1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
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 Free Software Foundation, Inc.
16 Permission is granted to copy, distribute and/or modify this document
17 under the terms of the GNU Free Documentation License, Version 1.2 or
18 any later version published by the Free Software Foundation; with the
19 Invariant Sections being ``GNU General Public License'' and ``Funding
20 Free Software'', the Front-Cover texts being (a) (see below), and with
21 the Back-Cover Texts being (b) (see below). A copy of the license is
22 included in the gfdl(7) man page.
24 (a) The FSF's Front-Cover Text is:
28 (b) The FSF's Back-Cover Text is:
30 You have freedom to copy and modify this GNU Manual, like GNU
31 software. Copies published by the Free Software Foundation raise
32 funds for GNU development.
34 @c Set file name and title for the man page.
36 @settitle GNU project C and C++ compiler
38 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
39 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
40 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
41 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
42 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
43 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
44 [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
46 Only the most useful options are listed here; see below for the
47 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
50 gpl(7), gfdl(7), fsf-funding(7),
51 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
52 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
53 @file{ld}, @file{binutils} and @file{gdb}.
56 For instructions on reporting bugs, see
57 @w{@uref{http://gcc.gnu.org/bugs.html}}.
60 See the Info entry for @command{gcc}, or
61 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
62 for contributors to GCC@.
67 @chapter GCC Command Options
68 @cindex GCC command options
69 @cindex command options
70 @cindex options, GCC command
72 @c man begin DESCRIPTION
73 When you invoke GCC, it normally does preprocessing, compilation,
74 assembly and linking. The ``overall options'' allow you to stop this
75 process at an intermediate stage. For example, the @option{-c} option
76 says not to run the linker. Then the output consists of object files
77 output by the assembler.
79 Other options are passed on to one stage of processing. Some options
80 control the preprocessor and others the compiler itself. Yet other
81 options control the assembler and linker; most of these are not
82 documented here, since you rarely need to use any of them.
84 @cindex C compilation options
85 Most of the command line options that you can use with GCC are useful
86 for C programs; when an option is only useful with another language
87 (usually C++), the explanation says so explicitly. If the description
88 for a particular option does not mention a source language, you can use
89 that option with all supported languages.
91 @cindex C++ compilation options
92 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
93 options for compiling C++ programs.
95 @cindex grouping options
96 @cindex options, grouping
97 The @command{gcc} program accepts options and file names as operands. Many
98 options have multi-letter names; therefore multiple single-letter options
99 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
102 @cindex order of options
103 @cindex options, order
104 You can mix options and other arguments. For the most part, the order
105 you use doesn't matter. Order does matter when you use several
106 options of the same kind; for example, if you specify @option{-L} more
107 than once, the directories are searched in the order specified. Also,
108 the placement of the @option{-l} option is significant.
110 Many options have long names starting with @samp{-f} or with
111 @samp{-W}---for example,
112 @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
113 these have both positive and negative forms; the negative form of
114 @option{-ffoo} would be @option{-fno-foo}. This manual documents
115 only one of these two forms, whichever one is not the default.
119 @xref{Option Index}, for an index to GCC's options.
122 * Option Summary:: Brief list of all options, without explanations.
123 * Overall Options:: Controlling the kind of output:
124 an executable, object files, assembler files,
125 or preprocessed source.
126 * Invoking G++:: Compiling C++ programs.
127 * C Dialect Options:: Controlling the variant of C language compiled.
128 * C++ Dialect Options:: Variations on C++.
129 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
131 * Language Independent Options:: Controlling how diagnostics should be
133 * Warning Options:: How picky should the compiler be?
134 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
135 * Optimize Options:: How much optimization?
136 * Preprocessor Options:: Controlling header files and macro definitions.
137 Also, getting dependency information for Make.
138 * Assembler Options:: Passing options to the assembler.
139 * Link Options:: Specifying libraries and so on.
140 * Directory Options:: Where to find header files and libraries.
141 Where to find the compiler executable files.
142 * Spec Files:: How to pass switches to sub-processes.
143 * Target Options:: Running a cross-compiler, or an old version of GCC.
144 * Submodel Options:: Specifying minor hardware or convention variations,
145 such as 68010 vs 68020.
146 * Code Gen Options:: Specifying conventions for function calls, data layout
148 * Environment Variables:: Env vars that affect GCC.
149 * Precompiled Headers:: Compiling a header once, and using it many times.
150 * Running Protoize:: Automatically adding or removing function prototypes.
156 @section Option Summary
158 Here is a summary of all the options, grouped by type. Explanations are
159 in the following sections.
162 @item Overall Options
163 @xref{Overall Options,,Options Controlling the Kind of Output}.
164 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
165 -x @var{language} -v -### --help@r{[}=@var{class}@r{]} --target-help @gol
166 --version @@@var{file}}
168 @item C Language Options
169 @xref{C Dialect Options,,Options Controlling C Dialect}.
170 @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
171 -aux-info @var{filename} @gol
172 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
173 -fhosted -ffreestanding -fopenmp -fms-extensions @gol
174 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
175 -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
176 -fsigned-bitfields -fsigned-char @gol
177 -funsigned-bitfields -funsigned-char}
179 @item C++ Language Options
180 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
181 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
182 -fconserve-space -ffriend-injection @gol
183 -fno-elide-constructors @gol
184 -fno-enforce-eh-specs @gol
185 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
186 -fno-implicit-templates @gol
187 -fno-implicit-inline-templates @gol
188 -fno-implement-inlines -fms-extensions @gol
189 -fno-nonansi-builtins -fno-operator-names @gol
190 -fno-optional-diags -fpermissive @gol
191 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
192 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
193 -fno-default-inline -fvisibility-inlines-hidden @gol
194 -fvisibility-ms-compat @gol
195 -Wabi -Wctor-dtor-privacy @gol
196 -Wnon-virtual-dtor -Wreorder @gol
197 -Weffc++ -Wno-deprecated -Wstrict-null-sentinel @gol
198 -Wno-non-template-friend -Wold-style-cast @gol
199 -Woverloaded-virtual -Wno-pmf-conversions @gol
202 @item Objective-C and Objective-C++ Language Options
203 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
204 Objective-C and Objective-C++ Dialects}.
205 @gccoptlist{-fconstant-string-class=@var{class-name} @gol
206 -fgnu-runtime -fnext-runtime @gol
207 -fno-nil-receivers @gol
208 -fobjc-call-cxx-cdtors @gol
209 -fobjc-direct-dispatch @gol
210 -fobjc-exceptions @gol
212 -freplace-objc-classes @gol
215 -Wassign-intercept @gol
216 -Wno-protocol -Wselector @gol
217 -Wstrict-selector-match @gol
218 -Wundeclared-selector}
220 @item Language Independent Options
221 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
222 @gccoptlist{-fmessage-length=@var{n} @gol
223 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
224 -fdiagnostics-show-option}
226 @item Warning Options
227 @xref{Warning Options,,Options to Request or Suppress Warnings}.
228 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
229 -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol
230 -Wno-attributes -Wc++-compat -Wc++0x-compat -Wcast-align -Wcast-qual @gol
231 -Wchar-subscripts -Wclobbered -Wcomment @gol
232 -Wconversion -Wcoverage-mismatch -Wno-deprecated-declarations @gol
233 -Wdisabled-optimization -Wno-div-by-zero @gol
234 -Wempty-body -Wno-endif-labels @gol
235 -Werror -Werror=* @gol
236 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
237 -Wno-format-extra-args -Wformat-nonliteral @gol
238 -Wformat-security -Wformat-y2k @gol
239 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
240 -Wimport -Wno-import -Winit-self -Winline @gol
241 -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol
242 -Winvalid-pch -Wlarger-than-@var{len} -Wunsafe-loop-optimizations @gol
243 -Wlogical-op -Wlong-long @gol
244 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
245 -Wmissing-format-attribute -Wmissing-include-dirs @gol
246 -Wmissing-noreturn @gol
247 -Wno-multichar -Wnonnull -Wno-overflow @gol
248 -Woverlength-strings -Wpacked -Wpadded @gol
249 -Wparentheses -Wpointer-arith -Wno-pointer-to-int-cast @gol
250 -Wredundant-decls @gol
251 -Wreturn-type -Wsequence-point -Wshadow @gol
252 -Wsign-compare -Wsign-conversion -Wstack-protector @gol
253 -Wstrict-aliasing -Wstrict-aliasing=n @gol
254 -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
255 -Wswitch -Wswitch-default -Wswitch-enum @gol
256 -Wsystem-headers -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized @gol
257 -Wunknown-pragmas -Wno-pragmas -Wunreachable-code @gol
258 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
259 -Wunused-value -Wunused-variable @gol
260 -Wvariadic-macros -Wvla @gol
261 -Wvolatile-register-var -Wwrite-strings}
263 @item C-only Warning Options
264 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
265 -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
266 -Wold-style-declaration -Wold-style-definition @gol
267 -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
268 -Wdeclaration-after-statement -Wpointer-sign}
270 @item Debugging Options
271 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
272 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
273 -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol
274 -fdump-noaddr -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
275 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
276 -fdump-ipa-all -fdump-ipa-cgraph @gol
278 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
279 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
280 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
281 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
283 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
284 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
285 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
286 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
287 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
288 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
289 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
290 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
291 -fdump-tree-nrv -fdump-tree-vect @gol
292 -fdump-tree-sink @gol
293 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
294 -fdump-tree-salias @gol
295 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
296 -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
297 -ftree-vectorizer-verbose=@var{n} @gol
298 -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
299 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
300 -feliminate-unused-debug-symbols -femit-class-debug-always @gol
301 -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol
302 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
303 -ftest-coverage -ftime-report -fvar-tracking @gol
304 -g -g@var{level} -gcoff -gdwarf-2 @gol
305 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
306 -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
307 -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
308 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
309 -print-multi-directory -print-multi-lib @gol
310 -print-prog-name=@var{program} -print-search-dirs -Q @gol
311 -print-sysroot-headers-suffix @gol
314 @item Optimization Options
315 @xref{Optimize Options,,Options that Control Optimization}.
316 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
317 -falign-labels=@var{n} -falign-loops=@var{n} @gol
318 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
319 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
320 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
321 -fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
322 -fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
323 -fdelayed-branch -fdelete-null-pointer-checks -fearly-inlining @gol
324 -fexpensive-optimizations -ffast-math -ffloat-store @gol
325 -fforce-addr -fforward-propagate -ffunction-sections @gol
326 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
327 -fcrossjumping -fif-conversion -fif-conversion2 @gol
328 -finline-functions -finline-functions-called-once @gol
329 -finline-limit=@var{n} -fkeep-inline-functions @gol
330 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
331 -fmodulo-sched -fno-branch-count-reg @gol
332 -fno-default-inline -fno-defer-pop -fmove-loop-invariants @gol
333 -fno-function-cse -fno-guess-branch-probability @gol
334 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
335 -funsafe-math-optimizations -funsafe-loop-optimizations @gol
336 -ffinite-math-only -fno-signed-zeros @gol
337 -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
338 -fomit-frame-pointer -foptimize-register-move @gol
339 -foptimize-sibling-calls -fpredictive-commoning -fprefetch-loop-arrays @gol
340 -fprofile-generate -fprofile-use @gol
341 -fregmove -frename-registers @gol
342 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
343 -frerun-cse-after-loop @gol
344 -frounding-math -frtl-abstract-sequences @gol
345 -fschedule-insns -fschedule-insns2 @gol
346 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
347 -fsched-spec-load-dangerous @gol
348 -fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
349 -fsched2-use-superblocks @gol
350 -fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops @gol
351 -fsection-anchors -fsignaling-nans -fsingle-precision-constant @gol
352 -fno-split-wide-types -fstack-protector -fstack-protector-all @gol
353 -fstrict-aliasing -fstrict-overflow -ftracer -fthread-jumps @gol
354 -funroll-all-loops -funroll-loops -fpeel-loops @gol
355 -fsplit-ivs-in-unroller -funswitch-loops @gol
356 -fvariable-expansion-in-unroller @gol
357 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
358 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
359 -fcheck-data-deps @gol
360 -ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
361 -ftree-ch -ftree-sra -ftree-ter -ftree-fre -ftree-vectorize @gol
362 -ftree-vect-loop-version -fvect-cost-model -ftree-salias -fipa-pta -fweb @gol
363 -ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
364 --param @var{name}=@var{value}
365 -O -O0 -O1 -O2 -O3 -Os}
367 @item Preprocessor Options
368 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
369 @gccoptlist{-A@var{question}=@var{answer} @gol
370 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
371 -C -dD -dI -dM -dN @gol
372 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
373 -idirafter @var{dir} @gol
374 -include @var{file} -imacros @var{file} @gol
375 -iprefix @var{file} -iwithprefix @var{dir} @gol
376 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
377 -imultilib @var{dir} -isysroot @var{dir} @gol
378 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
379 -P -fworking-directory -remap @gol
380 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
381 -Xpreprocessor @var{option}}
383 @item Assembler Option
384 @xref{Assembler Options,,Passing Options to the Assembler}.
385 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
388 @xref{Link Options,,Options for Linking}.
389 @gccoptlist{@var{object-file-name} -l@var{library} @gol
390 -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol
391 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
392 -Wl,@var{option} -Xlinker @var{option} @gol
395 @item Directory Options
396 @xref{Directory Options,,Options for Directory Search}.
397 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir}
398 -specs=@var{file} -I- --sysroot=@var{dir}}
401 @c I wrote this xref this way to avoid overfull hbox. -- rms
402 @xref{Target Options}.
403 @gccoptlist{-V @var{version} -b @var{machine}}
405 @item Machine Dependent Options
406 @xref{Submodel Options,,Hardware Models and Configurations}.
407 @c This list is ordered alphanumerically by subsection name.
408 @c Try and put the significant identifier (CPU or system) first,
409 @c so users have a clue at guessing where the ones they want will be.
