397 Makes the compiler print some statistics about the time consumed by each
4398 pass when it finishes.
4401 @opindex fmem-report
4402 Makes the compiler print some statistics about permanent memory
4403 allocation when it finishes.
4405 @item -fpre-ipa-mem-report
4406 @opindex fpre-ipa-mem-report
4407 @item -fpost-ipa-mem-report
4408 @opindex fpost-ipa-mem-report
4409 Makes the compiler print some statistics about permanent memory
4410 allocation before or after interprocedural optimization.
4412 @item -fprofile-arcs
4413 @opindex fprofile-arcs
4414 Add code so that program flow @dfn{arcs} are instrumented. During
4415 execution the program records how many times each branch and call is
4416 executed and how many times it is taken or returns. When the compiled
4417 program exits it saves this data to a file called
4418 @file{@var{auxname}.gcda} for each source file. The data may be used for
4419 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4420 test coverage analysis (@option{-ftest-coverage}). Each object file's
4421 @var{auxname} is generated from the name of the output file, if
4422 explicitly specified and it is not the final executable, otherwise it is
4423 the basename of the source file. In both cases any suffix is removed
4424 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4425 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4426 @xref{Cross-profiling}.
4428 @cindex @command{gcov}
4432 This option is used to compile and link code instrumented for coverage
4433 analysis. The option is a synonym for @option{-fprofile-arcs}
4434 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4435 linking). See the documentation for those options for more details.
4440 Compile the source files with @option{-fprofile-arcs} plus optimization
4441 and code generation options. For test coverage analysis, use the
4442 additional @option{-ftest-coverage} option. You do not need to profile
4443 every source file in a program.
4446 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4447 (the latter implies the former).
4450 Run the program on a representative workload to generate the arc profile
4451 information. This may be repeated any number of times. You can run
4452 concurrent instances of your program, and provided that the file system
4453 supports locking, the data files will be correctly updated. Also
4454 @code{fork} calls are detected and correctly handled (double counting
4458 For profile-directed optimizations, compile the source files again with
4459 the same optimization and code generation options plus
4460 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4461 Control Optimization}).
4464 For test coverage analysis, use @command{gcov} to produce human readable
4465 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4466 @command{gcov} documentation for further information.
4470 With @option{-fprofile-arcs}, for each function of your program GCC
4471 creates a program flow graph, then finds a spanning tree for the graph.
4472 Only arcs that are not on the spanning tree have to be instrumented: the
4473 compiler adds code to count the number of times that these arcs are
4474 executed. When an arc is the only exit or only entrance to a block, the
4475 instrumentation code can be added to the block; otherwise, a new basic
4476 block must be created to hold the instrumentation code.
4479 @item -ftest-coverage
4480 @opindex ftest-coverage
4481 Produce a notes file that the @command{gcov} code-coverage utility
4482 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4483 show program coverage. Each source file's note file is called
4484 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4485 above for a description of @var{auxname} and instructions on how to
4486 generate test coverage data. Coverage data will match the source files
4487 more closely, if you do not optimize.
4489 @item -fdbg-cnt-list
4490 @opindex fdbg-cnt-list
4491 Print the name and the counter upperbound for all debug counters.
4493 @item -fdbg-cnt=@var{counter-value-list}
4495 Set the internal debug counter upperbound. @var{counter-value-list}
4496 is a comma-separated list of @var{name}:@var{value} pairs
4497 which sets the upperbound of each debug counter @var{name} to @var{value}.
4498 All debug counters have the initial upperbound of @var{UINT_MAX},
4499 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4500 e.g. With -fdbg-cnt=dce:10,tail_call:0
4501 dbg_cnt(dce) will return true only for first 10 invocations
4502 and dbg_cnt(tail_call) will return false always.
4504 @item -d@var{letters}
4505 @itemx -fdump-rtl-@var{pass}
4507 Says to make debugging dumps during compilation at times specified by
4508 @var{letters}. This is used for debugging the RTL-based passes of the
4509 compiler. The file names for most of the dumps are made by appending a
4510 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4511 from the name of the output file, if explicitly specified and it is not
4512 an executable, otherwise it is the basename of the source file. These
4513 switches may have different effects when @option{-E} is used for
4516 Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
4517 @option{-d} option @var{letters}. Here are the possible
4518 letters for use in @var{letters} and @var{pass}, and their meanings:
4523 Annotate the assembler output with miscellaneous debugging information.
4525 @item -fdump-rtl-bbro
4526 @opindex fdump-rtl-bbro
4527 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4529 @item -fdump-rtl-combine
4530 @opindex fdump-rtl-combine
4531 Dump after the RTL instruction combination pass, to the file
4532 @file{@var{file}.129r.combine}.
4534 @item -fdump-rtl-ce1
4535 @itemx -fdump-rtl-ce2
4536 @opindex fdump-rtl-ce1
4537 @opindex fdump-rtl-ce2
4538 @option{-fdump-rtl-ce1} enable dumping after the
4539 first if conversion, to the file @file{@var{file}.117r.ce1}.
4540 @option{-fdump-rtl-ce2} enable dumping after the second if
4541 conversion, to the file @file{@var{file}.130r.ce2}.
4543 @item -fdump-rtl-btl
4544 @itemx -fdump-rtl-dbr
4545 @opindex fdump-rtl-btl
4546 @opindex fdump-rtl-dbr
4547 @option{-fdump-rtl-btl} enable dumping after branch
4548 target load optimization, to @file{@var{file}.31.btl}.
4549 @option{-fdump-rtl-dbr} enable dumping after delayed branch
4550 scheduling, to @file{@var{file}.36.dbr}.
4554 Dump all macro definitions, at the end of preprocessing, in addition to
4557 @item -fdump-rtl-ce3
4558 @opindex fdump-rtl-ce3
4559 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4561 @item -fdump-rtl-cfg
4562 @itemx -fdump-rtl-life
4563 @opindex fdump-rtl-cfg
4564 @opindex fdump-rtl-life
4565 @option{-fdump-rtl-cfg} enable dumping after control
4566 and data flow analysis, to @file{@var{file}.116r.cfg}.
4567 @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4568 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4570 @item -fdump-rtl-greg
4571 @opindex fdump-rtl-greg
4572 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4574 @item -fdump-rtl-gcse
4575 @itemx -fdump-rtl-bypass
4576 @opindex fdump-rtl-gcse
4577 @opindex fdump-rtl-bypass
4578 @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4579 @file{@var{file}.114r.gcse}. @option{-fdump-rtl-bypass}
4580 enable dumping after jump bypassing and control flow optimizations, to
4581 @file{@var{file}.115r.bypass}.
4584 @opindex fdump-rtl-eh
4585 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4587 @item -fdump-rtl-sibling
4588 @opindex fdump-rtl-sibling
4589 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4591 @item -fdump-rtl-jump
4592 @opindex fdump-rtl-jump
4593 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4595 @item -fdump-rtl-stack
4596 @opindex fdump-rtl-stack
4597 Dump after conversion from GCC's "flat register file" registers to the
4598 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4600 @item -fdump-rtl-lreg
4601 @opindex fdump-rtl-lreg
4602 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4604 @item -fdump-rtl-loop2
4605 @opindex fdump-rtl-loop2
4606 @option{-fdump-rtl-loop2} enables dumping after the
4607 loop optimization pass, to @file{@var{file}.119r.loop2},
4608 @file{@var{file}.120r.loop2_init},
4609 @file{@var{file}.121r.loop2_invariant}, and
4610 @file{@var{file}.125r.loop2_done}.
4612 @item -fdump-rtl-sms
4613 @opindex fdump-rtl-sms
4614 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4616 @item -fdump-rtl-mach
4617 @opindex fdump-rtl-mach
4618 Dump after performing the machine dependent reorganization pass, to
4619 @file{@var{file}.155r.mach} if that pass exists.
4621 @item -fdump-rtl-rnreg
4622 @opindex fdump-rtl-rnreg
4623 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4625 @item -fdump-rtl-regmove
4626 @opindex fdump-rtl-regmove
4627 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4629 @item -fdump-rtl-postreload
4630 @opindex fdump-rtl-postreload
4631 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4633 @item -fdump-rtl-expand
4634 @opindex fdump-rtl-expand
4635 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4637 @item -fdump-rtl-sched2
4638 @opindex fdump-rtl-sched2
4639 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4641 @item -fdump-rtl-cse
4642 @opindex fdump-rtl-cse
4643 Dump after CSE (including the jump optimization that sometimes follows
4644 CSE), to @file{@var{file}.113r.cse}.
4646 @item -fdump-rtl-sched1
4647 @opindex fdump-rtl-sched1
4648 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4650 @item -fdump-rtl-cse2
4651 @opindex fdump-rtl-cse2
4652 Dump after the second CSE pass (including the jump optimization that
4653 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4655 @item -fdump-rtl-tracer
4656 @opindex fdump-rtl-tracer
4657 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4659 @item -fdump-rtl-vpt
4660 @itemx -fdump-rtl-vartrack
4661 @opindex fdump-rtl-vpt
4662 @opindex fdump-rtl-vartrack
4663 @option{-fdump-rtl-vpt} enable dumping after the value
4664 profile transformations, to @file{@var{file}.10.vpt}.
4665 @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4666 to @file{@var{file}.154r.vartrack}.
4668 @item -fdump-rtl-flow2
4669 @opindex fdump-rtl-flow2
4670 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4672 @item -fdump-rtl-peephole2
4673 @opindex fdump-rtl-peephole2
4674 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4676 @item -fdump-rtl-web
4677 @opindex fdump-rtl-web
4678 Dump after live range splitting, to @file{@var{file}.126r.web}.
4680 @item -fdump-rtl-all
4681 @opindex fdump-rtl-all
4682 Produce all the dumps listed above.
4686 Produce a core dump whenever an error occurs.
4690 Print statistics on memory usage, at the end of the run, to
4695 Annotate the assembler output with a comment indicating which
4696 pattern and alternative was used. The length of each instruction is
4701 Dump the RTL in the assembler output as a comment before each instruction.
4702 Also turns on @option{-dp} annotation.
4706 For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
4707 dump a representation of the control flow graph suitable for viewing with VCG
4708 to @file{@var{file}.@var{pass}.vcg}.
4712 Just generate RTL for a function instead of compiling it. Usually used
4713 with @option{-fdump-rtl-expand}.
4717 Dump debugging information during parsing, to standard error.
4721 @opindex fdump-noaddr
4722 When doing debugging dumps, suppress address output. This makes it more
4723 feasible to use diff on debugging dumps for compiler invocations with
4724 different compiler binaries and/or different
4725 text / bss / data / heap / stack / dso start locations.
4727 @item -fdump-unnumbered
4728 @opindex fdump-unnumbered
4729 When doing debugging dumps, suppress instruction numbers and address output.
4730 This makes it more feasible to use diff on debugging dumps for compiler
4731 invocations with different options, in particular with and without
4734 @item -fdump-translation-unit @r{(C++ only)}
4735 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4736 @opindex fdump-translation-unit
4737 Dump a representation of the tree structure for the entire translation
4738 unit to a file. The file name is made by appending @file{.tu} to the
4739 source file name. If the @samp{-@var{options}} form is used, @var{options}
4740 controls the details of the dump as described for the
4741 @option{-fdump-tree} options.
4743 @item -fdump-class-hierarchy @r{(C++ only)}
4744 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4745 @opindex fdump-class-hierarchy
4746 Dump a representation of each class's hierarchy and virtual function
4747 table layout to a file. The file name is made by appending @file{.class}
4748 to the source file name. If the @samp{-@var{options}} form is used,
4749 @var{options} controls the details of the dump as described for the
4750 @option{-fdump-tree} options.
4752 @item -fdump-ipa-@var{switch}
4754 Control the dumping at various stages of inter-procedural analysis
4755 language tree to a file. The file name is generated by appending a switch
4756 specific suffix to the source file name. The following dumps are possible:
4760 Enables all inter-procedural analysis dumps.
4763 Dumps information about call-graph optimization, unused function removal,
4764 and inlining decisions.
4767 Dump after function inlining.
4771 @item -fdump-statistics-@var{option}
4772 @opindex -fdump-statistics
4773 Enable and control dumping of pass statistics in a separate file. The
4774 file name is generated by appending a suffix ending in @samp{.statistics}
4775 to the source file name. If the @samp{-@var{option}} form is used,
4776 @samp{-stats} will cause counters to be summed over the whole compilation unit
4777 while @samp{-details} will dump every event as the passes generate them.
4778 The default with no option is to sum counters for each function compiled.
4780 @item -fdump-tree-@var{switch}
4781 @itemx -fdump-tree-@var{switch}-@var{options}
4783 Control the dumping at various stages of processing the intermediate
4784 language tree to a file. The file name is generated by appending a switch
4785 specific suffix to the source file name. If the @samp{-@var{options}}
4786 form is used, @var{options} is a list of @samp{-} separated options that
4787 control the details of the dump. Not all options are applicable to all
4788 dumps, those which are not meaningful will be ignored. The following
4789 options are available
4793 Print the address of each node. Usually this is not meaningful as it
4794 changes according to the environment and source file. Its primary use
4795 is for tying up a dump file with a debug environment.
4797 Inhibit dumping of members of a scope or body of a function merely
4798 because that scope has been reached. Only dump such items when they
4799 are directly reachable by some other path. When dumping pretty-printed
4800 trees, this option inhibits dumping the bodies of control structures.
4802 Print a raw representation of the tree. By default, trees are
4803 pretty-printed into a C-like representation.
4805 Enable more detailed dumps (not honored by every dump option).
4807 Enable dumping various statistics about the pass (not honored by every dump
4810 Enable showing basic block boundaries (disabled in raw dumps).
4812 Enable showing virtual operands for every statement.
4814 Enable showing line numbers for statements.
4816 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4818 Enable showing the tree dump for each statement.
4820 Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
4821 and @option{lineno}.
4824 The following tree dumps are possible:
4828 Dump before any tree based optimization, to @file{@var{file}.original}.
4831 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4834 @opindex fdump-tree-gimple
4835 Dump each function before and after the gimplification pass to a file. The
4836 file name is made by appending @file{.gimple} to the source file name.
4839 @opindex fdump-tree-cfg
4840 Dump the control flow graph of each function to a file. The file name is
4841 made by appending @file{.cfg} to the source file name.
4844 @opindex fdump-tree-vcg
4845 Dump the control flow graph of each function to a file in VCG format. The
4846 file name is made by appending @file{.vcg} to the source file name. Note
4847 that if the file contains more than one function, the generated file cannot
4848 be used directly by VCG@. You will need to cut and paste each function's
4849 graph into its own separate file first.
4852 @opindex fdump-tree-ch
4853 Dump each function after copying loop headers. The file name is made by
4854 appending @file{.ch} to the source file name.
4857 @opindex fdump-tree-ssa
4858 Dump SSA related information to a file. The file name is made by appending
4859 @file{.ssa} to the source file name.
4862 @opindex fdump-tree-alias
4863 Dump aliasing information for each function. The file name is made by
4864 appending @file{.alias} to the source file name.
4867 @opindex fdump-tree-ccp
4868 Dump each function after CCP@. The file name is made by appending
4869 @file{.ccp} to the source file name.
4872 @opindex fdump-tree-storeccp
4873 Dump each function after STORE-CCP@. The file name is made by appending
4874 @file{.storeccp} to the source file name.
4877 @opindex fdump-tree-pre
4878 Dump trees after partial redundancy elimination. The file name is made
4879 by appending @file{.pre} to the source file name.
4882 @opindex fdump-tree-fre
4883 Dump trees after full redundancy elimination. The file name is made
4884 by appending @file{.fre} to the source file name.
4887 @opindex fdump-tree-copyprop
4888 Dump trees after copy propagation. The file name is made
4889 by appending @file{.copyprop} to the source file name.
4891 @item store_copyprop
4892 @opindex fdump-tree-store_copyprop
4893 Dump trees after store copy-propagation. The file name is made
4894 by appending @file{.store_copyprop} to the source file name.
4897 @opindex fdump-tree-dce
4898 Dump each function after dead code elimination. The file name is made by
4899 appending @file{.dce} to the source file name.
4902 @opindex fdump-tree-mudflap
4903 Dump each function after adding mudflap instrumentation. The file name is
4904 made by appending @file{.mudflap} to the source file name.
4907 @opindex fdump-tree-sra
4908 Dump each function after performing scalar replacement of aggregates. The
4909 file name is made by appending @file{.sra} to the source file name.
4912 @opindex fdump-tree-sink
4913 Dump each function after performing code sinking. The file name is made
4914 by appending @file{.sink} to the source file name.
4917 @opindex fdump-tree-dom
4918 Dump each function after applying dominator tree optimizations. The file
4919 name is made by appending @file{.dom} to the source file name.
4922 @opindex fdump-tree-dse
4923 Dump each function after applying dead store elimination. The file
4924 name is made by appending @file{.dse} to the source file name.
4927 @opindex fdump-tree-phiopt
4928 Dump each function after optimizing PHI nodes into straightline code. The file
4929 name is made by appending @file{.phiopt} to the source file name.
4932 @opindex fdump-tree-forwprop
4933 Dump each function after forward propagating single use variables. The file
4934 name is made by appending @file{.forwprop} to the source file name.
4937 @opindex fdump-tree-copyrename
4938 Dump each function after applying the copy rename optimization. The file
4939 name is made by appending @file{.copyrename} to the source file name.
4942 @opindex fdump-tree-nrv
4943 Dump each function after applying the named return value optimization on
4944 generic trees. The file name is made by appending @file{.nrv} to the source
4948 @opindex fdump-tree-vect
4949 Dump each function after applying vectorization of loops. The file name is
4950 made by appending @file{.vect} to the source file name.
4953 @opindex fdump-tree-vrp
4954 Dump each function after Value Range Propagation (VRP). The file name
4955 is made by appending @file{.vrp} to the source file name.
4958 @opindex fdump-tree-all
4959 Enable all the available tree dumps with the flags provided in this option.
4962 @item -ftree-vectorizer-verbose=@var{n}
4963 @opindex ftree-vectorizer-verbose
4964 This option controls the amount of debugging output the vectorizer prints.
4965 This information is written to standard error, unless
4966 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4967 in which case it is output to the usual dump listing file, @file{.vect}.
4968 For @var{n}=0 no diagnostic information is reported.
4969 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4970 and the total number of loops that got vectorized.
4971 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4972 the first analysis phase (vect_analyze_loop_form) - i.e.@: countable,
4973 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4974 level that @option{-fdump-tree-vect-stats} uses.
4975 Higher verbosity levels mean either more information dumped for each
4976 reported loop, or same amount of information reported for more loops:
4977 If @var{n}=3, alignment related information is added to the reports.
4978 If @var{n}=4, data-references related information (e.g.@: memory dependences,
4979 memory access-patterns) is added to the reports.
4980 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4981 that did not pass the first analysis phase (i.e., may not be countable, or
4982 may have complicated control-flow).
4983 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4984 For @var{n}=7, all the information the vectorizer generates during its
4985 analysis and transformation is reported. This is the same verbosity level
4986 that @option{-fdump-tree-vect-details} uses.
4988 @item -frandom-seed=@var{string}
4989 @opindex frandom-string
4990 This option provides a seed that GCC uses when it would otherwise use
4991 random numbers. It is used to generate certain symbol names
4992 that have to be different in every compiled file. It is also used to
4993 place unique stamps in coverage data files and the object files that
4994 produce them. You can use the @option{-frandom-seed} option to produce
4995 reproducibly identical object files.
4997 The @var{string} should be different for every file you compile.
4999 @item -fsched-verbose=@var{n}
5000 @opindex fsched-verbose
5001 On targets that use instruction scheduling, this option controls the
5002 amount of debugging output the scheduler prints. This information is
5003 written to standard error, unless @option{-fdump-rtl-sched1} or
5004 @option{-fdump-rtl-sched2} is specified, in which case it is output
5005 to the usual dump listing file, @file{.sched} or @file{.sched2}
5006 respectively. However for @var{n} greater than nine, the output is
5007 always printed to standard error.
5009 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
5010 same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
5011 For @var{n} greater than one, it also output basic block probabilities,
5012 detailed ready list information and unit/insn info. For @var{n} greater
5013 than two, it includes RTL at abort point, control-flow and regions info.
5014 And for @var{n} over four, @option{-fsched-verbose} also includes
5019 Store the usual ``temporary'' intermediate files permanently; place them
5020 in the current directory and name them based on the source file. Thus,
5021 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
5022 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
5023 preprocessed @file{foo.i} output file even though the compiler now
5024 normally uses an integrated preprocessor.
5026 When used in combination with the @option{-x} command line option,
5027 @option{-save-temps} is sensible enough to avoid over writing an
5028 input source file with the same extension as an intermediate file.
5029 The corresponding intermediate file may be obtained by renaming the
5030 source file before using @option{-save-temps}.
5034 Report the CPU time taken by each subprocess in the compilation
5035 sequence. For C source files, this is the compiler proper and assembler
5036 (plus the linker if linking is done). The output looks like this:
5043 The first number on each line is the ``user time'', that is time spent
5044 executing the program itself. The second number is ``system time'',
5045 time spent executing operating system routines on behalf of the program.
5046 Both numbers are in seconds.
5048 @item -fvar-tracking
5049 @opindex fvar-tracking
5050 Run variable tracking pass. It computes where variables are stored at each
5051 position in code. Better debugging information is then generated
5052 (if the debugging information format supports this information).
5054 It is enabled by default when compiling with optimization (@option{-Os},
5055 @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
5056 the debug info format supports it.
5058 @item -print-file-name=@var{library}
5059 @opindex print-file-name
5060 Print the full absolute name of the library file @var{library} that
5061 would be used when linking---and don't do anything else. With this
5062 option, GCC does not compile or link anything; it just prints the
5065 @item -print-multi-directory
5066 @opindex print-multi-directory
5067 Print the directory name corresponding to the multilib selected by any
5068 other switches present in the command line. This directory is supposed
5069 to exist in @env{GCC_EXEC_PREFIX}.
5071 @item -print-multi-lib
5072 @opindex print-multi-lib
5073 Print the mapping from multilib directory names to compiler switches
5074 that enable them. The directory name is separated from the switches by
5075 @samp{;}, and each switch starts with an @samp{@@} instead of the
5076 @samp{-}, without spaces between multiple switches. This is supposed to
5077 ease shell-processing.
5079 @item -print-prog-name=@var{program}
5080 @opindex print-prog-name
5081 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
5083 @item -print-libgcc-file-name
5084 @opindex print-libgcc-file-name
5085 Same as @option{-print-file-name=libgcc.a}.
5087 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
5088 but you do want to link with @file{libgcc.a}. You can do
5091 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
5094 @item -print-search-dirs
5095 @opindex print-search-dirs
5096 Print the name of the configured installation directory and a list of
5097 program and library directories @command{gcc} will search---and don't do anything else.
5099 This is useful when @command{gcc} prints the error message
5100 @samp{installation problem, cannot exec cpp0: No such file or directory}.
5101 To resolve this you either need to put @file{cpp0} and the other compiler
5102 components where @command{gcc} expects to find them, or you can set the environment
5103 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
5104 Don't forget the trailing @samp{/}.
5105 @xref{Environment Variables}.
5107 @item -print-sysroot
5108 @opindex print-sysroot
5109 Print the target sysroot directory that will be used during
5110 compilation. This is the target sysroot specified either at configure
5111 time or using the @option{--sysroot} option, possibly with an extra
5112 suffix that depends on compilation options. If no target sysroot is
5113 specified, the option prints nothing.
5115 @item -print-sysroot-headers-suffix
5116 @opindex print-sysroot-headers-suffix
5117 Print the suffix added to the target sysroot when searching for
5118 headers, or give an error if the compiler is not configured with such
5119 a suffix---and don't do anything else.
5122 @opindex dumpmachine
5123 Print the compiler's target machine (for example,
5124 @samp{i686-pc-linux-gnu})---and don't do anything else.
5127 @opindex dumpversion
5128 Print the compiler version (for example, @samp{3.0})---and don't do
5133 Print the compiler's built-in specs---and don't do anything else. (This
5134 is used when GCC itself is being built.) @xref{Spec Files}.
5136 @item -feliminate-unused-debug-types
5137 @opindex feliminate-unused-debug-types
5138 Normally, when producing DWARF2 output, GCC will emit debugging
5139 information for all types declared in a compilation
5140 unit, regardless of whether or not they are actually used
5141 in that compilation unit. Sometimes this is useful, such as
5142 if, in the debugger, you want to cast a value to a type that is
5143 not actually used in your program (but is declared). More often,
5144 however, this results in a significant amount of wasted space.
5145 With this option, GCC will avoid producing debug symbol output
5146 for types that are nowhere used in the source file being compiled.
5149 @node Optimize Options
5150 @section Options That Control Optimization
5151 @cindex optimize options
5152 @cindex options, optimization
5154 These options control various sorts of optimizations.
5156 Without any optimization option, the compiler's goal is to reduce the
5157 cost of compilation and to make debugging produce the expected
5158 results. Statements are independent: if you stop the program with a
5159 breakpoint between statements, you can then assign a new value to any
5160 variable or change the program counter to any other statement in the
5161 function and get exactly the results you would expect from the source
5164 Turning on optimization flags makes the compiler attempt to improve
5165 the performance and/or code size at the expense of compilation time
5166 and possibly the ability to debug the program.
5168 The compiler performs optimization based on the knowledge it has of the
5169 program. Compiling multiple files at once to a single output file mode allows
5170 the compiler to use information gained from all of the files when compiling
5173 Not all optimizations are controlled directly by a flag. Only
5174 optimizations that have a flag are listed.
5181 Optimize. Optimizing compilation takes somewhat more time, and a lot
5182 more memory for a large function.
5184 With @option{-O}, the compiler tries to reduce code size and execution
5185 time, without performing any optimizations that take a great deal of
5188 @option{-O} turns on the following optimization flags:
5191 -fcprop-registers @gol
5194 -fdelayed-branch @gol
5196 -fguess-branch-probability @gol
5197 -fif-conversion2 @gol
5198 -fif-conversion @gol
5199 -finline-small-functions @gol
5200 -fipa-pure-const @gol
5201 -fipa-reference @gol
5203 -fsplit-wide-types @gol
5204 -ftree-builtin-call-dce @gol
5207 -ftree-copyrename @gol
5209 -ftree-dominator-opts @gol
5216 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5217 where doing so does not interfere with debugging.
5221 Optimize even more. GCC performs nearly all supported optimizations
5222 that do not involve a space-speed tradeoff. The compiler does not
5223 perform loop unrolling or function inlining when you specify @option{-O2}.
5224 As compared to @option{-O}, this option increases both compilation time
5225 and the performance of the generated code.
5227 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5228 also turns on the following optimization flags:
5229 @gccoptlist{-fthread-jumps @gol
5230 -falign-functions -falign-jumps @gol
5231 -falign-loops -falign-labels @gol
5234 -fcse-follow-jumps -fcse-skip-blocks @gol
5235 -fdelete-null-pointer-checks @gol
5236 -fexpensive-optimizations @gol
5237 -fgcse -fgcse-lm @gol
5238 -findirect-inlining @gol
5239 -foptimize-sibling-calls @gol
5242 -freorder-blocks -freorder-functions @gol
5243 -frerun-cse-after-loop @gol
5244 -fsched-interblock -fsched-spec @gol
5245 -fschedule-insns -fschedule-insns2 @gol
5246 -fstrict-aliasing -fstrict-overflow @gol
5247 -ftree-switch-conversion @gol
5251 Please note the warning under @option{-fgcse} about
5252 invoking @option{-O2} on programs that use computed gotos.
5256 Optimize yet more. @option{-O3} turns on all optimizations specified
5257 by @option{-O2} and also turns on the @option{-finline-functions},
5258 @option{-funswitch-loops}, @option{-fpredictive-commoning},
5259 @option{-fgcse-after-reload} and @option{-ftree-vectorize} options.
5263 Reduce compilation time and make debugging produce the expected
5264 results. This is the default.
5268 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5269 do not typically increase code size. It also performs further
5270 optimizations designed to reduce code size.
5272 @option{-Os} disables the following optimization flags:
5273 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5274 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5275 -fprefetch-loop-arrays -ftree-vect-loop-version}
5277 If you use multiple @option{-O} options, with or without level numbers,
5278 the last such option is the one that is effective.
5281 Options of the form @option{-f@var{flag}} specify machine-independent
5282 flags. Most flags have both positive and negative forms; the negative
5283 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5284 below, only one of the forms is listed---the one you typically will
5285 use. You can figure out the other form by either removing @samp{no-}
5288 The following options control specific optimizations. They are either
5289 activated by @option{-O} options or are related to ones that are. You
5290 can use the following flags in the rare cases when ``fine-tuning'' of
5291 optimizations to be performed is desired.
5294 @item -fno-default-inline
5295 @opindex fno-default-inline
5296 Do not make member functions inline by default merely because they are
5297 defined inside the class scope (C++ only). Otherwise, when you specify
5298 @w{@option{-O}}, member functions defined inside class scope are compiled
5299 inline by default; i.e., you don't need to add @samp{inline} in front of
5300 the member function name.
5302 @item -fno-defer-pop
5303 @opindex fno-defer-pop
5304 Always pop the arguments to each function call as soon as that function
5305 returns. For machines which must pop arguments after a function call,
5306 the compiler normally lets arguments accumulate on the stack for several
5307 function calls and pops them all at once.
5309 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5311 @item -fforward-propagate
5312 @opindex fforward-propagate
5313 Perform a forward propagation pass on RTL@. The pass tries to combine two
5314 instructions and checks if the result can be simplified. If loop unrolling
5315 is active, two passes are performed and the second is scheduled after
5318 This option is enabled by default at optimization levels @option{-O2},
5319 @option{-O3}, @option{-Os}.
5321 @item -fomit-frame-pointer
5322 @opindex fomit-frame-pointer
5323 Don't keep the frame pointer in a register for functions that
5324 don't need one. This avoids the instructions to save, set up and
5325 restore frame pointers; it also makes an extra register available
5326 in many functions. @strong{It also makes debugging impossible on
5329 On some machines, such as the VAX, this flag has no effect, because
5330 the standard calling sequence automatically handles the frame pointer
5331 and nothing is saved by pretending it doesn't exist. The
5332 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5333 whether a target machine supports this flag. @xref{Registers,,Register
5334 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5336 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5338 @item -foptimize-sibling-calls
5339 @opindex foptimize-sibling-calls
5340 Optimize sibling and tail recursive calls.
5342 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5346 Don't pay attention to the @code{inline} keyword. Normally this option
5347 is used to keep the compiler from expanding any functions inline.
5348 Note that if you are not optimizing, no functions can be expanded inline.
5350 @item -finline-small-functions
5351 @opindex finline-small-functions
5352 Integrate functions into their callers when their body is smaller than expected
5353 function call code (so overall size of program gets smaller). The compiler
5354 heuristically decides which functions are simple enough to be worth integrating
5357 Enabled at level @option{-O2}.
5359 @item -findirect-inlining
5360 @opindex findirect-inlining
5361 Inline also indirect calls that are discovered to be known at compile
5362 time thanks to previous inlining. This option has any effect only
5363 when inlining itself is turned on by the @option{-finline-functions}
5364 or @option{-finline-small-functions} options.
5366 Enabled at level @option{-O2}.
5368 @item -finline-functions
5369 @opindex finline-functions
5370 Integrate all simple functions into their callers. The compiler
5371 heuristically decides which functions are simple enough to be worth
5372 integrating in this way.
5374 If all calls to a given function are integrated, and the function is
5375 declared @code{static}, then the function is normally not output as
5376 assembler code in its own right.
5378 Enabled at level @option{-O3}.
5380 @item -finline-functions-called-once
5381 @opindex finline-functions-called-once
5382 Consider all @code{static} functions called once for inlining into their
5383 caller even if they are not marked @code{inline}. If a call to a given
5384 function is integrated, then the function is not output as assembler code
5387 Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
5389 @item -fearly-inlining
5390 @opindex fearly-inlining
5391 Inline functions marked by @code{always_inline} and functions whose body seems
5392 smaller than the function call overhead early before doing
5393 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5394 makes profiling significantly cheaper and usually inlining faster on programs
5395 having large chains of nested wrapper functions.
5399 @item -finline-limit=@var{n}
5400 @opindex finline-limit
5401 By default, GCC limits the size of functions that can be inlined. This flag
5402 allows coarse control of this limit. @var{n} is the size of functions that
5403 can be inlined in number of pseudo instructions.
5405 Inlining is actually controlled by a number of parameters, which may be
5406 specified individually by using @option{--param @var{name}=@var{value}}.
5407 The @option{-finline-limit=@var{n}} option sets some of these parameters
5411 @item max-inline-insns-single
5412 is set to @var{n}/2.
5413 @item max-inline-insns-auto
5414 is set to @var{n}/2.
5417 See below for a documentation of the individual
5418 parameters controlling inlining and for the defaults of these parameters.
5420 @emph{Note:} there may be no value to @option{-finline-limit} that results
5421 in default behavior.
5423 @emph{Note:} pseudo instruction represents, in this particular context, an
5424 abstract measurement of function's size. In no way does it represent a count
5425 of assembly instructions and as such its exact meaning might change from one
5426 release to an another.
5428 @item -fkeep-inline-functions
5429 @opindex fkeep-inline-functions
5430 In C, emit @code{static} functions that are declared @code{inline}
5431 into the object file, even if the function has been inlined into all
5432 of its callers. This switch does not affect functions using the
5433 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5434 inline functions into the object file.
5436 @item -fkeep-static-consts
5437 @opindex fkeep-static-consts
5438 Emit variables declared @code{static const} when optimization isn't turned
5439 on, even if the variables aren't referenced.
5441 GCC enables this option by default. If you want to force the compiler to
5442 check if the variable was referenced, regardless of whether or not
5443 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5445 @item -fmerge-constants
5446 @opindex fmerge-constants
5447 Attempt to merge identical constants (string constants and floating point
5448 constants) across compilation units.
5450 This option is the default for optimized compilation if the assembler and
5451 linker support it. Use @option{-fno-merge-constants} to inhibit this
5454 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5456 @item -fmerge-all-constants
5457 @opindex fmerge-all-constants
5458 Attempt to merge identical constants and identical variables.
5460 This option implies @option{-fmerge-constants}. In addition to
5461 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5462 arrays or initialized constant variables with integral or floating point
5463 types. Languages like C or C++ require each non-automatic variable to
5464 have distinct location, so using this option will result in non-conforming
5467 @item -fmodulo-sched
5468 @opindex fmodulo-sched
5469 Perform swing modulo scheduling immediately before the first scheduling
5470 pass. This pass looks at innermost loops and reorders their
5471 instructions by overlapping different iterations.
5473 @item -fmodulo-sched-allow-regmoves
5474 @opindex fmodulo-sched-allow-regmoves
5475 Perform more aggressive SMS based modulo scheduling with register moves
5476 allowed. By setting this flag certain anti-dependences edges will be
5477 deleted which will trigger the generation of reg-moves based on the
5478 life-range analysis. This option is effective only with
5479 @option{-fmodulo-sched} enabled.
5481 @item -fno-branch-count-reg
5482 @opindex fno-branch-count-reg
5483 Do not use ``decrement and branch'' instructions on a count register,
5484 but instead generate a sequence of instructions that decrement a
5485 register, compare it against zero, then branch based upon the result.
5486 This option is only meaningful on architectures that support such
5487 instructions, which include x86, PowerPC, IA-64 and S/390.
5489 The default is @option{-fbranch-count-reg}.
5491 @item -fno-function-cse
5492 @opindex fno-function-cse
5493 Do not put function addresses in registers; make each instruction that
5494 calls a constant function contain the function's address explicitly.
5496 This option results in less efficient code, but some strange hacks
5497 that alter the assembler output may be confused by the optimizations
5498 performed when this option is not used.
5500 The default is @option{-ffunction-cse}
5502 @item -fno-zero-initialized-in-bss
5503 @opindex fno-zero-initialized-in-bss
5504 If the target supports a BSS section, GCC by default puts variables that
5505 are initialized to zero into BSS@. This can save space in the resulting
5508 This option turns off this behavior because some programs explicitly
5509 rely on variables going to the data section. E.g., so that the
5510 resulting executable can find the beginning of that section and/or make
5511 assumptions based on that.
5513 The default is @option{-fzero-initialized-in-bss}.
5515 @item -fmudflap -fmudflapth -fmudflapir
5519 @cindex bounds checking
5521 For front-ends that support it (C and C++), instrument all risky
5522 pointer/array dereferencing operations, some standard library
5523 string/heap functions, and some other associated constructs with
5524 range/validity tests. Modules so instrumented should be immune to
5525 buffer overflows, invalid heap use, and some other classes of C/C++
5526 programming errors. The instrumentation relies on a separate runtime
5527 library (@file{libmudflap}), which will be linked into a program if
5528 @option{-fmudflap} is given at link time. Run-time behavior of the
5529 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5530 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5533 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5534 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5535 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5536 instrumentation should ignore pointer reads. This produces less
5537 instrumentation (and therefore faster execution) and still provides
5538 some protection against outright memory corrupting writes, but allows
5539 erroneously read data to propagate within a program.
5541 @item -fthread-jumps
5542 @opindex fthread-jumps
5543 Perform optimizations where we check to see if a jump branches to a
5544 location where another comparison subsumed by the first is found. If
5545 so, the first branch is redirected to either the destination of the
5546 second branch or a point immediately following it, depending on whether
5547 the condition is known to be true or false.
5549 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5551 @item -fsplit-wide-types
5552 @opindex fsplit-wide-types
5553 When using a type that occupies multiple registers, such as @code{long
5554 long} on a 32-bit system, split the registers apart and allocate them
5555 independently. This normally generates better code for those types,
5556 but may make debugging more difficult.
5558 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5561 @item -fcse-follow-jumps
5562 @opindex fcse-follow-jumps
5563 In common subexpression elimination (CSE), scan through jump instructions
5564 when the target of the jump is not reached by any other path. For
5565 example, when CSE encounters an @code{if} statement with an
5566 @code{else} clause, CSE will follow the jump when the condition
5569 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5571 @item -fcse-skip-blocks
5572 @opindex fcse-skip-blocks
5573 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5574 follow jumps which conditionally skip over blocks. When CSE
5575 encounters a simple @code{if} statement with no else clause,
5576 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5577 body of the @code{if}.
5579 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5581 @item -frerun-cse-after-loop
5582 @opindex frerun-cse-after-loop
5583 Re-run common subexpression elimination after loop optimizations has been
5586 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5590 Perform a global common subexpression elimination pass.
5591 This pass also performs global constant and copy propagation.
5593 @emph{Note:} When compiling a program using computed gotos, a GCC
5594 extension, you may get better runtime performance if you disable
5595 the global common subexpression elimination pass by adding
5596 @option{-fno-gcse} to the command line.
5598 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5602 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5603 attempt to move loads which are only killed by stores into themselves. This
5604 allows a loop containing a load/store sequence to be changed to a load outside
5605 the loop, and a copy/store within the loop.
5607 Enabled by default when gcse is enabled.
5611 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5612 global common subexpression elimination. This pass will attempt to move
5613 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5614 loops containing a load/store sequence can be changed to a load before
5615 the loop and a store after the loop.
5617 Not enabled at any optimization level.
5621 When @option{-fgcse-las} is enabled, the global common subexpression
5622 elimination pass eliminates redundant loads that come after stores to the
5623 same memory location (both partial and full redundancies).
5625 Not enabled at any optimization level.
5627 @item -fgcse-after-reload
5628 @opindex fgcse-after-reload
5629 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5630 pass is performed after reload. The purpose of this pass is to cleanup
5633 @item -funsafe-loop-optimizations
5634 @opindex funsafe-loop-optimizations
5635 If given, the loop optimizer will assume that loop indices do not
5636 overflow, and that the loops with nontrivial exit condition are not
5637 infinite. This enables a wider range of loop optimizations even if
5638 the loop optimizer itself cannot prove that these assumptions are valid.
5639 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5640 if it finds this kind of loop.
5642 @item -fcrossjumping
5643 @opindex fcrossjumping
5644 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5645 resulting code may or may not perform better than without cross-jumping.
5647 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5649 @item -fauto-inc-dec
5650 @opindex fauto-inc-dec
5651 Combine increments or decrements of addresses with memory accesses.
5652 This pass is always skipped on architectures that do not have
5653 instructions to support this. Enabled by default at @option{-O} and
5654 higher on architectures that support this.
5658 Perform dead code elimination (DCE) on RTL@.
5659 Enabled by default at @option{-O} and higher.
5663 Perform dead store elimination (DSE) on RTL@.
5664 Enabled by default at @option{-O} and higher.
5666 @item -fif-conversion
5667 @opindex fif-conversion
5668 Attempt to transform conditional jumps into branch-less equivalents. This
5669 include use of conditional moves, min, max, set flags and abs instructions, and
5670 some tricks doable by standard arithmetics. The use of conditional execution
5671 on chips where it is available is controlled by @code{if-conversion2}.
5673 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5675 @item -fif-conversion2
5676 @opindex fif-conversion2
5677 Use conditional execution (where available) to transform conditional jumps into
5678 branch-less equivalents.
5680 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5682 @item -fdelete-null-pointer-checks
5683 @opindex fdelete-null-pointer-checks
5684 Use global dataflow analysis to identify and eliminate useless checks
5685 for null pointers. The compiler assumes that dereferencing a null
5686 pointer would have halted the program. If a pointer is checked after
5687 it has already been dereferenced, it cannot be null.
5689 In some environments, this assumption is not true, and programs can
5690 safely dereference null pointers. Use
5691 @option{-fno-delete-null-pointer-checks} to disable this optimization
5692 for programs which depend on that behavior.
5694 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5696 @item -fexpensive-optimizations
5697 @opindex fexpensive-optimizations
5698 Perform a number of minor optimizations that are relatively expensive.
5700 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5702 @item -foptimize-register-move
5704 @opindex foptimize-register-move
5706 Attempt to reassign register numbers in move instructions and as
5707 operands of other simple instructions in order to maximize the amount of
5708 register tying. This is especially helpful on machines with two-operand
5711 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5714 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5718 Use the integrated register allocator (@acronym{IRA}) for register
5719 allocation. It is a default if @acronym{IRA} has been ported for the
5722 @item -fira-algorithm=@var{algorithm}
5723 Use specified algorithm for the integrated register allocator. The
5724 @var{algorithm} argument should be one of @code{regional}, @code{CB},
5725 or @code{mixed}. The second algorithm specifies Chaitin-Briggs
5726 coloring, the first one specifies regional coloring based on
5727 Chaitin-Briggs coloring, and the third one which is the default
5728 specifies a mix of Chaitin-Briggs and regional algorithms where loops
5729 with small register pressure are ignored. The first algorithm can
5730 give best result for machines with small size and irregular register
5731 set, the second one is faster and generates decent code and the
5732 smallest size code, and the mixed algorithm usually give the best
5733 results in most cases and for most architectures.
5735 @item -fira-coalesce
5736 @opindex fira-coalesce
5737 Do optimistic register coalescing. This option might be profitable for
5738 architectures with big regular register files.
5740 @item -fno-ira-share-save-slots
5741 @opindex fno-ira-share-save-slots
5742 Switch off sharing stack slots used for saving call used hard
5743 registers living through a call. Each hard register will get a
5744 separate stack slot and as a result function stack frame will be
5747 @item -fno-ira-share-spill-slots
5748 @opindex fno-ira-share-spill-slots
5749 Switch off sharing stack slots allocated for pseudo-registers. Each
5750 pseudo-register which did not get a hard register will get a separate
5751 stack slot and as a result function stack frame will be bigger.
5753 @item -fira-verbose=@var{n}
5754 @opindex fira-verbose
5755 Set up how verbose dump file for the integrated register allocator
5756 will be. Default value is 5. If the value is greater or equal to 10,
5757 the dump file will be stderr as if the value were @var{n} minus 10.
5759 @item -fdelayed-branch
5760 @opindex fdelayed-branch
5761 If supported for the target machine, attempt to reorder instructions
5762 to exploit instruction slots available after delayed branch
5765 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5767 @item -fschedule-insns
5768 @opindex fschedule-insns
5769 If supported for the target machine, attempt to reorder instructions to
5770 eliminate execution stalls due to required data being unavailable. This
5771 helps machines that have slow floating point or memory load instructions
5772 by allowing other instructions to be issued until the result of the load
5773 or floating point instruction is required.
5775 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5777 @item -fschedule-insns2
5778 @opindex fschedule-insns2
5779 Similar to @option{-fschedule-insns}, but requests an additional pass of
5780 instruction scheduling after register allocation has been done. This is
5781 especially useful on machines with a relatively small number of
5782 registers and where memory load instructions take more than one cycle.
5784 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5786 @item -fno-sched-interblock
5787 @opindex fno-sched-interblock
5788 Don't schedule instructions across basic blocks. This is normally
5789 enabled by default when scheduling before register allocation, i.e.@:
5790 with @option{-fschedule-insns} or at @option{-O2} or higher.
5792 @item -fno-sched-spec
5793 @opindex fno-sched-spec
5794 Don't allow speculative motion of non-load instructions. This is normally
5795 enabled by default when scheduling before register allocation, i.e.@:
5796 with @option{-fschedule-insns} or at @option{-O2} or higher.
5798 @item -fsched-spec-load
5799 @opindex fsched-spec-load
5800 Allow speculative motion of some load instructions. This only makes
5801 sense when scheduling before register allocation, i.e.@: with
5802 @option{-fschedule-insns} or at @option{-O2} or higher.
5804 @item -fsched-spec-load-dangerous
5805 @opindex fsched-spec-load-dangerous
5806 Allow speculative motion of more load instructions. This only makes
5807 sense when scheduling before register allocation, i.e.@: with
5808 @option{-fschedule-insns} or at @option{-O2} or higher.
5810 @item -fsched-stalled-insns
5811 @itemx -fsched-stalled-insns=@var{n}
5812 @opindex fsched-stalled-insns
5813 Define how many insns (if any) can be moved prematurely from the queue
5814 of stalled insns into the ready list, during the second scheduling pass.
5815 @option{-fno-sched-stalled-insns} means that no insns will be moved
5816 prematurely, @option{-fsched-stalled-insns=0} means there is no limit
5817 on how many queued insns can be moved prematurely.
5818 @option{-fsched-stalled-insns} without a value is equivalent to
5819 @option{-fsched-stalled-insns=1}.
5821 @item -fsched-stalled-insns-dep
5822 @itemx -fsched-stalled-insns-dep=@var{n}
5823 @opindex fsched-stalled-insns-dep
5824 Define how many insn groups (cycles) will be examined for a dependency
5825 on a stalled insn that is candidate for premature removal from the queue
5826 of stalled insns. This has an effect only during the second scheduling pass,
5827 and only if @option{-fsched-stalled-insns} is used.
5828 @option{-fno-sched-stalled-insns-dep} is equivalent to
5829 @option{-fsched-stalled-insns-dep=0}.
5830 @option{-fsched-stalled-insns-dep} without a value is equivalent to
5831 @option{-fsched-stalled-insns-dep=1}.