412 @gccoptlist{-EB -EL @gol
413 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
414 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
417 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
418 -mabi=@var{name} @gol
419 -mapcs-stack-check -mno-apcs-stack-check @gol
420 -mapcs-float -mno-apcs-float @gol
421 -mapcs-reentrant -mno-apcs-reentrant @gol
422 -msched-prolog -mno-sched-prolog @gol
423 -mlittle-endian -mbig-endian -mwords-little-endian @gol
424 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
425 -mthumb-interwork -mno-thumb-interwork @gol
426 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
427 -mstructure-size-boundary=@var{n} @gol
428 -mabort-on-noreturn @gol
429 -mlong-calls -mno-long-calls @gol
430 -msingle-pic-base -mno-single-pic-base @gol
431 -mpic-register=@var{reg} @gol
432 -mnop-fun-dllimport @gol
433 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
434 -mpoke-function-name @gol
436 -mtpcs-frame -mtpcs-leaf-frame @gol
437 -mcaller-super-interworking -mcallee-super-interworking @gol
441 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
442 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
444 @emph{Blackfin Options}
445 @gccoptlist{-mcpu=@var{cpu} -msim -momit-leaf-frame-pointer @gol
446 -mno-omit-leaf-frame-pointer -mspecld-anomaly -mno-specld-anomaly @gol
447 -mcsync-anomaly -mno-csync-anomaly -mlow-64k -mno-low64k @gol
448 -mstack-check-l1 -mid-shared-library -mno-id-shared-library @gol
449 -mshared-library-id=@var{n} -mleaf-id-shared-library @gol
450 -mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls @gol
454 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
455 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
456 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
457 -mstack-align -mdata-align -mconst-align @gol
458 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
459 -melf -maout -melinux -mlinux -sim -sim2 @gol
460 -mmul-bug-workaround -mno-mul-bug-workaround}
463 @gccoptlist{-mmac -mpush-args}
465 @emph{Darwin Options}
466 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
467 -arch_only -bind_at_load -bundle -bundle_loader @gol
468 -client_name -compatibility_version -current_version @gol
470 -dependency-file -dylib_file -dylinker_install_name @gol
471 -dynamic -dynamiclib -exported_symbols_list @gol
472 -filelist -flat_namespace -force_cpusubtype_ALL @gol
473 -force_flat_namespace -headerpad_max_install_names @gol
475 -image_base -init -install_name -keep_private_externs @gol
476 -multi_module -multiply_defined -multiply_defined_unused @gol
477 -noall_load -no_dead_strip_inits_and_terms @gol
478 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
479 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
480 -private_bundle -read_only_relocs -sectalign @gol
481 -sectobjectsymbols -whyload -seg1addr @gol
482 -sectcreate -sectobjectsymbols -sectorder @gol
483 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
484 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
485 -segprot -segs_read_only_addr -segs_read_write_addr @gol
486 -single_module -static -sub_library -sub_umbrella @gol
487 -twolevel_namespace -umbrella -undefined @gol
488 -unexported_symbols_list -weak_reference_mismatches @gol
489 -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
490 -mkernel -mone-byte-bool}
492 @emph{DEC Alpha Options}
493 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
494 -mieee -mieee-with-inexact -mieee-conformant @gol
495 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
496 -mtrap-precision=@var{mode} -mbuild-constants @gol
497 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
498 -mbwx -mmax -mfix -mcix @gol
499 -mfloat-vax -mfloat-ieee @gol
500 -mexplicit-relocs -msmall-data -mlarge-data @gol
501 -msmall-text -mlarge-text @gol
502 -mmemory-latency=@var{time}}
504 @emph{DEC Alpha/VMS Options}
505 @gccoptlist{-mvms-return-codes}
508 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
509 -mhard-float -msoft-float @gol
510 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
511 -mdouble -mno-double @gol
512 -mmedia -mno-media -mmuladd -mno-muladd @gol
513 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
514 -mlinked-fp -mlong-calls -malign-labels @gol
515 -mlibrary-pic -macc-4 -macc-8 @gol
516 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
517 -moptimize-membar -mno-optimize-membar @gol
518 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
519 -mvliw-branch -mno-vliw-branch @gol
520 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
521 -mno-nested-cond-exec -mtomcat-stats @gol
525 @emph{GNU/Linux Options}
526 @gccoptlist{-muclibc}
528 @emph{H8/300 Options}
529 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
532 @gccoptlist{-march=@var{architecture-type} @gol
533 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
534 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
535 -mfixed-range=@var{register-range} @gol
536 -mjump-in-delay -mlinker-opt -mlong-calls @gol
537 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
538 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
539 -mno-jump-in-delay -mno-long-load-store @gol
540 -mno-portable-runtime -mno-soft-float @gol
541 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
542 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
543 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
544 -munix=@var{unix-std} -nolibdld -static -threads}
546 @emph{i386 and x86-64 Options}
547 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
548 -mfpmath=@var{unit} @gol
549 -masm=@var{dialect} -mno-fancy-math-387 @gol
550 -mno-fp-ret-in-387 -msoft-float @gol
551 -mno-wide-multiply -mrtd -malign-double @gol
552 -mpreferred-stack-boundary=@var{num} -mcx16 -msahf -mrecip @gol
553 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 @gol
554 -msse4a -m3dnow -mpopcnt -mabm @gol
555 -mthreads -mno-align-stringops -minline-all-stringops @gol
556 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
557 -m96bit-long-double -mregparm=@var{num} -msseregparm @gol
558 -mpc32 -mpc64 -mpc80 mstackrealign @gol
559 -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
560 -mcmodel=@var{code-model} @gol
561 -m32 -m64 -mlarge-data-threshold=@var{num}}
564 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
565 -mvolatile-asm-stop -mregister-names -mno-sdata @gol
566 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
567 -minline-float-divide-max-throughput @gol
568 -minline-int-divide-min-latency @gol
569 -minline-int-divide-max-throughput @gol
570 -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
571 -mno-dwarf2-asm -mearly-stop-bits @gol
572 -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
573 -mtune=@var{cpu-type} -mt -pthread -milp32 -mlp64 @gol
574 -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec @gol
575 -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
576 -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose @gol
577 -mno-sched-prefer-non-data-spec-insns @gol
578 -mno-sched-prefer-non-control-spec-insns @gol
579 -mno-sched-count-spec-in-critical-path}
581 @emph{M32R/D Options}
582 @gccoptlist{-m32r2 -m32rx -m32r @gol
584 -malign-loops -mno-align-loops @gol
585 -missue-rate=@var{number} @gol
586 -mbranch-cost=@var{number} @gol
587 -mmodel=@var{code-size-model-type} @gol
588 -msdata=@var{sdata-type} @gol
589 -mno-flush-func -mflush-func=@var{name} @gol
590 -mno-flush-trap -mflush-trap=@var{number} @gol
594 @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
596 @emph{M680x0 Options}
597 @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune}
598 -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
599 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
600 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
601 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
602 -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
603 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
604 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
606 @emph{M68hc1x Options}
607 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
608 -mauto-incdec -minmax -mlong-calls -mshort @gol
609 -msoft-reg-count=@var{count}}
612 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
613 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
614 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
615 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
616 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
619 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
620 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
621 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
622 -mshared -mno-shared -mxgot -mno-xgot -mgp32 -mgp64 @gol
623 -mfp32 -mfp64 -mhard-float -msoft-float @gol
624 -msingle-float -mdouble-float -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
625 -msmartmips -mno-smartmips @gol
626 -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
627 -mips3d -mno-mips3d -mmt -mno-mt @gol
628 -mlong64 -mlong32 -msym32 -mno-sym32 @gol
629 -G@var{num} -membedded-data -mno-embedded-data @gol
630 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
631 -msplit-addresses -mno-split-addresses @gol
632 -mexplicit-relocs -mno-explicit-relocs @gol
633 -mcheck-zero-division -mno-check-zero-division @gol
634 -mdivide-traps -mdivide-breaks @gol
635 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
636 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
637 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
638 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 @gol
639 -mfix-sb1 -mno-fix-sb1 @gol
640 -mflush-func=@var{func} -mno-flush-func @gol
641 -mbranch-likely -mno-branch-likely @gol
642 -mfp-exceptions -mno-fp-exceptions @gol
643 -mvr4130-align -mno-vr4130-align}
646 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
647 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
648 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
649 -mno-base-addresses -msingle-exit -mno-single-exit}
651 @emph{MN10300 Options}
652 @gccoptlist{-mmult-bug -mno-mult-bug @gol
653 -mam33 -mno-am33 @gol
654 -mam33-2 -mno-am33-2 @gol
655 -mreturn-pointer-on-d0 @gol
659 @gccoptlist{-mno-crt0 -mbacc -msim @gol
660 -march=@var{cpu-type} }
662 @emph{PDP-11 Options}
663 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
664 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
665 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
666 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
667 -mbranch-expensive -mbranch-cheap @gol
668 -msplit -mno-split -munix-asm -mdec-asm}
670 @emph{PowerPC Options}
671 See RS/6000 and PowerPC Options.
673 @emph{RS/6000 and PowerPC Options}
674 @gccoptlist{-mcpu=@var{cpu-type} @gol
675 -mtune=@var{cpu-type} @gol
676 -mpower -mno-power -mpower2 -mno-power2 @gol
677 -mpowerpc -mpowerpc64 -mno-powerpc @gol
678 -maltivec -mno-altivec @gol
679 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
680 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
681 -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mfprnd -mno-fprnd @gol
682 -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mdfp -mno-dfp @gol
683 -mnew-mnemonics -mold-mnemonics @gol
684 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
685 -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
686 -malign-power -malign-natural @gol
687 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
688 -mstring -mno-string -mupdate -mno-update @gol
689 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
690 -mstrict-align -mno-strict-align -mrelocatable @gol
691 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
692 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
693 -mdynamic-no-pic -maltivec -mswdiv @gol
694 -mprioritize-restricted-insns=@var{priority} @gol
695 -msched-costly-dep=@var{dependence_type} @gol
696 -minsert-sched-nops=@var{scheme} @gol
697 -mcall-sysv -mcall-netbsd @gol
698 -maix-struct-return -msvr4-struct-return @gol
699 -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
700 -misel -mno-isel @gol
701 -misel=yes -misel=no @gol
703 -mspe=yes -mspe=no @gol
704 -mvrsave -mno-vrsave @gol
705 -mmulhw -mno-mulhw @gol
706 -mdlmzb -mno-dlmzb @gol
707 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
708 -mprototype -mno-prototype @gol
709 -msim -mmvme -mads -myellowknife -memb -msdata @gol
710 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
712 @emph{S/390 and zSeries Options}
713 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
714 -mhard-float -msoft-float -mlong-double-64 -mlong-double-128 @gol
715 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
716 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
717 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
718 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
719 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
722 @gccoptlist{-meb -mel @gol
726 -mscore5 -mscore5u -mscore7 -mscore7d}
729 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
730 -m4-nofpu -m4-single-only -m4-single -m4 @gol
731 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
732 -m5-64media -m5-64media-nofpu @gol
733 -m5-32media -m5-32media-nofpu @gol
734 -m5-compact -m5-compact-nofpu @gol
735 -mb -ml -mdalign -mrelax @gol
736 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
737 -mieee -misize -minline-ic_invalidate -mpadstruct -mspace @gol
738 -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
739 -mdivsi3_libfunc=@var{name} @gol
740 -madjust-unroll -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol
744 @gccoptlist{-mcpu=@var{cpu-type} @gol
745 -mtune=@var{cpu-type} @gol
746 -mcmodel=@var{code-model} @gol
747 -m32 -m64 -mapp-regs -mno-app-regs @gol
748 -mfaster-structs -mno-faster-structs @gol
749 -mfpu -mno-fpu -mhard-float -msoft-float @gol
750 -mhard-quad-float -msoft-quad-float @gol
751 -mimpure-text -mno-impure-text -mlittle-endian @gol
752 -mstack-bias -mno-stack-bias @gol
753 -munaligned-doubles -mno-unaligned-doubles @gol
754 -mv8plus -mno-v8plus -mvis -mno-vis
755 -threads -pthreads -pthread}
758 @gccoptlist{-mwarn-reloc -merror-reloc @gol
759 -msafe-dma -munsafe-dma @gol
761 -msmall-mem -mlarge-mem -mstdmain @gol
762 -mfixed-range=@var{register-range}}
764 @emph{System V Options}
765 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
767 @emph{TMS320C3x/C4x Options}
768 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
769 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
770 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
771 -mparallel-insns -mparallel-mpy -mpreserve-float}
774 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
775 -mprolog-function -mno-prolog-function -mspace @gol
776 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
777 -mapp-regs -mno-app-regs @gol
778 -mdisable-callt -mno-disable-callt @gol
784 @gccoptlist{-mg -mgnu -munix}
786 @emph{VxWorks Options}
787 @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
788 -Xbind-lazy -Xbind-now}
790 @emph{x86-64 Options}
791 See i386 and x86-64 Options.
793 @emph{Xstormy16 Options}
796 @emph{Xtensa Options}
797 @gccoptlist{-mconst16 -mno-const16 @gol
798 -mfused-madd -mno-fused-madd @gol
799 -mtext-section-literals -mno-text-section-literals @gol
800 -mtarget-align -mno-target-align @gol
801 -mlongcalls -mno-longcalls}
803 @emph{zSeries Options}
804 See S/390 and zSeries Options.
806 @item Code Generation Options
807 @xref{Code Gen Options,,Options for Code Generation Conventions}.
808 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
809 -ffixed-@var{reg} -fexceptions @gol
810 -fnon-call-exceptions -funwind-tables @gol
811 -fasynchronous-unwind-tables @gol
812 -finhibit-size-directive -finstrument-functions @gol
813 -fno-common -fno-ident @gol
814 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
815 -fno-jump-tables @gol
816 -frecord-gcc-switches @gol
817 -freg-struct-return -fshort-enums @gol
818 -fshort-double -fshort-wchar @gol
819 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
820 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
821 -fargument-alias -fargument-noalias @gol
822 -fargument-noalias-global -fargument-noalias-anything
823 -fleading-underscore -ftls-model=@var{model} @gol
824 -ftrapv -fwrapv -fbounds-check @gol
829 * Overall Options:: Controlling the kind of output:
830 an executable, object files, assembler files,
831 or preprocessed source.
832 * C Dialect Options:: Controlling the variant of C language compiled.
833 * C++ Dialect Options:: Variations on C++.
834 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
836 * Language Independent Options:: Controlling how diagnostics should be
838 * Warning Options:: How picky should the compiler be?
839 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
840 * Optimize Options:: How much optimization?
841 * Preprocessor Options:: Controlling header files and macro definitions.
842 Also, getting dependency information for Make.
843 * Assembler Options:: Passing options to the assembler.
844 * Link Options:: Specifying libraries and so on.
845 * Directory Options:: Where to find header files and libraries.
846 Where to find the compiler executable files.
847 * Spec Files:: How to pass switches to sub-processes.
848 * Target Options:: Running a cross-compiler, or an old version of GCC.
851 @node Overall Options
852 @section Options Controlling the Kind of Output
854 Compilation can involve up to four stages: preprocessing, compilation
855 proper, assembly and linking, always in that order. GCC is capable of
856 preprocessing and compiling several files either into several
857 assembler input files, or into one assembler input file; then each
858 assembler input file produces an object file, and linking combines all
859 the object files (those newly compiled, and those specified as input)
860 into an executable file.
862 @cindex file name suffix
863 For any given input file, the file name suffix determines what kind of
868 C source code which must be preprocessed.
871 C source code which should not be preprocessed.
874 C++ source code which should not be preprocessed.
877 Objective-C source code. Note that you must link with the @file{libobjc}
878 library to make an Objective-C program work.
881 Objective-C source code which should not be preprocessed.
885 Objective-C++ source code. Note that you must link with the @file{libobjc}
886 library to make an Objective-C++ program work. Note that @samp{.M} refers
887 to a literal capital M@.
890 Objective-C++ source code which should not be preprocessed.
893 C, C++, Objective-C or Objective-C++ header file to be turned into a
898 @itemx @var{file}.cxx
899 @itemx @var{file}.cpp
900 @itemx @var{file}.CPP
901 @itemx @var{file}.c++
903 C++ source code which must be preprocessed. Note that in @samp{.cxx},
904 the last two letters must both be literally @samp{x}. Likewise,
905 @samp{.C} refers to a literal capital C@.
909 Objective-C++ source code which must be preprocessed.
912 Objective-C++ source code which should not be preprocessed.
916 C++ header file to be turned into a precompiled header.
919 @itemx @var{file}.for
920 @itemx @var{file}.FOR
921 Fixed form Fortran source code which should not be preprocessed.
924 @itemx @var{file}.fpp
925 @itemx @var{file}.FPP
926 Fixed form Fortran source code which must be preprocessed (with the traditional
930 @itemx @var{file}.f95
931 Free form Fortran source code which should not be preprocessed.
934 @itemx @var{file}.F95
935 Free form Fortran source code which must be preprocessed (with the
936 traditional preprocessor).
938 @c FIXME: Descriptions of Java file types.
945 Ada source code file which contains a library unit declaration (a
946 declaration of a package, subprogram, or generic, or a generic
947 instantiation), or a library unit renaming declaration (a package,
948 generic, or subprogram renaming declaration). Such files are also
951 @itemx @var{file}.adb
952 Ada source code file containing a library unit body (a subprogram or
953 package body). Such files are also called @dfn{bodies}.
955 @c GCC also knows about some suffixes for languages not yet included:
966 Assembler code which must be preprocessed.
969 An object file to be fed straight into linking.
970 Any file name with no recognized suffix is treated this way.
974 You can specify the input language explicitly with the @option{-x} option:
977 @item -x @var{language}
978 Specify explicitly the @var{language} for the following input files
979 (rather than letting the compiler choose a default based on the file
980 name suffix). This option applies to all following input files until
981 the next @option{-x} option. Possible values for @var{language} are:
983 c c-header c-cpp-output
984 c++ c++-header c++-cpp-output
985 objective-c objective-c-header objective-c-cpp-output
986 objective-c++ objective-c++-header objective-c++-cpp-output
987 assembler assembler-with-cpp
995 Turn off any specification of a language, so that subsequent files are
996 handled according to their file name suffixes (as they are if @option{-x}
997 has not been used at all).
999 @item -pass-exit-codes
1000 @opindex pass-exit-codes
1001 Normally the @command{gcc} program will exit with the code of 1 if any
1002 phase of the compiler returns a non-success return code. If you specify
1003 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
1004 numerically highest error produced by any phase that returned an error
1005 indication. The C, C++, and Fortran frontends return 4, if an internal
1006 compiler error is encountered.
1009 If you only want some of the stages of compilation, you can use
1010 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
1011 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
1012 @command{gcc} is to stop. Note that some combinations (for example,
1013 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
1018 Compile or assemble the source files, but do not link. The linking
1019 stage simply is not done. The ultimate output is in the form of an
1020 object file for each source file.
1022 By default, the object file name for a source file is made by replacing
1023 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
1025 Unrecognized input files, not requiring compilation or assembly, are
1030 Stop after the stage of compilation proper; do not assemble. The output
1031 is in the form of an assembler code file for each non-assembler input
1034 By default, the assembler file name for a source file is made by
1035 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
1037 Input files that don't require compilation are ignored.
1041 Stop after the preprocessing stage; do not run the compiler proper. The
1042 output is in the form of preprocessed source code, which is sent to the
1045 Input files which don't require preprocessing are ignored.
1047 @cindex output file option
1050 Place output in file @var{file}. This applies regardless to whatever
1051 sort of output is being produced, whether it be an executable file,
1052 an object file, an assembler file or preprocessed C code.
1054 If @option{-o} is not specified, the default is to put an executable
1055 file in @file{a.out}, the object file for
1056 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
1057 assembler file in @file{@var{source}.s}, a precompiled header file in
1058 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
1063 Print (on standard error output) the commands executed to run the stages
1064 of compilation. Also print the version number of the compiler driver
1065 program and of the preprocessor and the compiler proper.
1069 Like @option{-v} except the commands are not executed and all command
1070 arguments are quoted. This is useful for shell scripts to capture the
1071 driver-generated command lines.
1075 Use pipes rather than temporary files for communication between the
1076 various stages of compilation. This fails to work on some systems where
1077 the assembler is unable to read from a pipe; but the GNU assembler has
1082 If you are compiling multiple source files, this option tells the driver
1083 to pass all the source files to the compiler at once (for those
1084 languages for which the compiler can handle this). This will allow
1085 intermodule analysis (IMA) to be performed by the compiler. Currently the only
1086 language for which this is supported is C@. If you pass source files for
1087 multiple languages to the driver, using this option, the driver will invoke
1088 the compiler(s) that support IMA once each, passing each compiler all the
1089 source files appropriate for it. For those languages that do not support
1090 IMA this option will be ignored, and the compiler will be invoked once for
1091 each source file in that language. If you use this option in conjunction
1092 with @option{-save-temps}, the compiler will generate multiple
1094 (one for each source file), but only one (combined) @file{.o} or
1099 Print (on the standard output) a description of the command line options
1100 understood by @command{gcc}. If the @option{-v} option is also specified
1101 then @option{--help} will also be passed on to the various processes
1102 invoked by @command{gcc}, so that they can display the command line options
1103 they accept. If the @option{-Wextra} option has also been specified
1104 (prior to the @option{--help} option), then command line options which
1105 have no documentation associated with them will also be displayed.
1108 @opindex target-help
1109 Print (on the standard output) a description of target-specific command
1110 line options for each tool. For some targets extra target-specific
1111 information may also be printed.
1113 @item --help=@var{class}@r{[},@var{qualifier}@r{]}
1114 Print (on the standard output) a description of the command line
1115 options understood by the compiler that fit into a specific class.
1116 The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
1117 @samp{params}, or @var{language}:
1120 @item @samp{optimizers}
1121 This will display all of the optimization options supported by the
1124 @item @samp{warnings}
1125 This will display all of the options controlling warning messages
1126 produced by the compiler.
1129 This will display target-specific options. Unlike the
1130 @option{--target-help} option however, target-specific options of the
1131 linker and assembler will not be displayed. This is because those
1132 tools do not currently support the extended @option{--help=} syntax.
1135 This will display the values recognized by the @option{--param}
1138 @item @var{language}
1139 This will display the options supported for @var{language}, where
1140 @var{language} is the name of one of the languages supported in this
1144 This will display the options that are common to all languages.
1147 It is possible to further refine the output of the @option{--help=}
1148 option by adding a comma separated list of qualifiers after the
1149 class. These can be any from the following list:
1152 @item @samp{undocumented}
1153 Display only those options which are undocumented.
1156 Display options which take an argument that appears after an equal
1157 sign in the same continuous piece of text, such as:
1158 @samp{--help=target}.
1160 @item @samp{separate}
1161 Display options which take an argument that appears as a separate word
1162 following the original option, such as: @samp{-o output-file}.
1165 Thus for example to display all the undocumented target-specific
1166 switches supported by the compiler the following can be used:
1169 --help=target,undocumented
1172 The sense of a qualifier can be inverted by prefixing it with the
1173 @var{^} character, so for example to display all binary warning
1174 options (i.e. ones that are either on or off and that do not take an
1175 argument), which have a description the following can be used:
1178 --help=warnings,^joined,^undocumented
1181 A class can also be used as a qualifier, although this usually
1182 restricts the output by so much that there is nothing to display. One
1183 case where it does work however is when one of the classes is
1184 @var{target}. So for example to display all the target-specific
1185 optimization options the following can be used:
1188 --help=target,optimizers
1191 The @option{--help=} option can be repeated on the command line. Each
1192 successive use will display its requested class of options, skipping
1193 those that have already been displayed.
1195 If the @option{-Q} option appears on the command line before the
1196 @option{--help=} option, then the descriptive text displayed by
1197 @option{--help=} is changed. Instead of describing the displayed
1198 options, an indication is given as to whether the option is enabled,
1199 disabled or set to a specific value (assuming that the compiler
1200 knows this at the point where the @option{--help=} option is used).
1202 Here is a truncated example from the ARM port of @command{gcc}:
1205 % gcc -Q -mabi=2 --help=target -c
1206 The following options are target specific:
1208 -mabort-on-noreturn [disabled]
1212 The output is sensitive to the effects of previous command line
1213 options, so for example it is possible to find out which optimizations
1214 are enabled at @option{-O2} by using:
1217 -O2 --help=optimizers
1220 Alternatively you can discover which binary optimizations are enabled
1221 by @option{-O3} by using:
1224 gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
1225 gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
1226 diff /tmp/O2-opts /tmp/O3-opts | grep enabled
1231 Display the version number and copyrights of the invoked GCC@.
1233 @include @value{srcdir}/../libiberty/at-file.texi
1237 @section Compiling C++ Programs
1239 @cindex suffixes for C++ source
1240 @cindex C++ source file suffixes
1241 C++ source files conventionally use one of the suffixes @samp{.C},
1242 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1243 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1244 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1245 files with these names and compiles them as C++ programs even if you
1246 call the compiler the same way as for compiling C programs (usually
1247 with the name @command{gcc}).
1251 However, the use of @command{gcc} does not add the C++ library.
1252 @command{g++} is a program that calls GCC and treats @samp{.c},
1253 @samp{.h} and @samp{.i} files as C++ source files instead of C source
1254 files unless @option{-x} is used, and automatically specifies linking
1255 against the C++ library. This program is also useful when
1256 precompiling a C header file with a @samp{.h} extension for use in C++
1257 compilations. On many systems, @command{g++} is also installed with
1258 the name @command{c++}.
1260 @cindex invoking @command{g++}
1261 When you compile C++ programs, you may specify many of the same
1262 command-line options that you use for compiling programs in any
1263 language; or command-line options meaningful for C and related
1264 languages; or options that are meaningful only for C++ programs.
1265 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1266 explanations of options for languages related to C@.
1267 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1268 explanations of options that are meaningful only for C++ programs.
1270 @node C Dialect Options
1271 @section Options Controlling C Dialect
1272 @cindex dialect options
1273 @cindex language dialect options
1274 @cindex options, dialect
1276 The following options control the dialect of C (or languages derived
1277 from C, such as C++, Objective-C and Objective-C++) that the compiler
1281 @cindex ANSI support
1285 In C mode, support all ISO C90 programs. In C++ mode,
1286 remove GNU extensions that conflict with ISO C++.
1288 This turns off certain features of GCC that are incompatible with ISO
1289 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1290 such as the @code{asm} and @code{typeof} keywords, and
1291 predefined macros such as @code{unix} and @code{vax} that identify the
1292 type of system you are using. It also enables the undesirable and
1293 rarely used ISO trigraph feature. For the C compiler,
1294 it disables recognition of C++ style @samp{//} comments as well as
1295 the @code{inline} keyword.
1297 The alternate keywords @code{__asm__}, @code{__extension__},
1298 @code{__inline__} and @code{__typeof__} continue to work despite
1299 @option{-ansi}. You would not want to use them in an ISO C program, of
1300 course, but it is useful to put them in header files that might be included
1301 in compilations done with @option{-ansi}. Alternate predefined macros
1302 such as @code{__unix__} and @code{__vax__} are also available, with or
1303 without @option{-ansi}.
1305 The @option{-ansi} option does not cause non-ISO programs to be
1306 rejected gratuitously. For that, @option{-pedantic} is required in
1307 addition to @option{-ansi}. @xref{Warning Options}.
1309 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1310 option is used. Some header files may notice this macro and refrain
1311 from declaring certain functions or defining certain macros that the
1312 ISO standard doesn't call for; this is to avoid interfering with any
1313 programs that might use these names for other things.
1315 Functions which would normally be built in but do not have semantics
1316 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1317 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1318 built-in functions provided by GCC}, for details of the functions
1323 Determine the language standard. This option is currently only
1324 supported when compiling C or C++. A value for this option must be
1325 provided; possible values are
1330 ISO C90 (same as @option{-ansi}).
1332 @item iso9899:199409
1333 ISO C90 as modified in amendment 1.
1339 ISO C99. Note that this standard is not yet fully supported; see
1340 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1341 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1344 Default, ISO C90 plus GNU extensions (including some C99 features).
1348 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1349 this will become the default. The name @samp{gnu9x} is deprecated.
1352 The 1998 ISO C++ standard plus amendments.
1355 The same as @option{-std=c++98} plus GNU extensions. This is the
1356 default for C++ code.
1359 The working draft of the upcoming ISO C++0x standard. This option
1360 enables experimental features that are likely to be included in
1361 C++0x. The working draft is constantly changing, and any feature that is
1362 enabled by this flag may be removed from future versions of GCC if it is
1363 not part of the C++0x standard.
1366 The same as @option{-std=c++0x} plus GNU extensions. As with
1367 @option{-std=c++0x}, this option enables experimental features that may
1368 be removed in future versions of GCC.
1371 Even when this option is not specified, you can still use some of the
1372 features of newer standards in so far as they do not conflict with
1373 previous C standards. For example, you may use @code{__restrict__} even
1374 when @option{-std=c99} is not specified.
1376 The @option{-std} options specifying some version of ISO C have the same
1377 effects as @option{-ansi}, except that features that were not in ISO C90
1378 but are in the specified version (for example, @samp{//} comments and
1379 the @code{inline} keyword in ISO C99) are not disabled.