5833 @item -fsched2-use-superblocks
5834 @opindex fsched2-use-superblocks
5835 When scheduling after register allocation, do use superblock scheduling
5836 algorithm. Superblock scheduling allows motion across basic block boundaries
5837 resulting on faster schedules. This option is experimental, as not all machine
5838 descriptions used by GCC model the CPU closely enough to avoid unreliable
5839 results from the algorithm.
5841 This only makes sense when scheduling after register allocation, i.e.@: with
5842 @option{-fschedule-insns2} or at @option{-O2} or higher.
5844 @item -fsched2-use-traces
5845 @opindex fsched2-use-traces
5846 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5847 allocation and additionally perform code duplication in order to increase the
5848 size of superblocks using tracer pass. See @option{-ftracer} for details on
5851 This mode should produce faster but significantly longer programs. Also
5852 without @option{-fbranch-probabilities} the traces constructed may not
5853 match the reality and hurt the performance. This only makes
5854 sense when scheduling after register allocation, i.e.@: with
5855 @option{-fschedule-insns2} or at @option{-O2} or higher.
5859 Eliminate redundant sign extension instructions and move the non-redundant
5860 ones to optimal placement using lazy code motion (LCM).
5862 @item -freschedule-modulo-scheduled-loops
5863 @opindex freschedule-modulo-scheduled-loops
5864 The modulo scheduling comes before the traditional scheduling, if a loop
5865 was modulo scheduled we may want to prevent the later scheduling passes
5866 from changing its schedule, we use this option to control that.
5868 @item -fselective-scheduling
5869 @opindex fselective-scheduling
5870 Schedule instructions using selective scheduling algorithm. Selective
5871 scheduling runs instead of the first scheduler pass.
5873 @item -fselective-scheduling2
5874 @opindex fselective-scheduling2
5875 Schedule instructions using selective scheduling algorithm. Selective
5876 scheduling runs instead of the second scheduler pass.
5878 @item -fsel-sched-pipelining
5879 @opindex fsel-sched-pipelining
5880 Enable software pipelining of innermost loops during selective scheduling.
5881 This option has no effect until one of @option{-fselective-scheduling} or
5882 @option{-fselective-scheduling2} is turned on.
5884 @item -fsel-sched-pipelining-outer-loops
5885 @opindex fsel-sched-pipelining-outer-loops
5886 When pipelining loops during selective scheduling, also pipeline outer loops.
5887 This option has no effect until @option{-fsel-sched-pipelining} is turned on.
5889 @item -fcaller-saves
5890 @opindex fcaller-saves
5891 Enable values to be allocated in registers that will be clobbered by
5892 function calls, by emitting extra instructions to save and restore the
5893 registers around such calls. Such allocation is done only when it
5894 seems to result in better code than would otherwise be produced.
5896 This option is always enabled by default on certain machines, usually
5897 those which have no call-preserved registers to use instead.
5899 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5901 @item -fconserve-stack
5902 @opindex fconserve-stack
5903 Attempt to minimize stack usage. The compiler will attempt to use less
5904 stack space, even if that makes the program slower. This option
5905 implies setting the @option{large-stack-frame} parameter to 100
5906 and the @option{large-stack-frame-growth} parameter to 400.
5908 @item -ftree-reassoc
5909 @opindex ftree-reassoc
5910 Perform reassociation on trees. This flag is enabled by default
5911 at @option{-O} and higher.
5915 Perform partial redundancy elimination (PRE) on trees. This flag is
5916 enabled by default at @option{-O2} and @option{-O3}.
5920 Perform full redundancy elimination (FRE) on trees. The difference
5921 between FRE and PRE is that FRE only considers expressions
5922 that are computed on all paths leading to the redundant computation.
5923 This analysis is faster than PRE, though it exposes fewer redundancies.
5924 This flag is enabled by default at @option{-O} and higher.
5926 @item -ftree-copy-prop
5927 @opindex ftree-copy-prop
5928 Perform copy propagation on trees. This pass eliminates unnecessary
5929 copy operations. This flag is enabled by default at @option{-O} and
5932 @item -fipa-pure-const
5933 @opindex fipa-pure-const
5934 Discover which functions are pure or constant.
5935 Enabled by default at @option{-O} and higher.
5937 @item -fipa-reference
5938 @opindex fipa-reference
5939 Discover which static variables do not escape cannot escape the
5941 Enabled by default at @option{-O} and higher.
5943 @item -fipa-struct-reorg
5944 @opindex fipa-struct-reorg
5945 Perform structure reorganization optimization, that change C-like structures
5946 layout in order to better utilize spatial locality. This transformation is
5947 affective for programs containing arrays of structures. Available in two
5948 compilation modes: profile-based (enabled with @option{-fprofile-generate})
5949 or static (which uses built-in heuristics). Require @option{-fipa-type-escape}
5950 to provide the safety of this transformation. It works only in whole program
5951 mode, so it requires @option{-fwhole-program} and @option{-combine} to be
5952 enabled. Structures considered @samp{cold} by this transformation are not
5953 affected (see @option{--param struct-reorg-cold-struct-ratio=@var{value}}).
5955 With this flag, the program debug info reflects a new structure layout.
5959 Perform interprocedural pointer analysis. This option is experimental
5960 and does not affect generated code.
5964 Perform interprocedural constant propagation.
5965 This optimization analyzes the program to determine when values passed
5966 to functions are constants and then optimizes accordingly.
5967 This optimization can substantially increase performance
5968 if the application has constants passed to functions.
5969 This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
5971 @item -fipa-cp-clone
5972 @opindex fipa-cp-clone
5973 Perform function cloning to make interprocedural constant propagation stronger.
5974 When enabled, interprocedural constant propagation will perform function cloning
5975 when externally visible function can be called with constant arguments.
5976 Because this optimization can create multiple copies of functions,
5977 it may significantly increase code size
5978 (see @option{--param ipcp-unit-growth=@var{value}}).
5979 This flag is enabled by default at @option{-O3}.
5981 @item -fipa-matrix-reorg
5982 @opindex fipa-matrix-reorg
5983 Perform matrix flattening and transposing.
5984 Matrix flattening tries to replace a m-dimensional matrix
5985 with its equivalent n-dimensional matrix, where n < m.
5986 This reduces the level of indirection needed for accessing the elements
5987 of the matrix. The second optimization is matrix transposing that
5988 attemps to change the order of the matrix's dimensions in order to
5989 improve cache locality.
5990 Both optimizations need fwhole-program flag.
5991 Transposing is enabled only if profiling information is avaliable.
5996 Perform forward store motion on trees. This flag is
5997 enabled by default at @option{-O} and higher.
6001 Perform sparse conditional constant propagation (CCP) on trees. This
6002 pass only operates on local scalar variables and is enabled by default
6003 at @option{-O} and higher.
6005 @item -ftree-switch-conversion
6006 Perform conversion of simple initializations in a switch to
6007 initializations from a scalar array. This flag is enabled by default
6008 at @option{-O2} and higher.
6012 Perform dead code elimination (DCE) on trees. This flag is enabled by
6013 default at @option{-O} and higher.
6015 @item -ftree-builtin-call-dce
6016 @opindex ftree-builtin-call-dce
6017 Perform conditional dead code elimination (DCE) for calls to builtin functions
6018 that may set @code{errno} but are otherwise side-effect free. This flag is
6019 enabled by default at @option{-O2} and higher if @option{-Os} is not also
6022 @item -ftree-dominator-opts
6023 @opindex ftree-dominator-opts
6024 Perform a variety of simple scalar cleanups (constant/copy
6025 propagation, redundancy elimination, range propagation and expression
6026 simplification) based on a dominator tree traversal. This also
6027 performs jump threading (to reduce jumps to jumps). This flag is
6028 enabled by default at @option{-O} and higher.
6032 Perform dead store elimination (DSE) on trees. A dead store is a store into
6033 a memory location which will later be overwritten by another store without
6034 any intervening loads. In this case the earlier store can be deleted. This
6035 flag is enabled by default at @option{-O} and higher.
6039 Perform loop header copying on trees. This is beneficial since it increases
6040 effectiveness of code motion optimizations. It also saves one jump. This flag
6041 is enabled by default at @option{-O} and higher. It is not enabled
6042 for @option{-Os}, since it usually increases code size.
6044 @item -ftree-loop-optimize
6045 @opindex ftree-loop-optimize
6046 Perform loop optimizations on trees. This flag is enabled by default
6047 at @option{-O} and higher.
6049 @item -ftree-loop-linear
6050 @opindex ftree-loop-linear
6051 Perform linear loop transformations on tree. This flag can improve cache
6052 performance and allow further loop optimizations to take place.
6054 @item -floop-interchange
6055 Perform loop interchange transformations on loops. Interchanging two
6056 nested loops switches the inner and outer loops. For example, given a
6061 A(J, I) = A(J, I) * C
6065 loop interchange will transform the loop as if the user had written:
6069 A(J, I) = A(J, I) * C
6073 which can be beneficial when @code{N} is larger than the caches,
6074 because in Fortran, the elements of an array are stored in memory
6075 contiguously by column, and the original loop iterates over rows,
6076 potentially creating at each access a cache miss. This optimization
6077 applies to all the languages supported by GCC and is not limited to
6080 @item -floop-strip-mine
6081 Perform loop strip mining transformations on loops. Strip mining
6082 splits a loop into two nested loops. The outer loop has strides
6083 equal to the strip size and the inner loop has strides of the
6084 original loop within a strip. For example, given a loop like:
6090 loop strip mining will transform the loop as if the user had written:
6093 DO I = II, min (II + 3, N)
6098 This optimization applies to all the languages supported by GCC and is
6099 not limited to Fortran.
6102 Perform loop blocking transformations on loops. Blocking strip mines
6103 each loop in the loop nest such that the memory accesses of the
6104 element loops fit inside caches. For example, given a loop like:
6108 A(J, I) = B(I) + C(J)
6112 loop blocking will transform the loop as if the user had written:
6116 DO I = II, min (II + 63, N)
6117 DO J = JJ, min (JJ + 63, M)
6118 A(J, I) = B(I) + C(J)
6124 which can be beneficial when @code{M} is larger than the caches,
6125 because the innermost loop will iterate over a smaller amount of data
6126 that can be kept in the caches. This optimization applies to all the
6127 languages supported by GCC and is not limited to Fortran.
6129 @item -fcheck-data-deps
6130 @opindex fcheck-data-deps
6131 Compare the results of several data dependence analyzers. This option
6132 is used for debugging the data dependence analyzers.
6134 @item -ftree-loop-distribution
6135 Perform loop distribution. This flag can improve cache performance on
6136 big loop bodies and allow further loop optimizations, like
6137 parallelization or vectorization, to take place. For example, the loop
6154 @item -ftree-loop-im
6155 @opindex ftree-loop-im
6156 Perform loop invariant motion on trees. This pass moves only invariants that
6157 would be hard to handle at RTL level (function calls, operations that expand to
6158 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
6159 operands of conditions that are invariant out of the loop, so that we can use
6160 just trivial invariantness analysis in loop unswitching. The pass also includes
6163 @item -ftree-loop-ivcanon
6164 @opindex ftree-loop-ivcanon
6165 Create a canonical counter for number of iterations in the loop for that
6166 determining number of iterations requires complicated analysis. Later
6167 optimizations then may determine the number easily. Useful especially
6168 in connection with unrolling.
6172 Perform induction variable optimizations (strength reduction, induction
6173 variable merging and induction variable elimination) on trees.
6175 @item -ftree-parallelize-loops=n
6176 @opindex ftree-parallelize-loops
6177 Parallelize loops, i.e., split their iteration space to run in n threads.
6178 This is only possible for loops whose iterations are independent
6179 and can be arbitrarily reordered. The optimization is only
6180 profitable on multiprocessor machines, for loops that are CPU-intensive,
6181 rather than constrained e.g.@: by memory bandwidth. This option
6182 implies @option{-pthread}, and thus is only supported on targets
6183 that have support for @option{-pthread}.
6187 Perform scalar replacement of aggregates. This pass replaces structure
6188 references with scalars to prevent committing structures to memory too
6189 early. This flag is enabled by default at @option{-O} and higher.
6191 @item -ftree-copyrename
6192 @opindex ftree-copyrename
6193 Perform copy renaming on trees. This pass attempts to rename compiler
6194 temporaries to other variables at copy locations, usually resulting in
6195 variable names which more closely resemble the original variables. This flag
6196 is enabled by default at @option{-O} and higher.
6200 Perform temporary expression replacement during the SSA->normal phase. Single
6201 use/single def temporaries are replaced at their use location with their
6202 defining expression. This results in non-GIMPLE code, but gives the expanders
6203 much more complex trees to work on resulting in better RTL generation. This is
6204 enabled by default at @option{-O} and higher.
6206 @item -ftree-vectorize
6207 @opindex ftree-vectorize
6208 Perform loop vectorization on trees. This flag is enabled by default at
6211 @item -ftree-vect-loop-version
6212 @opindex ftree-vect-loop-version
6213 Perform loop versioning when doing loop vectorization on trees. When a loop
6214 appears to be vectorizable except that data alignment or data dependence cannot
6215 be determined at compile time then vectorized and non-vectorized versions of
6216 the loop are generated along with runtime checks for alignment or dependence
6217 to control which version is executed. This option is enabled by default
6218 except at level @option{-Os} where it is disabled.
6220 @item -fvect-cost-model
6221 @opindex fvect-cost-model
6222 Enable cost model for vectorization.
6226 Perform Value Range Propagation on trees. This is similar to the
6227 constant propagation pass, but instead of values, ranges of values are
6228 propagated. This allows the optimizers to remove unnecessary range
6229 checks like array bound checks and null pointer checks. This is
6230 enabled by default at @option{-O2} and higher. Null pointer check
6231 elimination is only done if @option{-fdelete-null-pointer-checks} is
6236 Perform tail duplication to enlarge superblock size. This transformation
6237 simplifies the control flow of the function allowing other optimizations to do
6240 @item -funroll-loops
6241 @opindex funroll-loops
6242 Unroll loops whose number of iterations can be determined at compile
6243 time or upon entry to the loop. @option{-funroll-loops} implies
6244 @option{-frerun-cse-after-loop}. This option makes code larger,
6245 and may or may not make it run faster.
6247 @item -funroll-all-loops
6248 @opindex funroll-all-loops
6249 Unroll all loops, even if their number of iterations is uncertain when
6250 the loop is entered. This usually makes programs run more slowly.
6251 @option{-funroll-all-loops} implies the same options as
6252 @option{-funroll-loops},
6254 @item -fsplit-ivs-in-unroller
6255 @opindex fsplit-ivs-in-unroller
6256 Enables expressing of values of induction variables in later iterations
6257 of the unrolled loop using the value in the first iteration. This breaks
6258 long dependency chains, thus improving efficiency of the scheduling passes.
6260 Combination of @option{-fweb} and CSE is often sufficient to obtain the
6261 same effect. However in cases the loop body is more complicated than
6262 a single basic block, this is not reliable. It also does not work at all
6263 on some of the architectures due to restrictions in the CSE pass.
6265 This optimization is enabled by default.
6267 @item -fvariable-expansion-in-unroller
6268 @opindex fvariable-expansion-in-unroller
6269 With this option, the compiler will create multiple copies of some
6270 local variables when unrolling a loop which can result in superior code.
6272 @item -fpredictive-commoning
6273 @opindex fpredictive-commoning
6274 Perform predictive commoning optimization, i.e., reusing computations
6275 (especially memory loads and stores) performed in previous
6276 iterations of loops.
6278 This option is enabled at level @option{-O3}.
6280 @item -fprefetch-loop-arrays
6281 @opindex fprefetch-loop-arrays
6282 If supported by the target machine, generate instructions to prefetch
6283 memory to improve the performance of loops that access large arrays.
6285 This option may generate better or worse code; results are highly
6286 dependent on the structure of loops within the source code.
6288 Disabled at level @option{-Os}.
6291 @itemx -fno-peephole2
6292 @opindex fno-peephole
6293 @opindex fno-peephole2
6294 Disable any machine-specific peephole optimizations. The difference
6295 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
6296 are implemented in the compiler; some targets use one, some use the
6297 other, a few use both.
6299 @option{-fpeephole} is enabled by default.
6300 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6302 @item -fno-guess-branch-probability
6303 @opindex fno-guess-branch-probability
6304 Do not guess branch probabilities using heuristics.
6306 GCC will use heuristics to guess branch probabilities if they are
6307 not provided by profiling feedback (@option{-fprofile-arcs}). These
6308 heuristics are based on the control flow graph. If some branch probabilities
6309 are specified by @samp{__builtin_expect}, then the heuristics will be
6310 used to guess branch probabilities for the rest of the control flow graph,
6311 taking the @samp{__builtin_expect} info into account. The interactions
6312 between the heuristics and @samp{__builtin_expect} can be complex, and in
6313 some cases, it may be useful to disable the heuristics so that the effects
6314 of @samp{__builtin_expect} are easier to understand.
6316 The default is @option{-fguess-branch-probability} at levels
6317 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6319 @item -freorder-blocks
6320 @opindex freorder-blocks
6321 Reorder basic blocks in the compiled function in order to reduce number of
6322 taken branches and improve code locality.
6324 Enabled at levels @option{-O2}, @option{-O3}.
6326 @item -freorder-blocks-and-partition
6327 @opindex freorder-blocks-and-partition
6328 In addition to reordering basic blocks in the compiled function, in order
6329 to reduce number of taken branches, partitions hot and cold basic blocks
6330 into separate sections of the assembly and .o files, to improve
6331 paging and cache locality performance.
6333 This optimization is automatically turned off in the presence of
6334 exception handling, for linkonce sections, for functions with a user-defined
6335 section attribute and on any architecture that does not support named
6338 @item -freorder-functions
6339 @opindex freorder-functions
6340 Reorder functions in the object file in order to
6341 improve code locality. This is implemented by using special
6342 subsections @code{.text.hot} for most frequently executed functions and
6343 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
6344 the linker so object file format must support named sections and linker must
6345 place them in a reasonable way.
6347 Also profile feedback must be available in to make this option effective. See
6348 @option{-fprofile-arcs} for details.
6350 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
6352 @item -fstrict-aliasing
6353 @opindex fstrict-aliasing
6354 Allows the compiler to assume the strictest aliasing rules applicable to
6355 the language being compiled. For C (and C++), this activates
6356 optimizations based on the type of expressions. In particular, an
6357 object of one type is assumed never to reside at the same address as an
6358 object of a different type, unless the types are almost the same. For
6359 example, an @code{unsigned int} can alias an @code{int}, but not a
6360 @code{void*} or a @code{double}. A character type may alias any other
6363 @anchor{Type-punning}Pay special attention to code like this:
6376 The practice of reading from a different union member than the one most
6377 recently written to (called ``type-punning'') is common. Even with
6378 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
6379 is accessed through the union type. So, the code above will work as
6380 expected. @xref{Structures unions enumerations and bit-fields
6381 implementation}. However, this code might not:
6392 Similarly, access by taking the address, casting the resulting pointer
6393 and dereferencing the result has undefined behavior, even if the cast
6394 uses a union type, e.g.:
6398 return ((union a_union *) &d)->i;
6402 The @option{-fstrict-aliasing} option is enabled at levels
6403 @option{-O2}, @option{-O3}, @option{-Os}.
6405 @item -fstrict-overflow
6406 @opindex fstrict-overflow
6407 Allow the compiler to assume strict signed overflow rules, depending
6408 on the language being compiled. For C (and C++) this means that
6409 overflow when doing arithmetic with signed numbers is undefined, which
6410 means that the compiler may assume that it will not happen. This
6411 permits various optimizations. For example, the compiler will assume
6412 that an expression like @code{i + 10 > i} will always be true for
6413 signed @code{i}. This assumption is only valid if signed overflow is
6414 undefined, as the expression is false if @code{i + 10} overflows when
6415 using twos complement arithmetic. When this option is in effect any
6416 attempt to determine whether an operation on signed numbers will
6417 overflow must be written carefully to not actually involve overflow.
6419 This option also allows the compiler to assume strict pointer
6420 semantics: given a pointer to an object, if adding an offset to that
6421 pointer does not produce a pointer to the same object, the addition is
6422 undefined. This permits the compiler to conclude that @code{p + u >
6423 p} is always true for a pointer @code{p} and unsigned integer
6424 @code{u}. This assumption is only valid because pointer wraparound is
6425 undefined, as the expression is false if @code{p + u} overflows using
6426 twos complement arithmetic.
6428 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
6429 that integer signed overflow is fully defined: it wraps. When
6430 @option{-fwrapv} is used, there is no difference between
6431 @option{-fstrict-overflow} and @option{-fno-strict-overflow} for
6432 integers. With @option{-fwrapv} certain types of overflow are
6433 permitted. For example, if the compiler gets an overflow when doing
6434 arithmetic on constants, the overflowed value can still be used with
6435 @option{-fwrapv}, but not otherwise.
6437 The @option{-fstrict-overflow} option is enabled at levels
6438 @option{-O2}, @option{-O3}, @option{-Os}.
6440 @item -falign-functions
6441 @itemx -falign-functions=@var{n}
6442 @opindex falign-functions
6443 Align the start of functions to the next power-of-two greater than
6444 @var{n}, skipping up to @var{n} bytes. For instance,
6445 @option{-falign-functions=32} aligns functions to the next 32-byte
6446 boundary, but @option{-falign-functions=24} would align to the next
6447 32-byte boundary only if this can be done by skipping 23 bytes or less.
6449 @option{-fno-align-functions} and @option{-falign-functions=1} are
6450 equivalent and mean that functions will not be aligned.
6452 Some assemblers only support this flag when @var{n} is a power of two;
6453 in that case, it is rounded up.
6455 If @var{n} is not specified or is zero, use a machine-dependent default.
6457 Enabled at levels @option{-O2}, @option{-O3}.
6459 @item -falign-labels
6460 @itemx -falign-labels=@var{n}
6461 @opindex falign-labels
6462 Align all branch targets to a power-of-two boundary, skipping up to
6463 @var{n} bytes like @option{-falign-functions}. This option can easily
6464 make code slower, because it must insert dummy operations for when the
6465 branch target is reached in the usual flow of the code.
6467 @option{-fno-align-labels} and @option{-falign-labels=1} are
6468 equivalent and mean that labels will not be aligned.
6470 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
6471 are greater than this value, then their values are used instead.
6473 If @var{n} is not specified or is zero, use a machine-dependent default
6474 which is very likely to be @samp{1}, meaning no alignment.
6476 Enabled at levels @option{-O2}, @option{-O3}.
6479 @itemx -falign-loops=@var{n}
6480 @opindex falign-loops
6481 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
6482 like @option{-falign-functions}. The hope is that the loop will be
6483 executed many times, which will make up for any execution of the dummy
6486 @option{-fno-align-loops} and @option{-falign-loops=1} are
6487 equivalent and mean that loops will not be aligned.
6489 If @var{n} is not specified or is zero, use a machine-dependent default.
6491 Enabled at levels @option{-O2}, @option{-O3}.
6494 @itemx -falign-jumps=@var{n}
6495 @opindex falign-jumps
6496 Align branch targets to a power-of-two boundary, for branch targets
6497 where the targets can only be reached by jumping, skipping up to @var{n}
6498 bytes like @option{-falign-functions}. In this case, no dummy operations
6501 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
6502 equivalent and mean that loops will not be aligned.
6504 If @var{n} is not specified or is zero, use a machine-dependent default.
6506 Enabled at levels @option{-O2}, @option{-O3}.
6508 @item -funit-at-a-time
6509 @opindex funit-at-a-time
6510 This option is left for compatibility reasons. @option{-funit-at-a-time}
6511 has no effect, while @option{-fno-unit-at-a-time} implies
6512 @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
6516 @item -fno-toplevel-reorder
6517 @opindex fno-toplevel-reorder
6518 Do not reorder top-level functions, variables, and @code{asm}
6519 statements. Output them in the same order that they appear in the
6520 input file. When this option is used, unreferenced static variables
6521 will not be removed. This option is intended to support existing code
6522 which relies on a particular ordering. For new code, it is better to
6525 Enabled at level @option{-O0}. When disabled explicitly, it also imply
6526 @option{-fno-section-anchors} that is otherwise enabled at @option{-O0} on some
6531 Constructs webs as commonly used for register allocation purposes and assign
6532 each web individual pseudo register. This allows the register allocation pass
6533 to operate on pseudos directly, but also strengthens several other optimization
6534 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6535 however, make debugging impossible, since variables will no longer stay in a
6538 Enabled by default with @option{-funroll-loops}.
6540 @item -fwhole-program
6541 @opindex fwhole-program
6542 Assume that the current compilation unit represents whole program being
6543 compiled. All public functions and variables with the exception of @code{main}
6544 and those merged by attribute @code{externally_visible} become static functions
6545 and in a affect gets more aggressively optimized by interprocedural optimizers.
6546 While this option is equivalent to proper use of @code{static} keyword for
6547 programs consisting of single file, in combination with option
6548 @option{--combine} this flag can be used to compile most of smaller scale C
6549 programs since the functions and variables become local for the whole combined
6550 compilation unit, not for the single source file itself.
6552 This option is not supported for Fortran programs.
6554 @item -fcprop-registers
6555 @opindex fcprop-registers
6556 After register allocation and post-register allocation instruction splitting,
6557 we perform a copy-propagation pass to try to reduce scheduling dependencies
6558 and occasionally eliminate the copy.
6560 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6562 @item -fprofile-correction
6563 @opindex fprofile-correction
6564 Profiles collected using an instrumented binary for multi-threaded programs may
6565 be inconsistent due to missed counter updates. When this option is specified,
6566 GCC will use heuristics to correct or smooth out such inconsistencies. By
6567 default, GCC will emit an error message when an inconsistent profile is detected.
6569 @item -fprofile-dir=@var{path}
6570 @opindex fprofile-dir
6572 Set the directory to search the profile data files in to @var{path}.
6573 This option affects only the profile data generated by
6574 @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
6575 and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
6576 and its related options.
6577 By default, GCC will use the current directory as @var{path}
6578 thus the profile data file will appear in the same directory as the object file.
6580 @item -fprofile-generate
6581 @itemx -fprofile-generate=@var{path}
6582 @opindex fprofile-generate
6584 Enable options usually used for instrumenting application to produce
6585 profile useful for later recompilation with profile feedback based
6586 optimization. You must use @option{-fprofile-generate} both when
6587 compiling and when linking your program.
6589 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6591 If @var{path} is specified, GCC will look at the @var{path} to find
6592 the profile feeedback data files. See @option{-fprofile-dir}.
6595 @itemx -fprofile-use=@var{path}
6596 @opindex fprofile-use
6597 Enable profile feedback directed optimizations, and optimizations
6598 generally profitable only with profile feedback available.
6600 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6601 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6603 By default, GCC emits an error message if the feedback profiles do not
6604 match the source code. This error can be turned into a warning by using
6605 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6608 If @var{path} is specified, GCC will look at the @var{path} to find
6609 the profile feedback data files. See @option{-fprofile-dir}.
6612 The following options control compiler behavior regarding floating
6613 point arithmetic. These options trade off between speed and
6614 correctness. All must be specifically enabled.
6618 @opindex ffloat-store
6619 Do not store floating point variables in registers, and inhibit other
6620 options that might change whether a floating point value is taken from a
6623 @cindex floating point precision
6624 This option prevents undesirable excess precision on machines such as
6625 the 68000 where the floating registers (of the 68881) keep more
6626 precision than a @code{double} is supposed to have. Similarly for the
6627 x86 architecture. For most programs, the excess precision does only
6628 good, but a few programs rely on the precise definition of IEEE floating
6629 point. Use @option{-ffloat-store} for such programs, after modifying
6630 them to store all pertinent intermediate computations into variables.
6634 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
6635 @option{-ffinite-math-only}, @option{-fno-rounding-math},
6636 @option{-fno-signaling-nans} and @option{-fcx-limited-range}.
6638 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6640 This option is not turned on by any @option{-O} option since
6641 it can result in incorrect output for programs which depend on
6642 an exact implementation of IEEE or ISO rules/specifications for
6643 math functions. It may, however, yield faster code for programs
6644 that do not require the guarantees of these specifications.
6646 @item -fno-math-errno
6647 @opindex fno-math-errno
6648 Do not set ERRNO after calling math functions that are executed
6649 with a single instruction, e.g., sqrt. A program that relies on
6650 IEEE exceptions for math error handling may want to use this flag
6651 for speed while maintaining IEEE arithmetic compatibility.
6653 This option is not turned on by any @option{-O} option since
6654 it can result in incorrect output for programs which depend on
6655 an exact implementation of IEEE or ISO rules/specifications for
6656 math functions. It may, however, yield faster code for programs
6657 that do not require the guarantees of these specifications.
6659 The default is @option{-fmath-errno}.
6661 On Darwin systems, the math library never sets @code{errno}. There is
6662 therefore no reason for the compiler to consider the possibility that
6663 it might, and @option{-fno-math-errno} is the default.
6665 @item -funsafe-math-optimizations
6666 @opindex funsafe-math-optimizations
6668 Allow optimizations for floating-point arithmetic that (a) assume
6669 that arguments and results are valid and (b) may violate IEEE or
6670 ANSI standards. When used at link-time, it may include libraries
6671 or startup files that change the default FPU control word or other
6672 similar optimizations.
6674 This option is not turned on by any @option{-O} option since
6675 it can result in incorrect output for programs which depend on
6676 an exact implementation of IEEE or ISO rules/specifications for
6677 math functions. It may, however, yield faster code for programs
6678 that do not require the guarantees of these specifications.
6679 Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
6680 @option{-fassociative-math} and @option{-freciprocal-math}.
6682 The default is @option{-fno-unsafe-math-optimizations}.
6684 @item -fassociative-math
6685 @opindex fassociative-math
6687 Allow re-association of operands in series of floating-point operations.
6688 This violates the ISO C and C++ language standard by possibly changing
6689 computation result. NOTE: re-ordering may change the sign of zero as
6690 well as ignore NaNs and inhibit or create underflow or overflow (and
6691 thus cannot be used on a code which relies on rounding behavior like
6692 @code{(x + 2**52) - 2**52)}. May also reorder floating-point comparisons
6693 and thus may not be used when ordered comparisons are required.
6694 This option requires that both @option{-fno-signed-zeros} and
6695 @option{-fno-trapping-math} be in effect. Moreover, it doesn't make
6696 much sense with @option{-frounding-math}.
6698 The default is @option{-fno-associative-math}.
6700 @item -freciprocal-math
6701 @opindex freciprocal-math
6703 Allow the reciprocal of a value to be used instead of dividing by
6704 the value if this enables optimizations. For example @code{x / y}
6705 can be replaced with @code{x * (1/y)} which is useful if @code{(1/y)}
6706 is subject to common subexpression elimination. Note that this loses
6707 precision and increases the number of flops operating on the value.
6709 The default is @option{-fno-reciprocal-math}.
6711 @item -ffinite-math-only
6712 @opindex ffinite-math-only
6713 Allow optimizations for floating-point arithmetic that assume
6714 that arguments and results are not NaNs or +-Infs.
6716 This option is not turned on by any @option{-O} option since
6717 it can result in incorrect output for programs which depend on
6718 an exact implementation of IEEE or ISO rules/specifications for
6719 math functions. It may, however, yield faster code for programs
6720 that do not require the guarantees of these specifications.
6722 The default is @option{-fno-finite-math-only}.
6724 @item -fno-signed-zeros
6725 @opindex fno-signed-zeros
6726 Allow optimizations for floating point arithmetic that ignore the
6727 signedness of zero. IEEE arithmetic specifies the behavior of
6728 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6729 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6730 This option implies that the sign of a zero result isn't significant.
6732 The default is @option{-fsigned-zeros}.
6734 @item -fno-trapping-math
6735 @opindex fno-trapping-math
6736 Compile code assuming that floating-point operations cannot generate
6737 user-visible traps. These traps include division by zero, overflow,
6738 underflow, inexact result and invalid operation. This option requires
6739 that @option{-fno-signaling-nans} be in effect. Setting this option may
6740 allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
6742 This option should never be turned on by any @option{-O} option since
6743 it can result in incorrect output for programs which depend on
6744 an exact implementation of IEEE or ISO rules/specifications for
6747 The default is @option{-ftrapping-math}.
6749 @item -frounding-math
6750 @opindex frounding-math
6751 Disable transformations and optimizations that assume default floating
6752 point rounding behavior. This is round-to-zero for all floating point
6753 to integer conversions, and round-to-nearest for all other arithmetic
6754 truncations. This option should be specified for programs that change
6755 the FP rounding mode dynamically, or that may be executed with a
6756 non-default rounding mode. This option disables constant folding of
6757 floating point expressions at compile-time (which may be affected by
6758 rounding mode) and arithmetic transformations that are unsafe in the
6759 presence of sign-dependent rounding modes.
6761 The default is @option{-fno-rounding-math}.
6763 This option is experimental and does not currently guarantee to
6764 disable all GCC optimizations that are affected by rounding mode.
6765 Future versions of GCC may provide finer control of this setting
6766 using C99's @code{FENV_ACCESS} pragma. This command line option
6767 will be used to specify the default state for @code{FENV_ACCESS}.
6769 @item -frtl-abstract-sequences
6770 @opindex frtl-abstract-sequences
6771 It is a size optimization method. This option is to find identical
6772 sequences of code, which can be turned into pseudo-procedures and
6773 then replace all occurrences with calls to the newly created
6774 subroutine. It is kind of an opposite of @option{-finline-functions}.
6775 This optimization runs at RTL level.
6777 @item -fsignaling-nans
6778 @opindex fsignaling-nans
6779 Compile code assuming that IEEE signaling NaNs may generate user-visible
6780 traps during floating-point operations. Setting this option disables
6781 optimizations that may change the number of exceptions visible with
6782 signaling NaNs. This option implies @option{-ftrapping-math}.
6784 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6787 The default is @option{-fno-signaling-nans}.
6789 This option is experimental and does not currently guarantee to
6790 disable all GCC optimizations that affect signaling NaN behavior.
6792 @item -fsingle-precision-constant
6793 @opindex fsingle-precision-constant
6794 Treat floating point constant as single precision constant instead of
6795 implicitly converting it to double precision constant.
6797 @item -fcx-limited-range
6798 @opindex fcx-limited-range
6799 When enabled, this option states that a range reduction step is not
6800 needed when performing complex division. Also, there is no checking
6801 whether the result of a complex multiplication or division is @code{NaN
6802 + I*NaN}, with an attempt to rescue the situation in that case. The
6803 default is @option{-fno-cx-limited-range}, but is enabled by
6804 @option{-ffast-math}.
6806 This option controls the default setting of the ISO C99
6807 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6810 @item -fcx-fortran-rules
6811 @opindex fcx-fortran-rules
6812 Complex multiplication and division follow Fortran rules. Range
6813 reduction is done as part of complex division, but there is no checking
6814 whether the result of a complex multiplication or division is @code{NaN
6815 + I*NaN}, with an attempt to rescue the situation in that case.
6817 The default is @option{-fno-cx-fortran-rules}.
6821 The following options control optimizations that may improve
6822 performance, but are not enabled by any @option{-O} options. This
6823 section includes experimental options that may produce broken code.
6826 @item -fbranch-probabilities
6827 @opindex fbranch-probabilities
6828 After running a program compiled with @option{-fprofile-arcs}
6829 (@pxref{Debugging Options,, Options for Debugging Your Program or
6830 @command{gcc}}), you can compile it a second time using
6831 @option{-fbranch-probabilities}, to improve optimizations based on
6832 the number of times each branch was taken. When the program
6833 compiled with @option{-fprofile-arcs} exits it saves arc execution
6834 counts to a file called @file{@var{sourcename}.gcda} for each source
6835 file. The information in this data file is very dependent on the
6836 structure of the generated code, so you must use the same source code
6837 and the same optimization options for both compilations.
6839 With @option{-fbranch-probabilities}, GCC puts a
6840 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6841 These can be used to improve optimization. Currently, they are only
6842 used in one place: in @file{reorg.c}, instead of guessing which path a
6843 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6844 exactly determine which path is taken more often.
6846 @item -fprofile-values
6847 @opindex fprofile-values
6848 If combined with @option{-fprofile-arcs}, it adds code so that some
6849 data about values of expressions in the program is gathered.
6851 With @option{-fbranch-probabilities}, it reads back the data gathered
6852 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6853 notes to instructions for their later usage in optimizations.
6855 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6859 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6860 a code to gather information about values of expressions.
6862 With @option{-fbranch-probabilities}, it reads back the data gathered
6863 and actually performs the optimizations based on them.
6864 Currently the optimizations include specialization of division operation
6865 using the knowledge about the value of the denominator.
6867 @item -frename-registers
6868 @opindex frename-registers
6869 Attempt to avoid false dependencies in scheduled code by making use
6870 of registers left over after register allocation. This optimization
6871 will most benefit processors with lots of registers. Depending on the
6872 debug information format adopted by the target, however, it can
6873 make debugging impossible, since variables will no longer stay in
6874 a ``home register''.
6876 Enabled by default with @option{-funroll-loops}.
6880 Perform tail duplication to enlarge superblock size. This transformation
6881 simplifies the control flow of the function allowing other optimizations to do
6884 Enabled with @option{-fprofile-use}.
6886 @item -funroll-loops
6887 @opindex funroll-loops
6888 Unroll loops whose number of iterations can be determined at compile time or
6889 upon entry to the loop. @option{-funroll-loops} implies
6890 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6891 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6892 small constant number of iterations). This option makes code larger, and may
6893 or may not make it run faster.
6895 Enabled with @option{-fprofile-use}.
6897 @item -funroll-all-loops
6898 @opindex funroll-all-loops
6899 Unroll all loops, even if their number of iterations is uncertain when
6900 the loop is entered. This usually makes programs run more slowly.
6901 @option{-funroll-all-loops} implies the same options as
6902 @option{-funroll-loops}.
6905 @opindex fpeel-loops
6906 Peels the loops for that there is enough information that they do not
6907 roll much (from profile feedback). It also turns on complete loop peeling
6908 (i.e.@: complete removal of loops with small constant number of iterations).
6910 Enabled with @option{-fprofile-use}.
6912 @item -fmove-loop-invariants
6913 @opindex fmove-loop-invariants
6914 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6915 at level @option{-O1}
6917 @item -funswitch-loops
6918 @opindex funswitch-loops
6919 Move branches with loop invariant conditions out of the loop, with duplicates
6920 of the loop on both branches (modified according to result of the condition).
6922 @item -ffunction-sections
6923 @itemx -fdata-sections
6924 @opindex ffunction-sections
6925 @opindex fdata-sections
6926 Place each function or data item into its own section in the output
6927 file if the target supports arbitrary sections. The name of the
6928 function or the name of the data item determines the section's name
6931 Use these options on systems where the linker can perform optimizations
6932 to improve locality of reference in the instruction space. Most systems
6933 using the ELF object format and SPARC processors running Solaris 2 have
6934 linkers with such optimizations. AIX may have these optimizations in
6937 Only use these options when there are significant benefits from doing
6938 so. When you specify these options, the assembler and linker will
6939 create larger object and executable files and will also be slower.
6940 You will not be able to use @code{gprof} on all systems if you
6941 specify this option and you may have problems with debugging if
6942 you specify both this option and @option{-g}.
6944 @item -fbranch-target-load-optimize
6945 @opindex fbranch-target-load-optimize
6946 Perform branch target register load optimization before prologue / epilogue
6948 The use of target registers can typically be exposed only during reload,
6949 thus hoisting loads out of loops and doing inter-block scheduling needs
6950 a separate optimization pass.
6952 @item -fbranch-target-load-optimize2
6953 @opindex fbranch-target-load-optimize2
6954 Perform branch target register load optimization after prologue / epilogue
6957 @item -fbtr-bb-exclusive
6958 @opindex fbtr-bb-exclusive
6959 When performing branch target register load optimization, don't reuse
6960 branch target registers in within any basic block.
6962 @item -fstack-protector
6963 @opindex fstack-protector
6964 Emit extra code to check for buffer overflows, such as stack smashing
6965 attacks. This is done by adding a guard variable to functions with
6966 vulnerable objects. This includes functions that call alloca, and
6967 functions with buffers larger than 8 bytes. The guards are initialized
6968 when a function is entered and then checked when the function exits.
6969 If a guard check fails, an error message is printed and the program exits.
6971 @item -fstack-protector-all
6972 @opindex fstack-protector-all
6973 Like @option{-fstack-protector} except that all functions are protected.
6975 @item -fsection-anchors
6976 @opindex fsection-anchors
6977 Try to reduce the number of symbolic address calculations by using
6978 shared ``anchor'' symbols to address nearby objects. This transformation
6979 can help to reduce the number of GOT entries and GOT accesses on some
6982 For example, the implementation of the following function @code{foo}:
6986 int foo (void) @{ return a + b + c; @}
6989 would usually calculate the addresses of all three variables, but if you
6990 compile it with @option{-fsection-anchors}, it will access the variables
6991 from a common anchor point instead. The effect is similar to the
6992 following pseudocode (which isn't valid C):
6997 register int *xr = &x;
6998 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
7002 Not all targets support this option.
7004 @item --param @var{name}=@var{value}
7006 In some places, GCC uses various constants to control the amount of
7007 optimization that is done. For example, GCC will not inline functions
7008 that contain more that a certain number of instructions. You can
7009 control some of these constants on the command-line using the
7010 @option{--param} option.
7012 The names of specific parameters, and the meaning of the values, are
7013 tied to the internals of the compiler, and are subject to change
7014 without notice in future releases.
7016 In each case, the @var{value} is an integer. The allowable choices for
7017 @var{name} are given in the following table:
7020 @item sra-max-structure-size
7021 The maximum structure size, in bytes, at which the scalar replacement
7022 of aggregates (SRA) optimization will perform block copies. The
7023 default value, 0, implies that GCC will select the most appropriate
7026 @item sra-field-structure-ratio
7027 The threshold ratio (as a percentage) between instantiated fields and
7028 the complete structure size. We say that if the ratio of the number
7029 of bytes in instantiated fields to the number of bytes in the complete
7030 structure exceeds this parameter, then block copies are not used. The
7033 @item struct-reorg-cold-struct-ratio
7034 The threshold ratio (as a percentage) between a structure frequency
7035 and the frequency of the hottest structure in the program. This parameter
7036 is used by struct-reorg optimization enabled by @option{-fipa-struct-reorg}.
7037 We say that if the ratio of a structure frequency, calculated by profiling,
7038 to the hottest structure frequency in the program is less than this
7039 parameter, then structure reorganization is not applied to this structure.
7042 @item predictable-branch-cost-outcome
7043 When branch is predicted to be taken with probability lower than this threshold
7044 (in percent), then it is considered well predictable. The default is 10.
7046 @item max-crossjump-edges
7047 The maximum number of incoming edges to consider for crossjumping.
7048 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
7049 the number of edges incoming to each block. Increasing values mean
7050 more aggressive optimization, making the compile time increase with
7051 probably small improvement in executable size.
7053 @item min-crossjump-insns
7054 The minimum number of instructions which must be matched at the end
7055 of two blocks before crossjumping will be performed on them. This
7056 value is ignored in the case where all instructions in the block being
7057 crossjumped from are matched. The default value is 5.
7059 @item max-grow-copy-bb-insns
7060 The maximum code size expansion factor when copying basic blocks
7061 instead of jumping. The expansion is relative to a jump instruction.
7062 The default value is 8.
7064 @item max-goto-duplication-insns
7065 The maximum number of instructions to duplicate to a block that jumps
7066 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
7067 passes, GCC factors computed gotos early in the compilation process,
7068 and unfactors them as late as possible. Only computed jumps at the
7069 end of a basic blocks with no more than max-goto-duplication-insns are
7070 unfactored. The default value is 8.
7072 @item max-delay-slot-insn-search
7073 The maximum number of instructions to consider when looking for an
7074 instruction to fill a delay slot. If more than this arbitrary number of
7075 instructions is searched, the time savings from filling the delay slot
7076 will be minimal so stop searching. Increasing values mean more
7077 aggressive optimization, making the compile time increase with probably
7078 small improvement in executable run time.
7080 @item max-delay-slot-live-search
7081 When trying to fill delay slots, the maximum number of instructions to
7082 consider when searching for a block with valid live register
7083 information. Increasing this arbitrarily chosen value means more
7084 aggressive optimization, increasing the compile time. This parameter
7085 should be removed when the delay slot code is rewritten to maintain the
7088 @item max-gcse-memory
7089 The approximate maximum amount of memory that will be allocated in
7090 order to perform the global common subexpression elimination
7091 optimization. If more memory than specified is required, the
7092 optimization will not be done.
7094 @item max-gcse-passes
7095 The maximum number of passes of GCSE to run. The default is 1.
7097 @item max-pending-list-length
7098 The maximum number of pending dependencies scheduling will allow
7099 before flushing the current state and starting over. Large functions
7100 with few branches or calls can create excessively large lists which
7101 needlessly consume memory and resources.
7103 @item max-inline-insns-single
7104 Several parameters control the tree inliner used in gcc.
7105 This number sets the maximum number of instructions (counted in GCC's
7106 internal representation) in a single function that the tree inliner
7107 will consider for inlining. This only affects functions declared
7108 inline and methods implemented in a class declaration (C++).
7109 The default value is 450.
7111 @item max-inline-insns-auto
7112 When you use @option{-finline-functions} (included in @option{-O3}),
7113 a lot of functions that would otherwise not be considered for inlining
7114 by the compiler will be investigated. To those functions, a different
7115 (more restrictive) limit compared to functions declared inline can
7117 The default value is 90.
7119 @item large-function-insns
7120 The limit specifying really large functions. For functions larger than this
7121 limit after inlining, inlining is constrained by
7122 @option{--param large-function-growth}. This parameter is useful primarily
7123 to avoid extreme compilation time caused by non-linear algorithms used by the
7125 The default value is 2700.
7127 @item large-function-growth
7128 Specifies maximal growth of large function caused by inlining in percents.
7129 The default value is 100 which limits large function growth to 2.0 times
7132 @item large-unit-insns
7133 The limit specifying large translation unit. Growth caused by inlining of
7134 units larger than this limit is limited by @option{--param inline-unit-growth}.
7135 For small units this might be too tight (consider unit consisting of function A
7136 that is inline and B that just calls A three time. If B is small relative to
7137 A, the growth of unit is 300\% and yet such inlining is very sane. For very
7138 large units consisting of small inlineable functions however the overall unit
7139 growth limit is needed to avoid exponential explosion of code size. Thus for
7140 smaller units, the size is increased to @option{--param large-unit-insns}
7141 before applying @option{--param inline-unit-growth}. The default is 10000
7143 @item inline-unit-growth
7144 Specifies maximal overall growth of the compilation unit caused by inlining.
7145 The default value is 30 which limits unit growth to 1.3 times the original
7148 @item ipcp-unit-growth
7149 Specifies maximal overall growth of the compilation unit caused by
7150 interprocedural constant propagation. The default value is 10 which limits
7151 unit growth to 1.1 times the original size.
7153 @item large-stack-frame
7154 The limit specifying large stack frames. While inlining the algorithm is trying
7155 to not grow past this limit too much. Default value is 256 bytes.