1381 @xref{Standards,,Language Standards Supported by GCC}, for details of
1382 these standard versions.
1384 @item -fgnu89-inline
1385 @opindex fgnu89-inline
1386 The option @option{-fgnu89-inline} tells GCC to use the traditional
1387 GNU semantics for @code{inline} functions when in C99 mode.
1388 @xref{Inline,,An Inline Function is As Fast As a Macro}. This option
1389 is accepted and ignored by GCC versions 4.1.3 up to but not including
1390 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in
1391 C99 mode. Using this option is roughly equivalent to adding the
1392 @code{gnu_inline} function attribute to all inline functions
1393 (@pxref{Function Attributes}).
1395 The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
1396 C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
1397 specifies the default behavior). This option was first supported in
1398 GCC 4.3. This option is not supported in C89 or gnu89 mode.
1400 The preprocessor macros @code{__GNUC_GNU_INLINE__} and
1401 @code{__GNUC_STDC_INLINE__} may be used to check which semantics are
1402 in effect for @code{inline} functions. @xref{Common Predefined
1403 Macros,,,cpp,The C Preprocessor}.
1405 @item -aux-info @var{filename}
1407 Output to the given filename prototyped declarations for all functions
1408 declared and/or defined in a translation unit, including those in header
1409 files. This option is silently ignored in any language other than C@.
1411 Besides declarations, the file indicates, in comments, the origin of
1412 each declaration (source file and line), whether the declaration was
1413 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1414 @samp{O} for old, respectively, in the first character after the line
1415 number and the colon), and whether it came from a declaration or a
1416 definition (@samp{C} or @samp{F}, respectively, in the following
1417 character). In the case of function definitions, a K&R-style list of
1418 arguments followed by their declarations is also provided, inside
1419 comments, after the declaration.
1423 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1424 keyword, so that code can use these words as identifiers. You can use
1425 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1426 instead. @option{-ansi} implies @option{-fno-asm}.
1428 In C++, this switch only affects the @code{typeof} keyword, since
1429 @code{asm} and @code{inline} are standard keywords. You may want to
1430 use the @option{-fno-gnu-keywords} flag instead, which has the same
1431 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1432 switch only affects the @code{asm} and @code{typeof} keywords, since
1433 @code{inline} is a standard keyword in ISO C99.
1436 @itemx -fno-builtin-@var{function}
1437 @opindex fno-builtin
1438 @cindex built-in functions
1439 Don't recognize built-in functions that do not begin with
1440 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1441 functions provided by GCC}, for details of the functions affected,
1442 including those which are not built-in functions when @option{-ansi} or
1443 @option{-std} options for strict ISO C conformance are used because they
1444 do not have an ISO standard meaning.
1446 GCC normally generates special code to handle certain built-in functions
1447 more efficiently; for instance, calls to @code{alloca} may become single
1448 instructions that adjust the stack directly, and calls to @code{memcpy}
1449 may become inline copy loops. The resulting code is often both smaller
1450 and faster, but since the function calls no longer appear as such, you
1451 cannot set a breakpoint on those calls, nor can you change the behavior
1452 of the functions by linking with a different library. In addition,
1453 when a function is recognized as a built-in function, GCC may use
1454 information about that function to warn about problems with calls to
1455 that function, or to generate more efficient code, even if the
1456 resulting code still contains calls to that function. For example,
1457 warnings are given with @option{-Wformat} for bad calls to
1458 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1459 known not to modify global memory.
1461 With the @option{-fno-builtin-@var{function}} option
1462 only the built-in function @var{function} is
1463 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1464 function is named this is not built-in in this version of GCC, this
1465 option is ignored. There is no corresponding
1466 @option{-fbuiltin-@var{function}} option; if you wish to enable
1467 built-in functions selectively when using @option{-fno-builtin} or
1468 @option{-ffreestanding}, you may define macros such as:
1471 #define abs(n) __builtin_abs ((n))
1472 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1477 @cindex hosted environment
1479 Assert that compilation takes place in a hosted environment. This implies
1480 @option{-fbuiltin}. A hosted environment is one in which the
1481 entire standard library is available, and in which @code{main} has a return
1482 type of @code{int}. Examples are nearly everything except a kernel.
1483 This is equivalent to @option{-fno-freestanding}.
1485 @item -ffreestanding
1486 @opindex ffreestanding
1487 @cindex hosted environment
1489 Assert that compilation takes place in a freestanding environment. This
1490 implies @option{-fno-builtin}. A freestanding environment
1491 is one in which the standard library may not exist, and program startup may
1492 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1493 This is equivalent to @option{-fno-hosted}.
1495 @xref{Standards,,Language Standards Supported by GCC}, for details of
1496 freestanding and hosted environments.
1500 @cindex openmp parallel
1501 Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
1502 @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
1503 compiler generates parallel code according to the OpenMP Application
1504 Program Interface v2.5 @w{@uref{http://www.openmp.org/}}.
1506 @item -fms-extensions
1507 @opindex fms-extensions
1508 Accept some non-standard constructs used in Microsoft header files.
1510 Some cases of unnamed fields in structures and unions are only
1511 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1512 fields within structs/unions}, for details.
1516 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1517 options for strict ISO C conformance) implies @option{-trigraphs}.
1519 @item -no-integrated-cpp
1520 @opindex no-integrated-cpp
1521 Performs a compilation in two passes: preprocessing and compiling. This
1522 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1523 @option{-B} option. The user supplied compilation step can then add in
1524 an additional preprocessing step after normal preprocessing but before
1525 compiling. The default is to use the integrated cpp (internal cpp)
1527 The semantics of this option will change if "cc1", "cc1plus", and
1528 "cc1obj" are merged.
1530 @cindex traditional C language
1531 @cindex C language, traditional
1533 @itemx -traditional-cpp
1534 @opindex traditional-cpp
1535 @opindex traditional
1536 Formerly, these options caused GCC to attempt to emulate a pre-standard
1537 C compiler. They are now only supported with the @option{-E} switch.
1538 The preprocessor continues to support a pre-standard mode. See the GNU
1539 CPP manual for details.
1541 @item -fcond-mismatch
1542 @opindex fcond-mismatch
1543 Allow conditional expressions with mismatched types in the second and
1544 third arguments. The value of such an expression is void. This option
1545 is not supported for C++.
1547 @item -flax-vector-conversions
1548 @opindex flax-vector-conversions
1549 Allow implicit conversions between vectors with differing numbers of
1550 elements and/or incompatible element types. This option should not be
1553 @item -funsigned-char
1554 @opindex funsigned-char
1555 Let the type @code{char} be unsigned, like @code{unsigned char}.
1557 Each kind of machine has a default for what @code{char} should
1558 be. It is either like @code{unsigned char} by default or like
1559 @code{signed char} by default.
1561 Ideally, a portable program should always use @code{signed char} or
1562 @code{unsigned char} when it depends on the signedness of an object.
1563 But many programs have been written to use plain @code{char} and
1564 expect it to be signed, or expect it to be unsigned, depending on the
1565 machines they were written for. This option, and its inverse, let you
1566 make such a program work with the opposite default.
1568 The type @code{char} is always a distinct type from each of
1569 @code{signed char} or @code{unsigned char}, even though its behavior
1570 is always just like one of those two.
1573 @opindex fsigned-char
1574 Let the type @code{char} be signed, like @code{signed char}.
1576 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1577 the negative form of @option{-funsigned-char}. Likewise, the option
1578 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1580 @item -fsigned-bitfields
1581 @itemx -funsigned-bitfields
1582 @itemx -fno-signed-bitfields
1583 @itemx -fno-unsigned-bitfields
1584 @opindex fsigned-bitfields
1585 @opindex funsigned-bitfields
1586 @opindex fno-signed-bitfields
1587 @opindex fno-unsigned-bitfields
1588 These options control whether a bit-field is signed or unsigned, when the
1589 declaration does not use either @code{signed} or @code{unsigned}. By
1590 default, such a bit-field is signed, because this is consistent: the
1591 basic integer types such as @code{int} are signed types.
1594 @node C++ Dialect Options
1595 @section Options Controlling C++ Dialect
1597 @cindex compiler options, C++
1598 @cindex C++ options, command line
1599 @cindex options, C++
1600 This section describes the command-line options that are only meaningful
1601 for C++ programs; but you can also use most of the GNU compiler options
1602 regardless of what language your program is in. For example, you
1603 might compile a file @code{firstClass.C} like this:
1606 g++ -g -frepo -O -c firstClass.C
1610 In this example, only @option{-frepo} is an option meant
1611 only for C++ programs; you can use the other options with any
1612 language supported by GCC@.
1614 Here is a list of options that are @emph{only} for compiling C++ programs:
1618 @item -fabi-version=@var{n}
1619 @opindex fabi-version
1620 Use version @var{n} of the C++ ABI@. Version 2 is the version of the
1621 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1622 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1623 the version that conforms most closely to the C++ ABI specification.
1624 Therefore, the ABI obtained using version 0 will change as ABI bugs
1627 The default is version 2.
1629 @item -fno-access-control
1630 @opindex fno-access-control
1631 Turn off all access checking. This switch is mainly useful for working
1632 around bugs in the access control code.
1636 Check that the pointer returned by @code{operator new} is non-null
1637 before attempting to modify the storage allocated. This check is
1638 normally unnecessary because the C++ standard specifies that
1639 @code{operator new} will only return @code{0} if it is declared
1640 @samp{throw()}, in which case the compiler will always check the
1641 return value even without this option. In all other cases, when
1642 @code{operator new} has a non-empty exception specification, memory
1643 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1644 @samp{new (nothrow)}.
1646 @item -fconserve-space
1647 @opindex fconserve-space
1648 Put uninitialized or runtime-initialized global variables into the
1649 common segment, as C does. This saves space in the executable at the
1650 cost of not diagnosing duplicate definitions. If you compile with this
1651 flag and your program mysteriously crashes after @code{main()} has
1652 completed, you may have an object that is being destroyed twice because
1653 two definitions were merged.
1655 This option is no longer useful on most targets, now that support has
1656 been added for putting variables into BSS without making them common.
1658 @item -ffriend-injection
1659 @opindex ffriend-injection
1660 Inject friend functions into the enclosing namespace, so that they are
1661 visible outside the scope of the class in which they are declared.
1662 Friend functions were documented to work this way in the old Annotated
1663 C++ Reference Manual, and versions of G++ before 4.1 always worked
1664 that way. However, in ISO C++ a friend function which is not declared
1665 in an enclosing scope can only be found using argument dependent
1666 lookup. This option causes friends to be injected as they were in
1669 This option is for compatibility, and may be removed in a future
1672 @item -fno-elide-constructors
1673 @opindex fno-elide-constructors
1674 The C++ standard allows an implementation to omit creating a temporary
1675 which is only used to initialize another object of the same type.
1676 Specifying this option disables that optimization, and forces G++ to
1677 call the copy constructor in all cases.
1679 @item -fno-enforce-eh-specs
1680 @opindex fno-enforce-eh-specs
1681 Don't generate code to check for violation of exception specifications
1682 at runtime. This option violates the C++ standard, but may be useful
1683 for reducing code size in production builds, much like defining
1684 @samp{NDEBUG}. This does not give user code permission to throw
1685 exceptions in violation of the exception specifications; the compiler
1686 will still optimize based on the specifications, so throwing an
1687 unexpected exception will result in undefined behavior.
1690 @itemx -fno-for-scope
1692 @opindex fno-for-scope
1693 If @option{-ffor-scope} is specified, the scope of variables declared in
1694 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1695 as specified by the C++ standard.
1696 If @option{-fno-for-scope} is specified, the scope of variables declared in
1697 a @i{for-init-statement} extends to the end of the enclosing scope,
1698 as was the case in old versions of G++, and other (traditional)
1699 implementations of C++.
1701 The default if neither flag is given to follow the standard,
1702 but to allow and give a warning for old-style code that would
1703 otherwise be invalid, or have different behavior.
1705 @item -fno-gnu-keywords
1706 @opindex fno-gnu-keywords
1707 Do not recognize @code{typeof} as a keyword, so that code can use this
1708 word as an identifier. You can use the keyword @code{__typeof__} instead.
1709 @option{-ansi} implies @option{-fno-gnu-keywords}.
1711 @item -fno-implicit-templates
1712 @opindex fno-implicit-templates
1713 Never emit code for non-inline templates which are instantiated
1714 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1715 @xref{Template Instantiation}, for more information.
1717 @item -fno-implicit-inline-templates
1718 @opindex fno-implicit-inline-templates
1719 Don't emit code for implicit instantiations of inline templates, either.
1720 The default is to handle inlines differently so that compiles with and
1721 without optimization will need the same set of explicit instantiations.
1723 @item -fno-implement-inlines
1724 @opindex fno-implement-inlines
1725 To save space, do not emit out-of-line copies of inline functions
1726 controlled by @samp{#pragma implementation}. This will cause linker
1727 errors if these functions are not inlined everywhere they are called.
1729 @item -fms-extensions
1730 @opindex fms-extensions
1731 Disable pedantic warnings about constructs used in MFC, such as implicit
1732 int and getting a pointer to member function via non-standard syntax.
1734 @item -fno-nonansi-builtins
1735 @opindex fno-nonansi-builtins
1736 Disable built-in declarations of functions that are not mandated by
1737 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1738 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1740 @item -fno-operator-names
1741 @opindex fno-operator-names
1742 Do not treat the operator name keywords @code{and}, @code{bitand},
1743 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1744 synonyms as keywords.
1746 @item -fno-optional-diags
1747 @opindex fno-optional-diags
1748 Disable diagnostics that the standard says a compiler does not need to
1749 issue. Currently, the only such diagnostic issued by G++ is the one for
1750 a name having multiple meanings within a class.
1753 @opindex fpermissive
1754 Downgrade some diagnostics about nonconformant code from errors to
1755 warnings. Thus, using @option{-fpermissive} will allow some
1756 nonconforming code to compile.
1760 Enable automatic template instantiation at link time. This option also
1761 implies @option{-fno-implicit-templates}. @xref{Template
1762 Instantiation}, for more information.
1766 Disable generation of information about every class with virtual
1767 functions for use by the C++ runtime type identification features
1768 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1769 of the language, you can save some space by using this flag. Note that
1770 exception handling uses the same information, but it will generate it as
1771 needed. The @samp{dynamic_cast} operator can still be used for casts that
1772 do not require runtime type information, i.e. casts to @code{void *} or to
1773 unambiguous base classes.