7157 @item large-stack-frame-growth
7158 Specifies maximal growth of large stack frames caused by inlining in percents.
7159 The default value is 1000 which limits large stack frame growth to 11 times
7162 @item max-inline-insns-recursive
7163 @itemx max-inline-insns-recursive-auto
7164 Specifies maximum number of instructions out-of-line copy of self recursive inline
7165 function can grow into by performing recursive inlining.
7167 For functions declared inline @option{--param max-inline-insns-recursive} is
7168 taken into account. For function not declared inline, recursive inlining
7169 happens only when @option{-finline-functions} (included in @option{-O3}) is
7170 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
7171 default value is 450.
7173 @item max-inline-recursive-depth
7174 @itemx max-inline-recursive-depth-auto
7175 Specifies maximum recursion depth used by the recursive inlining.
7177 For functions declared inline @option{--param max-inline-recursive-depth} is
7178 taken into account. For function not declared inline, recursive inlining
7179 happens only when @option{-finline-functions} (included in @option{-O3}) is
7180 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
7183 @item min-inline-recursive-probability
7184 Recursive inlining is profitable only for function having deep recursion
7185 in average and can hurt for function having little recursion depth by
7186 increasing the prologue size or complexity of function body to other
7189 When profile feedback is available (see @option{-fprofile-generate}) the actual
7190 recursion depth can be guessed from probability that function will recurse via
7191 given call expression. This parameter limits inlining only to call expression
7192 whose probability exceeds given threshold (in percents). The default value is
7195 @item inline-call-cost
7196 Specify cost of call instruction relative to simple arithmetics operations
7197 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
7198 functions and at the same time increases size of leaf function that is believed to
7199 reduce function size by being inlined. In effect it increases amount of
7200 inlining for code having large abstraction penalty (many functions that just
7201 pass the arguments to other functions) and decrease inlining for code with low
7202 abstraction penalty. The default value is 12.
7204 @item min-vect-loop-bound
7205 The minimum number of iterations under which a loop will not get vectorized
7206 when @option{-ftree-vectorize} is used. The number of iterations after
7207 vectorization needs to be greater than the value specified by this option
7208 to allow vectorization. The default value is 0.
7210 @item max-unrolled-insns
7211 The maximum number of instructions that a loop should have if that loop
7212 is unrolled, and if the loop is unrolled, it determines how many times
7213 the loop code is unrolled.
7215 @item max-average-unrolled-insns
7216 The maximum number of instructions biased by probabilities of their execution
7217 that a loop should have if that loop is unrolled, and if the loop is unrolled,
7218 it determines how many times the loop code is unrolled.
7220 @item max-unroll-times
7221 The maximum number of unrollings of a single loop.
7223 @item max-peeled-insns
7224 The maximum number of instructions that a loop should have if that loop
7225 is peeled, and if the loop is peeled, it determines how many times
7226 the loop code is peeled.
7228 @item max-peel-times
7229 The maximum number of peelings of a single loop.
7231 @item max-completely-peeled-insns
7232 The maximum number of insns of a completely peeled loop.
7234 @item max-completely-peel-times
7235 The maximum number of iterations of a loop to be suitable for complete peeling.
7237 @item max-unswitch-insns
7238 The maximum number of insns of an unswitched loop.
7240 @item max-unswitch-level
7241 The maximum number of branches unswitched in a single loop.
7244 The minimum cost of an expensive expression in the loop invariant motion.
7246 @item iv-consider-all-candidates-bound
7247 Bound on number of candidates for induction variables below that
7248 all candidates are considered for each use in induction variable
7249 optimizations. Only the most relevant candidates are considered
7250 if there are more candidates, to avoid quadratic time complexity.
7252 @item iv-max-considered-uses
7253 The induction variable optimizations give up on loops that contain more
7254 induction variable uses.
7256 @item iv-always-prune-cand-set-bound
7257 If number of candidates in the set is smaller than this value,
7258 we always try to remove unnecessary ivs from the set during its
7259 optimization when a new iv is added to the set.
7261 @item scev-max-expr-size
7262 Bound on size of expressions used in the scalar evolutions analyzer.
7263 Large expressions slow the analyzer.
7265 @item omega-max-vars
7266 The maximum number of variables in an Omega constraint system.
7267 The default value is 128.
7269 @item omega-max-geqs
7270 The maximum number of inequalities in an Omega constraint system.
7271 The default value is 256.
7274 The maximum number of equalities in an Omega constraint system.
7275 The default value is 128.
7277 @item omega-max-wild-cards
7278 The maximum number of wildcard variables that the Omega solver will
7279 be able to insert. The default value is 18.
7281 @item omega-hash-table-size
7282 The size of the hash table in the Omega solver. The default value is
7285 @item omega-max-keys
7286 The maximal number of keys used by the Omega solver. The default
7289 @item omega-eliminate-redundant-constraints
7290 When set to 1, use expensive methods to eliminate all redundant
7291 constraints. The default value is 0.
7293 @item vect-max-version-for-alignment-checks
7294 The maximum number of runtime checks that can be performed when
7295 doing loop versioning for alignment in the vectorizer. See option
7296 ftree-vect-loop-version for more information.
7298 @item vect-max-version-for-alias-checks
7299 The maximum number of runtime checks that can be performed when
7300 doing loop versioning for alias in the vectorizer. See option
7301 ftree-vect-loop-version for more information.
7303 @item max-iterations-to-track
7305 The maximum number of iterations of a loop the brute force algorithm
7306 for analysis of # of iterations of the loop tries to evaluate.
7308 @item hot-bb-count-fraction
7309 Select fraction of the maximal count of repetitions of basic block in program
7310 given basic block needs to have to be considered hot.
7312 @item hot-bb-frequency-fraction
7313 Select fraction of the maximal frequency of executions of basic block in
7314 function given basic block needs to have to be considered hot
7316 @item max-predicted-iterations
7317 The maximum number of loop iterations we predict statically. This is useful
7318 in cases where function contain single loop with known bound and other loop
7319 with unknown. We predict the known number of iterations correctly, while
7320 the unknown number of iterations average to roughly 10. This means that the
7321 loop without bounds would appear artificially cold relative to the other one.
7323 @item align-threshold
7325 Select fraction of the maximal frequency of executions of basic block in
7326 function given basic block will get aligned.
7328 @item align-loop-iterations
7330 A loop expected to iterate at lest the selected number of iterations will get
7333 @item tracer-dynamic-coverage
7334 @itemx tracer-dynamic-coverage-feedback
7336 This value is used to limit superblock formation once the given percentage of
7337 executed instructions is covered. This limits unnecessary code size
7340 The @option{tracer-dynamic-coverage-feedback} is used only when profile
7341 feedback is available. The real profiles (as opposed to statically estimated
7342 ones) are much less balanced allowing the threshold to be larger value.
7344 @item tracer-max-code-growth
7345 Stop tail duplication once code growth has reached given percentage. This is
7346 rather hokey argument, as most of the duplicates will be eliminated later in
7347 cross jumping, so it may be set to much higher values than is the desired code
7350 @item tracer-min-branch-ratio
7352 Stop reverse growth when the reverse probability of best edge is less than this
7353 threshold (in percent).
7355 @item tracer-min-branch-ratio
7356 @itemx tracer-min-branch-ratio-feedback
7358 Stop forward growth if the best edge do have probability lower than this
7361 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
7362 compilation for profile feedback and one for compilation without. The value
7363 for compilation with profile feedback needs to be more conservative (higher) in
7364 order to make tracer effective.
7366 @item max-cse-path-length
7368 Maximum number of basic blocks on path that cse considers. The default is 10.
7371 The maximum instructions CSE process before flushing. The default is 1000.
7373 @item max-aliased-vops
7375 Maximum number of virtual operands per function allowed to represent
7376 aliases before triggering the alias partitioning heuristic. Alias
7377 partitioning reduces compile times and memory consumption needed for
7378 aliasing at the expense of precision loss in alias information. The
7379 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
7382 Notice that if a function contains more memory statements than the
7383 value of this parameter, it is not really possible to achieve this
7384 reduction. In this case, the compiler will use the number of memory
7385 statements as the value for @option{max-aliased-vops}.
7387 @item avg-aliased-vops
7389 Average number of virtual operands per statement allowed to represent
7390 aliases before triggering the alias partitioning heuristic. This
7391 works in conjunction with @option{max-aliased-vops}. If a function
7392 contains more than @option{max-aliased-vops} virtual operators, then
7393 memory symbols will be grouped into memory partitions until either the
7394 total number of virtual operators is below @option{max-aliased-vops}
7395 or the average number of virtual operators per memory statement is
7396 below @option{avg-aliased-vops}. The default value for this parameter
7397 is 1 for -O1 and -O2, and 3 for -O3.
7399 @item ggc-min-expand
7401 GCC uses a garbage collector to manage its own memory allocation. This
7402 parameter specifies the minimum percentage by which the garbage
7403 collector's heap should be allowed to expand between collections.
7404 Tuning this may improve compilation speed; it has no effect on code
7407 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
7408 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
7409 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
7410 GCC is not able to calculate RAM on a particular platform, the lower
7411 bound of 30% is used. Setting this parameter and
7412 @option{ggc-min-heapsize} to zero causes a full collection to occur at
7413 every opportunity. This is extremely slow, but can be useful for
7416 @item ggc-min-heapsize
7418 Minimum size of the garbage collector's heap before it begins bothering
7419 to collect garbage. The first collection occurs after the heap expands
7420 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
7421 tuning this may improve compilation speed, and has no effect on code
7424 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
7425 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
7426 with a lower bound of 4096 (four megabytes) and an upper bound of
7427 131072 (128 megabytes). If GCC is not able to calculate RAM on a
7428 particular platform, the lower bound is used. Setting this parameter
7429 very large effectively disables garbage collection. Setting this
7430 parameter and @option{ggc-min-expand} to zero causes a full collection
7431 to occur at every opportunity.
7433 @item max-reload-search-insns
7434 The maximum number of instruction reload should look backward for equivalent
7435 register. Increasing values mean more aggressive optimization, making the
7436 compile time increase with probably slightly better performance. The default
7439 @item max-cselib-memory-locations
7440 The maximum number of memory locations cselib should take into account.
7441 Increasing values mean more aggressive optimization, making the compile time
7442 increase with probably slightly better performance. The default value is 500.
7444 @item reorder-blocks-duplicate
7445 @itemx reorder-blocks-duplicate-feedback
7447 Used by basic block reordering pass to decide whether to use unconditional
7448 branch or duplicate the code on its destination. Code is duplicated when its
7449 estimated size is smaller than this value multiplied by the estimated size of
7450 unconditional jump in the hot spots of the program.
7452 The @option{reorder-block-duplicate-feedback} is used only when profile
7453 feedback is available and may be set to higher values than
7454 @option{reorder-block-duplicate} since information about the hot spots is more
7457 @item max-sched-ready-insns
7458 The maximum number of instructions ready to be issued the scheduler should
7459 consider at any given time during the first scheduling pass. Increasing
7460 values mean more thorough searches, making the compilation time increase
7461 with probably little benefit. The default value is 100.
7463 @item max-sched-region-blocks
7464 The maximum number of blocks in a region to be considered for
7465 interblock scheduling. The default value is 10.
7467 @item max-pipeline-region-blocks
7468 The maximum number of blocks in a region to be considered for
7469 pipelining in the selective scheduler. The default value is 15.
7471 @item max-sched-region-insns
7472 The maximum number of insns in a region to be considered for
7473 interblock scheduling. The default value is 100.
7475 @item max-pipeline-region-insns
7476 The maximum number of insns in a region to be considered for
7477 pipelining in the selective scheduler. The default value is 200.
7480 The minimum probability (in percents) of reaching a source block
7481 for interblock speculative scheduling. The default value is 40.
7483 @item max-sched-extend-regions-iters
7484 The maximum number of iterations through CFG to extend regions.
7485 0 - disable region extension,
7486 N - do at most N iterations.
7487 The default value is 0.
7489 @item max-sched-insn-conflict-delay
7490 The maximum conflict delay for an insn to be considered for speculative motion.
7491 The default value is 3.
7493 @item sched-spec-prob-cutoff
7494 The minimal probability of speculation success (in percents), so that
7495 speculative insn will be scheduled.
7496 The default value is 40.
7498 @item sched-mem-true-dep-cost
7499 Minimal distance (in CPU cycles) between store and load targeting same
7500 memory locations. The default value is 1.
7502 @item selsched-max-lookahead
7503 The maximum size of the lookahead window of selective scheduling. It is a
7504 depth of search for available instructions.
7505 The default value is 50.
7507 @item selsched-max-sched-times
7508 The maximum number of times that an instruction will be scheduled during
7509 selective scheduling. This is the limit on the number of iterations
7510 through which the instruction may be pipelined. The default value is 2.
7512 @item selsched-max-insns-to-rename
7513 The maximum number of best instructions in the ready list that are considered
7514 for renaming in the selective scheduler. The default value is 2.
7516 @item max-last-value-rtl
7517 The maximum size measured as number of RTLs that can be recorded in an expression
7518 in combiner for a pseudo register as last known value of that register. The default
7521 @item integer-share-limit
7522 Small integer constants can use a shared data structure, reducing the
7523 compiler's memory usage and increasing its speed. This sets the maximum
7524 value of a shared integer constant. The default value is 256.
7526 @item min-virtual-mappings
7527 Specifies the minimum number of virtual mappings in the incremental
7528 SSA updater that should be registered to trigger the virtual mappings
7529 heuristic defined by virtual-mappings-ratio. The default value is
7532 @item virtual-mappings-ratio
7533 If the number of virtual mappings is virtual-mappings-ratio bigger
7534 than the number of virtual symbols to be updated, then the incremental
7535 SSA updater switches to a full update for those symbols. The default
7538 @item ssp-buffer-size
7539 The minimum size of buffers (i.e.@: arrays) that will receive stack smashing
7540 protection when @option{-fstack-protection} is used.
7542 @item max-jump-thread-duplication-stmts
7543 Maximum number of statements allowed in a block that needs to be
7544 duplicated when threading jumps.
7546 @item max-fields-for-field-sensitive
7547 Maximum number of fields in a structure we will treat in
7548 a field sensitive manner during pointer analysis. The default is zero
7549 for -O0, and -O1 and 100 for -Os, -O2, and -O3.
7551 @item prefetch-latency
7552 Estimate on average number of instructions that are executed before
7553 prefetch finishes. The distance we prefetch ahead is proportional
7554 to this constant. Increasing this number may also lead to less
7555 streams being prefetched (see @option{simultaneous-prefetches}).
7557 @item simultaneous-prefetches
7558 Maximum number of prefetches that can run at the same time.
7560 @item l1-cache-line-size
7561 The size of cache line in L1 cache, in bytes.
7564 The size of L1 cache, in kilobytes.
7567 The size of L2 cache, in kilobytes.
7569 @item use-canonical-types
7570 Whether the compiler should use the ``canonical'' type system. By
7571 default, this should always be 1, which uses a more efficient internal
7572 mechanism for comparing types in C++ and Objective-C++. However, if
7573 bugs in the canonical type system are causing compilation failures,
7574 set this value to 0 to disable canonical types.
7576 @item switch-conversion-max-branch-ratio
7577 Switch initialization conversion will refuse to create arrays that are
7578 bigger than @option{switch-conversion-max-branch-ratio} times the number of
7579 branches in the switch.
7581 @item max-partial-antic-length
7582 Maximum length of the partial antic set computed during the tree
7583 partial redundancy elimination optimization (@option{-ftree-pre}) when
7584 optimizing at @option{-O3} and above. For some sorts of source code
7585 the enhanced partial redundancy elimination optimization can run away,
7586 consuming all of the memory available on the host machine. This
7587 parameter sets a limit on the length of the sets that are computed,
7588 which prevents the runaway behaviour. Setting a value of 0 for
7589 this paramter will allow an unlimited set length.
7591 @item sccvn-max-scc-size
7592 Maximum size of a strongly connected component (SCC) during SCCVN
7593 processing. If this limit is hit, SCCVN processing for the whole
7594 function will not be done and optimizations depending on it will
7595 be disabled. The default maximum SCC size is 10000.
7597 @item ira-max-loops-num
7598 IRA uses a regional register allocation by default. If a function
7599 contains loops more than number given by the parameter, non-regional
7600 register allocator will be used even when option
7601 @option{-fira-algorithm} is given. The default value of the parameter
7607 @node Preprocessor Options
7608 @section Options Controlling the Preprocessor
7609 @cindex preprocessor options
7610 @cindex options, preprocessor
7612 These options control the C preprocessor, which is run on each C source
7613 file before actual compilation.
7615 If you use the @option{-E} option, nothing is done except preprocessing.
7616 Some of these options make sense only together with @option{-E} because
7617 they cause the preprocessor output to be unsuitable for actual
7622 You can use @option{-Wp,@var{option}} to bypass the compiler driver
7623 and pass @var{option} directly through to the preprocessor. If
7624 @var{option} contains commas, it is split into multiple options at the
7625 commas. However, many options are modified, translated or interpreted
7626 by the compiler driver before being passed to the preprocessor, and
7627 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
7628 interface is undocumented and subject to change, so whenever possible
7629 you should avoid using @option{-Wp} and let the driver handle the
7632 @item -Xpreprocessor @var{option}
7633 @opindex preprocessor
7634 Pass @var{option} as an option to the preprocessor. You can use this to
7635 supply system-specific preprocessor options which GCC does not know how to
7638 If you want to pass an option that takes an argument, you must use
7639 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7642 @include cppopts.texi
7644 @node Assembler Options
7645 @section Passing Options to the Assembler
7647 @c prevent bad page break with this line
7648 You can pass options to the assembler.
7651 @item -Wa,@var{option}
7653 Pass @var{option} as an option to the assembler. If @var{option}
7654 contains commas, it is split into multiple options at the commas.
7656 @item -Xassembler @var{option}
7658 Pass @var{option} as an option to the assembler. You can use this to
7659 supply system-specific assembler options which GCC does not know how to
7662 If you want to pass an option that takes an argument, you must use
7663 @option{-Xassembler} twice, once for the option and once for the argument.
7668 @section Options for Linking
7669 @cindex link options
7670 @cindex options, linking
7672 These options come into play when the compiler links object files into
7673 an executable output file. They are meaningless if the compiler is
7674 not doing a link step.
7678 @item @var{object-file-name}
7679 A file name that does not end in a special recognized suffix is
7680 considered to name an object file or library. (Object files are
7681 distinguished from libraries by the linker according to the file
7682 contents.) If linking is done, these object files are used as input
7691 If any of these options is used, then the linker is not run, and
7692 object file names should not be used as arguments. @xref{Overall
7696 @item -l@var{library}
7697 @itemx -l @var{library}
7699 Search the library named @var{library} when linking. (The second
7700 alternative with the library as a separate argument is only for
7701 POSIX compliance and is not recommended.)
7703 It makes a difference where in the command you write this option; the
7704 linker searches and processes libraries and object files in the order they
7705 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7706 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7707 to functions in @samp{z}, those functions may not be loaded.
7709 The linker searches a standard list of directories for the library,
7710 which is actually a file named @file{lib@var{library}.a}. The linker
7711 then uses this file as if it had been specified precisely by name.
7713 The directories searched include several standard system directories
7714 plus any that you specify with @option{-L}.
7716 Normally the files found this way are library files---archive files
7717 whose members are object files. The linker handles an archive file by
7718 scanning through it for members which define symbols that have so far
7719 been referenced but not defined. But if the file that is found is an
7720 ordinary object file, it is linked in the usual fashion. The only
7721 difference between using an @option{-l} option and specifying a file name
7722 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7723 and searches several directories.
7727 You need this special case of the @option{-l} option in order to
7728 link an Objective-C or Objective-C++ program.
7731 @opindex nostartfiles
7732 Do not use the standard system startup files when linking.
7733 The standard system libraries are used normally, unless @option{-nostdlib}
7734 or @option{-nodefaultlibs} is used.
7736 @item -nodefaultlibs
7737 @opindex nodefaultlibs
7738 Do not use the standard system libraries when linking.
7739 Only the libraries you specify will be passed to the linker.
7740 The standard startup files are used normally, unless @option{-nostartfiles}
7741 is used. The compiler may generate calls to @code{memcmp},
7742 @code{memset}, @code{memcpy} and @code{memmove}.
7743 These entries are usually resolved by entries in
7744 libc. These entry points should be supplied through some other
7745 mechanism when this option is specified.
7749 Do not use the standard system startup files or libraries when linking.
7750 No startup files and only the libraries you specify will be passed to
7751 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7752 @code{memcpy} and @code{memmove}.
7753 These entries are usually resolved by entries in
7754 libc. These entry points should be supplied through some other
7755 mechanism when this option is specified.
7757 @cindex @option{-lgcc}, use with @option{-nostdlib}
7758 @cindex @option{-nostdlib} and unresolved references
7759 @cindex unresolved references and @option{-nostdlib}
7760 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7761 @cindex @option{-nodefaultlibs} and unresolved references
7762 @cindex unresolved references and @option{-nodefaultlibs}
7763 One of the standard libraries bypassed by @option{-nostdlib} and
7764 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7765 that GCC uses to overcome shortcomings of particular machines, or special
7766 needs for some languages.
7767 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7768 Collection (GCC) Internals},
7769 for more discussion of @file{libgcc.a}.)
7770 In most cases, you need @file{libgcc.a} even when you want to avoid
7771 other standard libraries. In other words, when you specify @option{-nostdlib}
7772 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7773 This ensures that you have no unresolved references to internal GCC
7774 library subroutines. (For example, @samp{__main}, used to ensure C++
7775 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7776 GNU Compiler Collection (GCC) Internals}.)
7780 Produce a position independent executable on targets which support it.
7781 For predictable results, you must also specify the same set of options
7782 that were used to generate code (@option{-fpie}, @option{-fPIE},
7783 or model suboptions) when you specify this option.
7787 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7788 that support it. This instructs the linker to add all symbols, not
7789 only used ones, to the dynamic symbol table. This option is needed
7790 for some uses of @code{dlopen} or to allow obtaining backtraces
7791 from within a program.
7795 Remove all symbol table and relocation information from the executable.
7799 On systems that support dynamic linking, this prevents linking with the shared
7800 libraries. On other systems, this option has no effect.
7804 Produce a shared object which can then be linked with other objects to
7805 form an executable. Not all systems support this option. For predictable
7806 results, you must also specify the same set of options that were used to
7807 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7808 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7809 needs to build supplementary stub code for constructors to work. On
7810 multi-libbed systems, @samp{gcc -shared} must select the correct support
7811 libraries to link against. Failing to supply the correct flags may lead
7812 to subtle defects. Supplying them in cases where they are not necessary
7815 @item -shared-libgcc
7816 @itemx -static-libgcc
7817 @opindex shared-libgcc
7818 @opindex static-libgcc
7819 On systems that provide @file{libgcc} as a shared library, these options
7820 force the use of either the shared or static version respectively.
7821 If no shared version of @file{libgcc} was built when the compiler was
7822 configured, these options have no effect.
7824 There are several situations in which an application should use the
7825 shared @file{libgcc} instead of the static version. The most common
7826 of these is when the application wishes to throw and catch exceptions
7827 across different shared libraries. In that case, each of the libraries
7828 as well as the application itself should use the shared @file{libgcc}.
7830 Therefore, the G++ and GCJ drivers automatically add
7831 @option{-shared-libgcc} whenever you build a shared library or a main
7832 executable, because C++ and Java programs typically use exceptions, so
7833 this is the right thing to do.
7835 If, instead, you use the GCC driver to create shared libraries, you may
7836 find that they will not always be linked with the shared @file{libgcc}.
7837 If GCC finds, at its configuration time, that you have a non-GNU linker
7838 or a GNU linker that does not support option @option{--eh-frame-hdr},
7839 it will link the shared version of @file{libgcc} into shared libraries
7840 by default. Otherwise, it will take advantage of the linker and optimize
7841 away the linking with the shared version of @file{libgcc}, linking with
7842 the static version of libgcc by default. This allows exceptions to
7843 propagate through such shared libraries, without incurring relocation
7844 costs at library load time.
7846 However, if a library or main executable is supposed to throw or catch
7847 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7848 for the languages used in the program, or using the option
7849 @option{-shared-libgcc}, such that it is linked with the shared
7854 Bind references to global symbols when building a shared object. Warn
7855 about any unresolved references (unless overridden by the link editor
7856 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7859 @item -T @var{script}
7861 @cindex linker script
7862 Use @var{script} as the linker script. This option is supported by most
7863 systems using the GNU linker. On some targets, such as bare-board
7864 targets without an operating system, the @option{-T} option may be required
7865 when linking to avoid references to undefined symbols.
7867 @item -Xlinker @var{option}
7869 Pass @var{option} as an option to the linker. You can use this to
7870 supply system-specific linker options which GCC does not know how to
7873 If you want to pass an option that takes an argument, you must use
7874 @option{-Xlinker} twice, once for the option and once for the argument.
7875 For example, to pass @option{-assert definitions}, you must write
7876 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7877 @option{-Xlinker "-assert definitions"}, because this passes the entire
7878 string as a single argument, which is not what the linker expects.
7880 @item -Wl,@var{option}
7882 Pass @var{option} as an option to the linker. If @var{option} contains
7883 commas, it is split into multiple options at the commas.
7885 @item -u @var{symbol}
7887 Pretend the symbol @var{symbol} is undefined, to force linking of
7888 library modules to define it. You can use @option{-u} multiple times with
7889 different symbols to force loading of additional library modules.
7892 @node Directory Options
7893 @section Options for Directory Search
7894 @cindex directory options
7895 @cindex options, directory search
7898 These options specify directories to search for header files, for
7899 libraries and for parts of the compiler:
7904 Add the directory @var{dir} to the head of the list of directories to be
7905 searched for header files. This can be used to override a system header
7906 file, substituting your own version, since these directories are
7907 searched before the system header file directories. However, you should
7908 not use this option to add directories that contain vendor-supplied
7909 system header files (use @option{-isystem} for that). If you use more than
7910 one @option{-I} option, the directories are scanned in left-to-right
7911 order; the standard system directories come after.
7913 If a standard system include directory, or a directory specified with
7914 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7915 option will be ignored. The directory will still be searched but as a
7916 system directory at its normal position in the system include chain.
7917 This is to ensure that GCC's procedure to fix buggy system headers and
7918 the ordering for the include_next directive are not inadvertently changed.
7919 If you really need to change the search order for system directories,
7920 use the @option{-nostdinc} and/or @option{-isystem} options.
7922 @item -iquote@var{dir}
7924 Add the directory @var{dir} to the head of the list of directories to
7925 be searched for header files only for the case of @samp{#include
7926 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7927 otherwise just like @option{-I}.
7931 Add directory @var{dir} to the list of directories to be searched
7934 @item -B@var{prefix}
7936 This option specifies where to find the executables, libraries,
7937 include files, and data files of the compiler itself.
7939 The compiler driver program runs one or more of the subprograms
7940 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7941 @var{prefix} as a prefix for each program it tries to run, both with and
7942 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7944 For each subprogram to be run, the compiler driver first tries the
7945 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7946 was not specified, the driver tries two standard prefixes, which are
7947 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7948 those results in a file name that is found, the unmodified program
7949 name is searched for using the directories specified in your
7950 @env{PATH} environment variable.
7952 The compiler will check to see if the path provided by the @option{-B}
7953 refers to a directory, and if necessary it will add a directory
7954 separator character at the end of the path.
7956 @option{-B} prefixes that effectively specify directory names also apply
7957 to libraries in the linker, because the compiler translates these
7958 options into @option{-L} options for the linker. They also apply to
7959 includes files in the preprocessor, because the compiler translates these
7960 options into @option{-isystem} options for the preprocessor. In this case,
7961 the compiler appends @samp{include} to the prefix.
7963 The run-time support file @file{libgcc.a} can also be searched for using
7964 the @option{-B} prefix, if needed. If it is not found there, the two
7965 standard prefixes above are tried, and that is all. The file is left
7966 out of the link if it is not found by those means.
7968 Another way to specify a prefix much like the @option{-B} prefix is to use
7969 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
7972 As a special kludge, if the path provided by @option{-B} is
7973 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
7974 9, then it will be replaced by @file{[dir/]include}. This is to help
7975 with boot-strapping the compiler.
7977 @item -specs=@var{file}
7979 Process @var{file} after the compiler reads in the standard @file{specs}
7980 file, in order to override the defaults that the @file{gcc} driver
7981 program uses when determining what switches to pass to @file{cc1},
7982 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
7983 @option{-specs=@var{file}} can be specified on the command line, and they
7984 are processed in order, from left to right.
7986 @item --sysroot=@var{dir}
7988 Use @var{dir} as the logical root directory for headers and libraries.
7989 For example, if the compiler would normally search for headers in
7990 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
7991 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
7993 If you use both this option and the @option{-isysroot} option, then
7994 the @option{--sysroot} option will apply to libraries, but the
7995 @option{-isysroot} option will apply to header files.
7997 The GNU linker (beginning with version 2.16) has the necessary support
7998 for this option. If your linker does not support this option, the
7999 header file aspect of @option{--sysroot} will still work, but the
8000 library aspect will not.
8004 This option has been deprecated. Please use @option{-iquote} instead for
8005 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
8006 Any directories you specify with @option{-I} options before the @option{-I-}
8007 option are searched only for the case of @samp{#include "@var{file}"};
8008 they are not searched for @samp{#include <@var{file}>}.
8010 If additional directories are specified with @option{-I} options after
8011 the @option{-I-}, these directories are searched for all @samp{#include}
8012 directives. (Ordinarily @emph{all} @option{-I} directories are used
8015 In addition, the @option{-I-} option inhibits the use of the current
8016 directory (where the current input file came from) as the first search
8017 directory for @samp{#include "@var{file}"}. There is no way to
8018 override this effect of @option{-I-}. With @option{-I.} you can specify
8019 searching the directory which was current when the compiler was
8020 invoked. That is not exactly the same as what the preprocessor does
8021 by default, but it is often satisfactory.
8023 @option{-I-} does not inhibit the use of the standard system directories
8024 for header files. Thus, @option{-I-} and @option{-nostdinc} are
8031 @section Specifying subprocesses and the switches to pass to them
8034 @command{gcc} is a driver program. It performs its job by invoking a
8035 sequence of other programs to do the work of compiling, assembling and
8036 linking. GCC interprets its command-line parameters and uses these to
8037 deduce which programs it should invoke, and which command-line options
8038 it ought to place on their command lines. This behavior is controlled
8039 by @dfn{spec strings}. In most cases there is one spec string for each
8040 program that GCC can invoke, but a few programs have multiple spec
8041 strings to control their behavior. The spec strings built into GCC can
8042 be overridden by using the @option{-specs=} command-line switch to specify
8045 @dfn{Spec files} are plaintext files that are used to construct spec
8046 strings. They consist of a sequence of directives separated by blank
8047 lines. The type of directive is determined by the first non-whitespace
8048 character on the line and it can be one of the following:
8051 @item %@var{command}
8052 Issues a @var{command} to the spec file processor. The commands that can
8056 @item %include <@var{file}>
8058 Search for @var{file} and insert its text at the current point in the
8061 @item %include_noerr <@var{file}>
8062 @cindex %include_noerr
8063 Just like @samp{%include}, but do not generate an error message if the include
8064 file cannot be found.
8066 @item %rename @var{old_name} @var{new_name}
8068 Rename the spec string @var{old_name} to @var{new_name}.
8072 @item *[@var{spec_name}]:
8073 This tells the compiler to create, override or delete the named spec
8074 string. All lines after this directive up to the next directive or
8075 blank line are considered to be the text for the spec string. If this
8076 results in an empty string then the spec will be deleted. (Or, if the
8077 spec did not exist, then nothing will happened.) Otherwise, if the spec
8078 does not currently exist a new spec will be created. If the spec does
8079 exist then its contents will be overridden by the text of this
8080 directive, unless the first character of that text is the @samp{+}
8081 character, in which case the text will be appended to the spec.
8083 @item [@var{suffix}]:
8084 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
8085 and up to the next directive or blank line are considered to make up the
8086 spec string for the indicated suffix. When the compiler encounters an
8087 input file with the named suffix, it will processes the spec string in
8088 order to work out how to compile that file. For example:
8095 This says that any input file whose name ends in @samp{.ZZ} should be
8096 passed to the program @samp{z-compile}, which should be invoked with the
8097 command-line switch @option{-input} and with the result of performing the
8098 @samp{%i} substitution. (See below.)
8100 As an alternative to providing a spec string, the text that follows a
8101 suffix directive can be one of the following:
8104 @item @@@var{language}
8105 This says that the suffix is an alias for a known @var{language}. This is
8106 similar to using the @option{-x} command-line switch to GCC to specify a
8107 language explicitly. For example:
8114 Says that .ZZ files are, in fact, C++ source files.
8117 This causes an error messages saying:
8120 @var{name} compiler not installed on this system.
8124 GCC already has an extensive list of suffixes built into it.
8125 This directive will add an entry to the end of the list of suffixes, but
8126 since the list is searched from the end backwards, it is effectively
8127 possible to override earlier entries using this technique.
8131 GCC has the following spec strings built into it. Spec files can
8132 override these strings or create their own. Note that individual
8133 targets can also add their own spec strings to this list.
8136 asm Options to pass to the assembler
8137 asm_final Options to pass to the assembler post-processor
8138 cpp Options to pass to the C preprocessor
8139 cc1 Options to pass to the C compiler
8140 cc1plus Options to pass to the C++ compiler
8141 endfile Object files to include at the end of the link
8142 link Options to pass to the linker
8143 lib Libraries to include on the command line to the linker
8144 libgcc Decides which GCC support library to pass to the linker
8145 linker Sets the name of the linker
8146 predefines Defines to be passed to the C preprocessor
8147 signed_char Defines to pass to CPP to say whether @code{char} is signed
8149 startfile Object files to include at the start of the link
8152 Here is a small example of a spec file:
8158 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
8161 This example renames the spec called @samp{lib} to @samp{old_lib} and
8162 then overrides the previous definition of @samp{lib} with a new one.
8163 The new definition adds in some extra command-line options before
8164 including the text of the old definition.
8166 @dfn{Spec strings} are a list of command-line options to be passed to their
8167 corresponding program. In addition, the spec strings can contain
8168 @samp{%}-prefixed sequences to substitute variable text or to
8169 conditionally insert text into the command line. Using these constructs
8170 it is possible to generate quite complex command lines.
8172 Here is a table of all defined @samp{%}-sequences for spec
8173 strings. Note that spaces are not generated automatically around the
8174 results of expanding these sequences. Therefore you can concatenate them
8175 together or combine them with constant text in a single argument.
8179 Substitute one @samp{%} into the program name or argument.
8182 Substitute the name of the input file being processed.
8185 Substitute the basename of the input file being processed.
8186 This is the substring up to (and not including) the last period
8187 and not including the directory.
8190 This is the same as @samp{%b}, but include the file suffix (text after
8194 Marks the argument containing or following the @samp{%d} as a
8195 temporary file name, so that that file will be deleted if GCC exits
8196 successfully. Unlike @samp{%g}, this contributes no text to the
8199 @item %g@var{suffix}
8200 Substitute a file name that has suffix @var{suffix} and is chosen
8201 once per compilation, and mark the argument in the same way as
8202 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
8203 name is now chosen in a way that is hard to predict even when previously
8204 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
8205 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
8206 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
8207 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
8208 was simply substituted with a file name chosen once per compilation,
8209 without regard to any appended suffix (which was therefore treated
8210 just like ordinary text), making such attacks more likely to succeed.
8212 @item %u@var{suffix}
8213 Like @samp{%g}, but generates a new temporary file name even if
8214 @samp{%u@var{suffix}} was already seen.
8216 @item %U@var{suffix}
8217 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
8218 new one if there is no such last file name. In the absence of any
8219 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
8220 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
8221 would involve the generation of two distinct file names, one
8222 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
8223 simply substituted with a file name chosen for the previous @samp{%u},
8224 without regard to any appended suffix.
8226 @item %j@var{suffix}
8227 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
8228 writable, and if save-temps is off; otherwise, substitute the name
8229 of a temporary file, just like @samp{%u}. This temporary file is not
8230 meant for communication between processes, but rather as a junk
8233 @item %|@var{suffix}
8234 @itemx %m@var{suffix}
8235 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
8236 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
8237 all. These are the two most common ways to instruct a program that it
8238 should read from standard input or write to standard output. If you
8239 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
8240 construct: see for example @file{f/lang-specs.h}.
8242 @item %.@var{SUFFIX}
8243 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
8244 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
8245 terminated by the next space or %.
8248 Marks the argument containing or following the @samp{%w} as the
8249 designated output file of this compilation. This puts the argument
8250 into the sequence of arguments that @samp{%o} will substitute later.
8253 Substitutes the names of all the output files, with spaces
8254 automatically placed around them. You should write spaces
8255 around the @samp{%o} as well or the results are undefined.
8256 @samp{%o} is for use in the specs for running the linker.
8257 Input files whose names have no recognized suffix are not compiled
8258 at all, but they are included among the output files, so they will
8262 Substitutes the suffix for object files. Note that this is
8263 handled specially when it immediately follows @samp{%g, %u, or %U},
8264 because of the need for those to form complete file names. The
8265 handling is such that @samp{%O} is treated exactly as if it had already
8266 been substituted, except that @samp{%g, %u, and %U} do not currently
8267 support additional @var{suffix} characters following @samp{%O} as they would
8268 following, for example, @samp{.o}.
8271 Substitutes the standard macro predefinitions for the
8272 current target machine. Use this when running @code{cpp}.
8275 Like @samp{%p}, but puts @samp{__} before and after the name of each
8276 predefined macro, except for macros that start with @samp{__} or with
8277 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
8281 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
8282 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
8283 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
8284 and @option{-imultilib} as necessary.
8287 Current argument is the name of a library or startup file of some sort.
8288 Search for that file in a standard list of directories and substitute
8289 the full name found.
8292 Print @var{str} as an error message. @var{str} is terminated by a newline.
8293 Use this when inconsistent options are detected.
8296 Substitute the contents of spec string @var{name} at this point.
8299 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
8301 @item %x@{@var{option}@}
8302 Accumulate an option for @samp{%X}.
8305 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
8309 Output the accumulated assembler options specified by @option{-Wa}.
8312 Output the accumulated preprocessor options specified by @option{-Wp}.
8315 Process the @code{asm} spec. This is used to compute the
8316 switches to be passed to the assembler.
8319 Process the @code{asm_final} spec. This is a spec string for
8320 passing switches to an assembler post-processor, if such a program is
8324 Process the @code{link} spec. This is the spec for computing the
8325 command line passed to the linker. Typically it will make use of the
8326 @samp{%L %G %S %D and %E} sequences.
8329 Dump out a @option{-L} option for each directory that GCC believes might
8330 contain startup files. If the target supports multilibs then the
8331 current multilib directory will be prepended to each of these paths.
8334 Process the @code{lib} spec. This is a spec string for deciding which
8335 libraries should be included on the command line to the linker.
8338 Process the @code{libgcc} spec. This is a spec string for deciding
8339 which GCC support library should be included on the command line to the linker.
8342 Process the @code{startfile} spec. This is a spec for deciding which
8343 object files should be the first ones passed to the linker. Typically
8344 this might be a file named @file{crt0.o}.
8347 Process the @code{endfile} spec. This is a spec string that specifies
8348 the last object files that will be passed to the linker.
8351 Process the @code{cpp} spec. This is used to construct the arguments
8352 to be passed to the C preprocessor.
8355 Process the @code{cc1} spec. This is used to construct the options to be
8356 passed to the actual C compiler (@samp{cc1}).
8359 Process the @code{cc1plus} spec. This is used to construct the options to be
8360 passed to the actual C++ compiler (@samp{cc1plus}).
8363 Substitute the variable part of a matched option. See below.
8364 Note that each comma in the substituted string is replaced by
8368 Remove all occurrences of @code{-S} from the command line. Note---this
8369 command is position dependent. @samp{%} commands in the spec string
8370 before this one will see @code{-S}, @samp{%} commands in the spec string
8371 after this one will not.
8373 @item %:@var{function}(@var{args})
8374 Call the named function @var{function}, passing it @var{args}.
8375 @var{args} is first processed as a nested spec string, then split
8376 into an argument vector in the usual fashion. The function returns
8377 a string which is processed as if it had appeared literally as part
8378 of the current spec.
8380 The following built-in spec functions are provided:
8384 The @code{getenv} spec function takes two arguments: an environment
8385 variable name and a string. If the environment variable is not
8386 defined, a fatal error is issued. Otherwise, the return value is the
8387 value of the environment variable concatenated with the string. For
8388 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
8391 %:getenv(TOPDIR /include)
8394 expands to @file{/path/to/top/include}.
8396 @item @code{if-exists}
8397 The @code{if-exists} spec function takes one argument, an absolute
8398 pathname to a file. If the file exists, @code{if-exists} returns the
8399 pathname. Here is a small example of its usage:
8403 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
8406 @item @code{if-exists-else}
8407 The @code{if-exists-else} spec function is similar to the @code{if-exists}
8408 spec function, except that it takes two arguments. The first argument is
8409 an absolute pathname to a file. If the file exists, @code{if-exists-else}
8410 returns the pathname. If it does not exist, it returns the second argument.
8411 This way, @code{if-exists-else} can be used to select one file or another,
8412 based on the existence of the first. Here is a small example of its usage:
8416 crt0%O%s %:if-exists(crti%O%s) \
8417 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
8420 @item @code{replace-outfile}
8421 The @code{replace-outfile} spec function takes two arguments. It looks for the
8422 first argument in the outfiles array and replaces it with the second argument. Here
8423 is a small example of its usage:
8426 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
8429 @item @code{print-asm-header}
8430 The @code{print-asm-header} function takes no arguments and simply
8431 prints a banner like:
8437 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
8440 It is used to separate compiler options from assembler options
8441 in the @option{--target-help} output.
8445 Substitutes the @code{-S} switch, if that switch was given to GCC@.
8446 If that switch was not specified, this substitutes nothing. Note that
8447 the leading dash is omitted when specifying this option, and it is
8448 automatically inserted if the substitution is performed. Thus the spec
8449 string @samp{%@{foo@}} would match the command-line option @option{-foo}
8450 and would output the command line option @option{-foo}.
8452 @item %W@{@code{S}@}
8453 Like %@{@code{S}@} but mark last argument supplied within as a file to be
8456 @item %@{@code{S}*@}
8457 Substitutes all the switches specified to GCC whose names start
8458 with @code{-S}, but which also take an argument. This is used for
8459 switches like @option{-o}, @option{-D}, @option{-I}, etc.
8460 GCC considers @option{-o foo} as being
8461 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
8462 text, including the space. Thus two arguments would be generated.
8464 @item %@{@code{S}*&@code{T}*@}
8465 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
8466 (the order of @code{S} and @code{T} in the spec is not significant).
8467 There can be any number of ampersand-separated variables; for each the
8468 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
8470 @item %@{@code{S}:@code{X}@}
8471 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
8473 @item %@{!@code{S}:@code{X}@}
8474 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
8476 @item %@{@code{S}*:@code{X}@}
8477 Substitutes @code{X} if one or more switches whose names start with
8478 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
8479 once, no matter how many such switches appeared. However, if @code{%*}
8480 appears somewhere in @code{X}, then @code{X} will be substituted once
8481 for each matching switch, with the @code{%*} replaced by the part of
8482 that switch that matched the @code{*}.
8484 @item %@{.@code{S}:@code{X}@}
8485 Substitutes @code{X}, if processing a file with suffix @code{S}.
8487 @item %@{!.@code{S}:@code{X}@}
8488 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
8490 @item %@{,@code{S}:@code{X}@}
8491 Substitutes @code{X}, if processing a file for language @code{S}.
8493 @item %@{!,@code{S}:@code{X}@}
8494 Substitutes @code{X}, if not processing a file for language @code{S}.
8496 @item %@{@code{S}|@code{P}:@code{X}@}
8497 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
8498 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
8499 @code{*} sequences as well, although they have a stronger binding than
8500 the @samp{|}. If @code{%*} appears in @code{X}, all of the
8501 alternatives must be starred, and only the first matching alternative
8504 For example, a spec string like this:
8507 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
8510 will output the following command-line options from the following input
8511 command-line options:
8516 -d fred.c -foo -baz -boggle
8517 -d jim.d -bar -baz -boggle
8520 @item %@{S:X; T:Y; :D@}
8522 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
8523 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
8524 be as many clauses as you need. This may be combined with @code{.},
8525 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
8530 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
8531 construct may contain other nested @samp{%} constructs or spaces, or
8532 even newlines. They are processed as usual, as described above.
8533 Trailing white space in @code{X} is ignored. White space may also
8534 appear anywhere on the left side of the colon in these constructs,
8535 except between @code{.} or @code{*} and the corresponding word.
8537 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
8538 handled specifically in these constructs. If another value of
8539 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
8540 @option{-W} switch is found later in the command line, the earlier
8541 switch value is ignored, except with @{@code{S}*@} where @code{S} is
8542 just one letter, which passes all matching options.
8544 The character @samp{|} at the beginning of the predicate text is used to
8545 indicate that a command should be piped to the following command, but
8546 only if @option{-pipe} is specified.
8548 It is built into GCC which switches take arguments and which do not.
8549 (You might think it would be useful to generalize this to allow each
8550 compiler's spec to say which switches take arguments. But this cannot
8551 be done in a consistent fashion. GCC cannot even decide which input
8552 files have been specified without knowing which switches take arguments,
8553 and it must know which input files to compile in order to tell which
8556 GCC also knows implicitly that arguments starting in @option{-l} are to be
8557 treated as compiler output files, and passed to the linker in their
8558 proper position among the other output files.
8560 @c man begin OPTIONS
8562 @node Target Options
8563 @section Specifying Target Machine and Compiler Version
8564 @cindex target options
8565 @cindex cross compiling
8566 @cindex specifying machine version
8567 @cindex specifying compiler version and target machine
8568 @cindex compiler version, specifying
8569 @cindex target machine, specifying
8571 The usual way to run GCC is to run the executable called @file{gcc}, or
8572 @file{<machine>-gcc} when cross-compiling, or
8573 @file{<machine>-gcc-<version>} to run a version other than the one that
8574 was installed last. Sometimes this is inconvenient, so GCC provides
8575 options that will switch to another cross-compiler or version.
8578 @item -b @var{machine}
8580 The argument @var{machine} specifies the target machine for compilation.
8582 The value to use for @var{machine} is the same as was specified as the
8583 machine type when configuring GCC as a cross-compiler. For
8584 example, if a cross-compiler was configured with @samp{configure
8585 arm-elf}, meaning to compile for an arm processor with elf binaries,
8586 then you would specify @option{-b arm-elf} to run that cross compiler.
8587 Because there are other options beginning with @option{-b}, the
8588 configuration must contain a hyphen.
8590 @item -V @var{version}
8592 The argument @var{version} specifies which version of GCC to run.
8593 This is useful when multiple versions are installed. For example,
8594 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
8597 The @option{-V} and @option{-b} options work by running the
8598 @file{<machine>-gcc-<version>} executable, so there's no real reason to
8599 use them if you can just run that directly.