1777 Emit statistics about front-end processing at the end of the compilation.
1778 This information is generally only useful to the G++ development team.
1780 @item -ftemplate-depth-@var{n}
1781 @opindex ftemplate-depth
1782 Set the maximum instantiation depth for template classes to @var{n}.
1783 A limit on the template instantiation depth is needed to detect
1784 endless recursions during template class instantiation. ANSI/ISO C++
1785 conforming programs must not rely on a maximum depth greater than 17.
1787 @item -fno-threadsafe-statics
1788 @opindex fno-threadsafe-statics
1789 Do not emit the extra code to use the routines specified in the C++
1790 ABI for thread-safe initialization of local statics. You can use this
1791 option to reduce code size slightly in code that doesn't need to be
1794 @item -fuse-cxa-atexit
1795 @opindex fuse-cxa-atexit
1796 Register destructors for objects with static storage duration with the
1797 @code{__cxa_atexit} function rather than the @code{atexit} function.
1798 This option is required for fully standards-compliant handling of static
1799 destructors, but will only work if your C library supports
1800 @code{__cxa_atexit}.
1802 @item -fno-use-cxa-get-exception-ptr
1803 @opindex fno-use-cxa-get-exception-ptr
1804 Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
1805 will cause @code{std::uncaught_exception} to be incorrect, but is necessary
1806 if the runtime routine is not available.
1808 @item -fvisibility-inlines-hidden
1809 @opindex fvisibility-inlines-hidden
1810 This switch declares that the user does not attempt to compare
1811 pointers to inline methods where the addresses of the two functions
1812 were taken in different shared objects.
1814 The effect of this is that GCC may, effectively, mark inline methods with
1815 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1816 appear in the export table of a DSO and do not require a PLT indirection
1817 when used within the DSO@. Enabling this option can have a dramatic effect
1818 on load and link times of a DSO as it massively reduces the size of the
1819 dynamic export table when the library makes heavy use of templates.
1821 The behavior of this switch is not quite the same as marking the
1822 methods as hidden directly, because it does not affect static variables
1823 local to the function or cause the compiler to deduce that
1824 the function is defined in only one shared object.
1826 You may mark a method as having a visibility explicitly to negate the
1827 effect of the switch for that method. For example, if you do want to
1828 compare pointers to a particular inline method, you might mark it as
1829 having default visibility. Marking the enclosing class with explicit
1830 visibility will have no effect.
1832 Explicitly instantiated inline methods are unaffected by this option
1833 as their linkage might otherwise cross a shared library boundary.
1834 @xref{Template Instantiation}.
1836 @item -fvisibility-ms-compat
1837 @opindex fvisibility-ms-compat
1838 This flag attempts to use visibility settings to make GCC's C++
1839 linkage model compatible with that of Microsoft Visual Studio.
1841 The flag makes these changes to GCC's linkage model:
1845 It sets the default visibility to @code{hidden}, like
1846 @option{-fvisibility=hidden}.
1849 Types, but not their members, are not hidden by default.
1852 The One Definition Rule is relaxed for types without explicit
1853 visibility specifications which are defined in more than one different
1854 shared object: those declarations are permitted if they would have
1855 been permitted when this option was not used.
1858 In new code it is better to use @option{-fvisibility=hidden} and
1859 export those classes which are intended to be externally visible.
1860 Unfortunately it is possible for code to rely, perhaps accidentally,
1861 on the Visual Studio behaviour.
1863 Among the consequences of these changes are that static data members
1864 of the same type with the same name but defined in different shared
1865 objects will be different, so changing one will not change the other;
1866 and that pointers to function members defined in different shared
1867 objects may not compare equal. When this flag is given, it is a
1868 violation of the ODR to define types with the same name differently.
1872 Do not use weak symbol support, even if it is provided by the linker.
1873 By default, G++ will use weak symbols if they are available. This
1874 option exists only for testing, and should not be used by end-users;
1875 it will result in inferior code and has no benefits. This option may
1876 be removed in a future release of G++.
1880 Do not search for header files in the standard directories specific to
1881 C++, but do still search the other standard directories. (This option
1882 is used when building the C++ library.)
1885 In addition, these optimization, warning, and code generation options
1886 have meanings only for C++ programs:
1889 @item -fno-default-inline
1890 @opindex fno-default-inline
1891 Do not assume @samp{inline} for functions defined inside a class scope.
1892 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1893 functions will have linkage like inline functions; they just won't be
1896 @item -Wabi @r{(C++ only)}
1898 Warn when G++ generates code that is probably not compatible with the
1899 vendor-neutral C++ ABI@. Although an effort has been made to warn about
1900 all such cases, there are probably some cases that are not warned about,
1901 even though G++ is generating incompatible code. There may also be
1902 cases where warnings are emitted even though the code that is generated
1905 You should rewrite your code to avoid these warnings if you are
1906 concerned about the fact that code generated by G++ may not be binary
1907 compatible with code generated by other compilers.
1909 The known incompatibilities at this point include:
1914 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1915 pack data into the same byte as a base class. For example:
1918 struct A @{ virtual void f(); int f1 : 1; @};
1919 struct B : public A @{ int f2 : 1; @};
1923 In this case, G++ will place @code{B::f2} into the same byte
1924 as@code{A::f1}; other compilers will not. You can avoid this problem
1925 by explicitly padding @code{A} so that its size is a multiple of the
1926 byte size on your platform; that will cause G++ and other compilers to
1927 layout @code{B} identically.
1930 Incorrect handling of tail-padding for virtual bases. G++ does not use
1931 tail padding when laying out virtual bases. For example:
1934 struct A @{ virtual void f(); char c1; @};
1935 struct B @{ B(); char c2; @};
1936 struct C : public A, public virtual B @{@};
1940 In this case, G++ will not place @code{B} into the tail-padding for
1941 @code{A}; other compilers will. You can avoid this problem by
1942 explicitly padding @code{A} so that its size is a multiple of its
1943 alignment (ignoring virtual base classes); that will cause G++ and other
1944 compilers to layout @code{C} identically.
1947 Incorrect handling of bit-fields with declared widths greater than that
1948 of their underlying types, when the bit-fields appear in a union. For
1952 union U @{ int i : 4096; @};
1956 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1957 union too small by the number of bits in an @code{int}.
1960 Empty classes can be placed at incorrect offsets. For example:
1970 struct C : public B, public A @{@};
1974 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1975 it should be placed at offset zero. G++ mistakenly believes that the
1976 @code{A} data member of @code{B} is already at offset zero.
1979 Names of template functions whose types involve @code{typename} or
1980 template template parameters can be mangled incorrectly.
1983 template <typename Q>
1984 void f(typename Q::X) @{@}
1986 template <template <typename> class Q>
1987 void f(typename Q<int>::X) @{@}
1991 Instantiations of these templates may be mangled incorrectly.
1995 @item -Wctor-dtor-privacy @r{(C++ only)}
1996 @opindex Wctor-dtor-privacy
1997 Warn when a class seems unusable because all the constructors or
1998 destructors in that class are private, and it has neither friends nor
1999 public static member functions.
2001 @item -Wnon-virtual-dtor @r{(C++ only)}
2002 @opindex Wnon-virtual-dtor
2003 Warn when a class appears to be polymorphic, thereby requiring a virtual
2004 destructor, yet it declares a non-virtual one. This warning is also
2005 enabled if -Weffc++ is specified.
2007 @item -Wreorder @r{(C++ only)}
2009 @cindex reordering, warning
2010 @cindex warning for reordering of member initializers
2011 Warn when the order of member initializers given in the code does not
2012 match the order in which they must be executed. For instance:
2018 A(): j (0), i (1) @{ @}
2022 The compiler will rearrange the member initializers for @samp{i}
2023 and @samp{j} to match the declaration order of the members, emitting
2024 a warning to that effect. This warning is enabled by @option{-Wall}.
2027 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
2030 @item -Weffc++ @r{(C++ only)}
2032 Warn about violations of the following style guidelines from Scott Meyers'
2033 @cite{Effective C++} book:
2037 Item 11: Define a copy constructor and an assignment operator for classes
2038 with dynamically allocated memory.
2041 Item 12: Prefer initialization to assignment in constructors.
2044 Item 14: Make destructors virtual in base classes.
2047 Item 15: Have @code{operator=} return a reference to @code{*this}.
2050 Item 23: Don't try to return a reference when you must return an object.
2054 Also warn about violations of the following style guidelines from
2055 Scott Meyers' @cite{More Effective C++} book:
2059 Item 6: Distinguish between prefix and postfix forms of increment and
2060 decrement operators.
2063 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
2067 When selecting this option, be aware that the standard library
2068 headers do not obey all of these guidelines; use @samp{grep -v}
2069 to filter out those warnings.
2071 @item -Wno-deprecated @r{(C++ only)}
2072 @opindex Wno-deprecated
2073 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
2075 @item -Wstrict-null-sentinel @r{(C++ only)}
2076 @opindex Wstrict-null-sentinel
2077 Warn also about the use of an uncasted @code{NULL} as sentinel. When
2078 compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
2079 to @code{__null}. Although it is a null pointer constant not a null pointer,
2080 it is guaranteed to of the same size as a pointer. But this use is
2081 not portable across different compilers.
2083 @item -Wno-non-template-friend @r{(C++ only)}
2084 @opindex Wno-non-template-friend
2085 Disable warnings when non-templatized friend functions are declared
2086 within a template. Since the advent of explicit template specification
2087 support in G++, if the name of the friend is an unqualified-id (i.e.,
2088 @samp{friend foo(int)}), the C++ language specification demands that the
2089 friend declare or define an ordinary, nontemplate function. (Section
2090 14.5.3). Before G++ implemented explicit specification, unqualified-ids
2091 could be interpreted as a particular specialization of a templatized
2092 function. Because this non-conforming behavior is no longer the default
2093 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
2094 check existing code for potential trouble spots and is on by default.
2095 This new compiler behavior can be turned off with
2096 @option{-Wno-non-template-friend} which keeps the conformant compiler code
2097 but disables the helpful warning.
2099 @item -Wold-style-cast @r{(C++ only)}
2100 @opindex Wold-style-cast
2101 Warn if an old-style (C-style) cast to a non-void type is used within
2102 a C++ program. The new-style casts (@samp{dynamic_cast},
2103 @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are
2104 less vulnerable to unintended effects and much easier to search for.
2106 @item -Woverloaded-virtual @r{(C++ only)}
2107 @opindex Woverloaded-virtual
2108 @cindex overloaded virtual fn, warning
2109 @cindex warning for overloaded virtual fn
2110 Warn when a function declaration hides virtual functions from a
2111 base class. For example, in:
2118 struct B: public A @{
2123 the @code{A} class version of @code{f} is hidden in @code{B}, and code
2131 will fail to compile.
2133 @item -Wno-pmf-conversions @r{(C++ only)}
2134 @opindex Wno-pmf-conversions
2135 Disable the diagnostic for converting a bound pointer to member function
2138 @item -Wsign-promo @r{(C++ only)}
2139 @opindex Wsign-promo
2140 Warn when overload resolution chooses a promotion from unsigned or
2141 enumerated type to a signed type, over a conversion to an unsigned type of
2142 the same size. Previous versions of G++ would try to preserve
2143 unsignedness, but the standard mandates the current behavior.
2148 A& operator = (int);
2158 In this example, G++ will synthesize a default @samp{A& operator =
2159 (const A&);}, while cfront will use the user-defined @samp{operator =}.
2162 @node Objective-C and Objective-C++ Dialect Options
2163 @section Options Controlling Objective-C and Objective-C++ Dialects
2165 @cindex compiler options, Objective-C and Objective-C++
2166 @cindex Objective-C and Objective-C++ options, command line
2167 @cindex options, Objective-C and Objective-C++
2168 (NOTE: This manual does not describe the Objective-C and Objective-C++
2169 languages themselves. See @xref{Standards,,Language Standards
2170 Supported by GCC}, for references.)
2172 This section describes the command-line options that are only meaningful
2173 for Objective-C and Objective-C++ programs, but you can also use most of
2174 the language-independent GNU compiler options.
2175 For example, you might compile a file @code{some_class.m} like this:
2178 gcc -g -fgnu-runtime -O -c some_class.m
2182 In this example, @option{-fgnu-runtime} is an option meant only for
2183 Objective-C and Objective-C++ programs; you can use the other options with
2184 any language supported by GCC@.
2186 Note that since Objective-C is an extension of the C language, Objective-C
2187 compilations may also use options specific to the C front-end (e.g.,
2188 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
2189 C++-specific options (e.g., @option{-Wabi}).
2191 Here is a list of options that are @emph{only} for compiling Objective-C
2192 and Objective-C++ programs:
2195 @item -fconstant-string-class=@var{class-name}
2196 @opindex fconstant-string-class
2197 Use @var{class-name} as the name of the class to instantiate for each
2198 literal string specified with the syntax @code{@@"@dots{}"}. The default
2199 class name is @code{NXConstantString} if the GNU runtime is being used, and
2200 @code{NSConstantString} if the NeXT runtime is being used (see below). The
2201 @option{-fconstant-cfstrings} option, if also present, will override the
2202 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
2203 to be laid out as constant CoreFoundation strings.
2206 @opindex fgnu-runtime
2207 Generate object code compatible with the standard GNU Objective-C
2208 runtime. This is the default for most types of systems.
2210 @item -fnext-runtime
2211 @opindex fnext-runtime
2212 Generate output compatible with the NeXT runtime. This is the default
2213 for NeXT-based systems, including Darwin and Mac OS X@. The macro
2214 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
2217 @item -fno-nil-receivers
2218 @opindex fno-nil-receivers
2219 Assume that all Objective-C message dispatches (e.g.,
2220 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
2221 is not @code{nil}. This allows for more efficient entry points in the runtime
2222 to be used. Currently, this option is only available in conjunction with
2223 the NeXT runtime on Mac OS X 10.3 and later.
2225 @item -fobjc-call-cxx-cdtors
2226 @opindex fobjc-call-cxx-cdtors
2227 For each Objective-C class, check if any of its instance variables is a
2228 C++ object with a non-trivial default constructor. If so, synthesize a
2229 special @code{- (id) .cxx_construct} instance method that will run
2230 non-trivial default constructors on any such instance variables, in order,
2231 and then return @code{self}. Similarly, check if any instance variable
2232 is a C++ object with a non-trivial destructor, and if so, synthesize a
2233 special @code{- (void) .cxx_destruct} method that will run
2234 all such default destructors, in reverse order.