8601 @node Submodel Options
8602 @section Hardware Models and Configurations
8603 @cindex submodel options
8604 @cindex specifying hardware config
8605 @cindex hardware models and configurations, specifying
8606 @cindex machine dependent options
8608 Earlier we discussed the standard option @option{-b} which chooses among
8609 different installed compilers for completely different target
8610 machines, such as VAX vs.@: 68000 vs.@: 80386.
8612 In addition, each of these target machine types can have its own
8613 special options, starting with @samp{-m}, to choose among various
8614 hardware models or configurations---for example, 68010 vs 68020,
8615 floating coprocessor or none. A single installed version of the
8616 compiler can compile for any model or configuration, according to the
8619 Some configurations of the compiler also support additional special
8620 options, usually for compatibility with other compilers on the same
8623 @c This list is ordered alphanumerically by subsection name.
8624 @c It should be the same order and spelling as these options are listed
8625 @c in Machine Dependent Options
8631 * Blackfin Options::
8635 * DEC Alpha Options::
8636 * DEC Alpha/VMS Options::
8638 * GNU/Linux Options::
8641 * i386 and x86-64 Options::
8652 * picoChip Options::
8654 * RS/6000 and PowerPC Options::
8655 * S/390 and zSeries Options::
8660 * System V Options::
8665 * Xstormy16 Options::
8671 @subsection ARC Options
8674 These options are defined for ARC implementations:
8679 Compile code for little endian mode. This is the default.
8683 Compile code for big endian mode.
8686 @opindex mmangle-cpu
8687 Prepend the name of the cpu to all public symbol names.
8688 In multiple-processor systems, there are many ARC variants with different
8689 instruction and register set characteristics. This flag prevents code
8690 compiled for one cpu to be linked with code compiled for another.
8691 No facility exists for handling variants that are ``almost identical''.
8692 This is an all or nothing option.
8694 @item -mcpu=@var{cpu}
8696 Compile code for ARC variant @var{cpu}.
8697 Which variants are supported depend on the configuration.
8698 All variants support @option{-mcpu=base}, this is the default.
8700 @item -mtext=@var{text-section}
8701 @itemx -mdata=@var{data-section}
8702 @itemx -mrodata=@var{readonly-data-section}
8706 Put functions, data, and readonly data in @var{text-section},
8707 @var{data-section}, and @var{readonly-data-section} respectively
8708 by default. This can be overridden with the @code{section} attribute.
8709 @xref{Variable Attributes}.
8714 @subsection ARM Options
8717 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8721 @item -mabi=@var{name}
8723 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8724 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8727 @opindex mapcs-frame
8728 Generate a stack frame that is compliant with the ARM Procedure Call
8729 Standard for all functions, even if this is not strictly necessary for
8730 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8731 with this option will cause the stack frames not to be generated for
8732 leaf functions. The default is @option{-mno-apcs-frame}.
8736 This is a synonym for @option{-mapcs-frame}.
8739 @c not currently implemented
8740 @item -mapcs-stack-check
8741 @opindex mapcs-stack-check
8742 Generate code to check the amount of stack space available upon entry to
8743 every function (that actually uses some stack space). If there is
8744 insufficient space available then either the function
8745 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8746 called, depending upon the amount of stack space required. The run time
8747 system is required to provide these functions. The default is
8748 @option{-mno-apcs-stack-check}, since this produces smaller code.
8750 @c not currently implemented
8752 @opindex mapcs-float
8753 Pass floating point arguments using the float point registers. This is
8754 one of the variants of the APCS@. This option is recommended if the
8755 target hardware has a floating point unit or if a lot of floating point
8756 arithmetic is going to be performed by the code. The default is
8757 @option{-mno-apcs-float}, since integer only code is slightly increased in
8758 size if @option{-mapcs-float} is used.
8760 @c not currently implemented
8761 @item -mapcs-reentrant
8762 @opindex mapcs-reentrant
8763 Generate reentrant, position independent code. The default is
8764 @option{-mno-apcs-reentrant}.
8767 @item -mthumb-interwork
8768 @opindex mthumb-interwork
8769 Generate code which supports calling between the ARM and Thumb
8770 instruction sets. Without this option the two instruction sets cannot
8771 be reliably used inside one program. The default is
8772 @option{-mno-thumb-interwork}, since slightly larger code is generated
8773 when @option{-mthumb-interwork} is specified.
8775 @item -mno-sched-prolog
8776 @opindex mno-sched-prolog
8777 Prevent the reordering of instructions in the function prolog, or the
8778 merging of those instruction with the instructions in the function's
8779 body. This means that all functions will start with a recognizable set
8780 of instructions (or in fact one of a choice from a small set of
8781 different function prologues), and this information can be used to
8782 locate the start if functions inside an executable piece of code. The
8783 default is @option{-msched-prolog}.
8785 @item -mfloat-abi=@var{name}
8787 Specifies which floating-point ABI to use. Permissible values
8788 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8790 Specifying @samp{soft} causes GCC to generate output containing
8791 library calls for floating-point operations.
8792 @samp{softfp} allows the generation of code using hardware floating-point
8793 instructions, but still uses the soft-float calling conventions.
8794 @samp{hard} allows generation of floating-point instructions
8795 and uses FPU-specific calling conventions.
8797 Using @option{-mfloat-abi=hard} with VFP coprocessors is not supported.
8798 Use @option{-mfloat-abi=softfp} with the appropriate @option{-mfpu} option
8799 to allow the compiler to generate code that makes use of the hardware
8800 floating-point capabilities for these CPUs.
8802 The default depends on the specific target configuration. Note that
8803 the hard-float and soft-float ABIs are not link-compatible; you must
8804 compile your entire program with the same ABI, and link with a
8805 compatible set of libraries.
8808 @opindex mhard-float
8809 Equivalent to @option{-mfloat-abi=hard}.
8812 @opindex msoft-float
8813 Equivalent to @option{-mfloat-abi=soft}.
8815 @item -mlittle-endian
8816 @opindex mlittle-endian
8817 Generate code for a processor running in little-endian mode. This is
8818 the default for all standard configurations.
8821 @opindex mbig-endian
8822 Generate code for a processor running in big-endian mode; the default is
8823 to compile code for a little-endian processor.
8825 @item -mwords-little-endian
8826 @opindex mwords-little-endian
8827 This option only applies when generating code for big-endian processors.
8828 Generate code for a little-endian word order but a big-endian byte
8829 order. That is, a byte order of the form @samp{32107654}. Note: this
8830 option should only be used if you require compatibility with code for
8831 big-endian ARM processors generated by versions of the compiler prior to
8834 @item -mcpu=@var{name}
8836 This specifies the name of the target ARM processor. GCC uses this name
8837 to determine what kind of instructions it can emit when generating
8838 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8839 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8840 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8841 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8842 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8843 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8844 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8845 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8846 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8847 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8848 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8849 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8850 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8851 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8852 @samp{cortex-a8}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-m3},
8854 @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
8856 @item -mtune=@var{name}
8858 This option is very similar to the @option{-mcpu=} option, except that
8859 instead of specifying the actual target processor type, and hence
8860 restricting which instructions can be used, it specifies that GCC should
8861 tune the performance of the code as if the target were of the type
8862 specified in this option, but still choosing the instructions that it
8863 will generate based on the cpu specified by a @option{-mcpu=} option.
8864 For some ARM implementations better performance can be obtained by using
8867 @item -march=@var{name}
8869 This specifies the name of the target ARM architecture. GCC uses this
8870 name to determine what kind of instructions it can emit when generating
8871 assembly code. This option can be used in conjunction with or instead
8872 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8873 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8874 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
8875 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
8876 @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m},
8877 @samp{iwmmxt}, @samp{ep9312}.
8879 @item -mfpu=@var{name}
8880 @itemx -mfpe=@var{number}
8881 @itemx -mfp=@var{number}
8885 This specifies what floating point hardware (or hardware emulation) is
8886 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8887 @samp{fpe3}, @samp{maverick}, @samp{vfp}, @samp{vfpv3}, @samp{vfpv3-d16} and
8888 @samp{neon}. @option{-mfp} and @option{-mfpe}
8889 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8890 with older versions of GCC@.
8892 If @option{-msoft-float} is specified this specifies the format of
8893 floating point values.
8895 @item -mstructure-size-boundary=@var{n}
8896 @opindex mstructure-size-boundary
8897 The size of all structures and unions will be rounded up to a multiple
8898 of the number of bits set by this option. Permissible values are 8, 32
8899 and 64. The default value varies for different toolchains. For the COFF
8900 targeted toolchain the default value is 8. A value of 64 is only allowed
8901 if the underlying ABI supports it.
8903 Specifying the larger number can produce faster, more efficient code, but
8904 can also increase the size of the program. Different values are potentially
8905 incompatible. Code compiled with one value cannot necessarily expect to
8906 work with code or libraries compiled with another value, if they exchange
8907 information using structures or unions.
8909 @item -mabort-on-noreturn
8910 @opindex mabort-on-noreturn
8911 Generate a call to the function @code{abort} at the end of a
8912 @code{noreturn} function. It will be executed if the function tries to
8916 @itemx -mno-long-calls
8917 @opindex mlong-calls
8918 @opindex mno-long-calls
8919 Tells the compiler to perform function calls by first loading the
8920 address of the function into a register and then performing a subroutine
8921 call on this register. This switch is needed if the target function
8922 will lie outside of the 64 megabyte addressing range of the offset based
8923 version of subroutine call instruction.
8925 Even if this switch is enabled, not all function calls will be turned
8926 into long calls. The heuristic is that static functions, functions
8927 which have the @samp{short-call} attribute, functions that are inside
8928 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8929 definitions have already been compiled within the current compilation
8930 unit, will not be turned into long calls. The exception to this rule is
8931 that weak function definitions, functions with the @samp{long-call}
8932 attribute or the @samp{section} attribute, and functions that are within
8933 the scope of a @samp{#pragma long_calls} directive, will always be
8934 turned into long calls.
8936 This feature is not enabled by default. Specifying
8937 @option{-mno-long-calls} will restore the default behavior, as will
8938 placing the function calls within the scope of a @samp{#pragma
8939 long_calls_off} directive. Note these switches have no effect on how
8940 the compiler generates code to handle function calls via function
8943 @item -mnop-fun-dllimport
8944 @opindex mnop-fun-dllimport
8945 Disable support for the @code{dllimport} attribute.
8947 @item -msingle-pic-base
8948 @opindex msingle-pic-base
8949 Treat the register used for PIC addressing as read-only, rather than
8950 loading it in the prologue for each function. The run-time system is
8951 responsible for initializing this register with an appropriate value
8952 before execution begins.
8954 @item -mpic-register=@var{reg}
8955 @opindex mpic-register
8956 Specify the register to be used for PIC addressing. The default is R10
8957 unless stack-checking is enabled, when R9 is used.
8959 @item -mcirrus-fix-invalid-insns
8960 @opindex mcirrus-fix-invalid-insns
8961 @opindex mno-cirrus-fix-invalid-insns
8962 Insert NOPs into the instruction stream to in order to work around
8963 problems with invalid Maverick instruction combinations. This option
8964 is only valid if the @option{-mcpu=ep9312} option has been used to
8965 enable generation of instructions for the Cirrus Maverick floating
8966 point co-processor. This option is not enabled by default, since the
8967 problem is only present in older Maverick implementations. The default
8968 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
8971 @item -mpoke-function-name
8972 @opindex mpoke-function-name
8973 Write the name of each function into the text section, directly
8974 preceding the function prologue. The generated code is similar to this:
8978 .ascii "arm_poke_function_name", 0
8981 .word 0xff000000 + (t1 - t0)
8982 arm_poke_function_name
8984 stmfd sp!, @{fp, ip, lr, pc@}
8988 When performing a stack backtrace, code can inspect the value of
8989 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
8990 location @code{pc - 12} and the top 8 bits are set, then we know that
8991 there is a function name embedded immediately preceding this location
8992 and has length @code{((pc[-3]) & 0xff000000)}.
8996 Generate code for the Thumb instruction set. The default is to
8997 use the 32-bit ARM instruction set.
8998 This option automatically enables either 16-bit Thumb-1 or
8999 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
9000 and @option{-march=@var{name}} options.
9003 @opindex mtpcs-frame
9004 Generate a stack frame that is compliant with the Thumb Procedure Call
9005 Standard for all non-leaf functions. (A leaf function is one that does
9006 not call any other functions.) The default is @option{-mno-tpcs-frame}.
9008 @item -mtpcs-leaf-frame
9009 @opindex mtpcs-leaf-frame
9010 Generate a stack frame that is compliant with the Thumb Procedure Call
9011 Standard for all leaf functions. (A leaf function is one that does
9012 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
9014 @item -mcallee-super-interworking
9015 @opindex mcallee-super-interworking
9016 Gives all externally visible functions in the file being compiled an ARM
9017 instruction set header which switches to Thumb mode before executing the
9018 rest of the function. This allows these functions to be called from
9019 non-interworking code.
9021 @item -mcaller-super-interworking
9022 @opindex mcaller-super-interworking
9023 Allows calls via function pointers (including virtual functions) to
9024 execute correctly regardless of whether the target code has been
9025 compiled for interworking or not. There is a small overhead in the cost
9026 of executing a function pointer if this option is enabled.
9028 @item -mtp=@var{name}
9030 Specify the access model for the thread local storage pointer. The valid
9031 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
9032 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
9033 (supported in the arm6k architecture), and @option{auto}, which uses the
9034 best available method for the selected processor. The default setting is
9037 @item -mword-relocations
9038 @opindex mword-relocations
9039 Only generate absolute relocations on word sized values (i.e. R_ARM_ABS32).
9040 This is enabled by default on targets (uClinux, SymbianOS) where the runtime
9041 loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
9047 @subsection AVR Options
9050 These options are defined for AVR implementations:
9053 @item -mmcu=@var{mcu}
9055 Specify ATMEL AVR instruction set or MCU type.
9057 Instruction set avr1 is for the minimal AVR core, not supported by the C
9058 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
9059 attiny11, attiny12, attiny15, attiny28).
9061 Instruction set avr2 (default) is for the classic AVR core with up to
9062 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
9063 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
9064 at90c8534, at90s8535).
9066 Instruction set avr3 is for the classic AVR core with up to 128K program
9067 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
9069 Instruction set avr4 is for the enhanced AVR core with up to 8K program
9070 memory space (MCU types: atmega8, atmega83, atmega85).
9072 Instruction set avr5 is for the enhanced AVR core with up to 128K program
9073 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
9074 atmega64, atmega128, at43usb355, at94k).
9078 Output instruction sizes to the asm file.
9080 @item -minit-stack=@var{N}
9081 @opindex minit-stack
9082 Specify the initial stack address, which may be a symbol or numeric value,
9083 @samp{__stack} is the default.
9085 @item -mno-interrupts
9086 @opindex mno-interrupts
9087 Generated code is not compatible with hardware interrupts.
9088 Code size will be smaller.
9090 @item -mcall-prologues
9091 @opindex mcall-prologues
9092 Functions prologues/epilogues expanded as call to appropriate
9093 subroutines. Code size will be smaller.
9095 @item -mno-tablejump
9096 @opindex mno-tablejump
9097 Do not generate tablejump insns which sometimes increase code size.
9100 @opindex mtiny-stack
9101 Change only the low 8 bits of the stack pointer.
9105 Assume int to be 8 bit integer. This affects the sizes of all types: A
9106 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
9107 and long long will be 4 bytes. Please note that this option does not
9108 comply to the C standards, but it will provide you with smaller code
9112 @node Blackfin Options
9113 @subsection Blackfin Options
9114 @cindex Blackfin Options
9117 @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
9119 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
9120 can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
9121 @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
9122 @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
9123 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
9124 @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
9126 The optional @var{sirevision} specifies the silicon revision of the target
9127 Blackfin processor. Any workarounds available for the targeted silicon revision
9128 will be enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
9129 If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
9130 will be enabled. The @code{__SILICON_REVISION__} macro is defined to two
9131 hexadecimal digits representing the major and minor numbers in the silicon
9132 revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
9133 is not defined. If @var{sirevision} is @samp{any}, the
9134 @code{__SILICON_REVISION__} is defined to be @code{0xffff}.
9135 If this optional @var{sirevision} is not used, GCC assumes the latest known
9136 silicon revision of the targeted Blackfin processor.
9138 Support for @samp{bf561} is incomplete. For @samp{bf561},
9139 Only the processor macro is defined.
9140 Without this option, @samp{bf532} is used as the processor by default.
9141 The corresponding predefined processor macros for @var{cpu} is to
9142 be defined. And for @samp{bfin-elf} toolchain, this causes the hardware BSP
9143 provided by libgloss to be linked in if @option{-msim} is not given.
9147 Specifies that the program will be run on the simulator. This causes
9148 the simulator BSP provided by libgloss to be linked in. This option
9149 has effect only for @samp{bfin-elf} toolchain.
9150 Certain other options, such as @option{-mid-shared-library} and
9151 @option{-mfdpic}, imply @option{-msim}.
9153 @item -momit-leaf-frame-pointer
9154 @opindex momit-leaf-frame-pointer
9155 Don't keep the frame pointer in a register for leaf functions. This
9156 avoids the instructions to save, set up and restore frame pointers and
9157 makes an extra register available in leaf functions. The option
9158 @option{-fomit-frame-pointer} removes the frame pointer for all functions
9159 which might make debugging harder.
9161 @item -mspecld-anomaly
9162 @opindex mspecld-anomaly
9163 When enabled, the compiler will ensure that the generated code does not
9164 contain speculative loads after jump instructions. If this option is used,
9165 @code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
9167 @item -mno-specld-anomaly
9168 @opindex mno-specld-anomaly
9169 Don't generate extra code to prevent speculative loads from occurring.
9171 @item -mcsync-anomaly
9172 @opindex mcsync-anomaly
9173 When enabled, the compiler will ensure that the generated code does not
9174 contain CSYNC or SSYNC instructions too soon after conditional branches.
9175 If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
9177 @item -mno-csync-anomaly
9178 @opindex mno-csync-anomaly
9179 Don't generate extra code to prevent CSYNC or SSYNC instructions from
9180 occurring too soon after a conditional branch.
9184 When enabled, the compiler is free to take advantage of the knowledge that
9185 the entire program fits into the low 64k of memory.
9188 @opindex mno-low-64k
9189 Assume that the program is arbitrarily large. This is the default.
9191 @item -mstack-check-l1
9192 @opindex mstack-check-l1
9193 Do stack checking using information placed into L1 scratchpad memory by the
9196 @item -mid-shared-library
9197 @opindex mid-shared-library
9198 Generate code that supports shared libraries via the library ID method.
9199 This allows for execute in place and shared libraries in an environment
9200 without virtual memory management. This option implies @option{-fPIC}.
9201 With a @samp{bfin-elf} target, this option implies @option{-msim}.
9203 @item -mno-id-shared-library
9204 @opindex mno-id-shared-library
9205 Generate code that doesn't assume ID based shared libraries are being used.
9206 This is the default.
9208 @item -mleaf-id-shared-library
9209 @opindex mleaf-id-shared-library
9210 Generate code that supports shared libraries via the library ID method,
9211 but assumes that this library or executable won't link against any other
9212 ID shared libraries. That allows the compiler to use faster code for jumps
9215 @item -mno-leaf-id-shared-library
9216 @opindex mno-leaf-id-shared-library
9217 Do not assume that the code being compiled won't link against any ID shared
9218 libraries. Slower code will be generated for jump and call insns.
9220 @item -mshared-library-id=n
9221 @opindex mshared-library-id
9222 Specified the identification number of the ID based shared library being
9223 compiled. Specifying a value of 0 will generate more compact code, specifying
9224 other values will force the allocation of that number to the current
9225 library but is no more space or time efficient than omitting this option.
9229 Generate code that allows the data segment to be located in a different
9230 area of memory from the text segment. This allows for execute in place in
9231 an environment without virtual memory management by eliminating relocations
9232 against the text section.
9235 @opindex mno-sep-data
9236 Generate code that assumes that the data segment follows the text segment.
9237 This is the default.
9240 @itemx -mno-long-calls
9241 @opindex mlong-calls
9242 @opindex mno-long-calls
9243 Tells the compiler to perform function calls by first loading the
9244 address of the function into a register and then performing a subroutine
9245 call on this register. This switch is needed if the target function
9246 will lie outside of the 24 bit addressing range of the offset based
9247 version of subroutine call instruction.
9249 This feature is not enabled by default. Specifying
9250 @option{-mno-long-calls} will restore the default behavior. Note these
9251 switches have no effect on how the compiler generates code to handle
9252 function calls via function pointers.
9256 Link with the fast floating-point library. This library relaxes some of
9257 the IEEE floating-point standard's rules for checking inputs against
9258 Not-a-Number (NAN), in the interest of performance.
9261 @opindex minline-plt
9262 Enable inlining of PLT entries in function calls to functions that are
9263 not known to bind locally. It has no effect without @option{-mfdpic}.
9267 Build standalone application for multicore Blackfin processor. Proper
9268 start files and link scripts will be used to support multicore.
9269 This option defines @code{__BFIN_MULTICORE}. It can only be used with
9270 @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. It can be used with
9271 @option{-mcorea} or @option{-mcoreb}. If it's used without
9272 @option{-mcorea} or @option{-mcoreb}, single application/dual core
9273 programming model is used. In this model, the main function of Core B
9274 should be named as coreb_main. If it's used with @option{-mcorea} or
9275 @option{-mcoreb}, one application per core programming model is used.
9276 If this option is not used, single core application programming
9281 Build standalone application for Core A of BF561 when using
9282 one application per core programming model. Proper start files
9283 and link scripts will be used to support Core A. This option
9284 defines @code{__BFIN_COREA}. It must be used with @option{-mmulticore}.
9288 Build standalone application for Core B of BF561 when using
9289 one application per core programming model. Proper start files
9290 and link scripts will be used to support Core B. This option
9291 defines @code{__BFIN_COREB}. When this option is used, coreb_main
9292 should be used instead of main. It must be used with
9293 @option{-mmulticore}.
9297 Build standalone application for SDRAM. Proper start files and
9298 link scripts will be used to put the application into SDRAM.
9299 Loader should initialize SDRAM before loading the application
9300 into SDRAM. This option defines @code{__BFIN_SDRAM}.
9304 @subsection CRIS Options
9305 @cindex CRIS Options
9307 These options are defined specifically for the CRIS ports.
9310 @item -march=@var{architecture-type}
9311 @itemx -mcpu=@var{architecture-type}
9314 Generate code for the specified architecture. The choices for
9315 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
9316 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
9317 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
9320 @item -mtune=@var{architecture-type}
9322 Tune to @var{architecture-type} everything applicable about the generated
9323 code, except for the ABI and the set of available instructions. The
9324 choices for @var{architecture-type} are the same as for
9325 @option{-march=@var{architecture-type}}.
9327 @item -mmax-stack-frame=@var{n}
9328 @opindex mmax-stack-frame
9329 Warn when the stack frame of a function exceeds @var{n} bytes.
9335 The options @option{-metrax4} and @option{-metrax100} are synonyms for
9336 @option{-march=v3} and @option{-march=v8} respectively.
9338 @item -mmul-bug-workaround
9339 @itemx -mno-mul-bug-workaround
9340 @opindex mmul-bug-workaround
9341 @opindex mno-mul-bug-workaround
9342 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
9343 models where it applies. This option is active by default.
9347 Enable CRIS-specific verbose debug-related information in the assembly
9348 code. This option also has the effect to turn off the @samp{#NO_APP}
9349 formatted-code indicator to the assembler at the beginning of the
9354 Do not use condition-code results from previous instruction; always emit
9355 compare and test instructions before use of condition codes.
9357 @item -mno-side-effects
9358 @opindex mno-side-effects
9359 Do not emit instructions with side-effects in addressing modes other than
9363 @itemx -mno-stack-align
9365 @itemx -mno-data-align
9366 @itemx -mconst-align
9367 @itemx -mno-const-align
9368 @opindex mstack-align
9369 @opindex mno-stack-align
9370 @opindex mdata-align
9371 @opindex mno-data-align
9372 @opindex mconst-align
9373 @opindex mno-const-align
9374 These options (no-options) arranges (eliminate arrangements) for the
9375 stack-frame, individual data and constants to be aligned for the maximum
9376 single data access size for the chosen CPU model. The default is to
9377 arrange for 32-bit alignment. ABI details such as structure layout are
9378 not affected by these options.
9386 Similar to the stack- data- and const-align options above, these options
9387 arrange for stack-frame, writable data and constants to all be 32-bit,
9388 16-bit or 8-bit aligned. The default is 32-bit alignment.
9390 @item -mno-prologue-epilogue
9391 @itemx -mprologue-epilogue
9392 @opindex mno-prologue-epilogue
9393 @opindex mprologue-epilogue
9394 With @option{-mno-prologue-epilogue}, the normal function prologue and
9395 epilogue that sets up the stack-frame are omitted and no return
9396 instructions or return sequences are generated in the code. Use this
9397 option only together with visual inspection of the compiled code: no
9398 warnings or errors are generated when call-saved registers must be saved,
9399 or storage for local variable needs to be allocated.
9405 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
9406 instruction sequences that load addresses for functions from the PLT part
9407 of the GOT rather than (traditional on other architectures) calls to the
9408 PLT@. The default is @option{-mgotplt}.
9412 Legacy no-op option only recognized with the cris-axis-elf and
9413 cris-axis-linux-gnu targets.
9417 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
9421 This option, recognized for the cris-axis-elf arranges
9422 to link with input-output functions from a simulator library. Code,
9423 initialized data and zero-initialized data are allocated consecutively.
9427 Like @option{-sim}, but pass linker options to locate initialized data at
9428 0x40000000 and zero-initialized data at 0x80000000.
9432 @subsection CRX Options
9435 These options are defined specifically for the CRX ports.
9441 Enable the use of multiply-accumulate instructions. Disabled by default.
9445 Push instructions will be used to pass outgoing arguments when functions
9446 are called. Enabled by default.
9449 @node Darwin Options
9450 @subsection Darwin Options
9451 @cindex Darwin options
9453 These options are defined for all architectures running the Darwin operating
9456 FSF GCC on Darwin does not create ``fat'' object files; it will create
9457 an object file for the single architecture that it was built to
9458 target. Apple's GCC on Darwin does create ``fat'' files if multiple
9459 @option{-arch} options are used; it does so by running the compiler or
9460 linker multiple times and joining the results together with
9463 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
9464 @samp{i686}) is determined by the flags that specify the ISA
9465 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
9466 @option{-force_cpusubtype_ALL} option can be used to override this.
9468 The Darwin tools vary in their behavior when presented with an ISA
9469 mismatch. The assembler, @file{as}, will only permit instructions to
9470 be used that are valid for the subtype of the file it is generating,
9471 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
9472 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
9473 and print an error if asked to create a shared library with a less
9474 restrictive subtype than its input files (for instance, trying to put
9475 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
9476 for executables, @file{ld}, will quietly give the executable the most
9477 restrictive subtype of any of its input files.
9482 Add the framework directory @var{dir} to the head of the list of
9483 directories to be searched for header files. These directories are
9484 interleaved with those specified by @option{-I} options and are
9485 scanned in a left-to-right order.
9487 A framework directory is a directory with frameworks in it. A
9488 framework is a directory with a @samp{"Headers"} and/or
9489 @samp{"PrivateHeaders"} directory contained directly in it that ends
9490 in @samp{".framework"}. The name of a framework is the name of this
9491 directory excluding the @samp{".framework"}. Headers associated with
9492 the framework are found in one of those two directories, with
9493 @samp{"Headers"} being searched first. A subframework is a framework
9494 directory that is in a framework's @samp{"Frameworks"} directory.
9495 Includes of subframework headers can only appear in a header of a
9496 framework that contains the subframework, or in a sibling subframework
9497 header. Two subframeworks are siblings if they occur in the same
9498 framework. A subframework should not have the same name as a
9499 framework, a warning will be issued if this is violated. Currently a
9500 subframework cannot have subframeworks, in the future, the mechanism
9501 may be extended to support this. The standard frameworks can be found
9502 in @samp{"/System/Library/Frameworks"} and
9503 @samp{"/Library/Frameworks"}. An example include looks like
9504 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
9505 the name of the framework and header.h is found in the
9506 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
9508 @item -iframework@var{dir}
9510 Like @option{-F} except the directory is a treated as a system
9511 directory. The main difference between this @option{-iframework} and
9512 @option{-F} is that with @option{-iframework} the compiler does not
9513 warn about constructs contained within header files found via
9514 @var{dir}. This option is valid only for the C family of languages.
9518 Emit debugging information for symbols that are used. For STABS
9519 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
9520 This is by default ON@.
9524 Emit debugging information for all symbols and types.
9526 @item -mmacosx-version-min=@var{version}
9527 The earliest version of MacOS X that this executable will run on
9528 is @var{version}. Typical values of @var{version} include @code{10.1},
9529 @code{10.2}, and @code{10.3.9}.
9531 If the compiler was built to use the system's headers by default,
9532 then the default for this option is the system version on which the
9533 compiler is running, otherwise the default is to make choices which
9534 are compatible with as many systems and code bases as possible.
9538 Enable kernel development mode. The @option{-mkernel} option sets
9539 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
9540 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
9541 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
9542 applicable. This mode also sets @option{-mno-altivec},
9543 @option{-msoft-float}, @option{-fno-builtin} and
9544 @option{-mlong-branch} for PowerPC targets.
9546 @item -mone-byte-bool
9547 @opindex mone-byte-bool
9548 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
9549 By default @samp{sizeof(bool)} is @samp{4} when compiling for
9550 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
9551 option has no effect on x86.
9553 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
9554 to generate code that is not binary compatible with code generated
9555 without that switch. Using this switch may require recompiling all
9556 other modules in a program, including system libraries. Use this
9557 switch to conform to a non-default data model.
9559 @item -mfix-and-continue
9560 @itemx -ffix-and-continue
9561 @itemx -findirect-data
9562 @opindex mfix-and-continue
9563 @opindex ffix-and-continue
9564 @opindex findirect-data
9565 Generate code suitable for fast turn around development. Needed to
9566 enable gdb to dynamically load @code{.o} files into already running
9567 programs. @option{-findirect-data} and @option{-ffix-and-continue}
9568 are provided for backwards compatibility.
9572 Loads all members of static archive libraries.
9573 See man ld(1) for more information.
9575 @item -arch_errors_fatal
9576 @opindex arch_errors_fatal
9577 Cause the errors having to do with files that have the wrong architecture
9581 @opindex bind_at_load
9582 Causes the output file to be marked such that the dynamic linker will
9583 bind all undefined references when the file is loaded or launched.
9587 Produce a Mach-o bundle format file.
9588 See man ld(1) for more information.
9590 @item -bundle_loader @var{executable}
9591 @opindex bundle_loader
9592 This option specifies the @var{executable} that will be loading the build
9593 output file being linked. See man ld(1) for more information.
9597 When passed this option, GCC will produce a dynamic library instead of
9598 an executable when linking, using the Darwin @file{libtool} command.
9600 @item -force_cpusubtype_ALL
9601 @opindex force_cpusubtype_ALL
9602 This causes GCC's output file to have the @var{ALL} subtype, instead of
9603 one controlled by the @option{-mcpu} or @option{-march} option.
9605 @item -allowable_client @var{client_name}
9607 @itemx -compatibility_version
9608 @itemx -current_version
9610 @itemx -dependency-file
9612 @itemx -dylinker_install_name
9614 @itemx -exported_symbols_list
9616 @itemx -flat_namespace
9617 @itemx -force_flat_namespace
9618 @itemx -headerpad_max_install_names
9621 @itemx -install_name
9622 @itemx -keep_private_externs
9623 @itemx -multi_module
9624 @itemx -multiply_defined
9625 @itemx -multiply_defined_unused
9627 @itemx -no_dead_strip_inits_and_terms
9628 @itemx -nofixprebinding
9631 @itemx -noseglinkedit
9632 @itemx -pagezero_size
9634 @itemx -prebind_all_twolevel_modules
9635 @itemx -private_bundle
9636 @itemx -read_only_relocs
9638 @itemx -sectobjectsymbols
9642 @itemx -sectobjectsymbols
9645 @itemx -segs_read_only_addr
9646 @itemx -segs_read_write_addr
9647 @itemx -seg_addr_table
9648 @itemx -seg_addr_table_filename
9651 @itemx -segs_read_only_addr
9652 @itemx -segs_read_write_addr
9653 @itemx -single_module
9656 @itemx -sub_umbrella
9657 @itemx -twolevel_namespace
9660 @itemx -unexported_symbols_list
9661 @itemx -weak_reference_mismatches
9663 @opindex allowable_client
9664 @opindex client_name
9665 @opindex compatibility_version
9666 @opindex current_version
9668 @opindex dependency-file
9670 @opindex dylinker_install_name
9672 @opindex exported_symbols_list
9674 @opindex flat_namespace
9675 @opindex force_flat_namespace
9676 @opindex headerpad_max_install_names
9679 @opindex install_name
9680 @opindex keep_private_externs
9681 @opindex multi_module
9682 @opindex multiply_defined
9683 @opindex multiply_defined_unused
9685 @opindex no_dead_strip_inits_and_terms
9686 @opindex nofixprebinding
9687 @opindex nomultidefs
9689 @opindex noseglinkedit
9690 @opindex pagezero_size
9692 @opindex prebind_all_twolevel_modules
9693 @opindex private_bundle
9694 @opindex read_only_relocs
9696 @opindex sectobjectsymbols
9700 @opindex sectobjectsymbols
9703 @opindex segs_read_only_addr
9704 @opindex segs_read_write_addr
9705 @opindex seg_addr_table
9706 @opindex seg_addr_table_filename
9707 @opindex seglinkedit
9709 @opindex segs_read_only_addr
9710 @opindex segs_read_write_addr
9711 @opindex single_module
9713 @opindex sub_library
9714 @opindex sub_umbrella
9715 @opindex twolevel_namespace
9718 @opindex unexported_symbols_list
9719 @opindex weak_reference_mismatches
9720 @opindex whatsloaded
9721 These options are passed to the Darwin linker. The Darwin linker man page
9722 describes them in detail.
9725 @node DEC Alpha Options
9726 @subsection DEC Alpha Options
9728 These @samp{-m} options are defined for the DEC Alpha implementations:
9731 @item -mno-soft-float
9733 @opindex mno-soft-float
9734 @opindex msoft-float
9735 Use (do not use) the hardware floating-point instructions for
9736 floating-point operations. When @option{-msoft-float} is specified,
9737 functions in @file{libgcc.a} will be used to perform floating-point
9738 operations. Unless they are replaced by routines that emulate the
9739 floating-point operations, or compiled in such a way as to call such
9740 emulations routines, these routines will issue floating-point
9741 operations. If you are compiling for an Alpha without floating-point
9742 operations, you must ensure that the library is built so as not to call
9745 Note that Alpha implementations without floating-point operations are
9746 required to have floating-point registers.
9751 @opindex mno-fp-regs
9752 Generate code that uses (does not use) the floating-point register set.
9753 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9754 register set is not used, floating point operands are passed in integer
9755 registers as if they were integers and floating-point results are passed
9756 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9757 so any function with a floating-point argument or return value called by code
9758 compiled with @option{-mno-fp-regs} must also be compiled with that
9761 A typical use of this option is building a kernel that does not use,
9762 and hence need not save and restore, any floating-point registers.
9766 The Alpha architecture implements floating-point hardware optimized for
9767 maximum performance. It is mostly compliant with the IEEE floating
9768 point standard. However, for full compliance, software assistance is
9769 required. This option generates code fully IEEE compliant code
9770 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9771 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9772 defined during compilation. The resulting code is less efficient but is
9773 able to correctly support denormalized numbers and exceptional IEEE
9774 values such as not-a-number and plus/minus infinity. Other Alpha
9775 compilers call this option @option{-ieee_with_no_inexact}.
9777 @item -mieee-with-inexact
9778 @opindex mieee-with-inexact
9779 This is like @option{-mieee} except the generated code also maintains
9780 the IEEE @var{inexact-flag}. Turning on this option causes the
9781 generated code to implement fully-compliant IEEE math. In addition to
9782 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9783 macro. On some Alpha implementations the resulting code may execute
9784 significantly slower than the code generated by default. Since there is
9785 very little code that depends on the @var{inexact-flag}, you should
9786 normally not specify this option. Other Alpha compilers call this
9787 option @option{-ieee_with_inexact}.
9789 @item -mfp-trap-mode=@var{trap-mode}
9790 @opindex mfp-trap-mode
9791 This option controls what floating-point related traps are enabled.
9792 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9793 The trap mode can be set to one of four values:
9797 This is the default (normal) setting. The only traps that are enabled
9798 are the ones that cannot be disabled in software (e.g., division by zero
9802 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9806 Like @samp{u}, but the instructions are marked to be safe for software
9807 completion (see Alpha architecture manual for details).
9810 Like @samp{su}, but inexact traps are enabled as well.
9813 @item -mfp-rounding-mode=@var{rounding-mode}
9814 @opindex mfp-rounding-mode
9815 Selects the IEEE rounding mode. Other Alpha compilers call this option
9816 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9821 Normal IEEE rounding mode. Floating point numbers are rounded towards
9822 the nearest machine number or towards the even machine number in case
9826 Round towards minus infinity.
9829 Chopped rounding mode. Floating point numbers are rounded towards zero.
9832 Dynamic rounding mode. A field in the floating point control register
9833 (@var{fpcr}, see Alpha architecture reference manual) controls the
9834 rounding mode in effect. The C library initializes this register for
9835 rounding towards plus infinity. Thus, unless your program modifies the
9836 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9839 @item -mtrap-precision=@var{trap-precision}
9840 @opindex mtrap-precision
9841 In the Alpha architecture, floating point traps are imprecise. This
9842 means without software assistance it is impossible to recover from a
9843 floating trap and program execution normally needs to be terminated.
9844 GCC can generate code that can assist operating system trap handlers
9845 in determining the exact location that caused a floating point trap.
9846 Depending on the requirements of an application, different levels of
9847 precisions can be selected:
9851 Program precision. This option is the default and means a trap handler
9852 can only identify which program caused a floating point exception.
9855 Function precision. The trap handler can determine the function that
9856 caused a floating point exception.
9859 Instruction precision. The trap handler can determine the exact
9860 instruction that caused a floating point exception.
9863 Other Alpha compilers provide the equivalent options called
9864 @option{-scope_safe} and @option{-resumption_safe}.
9866 @item -mieee-conformant
9867 @opindex mieee-conformant
9868 This option marks the generated code as IEEE conformant. You must not
9869 use this option unless you also specify @option{-mtrap-precision=i} and either
9870 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9871 is to emit the line @samp{.eflag 48} in the function prologue of the
9872 generated assembly file. Under DEC Unix, this has the effect that
9873 IEEE-conformant math library routines will be linked in.
9875 @item -mbuild-constants
9876 @opindex mbuild-constants
9877 Normally GCC examines a 32- or 64-bit integer constant to
9878 see if it can construct it from smaller constants in two or three
9879 instructions. If it cannot, it will output the constant as a literal and
9880 generate code to load it from the data segment at runtime.
9882 Use this option to require GCC to construct @emph{all} integer constants
9883 using code, even if it takes more instructions (the maximum is six).
9885 You would typically use this option to build a shared library dynamic
9886 loader. Itself a shared library, it must relocate itself in memory
9887 before it can find the variables and constants in its own data segment.
9893 Select whether to generate code to be assembled by the vendor-supplied
9894 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9912 Indicate whether GCC should generate code to use the optional BWX,
9913 CIX, FIX and MAX instruction sets. The default is to use the instruction
9914 sets supported by the CPU type specified via @option{-mcpu=} option or that
9915 of the CPU on which GCC was built if none was specified.
9920 @opindex mfloat-ieee
9921 Generate code that uses (does not use) VAX F and G floating point
9922 arithmetic instead of IEEE single and double precision.
9924 @item -mexplicit-relocs
9925 @itemx -mno-explicit-relocs
9926 @opindex mexplicit-relocs
9927 @opindex mno-explicit-relocs
9928 Older Alpha assemblers provided no way to generate symbol relocations
9929 except via assembler macros. Use of these macros does not allow
9930 optimal instruction scheduling. GNU binutils as of version 2.12
9931 supports a new syntax that allows the compiler to explicitly mark
9932 which relocations should apply to which instructions. This option
9933 is mostly useful for debugging, as GCC detects the capabilities of
9934 the assembler when it is built and sets the default accordingly.
9938 @opindex msmall-data
9939 @opindex mlarge-data
9940 When @option{-mexplicit-relocs} is in effect, static data is
9941 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9942 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9943 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9944 16-bit relocations off of the @code{$gp} register. This limits the
9945 size of the small data area to 64KB, but allows the variables to be
9946 directly accessed via a single instruction.
9948 The default is @option{-mlarge-data}. With this option the data area
9949 is limited to just below 2GB@. Programs that require more than 2GB of
9950 data must use @code{malloc} or @code{mmap} to allocate the data in the
9951 heap instead of in the program's data segment.
9953 When generating code for shared libraries, @option{-fpic} implies
9954 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9958 @opindex msmall-text
9959 @opindex mlarge-text
9960 When @option{-msmall-text} is used, the compiler assumes that the
9961 code of the entire program (or shared library) fits in 4MB, and is
9962 thus reachable with a branch instruction. When @option{-msmall-data}
9963 is used, the compiler can assume that all local symbols share the
9964 same @code{$gp} value, and thus reduce the number of instructions
9965 required for a function call from 4 to 1.
9967 The default is @option{-mlarge-text}.
9969 @item -mcpu=@var{cpu_type}
9971 Set the instruction set and instruction scheduling parameters for
9972 machine type @var{cpu_type}. You can specify either the @samp{EV}
9973 style name or the corresponding chip number. GCC supports scheduling
9974 parameters for the EV4, EV5 and EV6 family of processors and will
9975 choose the default values for the instruction set from the processor
9976 you specify. If you do not specify a processor type, GCC will default
9977 to the processor on which the compiler was built.
9979 Supported values for @var{cpu_type} are
9985 Schedules as an EV4 and has no instruction set extensions.
9989 Schedules as an EV5 and has no instruction set extensions.
9993 Schedules as an EV5 and supports the BWX extension.
9998 Schedules as an EV5 and supports the BWX and MAX extensions.
10002 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
10006 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
10009 @item -mtune=@var{cpu_type}
10011 Set only the instruction scheduling parameters for machine type
10012 @var{cpu_type}. The instruction set is not changed.
10014 @item -mmemory-latency=@var{time}
10015 @opindex mmemory-latency
10016 Sets the latency the scheduler should assume for typical memory
10017 references as seen by the application. This number is highly
10018 dependent on the memory access patterns used by the application
10019 and the size of the external cache on the machine.
10021 Valid options for @var{time} are
10025 A decimal number representing clock cycles.
10031 The compiler contains estimates of the number of clock cycles for
10032 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
10033 (also called Dcache, Scache, and Bcache), as well as to main memory.
10034 Note that L3 is only valid for EV5.
10039 @node DEC Alpha/VMS Options
10040 @subsection DEC Alpha/VMS Options
10042 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
10045 @item -mvms-return-codes
10046 @opindex mvms-return-codes
10047 Return VMS condition codes from main. The default is to return POSIX
10048 style condition (e.g.@: error) codes.
10052 @subsection FRV Options
10053 @cindex FRV Options
10059 Only use the first 32 general purpose registers.
10064 Use all 64 general purpose registers.
10069 Use only the first 32 floating point registers.
10074 Use all 64 floating point registers
10077 @opindex mhard-float
10079 Use hardware instructions for floating point operations.
10082 @opindex msoft-float
10084 Use library routines for floating point operations.
10089 Dynamically allocate condition code registers.
10094 Do not try to dynamically allocate condition code registers, only
10095 use @code{icc0} and @code{fcc0}.
10100 Change ABI to use double word insns.
10105 Do not use double word instructions.
10110 Use floating point double instructions.
10113 @opindex mno-double
10115 Do not use floating point double instructions.
10120 Use media instructions.
10125 Do not use media instructions.
10130 Use multiply and add/subtract instructions.
10133 @opindex mno-muladd
10135 Do not use multiply and add/subtract instructions.
10140 Select the FDPIC ABI, that uses function descriptors to represent
10141 pointers to functions. Without any PIC/PIE-related options, it
10142 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
10143 assumes GOT entries and small data are within a 12-bit range from the
10144 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
10145 are computed with 32 bits.
10146 With a @samp{bfin-elf} target, this option implies @option{-msim}.
10149 @opindex minline-plt
10151 Enable inlining of PLT entries in function calls to functions that are
10152 not known to bind locally. It has no effect without @option{-mfdpic}.
10153 It's enabled by default if optimizing for speed and compiling for
10154 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
10155 optimization option such as @option{-O3} or above is present in the
10161 Assume a large TLS segment when generating thread-local code.
10166 Do not assume a large TLS segment when generating thread-local code.
10171 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
10172 that is known to be in read-only sections. It's enabled by default,
10173 except for @option{-fpic} or @option{-fpie}: even though it may help
10174 make the global offset table smaller, it trades 1 instruction for 4.
10175 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
10176 one of which may be shared by multiple symbols, and it avoids the need
10177 for a GOT entry for the referenced symbol, so it's more likely to be a
10178 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
10180 @item -multilib-library-pic
10181 @opindex multilib-library-pic
10183 Link with the (library, not FD) pic libraries. It's implied by
10184 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
10185 @option{-fpic} without @option{-mfdpic}. You should never have to use
10189 @opindex mlinked-fp
10191 Follow the EABI requirement of always creating a frame pointer whenever
10192 a stack frame is allocated. This option is enabled by default and can
10193 be disabled with @option{-mno-linked-fp}.
10196 @opindex mlong-calls
10198 Use indirect addressing to call functions outside the current
10199 compilation unit. This allows the functions to be placed anywhere
10200 within the 32-bit address space.
10202 @item -malign-labels
10203 @opindex malign-labels
10205 Try to align labels to an 8-byte boundary by inserting nops into the
10206 previous packet. This option only has an effect when VLIW packing
10207 is enabled. It doesn't create new packets; it merely adds nops to
10210 @item -mlibrary-pic
10211 @opindex mlibrary-pic
10213 Generate position-independent EABI code.
10218 Use only the first four media accumulator registers.
10223 Use all eight media accumulator registers.
10228 Pack VLIW instructions.
10233 Do not pack VLIW instructions.
10236 @opindex mno-eflags
10238 Do not mark ABI switches in e_flags.
10241 @opindex mcond-move
10243 Enable the use of conditional-move instructions (default).
10245 This switch is mainly for debugging the compiler and will likely be removed
10246 in a future version.
10248 @item -mno-cond-move
10249 @opindex mno-cond-move
10251 Disable the use of conditional-move instructions.
10253 This switch is mainly for debugging the compiler and will likely be removed
10254 in a future version.
10259 Enable the use of conditional set instructions (default).
10261 This switch is mainly for debugging the compiler and will likely be removed
10262 in a future version.
10267 Disable the use of conditional set instructions.
10269 This switch is mainly for debugging the compiler and will likely be removed
10270 in a future version.
10273 @opindex mcond-exec
10275 Enable the use of conditional execution (default).
10277 This switch is mainly for debugging the compiler and will likely be removed
10278 in a future version.
10280 @item -mno-cond-exec
10281 @opindex mno-cond-exec
10283 Disable the use of conditional execution.
10285 This switch is mainly for debugging the compiler and will likely be removed
10286 in a future version.
10288 @item -mvliw-branch
10289 @opindex mvliw-branch
10291 Run a pass to pack branches into VLIW instructions (default).
10293 This switch is mainly for debugging the compiler and will likely be removed
10294 in a future version.
10296 @item -mno-vliw-branch
10297 @opindex mno-vliw-branch
10299 Do not run a pass to pack branches into VLIW instructions.
10301 This switch is mainly for debugging the compiler and will likely be removed
10302 in a future version.
10304 @item -mmulti-cond-exec
10305 @opindex mmulti-cond-exec
10307 Enable optimization of @code{&&} and @code{||} in conditional execution
10310 This switch is mainly for debugging the compiler and will likely be removed
10311 in a future version.
10313 @item -mno-multi-cond-exec
10314 @opindex mno-multi-cond-exec
10316 Disable optimization of @code{&&} and @code{||} in conditional execution.
10318 This switch is mainly for debugging the compiler and will likely be removed
10319 in a future version.
10321 @item -mnested-cond-exec
10322 @opindex mnested-cond-exec
10324 Enable nested conditional execution optimizations (default).
10326 This switch is mainly for debugging the compiler and will likely be removed
10327 in a future version.
10329 @item -mno-nested-cond-exec
10330 @opindex mno-nested-cond-exec
10332 Disable nested conditional execution optimizations.
10334 This switch is mainly for debugging the compiler and will likely be removed
10335 in a future version.
10337 @item -moptimize-membar
10338 @opindex moptimize-membar
10340 This switch removes redundant @code{membar} instructions from the
10341 compiler generated code. It is enabled by default.
10343 @item -mno-optimize-membar
10344 @opindex mno-optimize-membar
10346 This switch disables the automatic removal of redundant @code{membar}
10347 instructions from the generated code.
10349 @item -mtomcat-stats
10350 @opindex mtomcat-stats
10352 Cause gas to print out tomcat statistics.
10354 @item -mcpu=@var{cpu}
10357 Select the processor type for which to generate code. Possible values are
10358 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
10359 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
10363 @node GNU/Linux Options
10364 @subsection GNU/Linux Options
10366 These @samp{-m} options are defined for GNU/Linux targets:
10371 Use the GNU C library instead of uClibc. This is the default except
10372 on @samp{*-*-linux-*uclibc*} targets.
10376 Use uClibc instead of the GNU C library. This is the default on
10377 @samp{*-*-linux-*uclibc*} targets.
10380 @node H8/300 Options
10381 @subsection H8/300 Options
10383 These @samp{-m} options are defined for the H8/300 implementations:
10388 Shorten some address references at link time, when possible; uses the
10389 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
10390 ld, Using ld}, for a fuller description.
10394 Generate code for the H8/300H@.
10398 Generate code for the H8S@.
10402 Generate code for the H8S and H8/300H in the normal mode. This switch
10403 must be used either with @option{-mh} or @option{-ms}.
10407 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
10411 Make @code{int} data 32 bits by default.
10414 @opindex malign-300
10415 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
10416 The default for the H8/300H and H8S is to align longs and floats on 4
10418 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
10419 This option has no effect on the H8/300.
10423 @subsection HPPA Options
10424 @cindex HPPA Options
10426 These @samp{-m} options are defined for the HPPA family of computers:
10429 @item -march=@var{architecture-type}
10431 Generate code for the specified architecture. The choices for
10432 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
10433 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
10434 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
10435 architecture option for your machine. Code compiled for lower numbered
10436 architectures will run on higher numbered architectures, but not the
10439 @item -mpa-risc-1-0
10440 @itemx -mpa-risc-1-1
10441 @itemx -mpa-risc-2-0
10442 @opindex mpa-risc-1-0
10443 @opindex mpa-risc-1-1
10444 @opindex mpa-risc-2-0
10445 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
10448 @opindex mbig-switch
10449 Generate code suitable for big switch tables. Use this option only if
10450 the assembler/linker complain about out of range branches within a switch
10453 @item -mjump-in-delay
10454 @opindex mjump-in-delay
10455 Fill delay slots of function calls with unconditional jump instructions
10456 by modifying the return pointer for the function call to be the target
10457 of the conditional jump.
10459 @item -mdisable-fpregs
10460 @opindex mdisable-fpregs
10461 Prevent floating point registers from being used in any manner. This is
10462 necessary for compiling kernels which perform lazy context switching of
10463 floating point registers. If you use this option and attempt to perform
10464 floating point operations, the compiler will abort.
10466 @item -mdisable-indexing
10467 @opindex mdisable-indexing
10468 Prevent the compiler from using indexing address modes. This avoids some
10469 rather obscure problems when compiling MIG generated code under MACH@.
10471 @item -mno-space-regs
10472 @opindex mno-space-regs
10473 Generate code that assumes the target has no space registers. This allows
10474 GCC to generate faster indirect calls and use unscaled index address modes.
10476 Such code is suitable for level 0 PA systems and kernels.
10478 @item -mfast-indirect-calls
10479 @opindex mfast-indirect-calls
10480 Generate code that assumes calls never cross space boundaries. This
10481 allows GCC to emit code which performs faster indirect calls.
10483 This option will not work in the presence of shared libraries or nested
10486 @item -mfixed-range=@var{register-range}
10487 @opindex mfixed-range
10488 Generate code treating the given register range as fixed registers.
10489 A fixed register is one that the register allocator can not use. This is
10490 useful when compiling kernel code. A register range is specified as
10491 two registers separated by a dash. Multiple register ranges can be
10492 specified separated by a comma.
10494 @item -mlong-load-store
10495 @opindex mlong-load-store
10496 Generate 3-instruction load and store sequences as sometimes required by
10497 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
10500 @item -mportable-runtime
10501 @opindex mportable-runtime
10502 Use the portable calling conventions proposed by HP for ELF systems.
10506 Enable the use of assembler directives only GAS understands.
10508 @item -mschedule=@var{cpu-type}
10510 Schedule code according to the constraints for the machine type
10511 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
10512 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
10513 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
10514 proper scheduling option for your machine. The default scheduling is
10518 @opindex mlinker-opt
10519 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
10520 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
10521 linkers in which they give bogus error messages when linking some programs.
10524 @opindex msoft-float
10525 Generate output containing library calls for floating point.
10526 @strong{Warning:} the requisite libraries are not available for all HPPA
10527 targets. Normally the facilities of the machine's usual C compiler are
10528 used, but this cannot be done directly in cross-compilation. You must make
10529 your own arrangements to provide suitable library functions for
10532 @option{-msoft-float} changes the calling convention in the output file;
10533 therefore, it is only useful if you compile @emph{all} of a program with
10534 this option. In particular, you need to compile @file{libgcc.a}, the
10535 library that comes with GCC, with @option{-msoft-float} in order for
10540 Generate the predefine, @code{_SIO}, for server IO@. The default is
10541 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
10542 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
10543 options are available under HP-UX and HI-UX@.
10547 Use GNU ld specific options. This passes @option{-shared} to ld when
10548 building a shared library. It is the default when GCC is configured,
10549 explicitly or implicitly, with the GNU linker. This option does not
10550 have any affect on which ld is called, it only changes what parameters
10551 are passed to that ld. The ld that is called is determined by the
10552 @option{--with-ld} configure option, GCC's program search path, and
10553 finally by the user's @env{PATH}. The linker used by GCC can be printed
10554 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
10555 on the 64 bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10559 Use HP ld specific options. This passes @option{-b} to ld when building
10560 a shared library and passes @option{+Accept TypeMismatch} to ld on all
10561 links. It is the default when GCC is configured, explicitly or
10562 implicitly, with the HP linker. This option does not have any affect on
10563 which ld is called, it only changes what parameters are passed to that
10564 ld. The ld that is called is determined by the @option{--with-ld}
10565 configure option, GCC's program search path, and finally by the user's
10566 @env{PATH}. The linker used by GCC can be printed using @samp{which
10567 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
10568 HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
10571 @opindex mno-long-calls
10572 Generate code that uses long call sequences. This ensures that a call
10573 is always able to reach linker generated stubs. The default is to generate
10574 long calls only when the distance from the call site to the beginning
10575 of the function or translation unit, as the case may be, exceeds a
10576 predefined limit set by the branch type being used. The limits for
10577 normal calls are 7,600,000 and 240,000 bytes, respectively for the
10578 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
10581 Distances are measured from the beginning of functions when using the
10582 @option{-ffunction-sections} option, or when using the @option{-mgas}
10583 and @option{-mno-portable-runtime} options together under HP-UX with
10586 It is normally not desirable to use this option as it will degrade
10587 performance. However, it may be useful in large applications,
10588 particularly when partial linking is used to build the application.
10590 The types of long calls used depends on the capabilities of the
10591 assembler and linker, and the type of code being generated. The
10592 impact on systems that support long absolute calls, and long pic
10593 symbol-difference or pc-relative calls should be relatively small.
10594 However, an indirect call is used on 32-bit ELF systems in pic code
10595 and it is quite long.
10597 @item -munix=@var{unix-std}
10599 Generate compiler predefines and select a startfile for the specified
10600 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
10601 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
10602 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
10603 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
10604 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
10607 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
10608 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
10609 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
10610 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
10611 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
10612 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
10614 It is @emph{important} to note that this option changes the interfaces
10615 for various library routines. It also affects the operational behavior
10616 of the C library. Thus, @emph{extreme} care is needed in using this
10619 Library code that is intended to operate with more than one UNIX
10620 standard must test, set and restore the variable @var{__xpg4_extended_mask}
10621 as appropriate. Most GNU software doesn't provide this capability.
10625 Suppress the generation of link options to search libdld.sl when the
10626 @option{-static} option is specified on HP-UX 10 and later.
10630 The HP-UX implementation of setlocale in libc has a dependency on
10631 libdld.sl. There isn't an archive version of libdld.sl. Thus,
10632 when the @option{-static} option is specified, special link options
10633 are needed to resolve this dependency.
10635 On HP-UX 10 and later, the GCC driver adds the necessary options to
10636 link with libdld.sl when the @option{-static} option is specified.
10637 This causes the resulting binary to be dynamic. On the 64-bit port,
10638 the linkers generate dynamic binaries by default in any case. The
10639 @option{-nolibdld} option can be used to prevent the GCC driver from
10640 adding these link options.
10644 Add support for multithreading with the @dfn{dce thread} library
10645 under HP-UX@. This option sets flags for both the preprocessor and
10649 @node i386 and x86-64 Options
10650 @subsection Intel 386 and AMD x86-64 Options
10651 @cindex i386 Options
10652 @cindex x86-64 Options
10653 @cindex Intel 386 Options
10654 @cindex AMD x86-64 Options
10656 These @samp{-m} options are defined for the i386 and x86-64 family of
10660 @item -mtune=@var{cpu-type}
10662 Tune to @var{cpu-type} everything applicable about the generated code, except
10663 for the ABI and the set of available instructions. The choices for
10664 @var{cpu-type} are:
10667 Produce code optimized for the most common IA32/AMD64/EM64T processors.
10668 If you know the CPU on which your code will run, then you should use
10669 the corresponding @option{-mtune} option instead of
10670 @option{-mtune=generic}. But, if you do not know exactly what CPU users
10671 of your application will have, then you should use this option.
10673 As new processors are deployed in the marketplace, the behavior of this
10674 option will change. Therefore, if you upgrade to a newer version of
10675 GCC, the code generated option will change to reflect the processors
10676 that were most common when that version of GCC was released.
10678 There is no @option{-march=generic} option because @option{-march}
10679 indicates the instruction set the compiler can use, and there is no
10680 generic instruction set applicable to all processors. In contrast,
10681 @option{-mtune} indicates the processor (or, in this case, collection of
10682 processors) for which the code is optimized.
10684 This selects the CPU to tune for at compilation time by determining
10685 the processor type of the compiling machine. Using @option{-mtune=native}
10686 will produce code optimized for the local machine under the constraints
10687 of the selected instruction set. Using @option{-march=native} will
10688 enable all instruction subsets supported by the local machine (hence
10689 the result might not run on different machines).
10691 Original Intel's i386 CPU@.
10693 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
10694 @item i586, pentium
10695 Intel Pentium CPU with no MMX support.
10697 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
10699 Intel PentiumPro CPU@.
10701 Same as @code{generic}, but when used as @code{march} option, PentiumPro
10702 instruction set will be used, so the code will run on all i686 family chips.
10704 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10705 @item pentium3, pentium3m
10706 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10709 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10710 support. Used by Centrino notebooks.
10711 @item pentium4, pentium4m
10712 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10714 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10717 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10718 SSE2 and SSE3 instruction set support.
10720 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10721 instruction set support.
10723 AMD K6 CPU with MMX instruction set support.
10725 Improved versions of AMD K6 CPU with MMX and 3dNOW!@: instruction set support.
10726 @item athlon, athlon-tbird
10727 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and SSE prefetch instructions
10729 @item athlon-4, athlon-xp, athlon-mp
10730 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW!@: and full SSE
10731 instruction set support.
10732 @item k8, opteron, athlon64, athlon-fx
10733 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10734 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW!@: and 64-bit instruction set extensions.)
10735 @item k8-sse3, opteron-sse3, athlon64-sse3
10736 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10737 @item amdfam10, barcelona
10738 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10739 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10740 instruction set extensions.)
10742 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10745 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!@:
10746 instruction set support.
10748 Via C3 CPU with MMX and 3dNOW!@: instruction set support. (No scheduling is
10749 implemented for this chip.)
10751 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10752 implemented for this chip.)
10754 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10757 While picking a specific @var{cpu-type} will schedule things appropriately
10758 for that particular chip, the compiler will not generate any code that
10759 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10762 @item -march=@var{cpu-type}
10764 Generate instructions for the machine type @var{cpu-type}. The choices
10765 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10766 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10768 @item -mcpu=@var{cpu-type}
10770 A deprecated synonym for @option{-mtune}.
10772 @item -mfpmath=@var{unit}
10774 Generate floating point arithmetics for selected unit @var{unit}. The choices
10775 for @var{unit} are:
10779 Use the standard 387 floating point coprocessor present majority of chips and
10780 emulated otherwise. Code compiled with this option will run almost everywhere.
10781 The temporary results are computed in 80bit precision instead of precision
10782 specified by the type resulting in slightly different results compared to most
10783 of other chips. See @option{-ffloat-store} for more detailed description.
10785 This is the default choice for i386 compiler.
10788 Use scalar floating point instructions present in the SSE instruction set.
10789 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10790 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10791 instruction set supports only single precision arithmetics, thus the double and
10792 extended precision arithmetics is still done using 387. Later version, present
10793 only in Pentium4 and the future AMD x86-64 chips supports double precision
10796 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10797 or @option{-msse2} switches to enable SSE extensions and make this option
10798 effective. For the x86-64 compiler, these extensions are enabled by default.
10800 The resulting code should be considerably faster in the majority of cases and avoid
10801 the numerical instability problems of 387 code, but may break some existing
10802 code that expects temporaries to be 80bit.
10804 This is the default choice for the x86-64 compiler.
10809 Attempt to utilize both instruction sets at once. This effectively double the
10810 amount of available registers and on chips with separate execution units for
10811 387 and SSE the execution resources too. Use this option with care, as it is
10812 still experimental, because the GCC register allocator does not model separate
10813 functional units well resulting in instable performance.
10816 @item -masm=@var{dialect}
10817 @opindex masm=@var{dialect}
10818 Output asm instructions using selected @var{dialect}. Supported
10819 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10820 not support @samp{intel}.
10823 @itemx -mno-ieee-fp
10825 @opindex mno-ieee-fp
10826 Control whether or not the compiler uses IEEE floating point
10827 comparisons. These handle correctly the case where the result of a
10828 comparison is unordered.
10831 @opindex msoft-float
10832 Generate output containing library calls for floating point.
10833 @strong{Warning:} the requisite libraries are not part of GCC@.
10834 Normally the facilities of the machine's usual C compiler are used, but
10835 this can't be done directly in cross-compilation. You must make your
10836 own arrangements to provide suitable library functions for
10839 On machines where a function returns floating point results in the 80387
10840 register stack, some floating point opcodes may be emitted even if
10841 @option{-msoft-float} is used.
10843 @item -mno-fp-ret-in-387
10844 @opindex mno-fp-ret-in-387
10845 Do not use the FPU registers for return values of functions.
10847 The usual calling convention has functions return values of types
10848 @code{float} and @code{double} in an FPU register, even if there
10849 is no FPU@. The idea is that the operating system should emulate
10852 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10853 in ordinary CPU registers instead.
10855 @item -mno-fancy-math-387
10856 @opindex mno-fancy-math-387
10857 Some 387 emulators do not support the @code{sin}, @code{cos} and
10858 @code{sqrt} instructions for the 387. Specify this option to avoid
10859 generating those instructions. This option is the default on FreeBSD,
10860 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10861 indicates that the target cpu will always have an FPU and so the
10862 instruction will not need emulation. As of revision 2.6.1, these
10863 instructions are not generated unless you also use the
10864 @option{-funsafe-math-optimizations} switch.
10866 @item -malign-double
10867 @itemx -mno-align-double
10868 @opindex malign-double
10869 @opindex mno-align-double
10870 Control whether GCC aligns @code{double}, @code{long double}, and
10871 @code{long long} variables on a two word boundary or a one word
10872 boundary. Aligning @code{double} variables on a two word boundary will
10873 produce code that runs somewhat faster on a @samp{Pentium} at the
10874 expense of more memory.
10876 On x86-64, @option{-malign-double} is enabled by default.
10878 @strong{Warning:} if you use the @option{-malign-double} switch,
10879 structures containing the above types will be aligned differently than
10880 the published application binary interface specifications for the 386
10881 and will not be binary compatible with structures in code compiled
10882 without that switch.
10884 @item -m96bit-long-double
10885 @itemx -m128bit-long-double
10886 @opindex m96bit-long-double
10887 @opindex m128bit-long-double
10888 These switches control the size of @code{long double} type. The i386
10889 application binary interface specifies the size to be 96 bits,
10890 so @option{-m96bit-long-double} is the default in 32 bit mode.
10892 Modern architectures (Pentium and newer) would prefer @code{long double}
10893 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10894 conforming to the ABI, this would not be possible. So specifying a
10895 @option{-m128bit-long-double} will align @code{long double}
10896 to a 16 byte boundary by padding the @code{long double} with an additional
10899 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10900 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10902 Notice that neither of these options enable any extra precision over the x87
10903 standard of 80 bits for a @code{long double}.
10905 @strong{Warning:} if you override the default value for your target ABI, the
10906 structures and arrays containing @code{long double} variables will change
10907 their size as well as function calling convention for function taking
10908 @code{long double} will be modified. Hence they will not be binary
10909 compatible with arrays or structures in code compiled without that switch.
10911 @item -mlarge-data-threshold=@var{number}
10912 @opindex mlarge-data-threshold=@var{number}
10913 When @option{-mcmodel=medium} is specified, the data greater than
10914 @var{threshold} are placed in large data section. This value must be the
10915 same across all object linked into the binary and defaults to 65535.
10919 Use a different function-calling convention, in which functions that
10920 take a fixed number of arguments return with the @code{ret} @var{num}
10921 instruction, which pops their arguments while returning. This saves one
10922 instruction in the caller since there is no need to pop the arguments
10925 You can specify that an individual function is called with this calling
10926 sequence with the function attribute @samp{stdcall}. You can also
10927 override the @option{-mrtd} option by using the function attribute
10928 @samp{cdecl}. @xref{Function Attributes}.
10930 @strong{Warning:} this calling convention is incompatible with the one
10931 normally used on Unix, so you cannot use it if you need to call
10932 libraries compiled with the Unix compiler.
10934 Also, you must provide function prototypes for all functions that
10935 take variable numbers of arguments (including @code{printf});
10936 otherwise incorrect code will be generated for calls to those
10939 In addition, seriously incorrect code will result if you call a
10940 function with too many arguments. (Normally, extra arguments are
10941 harmlessly ignored.)
10943 @item -mregparm=@var{num}
10945 Control how many registers are used to pass integer arguments. By
10946 default, no registers are used to pass arguments, and at most 3
10947 registers can be used. You can control this behavior for a specific
10948 function by using the function attribute @samp{regparm}.
10949 @xref{Function Attributes}.
10951 @strong{Warning:} if you use this switch, and
10952 @var{num} is nonzero, then you must build all modules with the same
10953 value, including any libraries. This includes the system libraries and
10957 @opindex msseregparm
10958 Use SSE register passing conventions for float and double arguments
10959 and return values. You can control this behavior for a specific
10960 function by using the function attribute @samp{sseregparm}.
10961 @xref{Function Attributes}.
10963 @strong{Warning:} if you use this switch then you must build all
10964 modules with the same value, including any libraries. This includes
10965 the system libraries and startup modules.
10974 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
10975 is specified, the significands of results of floating-point operations are
10976 rounded to 24 bits (single precision); @option{-mpc64} rounds the
10977 significands of results of floating-point operations to 53 bits (double
10978 precision) and @option{-mpc80} rounds the significands of results of
10979 floating-point operations to 64 bits (extended double precision), which is
10980 the default. When this option is used, floating-point operations in higher
10981 precisions are not available to the programmer without setting the FPU
10982 control word explicitly.
10984 Setting the rounding of floating-point operations to less than the default
10985 80 bits can speed some programs by 2% or more. Note that some mathematical
10986 libraries assume that extended precision (80 bit) floating-point operations
10987 are enabled by default; routines in such libraries could suffer significant
10988 loss of accuracy, typically through so-called "catastrophic cancellation",
10989 when this option is used to set the precision to less than extended precision.
10991 @item -mstackrealign
10992 @opindex mstackrealign
10993 Realign the stack at entry. On the Intel x86, the @option{-mstackrealign}
10994 option will generate an alternate prologue and epilogue that realigns the
10995 runtime stack if necessary. This supports mixing legacy codes that keep
10996 a 4-byte aligned stack with modern codes that keep a 16-byte stack for
10997 SSE compatibility. See also the attribute @code{force_align_arg_pointer},
10998 applicable to individual functions.
11000 @item -mpreferred-stack-boundary=@var{num}
11001 @opindex mpreferred-stack-boundary
11002 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
11003 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
11004 the default is 4 (16 bytes or 128 bits).
11006 @item -mincoming-stack-boundary=@var{num}
11007 @opindex mincoming-stack-boundary
11008 Assume the incoming stack is aligned to a 2 raised to @var{num} byte
11009 boundary. If @option{-mincoming-stack-boundary} is not specified,
11010 the one specified by @option{-mpreferred-stack-boundary} will be used.
11012 On Pentium and PentiumPro, @code{double} and @code{long double} values
11013 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
11014 suffer significant run time performance penalties. On Pentium III, the
11015 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
11016 properly if it is not 16 byte aligned.
11018 To ensure proper alignment of this values on the stack, the stack boundary
11019 must be as aligned as that required by any value stored on the stack.
11020 Further, every function must be generated such that it keeps the stack
11021 aligned. Thus calling a function compiled with a higher preferred
11022 stack boundary from a function compiled with a lower preferred stack
11023 boundary will most likely misalign the stack. It is recommended that
11024 libraries that use callbacks always use the default setting.
11026 This extra alignment does consume extra stack space, and generally
11027 increases code size. Code that is sensitive to stack space usage, such
11028 as embedded systems and operating system kernels, may want to reduce the
11029 preferred alignment to @option{-mpreferred-stack-boundary=2}.
11069 These switches enable or disable the use of instructions in the MMX,
11070 SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, SSE4A, SSE5, ABM or
11071 3DNow!@: extended instruction sets.
11072 These extensions are also available as built-in functions: see
11073 @ref{X86 Built-in Functions}, for details of the functions enabled and
11074 disabled by these switches.
11076 To have SSE/SSE2 instructions generated automatically from floating-point
11077 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
11079 GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
11080 generates new AVX instructions or AVX equivalence for all SSEx instructions
11083 These options will enable GCC to use these extended instructions in
11084 generated code, even without @option{-mfpmath=sse}. Applications which
11085 perform runtime CPU detection must compile separate files for each
11086 supported architecture, using the appropriate flags. In particular,
11087 the file containing the CPU detection code should be compiled without
11092 This option instructs GCC to emit a @code{cld} instruction in the prologue
11093 of functions that use string instructions. String instructions depend on
11094 the DF flag to select between autoincrement or autodecrement mode. While the
11095 ABI specifies the DF flag to be cleared on function entry, some operating
11096 systems violate this specification by not clearing the DF flag in their
11097 exception dispatchers. The exception handler can be invoked with the DF flag
11098 set which leads to wrong direction mode, when string instructions are used.
11099 This option can be enabled by default on 32-bit x86 targets by configuring
11100 GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
11101 instructions can be suppressed with the @option{-mno-cld} compiler option
11106 This option will enable GCC to use CMPXCHG16B instruction in generated code.
11107 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
11108 data types. This is useful for high resolution counters that could be updated
11109 by multiple processors (or cores). This instruction is generated as part of
11110 atomic built-in functions: see @ref{Atomic Builtins} for details.
11114 This option will enable GCC to use SAHF instruction in generated 64-bit code.
11115 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
11116 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
11117 SAHF are load and store instructions, respectively, for certain status flags.
11118 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
11119 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
11123 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
11124 vectorized variants RCPPS and RSQRTPS) with an additional Newton-Rhapson step
11125 to increase precision instead of DIVSS and SQRTSS (and their vectorized
11126 variants) for single precision floating point arguments. These instructions
11127 are generated only when @option{-funsafe-math-optimizations} is enabled
11128 together with @option{-finite-math-only} and @option{-fno-trapping-math}.
11129 Note that while the throughput of the sequence is higher than the throughput
11130 of the non-reciprocal instruction, the precision of the sequence can be
11131 decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
11133 @item -mveclibabi=@var{type}
11134 @opindex mveclibabi
11135 Specifies the ABI type to use for vectorizing intrinsics using an
11136 external library. Supported types are @code{svml} for the Intel short
11137 vector math library and @code{acml} for the AMD math core library style
11138 of interfacing. GCC will currently emit calls to @code{vmldExp2},
11139 @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
11140 @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
11141 @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
11142 @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
11143 @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
11144 @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
11145 @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
11146 @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
11147 @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
11148 function type when @option{-mveclibabi=svml} is used and @code{__vrd2_sin},
11149 @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
11150 @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
11151 @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
11152 @code{__vrs4_log10f} and @code{__vrs4_powf} for corresponding function type
11153 when @option{-mveclibabi=acml} is used. Both @option{-ftree-vectorize} and
11154 @option{-funsafe-math-optimizations} have to be enabled. A SVML or ACML ABI
11155 compatible library will have to be specified at link time.
11158 @itemx -mno-push-args
11159 @opindex mpush-args
11160 @opindex mno-push-args
11161 Use PUSH operations to store outgoing parameters. This method is shorter
11162 and usually equally fast as method using SUB/MOV operations and is enabled
11163 by default. In some cases disabling it may improve performance because of
11164 improved scheduling and reduced dependencies.
11166 @item -maccumulate-outgoing-args
11167 @opindex maccumulate-outgoing-args
11168 If enabled, the maximum amount of space required for outgoing arguments will be
11169 computed in the function prologue. This is faster on most modern CPUs
11170 because of reduced dependencies, improved scheduling and reduced stack usage
11171 when preferred stack boundary is not equal to 2. The drawback is a notable
11172 increase in code size. This switch implies @option{-mno-push-args}.
11176 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
11177 on thread-safe exception handling must compile and link all code with the
11178 @option{-mthreads} option. When compiling, @option{-mthreads} defines
11179 @option{-D_MT}; when linking, it links in a special thread helper library
11180 @option{-lmingwthrd} which cleans up per thread exception handling data.
11182 @item -mno-align-stringops
11183 @opindex mno-align-stringops
11184 Do not align destination of inlined string operations. This switch reduces
11185 code size and improves performance in case the destination is already aligned,
11186 but GCC doesn't know about it.
11188 @item -minline-all-stringops
11189 @opindex minline-all-stringops
11190 By default GCC inlines string operations only when destination is known to be
11191 aligned at least to 4 byte boundary. This enables more inlining, increase code
11192 size, but may improve performance of code that depends on fast memcpy, strlen
11193 and memset for short lengths.
11195 @item -minline-stringops-dynamically
11196 @opindex minline-stringops-dynamically
11197 For string operation of unknown size, inline runtime checks so for small
11198 blocks inline code is used, while for large blocks library call is used.
11200 @item -mstringop-strategy=@var{alg}
11201 @opindex mstringop-strategy=@var{alg}
11202 Overwrite internal decision heuristic about particular algorithm to inline
11203 string operation with. The allowed values are @code{rep_byte},
11204 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
11205 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
11206 expanding inline loop, @code{libcall} for always expanding library call.
11208 @item -momit-leaf-frame-pointer
11209 @opindex momit-leaf-frame-pointer
11210 Don't keep the frame pointer in a register for leaf functions. This
11211 avoids the instructions to save, set up and restore frame pointers and
11212 makes an extra register available in leaf functions. The option
11213 @option{-fomit-frame-pointer} removes the frame pointer for all functions
11214 which might make debugging harder.
11216 @item -mtls-direct-seg-refs
11217 @itemx -mno-tls-direct-seg-refs
11218 @opindex mtls-direct-seg-refs
11219 Controls whether TLS variables may be accessed with offsets from the
11220 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
11221 or whether the thread base pointer must be added. Whether or not this
11222 is legal depends on the operating system, and whether it maps the
11223 segment to cover the entire TLS area.
11225 For systems that use GNU libc, the default is on.
11228 @itemx -mno-fused-madd
11229 @opindex mfused-madd
11230 Enable automatic generation of fused floating point multiply-add instructions
11231 if the ISA supports such instructions. The -mfused-madd option is on by
11232 default. The fused multiply-add instructions have a different
11233 rounding behavior compared to executing a multiply followed by an add.
11236 @itemx -mno-sse2avx
11238 Specify that the assembler should encode SSE instructions with VEX
11239 prefix. The option @option{-mavx} turns this on by default.
11242 These @samp{-m} switches are supported in addition to the above
11243 on AMD x86-64 processors in 64-bit environments.
11250 Generate code for a 32-bit or 64-bit environment.
11251 The 32-bit environment sets int, long and pointer to 32 bits and
11252 generates code that runs on any i386 system.
11253 The 64-bit environment sets int to 32 bits and long and pointer
11254 to 64 bits and generates code for AMD's x86-64 architecture. For
11255 darwin only the -m64 option turns off the @option{-fno-pic} and
11256 @option{-mdynamic-no-pic} options.
11258 @item -mno-red-zone
11259 @opindex no-red-zone
11260 Do not use a so called red zone for x86-64 code. The red zone is mandated
11261 by the x86-64 ABI, it is a 128-byte area beyond the location of the
11262 stack pointer that will not be modified by signal or interrupt handlers
11263 and therefore can be used for temporary data without adjusting the stack
11264 pointer. The flag @option{-mno-red-zone} disables this red zone.
11266 @item -mcmodel=small
11267 @opindex mcmodel=small
11268 Generate code for the small code model: the program and its symbols must
11269 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
11270 Programs can be statically or dynamically linked. This is the default
11273 @item -mcmodel=kernel
11274 @opindex mcmodel=kernel
11275 Generate code for the kernel code model. The kernel runs in the
11276 negative 2 GB of the address space.
11277 This model has to be used for Linux kernel code.
11279 @item -mcmodel=medium
11280 @opindex mcmodel=medium
11281 Generate code for the medium model: The program is linked in the lower 2
11282 GB of the address space and symbols with small size as well. Symbols
11283 with sizes larger than @option{-mlarge-data-threshold} are put into
11284 large data or bss sections and can be located above 2GB. Programs can
11285 be statically or dynamically linked.
11287 @item -mcmodel=large
11288 @opindex mcmodel=large
11289 Generate code for the large model: This model makes no assumptions
11290 about addresses and sizes of sections.
11293 @node IA-64 Options
11294 @subsection IA-64 Options
11295 @cindex IA-64 Options
11297 These are the @samp{-m} options defined for the Intel IA-64 architecture.
11301 @opindex mbig-endian
11302 Generate code for a big endian target. This is the default for HP-UX@.
11304 @item -mlittle-endian
11305 @opindex mlittle-endian
11306 Generate code for a little endian target. This is the default for AIX5
11312 @opindex mno-gnu-as
11313 Generate (or don't) code for the GNU assembler. This is the default.
11314 @c Also, this is the default if the configure option @option{--with-gnu-as}
11320 @opindex mno-gnu-ld
11321 Generate (or don't) code for the GNU linker. This is the default.
11322 @c Also, this is the default if the configure option @option{--with-gnu-ld}
11327 Generate code that does not use a global pointer register. The result
11328 is not position independent code, and violates the IA-64 ABI@.
11330 @item -mvolatile-asm-stop
11331 @itemx -mno-volatile-asm-stop
11332 @opindex mvolatile-asm-stop
11333 @opindex mno-volatile-asm-stop
11334 Generate (or don't) a stop bit immediately before and after volatile asm
11337 @item -mregister-names
11338 @itemx -mno-register-names
11339 @opindex mregister-names
11340 @opindex mno-register-names
11341 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
11342 the stacked registers. This may make assembler output more readable.
11348 Disable (or enable) optimizations that use the small data section. This may
11349 be useful for working around optimizer bugs.
11351 @item -mconstant-gp
11352 @opindex mconstant-gp
11353 Generate code that uses a single constant global pointer value. This is
11354 useful when compiling kernel code.
11358 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
11359 This is useful when compiling firmware code.
11361 @item -minline-float-divide-min-latency
11362 @opindex minline-float-divide-min-latency
11363 Generate code for inline divides of floating point values
11364 using the minimum latency algorithm.
11366 @item -minline-float-divide-max-throughput
11367 @opindex minline-float-divide-max-throughput
11368 Generate code for inline divides of floating point values
11369 using the maximum throughput algorithm.
11371 @item -minline-int-divide-min-latency
11372 @opindex minline-int-divide-min-latency
11373 Generate code for inline divides of integer values
11374 using the minimum latency algorithm.
11376 @item -minline-int-divide-max-throughput
11377 @opindex minline-int-divide-max-throughput
11378 Generate code for inline divides of integer values
11379 using the maximum throughput algorithm.
11381 @item -minline-sqrt-min-latency
11382 @opindex minline-sqrt-min-latency
11383 Generate code for inline square roots
11384 using the minimum latency algorithm.
11386 @item -minline-sqrt-max-throughput
11387 @opindex minline-sqrt-max-throughput
11388 Generate code for inline square roots
11389 using the maximum throughput algorithm.
11391 @item -mno-dwarf2-asm
11392 @itemx -mdwarf2-asm
11393 @opindex mno-dwarf2-asm
11394 @opindex mdwarf2-asm
11395 Don't (or do) generate assembler code for the DWARF2 line number debugging
11396 info. This may be useful when not using the GNU assembler.
11398 @item -mearly-stop-bits
11399 @itemx -mno-early-stop-bits
11400 @opindex mearly-stop-bits
11401 @opindex mno-early-stop-bits
11402 Allow stop bits to be placed earlier than immediately preceding the
11403 instruction that triggered the stop bit. This can improve instruction
11404 scheduling, but does not always do so.
11406 @item -mfixed-range=@var{register-range}
11407 @opindex mfixed-range
11408 Generate code treating the given register range as fixed registers.
11409 A fixed register is one that the register allocator can not use. This is
11410 useful when compiling kernel code. A register range is specified as
11411 two registers separated by a dash. Multiple register ranges can be
11412 specified separated by a comma.
11414 @item -mtls-size=@var{tls-size}
11416 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
11419 @item -mtune=@var{cpu-type}
11421 Tune the instruction scheduling for a particular CPU, Valid values are
11422 itanium, itanium1, merced, itanium2, and mckinley.
11428 Add support for multithreading using the POSIX threads library. This
11429 option sets flags for both the preprocessor and linker. It does
11430 not affect the thread safety of object code produced by the compiler or
11431 that of libraries supplied with it. These are HP-UX specific flags.
11437 Generate code for a 32-bit or 64-bit environment.
11438 The 32-bit environment sets int, long and pointer to 32 bits.
11439 The 64-bit environment sets int to 32 bits and long and pointer
11440 to 64 bits. These are HP-UX specific flags.
11442 @item -mno-sched-br-data-spec
11443 @itemx -msched-br-data-spec
11444 @opindex mno-sched-br-data-spec
11445 @opindex msched-br-data-spec
11446 (Dis/En)able data speculative scheduling before reload.
11447 This will result in generation of the ld.a instructions and
11448 the corresponding check instructions (ld.c / chk.a).
11449 The default is 'disable'.
11451 @item -msched-ar-data-spec
11452 @itemx -mno-sched-ar-data-spec
11453 @opindex msched-ar-data-spec
11454 @opindex mno-sched-ar-data-spec
11455 (En/Dis)able data speculative scheduling after reload.
11456 This will result in generation of the ld.a instructions and
11457 the corresponding check instructions (ld.c / chk.a).
11458 The default is 'enable'.
11460 @item -mno-sched-control-spec
11461 @itemx -msched-control-spec
11462 @opindex mno-sched-control-spec
11463 @opindex msched-control-spec
11464 (Dis/En)able control speculative scheduling. This feature is
11465 available only during region scheduling (i.e.@: before reload).
11466 This will result in generation of the ld.s instructions and
11467 the corresponding check instructions chk.s .
11468 The default is 'disable'.
11470 @item -msched-br-in-data-spec
11471 @itemx -mno-sched-br-in-data-spec
11472 @opindex msched-br-in-data-spec
11473 @opindex mno-sched-br-in-data-spec
11474 (En/Dis)able speculative scheduling of the instructions that
11475 are dependent on the data speculative loads before reload.
11476 This is effective only with @option{-msched-br-data-spec} enabled.
11477 The default is 'enable'.
11479 @item -msched-ar-in-data-spec
11480 @itemx -mno-sched-ar-in-data-spec
11481 @opindex msched-ar-in-data-spec
11482 @opindex mno-sched-ar-in-data-spec
11483 (En/Dis)able speculative scheduling of the instructions that
11484 are dependent on the data speculative loads after reload.
11485 This is effective only with @option{-msched-ar-data-spec} enabled.
11486 The default is 'enable'.
11488 @item -msched-in-control-spec
11489 @itemx -mno-sched-in-control-spec
11490 @opindex msched-in-control-spec
11491 @opindex mno-sched-in-control-spec
11492 (En/Dis)able speculative scheduling of the instructions that
11493 are dependent on the control speculative loads.
11494 This is effective only with @option{-msched-control-spec} enabled.
11495 The default is 'enable'.
11498 @itemx -mno-sched-ldc
11499 @opindex msched-ldc
11500 @opindex mno-sched-ldc
11501 (En/Dis)able use of simple data speculation checks ld.c .
11502 If disabled, only chk.a instructions will be emitted to check
11503 data speculative loads.
11504 The default is 'enable'.
11506 @item -mno-sched-control-ldc
11507 @itemx -msched-control-ldc
11508 @opindex mno-sched-control-ldc
11509 @opindex msched-control-ldc
11510 (Dis/En)able use of ld.c instructions to check control speculative loads.
11511 If enabled, in case of control speculative load with no speculatively
11512 scheduled dependent instructions this load will be emitted as ld.sa and
11513 ld.c will be used to check it.
11514 The default is 'disable'.
11516 @item -mno-sched-spec-verbose
11517 @itemx -msched-spec-verbose
11518 @opindex mno-sched-spec-verbose
11519 @opindex msched-spec-verbose
11520 (Dis/En)able printing of the information about speculative motions.
11522 @item -mno-sched-prefer-non-data-spec-insns
11523 @itemx -msched-prefer-non-data-spec-insns
11524 @opindex mno-sched-prefer-non-data-spec-insns
11525 @opindex msched-prefer-non-data-spec-insns
11526 If enabled, data speculative instructions will be chosen for schedule
11527 only if there are no other choices at the moment. This will make
11528 the use of the data speculation much more conservative.
11529 The default is 'disable'.
11531 @item -mno-sched-prefer-non-control-spec-insns
11532 @itemx -msched-prefer-non-control-spec-insns
11533 @opindex mno-sched-prefer-non-control-spec-insns
11534 @opindex msched-prefer-non-control-spec-insns
11535 If enabled, control speculative instructions will be chosen for schedule
11536 only if there are no other choices at the moment. This will make
11537 the use of the control speculation much more conservative.
11538 The default is 'disable'.
11540 @item -mno-sched-count-spec-in-critical-path
11541 @itemx -msched-count-spec-in-critical-path
11542 @opindex mno-sched-count-spec-in-critical-path
11543 @opindex msched-count-spec-in-critical-path
11544 If enabled, speculative dependencies will be considered during
11545 computation of the instructions priorities. This will make the use of the
11546 speculation a bit more conservative.
11547 The default is 'disable'.
11552 @subsection M32C Options
11553 @cindex M32C options
11556 @item -mcpu=@var{name}
11558 Select the CPU for which code is generated. @var{name} may be one of
11559 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
11560 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
11561 the M32C/80 series.
11565 Specifies that the program will be run on the simulator. This causes
11566 an alternate runtime library to be linked in which supports, for
11567 example, file I/O@. You must not use this option when generating
11568 programs that will run on real hardware; you must provide your own
11569 runtime library for whatever I/O functions are needed.
11571 @item -memregs=@var{number}
11573 Specifies the number of memory-based pseudo-registers GCC will use
11574 during code generation. These pseudo-registers will be used like real
11575 registers, so there is a tradeoff between GCC's ability to fit the
11576 code into available registers, and the performance penalty of using
11577 memory instead of registers. Note that all modules in a program must
11578 be compiled with the same value for this option. Because of that, you
11579 must not use this option with the default runtime libraries gcc
11584 @node M32R/D Options
11585 @subsection M32R/D Options
11586 @cindex M32R/D options
11588 These @option{-m} options are defined for Renesas M32R/D architectures:
11593 Generate code for the M32R/2@.
11597 Generate code for the M32R/X@.
11601 Generate code for the M32R@. This is the default.
11603 @item -mmodel=small
11604 @opindex mmodel=small
11605 Assume all objects live in the lower 16MB of memory (so that their addresses
11606 can be loaded with the @code{ld24} instruction), and assume all subroutines
11607 are reachable with the @code{bl} instruction.
11608 This is the default.
11610 The addressability of a particular object can be set with the
11611 @code{model} attribute.
11613 @item -mmodel=medium
11614 @opindex mmodel=medium
11615 Assume objects may be anywhere in the 32-bit address space (the compiler
11616 will generate @code{seth/add3} instructions to load their addresses), and
11617 assume all subroutines are reachable with the @code{bl} instruction.
11619 @item -mmodel=large
11620 @opindex mmodel=large
11621 Assume objects may be anywhere in the 32-bit address space (the compiler
11622 will generate @code{seth/add3} instructions to load their addresses), and
11623 assume subroutines may not be reachable with the @code{bl} instruction
11624 (the compiler will generate the much slower @code{seth/add3/jl}
11625 instruction sequence).
11628 @opindex msdata=none
11629 Disable use of the small data area. Variables will be put into
11630 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
11631 @code{section} attribute has been specified).
11632 This is the default.
11634 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
11635 Objects may be explicitly put in the small data area with the
11636 @code{section} attribute using one of these sections.
11638 @item -msdata=sdata
11639 @opindex msdata=sdata
11640 Put small global and static data in the small data area, but do not
11641 generate special code to reference them.
11644 @opindex msdata=use
11645 Put small global and static data in the small data area, and generate
11646 special instructions to reference them.
11650 @cindex smaller data references
11651 Put global and static objects less than or equal to @var{num} bytes
11652 into the small data or bss sections instead of the normal data or bss
11653 sections. The default value of @var{num} is 8.
11654 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
11655 for this option to have any effect.
11657 All modules should be compiled with the same @option{-G @var{num}} value.
11658 Compiling with different values of @var{num} may or may not work; if it
11659 doesn't the linker will give an error message---incorrect code will not be
11664 Makes the M32R specific code in the compiler display some statistics
11665 that might help in debugging programs.
11667 @item -malign-loops
11668 @opindex malign-loops
11669 Align all loops to a 32-byte boundary.
11671 @item -mno-align-loops
11672 @opindex mno-align-loops
11673 Do not enforce a 32-byte alignment for loops. This is the default.
11675 @item -missue-rate=@var{number}
11676 @opindex missue-rate=@var{number}
11677 Issue @var{number} instructions per cycle. @var{number} can only be 1
11680 @item -mbranch-cost=@var{number}
11681 @opindex mbranch-cost=@var{number}
11682 @var{number} can only be 1 or 2. If it is 1 then branches will be
11683 preferred over conditional code, if it is 2, then the opposite will
11686 @item -mflush-trap=@var{number}
11687 @opindex mflush-trap=@var{number}
11688 Specifies the trap number to use to flush the cache. The default is
11689 12. Valid numbers are between 0 and 15 inclusive.
11691 @item -mno-flush-trap
11692 @opindex mno-flush-trap
11693 Specifies that the cache cannot be flushed by using a trap.
11695 @item -mflush-func=@var{name}
11696 @opindex mflush-func=@var{name}
11697 Specifies the name of the operating system function to call to flush
11698 the cache. The default is @emph{_flush_cache}, but a function call
11699 will only be used if a trap is not available.
11701 @item -mno-flush-func
11702 @opindex mno-flush-func
11703 Indicates that there is no OS function for flushing the cache.
11707 @node M680x0 Options
11708 @subsection M680x0 Options
11709 @cindex M680x0 options
11711 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
11712 The default settings depend on which architecture was selected when
11713 the compiler was configured; the defaults for the most common choices
11717 @item -march=@var{arch}
11719 Generate code for a specific M680x0 or ColdFire instruction set
11720 architecture. Permissible values of @var{arch} for M680x0
11721 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
11722 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
11723 architectures are selected according to Freescale's ISA classification
11724 and the permissible values are: @samp{isaa}, @samp{isaaplus},
11725 @samp{isab} and @samp{isac}.
11727 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
11728 code for a ColdFire target. The @var{arch} in this macro is one of the
11729 @option{-march} arguments given above.
11731 When used together, @option{-march} and @option{-mtune} select code
11732 that runs on a family of similar processors but that is optimized
11733 for a particular microarchitecture.
11735 @item -mcpu=@var{cpu}
11737 Generate code for a specific M680x0 or ColdFire processor.
11738 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
11739 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
11740 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
11741 below, which also classifies the CPUs into families:
11743 @multitable @columnfractions 0.20 0.80
11744 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
11745 @item @samp{51qe} @tab @samp{51qe}
11746 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
11747 @item @samp{5206e} @tab @samp{5206e}
11748 @item @samp{5208} @tab @samp{5207} @samp{5208}
11749 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
11750 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
11751 @item @samp{5216} @tab @samp{5214} @samp{5216}
11752 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
11753 @item @samp{5225} @tab @samp{5224} @samp{5225}
11754 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
11755 @item @samp{5249} @tab @samp{5249}
11756 @item @samp{5250} @tab @samp{5250}
11757 @item @samp{5271} @tab @samp{5270} @samp{5271}
11758 @item @samp{5272} @tab @samp{5272}
11759 @item @samp{5275} @tab @samp{5274} @samp{5275}
11760 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
11761 @item @samp{5307} @tab @samp{5307}
11762 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
11763 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
11764 @item @samp{5407} @tab @samp{5407}
11765 @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}
11768 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
11769 @var{arch} is compatible with @var{cpu}. Other combinations of
11770 @option{-mcpu} and @option{-march} are rejected.