2236 The @code{- (id) .cxx_construct} and/or @code{- (void) .cxx_destruct} methods
2237 thusly generated will only operate on instance variables declared in the
2238 current Objective-C class, and not those inherited from superclasses. It
2239 is the responsibility of the Objective-C runtime to invoke all such methods
2240 in an object's inheritance hierarchy. The @code{- (id) .cxx_construct} methods
2241 will be invoked by the runtime immediately after a new object
2242 instance is allocated; the @code{- (void) .cxx_destruct} methods will
2243 be invoked immediately before the runtime deallocates an object instance.
2245 As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
2246 support for invoking the @code{- (id) .cxx_construct} and
2247 @code{- (void) .cxx_destruct} methods.
2249 @item -fobjc-direct-dispatch
2250 @opindex fobjc-direct-dispatch
2251 Allow fast jumps to the message dispatcher. On Darwin this is
2252 accomplished via the comm page.
2254 @item -fobjc-exceptions
2255 @opindex fobjc-exceptions
2256 Enable syntactic support for structured exception handling in Objective-C,
2257 similar to what is offered by C++ and Java. This option is
2258 unavailable in conjunction with the NeXT runtime on Mac OS X 10.2 and
2267 @@catch (AnObjCClass *exc) @{
2274 @@catch (AnotherClass *exc) @{
2277 @@catch (id allOthers) @{
2287 The @code{@@throw} statement may appear anywhere in an Objective-C or
2288 Objective-C++ program; when used inside of a @code{@@catch} block, the
2289 @code{@@throw} may appear without an argument (as shown above), in which case
2290 the object caught by the @code{@@catch} will be rethrown.
2292 Note that only (pointers to) Objective-C objects may be thrown and
2293 caught using this scheme. When an object is thrown, it will be caught
2294 by the nearest @code{@@catch} clause capable of handling objects of that type,
2295 analogously to how @code{catch} blocks work in C++ and Java. A
2296 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
2297 any and all Objective-C exceptions not caught by previous @code{@@catch}
2300 The @code{@@finally} clause, if present, will be executed upon exit from the
2301 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
2302 regardless of whether any exceptions are thrown, caught or rethrown
2303 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
2304 of the @code{finally} clause in Java.
2306 There are several caveats to using the new exception mechanism:
2310 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
2311 idioms provided by the @code{NSException} class, the new
2312 exceptions can only be used on Mac OS X 10.3 (Panther) and later
2313 systems, due to additional functionality needed in the (NeXT) Objective-C
2317 As mentioned above, the new exceptions do not support handling
2318 types other than Objective-C objects. Furthermore, when used from
2319 Objective-C++, the Objective-C exception model does not interoperate with C++
2320 exceptions at this time. This means you cannot @code{@@throw} an exception
2321 from Objective-C and @code{catch} it in C++, or vice versa
2322 (i.e., @code{throw @dots{} @@catch}).
2325 The @option{-fobjc-exceptions} switch also enables the use of synchronization
2326 blocks for thread-safe execution:
2329 @@synchronized (ObjCClass *guard) @{
2334 Upon entering the @code{@@synchronized} block, a thread of execution shall
2335 first check whether a lock has been placed on the corresponding @code{guard}
2336 object by another thread. If it has, the current thread shall wait until
2337 the other thread relinquishes its lock. Once @code{guard} becomes available,
2338 the current thread will place its own lock on it, execute the code contained in
2339 the @code{@@synchronized} block, and finally relinquish the lock (thereby
2340 making @code{guard} available to other threads).
2342 Unlike Java, Objective-C does not allow for entire methods to be marked
2343 @code{@@synchronized}. Note that throwing exceptions out of
2344 @code{@@synchronized} blocks is allowed, and will cause the guarding object
2345 to be unlocked properly.
2349 Enable garbage collection (GC) in Objective-C and Objective-C++ programs.
2351 @item -freplace-objc-classes
2352 @opindex freplace-objc-classes
2353 Emit a special marker instructing @command{ld(1)} not to statically link in
2354 the resulting object file, and allow @command{dyld(1)} to load it in at
2355 run time instead. This is used in conjunction with the Fix-and-Continue
2356 debugging mode, where the object file in question may be recompiled and
2357 dynamically reloaded in the course of program execution, without the need
2358 to restart the program itself. Currently, Fix-and-Continue functionality
2359 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
2364 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
2365 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
2366 compile time) with static class references that get initialized at load time,
2367 which improves run-time performance. Specifying the @option{-fzero-link} flag
2368 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
2369 to be retained. This is useful in Zero-Link debugging mode, since it allows
2370 for individual class implementations to be modified during program execution.
2374 Dump interface declarations for all classes seen in the source file to a
2375 file named @file{@var{sourcename}.decl}.
2377 @item -Wassign-intercept
2378 @opindex Wassign-intercept
2379 Warn whenever an Objective-C assignment is being intercepted by the
2383 @opindex Wno-protocol
2384 If a class is declared to implement a protocol, a warning is issued for
2385 every method in the protocol that is not implemented by the class. The
2386 default behavior is to issue a warning for every method not explicitly
2387 implemented in the class, even if a method implementation is inherited
2388 from the superclass. If you use the @option{-Wno-protocol} option, then
2389 methods inherited from the superclass are considered to be implemented,
2390 and no warning is issued for them.
2394 Warn if multiple methods of different types for the same selector are
2395 found during compilation. The check is performed on the list of methods
2396 in the final stage of compilation. Additionally, a check is performed
2397 for each selector appearing in a @code{@@selector(@dots{})}
2398 expression, and a corresponding method for that selector has been found
2399 during compilation. Because these checks scan the method table only at
2400 the end of compilation, these warnings are not produced if the final
2401 stage of compilation is not reached, for example because an error is
2402 found during compilation, or because the @option{-fsyntax-only} option is
2405 @item -Wstrict-selector-match
2406 @opindex Wstrict-selector-match
2407 Warn if multiple methods with differing argument and/or return types are
2408 found for a given selector when attempting to send a message using this
2409 selector to a receiver of type @code{id} or @code{Class}. When this flag
2410 is off (which is the default behavior), the compiler will omit such warnings
2411 if any differences found are confined to types which share the same size
2414 @item -Wundeclared-selector
2415 @opindex Wundeclared-selector
2416 Warn if a @code{@@selector(@dots{})} expression referring to an
2417 undeclared selector is found. A selector is considered undeclared if no
2418 method with that name has been declared before the
2419 @code{@@selector(@dots{})} expression, either explicitly in an
2420 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2421 an @code{@@implementation} section. This option always performs its
2422 checks as soon as a @code{@@selector(@dots{})} expression is found,
2423 while @option{-Wselector} only performs its checks in the final stage of
2424 compilation. This also enforces the coding style convention
2425 that methods and selectors must be declared before being used.
2427 @item -print-objc-runtime-info
2428 @opindex print-objc-runtime-info
2429 Generate C header describing the largest structure that is passed by
2434 @node Language Independent Options
2435 @section Options to Control Diagnostic Messages Formatting
2436 @cindex options to control diagnostics formatting
2437 @cindex diagnostic messages
2438 @cindex message formatting
2440 Traditionally, diagnostic messages have been formatted irrespective of
2441 the output device's aspect (e.g.@: its width, @dots{}). The options described
2442 below can be used to control the diagnostic messages formatting
2443 algorithm, e.g.@: how many characters per line, how often source location
2444 information should be reported. Right now, only the C++ front end can
2445 honor these options. However it is expected, in the near future, that
2446 the remaining front ends would be able to digest them correctly.
2449 @item -fmessage-length=@var{n}
2450 @opindex fmessage-length
2451 Try to format error messages so that they fit on lines of about @var{n}
2452 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2453 the front ends supported by GCC@. If @var{n} is zero, then no
2454 line-wrapping will be done; each error message will appear on a single
2457 @opindex fdiagnostics-show-location
2458 @item -fdiagnostics-show-location=once
2459 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2460 reporter to emit @emph{once} source location information; that is, in
2461 case the message is too long to fit on a single physical line and has to
2462 be wrapped, the source location won't be emitted (as prefix) again,
2463 over and over, in subsequent continuation lines. This is the default
2466 @item -fdiagnostics-show-location=every-line
2467 Only meaningful in line-wrapping mode. Instructs the diagnostic
2468 messages reporter to emit the same source location information (as
2469 prefix) for physical lines that result from the process of breaking
2470 a message which is too long to fit on a single line.
2472 @item -fdiagnostics-show-option
2473 @opindex fdiagnostics-show-option
2474 This option instructs the diagnostic machinery to add text to each
2475 diagnostic emitted, which indicates which command line option directly
2476 controls that diagnostic, when such an option is known to the
2477 diagnostic machinery.
2479 @item -Wcoverage-mismatch
2480 @opindex Wcoverage-mismatch
2481 Warn if feedback profiles do not match when using the
2482 @option{-fprofile-use} option.
2483 If a source file was changed between @option{-fprofile-gen} and
2484 @option{-fprofile-use}, the files with the profile feedback can fail
2485 to match the source file and GCC can not use the profile feedback
2486 information. By default, GCC emits an error message in this case.
2487 The option @option{-Wcoverage-mismatch} emits a warning instead of an
2488 error. GCC does not use appropriate feedback profiles, so using this
2489 option can result in poorly optimized code. This option is useful
2490 only in the case of very minor changes such as bug fixes to an
2495 @node Warning Options
2496 @section Options to Request or Suppress Warnings
2497 @cindex options to control warnings
2498 @cindex warning messages
2499 @cindex messages, warning
2500 @cindex suppressing warnings
2502 Warnings are diagnostic messages that report constructions which
2503 are not inherently erroneous but which are risky or suggest there
2504 may have been an error.
2506 You can request many specific warnings with options beginning @samp{-W},
2507 for example @option{-Wimplicit} to request warnings on implicit
2508 declarations. Each of these specific warning options also has a
2509 negative form beginning @samp{-Wno-} to turn off warnings;
2510 for example, @option{-Wno-implicit}. This manual lists only one of the
2511 two forms, whichever is not the default.
2513 The following options control the amount and kinds of warnings produced
2514 by GCC; for further, language-specific options also refer to
2515 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2519 @cindex syntax checking
2521 @opindex fsyntax-only
2522 Check the code for syntax errors, but don't do anything beyond that.
2526 Issue all the warnings demanded by strict ISO C and ISO C++;
2527 reject all programs that use forbidden extensions, and some other
2528 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2529 version of the ISO C standard specified by any @option{-std} option used.
2531 Valid ISO C and ISO C++ programs should compile properly with or without
2532 this option (though a rare few will require @option{-ansi} or a
2533 @option{-std} option specifying the required version of ISO C)@. However,
2534 without this option, certain GNU extensions and traditional C and C++
2535 features are supported as well. With this option, they are rejected.
2537 @option{-pedantic} does not cause warning messages for use of the
2538 alternate keywords whose names begin and end with @samp{__}. Pedantic
2539 warnings are also disabled in the expression that follows
2540 @code{__extension__}. However, only system header files should use
2541 these escape routes; application programs should avoid them.
2542 @xref{Alternate Keywords}.
2544 Some users try to use @option{-pedantic} to check programs for strict ISO
2545 C conformance. They soon find that it does not do quite what they want:
2546 it finds some non-ISO practices, but not all---only those for which
2547 ISO C @emph{requires} a diagnostic, and some others for which
2548 diagnostics have been added.
2550 A feature to report any failure to conform to ISO C might be useful in
2551 some instances, but would require considerable additional work and would
2552 be quite different from @option{-pedantic}. We don't have plans to
2553 support such a feature in the near future.
2555 Where the standard specified with @option{-std} represents a GNU
2556 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2557 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2558 extended dialect is based. Warnings from @option{-pedantic} are given
2559 where they are required by the base standard. (It would not make sense
2560 for such warnings to be given only for features not in the specified GNU
2561 C dialect, since by definition the GNU dialects of C include all
2562 features the compiler supports with the given option, and there would be
2563 nothing to warn about.)
2565 @item -pedantic-errors
2566 @opindex pedantic-errors
2567 Like @option{-pedantic}, except that errors are produced rather than
2572 Inhibit all warning messages.
2576 Inhibit warning messages about the use of @samp{#import}.
2578 @item -Wchar-subscripts
2579 @opindex Wchar-subscripts
2580 Warn if an array subscript has type @code{char}. This is a common cause
2581 of error, as programmers often forget that this type is signed on some
2583 This warning is enabled by @option{-Wall}.
2587 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2588 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2589 This warning is enabled by @option{-Wall}.
2591 @item -Wfatal-errors
2592 @opindex Wfatal-errors
2593 This option causes the compiler to abort compilation on the first error
2594 occurred rather than trying to keep going and printing further error
2599 @opindex ffreestanding
2600 @opindex fno-builtin
2601 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2602 the arguments supplied have types appropriate to the format string
2603 specified, and that the conversions specified in the format string make
2604 sense. This includes standard functions, and others specified by format
2605 attributes (@pxref{Function Attributes}), in the @code{printf},
2606 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2607 not in the C standard) families (or other target-specific families).
2608 Which functions are checked without format attributes having been
2609 specified depends on the standard version selected, and such checks of
2610 functions without the attribute specified are disabled by
2611 @option{-ffreestanding} or @option{-fno-builtin}.
2613 The formats are checked against the format features supported by GNU
2614 libc version 2.2. These include all ISO C90 and C99 features, as well
2615 as features from the Single Unix Specification and some BSD and GNU
2616 extensions. Other library implementations may not support all these
2617 features; GCC does not support warning about features that go beyond a
2618 particular library's limitations. However, if @option{-pedantic} is used
2619 with @option{-Wformat}, warnings will be given about format features not
2620 in the selected standard version (but not for @code{strfmon} formats,
2621 since those are not in any version of the C standard). @xref{C Dialect
2622 Options,,Options Controlling C Dialect}.
2624 Since @option{-Wformat} also checks for null format arguments for
2625 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2627 @option{-Wformat} is included in @option{-Wall}. For more control over some
2628 aspects of format checking, the options @option{-Wformat-y2k},
2629 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2630 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2631 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2634 @opindex Wformat-y2k
2635 If @option{-Wformat} is specified, also warn about @code{strftime}
2636 formats which may yield only a two-digit year.
2638 @item -Wno-format-extra-args
2639 @opindex Wno-format-extra-args
2640 If @option{-Wformat} is specified, do not warn about excess arguments to a
2641 @code{printf} or @code{scanf} format function. The C standard specifies
2642 that such arguments are ignored.