11772 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
11773 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
11774 where the value of @var{family} is given by the table above.
11776 @item -mtune=@var{tune}
11778 Tune the code for a particular microarchitecture, within the
11779 constraints set by @option{-march} and @option{-mcpu}.
11780 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11781 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11782 and @samp{cpu32}. The ColdFire microarchitectures
11783 are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11785 You can also use @option{-mtune=68020-40} for code that needs
11786 to run relatively well on 68020, 68030 and 68040 targets.
11787 @option{-mtune=68020-60} is similar but includes 68060 targets
11788 as well. These two options select the same tuning decisions as
11789 @option{-m68020-40} and @option{-m68020-60} respectively.
11791 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11792 when tuning for 680x0 architecture @var{arch}. It also defines
11793 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11794 option is used. If gcc is tuning for a range of architectures,
11795 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11796 it defines the macros for every architecture in the range.
11798 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11799 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11800 of the arguments given above.
11806 Generate output for a 68000. This is the default
11807 when the compiler is configured for 68000-based systems.
11808 It is equivalent to @option{-march=68000}.
11810 Use this option for microcontrollers with a 68000 or EC000 core,
11811 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11815 Generate output for a 68010. This is the default
11816 when the compiler is configured for 68010-based systems.
11817 It is equivalent to @option{-march=68010}.
11823 Generate output for a 68020. This is the default
11824 when the compiler is configured for 68020-based systems.
11825 It is equivalent to @option{-march=68020}.
11829 Generate output for a 68030. This is the default when the compiler is
11830 configured for 68030-based systems. It is equivalent to
11831 @option{-march=68030}.
11835 Generate output for a 68040. This is the default when the compiler is
11836 configured for 68040-based systems. It is equivalent to
11837 @option{-march=68040}.
11839 This option inhibits the use of 68881/68882 instructions that have to be
11840 emulated by software on the 68040. Use this option if your 68040 does not
11841 have code to emulate those instructions.
11845 Generate output for a 68060. This is the default when the compiler is
11846 configured for 68060-based systems. It is equivalent to
11847 @option{-march=68060}.
11849 This option inhibits the use of 68020 and 68881/68882 instructions that
11850 have to be emulated by software on the 68060. Use this option if your 68060
11851 does not have code to emulate those instructions.
11855 Generate output for a CPU32. This is the default
11856 when the compiler is configured for CPU32-based systems.
11857 It is equivalent to @option{-march=cpu32}.
11859 Use this option for microcontrollers with a
11860 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11861 68336, 68340, 68341, 68349 and 68360.
11865 Generate output for a 520X ColdFire CPU@. This is the default
11866 when the compiler is configured for 520X-based systems.
11867 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11868 in favor of that option.
11870 Use this option for microcontroller with a 5200 core, including
11871 the MCF5202, MCF5203, MCF5204 and MCF5206.
11875 Generate output for a 5206e ColdFire CPU@. The option is now
11876 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11880 Generate output for a member of the ColdFire 528X family.
11881 The option is now deprecated in favor of the equivalent
11882 @option{-mcpu=528x}.
11886 Generate output for a ColdFire 5307 CPU@. The option is now deprecated
11887 in favor of the equivalent @option{-mcpu=5307}.
11891 Generate output for a ColdFire 5407 CPU@. The option is now deprecated
11892 in favor of the equivalent @option{-mcpu=5407}.
11896 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11897 This includes use of hardware floating point instructions.
11898 The option is equivalent to @option{-mcpu=547x}, and is now
11899 deprecated in favor of that option.
11903 Generate output for a 68040, without using any of the new instructions.
11904 This results in code which can run relatively efficiently on either a
11905 68020/68881 or a 68030 or a 68040. The generated code does use the
11906 68881 instructions that are emulated on the 68040.
11908 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11912 Generate output for a 68060, without using any of the new instructions.
11913 This results in code which can run relatively efficiently on either a
11914 68020/68881 or a 68030 or a 68040. The generated code does use the
11915 68881 instructions that are emulated on the 68060.
11917 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11921 @opindex mhard-float
11923 Generate floating-point instructions. This is the default for 68020
11924 and above, and for ColdFire devices that have an FPU@. It defines the
11925 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11926 on ColdFire targets.
11929 @opindex msoft-float
11930 Do not generate floating-point instructions; use library calls instead.
11931 This is the default for 68000, 68010, and 68832 targets. It is also
11932 the default for ColdFire devices that have no FPU.
11938 Generate (do not generate) ColdFire hardware divide and remainder
11939 instructions. If @option{-march} is used without @option{-mcpu},
11940 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
11941 architectures. Otherwise, the default is taken from the target CPU
11942 (either the default CPU, or the one specified by @option{-mcpu}). For
11943 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
11944 @option{-mcpu=5206e}.
11946 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
11950 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11951 Additionally, parameters passed on the stack are also aligned to a
11952 16-bit boundary even on targets whose API mandates promotion to 32-bit.
11956 Do not consider type @code{int} to be 16 bits wide. This is the default.
11959 @itemx -mno-bitfield
11960 @opindex mnobitfield
11961 @opindex mno-bitfield
11962 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
11963 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
11967 Do use the bit-field instructions. The @option{-m68020} option implies
11968 @option{-mbitfield}. This is the default if you use a configuration
11969 designed for a 68020.
11973 Use a different function-calling convention, in which functions
11974 that take a fixed number of arguments return with the @code{rtd}
11975 instruction, which pops their arguments while returning. This
11976 saves one instruction in the caller since there is no need to pop
11977 the arguments there.
11979 This calling convention is incompatible with the one normally
11980 used on Unix, so you cannot use it if you need to call libraries
11981 compiled with the Unix compiler.
11983 Also, you must provide function prototypes for all functions that
11984 take variable numbers of arguments (including @code{printf});
11985 otherwise incorrect code will be generated for calls to those
11988 In addition, seriously incorrect code will result if you call a
11989 function with too many arguments. (Normally, extra arguments are
11990 harmlessly ignored.)
11992 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
11993 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
11997 Do not use the calling conventions selected by @option{-mrtd}.
11998 This is the default.
12001 @itemx -mno-align-int
12002 @opindex malign-int
12003 @opindex mno-align-int
12004 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
12005 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
12006 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
12007 Aligning variables on 32-bit boundaries produces code that runs somewhat
12008 faster on processors with 32-bit busses at the expense of more memory.
12010 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
12011 align structures containing the above types differently than
12012 most published application binary interface specifications for the m68k.
12016 Use the pc-relative addressing mode of the 68000 directly, instead of
12017 using a global offset table. At present, this option implies @option{-fpic},
12018 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
12019 not presently supported with @option{-mpcrel}, though this could be supported for
12020 68020 and higher processors.
12022 @item -mno-strict-align
12023 @itemx -mstrict-align
12024 @opindex mno-strict-align
12025 @opindex mstrict-align
12026 Do not (do) assume that unaligned memory references will be handled by
12030 Generate code that allows the data segment to be located in a different
12031 area of memory from the text segment. This allows for execute in place in
12032 an environment without virtual memory management. This option implies
12035 @item -mno-sep-data
12036 Generate code that assumes that the data segment follows the text segment.
12037 This is the default.
12039 @item -mid-shared-library
12040 Generate code that supports shared libraries via the library ID method.
12041 This allows for execute in place and shared libraries in an environment
12042 without virtual memory management. This option implies @option{-fPIC}.
12044 @item -mno-id-shared-library
12045 Generate code that doesn't assume ID based shared libraries are being used.
12046 This is the default.
12048 @item -mshared-library-id=n
12049 Specified the identification number of the ID based shared library being
12050 compiled. Specifying a value of 0 will generate more compact code, specifying
12051 other values will force the allocation of that number to the current
12052 library but is no more space or time efficient than omitting this option.
12058 When generating position-independent code for ColdFire, generate code
12059 that works if the GOT has more than 8192 entries. This code is
12060 larger and slower than code generated without this option. On M680x0
12061 processors, this option is not needed; @option{-fPIC} suffices.
12063 GCC normally uses a single instruction to load values from the GOT@.
12064 While this is relatively efficient, it only works if the GOT
12065 is smaller than about 64k. Anything larger causes the linker
12066 to report an error such as:
12068 @cindex relocation truncated to fit (ColdFire)
12070 relocation truncated to fit: R_68K_GOT16O foobar
12073 If this happens, you should recompile your code with @option{-mxgot}.
12074 It should then work with very large GOTs. However, code generated with
12075 @option{-mxgot} is less efficient, since it takes 4 instructions to fetch
12076 the value of a global symbol.
12078 Note that some linkers, including newer versions of the GNU linker,
12079 can create multiple GOTs and sort GOT entries. If you have such a linker,
12080 you should only need to use @option{-mxgot} when compiling a single
12081 object file that accesses more than 8192 GOT entries. Very few do.
12083 These options have no effect unless GCC is generating
12084 position-independent code.
12088 @node M68hc1x Options
12089 @subsection M68hc1x Options
12090 @cindex M68hc1x options
12092 These are the @samp{-m} options defined for the 68hc11 and 68hc12
12093 microcontrollers. The default values for these options depends on
12094 which style of microcontroller was selected when the compiler was configured;
12095 the defaults for the most common choices are given below.
12102 Generate output for a 68HC11. This is the default
12103 when the compiler is configured for 68HC11-based systems.
12109 Generate output for a 68HC12. This is the default
12110 when the compiler is configured for 68HC12-based systems.
12116 Generate output for a 68HCS12.
12118 @item -mauto-incdec
12119 @opindex mauto-incdec
12120 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
12127 Enable the use of 68HC12 min and max instructions.
12130 @itemx -mno-long-calls
12131 @opindex mlong-calls
12132 @opindex mno-long-calls
12133 Treat all calls as being far away (near). If calls are assumed to be
12134 far away, the compiler will use the @code{call} instruction to
12135 call a function and the @code{rtc} instruction for returning.
12139 Consider type @code{int} to be 16 bits wide, like @code{short int}.
12141 @item -msoft-reg-count=@var{count}
12142 @opindex msoft-reg-count
12143 Specify the number of pseudo-soft registers which are used for the
12144 code generation. The maximum number is 32. Using more pseudo-soft
12145 register may or may not result in better code depending on the program.
12146 The default is 4 for 68HC11 and 2 for 68HC12.
12150 @node MCore Options
12151 @subsection MCore Options
12152 @cindex MCore options
12154 These are the @samp{-m} options defined for the Motorola M*Core
12160 @itemx -mno-hardlit
12162 @opindex mno-hardlit
12163 Inline constants into the code stream if it can be done in two
12164 instructions or less.
12170 Use the divide instruction. (Enabled by default).
12172 @item -mrelax-immediate
12173 @itemx -mno-relax-immediate
12174 @opindex mrelax-immediate
12175 @opindex mno-relax-immediate
12176 Allow arbitrary sized immediates in bit operations.
12178 @item -mwide-bitfields
12179 @itemx -mno-wide-bitfields
12180 @opindex mwide-bitfields
12181 @opindex mno-wide-bitfields
12182 Always treat bit-fields as int-sized.
12184 @item -m4byte-functions
12185 @itemx -mno-4byte-functions
12186 @opindex m4byte-functions
12187 @opindex mno-4byte-functions
12188 Force all functions to be aligned to a four byte boundary.
12190 @item -mcallgraph-data
12191 @itemx -mno-callgraph-data
12192 @opindex mcallgraph-data
12193 @opindex mno-callgraph-data
12194 Emit callgraph information.
12197 @itemx -mno-slow-bytes
12198 @opindex mslow-bytes
12199 @opindex mno-slow-bytes
12200 Prefer word access when reading byte quantities.
12202 @item -mlittle-endian
12203 @itemx -mbig-endian
12204 @opindex mlittle-endian
12205 @opindex mbig-endian
12206 Generate code for a little endian target.
12212 Generate code for the 210 processor.
12216 @subsection MIPS Options
12217 @cindex MIPS options
12223 Generate big-endian code.
12227 Generate little-endian code. This is the default for @samp{mips*el-*-*}
12230 @item -march=@var{arch}
12232 Generate code that will run on @var{arch}, which can be the name of a
12233 generic MIPS ISA, or the name of a particular processor.
12235 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
12236 @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}.
12237 The processor names are:
12238 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
12239 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
12240 @samp{5kc}, @samp{5kf},
12242 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
12243 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
12244 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
12245 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
12246 @samp{loongson2e}, @samp{loongson2f},
12250 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
12251 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
12252 @samp{rm7000}, @samp{rm9000},
12253 @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
12256 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
12257 @samp{vr5000}, @samp{vr5400}, @samp{vr5500}
12259 The special value @samp{from-abi} selects the
12260 most compatible architecture for the selected ABI (that is,
12261 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
12263 Native Linux/GNU toolchains also support the value @samp{native},
12264 which selects the best architecture option for the host processor.
12265 @option{-march=native} has no effect if GCC does not recognize
12268 In processor names, a final @samp{000} can be abbreviated as @samp{k}
12269 (for example, @samp{-march=r2k}). Prefixes are optional, and
12270 @samp{vr} may be written @samp{r}.
12272 Names of the form @samp{@var{n}f2_1} refer to processors with
12273 FPUs clocked at half the rate of the core, names of the form
12274 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
12275 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
12276 processors with FPUs clocked a ratio of 3:2 with respect to the core.
12277 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
12278 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
12279 accepted as synonyms for @samp{@var{n}f1_1}.
12281 GCC defines two macros based on the value of this option. The first
12282 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
12283 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
12284 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
12285 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
12286 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
12288 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
12289 above. In other words, it will have the full prefix and will not
12290 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
12291 the macro names the resolved architecture (either @samp{"mips1"} or
12292 @samp{"mips3"}). It names the default architecture when no
12293 @option{-march} option is given.
12295 @item -mtune=@var{arch}
12297 Optimize for @var{arch}. Among other things, this option controls
12298 the way instructions are scheduled, and the perceived cost of arithmetic
12299 operations. The list of @var{arch} values is the same as for
12302 When this option is not used, GCC will optimize for the processor
12303 specified by @option{-march}. By using @option{-march} and
12304 @option{-mtune} together, it is possible to generate code that will
12305 run on a family of processors, but optimize the code for one
12306 particular member of that family.
12308 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
12309 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
12310 @samp{-march} ones described above.
12314 Equivalent to @samp{-march=mips1}.
12318 Equivalent to @samp{-march=mips2}.
12322 Equivalent to @samp{-march=mips3}.
12326 Equivalent to @samp{-march=mips4}.
12330 Equivalent to @samp{-march=mips32}.
12334 Equivalent to @samp{-march=mips32r2}.
12338 Equivalent to @samp{-march=mips64}.
12342 Equivalent to @samp{-march=mips64r2}.
12347 @opindex mno-mips16
12348 Generate (do not generate) MIPS16 code. If GCC is targetting a
12349 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
12351 MIPS16 code generation can also be controlled on a per-function basis
12352 by means of @code{mips16} and @code{nomips16} attributes.
12353 @xref{Function Attributes}, for more information.
12355 @item -mflip-mips16
12356 @opindex mflip-mips16
12357 Generate MIPS16 code on alternating functions. This option is provided
12358 for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
12359 not intended for ordinary use in compiling user code.
12361 @item -minterlink-mips16
12362 @itemx -mno-interlink-mips16
12363 @opindex minterlink-mips16
12364 @opindex mno-interlink-mips16
12365 Require (do not require) that non-MIPS16 code be link-compatible with
12368 For example, non-MIPS16 code cannot jump directly to MIPS16 code;
12369 it must either use a call or an indirect jump. @option{-minterlink-mips16}
12370 therefore disables direct jumps unless GCC knows that the target of the
12371 jump is not MIPS16.
12383 Generate code for the given ABI@.
12385 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
12386 generates 64-bit code when you select a 64-bit architecture, but you
12387 can use @option{-mgp32} to get 32-bit code instead.
12389 For information about the O64 ABI, see
12390 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
12392 GCC supports a variant of the o32 ABI in which floating-point registers
12393 are 64 rather than 32 bits wide. You can select this combination with
12394 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
12395 and @samp{mfhc1} instructions and is therefore only supported for
12396 MIPS32R2 processors.
12398 The register assignments for arguments and return values remain the
12399 same, but each scalar value is passed in a single 64-bit register
12400 rather than a pair of 32-bit registers. For example, scalar
12401 floating-point values are returned in @samp{$f0} only, not a
12402 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
12403 remains the same, but all 64 bits are saved.
12406 @itemx -mno-abicalls
12408 @opindex mno-abicalls
12409 Generate (do not generate) code that is suitable for SVR4-style
12410 dynamic objects. @option{-mabicalls} is the default for SVR4-based
12415 Generate (do not generate) code that is fully position-independent,
12416 and that can therefore be linked into shared libraries. This option
12417 only affects @option{-mabicalls}.
12419 All @option{-mabicalls} code has traditionally been position-independent,
12420 regardless of options like @option{-fPIC} and @option{-fpic}. However,
12421 as an extension, the GNU toolchain allows executables to use absolute
12422 accesses for locally-binding symbols. It can also use shorter GP
12423 initialization sequences and generate direct calls to locally-defined
12424 functions. This mode is selected by @option{-mno-shared}.
12426 @option{-mno-shared} depends on binutils 2.16 or higher and generates
12427 objects that can only be linked by the GNU linker. However, the option
12428 does not affect the ABI of the final executable; it only affects the ABI
12429 of relocatable objects. Using @option{-mno-shared} will generally make
12430 executables both smaller and quicker.
12432 @option{-mshared} is the default.
12438 Assume (do not assume) that the static and dynamic linkers
12439 support PLTs and copy relocations. This option only affects
12440 @samp{-mno-shared -mabicalls}. For the n64 ABI, this option
12441 has no effect without @samp{-msym32}.
12443 You can make @option{-mplt} the default by configuring
12444 GCC with @option{--with-mips-plt}. The default is
12445 @option{-mno-plt} otherwise.
12451 Lift (do not lift) the usual restrictions on the size of the global
12454 GCC normally uses a single instruction to load values from the GOT@.
12455 While this is relatively efficient, it will only work if the GOT
12456 is smaller than about 64k. Anything larger will cause the linker
12457 to report an error such as:
12459 @cindex relocation truncated to fit (MIPS)
12461 relocation truncated to fit: R_MIPS_GOT16 foobar
12464 If this happens, you should recompile your code with @option{-mxgot}.
12465 It should then work with very large GOTs, although it will also be
12466 less efficient, since it will take three instructions to fetch the
12467 value of a global symbol.
12469 Note that some linkers can create multiple GOTs. If you have such a
12470 linker, you should only need to use @option{-mxgot} when a single object
12471 file accesses more than 64k's worth of GOT entries. Very few do.
12473 These options have no effect unless GCC is generating position
12478 Assume that general-purpose registers are 32 bits wide.
12482 Assume that general-purpose registers are 64 bits wide.
12486 Assume that floating-point registers are 32 bits wide.
12490 Assume that floating-point registers are 64 bits wide.
12493 @opindex mhard-float
12494 Use floating-point coprocessor instructions.
12497 @opindex msoft-float
12498 Do not use floating-point coprocessor instructions. Implement
12499 floating-point calculations using library calls instead.
12501 @item -msingle-float
12502 @opindex msingle-float
12503 Assume that the floating-point coprocessor only supports single-precision
12506 @item -mdouble-float
12507 @opindex mdouble-float
12508 Assume that the floating-point coprocessor supports double-precision
12509 operations. This is the default.
12515 Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
12516 implement atomic memory built-in functions. When neither option is
12517 specified, GCC will use the instructions if the target architecture
12520 @option{-mllsc} is useful if the runtime environment can emulate the
12521 instructions and @option{-mno-llsc} can be useful when compiling for
12522 nonstandard ISAs. You can make either option the default by
12523 configuring GCC with @option{--with-llsc} and @option{--without-llsc}
12524 respectively. @option{--with-llsc} is the default for some
12525 configurations; see the installation documentation for details.
12531 Use (do not use) revision 1 of the MIPS DSP ASE@.
12532 @xref{MIPS DSP Built-in Functions}. This option defines the
12533 preprocessor macro @samp{__mips_dsp}. It also defines
12534 @samp{__mips_dsp_rev} to 1.
12540 Use (do not use) revision 2 of the MIPS DSP ASE@.
12541 @xref{MIPS DSP Built-in Functions}. This option defines the
12542 preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}.
12543 It also defines @samp{__mips_dsp_rev} to 2.
12546 @itemx -mno-smartmips
12547 @opindex msmartmips
12548 @opindex mno-smartmips
12549 Use (do not use) the MIPS SmartMIPS ASE.
12551 @item -mpaired-single
12552 @itemx -mno-paired-single
12553 @opindex mpaired-single
12554 @opindex mno-paired-single
12555 Use (do not use) paired-single floating-point instructions.
12556 @xref{MIPS Paired-Single Support}. This option requires
12557 hardware floating-point support to be enabled.
12563 Use (do not use) MIPS Digital Media Extension instructions.
12564 This option can only be used when generating 64-bit code and requires
12565 hardware floating-point support to be enabled.
12570 @opindex mno-mips3d
12571 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
12572 The option @option{-mips3d} implies @option{-mpaired-single}.
12578 Use (do not use) MT Multithreading instructions.
12582 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
12583 an explanation of the default and the way that the pointer size is
12588 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
12590 The default size of @code{int}s, @code{long}s and pointers depends on
12591 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
12592 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
12593 32-bit @code{long}s. Pointers are the same size as @code{long}s,
12594 or the same size as integer registers, whichever is smaller.
12600 Assume (do not assume) that all symbols have 32-bit values, regardless
12601 of the selected ABI@. This option is useful in combination with
12602 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
12603 to generate shorter and faster references to symbolic addresses.
12607 Put definitions of externally-visible data in a small data section
12608 if that data is no bigger than @var{num} bytes. GCC can then access
12609 the data more efficiently; see @option{-mgpopt} for details.
12611 The default @option{-G} option depends on the configuration.
12613 @item -mlocal-sdata
12614 @itemx -mno-local-sdata
12615 @opindex mlocal-sdata
12616 @opindex mno-local-sdata
12617 Extend (do not extend) the @option{-G} behavior to local data too,
12618 such as to static variables in C@. @option{-mlocal-sdata} is the
12619 default for all configurations.
12621 If the linker complains that an application is using too much small data,
12622 you might want to try rebuilding the less performance-critical parts with
12623 @option{-mno-local-sdata}. You might also want to build large
12624 libraries with @option{-mno-local-sdata}, so that the libraries leave
12625 more room for the main program.
12627 @item -mextern-sdata
12628 @itemx -mno-extern-sdata
12629 @opindex mextern-sdata
12630 @opindex mno-extern-sdata
12631 Assume (do not assume) that externally-defined data will be in
12632 a small data section if that data is within the @option{-G} limit.
12633 @option{-mextern-sdata} is the default for all configurations.
12635 If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
12636 @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
12637 that is no bigger than @var{num} bytes, you must make sure that @var{Var}
12638 is placed in a small data section. If @var{Var} is defined by another
12639 module, you must either compile that module with a high-enough
12640 @option{-G} setting or attach a @code{section} attribute to @var{Var}'s
12641 definition. If @var{Var} is common, you must link the application
12642 with a high-enough @option{-G} setting.
12644 The easiest way of satisfying these restrictions is to compile
12645 and link every module with the same @option{-G} option. However,
12646 you may wish to build a library that supports several different
12647 small data limits. You can do this by compiling the library with
12648 the highest supported @option{-G} setting and additionally using
12649 @option{-mno-extern-sdata} to stop the library from making assumptions
12650 about externally-defined data.
12656 Use (do not use) GP-relative accesses for symbols that are known to be
12657 in a small data section; see @option{-G}, @option{-mlocal-sdata} and
12658 @option{-mextern-sdata}. @option{-mgpopt} is the default for all
12661 @option{-mno-gpopt} is useful for cases where the @code{$gp} register
12662 might not hold the value of @code{_gp}. For example, if the code is
12663 part of a library that might be used in a boot monitor, programs that
12664 call boot monitor routines will pass an unknown value in @code{$gp}.
12665 (In such situations, the boot monitor itself would usually be compiled
12666 with @option{-G0}.)
12668 @option{-mno-gpopt} implies @option{-mno-local-sdata} and
12669 @option{-mno-extern-sdata}.
12671 @item -membedded-data
12672 @itemx -mno-embedded-data
12673 @opindex membedded-data
12674 @opindex mno-embedded-data
12675 Allocate variables to the read-only data section first if possible, then
12676 next in the small data section if possible, otherwise in data. This gives
12677 slightly slower code than the default, but reduces the amount of RAM required
12678 when executing, and thus may be preferred for some embedded systems.
12680 @item -muninit-const-in-rodata
12681 @itemx -mno-uninit-const-in-rodata
12682 @opindex muninit-const-in-rodata
12683 @opindex mno-uninit-const-in-rodata
12684 Put uninitialized @code{const} variables in the read-only data section.
12685 This option is only meaningful in conjunction with @option{-membedded-data}.
12687 @item -mcode-readable=@var{setting}
12688 @opindex mcode-readable
12689 Specify whether GCC may generate code that reads from executable sections.
12690 There are three possible settings:
12693 @item -mcode-readable=yes
12694 Instructions may freely access executable sections. This is the
12697 @item -mcode-readable=pcrel
12698 MIPS16 PC-relative load instructions can access executable sections,
12699 but other instructions must not do so. This option is useful on 4KSc
12700 and 4KSd processors when the code TLBs have the Read Inhibit bit set.
12701 It is also useful on processors that can be configured to have a dual
12702 instruction/data SRAM interface and that, like the M4K, automatically
12703 redirect PC-relative loads to the instruction RAM.
12705 @item -mcode-readable=no
12706 Instructions must not access executable sections. This option can be
12707 useful on targets that are configured to have a dual instruction/data
12708 SRAM interface but that (unlike the M4K) do not automatically redirect
12709 PC-relative loads to the instruction RAM.
12712 @item -msplit-addresses
12713 @itemx -mno-split-addresses
12714 @opindex msplit-addresses
12715 @opindex mno-split-addresses
12716 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
12717 relocation operators. This option has been superseded by
12718 @option{-mexplicit-relocs} but is retained for backwards compatibility.
12720 @item -mexplicit-relocs
12721 @itemx -mno-explicit-relocs
12722 @opindex mexplicit-relocs
12723 @opindex mno-explicit-relocs
12724 Use (do not use) assembler relocation operators when dealing with symbolic
12725 addresses. The alternative, selected by @option{-mno-explicit-relocs},
12726 is to use assembler macros instead.
12728 @option{-mexplicit-relocs} is the default if GCC was configured
12729 to use an assembler that supports relocation operators.
12731 @item -mcheck-zero-division
12732 @itemx -mno-check-zero-division
12733 @opindex mcheck-zero-division
12734 @opindex mno-check-zero-division
12735 Trap (do not trap) on integer division by zero.
12737 The default is @option{-mcheck-zero-division}.
12739 @item -mdivide-traps
12740 @itemx -mdivide-breaks
12741 @opindex mdivide-traps
12742 @opindex mdivide-breaks
12743 MIPS systems check for division by zero by generating either a
12744 conditional trap or a break instruction. Using traps results in
12745 smaller code, but is only supported on MIPS II and later. Also, some
12746 versions of the Linux kernel have a bug that prevents trap from
12747 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
12748 allow conditional traps on architectures that support them and
12749 @option{-mdivide-breaks} to force the use of breaks.
12751 The default is usually @option{-mdivide-traps}, but this can be
12752 overridden at configure time using @option{--with-divide=breaks}.
12753 Divide-by-zero checks can be completely disabled using
12754 @option{-mno-check-zero-division}.
12759 @opindex mno-memcpy
12760 Force (do not force) the use of @code{memcpy()} for non-trivial block
12761 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
12762 most constant-sized copies.
12765 @itemx -mno-long-calls
12766 @opindex mlong-calls
12767 @opindex mno-long-calls
12768 Disable (do not disable) use of the @code{jal} instruction. Calling
12769 functions using @code{jal} is more efficient but requires the caller
12770 and callee to be in the same 256 megabyte segment.
12772 This option has no effect on abicalls code. The default is
12773 @option{-mno-long-calls}.
12779 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
12780 instructions, as provided by the R4650 ISA@.
12783 @itemx -mno-fused-madd
12784 @opindex mfused-madd
12785 @opindex mno-fused-madd
12786 Enable (disable) use of the floating point multiply-accumulate
12787 instructions, when they are available. The default is
12788 @option{-mfused-madd}.
12790 When multiply-accumulate instructions are used, the intermediate
12791 product is calculated to infinite precision and is not subject to
12792 the FCSR Flush to Zero bit. This may be undesirable in some
12797 Tell the MIPS assembler to not run its preprocessor over user
12798 assembler files (with a @samp{.s} suffix) when assembling them.
12801 @itemx -mno-fix-r4000
12802 @opindex mfix-r4000
12803 @opindex mno-fix-r4000
12804 Work around certain R4000 CPU errata:
12807 A double-word or a variable shift may give an incorrect result if executed
12808 immediately after starting an integer division.
12810 A double-word or a variable shift may give an incorrect result if executed
12811 while an integer multiplication is in progress.
12813 An integer division may give an incorrect result if started in a delay slot
12814 of a taken branch or a jump.
12818 @itemx -mno-fix-r4400
12819 @opindex mfix-r4400
12820 @opindex mno-fix-r4400
12821 Work around certain R4400 CPU errata:
12824 A double-word or a variable shift may give an incorrect result if executed
12825 immediately after starting an integer division.
12829 @itemx -mno-fix-vr4120
12830 @opindex mfix-vr4120
12831 Work around certain VR4120 errata:
12834 @code{dmultu} does not always produce the correct result.
12836 @code{div} and @code{ddiv} do not always produce the correct result if one
12837 of the operands is negative.
12839 The workarounds for the division errata rely on special functions in
12840 @file{libgcc.a}. At present, these functions are only provided by
12841 the @code{mips64vr*-elf} configurations.
12843 Other VR4120 errata require a nop to be inserted between certain pairs of
12844 instructions. These errata are handled by the assembler, not by GCC itself.
12847 @opindex mfix-vr4130
12848 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
12849 workarounds are implemented by the assembler rather than by GCC,
12850 although GCC will avoid using @code{mflo} and @code{mfhi} if the
12851 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
12852 instructions are available instead.
12855 @itemx -mno-fix-sb1
12857 Work around certain SB-1 CPU core errata.
12858 (This flag currently works around the SB-1 revision 2
12859 ``F1'' and ``F2'' floating point errata.)
12861 @item -mr10k-cache-barrier=@var{setting}
12862 @opindex mr10k-cache-barrier
12863 Specify whether GCC should insert cache barriers to avoid the
12864 side-effects of speculation on R10K processors.
12866 In common with many processors, the R10K tries to predict the outcome
12867 of a conditional branch and speculatively executes instructions from
12868 the ``taken'' branch. It later aborts these instructions if the
12869 predicted outcome was wrong. However, on the R10K, even aborted
12870 instructions can have side effects.
12872 This problem only affects kernel stores and, depending on the system,
12873 kernel loads. As an example, a speculatively-executed store may load
12874 the target memory into cache and mark the cache line as dirty, even if
12875 the store itself is later aborted. If a DMA operation writes to the
12876 same area of memory before the ``dirty'' line is flushed, the cached
12877 data will overwrite the DMA-ed data. See the R10K processor manual
12878 for a full description, including other potential problems.
12880 One workaround is to insert cache barrier instructions before every memory
12881 access that might be speculatively executed and that might have side
12882 effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
12883 controls GCC's implementation of this workaround. It assumes that
12884 aborted accesses to any byte in the following regions will not have
12889 the memory occupied by the current function's stack frame;
12892 the memory occupied by an incoming stack argument;
12895 the memory occupied by an object with a link-time-constant address.
12898 It is the kernel's responsibility to ensure that speculative
12899 accesses to these regions are indeed safe.
12901 If the input program contains a function declaration such as:
12907 then the implementation of @code{foo} must allow @code{j foo} and
12908 @code{jal foo} to be executed speculatively. GCC honors this
12909 restriction for functions it compiles itself. It expects non-GCC
12910 functions (such as hand-written assembly code) to do the same.
12912 The option has three forms:
12915 @item -mr10k-cache-barrier=load-store
12916 Insert a cache barrier before a load or store that might be
12917 speculatively executed and that might have side effects even
12920 @item -mr10k-cache-barrier=store
12921 Insert a cache barrier before a store that might be speculatively
12922 executed and that might have side effects even if aborted.
12924 @item -mr10k-cache-barrier=none
12925 Disable the insertion of cache barriers. This is the default setting.
12928 @item -mflush-func=@var{func}
12929 @itemx -mno-flush-func
12930 @opindex mflush-func
12931 Specifies the function to call to flush the I and D caches, or to not
12932 call any such function. If called, the function must take the same
12933 arguments as the common @code{_flush_func()}, that is, the address of the
12934 memory range for which the cache is being flushed, the size of the
12935 memory range, and the number 3 (to flush both caches). The default
12936 depends on the target GCC was configured for, but commonly is either
12937 @samp{_flush_func} or @samp{__cpu_flush}.
12939 @item mbranch-cost=@var{num}
12940 @opindex mbranch-cost
12941 Set the cost of branches to roughly @var{num} ``simple'' instructions.
12942 This cost is only a heuristic and is not guaranteed to produce
12943 consistent results across releases. A zero cost redundantly selects
12944 the default, which is based on the @option{-mtune} setting.
12946 @item -mbranch-likely
12947 @itemx -mno-branch-likely
12948 @opindex mbranch-likely
12949 @opindex mno-branch-likely
12950 Enable or disable use of Branch Likely instructions, regardless of the
12951 default for the selected architecture. By default, Branch Likely
12952 instructions may be generated if they are supported by the selected
12953 architecture. An exception is for the MIPS32 and MIPS64 architectures
12954 and processors which implement those architectures; for those, Branch
12955 Likely instructions will not be generated by default because the MIPS32
12956 and MIPS64 architectures specifically deprecate their use.
12958 @item -mfp-exceptions
12959 @itemx -mno-fp-exceptions
12960 @opindex mfp-exceptions
12961 Specifies whether FP exceptions are enabled. This affects how we schedule
12962 FP instructions for some processors. The default is that FP exceptions are
12965 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
12966 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
12969 @item -mvr4130-align
12970 @itemx -mno-vr4130-align
12971 @opindex mvr4130-align
12972 The VR4130 pipeline is two-way superscalar, but can only issue two
12973 instructions together if the first one is 8-byte aligned. When this
12974 option is enabled, GCC will align pairs of instructions that it
12975 thinks should execute in parallel.
12977 This option only has an effect when optimizing for the VR4130.
12978 It normally makes code faster, but at the expense of making it bigger.
12979 It is enabled by default at optimization level @option{-O3}.
12983 @subsection MMIX Options
12984 @cindex MMIX Options
12986 These options are defined for the MMIX:
12990 @itemx -mno-libfuncs
12992 @opindex mno-libfuncs
12993 Specify that intrinsic library functions are being compiled, passing all
12994 values in registers, no matter the size.
12997 @itemx -mno-epsilon
12999 @opindex mno-epsilon
13000 Generate floating-point comparison instructions that compare with respect
13001 to the @code{rE} epsilon register.
13003 @item -mabi=mmixware
13005 @opindex mabi-mmixware
13007 Generate code that passes function parameters and return values that (in
13008 the called function) are seen as registers @code{$0} and up, as opposed to
13009 the GNU ABI which uses global registers @code{$231} and up.
13011 @item -mzero-extend
13012 @itemx -mno-zero-extend
13013 @opindex mzero-extend
13014 @opindex mno-zero-extend
13015 When reading data from memory in sizes shorter than 64 bits, use (do not
13016 use) zero-extending load instructions by default, rather than
13017 sign-extending ones.
13020 @itemx -mno-knuthdiv
13022 @opindex mno-knuthdiv
13023 Make the result of a division yielding a remainder have the same sign as
13024 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
13025 remainder follows the sign of the dividend. Both methods are
13026 arithmetically valid, the latter being almost exclusively used.
13028 @item -mtoplevel-symbols
13029 @itemx -mno-toplevel-symbols
13030 @opindex mtoplevel-symbols
13031 @opindex mno-toplevel-symbols
13032 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
13033 code can be used with the @code{PREFIX} assembly directive.
13037 Generate an executable in the ELF format, rather than the default
13038 @samp{mmo} format used by the @command{mmix} simulator.
13040 @item -mbranch-predict
13041 @itemx -mno-branch-predict
13042 @opindex mbranch-predict
13043 @opindex mno-branch-predict
13044 Use (do not use) the probable-branch instructions, when static branch
13045 prediction indicates a probable branch.
13047 @item -mbase-addresses
13048 @itemx -mno-base-addresses
13049 @opindex mbase-addresses
13050 @opindex mno-base-addresses
13051 Generate (do not generate) code that uses @emph{base addresses}. Using a
13052 base address automatically generates a request (handled by the assembler
13053 and the linker) for a constant to be set up in a global register. The
13054 register is used for one or more base address requests within the range 0
13055 to 255 from the value held in the register. The generally leads to short
13056 and fast code, but the number of different data items that can be
13057 addressed is limited. This means that a program that uses lots of static
13058 data may require @option{-mno-base-addresses}.
13060 @item -msingle-exit
13061 @itemx -mno-single-exit
13062 @opindex msingle-exit
13063 @opindex mno-single-exit
13064 Force (do not force) generated code to have a single exit point in each
13068 @node MN10300 Options
13069 @subsection MN10300 Options
13070 @cindex MN10300 options
13072 These @option{-m} options are defined for Matsushita MN10300 architectures:
13077 Generate code to avoid bugs in the multiply instructions for the MN10300
13078 processors. This is the default.
13080 @item -mno-mult-bug
13081 @opindex mno-mult-bug
13082 Do not generate code to avoid bugs in the multiply instructions for the
13083 MN10300 processors.
13087 Generate code which uses features specific to the AM33 processor.
13091 Do not generate code which uses features specific to the AM33 processor. This
13094 @item -mreturn-pointer-on-d0
13095 @opindex mreturn-pointer-on-d0
13096 When generating a function which returns a pointer, return the pointer
13097 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
13098 only in a0, and attempts to call such functions without a prototype
13099 would result in errors. Note that this option is on by default; use
13100 @option{-mno-return-pointer-on-d0} to disable it.
13104 Do not link in the C run-time initialization object file.
13108 Indicate to the linker that it should perform a relaxation optimization pass
13109 to shorten branches, calls and absolute memory addresses. This option only
13110 has an effect when used on the command line for the final link step.
13112 This option makes symbolic debugging impossible.
13115 @node PDP-11 Options
13116 @subsection PDP-11 Options
13117 @cindex PDP-11 Options
13119 These options are defined for the PDP-11:
13124 Use hardware FPP floating point. This is the default. (FIS floating
13125 point on the PDP-11/40 is not supported.)
13128 @opindex msoft-float
13129 Do not use hardware floating point.
13133 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
13137 Return floating-point results in memory. This is the default.
13141 Generate code for a PDP-11/40.
13145 Generate code for a PDP-11/45. This is the default.
13149 Generate code for a PDP-11/10.
13151 @item -mbcopy-builtin
13152 @opindex bcopy-builtin
13153 Use inline @code{movmemhi} patterns for copying memory. This is the
13158 Do not use inline @code{movmemhi} patterns for copying memory.
13164 Use 16-bit @code{int}. This is the default.
13170 Use 32-bit @code{int}.
13173 @itemx -mno-float32
13175 @opindex mno-float32
13176 Use 64-bit @code{float}. This is the default.
13179 @itemx -mno-float64
13181 @opindex mno-float64
13182 Use 32-bit @code{float}.
13186 Use @code{abshi2} pattern. This is the default.
13190 Do not use @code{abshi2} pattern.
13192 @item -mbranch-expensive
13193 @opindex mbranch-expensive
13194 Pretend that branches are expensive. This is for experimenting with
13195 code generation only.
13197 @item -mbranch-cheap
13198 @opindex mbranch-cheap
13199 Do not pretend that branches are expensive. This is the default.
13203 Generate code for a system with split I&D@.
13207 Generate code for a system without split I&D@. This is the default.
13211 Use Unix assembler syntax. This is the default when configured for
13212 @samp{pdp11-*-bsd}.
13216 Use DEC assembler syntax. This is the default when configured for any
13217 PDP-11 target other than @samp{pdp11-*-bsd}.
13220 @node picoChip Options
13221 @subsection picoChip Options
13222 @cindex picoChip options
13224 These @samp{-m} options are defined for picoChip implementations:
13228 @item -mae=@var{ae_type}
13230 Set the instruction set, register set, and instruction scheduling
13231 parameters for array element type @var{ae_type}. Supported values
13232 for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
13234 @option{-mae=ANY} selects a completely generic AE type. Code
13235 generated with this option will run on any of the other AE types. The
13236 code will not be as efficient as it would be if compiled for a specific
13237 AE type, and some types of operation (e.g., multiplication) will not
13238 work properly on all types of AE.
13240 @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
13241 for compiled code, and is the default.
13243 @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
13244 option may suffer from poor performance of byte (char) manipulation,
13245 since the DSP AE does not provide hardware support for byte load/stores.
13247 @item -msymbol-as-address
13248 Enable the compiler to directly use a symbol name as an address in a
13249 load/store instruction, without first loading it into a
13250 register. Typically, the use of this option will generate larger
13251 programs, which run faster than when the option isn't used. However, the
13252 results vary from program to program, so it is left as a user option,
13253 rather than being permanently enabled.
13255 @item -mno-inefficient-warnings
13256 Disables warnings about the generation of inefficient code. These
13257 warnings can be generated, for example, when compiling code which
13258 performs byte-level memory operations on the MAC AE type. The MAC AE has
13259 no hardware support for byte-level memory operations, so all byte
13260 load/stores must be synthesised from word load/store operations. This is
13261 inefficient and a warning will be generated indicating to the programmer
13262 that they should rewrite the code to avoid byte operations, or to target
13263 an AE type which has the necessary hardware support. This option enables
13264 the warning to be turned off.
13268 @node PowerPC Options
13269 @subsection PowerPC Options
13270 @cindex PowerPC options
13272 These are listed under @xref{RS/6000 and PowerPC Options}.
13274 @node RS/6000 and PowerPC Options
13275 @subsection IBM RS/6000 and PowerPC Options
13276 @cindex RS/6000 and PowerPC Options
13277 @cindex IBM RS/6000 and PowerPC Options
13279 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
13286 @itemx -mno-powerpc
13287 @itemx -mpowerpc-gpopt
13288 @itemx -mno-powerpc-gpopt
13289 @itemx -mpowerpc-gfxopt
13290 @itemx -mno-powerpc-gfxopt
13292 @itemx -mno-powerpc64
13296 @itemx -mno-popcntb
13304 @itemx -mno-hard-dfp
13308 @opindex mno-power2
13310 @opindex mno-powerpc
13311 @opindex mpowerpc-gpopt
13312 @opindex mno-powerpc-gpopt
13313 @opindex mpowerpc-gfxopt
13314 @opindex mno-powerpc-gfxopt
13315 @opindex mpowerpc64
13316 @opindex mno-powerpc64
13320 @opindex mno-popcntb
13326 @opindex mno-mfpgpr
13328 @opindex mno-hard-dfp
13329 GCC supports two related instruction set architectures for the
13330 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
13331 instructions supported by the @samp{rios} chip set used in the original
13332 RS/6000 systems and the @dfn{PowerPC} instruction set is the
13333 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
13334 the IBM 4xx, 6xx, and follow-on microprocessors.
13336 Neither architecture is a subset of the other. However there is a
13337 large common subset of instructions supported by both. An MQ
13338 register is included in processors supporting the POWER architecture.
13340 You use these options to specify which instructions are available on the
13341 processor you are using. The default value of these options is
13342 determined when configuring GCC@. Specifying the
13343 @option{-mcpu=@var{cpu_type}} overrides the specification of these
13344 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
13345 rather than the options listed above.
13347 The @option{-mpower} option allows GCC to generate instructions that
13348 are found only in the POWER architecture and to use the MQ register.
13349 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
13350 to generate instructions that are present in the POWER2 architecture but
13351 not the original POWER architecture.
13353 The @option{-mpowerpc} option allows GCC to generate instructions that
13354 are found only in the 32-bit subset of the PowerPC architecture.
13355 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
13356 GCC to use the optional PowerPC architecture instructions in the
13357 General Purpose group, including floating-point square root. Specifying
13358 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
13359 use the optional PowerPC architecture instructions in the Graphics
13360 group, including floating-point select.
13362 The @option{-mmfcrf} option allows GCC to generate the move from
13363 condition register field instruction implemented on the POWER4
13364 processor and other processors that support the PowerPC V2.01
13366 The @option{-mpopcntb} option allows GCC to generate the popcount and
13367 double precision FP reciprocal estimate instruction implemented on the
13368 POWER5 processor and other processors that support the PowerPC V2.02
13370 The @option{-mfprnd} option allows GCC to generate the FP round to
13371 integer instructions implemented on the POWER5+ processor and other
13372 processors that support the PowerPC V2.03 architecture.
13373 The @option{-mcmpb} option allows GCC to generate the compare bytes
13374 instruction implemented on the POWER6 processor and other processors
13375 that support the PowerPC V2.05 architecture.
13376 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
13377 general purpose register instructions implemented on the POWER6X
13378 processor and other processors that support the extended PowerPC V2.05
13380 The @option{-mhard-dfp} option allows GCC to generate the decimal floating
13381 point instructions implemented on some POWER processors.
13383 The @option{-mpowerpc64} option allows GCC to generate the additional
13384 64-bit instructions that are found in the full PowerPC64 architecture
13385 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
13386 @option{-mno-powerpc64}.
13388 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
13389 will use only the instructions in the common subset of both
13390 architectures plus some special AIX common-mode calls, and will not use
13391 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
13392 permits GCC to use any instruction from either architecture and to
13393 allow use of the MQ register; specify this for the Motorola MPC601.
13395 @item -mnew-mnemonics
13396 @itemx -mold-mnemonics
13397 @opindex mnew-mnemonics
13398 @opindex mold-mnemonics
13399 Select which mnemonics to use in the generated assembler code. With
13400 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
13401 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
13402 assembler mnemonics defined for the POWER architecture. Instructions
13403 defined in only one architecture have only one mnemonic; GCC uses that
13404 mnemonic irrespective of which of these options is specified.
13406 GCC defaults to the mnemonics appropriate for the architecture in
13407 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
13408 value of these option. Unless you are building a cross-compiler, you
13409 should normally not specify either @option{-mnew-mnemonics} or
13410 @option{-mold-mnemonics}, but should instead accept the default.
13412 @item -mcpu=@var{cpu_type}
13414 Set architecture type, register usage, choice of mnemonics, and
13415 instruction scheduling parameters for machine type @var{cpu_type}.
13416 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
13417 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
13418 @samp{505}, @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
13419 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
13420 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
13421 @samp{860}, @samp{970}, @samp{8540}, @samp{e300c2}, @samp{e300c3},
13422 @samp{e500mc}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
13423 @samp{power}, @samp{power2}, @samp{power3}, @samp{power4},
13424 @samp{power5}, @samp{power5+}, @samp{power6}, @samp{power6x}, @samp{power7}
13425 @samp{common}, @samp{powerpc}, @samp{powerpc64}, @samp{rios},
13426 @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
13428 @option{-mcpu=common} selects a completely generic processor. Code
13429 generated under this option will run on any POWER or PowerPC processor.
13430 GCC will use only the instructions in the common subset of both
13431 architectures, and will not use the MQ register. GCC assumes a generic
13432 processor model for scheduling purposes.
13434 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
13435 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
13436 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
13437 types, with an appropriate, generic processor model assumed for
13438 scheduling purposes.
13440 The other options specify a specific processor. Code generated under
13441 those options will run best on that processor, and may not run at all on
13444 The @option{-mcpu} options automatically enable or disable the
13447 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
13448 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
13449 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
13450 -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr}
13452 The particular options set for any particular CPU will vary between
13453 compiler versions, depending on what setting seems to produce optimal
13454 code for that CPU; it doesn't necessarily reflect the actual hardware's
13455 capabilities. If you wish to set an individual option to a particular
13456 value, you may specify it after the @option{-mcpu} option, like
13457 @samp{-mcpu=970 -mno-altivec}.
13459 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
13460 not enabled or disabled by the @option{-mcpu} option at present because
13461 AIX does not have full support for these options. You may still
13462 enable or disable them individually if you're sure it'll work in your
13465 @item -mtune=@var{cpu_type}
13467 Set the instruction scheduling parameters for machine type
13468 @var{cpu_type}, but do not set the architecture type, register usage, or
13469 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
13470 values for @var{cpu_type} are used for @option{-mtune} as for
13471 @option{-mcpu}. If both are specified, the code generated will use the
13472 architecture, registers, and mnemonics set by @option{-mcpu}, but the
13473 scheduling parameters set by @option{-mtune}.
13479 Generate code to compute division as reciprocal estimate and iterative
13480 refinement, creating opportunities for increased throughput. This
13481 feature requires: optional PowerPC Graphics instruction set for single
13482 precision and FRE instruction for double precision, assuming divides
13483 cannot generate user-visible traps, and the domain values not include
13484 Infinities, denormals or zero denominator.
13487 @itemx -mno-altivec
13489 @opindex mno-altivec
13490 Generate code that uses (does not use) AltiVec instructions, and also
13491 enable the use of built-in functions that allow more direct access to
13492 the AltiVec instruction set. You may also need to set
13493 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
13499 @opindex mno-vrsave
13500 Generate VRSAVE instructions when generating AltiVec code.
13502 @item -mgen-cell-microcode
13503 @opindex mgen-cell-microcode
13504 Generate Cell microcode instructions
13506 @item -mwarn-cell-microcode
13507 @opindex mwarn-cell-microcode
13508 Warning when a Cell microcode instruction is going to emitted. An example
13509 of a Cell microcode instruction is a variable shift.
13512 @opindex msecure-plt
13513 Generate code that allows ld and ld.so to build executables and shared
13514 libraries with non-exec .plt and .got sections. This is a PowerPC
13515 32-bit SYSV ABI option.
13519 Generate code that uses a BSS .plt section that ld.so fills in, and
13520 requires .plt and .got sections that are both writable and executable.
13521 This is a PowerPC 32-bit SYSV ABI option.
13527 This switch enables or disables the generation of ISEL instructions.
13529 @item -misel=@var{yes/no}
13530 This switch has been deprecated. Use @option{-misel} and
13531 @option{-mno-isel} instead.
13537 This switch enables or disables the generation of SPE simd
13543 @opindex mno-paired
13544 This switch enables or disables the generation of PAIRED simd
13547 @item -mspe=@var{yes/no}
13548 This option has been deprecated. Use @option{-mspe} and
13549 @option{-mno-spe} instead.
13551 @item -mfloat-gprs=@var{yes/single/double/no}
13552 @itemx -mfloat-gprs
13553 @opindex mfloat-gprs
13554 This switch enables or disables the generation of floating point
13555 operations on the general purpose registers for architectures that
13558 The argument @var{yes} or @var{single} enables the use of
13559 single-precision floating point operations.
13561 The argument @var{double} enables the use of single and
13562 double-precision floating point operations.
13564 The argument @var{no} disables floating point operations on the
13565 general purpose registers.
13567 This option is currently only available on the MPC854x.
13573 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
13574 targets (including GNU/Linux). The 32-bit environment sets int, long
13575 and pointer to 32 bits and generates code that runs on any PowerPC
13576 variant. The 64-bit environment sets int to 32 bits and long and
13577 pointer to 64 bits, and generates code for PowerPC64, as for
13578 @option{-mpowerpc64}.
13581 @itemx -mno-fp-in-toc
13582 @itemx -mno-sum-in-toc
13583 @itemx -mminimal-toc
13585 @opindex mno-fp-in-toc
13586 @opindex mno-sum-in-toc
13587 @opindex mminimal-toc
13588 Modify generation of the TOC (Table Of Contents), which is created for
13589 every executable file. The @option{-mfull-toc} option is selected by
13590 default. In that case, GCC will allocate at least one TOC entry for
13591 each unique non-automatic variable reference in your program. GCC
13592 will also place floating-point constants in the TOC@. However, only
13593 16,384 entries are available in the TOC@.
13595 If you receive a linker error message that saying you have overflowed
13596 the available TOC space, you can reduce the amount of TOC space used
13597 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
13598 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
13599 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
13600 generate code to calculate the sum of an address and a constant at
13601 run-time instead of putting that sum into the TOC@. You may specify one
13602 or both of these options. Each causes GCC to produce very slightly
13603 slower and larger code at the expense of conserving TOC space.
13605 If you still run out of space in the TOC even when you specify both of
13606 these options, specify @option{-mminimal-toc} instead. This option causes
13607 GCC to make only one TOC entry for every file. When you specify this
13608 option, GCC will produce code that is slower and larger but which
13609 uses extremely little TOC space. You may wish to use this option
13610 only on files that contain less frequently executed code.
13616 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
13617 @code{long} type, and the infrastructure needed to support them.
13618 Specifying @option{-maix64} implies @option{-mpowerpc64} and
13619 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
13620 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
13623 @itemx -mno-xl-compat
13624 @opindex mxl-compat
13625 @opindex mno-xl-compat
13626 Produce code that conforms more closely to IBM XL compiler semantics
13627 when using AIX-compatible ABI@. Pass floating-point arguments to
13628 prototyped functions beyond the register save area (RSA) on the stack
13629 in addition to argument FPRs. Do not assume that most significant
13630 double in 128-bit long double value is properly rounded when comparing
13631 values and converting to double. Use XL symbol names for long double
13634 The AIX calling convention was extended but not initially documented to
13635 handle an obscure K&R C case of calling a function that takes the
13636 address of its arguments with fewer arguments than declared. IBM XL
13637 compilers access floating point arguments which do not fit in the
13638 RSA from the stack when a subroutine is compiled without
13639 optimization. Because always storing floating-point arguments on the
13640 stack is inefficient and rarely needed, this option is not enabled by
13641 default and only is necessary when calling subroutines compiled by IBM
13642 XL compilers without optimization.
13646 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
13647 application written to use message passing with special startup code to
13648 enable the application to run. The system must have PE installed in the
13649 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
13650 must be overridden with the @option{-specs=} option to specify the
13651 appropriate directory location. The Parallel Environment does not
13652 support threads, so the @option{-mpe} option and the @option{-pthread}
13653 option are incompatible.
13655 @item -malign-natural
13656 @itemx -malign-power
13657 @opindex malign-natural
13658 @opindex malign-power
13659 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
13660 @option{-malign-natural} overrides the ABI-defined alignment of larger
13661 types, such as floating-point doubles, on their natural size-based boundary.
13662 The option @option{-malign-power} instructs GCC to follow the ABI-specified
13663 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
13665 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
13669 @itemx -mhard-float
13670 @opindex msoft-float
13671 @opindex mhard-float
13672 Generate code that does not use (uses) the floating-point register set.
13673 Software floating point emulation is provided if you use the
13674 @option{-msoft-float} option, and pass the option to GCC when linking.
13676 @item -msingle-float
13677 @itemx -mdouble-float
13678 @opindex msingle-float
13679 @opindex mdouble-float
13680 Generate code for single or double-precision floating point operations.
13681 @option{-mdouble-float} implies @option{-msingle-float}.
13684 @opindex msimple-fpu
13685 Do not generate sqrt and div instructions for hardware floating point unit.
13689 Specify type of floating point unit. Valid values are @var{sp_lite}
13690 (equivalent to -msingle-float -msimple-fpu), @var{dp_lite} (equivalent
13691 to -mdouble-float -msimple-fpu), @var{sp_full} (equivalent to -msingle-float),
13692 and @var{dp_full} (equivalent to -mdouble-float).
13695 @opindex mxilinx-fpu
13696 Perform optimizations for floating point unit on Xilinx PPC 405/440.
13699 @itemx -mno-multiple
13701 @opindex mno-multiple
13702 Generate code that uses (does not use) the load multiple word
13703 instructions and the store multiple word instructions. These
13704 instructions are generated by default on POWER systems, and not
13705 generated on PowerPC systems. Do not use @option{-mmultiple} on little
13706 endian PowerPC systems, since those instructions do not work when the
13707 processor is in little endian mode. The exceptions are PPC740 and
13708 PPC750 which permit the instructions usage in little endian mode.
13713 @opindex mno-string
13714 Generate code that uses (does not use) the load string instructions
13715 and the store string word instructions to save multiple registers and
13716 do small block moves. These instructions are generated by default on
13717 POWER systems, and not generated on PowerPC systems. Do not use
13718 @option{-mstring} on little endian PowerPC systems, since those
13719 instructions do not work when the processor is in little endian mode.
13720 The exceptions are PPC740 and PPC750 which permit the instructions
13721 usage in little endian mode.
13726 @opindex mno-update
13727 Generate code that uses (does not use) the load or store instructions
13728 that update the base register to the address of the calculated memory
13729 location. These instructions are generated by default. If you use
13730 @option{-mno-update}, there is a small window between the time that the
13731 stack pointer is updated and the address of the previous frame is
13732 stored, which means code that walks the stack frame across interrupts or
13733 signals may get corrupted data.
13736 @itemx -mno-fused-madd
13737 @opindex mfused-madd
13738 @opindex mno-fused-madd
13739 Generate code that uses (does not use) the floating point multiply and
13740 accumulate instructions. These instructions are generated by default if
13741 hardware floating is used.
13747 Generate code that uses (does not use) the half-word multiply and
13748 multiply-accumulate instructions on the IBM 405, 440 and 464 processors.
13749 These instructions are generated by default when targetting those
13756 Generate code that uses (does not use) the string-search @samp{dlmzb}
13757 instruction on the IBM 405, 440 and 464 processors. This instruction is
13758 generated by default when targetting those processors.
13760 @item -mno-bit-align
13762 @opindex mno-bit-align
13763 @opindex mbit-align
13764 On System V.4 and embedded PowerPC systems do not (do) force structures
13765 and unions that contain bit-fields to be aligned to the base type of the
13768 For example, by default a structure containing nothing but 8
13769 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
13770 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
13771 the structure would be aligned to a 1 byte boundary and be one byte in
13774 @item -mno-strict-align
13775 @itemx -mstrict-align
13776 @opindex mno-strict-align
13777 @opindex mstrict-align
13778 On System V.4 and embedded PowerPC systems do not (do) assume that
13779 unaligned memory references will be handled by the system.
13781 @item -mrelocatable
13782 @itemx -mno-relocatable
13783 @opindex mrelocatable
13784 @opindex mno-relocatable
13785 On embedded PowerPC systems generate code that allows (does not allow)
13786 the program to be relocated to a different address at runtime. If you
13787 use @option{-mrelocatable} on any module, all objects linked together must
13788 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
13790 @item -mrelocatable-lib
13791 @itemx -mno-relocatable-lib
13792 @opindex mrelocatable-lib
13793 @opindex mno-relocatable-lib
13794 On embedded PowerPC systems generate code that allows (does not allow)
13795 the program to be relocated to a different address at runtime. Modules
13796 compiled with @option{-mrelocatable-lib} can be linked with either modules
13797 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
13798 with modules compiled with the @option{-mrelocatable} options.
13804 On System V.4 and embedded PowerPC systems do not (do) assume that
13805 register 2 contains a pointer to a global area pointing to the addresses
13806 used in the program.
13809 @itemx -mlittle-endian
13811 @opindex mlittle-endian
13812 On System V.4 and embedded PowerPC systems compile code for the
13813 processor in little endian mode. The @option{-mlittle-endian} option is
13814 the same as @option{-mlittle}.
13817 @itemx -mbig-endian
13819 @opindex mbig-endian
13820 On System V.4 and embedded PowerPC systems compile code for the
13821 processor in big endian mode. The @option{-mbig-endian} option is
13822 the same as @option{-mbig}.
13824 @item -mdynamic-no-pic
13825 @opindex mdynamic-no-pic
13826 On Darwin and Mac OS X systems, compile code so that it is not
13827 relocatable, but that its external references are relocatable. The
13828 resulting code is suitable for applications, but not shared
13831 @item -mprioritize-restricted-insns=@var{priority}
13832 @opindex mprioritize-restricted-insns
13833 This option controls the priority that is assigned to
13834 dispatch-slot restricted instructions during the second scheduling
13835 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
13836 @var{no/highest/second-highest} priority to dispatch slot restricted
13839 @item -msched-costly-dep=@var{dependence_type}
13840 @opindex msched-costly-dep
13841 This option controls which dependences are considered costly
13842 by the target during instruction scheduling. The argument
13843 @var{dependence_type} takes one of the following values:
13844 @var{no}: no dependence is costly,
13845 @var{all}: all dependences are costly,
13846 @var{true_store_to_load}: a true dependence from store to load is costly,
13847 @var{store_to_load}: any dependence from store to load is costly,
13848 @var{number}: any dependence which latency >= @var{number} is costly.
13850 @item -minsert-sched-nops=@var{scheme}
13851 @opindex minsert-sched-nops
13852 This option controls which nop insertion scheme will be used during
13853 the second scheduling pass. The argument @var{scheme} takes one of the
13855 @var{no}: Don't insert nops.
13856 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
13857 according to the scheduler's grouping.
13858 @var{regroup_exact}: Insert nops to force costly dependent insns into
13859 separate groups. Insert exactly as many nops as needed to force an insn
13860 to a new group, according to the estimated processor grouping.
13861 @var{number}: Insert nops to force costly dependent insns into
13862 separate groups. Insert @var{number} nops to force an insn to a new group.
13865 @opindex mcall-sysv
13866 On System V.4 and embedded PowerPC systems compile code using calling
13867 conventions that adheres to the March 1995 draft of the System V
13868 Application Binary Interface, PowerPC processor supplement. This is the
13869 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
13871 @item -mcall-sysv-eabi
13872 @opindex mcall-sysv-eabi
13873 Specify both @option{-mcall-sysv} and @option{-meabi} options.
13875 @item -mcall-sysv-noeabi
13876 @opindex mcall-sysv-noeabi
13877 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
13879 @item -mcall-solaris
13880 @opindex mcall-solaris
13881 On System V.4 and embedded PowerPC systems compile code for the Solaris
13885 @opindex mcall-linux
13886 On System V.4 and embedded PowerPC systems compile code for the
13887 Linux-based GNU system.
13891 On System V.4 and embedded PowerPC systems compile code for the
13892 Hurd-based GNU system.
13894 @item -mcall-netbsd
13895 @opindex mcall-netbsd
13896 On System V.4 and embedded PowerPC systems compile code for the
13897 NetBSD operating system.
13899 @item -maix-struct-return
13900 @opindex maix-struct-return
13901 Return all structures in memory (as specified by the AIX ABI)@.
13903 @item -msvr4-struct-return
13904 @opindex msvr4-struct-return
13905 Return structures smaller than 8 bytes in registers (as specified by the
13908 @item -mabi=@var{abi-type}
13910 Extend the current ABI with a particular extension, or remove such extension.
13911 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
13912 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
13916 Extend the current ABI with SPE ABI extensions. This does not change
13917 the default ABI, instead it adds the SPE ABI extensions to the current
13921 @opindex mabi=no-spe
13922 Disable Booke SPE ABI extensions for the current ABI@.
13924 @item -mabi=ibmlongdouble
13925 @opindex mabi=ibmlongdouble
13926 Change the current ABI to use IBM extended precision long double.
13927 This is a PowerPC 32-bit SYSV ABI option.
13929 @item -mabi=ieeelongdouble
13930 @opindex mabi=ieeelongdouble
13931 Change the current ABI to use IEEE extended precision long double.
13932 This is a PowerPC 32-bit Linux ABI option.
13935 @itemx -mno-prototype
13936 @opindex mprototype
13937 @opindex mno-prototype
13938 On System V.4 and embedded PowerPC systems assume that all calls to
13939 variable argument functions are properly prototyped. Otherwise, the
13940 compiler must insert an instruction before every non prototyped call to
13941 set or clear bit 6 of the condition code register (@var{CR}) to
13942 indicate whether floating point values were passed in the floating point
13943 registers in case the function takes a variable arguments. With
13944 @option{-mprototype}, only calls to prototyped variable argument functions
13945 will set or clear the bit.
13949 On embedded PowerPC systems, assume that the startup module is called
13950 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
13951 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
13956 On embedded PowerPC systems, assume that the startup module is called
13957 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
13962 On embedded PowerPC systems, assume that the startup module is called
13963 @file{crt0.o} and the standard C libraries are @file{libads.a} and
13966 @item -myellowknife
13967 @opindex myellowknife
13968 On embedded PowerPC systems, assume that the startup module is called
13969 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
13974 On System V.4 and embedded PowerPC systems, specify that you are
13975 compiling for a VxWorks system.
13979 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
13980 header to indicate that @samp{eabi} extended relocations are used.
13986 On System V.4 and embedded PowerPC systems do (do not) adhere to the
13987 Embedded Applications Binary Interface (eabi) which is a set of
13988 modifications to the System V.4 specifications. Selecting @option{-meabi}
13989 means that the stack is aligned to an 8 byte boundary, a function
13990 @code{__eabi} is called to from @code{main} to set up the eabi
13991 environment, and the @option{-msdata} option can use both @code{r2} and
13992 @code{r13} to point to two separate small data areas. Selecting
13993 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
13994 do not call an initialization function from @code{main}, and the
13995 @option{-msdata} option will only use @code{r13} to point to a single
13996 small data area. The @option{-meabi} option is on by default if you
13997 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
14000 @opindex msdata=eabi
14001 On System V.4 and embedded PowerPC systems, put small initialized
14002 @code{const} global and static data in the @samp{.sdata2} section, which
14003 is pointed to by register @code{r2}. Put small initialized
14004 non-@code{const} global and static data in the @samp{.sdata} section,
14005 which is pointed to by register @code{r13}. Put small uninitialized
14006 global and static data in the @samp{.sbss} section, which is adjacent to
14007 the @samp{.sdata} section. The @option{-msdata=eabi} option is
14008 incompatible with the @option{-mrelocatable} option. The
14009 @option{-msdata=eabi} option also sets the @option{-memb} option.
14012 @opindex msdata=sysv
14013 On System V.4 and embedded PowerPC systems, put small global and static
14014 data in the @samp{.sdata} section, which is pointed to by register
14015 @code{r13}. Put small uninitialized global and static data in the
14016 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
14017 The @option{-msdata=sysv} option is incompatible with the
14018 @option{-mrelocatable} option.
14020 @item -msdata=default
14022 @opindex msdata=default
14024 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
14025 compile code the same as @option{-msdata=eabi}, otherwise compile code the
14026 same as @option{-msdata=sysv}.
14029 @opindex msdata-data
14030 On System V.4 and embedded PowerPC systems, put small global
14031 data in the @samp{.sdata} section. Put small uninitialized global
14032 data in the @samp{.sbss} section. Do not use register @code{r13}
14033 to address small data however. This is the default behavior unless
14034 other @option{-msdata} options are used.
14038 @opindex msdata=none
14040 On embedded PowerPC systems, put all initialized global and static data
14041 in the @samp{.data} section, and all uninitialized data in the
14042 @samp{.bss} section.
14046 @cindex smaller data references (PowerPC)
14047 @cindex .sdata/.sdata2 references (PowerPC)
14048 On embedded PowerPC systems, put global and static items less than or
14049 equal to @var{num} bytes into the small data or bss sections instead of
14050 the normal data or bss section. By default, @var{num} is 8. The
14051 @option{-G @var{num}} switch is also passed to the linker.
14052 All modules should be compiled with the same @option{-G @var{num}} value.
14055 @itemx -mno-regnames
14057 @opindex mno-regnames
14058 On System V.4 and embedded PowerPC systems do (do not) emit register
14059 names in the assembly language output using symbolic forms.
14062 @itemx -mno-longcall
14064 @opindex mno-longcall
14065 By default assume that all calls are far away so that a longer more
14066 expensive calling sequence is required. This is required for calls
14067 further than 32 megabytes (33,554,432 bytes) from the current location.
14068 A short call will be generated if the compiler knows
14069 the call cannot be that far away. This setting can be overridden by
14070 the @code{shortcall} function attribute, or by @code{#pragma
14073 Some linkers are capable of detecting out-of-range calls and generating
14074 glue code on the fly. On these systems, long calls are unnecessary and
14075 generate slower code. As of this writing, the AIX linker can do this,
14076 as can the GNU linker for PowerPC/64. It is planned to add this feature
14077 to the GNU linker for 32-bit PowerPC systems as well.
14079 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
14080 callee, L42'', plus a ``branch island'' (glue code). The two target
14081 addresses represent the callee and the ``branch island''. The
14082 Darwin/PPC linker will prefer the first address and generate a ``bl
14083 callee'' if the PPC ``bl'' instruction will reach the callee directly;
14084 otherwise, the linker will generate ``bl L42'' to call the ``branch
14085 island''. The ``branch island'' is appended to the body of the
14086 calling function; it computes the full 32-bit address of the callee
14089 On Mach-O (Darwin) systems, this option directs the compiler emit to
14090 the glue for every direct call, and the Darwin linker decides whether
14091 to use or discard it.
14093 In the future, we may cause GCC to ignore all longcall specifications
14094 when the linker is known to generate glue.
14098 Adds support for multithreading with the @dfn{pthreads} library.
14099 This option sets flags for both the preprocessor and linker.
14103 @node S/390 and zSeries Options
14104 @subsection S/390 and zSeries Options
14105 @cindex S/390 and zSeries Options
14107 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
14111 @itemx -msoft-float
14112 @opindex mhard-float
14113 @opindex msoft-float
14114 Use (do not use) the hardware floating-point instructions and registers
14115 for floating-point operations. When @option{-msoft-float} is specified,
14116 functions in @file{libgcc.a} will be used to perform floating-point
14117 operations. When @option{-mhard-float} is specified, the compiler
14118 generates IEEE floating-point instructions. This is the default.
14121 @itemx -mno-hard-dfp
14123 @opindex mno-hard-dfp
14124 Use (do not use) the hardware decimal-floating-point instructions for
14125 decimal-floating-point operations. When @option{-mno-hard-dfp} is
14126 specified, functions in @file{libgcc.a} will be used to perform
14127 decimal-floating-point operations. When @option{-mhard-dfp} is
14128 specified, the compiler generates decimal-floating-point hardware
14129 instructions. This is the default for @option{-march=z9-ec} or higher.
14131 @item -mlong-double-64
14132 @itemx -mlong-double-128
14133 @opindex mlong-double-64
14134 @opindex mlong-double-128
14135 These switches control the size of @code{long double} type. A size
14136 of 64bit makes the @code{long double} type equivalent to the @code{double}
14137 type. This is the default.
14140 @itemx -mno-backchain
14141 @opindex mbackchain
14142 @opindex mno-backchain
14143 Store (do not store) the address of the caller's frame as backchain pointer
14144 into the callee's stack frame.
14145 A backchain may be needed to allow debugging using tools that do not understand
14146 DWARF-2 call frame information.
14147 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
14148 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
14149 the backchain is placed into the topmost word of the 96/160 byte register
14152 In general, code compiled with @option{-mbackchain} is call-compatible with
14153 code compiled with @option{-mmo-backchain}; however, use of the backchain
14154 for debugging purposes usually requires that the whole binary is built with
14155 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
14156 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14157 to build a linux kernel use @option{-msoft-float}.
14159 The default is to not maintain the backchain.
14161 @item -mpacked-stack
14162 @itemx -mno-packed-stack
14163 @opindex mpacked-stack
14164 @opindex mno-packed-stack
14165 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
14166 specified, the compiler uses the all fields of the 96/160 byte register save
14167 area only for their default purpose; unused fields still take up stack space.
14168 When @option{-mpacked-stack} is specified, register save slots are densely
14169 packed at the top of the register save area; unused space is reused for other
14170 purposes, allowing for more efficient use of the available stack space.
14171 However, when @option{-mbackchain} is also in effect, the topmost word of
14172 the save area is always used to store the backchain, and the return address
14173 register is always saved two words below the backchain.
14175 As long as the stack frame backchain is not used, code generated with
14176 @option{-mpacked-stack} is call-compatible with code generated with
14177 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
14178 S/390 or zSeries generated code that uses the stack frame backchain at run
14179 time, not just for debugging purposes. Such code is not call-compatible
14180 with code compiled with @option{-mpacked-stack}. Also, note that the
14181 combination of @option{-mbackchain},
14182 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
14183 to build a linux kernel use @option{-msoft-float}.
14185 The default is to not use the packed stack layout.
14188 @itemx -mno-small-exec
14189 @opindex msmall-exec
14190 @opindex mno-small-exec
14191 Generate (or do not generate) code using the @code{bras} instruction
14192 to do subroutine calls.
14193 This only works reliably if the total executable size does not
14194 exceed 64k. The default is to use the @code{basr} instruction instead,
14195 which does not have this limitation.
14201 When @option{-m31} is specified, generate code compliant to the
14202 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
14203 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
14204 particular to generate 64-bit instructions. For the @samp{s390}
14205 targets, the default is @option{-m31}, while the @samp{s390x}
14206 targets default to @option{-m64}.
14212 When @option{-mzarch} is specified, generate code using the
14213 instructions available on z/Architecture.
14214 When @option{-mesa} is specified, generate code using the
14215 instructions available on ESA/390. Note that @option{-mesa} is
14216 not possible with @option{-m64}.
14217 When generating code compliant to the GNU/Linux for S/390 ABI,
14218 the default is @option{-mesa}. When generating code compliant
14219 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
14225 Generate (or do not generate) code using the @code{mvcle} instruction
14226 to perform block moves. When @option{-mno-mvcle} is specified,
14227 use a @code{mvc} loop instead. This is the default unless optimizing for
14234 Print (or do not print) additional debug information when compiling.
14235 The default is to not print debug information.
14237 @item -march=@var{cpu-type}
14239 Generate code that will run on @var{cpu-type}, which is the name of a system
14240 representing a certain processor type. Possible values for
14241 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990},
14242 @samp{z9-109}, @samp{z9-ec} and @samp{z10}.
14243 When generating code using the instructions available on z/Architecture,
14244 the default is @option{-march=z900}. Otherwise, the default is
14245 @option{-march=g5}.
14247 @item -mtune=@var{cpu-type}
14249 Tune to @var{cpu-type} everything applicable about the generated code,
14250 except for the ABI and the set of available instructions.
14251 The list of @var{cpu-type} values is the same as for @option{-march}.
14252 The default is the value used for @option{-march}.
14255 @itemx -mno-tpf-trace
14256 @opindex mtpf-trace
14257 @opindex mno-tpf-trace
14258 Generate code that adds (does not add) in TPF OS specific branches to trace
14259 routines in the operating system. This option is off by default, even
14260 when compiling for the TPF OS@.
14263 @itemx -mno-fused-madd
14264 @opindex mfused-madd
14265 @opindex mno-fused-madd
14266 Generate code that uses (does not use) the floating point multiply and
14267 accumulate instructions. These instructions are generated by default if
14268 hardware floating point is used.
14270 @item -mwarn-framesize=@var{framesize}
14271 @opindex mwarn-framesize
14272 Emit a warning if the current function exceeds the given frame size. Because
14273 this is a compile time check it doesn't need to be a real problem when the program
14274 runs. It is intended to identify functions which most probably cause
14275 a stack overflow. It is useful to be used in an environment with limited stack
14276 size e.g.@: the linux kernel.
14278 @item -mwarn-dynamicstack
14279 @opindex mwarn-dynamicstack
14280 Emit a warning if the function calls alloca or uses dynamically
14281 sized arrays. This is generally a bad idea with a limited stack size.
14283 @item -mstack-guard=@var{stack-guard}
14284 @itemx -mstack-size=@var{stack-size}
14285 @opindex mstack-guard
14286 @opindex mstack-size
14287 If these options are provided the s390 back end emits additional instructions in
14288 the function prologue which trigger a trap if the stack size is @var{stack-guard}
14289 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
14290 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
14291 the frame size of the compiled function is chosen.
14292 These options are intended to be used to help debugging stack overflow problems.
14293 The additionally emitted code causes only little overhead and hence can also be
14294 used in production like systems without greater performance degradation. The given
14295 values have to be exact powers of 2 and @var{stack-size} has to be greater than
14296 @var{stack-guard} without exceeding 64k.
14297 In order to be efficient the extra code makes the assumption that the stack starts
14298 at an address aligned to the value given by @var{stack-size}.
14299 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
14302 @node Score Options
14303 @subsection Score Options
14304 @cindex Score Options
14306 These options are defined for Score implementations:
14311 Compile code for big endian mode. This is the default.
14315 Compile code for little endian mode.
14319 Disable generate bcnz instruction.
14323 Enable generate unaligned load and store instruction.
14327 Enable the use of multiply-accumulate instructions. Disabled by default.
14331 Specify the SCORE5 as the target architecture.
14335 Specify the SCORE5U of the target architecture.
14339 Specify the SCORE7 as the target architecture. This is the default.
14343 Specify the SCORE7D as the target architecture.
14347 @subsection SH Options
14349 These @samp{-m} options are defined for the SH implementations:
14354 Generate code for the SH1.
14358 Generate code for the SH2.
14361 Generate code for the SH2e.
14365 Generate code for the SH3.
14369 Generate code for the SH3e.
14373 Generate code for the SH4 without a floating-point unit.
14375 @item -m4-single-only
14376 @opindex m4-single-only
14377 Generate code for the SH4 with a floating-point unit that only
14378 supports single-precision arithmetic.
14382 Generate code for the SH4 assuming the floating-point unit is in
14383 single-precision mode by default.
14387 Generate code for the SH4.
14391 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
14392 floating-point unit is not used.
14394 @item -m4a-single-only
14395 @opindex m4a-single-only
14396 Generate code for the SH4a, in such a way that no double-precision
14397 floating point operations are used.
14400 @opindex m4a-single
14401 Generate code for the SH4a assuming the floating-point unit is in
14402 single-precision mode by default.
14406 Generate code for the SH4a.
14410 Same as @option{-m4a-nofpu}, except that it implicitly passes
14411 @option{-dsp} to the assembler. GCC doesn't generate any DSP
14412 instructions at the moment.
14416 Compile code for the processor in big endian mode.
14420 Compile code for the processor in little endian mode.
14424 Align doubles at 64-bit boundaries. Note that this changes the calling
14425 conventions, and thus some functions from the standard C library will
14426 not work unless you recompile it first with @option{-mdalign}.
14430 Shorten some address references at link time, when possible; uses the
14431 linker option @option{-relax}.
14435 Use 32-bit offsets in @code{switch} tables. The default is to use
14440 Enable the use of bit manipulation instructions on SH2A.
14444 Enable the use of the instruction @code{fmovd}.
14448 Comply with the calling conventions defined by Renesas.
14452 Comply with the calling conventions defined by Renesas.
14456 Comply with the calling conventions defined for GCC before the Renesas
14457 conventions were available. This option is the default for all
14458 targets of the SH toolchain except for @samp{sh-symbianelf}.
14461 @opindex mnomacsave
14462 Mark the @code{MAC} register as call-clobbered, even if
14463 @option{-mhitachi} is given.
14467 Increase IEEE-compliance of floating-point code.
14468 At the moment, this is equivalent to @option{-fno-finite-math-only}.
14469 When generating 16 bit SH opcodes, getting IEEE-conforming results for
14470 comparisons of NANs / infinities incurs extra overhead in every
14471 floating point comparison, therefore the default is set to
14472 @option{-ffinite-math-only}.
14474 @item -minline-ic_invalidate
14475 @opindex minline-ic_invalidate
14476 Inline code to invalidate instruction cache entries after setting up
14477 nested function trampolines.
14478 This option has no effect if -musermode is in effect and the selected
14479 code generation option (e.g. -m4) does not allow the use of the icbi
14481 If the selected code generation option does not allow the use of the icbi
14482 instruction, and -musermode is not in effect, the inlined code will
14483 manipulate the instruction cache address array directly with an associative
14484 write. This not only requires privileged mode, but it will also
14485 fail if the cache line had been mapped via the TLB and has become unmapped.
14489 Dump instruction size and location in the assembly code.
14492 @opindex mpadstruct
14493 This option is deprecated. It pads structures to multiple of 4 bytes,
14494 which is incompatible with the SH ABI@.
14498 Optimize for space instead of speed. Implied by @option{-Os}.
14501 @opindex mprefergot
14502 When generating position-independent code, emit function calls using
14503 the Global Offset Table instead of the Procedure Linkage Table.
14507 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
14508 if the inlined code would not work in user mode.
14509 This is the default when the target is @code{sh-*-linux*}.
14511 @item -multcost=@var{number}
14512 @opindex multcost=@var{number}
14513 Set the cost to assume for a multiply insn.
14515 @item -mdiv=@var{strategy}
14516 @opindex mdiv=@var{strategy}
14517 Set the division strategy to use for SHmedia code. @var{strategy} must be
14518 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
14519 inv:call2, inv:fp .
14520 "fp" performs the operation in floating point. This has a very high latency,
14521 but needs only a few instructions, so it might be a good choice if
14522 your code has enough easily exploitable ILP to allow the compiler to
14523 schedule the floating point instructions together with other instructions.
14524 Division by zero causes a floating point exception.
14525 "inv" uses integer operations to calculate the inverse of the divisor,
14526 and then multiplies the dividend with the inverse. This strategy allows
14527 cse and hoisting of the inverse calculation. Division by zero calculates
14528 an unspecified result, but does not trap.
14529 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
14530 have been found, or if the entire operation has been hoisted to the same
14531 place, the last stages of the inverse calculation are intertwined with the
14532 final multiply to reduce the overall latency, at the expense of using a few
14533 more instructions, and thus offering fewer scheduling opportunities with
14535 "call" calls a library function that usually implements the inv:minlat
14537 This gives high code density for m5-*media-nofpu compilations.
14538 "call2" uses a different entry point of the same library function, where it
14539 assumes that a pointer to a lookup table has already been set up, which
14540 exposes the pointer load to cse / code hoisting optimizations.
14541 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
14542 code generation, but if the code stays unoptimized, revert to the "call",
14543 "call2", or "fp" strategies, respectively. Note that the
14544 potentially-trapping side effect of division by zero is carried by a
14545 separate instruction, so it is possible that all the integer instructions
14546 are hoisted out, but the marker for the side effect stays where it is.
14547 A recombination to fp operations or a call is not possible in that case.
14548 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
14549 that the inverse calculation was nor separated from the multiply, they speed
14550 up division where the dividend fits into 20 bits (plus sign where applicable),
14551 by inserting a test to skip a number of operations in this case; this test
14552 slows down the case of larger dividends. inv20u assumes the case of a such
14553 a small dividend to be unlikely, and inv20l assumes it to be likely.
14555 @item -mdivsi3_libfunc=@var{name}
14556 @opindex mdivsi3_libfunc=@var{name}
14557 Set the name of the library function used for 32 bit signed division to
14558 @var{name}. This only affect the name used in the call and inv:call
14559 division strategies, and the compiler will still expect the same
14560 sets of input/output/clobbered registers as if this option was not present.
14562 @item -mfixed-range=@var{register-range}
14563 @opindex mfixed-range
14564 Generate code treating the given register range as fixed registers.
14565 A fixed register is one that the register allocator can not use. This is
14566 useful when compiling kernel code. A register range is specified as
14567 two registers separated by a dash. Multiple register ranges can be
14568 specified separated by a comma.
14570 @item -madjust-unroll
14571 @opindex madjust-unroll
14572 Throttle unrolling to avoid thrashing target registers.
14573 This option only has an effect if the gcc code base supports the
14574 TARGET_ADJUST_UNROLL_MAX target hook.
14576 @item -mindexed-addressing
14577 @opindex mindexed-addressing
14578 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
14579 This is only safe if the hardware and/or OS implement 32 bit wrap-around
14580 semantics for the indexed addressing mode. The architecture allows the
14581 implementation of processors with 64 bit MMU, which the OS could use to
14582 get 32 bit addressing, but since no current hardware implementation supports
14583 this or any other way to make the indexed addressing mode safe to use in
14584 the 32 bit ABI, the default is -mno-indexed-addressing.
14586 @item -mgettrcost=@var{number}
14587 @opindex mgettrcost=@var{number}
14588 Set the cost assumed for the gettr instruction to @var{number}.
14589 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
14593 Assume pt* instructions won't trap. This will generally generate better
14594 scheduled code, but is unsafe on current hardware. The current architecture
14595 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
14596 This has the unintentional effect of making it unsafe to schedule ptabs /
14597 ptrel before a branch, or hoist it out of a loop. For example,
14598 __do_global_ctors, a part of libgcc that runs constructors at program
14599 startup, calls functions in a list which is delimited by @minus{}1. With the
14600 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
14601 That means that all the constructors will be run a bit quicker, but when
14602 the loop comes to the end of the list, the program crashes because ptabs
14603 loads @minus{}1 into a target register. Since this option is unsafe for any
14604 hardware implementing the current architecture specification, the default
14605 is -mno-pt-fixed. Unless the user specifies a specific cost with
14606 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
14607 this deters register allocation using target registers for storing
14610 @item -minvalid-symbols
14611 @opindex minvalid-symbols
14612 Assume symbols might be invalid. Ordinary function symbols generated by
14613 the compiler will always be valid to load with movi/shori/ptabs or
14614 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
14615 to generate symbols that will cause ptabs / ptrel to trap.
14616 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
14617 It will then prevent cross-basic-block cse, hoisting and most scheduling
14618 of symbol loads. The default is @option{-mno-invalid-symbols}.
14621 @node SPARC Options
14622 @subsection SPARC Options
14623 @cindex SPARC options
14625 These @samp{-m} options are supported on the SPARC:
14628 @item -mno-app-regs
14630 @opindex mno-app-regs
14632 Specify @option{-mapp-regs} to generate output using the global registers
14633 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
14636 To be fully SVR4 ABI compliant at the cost of some performance loss,
14637 specify @option{-mno-app-regs}. You should compile libraries and system
14638 software with this option.
14641 @itemx -mhard-float
14643 @opindex mhard-float
14644 Generate output containing floating point instructions. This is the
14648 @itemx -msoft-float
14650 @opindex msoft-float
14651 Generate output containing library calls for floating point.
14652 @strong{Warning:} the requisite libraries are not available for all SPARC
14653 targets. Normally the facilities of the machine's usual C compiler are
14654 used, but this cannot be done directly in cross-compilation. You must make
14655 your own arrangements to provide suitable library functions for
14656 cross-compilation. The embedded targets @samp{sparc-*-aout} and
14657 @samp{sparclite-*-*} do provide software floating point support.
14659 @option{-msoft-float} changes the calling convention in the output file;
14660 therefore, it is only useful if you compile @emph{all} of a program with
14661 this option. In particular, you need to compile @file{libgcc.a}, the
14662 library that comes with GCC, with @option{-msoft-float} in order for
14665 @item -mhard-quad-float
14666 @opindex mhard-quad-float
14667 Generate output containing quad-word (long double) floating point
14670 @item -msoft-quad-float
14671 @opindex msoft-quad-float
14672 Generate output containing library calls for quad-word (long double)
14673 floating point instructions. The functions called are those specified
14674 in the SPARC ABI@. This is the default.
14676 As of this writing, there are no SPARC implementations that have hardware
14677 support for the quad-word floating point instructions. They all invoke
14678 a trap handler for one of these instructions, and then the trap handler
14679 emulates the effect of the instruction. Because of the trap handler overhead,
14680 this is much slower than calling the ABI library routines. Thus the
14681 @option{-msoft-quad-float} option is the default.
14683 @item -mno-unaligned-doubles
14684 @itemx -munaligned-doubles
14685 @opindex mno-unaligned-doubles
14686 @opindex munaligned-doubles
14687 Assume that doubles have 8 byte alignment. This is the default.
14689 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
14690 alignment only if they are contained in another type, or if they have an
14691 absolute address. Otherwise, it assumes they have 4 byte alignment.
14692 Specifying this option avoids some rare compatibility problems with code
14693 generated by other compilers. It is not the default because it results
14694 in a performance loss, especially for floating point code.
14696 @item -mno-faster-structs
14697 @itemx -mfaster-structs
14698 @opindex mno-faster-structs
14699 @opindex mfaster-structs
14700 With @option{-mfaster-structs}, the compiler assumes that structures
14701 should have 8 byte alignment. This enables the use of pairs of
14702 @code{ldd} and @code{std} instructions for copies in structure
14703 assignment, in place of twice as many @code{ld} and @code{st} pairs.
14704 However, the use of this changed alignment directly violates the SPARC
14705 ABI@. Thus, it's intended only for use on targets where the developer
14706 acknowledges that their resulting code will not be directly in line with
14707 the rules of the ABI@.
14709 @item -mimpure-text
14710 @opindex mimpure-text
14711 @option{-mimpure-text}, used in addition to @option{-shared}, tells
14712 the compiler to not pass @option{-z text} to the linker when linking a
14713 shared object. Using this option, you can link position-dependent
14714 code into a shared object.
14716 @option{-mimpure-text} suppresses the ``relocations remain against
14717 allocatable but non-writable sections'' linker error message.
14718 However, the necessary relocations will trigger copy-on-write, and the
14719 shared object is not actually shared across processes. Instead of
14720 using @option{-mimpure-text}, you should compile all source code with
14721 @option{-fpic} or @option{-fPIC}.
14723 This option is only available on SunOS and Solaris.
14725 @item -mcpu=@var{cpu_type}
14727 Set the instruction set, register set, and instruction scheduling parameters
14728 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
14729 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
14730 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
14731 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
14732 @samp{ultrasparc3}, @samp{niagara} and @samp{niagara2}.
14734 Default instruction scheduling parameters are used for values that select
14735 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
14736 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
14738 Here is a list of each supported architecture and their supported
14743 v8: supersparc, hypersparc
14744 sparclite: f930, f934, sparclite86x
14746 v9: ultrasparc, ultrasparc3, niagara, niagara2
14749 By default (unless configured otherwise), GCC generates code for the V7
14750 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
14751 additionally optimizes it for the Cypress CY7C602 chip, as used in the
14752 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
14753 SPARCStation 1, 2, IPX etc.
14755 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
14756 architecture. The only difference from V7 code is that the compiler emits
14757 the integer multiply and integer divide instructions which exist in SPARC-V8
14758 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
14759 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
14762 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
14763 the SPARC architecture. This adds the integer multiply, integer divide step
14764 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
14765 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
14766 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
14767 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
14768 MB86934 chip, which is the more recent SPARClite with FPU@.
14770 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
14771 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
14772 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
14773 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
14774 optimizes it for the TEMIC SPARClet chip.
14776 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
14777 architecture. This adds 64-bit integer and floating-point move instructions,
14778 3 additional floating-point condition code registers and conditional move
14779 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
14780 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
14781 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
14782 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
14783 @option{-mcpu=niagara}, the compiler additionally optimizes it for
14784 Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
14785 additionally optimizes it for Sun UltraSPARC T2 chips.
14787 @item -mtune=@var{cpu_type}
14789 Set the instruction scheduling parameters for machine type
14790 @var{cpu_type}, but do not set the instruction set or register set that the
14791 option @option{-mcpu=@var{cpu_type}} would.
14793 The same values for @option{-mcpu=@var{cpu_type}} can be used for
14794 @option{-mtune=@var{cpu_type}}, but the only useful values are those
14795 that select a particular cpu implementation. Those are @samp{cypress},
14796 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
14797 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
14798 @samp{ultrasparc3}, @samp{niagara}, and @samp{niagara2}.
14803 @opindex mno-v8plus
14804 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
14805 difference from the V8 ABI is that the global and out registers are
14806 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
14807 mode for all SPARC-V9 processors.
14813 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
14814 Visual Instruction Set extensions. The default is @option{-mno-vis}.
14817 These @samp{-m} options are supported in addition to the above
14818 on SPARC-V9 processors in 64-bit environments:
14821 @item -mlittle-endian
14822 @opindex mlittle-endian
14823 Generate code for a processor running in little-endian mode. It is only
14824 available for a few configurations and most notably not on Solaris and Linux.
14830 Generate code for a 32-bit or 64-bit environment.
14831 The 32-bit environment sets int, long and pointer to 32 bits.
14832 The 64-bit environment sets int to 32 bits and long and pointer
14835 @item -mcmodel=medlow
14836 @opindex mcmodel=medlow
14837 Generate code for the Medium/Low code model: 64-bit addresses, programs
14838 must be linked in the low 32 bits of memory. Programs can be statically
14839 or dynamically linked.
14841 @item -mcmodel=medmid
14842 @opindex mcmodel=medmid
14843 Generate code for the Medium/Middle code model: 64-bit addresses, programs
14844 must be linked in the low 44 bits of memory, the text and data segments must
14845 be less than 2GB in size and the data segment must be located within 2GB of
14848 @item -mcmodel=medany
14849 @opindex mcmodel=medany
14850 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
14851 may be linked anywhere in memory, the text and data segments must be less
14852 than 2GB in size and the data segment must be located within 2GB of the
14855 @item -mcmodel=embmedany
14856 @opindex mcmodel=embmedany
14857 Generate code for the Medium/Anywhere code model for embedded systems:
14858 64-bit addresses, the text and data segments must be less than 2GB in
14859 size, both starting anywhere in memory (determined at link time). The
14860 global register %g4 points to the base of the data segment. Programs
14861 are statically linked and PIC is not supported.
14864 @itemx -mno-stack-bias
14865 @opindex mstack-bias
14866 @opindex mno-stack-bias
14867 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
14868 frame pointer if present, are offset by @minus{}2047 which must be added back
14869 when making stack frame references. This is the default in 64-bit mode.