2644 Where the unused arguments lie between used arguments that are
2645 specified with @samp{$} operand number specifications, normally
2646 warnings are still given, since the implementation could not know what
2647 type to pass to @code{va_arg} to skip the unused arguments. However,
2648 in the case of @code{scanf} formats, this option will suppress the
2649 warning if the unused arguments are all pointers, since the Single
2650 Unix Specification says that such unused arguments are allowed.
2652 @item -Wno-format-zero-length
2653 @opindex Wno-format-zero-length
2654 If @option{-Wformat} is specified, do not warn about zero-length formats.
2655 The C standard specifies that zero-length formats are allowed.
2657 @item -Wformat-nonliteral
2658 @opindex Wformat-nonliteral
2659 If @option{-Wformat} is specified, also warn if the format string is not a
2660 string literal and so cannot be checked, unless the format function
2661 takes its format arguments as a @code{va_list}.
2663 @item -Wformat-security
2664 @opindex Wformat-security
2665 If @option{-Wformat} is specified, also warn about uses of format
2666 functions that represent possible security problems. At present, this
2667 warns about calls to @code{printf} and @code{scanf} functions where the
2668 format string is not a string literal and there are no format arguments,
2669 as in @code{printf (foo);}. This may be a security hole if the format
2670 string came from untrusted input and contains @samp{%n}. (This is
2671 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2672 in future warnings may be added to @option{-Wformat-security} that are not
2673 included in @option{-Wformat-nonliteral}.)
2677 Enable @option{-Wformat} plus format checks not included in
2678 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2679 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2683 Warn about passing a null pointer for arguments marked as
2684 requiring a non-null value by the @code{nonnull} function attribute.
2686 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2687 can be disabled with the @option{-Wno-nonnull} option.
2689 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2691 Warn about uninitialized variables which are initialized with themselves.
2692 Note this option can only be used with the @option{-Wuninitialized} option,
2693 which in turn only works with @option{-O1} and above.
2695 For example, GCC will warn about @code{i} being uninitialized in the
2696 following snippet only when @option{-Winit-self} has been specified:
2707 @item -Wimplicit-int
2708 @opindex Wimplicit-int
2709 Warn when a declaration does not specify a type.
2710 This warning is enabled by @option{-Wall}.
2712 @item -Wimplicit-function-declaration
2713 @opindex Wimplicit-function-declaration
2714 @opindex Wno-implicit-function-declaration
2715 Give a warning whenever a function is used before being declared. In
2716 C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
2717 enabled by default and it is made into an error by
2718 @option{-pedantic-errors}. This warning is also enabled by
2723 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2724 This warning is enabled by @option{-Wall}.
2728 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2729 function with external linkage, returning int, taking either zero
2730 arguments, two, or three arguments of appropriate types.
2731 This warning is enabled by @option{-Wall}.
2733 @item -Wmissing-braces
2734 @opindex Wmissing-braces
2735 Warn if an aggregate or union initializer is not fully bracketed. In
2736 the following example, the initializer for @samp{a} is not fully
2737 bracketed, but that for @samp{b} is fully bracketed.
2740 int a[2][2] = @{ 0, 1, 2, 3 @};
2741 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2744 This warning is enabled by @option{-Wall}.
2746 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2747 @opindex Wmissing-include-dirs
2748 Warn if a user-supplied include directory does not exist.
2751 @opindex Wparentheses
2752 Warn if parentheses are omitted in certain contexts, such
2753 as when there is an assignment in a context where a truth value
2754 is expected, or when operators are nested whose precedence people
2755 often get confused about.
2757 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2758 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2759 interpretation from that of ordinary mathematical notation.
2761 Also warn about constructions where there may be confusion to which
2762 @code{if} statement an @code{else} branch belongs. Here is an example of
2777 In C/C++, every @code{else} branch belongs to the innermost possible
2778 @code{if} statement, which in this example is @code{if (b)}. This is
2779 often not what the programmer expected, as illustrated in the above
2780 example by indentation the programmer chose. When there is the
2781 potential for this confusion, GCC will issue a warning when this flag
2782 is specified. To eliminate the warning, add explicit braces around
2783 the innermost @code{if} statement so there is no way the @code{else}
2784 could belong to the enclosing @code{if}. The resulting code would
2801 This warning is enabled by @option{-Wall}.
2803 @item -Wsequence-point
2804 @opindex Wsequence-point
2805 Warn about code that may have undefined semantics because of violations
2806 of sequence point rules in the C and C++ standards.
2808 The C and C++ standards defines the order in which expressions in a C/C++
2809 program are evaluated in terms of @dfn{sequence points}, which represent
2810 a partial ordering between the execution of parts of the program: those
2811 executed before the sequence point, and those executed after it. These
2812 occur after the evaluation of a full expression (one which is not part
2813 of a larger expression), after the evaluation of the first operand of a
2814 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2815 function is called (but after the evaluation of its arguments and the
2816 expression denoting the called function), and in certain other places.
2817 Other than as expressed by the sequence point rules, the order of
2818 evaluation of subexpressions of an expression is not specified. All
2819 these rules describe only a partial order rather than a total order,
2820 since, for example, if two functions are called within one expression
2821 with no sequence point between them, the order in which the functions
2822 are called is not specified. However, the standards committee have
2823 ruled that function calls do not overlap.
2825 It is not specified when between sequence points modifications to the
2826 values of objects take effect. Programs whose behavior depends on this
2827 have undefined behavior; the C and C++ standards specify that ``Between
2828 the previous and next sequence point an object shall have its stored
2829 value modified at most once by the evaluation of an expression.
2830 Furthermore, the prior value shall be read only to determine the value
2831 to be stored.''. If a program breaks these rules, the results on any
2832 particular implementation are entirely unpredictable.
2834 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2835 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2836 diagnosed by this option, and it may give an occasional false positive
2837 result, but in general it has been found fairly effective at detecting
2838 this sort of problem in programs.
2840 The standard is worded confusingly, therefore there is some debate
2841 over the precise meaning of the sequence point rules in subtle cases.
2842 Links to discussions of the problem, including proposed formal
2843 definitions, may be found on the GCC readings page, at
2844 @w{@uref{http://gcc.gnu.org/readings.html}}.
2846 This warning is enabled by @option{-Wall} for C and C++.
2849 @opindex Wreturn-type
2850 @opindex Wno-return-type
2851 Warn whenever a function is defined with a return-type that defaults
2852 to @code{int}. Also warn about any @code{return} statement with no
2853 return-value in a function whose return-type is not @code{void}
2854 (falling off the end of the function body is considered returning
2855 without a value), and about a @code{return} statement with a
2856 expression in a function whose return-type is @code{void}.
2858 Also warn if the return type of a function has a type qualifier
2859 such as @code{const}. For ISO C such a type qualifier has no effect,
2860 since the value returned by a function is not an lvalue.
2861 For C++, the warning is only emitted for scalar types or @code{void}.
2862 ISO C prohibits qualified @code{void} return types on function
2863 definitions, so such return types always receive a warning
2864 even without this option.
2866 For C++, a function without return type always produces a diagnostic
2867 message, even when @option{-Wno-return-type} is specified. The only
2868 exceptions are @samp{main} and functions defined in system headers.
2870 This warning is enabled by @option{-Wall}.
2874 Warn whenever a @code{switch} statement has an index of enumerated type
2875 and lacks a @code{case} for one or more of the named codes of that
2876 enumeration. (The presence of a @code{default} label prevents this
2877 warning.) @code{case} labels outside the enumeration range also
2878 provoke warnings when this option is used.
2879 This warning is enabled by @option{-Wall}.
2881 @item -Wswitch-default
2882 @opindex Wswitch-switch
2883 Warn whenever a @code{switch} statement does not have a @code{default}
2887 @opindex Wswitch-enum
2888 Warn whenever a @code{switch} statement has an index of enumerated type
2889 and lacks a @code{case} for one or more of the named codes of that
2890 enumeration. @code{case} labels outside the enumeration range also
2891 provoke warnings when this option is used.
2895 Warn if any trigraphs are encountered that might change the meaning of
2896 the program (trigraphs within comments are not warned about).
2897 This warning is enabled by @option{-Wall}.
2899 @item -Wunused-function
2900 @opindex Wunused-function
2901 Warn whenever a static function is declared but not defined or a
2902 non-inline static function is unused.
2903 This warning is enabled by @option{-Wall}.
2905 @item -Wunused-label
2906 @opindex Wunused-label
2907 Warn whenever a label is declared but not used.
2908 This warning is enabled by @option{-Wall}.
2910 To suppress this warning use the @samp{unused} attribute
2911 (@pxref{Variable Attributes}).
2913 @item -Wunused-parameter
2914 @opindex Wunused-parameter
2915 Warn whenever a function parameter is unused aside from its declaration.
2917 To suppress this warning use the @samp{unused} attribute
2918 (@pxref{Variable Attributes}).
2920 @item -Wunused-variable
2921 @opindex Wunused-variable
2922 Warn whenever a local variable or non-constant static variable is unused
2923 aside from its declaration.
2924 This warning is enabled by @option{-Wall}.
2926 To suppress this warning use the @samp{unused} attribute
2927 (@pxref{Variable Attributes}).
2929 @item -Wunused-value
2930 @opindex Wunused-value
2931 Warn whenever a statement computes a result that is explicitly not
2932 used. To suppress this warning cast the unused expression to
2933 @samp{void}. This includes an expression-statement or the left-hand
2934 side of a comma expression that contains no side effects. For example,
2935 an expression such as @samp{x[i,j]} will cause a warning, while
2936 @samp{x[(void)i,j]} will not.
2938 This warning is enabled by @option{-Wall}.
2942 All the above @option{-Wunused} options combined.
2944 In order to get a warning about an unused function parameter, you must
2945 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2946 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2948 @item -Wuninitialized
2949 @opindex Wuninitialized
2950 Warn if an automatic variable is used without first being initialized or
2951 if a variable may be clobbered by a @code{setjmp} call.
2953 These warnings are possible only in optimizing compilation,
2954 because they require data flow information that is computed only
2955 when optimizing. If you do not specify @option{-O}, you will not get
2956 these warnings. Instead, GCC will issue a warning about @option{-Wuninitialized}
2957 requiring @option{-O}.
2959 If you want to warn about code which uses the uninitialized value of the
2960 variable in its own initializer, use the @option{-Winit-self} option.
2962 These warnings occur for individual uninitialized or clobbered
2963 elements of structure, union or array variables as well as for
2964 variables which are uninitialized or clobbered as a whole. They do
2965 not occur for variables or elements declared @code{volatile}. Because
2966 these warnings depend on optimization, the exact variables or elements
2967 for which there are warnings will depend on the precise optimization
2968 options and version of GCC used.
2970 Note that there may be no warning about a variable that is used only
2971 to compute a value that itself is never used, because such
2972 computations may be deleted by data flow analysis before the warnings
2975 These warnings are made optional because GCC is not smart
2976 enough to see all the reasons why the code might be correct
2977 despite appearing to have an error. Here is one example of how
2998 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2999 always initialized, but GCC doesn't know this. Here is
3000 another common case:
3005 if (change_y) save_y = y, y = new_y;
3007 if (change_y) y = save_y;
3012 This has no bug because @code{save_y} is used only if it is set.
3014 @cindex @code{longjmp} warnings
3015 This option also warns when a non-volatile automatic variable might be
3016 changed by a call to @code{longjmp}. These warnings as well are possible
3017 only in optimizing compilation.
3019 The compiler sees only the calls to @code{setjmp}. It cannot know
3020 where @code{longjmp} will be called; in fact, a signal handler could
3021 call it at any point in the code. As a result, you may get a warning
3022 even when there is in fact no problem because @code{longjmp} cannot
3023 in fact be called at the place which would cause a problem.
3025 Some spurious warnings can be avoided if you declare all the functions
3026 you use that never return as @code{noreturn}. @xref{Function
3029 This warning is enabled by @option{-Wall}.
3031 @item -Wunknown-pragmas
3032 @opindex Wunknown-pragmas
3033 @cindex warning for unknown pragmas
3034 @cindex unknown pragmas, warning
3035 @cindex pragmas, warning of unknown
3036 Warn when a #pragma directive is encountered which is not understood by
3037 GCC@. If this command line option is used, warnings will even be issued
3038 for unknown pragmas in system header files. This is not the case if
3039 the warnings were only enabled by the @option{-Wall} command line option.
3042 @opindex Wno-pragmas
3044 Do not warn about misuses of pragmas, such as incorrect parameters,
3045 invalid syntax, or conflicts between pragmas. See also
3046 @samp{-Wunknown-pragmas}.
3048 @item -Wstrict-aliasing
3049 @opindex Wstrict-aliasing
3050 This option is only active when @option{-fstrict-aliasing} is active.
3051 It warns about code which might break the strict aliasing rules that the
3052 compiler is using for optimization. The warning does not catch all
3053 cases, but does attempt to catch the more common pitfalls. It is
3054 included in @option{-Wall}.
3055 It is equivalent to -Wstrict-aliasing=3
3057 @item -Wstrict-aliasing=n
3058 @opindex Wstrict-aliasing=n
3059 This option is only active when @option{-fstrict-aliasing} is active.
3060 It warns about code which might break the strict aliasing rules that the
3061 compiler is using for optimization.
3062 Higher levels correspond to higher accuracy (fewer false positives).
3063 Higher levels also correspond to more effort, similar to the way -O works.
3064 @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=n},
3067 Level 1: Most aggressive, quick, least accurate.
3068 Possibly useful when higher levels
3069 do not warn but -fstrict-aliasing still breaks the code, as it has very few
3070 false negatives. However, it has many false positives.
3071 Warns for all pointer conversions between possibly incompatible types,
3072 even if never dereferenced. Runs in the frontend only.
3074 Level 2: Aggressive, quick, not too precise.
3075 May still have many false positives (not as many as level 1 though),
3076 and few false negatives (but possibly more than level 1).
3077 Unlike level 1, it only warns when an address is taken. Warns about
3078 incomplete types. Runs in the frontend only.
3080 Level 3 (default for @option{-Wstrict-aliasing}):
3081 Should have very few false positives and few false
3082 negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
3083 Takes care of the common punn+dereference pattern in the frontend:
3084 @code{*(int*)&some_float}.
3085 If optimization is enabled, it also runs in the backend, where it deals
3086 with multiple statement cases using flow-sensitive points-to information.