14870 Otherwise, assume no such offset is present.
14873 These switches are supported in addition to the above on Solaris:
14878 Add support for multithreading using the Solaris threads library. This
14879 option sets flags for both the preprocessor and linker. This option does
14880 not affect the thread safety of object code produced by the compiler or
14881 that of libraries supplied with it.
14885 Add support for multithreading using the POSIX threads library. This
14886 option sets flags for both the preprocessor and linker. This option does
14887 not affect the thread safety of object code produced by the compiler or
14888 that of libraries supplied with it.
14892 This is a synonym for @option{-pthreads}.
14896 @subsection SPU Options
14897 @cindex SPU options
14899 These @samp{-m} options are supported on the SPU:
14903 @itemx -merror-reloc
14904 @opindex mwarn-reloc
14905 @opindex merror-reloc
14907 The loader for SPU does not handle dynamic relocations. By default, GCC
14908 will give an error when it generates code that requires a dynamic
14909 relocation. @option{-mno-error-reloc} disables the error,
14910 @option{-mwarn-reloc} will generate a warning instead.
14913 @itemx -munsafe-dma
14915 @opindex munsafe-dma
14917 Instructions which initiate or test completion of DMA must not be
14918 reordered with respect to loads and stores of the memory which is being
14919 accessed. Users typically address this problem using the volatile
14920 keyword, but that can lead to inefficient code in places where the
14921 memory is known to not change. Rather than mark the memory as volatile
14922 we treat the DMA instructions as potentially effecting all memory. With
14923 @option{-munsafe-dma} users must use the volatile keyword to protect
14926 @item -mbranch-hints
14927 @opindex mbranch-hints
14929 By default, GCC will generate a branch hint instruction to avoid
14930 pipeline stalls for always taken or probably taken branches. A hint
14931 will not be generated closer than 8 instructions away from its branch.
14932 There is little reason to disable them, except for debugging purposes,
14933 or to make an object a little bit smaller.
14937 @opindex msmall-mem
14938 @opindex mlarge-mem
14940 By default, GCC generates code assuming that addresses are never larger
14941 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
14942 a full 32 bit address.
14947 By default, GCC links against startup code that assumes the SPU-style
14948 main function interface (which has an unconventional parameter list).
14949 With @option{-mstdmain}, GCC will link your program against startup
14950 code that assumes a C99-style interface to @code{main}, including a
14951 local copy of @code{argv} strings.
14953 @item -mfixed-range=@var{register-range}
14954 @opindex mfixed-range
14955 Generate code treating the given register range as fixed registers.
14956 A fixed register is one that the register allocator can not use. This is
14957 useful when compiling kernel code. A register range is specified as
14958 two registers separated by a dash. Multiple register ranges can be
14959 specified separated by a comma.
14962 @itemx -mdual-nops=@var{n}
14963 @opindex mdual-nops
14964 By default, GCC will insert nops to increase dual issue when it expects
14965 it to increase performance. @var{n} can be a value from 0 to 10. A
14966 smaller @var{n} will insert fewer nops. 10 is the default, 0 is the
14967 same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
14969 @item -mhint-max-nops=@var{n}
14970 @opindex mhint-max-nops
14971 Maximum number of nops to insert for a branch hint. A branch hint must
14972 be at least 8 instructions away from the branch it is effecting. GCC
14973 will insert up to @var{n} nops to enforce this, otherwise it will not
14974 generate the branch hint.
14976 @item -mhint-max-distance=@var{n}
14977 @opindex mhint-max-distance
14978 The encoding of the branch hint instruction limits the hint to be within
14979 256 instructions of the branch it is effecting. By default, GCC makes
14980 sure it is within 125.
14983 @opindex msafe-hints
14984 Work around a hardware bug which causes the SPU to stall indefinitely.
14985 By default, GCC will insert the @code{hbrp} instruction to make sure
14986 this stall won't happen.
14990 @node System V Options
14991 @subsection Options for System V
14993 These additional options are available on System V Release 4 for
14994 compatibility with other compilers on those systems:
14999 Create a shared object.
15000 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
15004 Identify the versions of each tool used by the compiler, in a
15005 @code{.ident} assembler directive in the output.
15009 Refrain from adding @code{.ident} directives to the output file (this is
15012 @item -YP,@var{dirs}
15014 Search the directories @var{dirs}, and no others, for libraries
15015 specified with @option{-l}.
15017 @item -Ym,@var{dir}
15019 Look in the directory @var{dir} to find the M4 preprocessor.
15020 The assembler uses this option.
15021 @c This is supposed to go with a -Yd for predefined M4 macro files, but
15022 @c the generic assembler that comes with Solaris takes just -Ym.
15026 @subsection V850 Options
15027 @cindex V850 Options
15029 These @samp{-m} options are defined for V850 implementations:
15033 @itemx -mno-long-calls
15034 @opindex mlong-calls
15035 @opindex mno-long-calls
15036 Treat all calls as being far away (near). If calls are assumed to be
15037 far away, the compiler will always load the functions address up into a
15038 register, and call indirect through the pointer.
15044 Do not optimize (do optimize) basic blocks that use the same index
15045 pointer 4 or more times to copy pointer into the @code{ep} register, and
15046 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
15047 option is on by default if you optimize.
15049 @item -mno-prolog-function
15050 @itemx -mprolog-function
15051 @opindex mno-prolog-function
15052 @opindex mprolog-function
15053 Do not use (do use) external functions to save and restore registers
15054 at the prologue and epilogue of a function. The external functions
15055 are slower, but use less code space if more than one function saves
15056 the same number of registers. The @option{-mprolog-function} option
15057 is on by default if you optimize.
15061 Try to make the code as small as possible. At present, this just turns
15062 on the @option{-mep} and @option{-mprolog-function} options.
15064 @item -mtda=@var{n}
15066 Put static or global variables whose size is @var{n} bytes or less into
15067 the tiny data area that register @code{ep} points to. The tiny data
15068 area can hold up to 256 bytes in total (128 bytes for byte references).
15070 @item -msda=@var{n}
15072 Put static or global variables whose size is @var{n} bytes or less into
15073 the small data area that register @code{gp} points to. The small data
15074 area can hold up to 64 kilobytes.
15076 @item -mzda=@var{n}
15078 Put static or global variables whose size is @var{n} bytes or less into
15079 the first 32 kilobytes of memory.
15083 Specify that the target processor is the V850.
15086 @opindex mbig-switch
15087 Generate code suitable for big switch tables. Use this option only if
15088 the assembler/linker complain about out of range branches within a switch
15093 This option will cause r2 and r5 to be used in the code generated by
15094 the compiler. This setting is the default.
15096 @item -mno-app-regs
15097 @opindex mno-app-regs
15098 This option will cause r2 and r5 to be treated as fixed registers.
15102 Specify that the target processor is the V850E1. The preprocessor
15103 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
15104 this option is used.
15108 Specify that the target processor is the V850E@. The preprocessor
15109 constant @samp{__v850e__} will be defined if this option is used.
15111 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
15112 are defined then a default target processor will be chosen and the
15113 relevant @samp{__v850*__} preprocessor constant will be defined.
15115 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
15116 defined, regardless of which processor variant is the target.
15118 @item -mdisable-callt
15119 @opindex mdisable-callt
15120 This option will suppress generation of the CALLT instruction for the
15121 v850e and v850e1 flavors of the v850 architecture. The default is
15122 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
15127 @subsection VAX Options
15128 @cindex VAX options
15130 These @samp{-m} options are defined for the VAX:
15135 Do not output certain jump instructions (@code{aobleq} and so on)
15136 that the Unix assembler for the VAX cannot handle across long
15141 Do output those jump instructions, on the assumption that you
15142 will assemble with the GNU assembler.
15146 Output code for g-format floating point numbers instead of d-format.
15149 @node VxWorks Options
15150 @subsection VxWorks Options
15151 @cindex VxWorks Options
15153 The options in this section are defined for all VxWorks targets.
15154 Options specific to the target hardware are listed with the other
15155 options for that target.
15160 GCC can generate code for both VxWorks kernels and real time processes
15161 (RTPs). This option switches from the former to the latter. It also
15162 defines the preprocessor macro @code{__RTP__}.
15165 @opindex non-static
15166 Link an RTP executable against shared libraries rather than static
15167 libraries. The options @option{-static} and @option{-shared} can
15168 also be used for RTPs (@pxref{Link Options}); @option{-static}
15175 These options are passed down to the linker. They are defined for
15176 compatibility with Diab.
15179 @opindex Xbind-lazy
15180 Enable lazy binding of function calls. This option is equivalent to
15181 @option{-Wl,-z,now} and is defined for compatibility with Diab.
15185 Disable lazy binding of function calls. This option is the default and
15186 is defined for compatibility with Diab.
15189 @node x86-64 Options
15190 @subsection x86-64 Options
15191 @cindex x86-64 options
15193 These are listed under @xref{i386 and x86-64 Options}.
15195 @node Xstormy16 Options
15196 @subsection Xstormy16 Options
15197 @cindex Xstormy16 Options
15199 These options are defined for Xstormy16:
15204 Choose startup files and linker script suitable for the simulator.
15207 @node Xtensa Options
15208 @subsection Xtensa Options
15209 @cindex Xtensa Options
15211 These options are supported for Xtensa targets:
15215 @itemx -mno-const16
15217 @opindex mno-const16
15218 Enable or disable use of @code{CONST16} instructions for loading
15219 constant values. The @code{CONST16} instruction is currently not a
15220 standard option from Tensilica. When enabled, @code{CONST16}
15221 instructions are always used in place of the standard @code{L32R}
15222 instructions. The use of @code{CONST16} is enabled by default only if
15223 the @code{L32R} instruction is not available.
15226 @itemx -mno-fused-madd
15227 @opindex mfused-madd
15228 @opindex mno-fused-madd
15229 Enable or disable use of fused multiply/add and multiply/subtract
15230 instructions in the floating-point option. This has no effect if the
15231 floating-point option is not also enabled. Disabling fused multiply/add
15232 and multiply/subtract instructions forces the compiler to use separate
15233 instructions for the multiply and add/subtract operations. This may be
15234 desirable in some cases where strict IEEE 754-compliant results are
15235 required: the fused multiply add/subtract instructions do not round the
15236 intermediate result, thereby producing results with @emph{more} bits of
15237 precision than specified by the IEEE standard. Disabling fused multiply
15238 add/subtract instructions also ensures that the program output is not
15239 sensitive to the compiler's ability to combine multiply and add/subtract
15242 @item -mserialize-volatile
15243 @itemx -mno-serialize-volatile
15244 @opindex mserialize-volatile
15245 @opindex mno-serialize-volatile
15246 When this option is enabled, GCC inserts @code{MEMW} instructions before
15247 @code{volatile} memory references to guarantee sequential consistency.
15248 The default is @option{-mserialize-volatile}. Use
15249 @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
15251 @item -mtext-section-literals
15252 @itemx -mno-text-section-literals
15253 @opindex mtext-section-literals
15254 @opindex mno-text-section-literals
15255 Control the treatment of literal pools. The default is
15256 @option{-mno-text-section-literals}, which places literals in a separate
15257 section in the output file. This allows the literal pool to be placed
15258 in a data RAM/ROM, and it also allows the linker to combine literal
15259 pools from separate object files to remove redundant literals and
15260 improve code size. With @option{-mtext-section-literals}, the literals
15261 are interspersed in the text section in order to keep them as close as
15262 possible to their references. This may be necessary for large assembly
15265 @item -mtarget-align
15266 @itemx -mno-target-align
15267 @opindex mtarget-align
15268 @opindex mno-target-align
15269 When this option is enabled, GCC instructs the assembler to
15270 automatically align instructions to reduce branch penalties at the
15271 expense of some code density. The assembler attempts to widen density
15272 instructions to align branch targets and the instructions following call
15273 instructions. If there are not enough preceding safe density
15274 instructions to align a target, no widening will be performed. The
15275 default is @option{-mtarget-align}. These options do not affect the
15276 treatment of auto-aligned instructions like @code{LOOP}, which the
15277 assembler will always align, either by widening density instructions or
15278 by inserting no-op instructions.
15281 @itemx -mno-longcalls
15282 @opindex mlongcalls
15283 @opindex mno-longcalls
15284 When this option is enabled, GCC instructs the assembler to translate
15285 direct calls to indirect calls unless it can determine that the target
15286 of a direct call is in the range allowed by the call instruction. This
15287 translation typically occurs for calls to functions in other source
15288 files. Specifically, the assembler translates a direct @code{CALL}
15289 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
15290 The default is @option{-mno-longcalls}. This option should be used in
15291 programs where the call target can potentially be out of range. This
15292 option is implemented in the assembler, not the compiler, so the
15293 assembly code generated by GCC will still show direct call
15294 instructions---look at the disassembled object code to see the actual
15295 instructions. Note that the assembler will use an indirect call for
15296 every cross-file call, not just those that really will be out of range.
15299 @node zSeries Options
15300 @subsection zSeries Options
15301 @cindex zSeries options
15303 These are listed under @xref{S/390 and zSeries Options}.
15305 @node Code Gen Options
15306 @section Options for Code Generation Conventions
15307 @cindex code generation conventions
15308 @cindex options, code generation
15309 @cindex run-time options
15311 These machine-independent options control the interface conventions
15312 used in code generation.
15314 Most of them have both positive and negative forms; the negative form
15315 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
15316 one of the forms is listed---the one which is not the default. You
15317 can figure out the other form by either removing @samp{no-} or adding
15321 @item -fbounds-check
15322 @opindex fbounds-check
15323 For front-ends that support it, generate additional code to check that
15324 indices used to access arrays are within the declared range. This is
15325 currently only supported by the Java and Fortran front-ends, where
15326 this option defaults to true and false respectively.
15330 This option generates traps for signed overflow on addition, subtraction,
15331 multiplication operations.
15335 This option instructs the compiler to assume that signed arithmetic
15336 overflow of addition, subtraction and multiplication wraps around
15337 using twos-complement representation. This flag enables some optimizations
15338 and disables others. This option is enabled by default for the Java
15339 front-end, as required by the Java language specification.
15342 @opindex fexceptions
15343 Enable exception handling. Generates extra code needed to propagate
15344 exceptions. For some targets, this implies GCC will generate frame
15345 unwind information for all functions, which can produce significant data
15346 size overhead, although it does not affect execution. If you do not
15347 specify this option, GCC will enable it by default for languages like
15348 C++ which normally require exception handling, and disable it for
15349 languages like C that do not normally require it. However, you may need
15350 to enable this option when compiling C code that needs to interoperate
15351 properly with exception handlers written in C++. You may also wish to
15352 disable this option if you are compiling older C++ programs that don't
15353 use exception handling.
15355 @item -fnon-call-exceptions
15356 @opindex fnon-call-exceptions
15357 Generate code that allows trapping instructions to throw exceptions.
15358 Note that this requires platform-specific runtime support that does
15359 not exist everywhere. Moreover, it only allows @emph{trapping}
15360 instructions to throw exceptions, i.e.@: memory references or floating
15361 point instructions. It does not allow exceptions to be thrown from
15362 arbitrary signal handlers such as @code{SIGALRM}.
15364 @item -funwind-tables
15365 @opindex funwind-tables
15366 Similar to @option{-fexceptions}, except that it will just generate any needed
15367 static data, but will not affect the generated code in any other way.
15368 You will normally not enable this option; instead, a language processor
15369 that needs this handling would enable it on your behalf.
15371 @item -fasynchronous-unwind-tables
15372 @opindex fasynchronous-unwind-tables
15373 Generate unwind table in dwarf2 format, if supported by target machine. The
15374 table is exact at each instruction boundary, so it can be used for stack
15375 unwinding from asynchronous events (such as debugger or garbage collector).
15377 @item -fpcc-struct-return
15378 @opindex fpcc-struct-return
15379 Return ``short'' @code{struct} and @code{union} values in memory like
15380 longer ones, rather than in registers. This convention is less
15381 efficient, but it has the advantage of allowing intercallability between
15382 GCC-compiled files and files compiled with other compilers, particularly
15383 the Portable C Compiler (pcc).
15385 The precise convention for returning structures in memory depends
15386 on the target configuration macros.
15388 Short structures and unions are those whose size and alignment match
15389 that of some integer type.
15391 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
15392 switch is not binary compatible with code compiled with the
15393 @option{-freg-struct-return} switch.
15394 Use it to conform to a non-default application binary interface.
15396 @item -freg-struct-return
15397 @opindex freg-struct-return
15398 Return @code{struct} and @code{union} values in registers when possible.
15399 This is more efficient for small structures than
15400 @option{-fpcc-struct-return}.
15402 If you specify neither @option{-fpcc-struct-return} nor
15403 @option{-freg-struct-return}, GCC defaults to whichever convention is
15404 standard for the target. If there is no standard convention, GCC
15405 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
15406 the principal compiler. In those cases, we can choose the standard, and
15407 we chose the more efficient register return alternative.
15409 @strong{Warning:} code compiled with the @option{-freg-struct-return}
15410 switch is not binary compatible with code compiled with the
15411 @option{-fpcc-struct-return} switch.
15412 Use it to conform to a non-default application binary interface.
15414 @item -fshort-enums
15415 @opindex fshort-enums
15416 Allocate to an @code{enum} type only as many bytes as it needs for the
15417 declared range of possible values. Specifically, the @code{enum} type
15418 will be equivalent to the smallest integer type which has enough room.
15420 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
15421 code that is not binary compatible with code generated without that switch.
15422 Use it to conform to a non-default application binary interface.
15424 @item -fshort-double
15425 @opindex fshort-double
15426 Use the same size for @code{double} as for @code{float}.
15428 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
15429 code that is not binary compatible with code generated without that switch.
15430 Use it to conform to a non-default application binary interface.
15432 @item -fshort-wchar
15433 @opindex fshort-wchar
15434 Override the underlying type for @samp{wchar_t} to be @samp{short
15435 unsigned int} instead of the default for the target. This option is
15436 useful for building programs to run under WINE@.
15438 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
15439 code that is not binary compatible with code generated without that switch.
15440 Use it to conform to a non-default application binary interface.
15443 @opindex fno-common
15444 In C, allocate even uninitialized global variables in the data section of the
15445 object file, rather than generating them as common blocks. This has the
15446 effect that if the same variable is declared (without @code{extern}) in
15447 two different compilations, you will get an error when you link them.
15448 The only reason this might be useful is if you wish to verify that the
15449 program will work on other systems which always work this way.
15453 Ignore the @samp{#ident} directive.
15455 @item -finhibit-size-directive
15456 @opindex finhibit-size-directive
15457 Don't output a @code{.size} assembler directive, or anything else that
15458 would cause trouble if the function is split in the middle, and the
15459 two halves are placed at locations far apart in memory. This option is
15460 used when compiling @file{crtstuff.c}; you should not need to use it
15463 @item -fverbose-asm
15464 @opindex fverbose-asm
15465 Put extra commentary information in the generated assembly code to
15466 make it more readable. This option is generally only of use to those
15467 who actually need to read the generated assembly code (perhaps while
15468 debugging the compiler itself).
15470 @option{-fno-verbose-asm}, the default, causes the
15471 extra information to be omitted and is useful when comparing two assembler
15474 @item -frecord-gcc-switches
15475 @opindex frecord-gcc-switches
15476 This switch causes the command line that was used to invoke the
15477 compiler to be recorded into the object file that is being created.
15478 This switch is only implemented on some targets and the exact format
15479 of the recording is target and binary file format dependent, but it
15480 usually takes the form of a section containing ASCII text. This
15481 switch is related to the @option{-fverbose-asm} switch, but that
15482 switch only records information in the assembler output file as
15483 comments, so it never reaches the object file.
15487 @cindex global offset table
15489 Generate position-independent code (PIC) suitable for use in a shared
15490 library, if supported for the target machine. Such code accesses all
15491 constant addresses through a global offset table (GOT)@. The dynamic
15492 loader resolves the GOT entries when the program starts (the dynamic
15493 loader is not part of GCC; it is part of the operating system). If
15494 the GOT size for the linked executable exceeds a machine-specific
15495 maximum size, you get an error message from the linker indicating that
15496 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
15497 instead. (These maximums are 8k on the SPARC and 32k
15498 on the m68k and RS/6000. The 386 has no such limit.)
15500 Position-independent code requires special support, and therefore works
15501 only on certain machines. For the 386, GCC supports PIC for System V
15502 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
15503 position-independent.
15505 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15510 If supported for the target machine, emit position-independent code,
15511 suitable for dynamic linking and avoiding any limit on the size of the
15512 global offset table. This option makes a difference on the m68k,
15513 PowerPC and SPARC@.
15515 Position-independent code requires special support, and therefore works
15516 only on certain machines.
15518 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
15525 These options are similar to @option{-fpic} and @option{-fPIC}, but
15526 generated position independent code can be only linked into executables.
15527 Usually these options are used when @option{-pie} GCC option will be
15528 used during linking.
15530 @option{-fpie} and @option{-fPIE} both define the macros
15531 @code{__pie__} and @code{__PIE__}. The macros have the value 1
15532 for @option{-fpie} and 2 for @option{-fPIE}.
15534 @item -fno-jump-tables
15535 @opindex fno-jump-tables
15536 Do not use jump tables for switch statements even where it would be
15537 more efficient than other code generation strategies. This option is
15538 of use in conjunction with @option{-fpic} or @option{-fPIC} for
15539 building code which forms part of a dynamic linker and cannot
15540 reference the address of a jump table. On some targets, jump tables
15541 do not require a GOT and this option is not needed.
15543 @item -ffixed-@var{reg}
15545 Treat the register named @var{reg} as a fixed register; generated code
15546 should never refer to it (except perhaps as a stack pointer, frame
15547 pointer or in some other fixed role).
15549 @var{reg} must be the name of a register. The register names accepted
15550 are machine-specific and are defined in the @code{REGISTER_NAMES}
15551 macro in the machine description macro file.
15553 This flag does not have a negative form, because it specifies a
15556 @item -fcall-used-@var{reg}
15557 @opindex fcall-used
15558 Treat the register named @var{reg} as an allocable register that is
15559 clobbered by function calls. It may be allocated for temporaries or
15560 variables that do not live across a call. Functions compiled this way
15561 will not save and restore the register @var{reg}.
15563 It is an error to used this flag with the frame pointer or stack pointer.
15564 Use of this flag for other registers that have fixed pervasive roles in
15565 the machine's execution model will produce disastrous results.
15567 This flag does not have a negative form, because it specifies a
15570 @item -fcall-saved-@var{reg}
15571 @opindex fcall-saved
15572 Treat the register named @var{reg} as an allocable register saved by
15573 functions. It may be allocated even for temporaries or variables that
15574 live across a call. Functions compiled this way will save and restore
15575 the register @var{reg} if they use it.
15577 It is an error to used this flag with the frame pointer or stack pointer.
15578 Use of this flag for other registers that have fixed pervasive roles in
15579 the machine's execution model will produce disastrous results.
15581 A different sort of disaster will result from the use of this flag for
15582 a register in which function values may be returned.
15584 This flag does not have a negative form, because it specifies a
15587 @item -fpack-struct[=@var{n}]
15588 @opindex fpack-struct
15589 Without a value specified, pack all structure members together without
15590 holes. When a value is specified (which must be a small power of two), pack
15591 structure members according to this value, representing the maximum
15592 alignment (that is, objects with default alignment requirements larger than
15593 this will be output potentially unaligned at the next fitting location.
15595 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
15596 code that is not binary compatible with code generated without that switch.
15597 Additionally, it makes the code suboptimal.
15598 Use it to conform to a non-default application binary interface.
15600 @item -finstrument-functions
15601 @opindex finstrument-functions
15602 Generate instrumentation calls for entry and exit to functions. Just
15603 after function entry and just before function exit, the following
15604 profiling functions will be called with the address of the current
15605 function and its call site. (On some platforms,
15606 @code{__builtin_return_address} does not work beyond the current
15607 function, so the call site information may not be available to the
15608 profiling functions otherwise.)
15611 void __cyg_profile_func_enter (void *this_fn,
15613 void __cyg_profile_func_exit (void *this_fn,
15617 The first argument is the address of the start of the current function,
15618 which may be looked up exactly in the symbol table.
15620 This instrumentation is also done for functions expanded inline in other
15621 functions. The profiling calls will indicate where, conceptually, the
15622 inline function is entered and exited. This means that addressable
15623 versions of such functions must be available. If all your uses of a
15624 function are expanded inline, this may mean an additional expansion of
15625 code size. If you use @samp{extern inline} in your C code, an
15626 addressable version of such functions must be provided. (This is
15627 normally the case anyways, but if you get lucky and the optimizer always
15628 expands the functions inline, you might have gotten away without
15629 providing static copies.)
15631 A function may be given the attribute @code{no_instrument_function}, in
15632 which case this instrumentation will not be done. This can be used, for
15633 example, for the profiling functions listed above, high-priority
15634 interrupt routines, and any functions from which the profiling functions
15635 cannot safely be called (perhaps signal handlers, if the profiling
15636 routines generate output or allocate memory).
15638 @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
15639 @opindex finstrument-functions-exclude-file-list
15641 Set the list of functions that are excluded from instrumentation (see
15642 the description of @code{-finstrument-functions}). If the file that
15643 contains a function definition matches with one of @var{file}, then
15644 that function is not instrumented. The match is done on substrings:
15645 if the @var{file} parameter is a substring of the file name, it is
15646 considered to be a match.
15649 @code{-finstrument-functions-exclude-file-list=/bits/stl,include/sys}
15650 will exclude any inline function defined in files whose pathnames
15651 contain @code{/bits/stl} or @code{include/sys}.
15653 If, for some reason, you want to include letter @code{','} in one of
15654 @var{sym}, write @code{'\,'}. For example,
15655 @code{-finstrument-functions-exclude-file-list='\,\,tmp'}
15656 (note the single quote surrounding the option).
15658 @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
15659 @opindex finstrument-functions-exclude-function-list
15661 This is similar to @code{-finstrument-functions-exclude-file-list},
15662 but this option sets the list of function names to be excluded from
15663 instrumentation. The function name to be matched is its user-visible
15664 name, such as @code{vector<int> blah(const vector<int> &)}, not the
15665 internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
15666 match is done on substrings: if the @var{sym} parameter is a substring
15667 of the function name, it is considered to be a match.
15669 @item -fstack-check
15670 @opindex fstack-check
15671 Generate code to verify that you do not go beyond the boundary of the
15672 stack. You should specify this flag if you are running in an
15673 environment with multiple threads, but only rarely need to specify it in
15674 a single-threaded environment since stack overflow is automatically
15675 detected on nearly all systems if there is only one stack.
15677 Note that this switch does not actually cause checking to be done; the
15678 operating system or the language runtime must do that. The switch causes
15679 generation of code to ensure that they see the stack being extended.
15681 You can additionally specify a string parameter: @code{no} means no
15682 checking, @code{generic} means force the use of old-style checking,
15683 @code{specific} means use the best checking method and is equivalent
15684 to bare @option{-fstack-check}.
15686 Old-style checking is a generic mechanism that requires no specific
15687 target support in the compiler but comes with the following drawbacks:
15691 Modified allocation strategy for large objects: they will always be
15692 allocated dynamically if their size exceeds a fixed threshold.
15695 Fixed limit on the size of the static frame of functions: when it is
15696 topped by a particular function, stack checking is not reliable and
15697 a warning is issued by the compiler.
15700 Inefficiency: because of both the modified allocation strategy and the
15701 generic implementation, the performances of the code are hampered.
15704 Note that old-style stack checking is also the fallback method for
15705 @code{specific} if no target support has been added in the compiler.
15707 @item -fstack-limit-register=@var{reg}
15708 @itemx -fstack-limit-symbol=@var{sym}
15709 @itemx -fno-stack-limit
15710 @opindex fstack-limit-register
15711 @opindex fstack-limit-symbol
15712 @opindex fno-stack-limit
15713 Generate code to ensure that the stack does not grow beyond a certain value,
15714 either the value of a register or the address of a symbol. If the stack
15715 would grow beyond the value, a signal is raised. For most targets,
15716 the signal is raised before the stack overruns the boundary, so
15717 it is possible to catch the signal without taking special precautions.
15719 For instance, if the stack starts at absolute address @samp{0x80000000}
15720 and grows downwards, you can use the flags
15721 @option{-fstack-limit-symbol=__stack_limit} and
15722 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
15723 of 128KB@. Note that this may only work with the GNU linker.
15725 @cindex aliasing of parameters
15726 @cindex parameters, aliased
15727 @item -fargument-alias
15728 @itemx -fargument-noalias
15729 @itemx -fargument-noalias-global
15730 @itemx -fargument-noalias-anything
15731 @opindex fargument-alias
15732 @opindex fargument-noalias
15733 @opindex fargument-noalias-global
15734 @opindex fargument-noalias-anything
15735 Specify the possible relationships among parameters and between
15736 parameters and global data.
15738 @option{-fargument-alias} specifies that arguments (parameters) may
15739 alias each other and may alias global storage.@*
15740 @option{-fargument-noalias} specifies that arguments do not alias
15741 each other, but may alias global storage.@*
15742 @option{-fargument-noalias-global} specifies that arguments do not
15743 alias each other and do not alias global storage.
15744 @option{-fargument-noalias-anything} specifies that arguments do not
15745 alias any other storage.
15747 Each language will automatically use whatever option is required by
15748 the language standard. You should not need to use these options yourself.
15750 @item -fleading-underscore
15751 @opindex fleading-underscore
15752 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
15753 change the way C symbols are represented in the object file. One use
15754 is to help link with legacy assembly code.
15756 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
15757 generate code that is not binary compatible with code generated without that
15758 switch. Use it to conform to a non-default application binary interface.
15759 Not all targets provide complete support for this switch.
15761 @item -ftls-model=@var{model}
15762 @opindex ftls-model
15763 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
15764 The @var{model} argument should be one of @code{global-dynamic},
15765 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
15767 The default without @option{-fpic} is @code{initial-exec}; with
15768 @option{-fpic} the default is @code{global-dynamic}.
15770 @item -fvisibility=@var{default|internal|hidden|protected}
15771 @opindex fvisibility
15772 Set the default ELF image symbol visibility to the specified option---all
15773 symbols will be marked with this unless overridden within the code.
15774 Using this feature can very substantially improve linking and
15775 load times of shared object libraries, produce more optimized
15776 code, provide near-perfect API export and prevent symbol clashes.
15777 It is @strong{strongly} recommended that you use this in any shared objects
15780 Despite the nomenclature, @code{default} always means public ie;
15781 available to be linked against from outside the shared object.
15782 @code{protected} and @code{internal} are pretty useless in real-world
15783 usage so the only other commonly used option will be @code{hidden}.
15784 The default if @option{-fvisibility} isn't specified is
15785 @code{default}, i.e., make every
15786 symbol public---this causes the same behavior as previous versions of
15789 A good explanation of the benefits offered by ensuring ELF
15790 symbols have the correct visibility is given by ``How To Write
15791 Shared Libraries'' by Ulrich Drepper (which can be found at
15792 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
15793 solution made possible by this option to marking things hidden when
15794 the default is public is to make the default hidden and mark things
15795 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
15796 and @code{__attribute__ ((visibility("default")))} instead of
15797 @code{__declspec(dllexport)} you get almost identical semantics with
15798 identical syntax. This is a great boon to those working with
15799 cross-platform projects.
15801 For those adding visibility support to existing code, you may find
15802 @samp{#pragma GCC visibility} of use. This works by you enclosing
15803 the declarations you wish to set visibility for with (for example)
15804 @samp{#pragma GCC visibility push(hidden)} and
15805 @samp{#pragma GCC visibility pop}.
15806 Bear in mind that symbol visibility should be viewed @strong{as
15807 part of the API interface contract} and thus all new code should
15808 always specify visibility when it is not the default ie; declarations
15809 only for use within the local DSO should @strong{always} be marked explicitly
15810 as hidden as so to avoid PLT indirection overheads---making this
15811 abundantly clear also aids readability and self-documentation of the code.
15812 Note that due to ISO C++ specification requirements, operator new and
15813 operator delete must always be of default visibility.
15815 Be aware that headers from outside your project, in particular system
15816 headers and headers from any other library you use, may not be
15817 expecting to be compiled with visibility other than the default. You
15818 may need to explicitly say @samp{#pragma GCC visibility push(default)}
15819 before including any such headers.
15821 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
15822 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
15823 no modifications. However, this means that calls to @samp{extern}
15824 functions with no explicit visibility will use the PLT, so it is more
15825 effective to use @samp{__attribute ((visibility))} and/or
15826 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
15827 declarations should be treated as hidden.
15829 Note that @samp{-fvisibility} does affect C++ vague linkage
15830 entities. This means that, for instance, an exception class that will
15831 be thrown between DSOs must be explicitly marked with default
15832 visibility so that the @samp{type_info} nodes will be unified between
15835 An overview of these techniques, their benefits and how to use them
15836 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
15842 @node Environment Variables
15843 @section Environment Variables Affecting GCC
15844 @cindex environment variables
15846 @c man begin ENVIRONMENT
15847 This section describes several environment variables that affect how GCC
15848 operates. Some of them work by specifying directories or prefixes to use
15849 when searching for various kinds of files. Some are used to specify other
15850 aspects of the compilation environment.
15852 Note that you can also specify places to search using options such as
15853 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
15854 take precedence over places specified using environment variables, which
15855 in turn take precedence over those specified by the configuration of GCC@.
15856 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
15857 GNU Compiler Collection (GCC) Internals}.
15862 @c @itemx LC_COLLATE
15864 @c @itemx LC_MONETARY
15865 @c @itemx LC_NUMERIC
15870 @c @findex LC_COLLATE
15871 @findex LC_MESSAGES
15872 @c @findex LC_MONETARY
15873 @c @findex LC_NUMERIC
15877 These environment variables control the way that GCC uses
15878 localization information that allow GCC to work with different
15879 national conventions. GCC inspects the locale categories
15880 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
15881 so. These locale categories can be set to any value supported by your
15882 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
15883 Kingdom encoded in UTF-8.
15885 The @env{LC_CTYPE} environment variable specifies character
15886 classification. GCC uses it to determine the character boundaries in
15887 a string; this is needed for some multibyte encodings that contain quote
15888 and escape characters that would otherwise be interpreted as a string
15891 The @env{LC_MESSAGES} environment variable specifies the language to
15892 use in diagnostic messages.
15894 If the @env{LC_ALL} environment variable is set, it overrides the value
15895 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
15896 and @env{LC_MESSAGES} default to the value of the @env{LANG}
15897 environment variable. If none of these variables are set, GCC
15898 defaults to traditional C English behavior.
15902 If @env{TMPDIR} is set, it specifies the directory to use for temporary
15903 files. GCC uses temporary files to hold the output of one stage of
15904 compilation which is to be used as input to the next stage: for example,
15905 the output of the preprocessor, which is the input to the compiler
15908 @item GCC_EXEC_PREFIX
15909 @findex GCC_EXEC_PREFIX
15910 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
15911 names of the subprograms executed by the compiler. No slash is added
15912 when this prefix is combined with the name of a subprogram, but you can
15913 specify a prefix that ends with a slash if you wish.
15915 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
15916 an appropriate prefix to use based on the pathname it was invoked with.
15918 If GCC cannot find the subprogram using the specified prefix, it
15919 tries looking in the usual places for the subprogram.
15921 The default value of @env{GCC_EXEC_PREFIX} is
15922 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
15923 the installed compiler. In many cases @var{prefix} is the value
15924 of @code{prefix} when you ran the @file{configure} script.
15926 Other prefixes specified with @option{-B} take precedence over this prefix.
15928 This prefix is also used for finding files such as @file{crt0.o} that are
15931 In addition, the prefix is used in an unusual way in finding the
15932 directories to search for header files. For each of the standard
15933 directories whose name normally begins with @samp{/usr/local/lib/gcc}
15934 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
15935 replacing that beginning with the specified prefix to produce an
15936 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
15937 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
15938 These alternate directories are searched first; the standard directories
15939 come next. If a standard directory begins with the configured
15940 @var{prefix} then the value of @var{prefix} is replaced by
15941 @env{GCC_EXEC_PREFIX} when looking for header files.
15943 @item COMPILER_PATH
15944 @findex COMPILER_PATH
15945 The value of @env{COMPILER_PATH} is a colon-separated list of
15946 directories, much like @env{PATH}. GCC tries the directories thus
15947 specified when searching for subprograms, if it can't find the
15948 subprograms using @env{GCC_EXEC_PREFIX}.
15951 @findex LIBRARY_PATH
15952 The value of @env{LIBRARY_PATH} is a colon-separated list of
15953 directories, much like @env{PATH}. When configured as a native compiler,
15954 GCC tries the directories thus specified when searching for special
15955 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
15956 using GCC also uses these directories when searching for ordinary
15957 libraries for the @option{-l} option (but directories specified with
15958 @option{-L} come first).
15962 @cindex locale definition
15963 This variable is used to pass locale information to the compiler. One way in
15964 which this information is used is to determine the character set to be used
15965 when character literals, string literals and comments are parsed in C and C++.
15966 When the compiler is configured to allow multibyte characters,
15967 the following values for @env{LANG} are recognized:
15971 Recognize JIS characters.
15973 Recognize SJIS characters.
15975 Recognize EUCJP characters.
15978 If @env{LANG} is not defined, or if it has some other value, then the
15979 compiler will use mblen and mbtowc as defined by the default locale to
15980 recognize and translate multibyte characters.
15984 Some additional environments variables affect the behavior of the
15987 @include cppenv.texi
15991 @node Precompiled Headers
15992 @section Using Precompiled Headers
15993 @cindex precompiled headers
15994 @cindex speed of compilation
15996 Often large projects have many header files that are included in every
15997 source file. The time the compiler takes to process these header files
15998 over and over again can account for nearly all of the time required to
15999 build the project. To make builds faster, GCC allows users to
16000 `precompile' a header file; then, if builds can use the precompiled
16001 header file they will be much faster.
16003 To create a precompiled header file, simply compile it as you would any
16004 other file, if necessary using the @option{-x} option to make the driver
16005 treat it as a C or C++ header file. You will probably want to use a
16006 tool like @command{make} to keep the precompiled header up-to-date when
16007 the headers it contains change.
16009 A precompiled header file will be searched for when @code{#include} is
16010 seen in the compilation. As it searches for the included file
16011 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
16012 compiler looks for a precompiled header in each directory just before it
16013 looks for the include file in that directory. The name searched for is
16014 the name specified in the @code{#include} with @samp{.gch} appended. If
16015 the precompiled header file can't be used, it is ignored.
16017 For instance, if you have @code{#include "all.h"}, and you have
16018 @file{all.h.gch} in the same directory as @file{all.h}, then the
16019 precompiled header file will be used if possible, and the original
16020 header will be used otherwise.
16022 Alternatively, you might decide to put the precompiled header file in a
16023 directory and use @option{-I} to ensure that directory is searched
16024 before (or instead of) the directory containing the original header.
16025 Then, if you want to check that the precompiled header file is always
16026 used, you can put a file of the same name as the original header in this
16027 directory containing an @code{#error} command.
16029 This also works with @option{-include}. So yet another way to use
16030 precompiled headers, good for projects not designed with precompiled
16031 header files in mind, is to simply take most of the header files used by
16032 a project, include them from another header file, precompile that header
16033 file, and @option{-include} the precompiled header. If the header files
16034 have guards against multiple inclusion, they will be skipped because
16035 they've already been included (in the precompiled header).
16037 If you need to precompile the same header file for different
16038 languages, targets, or compiler options, you can instead make a
16039 @emph{directory} named like @file{all.h.gch}, and put each precompiled
16040 header in the directory, perhaps using @option{-o}. It doesn't matter
16041 what you call the files in the directory, every precompiled header in
16042 the directory will be considered. The first precompiled header
16043 encountered in the directory that is valid for this compilation will
16044 be used; they're searched in no particular order.
16046 There are many other possibilities, limited only by your imagination,
16047 good sense, and the constraints of your build system.
16049 A precompiled header file can be used only when these conditions apply:
16053 Only one precompiled header can be used in a particular compilation.
16056 A precompiled header can't be used once the first C token is seen. You
16057 can have preprocessor directives before a precompiled header; you can
16058 even include a precompiled header from inside another header, so long as
16059 there are no C tokens before the @code{#include}.
16062 The precompiled header file must be produced for the same language as
16063 the current compilation. You can't use a C precompiled header for a C++
16067 The precompiled header file must have been produced by the same compiler
16068 binary as the current compilation is using.
16071 Any macros defined before the precompiled header is included must
16072 either be defined in the same way as when the precompiled header was
16073 generated, or must not affect the precompiled header, which usually
16074 means that they don't appear in the precompiled header at all.
16076 The @option{-D} option is one way to define a macro before a
16077 precompiled header is included; using a @code{#define} can also do it.
16078 There are also some options that define macros implicitly, like
16079 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
16082 @item If debugging information is output when using the precompiled
16083 header, using @option{-g} or similar, the same kind of debugging information
16084 must have been output when building the precompiled header. However,
16085 a precompiled header built using @option{-g} can be used in a compilation
16086 when no debugging information is being output.
16088 @item The same @option{-m} options must generally be used when building
16089 and using the precompiled header. @xref{Submodel Options},
16090 for any cases where this rule is relaxed.
16092 @item Each of the following options must be the same when building and using
16093 the precompiled header:
16095 @gccoptlist{-fexceptions}
16098 Some other command-line options starting with @option{-f},
16099 @option{-p}, or @option{-O} must be defined in the same way as when
16100 the precompiled header was generated. At present, it's not clear
16101 which options are safe to change and which are not; the safest choice
16102 is to use exactly the same options when generating and using the
16103 precompiled header. The following are known to be safe:
16105 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
16106 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
16107 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
16112 For all of these except the last, the compiler will automatically
16113 ignore the precompiled header if the conditions aren't met. If you
16114 find an option combination that doesn't work and doesn't cause the
16115 precompiled header to be ignored, please consider filing a bug report,
16118 If you do use differing options when generating and using the
16119 precompiled header, the actual behavior will be a mixture of the
16120 behavior for the options. For instance, if you use @option{-g} to
16121 generate the precompiled header but not when using it, you may or may
16122 not get debugging information for routines in the precompiled header.
16124 @node Running Protoize
16125 @section Running Protoize
16127 The program @code{protoize} is an optional part of GCC@. You can use
16128 it to add prototypes to a program, thus converting the program to ISO
16129 C in one respect. The companion program @code{unprotoize} does the
16130 reverse: it removes argument types from any prototypes that are found.
16132 When you run these programs, you must specify a set of source files as
16133 command line arguments. The conversion programs start out by compiling
16134 these files to see what functions they define. The information gathered
16135 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
16137 After scanning comes actual conversion. The specified files are all
16138 eligible to be converted; any files they include (whether sources or
16139 just headers) are eligible as well.
16141 But not all the eligible files are converted. By default,
16142 @code{protoize} and @code{unprotoize} convert only source and header
16143 files in the current directory. You can specify additional directories
16144 whose files should be converted with the @option{-d @var{directory}}
16145 option. You can also specify particular files to exclude with the
16146 @option{-x @var{file}} option. A file is converted if it is eligible, its
16147 directory name matches one of the specified directory names, and its
16148 name within the directory has not been excluded.
16150 Basic conversion with @code{protoize} consists of rewriting most
16151 function definitions and function declarations to specify the types of
16152 the arguments. The only ones not rewritten are those for varargs
16155 @code{protoize} optionally inserts prototype declarations at the
16156 beginning of the source file, to make them available for any calls that
16157 precede the function's definition. Or it can insert prototype
16158 declarations with block scope in the blocks where undeclared functions
16161 Basic conversion with @code{unprotoize} consists of rewriting most
16162 function declarations to remove any argument types, and rewriting
16163 function definitions to the old-style pre-ISO form.
16165 Both conversion programs print a warning for any function declaration or
16166 definition that they can't convert. You can suppress these warnings
16169 The output from @code{protoize} or @code{unprotoize} replaces the
16170 original source file. The original file is renamed to a name ending
16171 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
16172 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
16173 for DOS) file already exists, then the source file is simply discarded.
16175 @code{protoize} and @code{unprotoize} both depend on GCC itself to
16176 scan the program and collect information about the functions it uses.
16177 So neither of these programs will work until GCC is installed.
16179 Here is a table of the options you can use with @code{protoize} and
16180 @code{unprotoize}. Each option works with both programs unless
16184 @item -B @var{directory}
16185 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
16186 usual directory (normally @file{/usr/local/lib}). This file contains
16187 prototype information about standard system functions. This option
16188 applies only to @code{protoize}.
16190 @item -c @var{compilation-options}
16191 Use @var{compilation-options} as the options when running @command{gcc} to
16192 produce the @samp{.X} files. The special option @option{-aux-info} is
16193 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
16195 Note that the compilation options must be given as a single argument to
16196 @code{protoize} or @code{unprotoize}. If you want to specify several
16197 @command{gcc} options, you must quote the entire set of compilation options
16198 to make them a single word in the shell.
16200 There are certain @command{gcc} arguments that you cannot use, because they
16201 would produce the wrong kind of output. These include @option{-g},
16202 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
16203 the @var{compilation-options}, they are ignored.
16206 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
16207 systems) instead of @samp{.c}. This is convenient if you are converting
16208 a C program to C++. This option applies only to @code{protoize}.
16211 Add explicit global declarations. This means inserting explicit
16212 declarations at the beginning of each source file for each function
16213 that is called in the file and was not declared. These declarations
16214 precede the first function definition that contains a call to an
16215 undeclared function. This option applies only to @code{protoize}.
16217 @item -i @var{string}
16218 Indent old-style parameter declarations with the string @var{string}.
16219 This option applies only to @code{protoize}.
16221 @code{unprotoize} converts prototyped function definitions to old-style
16222 function definitions, where the arguments are declared between the
16223 argument list and the initial @samp{@{}. By default, @code{unprotoize}
16224 uses five spaces as the indentation. If you want to indent with just
16225 one space instead, use @option{-i " "}.
16228 Keep the @samp{.X} files. Normally, they are deleted after conversion
16232 Add explicit local declarations. @code{protoize} with @option{-l} inserts
16233 a prototype declaration for each function in each block which calls the
16234 function without any declaration. This option applies only to
16238 Make no real changes. This mode just prints information about the conversions
16239 that would have been done without @option{-n}.
16242 Make no @samp{.save} files. The original files are simply deleted.
16243 Use this option with caution.
16245 @item -p @var{program}
16246 Use the program @var{program} as the compiler. Normally, the name
16247 @file{gcc} is used.
16250 Work quietly. Most warnings are suppressed.
16253 Print the version number, just like @option{-v} for @command{gcc}.
16256 If you need special compiler options to compile one of your program's
16257 source files, then you should generate that file's @samp{.X} file
16258 specially, by running @command{gcc} on that source file with the
16259 appropriate options and the option @option{-aux-info}. Then run
16260 @code{protoize} on the entire set of files. @code{protoize} will use
16261 the existing @samp{.X} file because it is newer than the source file.
16265 gcc -Dfoo=bar file1.c -aux-info file1.X
16270 You need to include the special files along with the rest in the
16271 @code{protoize} command, even though their @samp{.X} files already
16272 exist, because otherwise they won't get converted.
16274 @xref{Protoize Caveats}, for more information on how to use
16275 @code{protoize} successfully.