3087 Only warns when the converted pointer is dereferenced.
3088 Does not warn about incomplete types.
3090 @item -Wstrict-overflow
3091 @item -Wstrict-overflow=@var{n}
3092 @opindex Wstrict-overflow
3093 This option is only active when @option{-fstrict-overflow} is active.
3094 It warns about cases where the compiler optimizes based on the
3095 assumption that signed overflow does not occur. Note that it does not
3096 warn about all cases where the code might overflow: it only warns
3097 about cases where the compiler implements some optimization. Thus
3098 this warning depends on the optimization level.
3100 An optimization which assumes that signed overflow does not occur is
3101 perfectly safe if the values of the variables involved are such that
3102 overflow never does, in fact, occur. Therefore this warning can
3103 easily give a false positive: a warning about code which is not
3104 actually a problem. To help focus on important issues, several
3105 warning levels are defined. No warnings are issued for the use of
3106 undefined signed overflow when estimating how many iterations a loop
3107 will require, in particular when determining whether a loop will be
3111 @item -Wstrict-overflow=1
3112 Warn about cases which are both questionable and easy to avoid. For
3113 example: @code{x + 1 > x}; with @option{-fstrict-overflow}, the
3114 compiler will simplify this to @code{1}. This level of
3115 @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
3116 are not, and must be explicitly requested.
3118 @item -Wstrict-overflow=2
3119 Also warn about other cases where a comparison is simplified to a
3120 constant. For example: @code{abs (x) >= 0}. This can only be
3121 simplified when @option{-fstrict-overflow} is in effect, because
3122 @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
3123 zero. @option{-Wstrict-overflow} (with no level) is the same as
3124 @option{-Wstrict-overflow=2}.
3126 @item -Wstrict-overflow=3
3127 Also warn about other cases where a comparison is simplified. For
3128 example: @code{x + 1 > 1} will be simplified to @code{x > 0}.
3130 @item -Wstrict-overflow=4
3131 Also warn about other simplifications not covered by the above cases.
3132 For example: @code{(x * 10) / 5} will be simplified to @code{x * 2}.
3134 @item -Wstrict-overflow=5
3135 Also warn about cases where the compiler reduces the magnitude of a
3136 constant involved in a comparison. For example: @code{x + 2 > y} will
3137 be simplified to @code{x + 1 >= y}. This is reported only at the
3138 highest warning level because this simplification applies to many
3139 comparisons, so this warning level will give a very large number of
3143 @item -Warray-bounds
3144 @opindex Wno-array-bounds
3145 @opindex Warray-bounds
3146 This option is only active when @option{-ftree-vrp} is active
3147 (default for -O2 and above). It warns about subscripts to arrays
3148 that are always out of bounds. This warning is enabled by @option{-Wall}.
3152 All of the above @samp{-W} options combined. This enables all the
3153 warnings about constructions that some users consider questionable, and
3154 that are easy to avoid (or modify to prevent the warning), even in
3155 conjunction with macros. This also enables some language-specific
3156 warnings described in @ref{C++ Dialect Options} and
3157 @ref{Objective-C and Objective-C++ Dialect Options}.
3160 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
3161 Some of them warn about constructions that users generally do not
3162 consider questionable, but which occasionally you might wish to check
3163 for; others warn about constructions that are necessary or hard to avoid
3164 in some cases, and there is no simple way to modify the code to suppress
3171 (This option used to be called @option{-W}. The older name is still
3172 supported, but the newer name is more descriptive.) Print extra warning
3173 messages for these events:
3177 Warn if a comparison is always true or always false due to the limited
3178 range of the data type, but do not warn for constant expressions. For
3179 example, warn if an unsigned variable is compared against zero with
3180 @samp{<} or @samp{>=}. This warning can be independently controlled
3181 by @option{-Wtype-limits}.
3184 Storage-class specifiers like @code{static} are not the first things
3185 in a declaration. According to the C Standard, this usage is
3186 obsolescent. This warning can be independently controlled by
3187 @option{-Wold-style-declaration}.
3190 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
3194 A comparison between signed and unsigned values could produce an
3195 incorrect result when the signed value is converted to unsigned.
3196 (But don't warn if @option{-Wno-sign-compare} is also specified.)
3199 An aggregate has an initializer which does not initialize all members.
3200 This warning can be independently controlled by
3201 @option{-Wmissing-field-initializers}.
3204 An initialized field without side effects is overridden when using
3205 designated initializers (@pxref{Designated Inits, , Designated
3206 Initializers}). This warning can be independently controlled by
3207 @option{-Woverride-init}.
3210 A function parameter is declared without a type specifier in K&R-style
3211 functions. This warning can be independently controlled by
3212 @option{-Wmissing-parameter-type}.
3215 An empty body occurs in an @samp{if}, @samp{else} or
3216 @samp{do while} statement. This warning can be independently
3217 controlled by @option{-Wempty-body}.
3219 @item @r{(C++ only)}
3220 An empty body occurs in a @samp{while} or @samp{for} statement with no
3221 whitespacing before the semicolon. This warning can be independently
3222 controlled by @option{-Wempty-body}.
3225 A pointer is compared against integer zero with @samp{<}, @samp{<=},
3226 @samp{>}, or @samp{>=}.
3229 A variable might be changed by @samp{longjmp} or @samp{vfork}.
3230 This warning can be independently controlled by @option{-Wclobbered}.
3232 @item @r{(C++ only)}
3233 An enumerator and a non-enumerator both appear in a conditional expression.
3235 @item @r{(C++ only)}
3236 A non-static reference or non-static @samp{const} member appears in a
3237 class without constructors.
3239 @item @r{(C++ only)}
3240 Ambiguous virtual bases.
3242 @item @r{(C++ only)}
3243 Subscripting an array which has been declared @samp{register}.
3245 @item @r{(C++ only)}
3246 Taking the address of a variable which has been declared @samp{register}.
3248 @item @r{(C++ only)}
3249 A base class is not initialized in a derived class' copy constructor.
3252 @item -Wno-div-by-zero
3253 @opindex Wno-div-by-zero
3254 @opindex Wdiv-by-zero
3255 Do not warn about compile-time integer division by zero. Floating point
3256 division by zero is not warned about, as it can be a legitimate way of
3257 obtaining infinities and NaNs.
3259 @item -Wsystem-headers
3260 @opindex Wsystem-headers
3261 @cindex warnings from system headers
3262 @cindex system headers, warnings from
3263 Print warning messages for constructs found in system header files.
3264 Warnings from system headers are normally suppressed, on the assumption
3265 that they usually do not indicate real problems and would only make the
3266 compiler output harder to read. Using this command line option tells
3267 GCC to emit warnings from system headers as if they occurred in user
3268 code. However, note that using @option{-Wall} in conjunction with this
3269 option will @emph{not} warn about unknown pragmas in system
3270 headers---for that, @option{-Wunknown-pragmas} must also be used.
3273 @opindex Wfloat-equal
3274 Warn if floating point values are used in equality comparisons.
3276 The idea behind this is that sometimes it is convenient (for the
3277 programmer) to consider floating-point values as approximations to
3278 infinitely precise real numbers. If you are doing this, then you need
3279 to compute (by analyzing the code, or in some other way) the maximum or
3280 likely maximum error that the computation introduces, and allow for it
3281 when performing comparisons (and when producing output, but that's a
3282 different problem). In particular, instead of testing for equality, you
3283 would check to see whether the two values have ranges that overlap; and
3284 this is done with the relational operators, so equality comparisons are
3287 @item -Wtraditional @r{(C only)}
3288 @opindex Wtraditional
3289 Warn about certain constructs that behave differently in traditional and
3290 ISO C@. Also warn about ISO C constructs that have no traditional C
3291 equivalent, and/or problematic constructs which should be avoided.
3295 Macro parameters that appear within string literals in the macro body.
3296 In traditional C macro replacement takes place within string literals,
3297 but does not in ISO C@.
3300 In traditional C, some preprocessor directives did not exist.
3301 Traditional preprocessors would only consider a line to be a directive
3302 if the @samp{#} appeared in column 1 on the line. Therefore
3303 @option{-Wtraditional} warns about directives that traditional C
3304 understands but would ignore because the @samp{#} does not appear as the
3305 first character on the line. It also suggests you hide directives like
3306 @samp{#pragma} not understood by traditional C by indenting them. Some
3307 traditional implementations would not recognize @samp{#elif}, so it
3308 suggests avoiding it altogether.
3311 A function-like macro that appears without arguments.
3314 The unary plus operator.
3317 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
3318 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
3319 constants.) Note, these suffixes appear in macros defined in the system
3320 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
3321 Use of these macros in user code might normally lead to spurious
3322 warnings, however GCC's integrated preprocessor has enough context to
3323 avoid warning in these cases.
3326 A function declared external in one block and then used after the end of
3330 A @code{switch} statement has an operand of type @code{long}.
3333 A non-@code{static} function declaration follows a @code{static} one.
3334 This construct is not accepted by some traditional C compilers.
3337 The ISO type of an integer constant has a different width or
3338 signedness from its traditional type. This warning is only issued if
3339 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
3340 typically represent bit patterns, are not warned about.
3343 Usage of ISO string concatenation is detected.
3346 Initialization of automatic aggregates.
3349 Identifier conflicts with labels. Traditional C lacks a separate
3350 namespace for labels.
3353 Initialization of unions. If the initializer is zero, the warning is
3354 omitted. This is done under the assumption that the zero initializer in
3355 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
3356 initializer warnings and relies on default initialization to zero in the
3360 Conversions by prototypes between fixed/floating point values and vice
3361 versa. The absence of these prototypes when compiling with traditional
3362 C would cause serious problems. This is a subset of the possible
3363 conversion warnings, for the full set use @option{-Wtraditional-conversion}.
3366 Use of ISO C style function definitions. This warning intentionally is
3367 @emph{not} issued for prototype declarations or variadic functions
3368 because these ISO C features will appear in your code when using
3369 libiberty's traditional C compatibility macros, @code{PARAMS} and
3370 @code{VPARAMS}. This warning is also bypassed for nested functions
3371 because that feature is already a GCC extension and thus not relevant to
3372 traditional C compatibility.
3375 @item -Wtraditional-conversion @r{(C only)}
3376 @opindex Wtraditional-conversion
3377 Warn if a prototype causes a type conversion that is different from what
3378 would happen to the same argument in the absence of a prototype. This
3379 includes conversions of fixed point to floating and vice versa, and
3380 conversions changing the width or signedness of a fixed point argument
3381 except when the same as the default promotion.
3383 @item -Wdeclaration-after-statement @r{(C only)}
3384 @opindex Wdeclaration-after-statement
3385 Warn when a declaration is found after a statement in a block. This
3386 construct, known from C++, was introduced with ISO C99 and is by default
3387 allowed in GCC@. It is not supported by ISO C90 and was not supported by
3388 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
3392 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
3394 @item -Wno-endif-labels
3395 @opindex Wno-endif-labels
3396 @opindex Wendif-labels
3397 Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
3401 Warn whenever a local variable shadows another local variable, parameter or
3402 global variable or whenever a built-in function is shadowed.
3404 @item -Wlarger-than-@var{len}
3405 @opindex Wlarger-than
3406 Warn whenever an object of larger than @var{len} bytes is defined.
3408 @item -Wunsafe-loop-optimizations
3409 @opindex Wunsafe-loop-optimizations
3410 Warn if the loop cannot be optimized because the compiler could not
3411 assume anything on the bounds of the loop indices. With
3412 @option{-funsafe-loop-optimizations} warn if the compiler made
3415 @item -Wpointer-arith
3416 @opindex Wpointer-arith
3417 Warn about anything that depends on the ``size of'' a function type or
3418 of @code{void}. GNU C assigns these types a size of 1, for
3419 convenience in calculations with @code{void *} pointers and pointers
3420 to functions. In C++, warn also when an arithmetic operation involves
3421 @code{NULL}. This warning is also enabled by @option{-pedantic}.
3424 @opindex Wtype-limits
3425 @opindex Wno-type-limits
3426 Warn if a comparison is always true or always false due to the limited
3427 range of the data type, but do not warn for constant expressions. For
3428 example, warn if an unsigned variable is compared against zero with
3429 @samp{<} or @samp{>=}. This warning is also enabled by
3432 @item -Wbad-function-cast @r{(C only)}
3433 @opindex Wbad-function-cast
3434 Warn whenever a function call is cast to a non-matching type.
3435 For example, warn if @code{int malloc()} is cast to @code{anything *}.
3438 Warn about ISO C constructs that are outside of the common subset of
3439 ISO C and ISO C++, e.g.@: request for implicit conversion from
3440 @code{void *} to a pointer to non-@code{void} type.
3442 @item -Wc++0x-compat @r{(C++ and Objective-C++ only)}
3443 Warn about C++ constructs whose meaning differs between ISO C++ 1998 and
3444 ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will become keywords
3445 in ISO C++ 200x. This warning is enabled by @option{-Wall}.
3449 Warn whenever a pointer is cast so as to remove a type qualifier from
3450 the target type. For example, warn if a @code{const char *} is cast
3451 to an ordinary @code{char *}.
3454 @opindex Wcast-align
3455 Warn whenever a pointer is cast such that the required alignment of the
3456 target is increased. For example, warn if a @code{char *} is cast to
3457 an @code{int *} on machines where integers can only be accessed at
3458 two- or four-byte boundaries.
3460 @item -Wwrite-strings
3461 @opindex Wwrite-strings
3462 When compiling C, give string constants the type @code{const
3463 char[@var{length}]} so that
3464 copying the address of one into a non-@code{const} @code{char *}
3465 pointer will get a warning; when compiling C++, warn about the
3466 deprecated conversion from string literals to @code{char *}. This
3467 warning, by default, is enabled for C++ programs.
3468 These warnings will help you find at
3469 compile time code that can try to write into a string constant, but
3470 only if you have been very careful about using @code{const} in
3471 declarations and prototypes. Otherwise, it will just be a nuisance;
3472 this is why we did not make @option{-Wall} request these warnings.
3476 Warn for variables that might be changed by @samp{longjmp} or
3477 @samp{vfork}. This warning is also enabled by @option{-Wextra}.
3480 @opindex Wconversion
3481 @opindex Wno-conversion
3482 Warn for implicit conversions that may alter a value. This includes
3483 conversions between real and integer, like @code{abs (x)} when
3484 @code{x} is @code{double}; conversions between signed and unsigned,
3485 like @code{unsigned ui = -1}; and conversions to smaller types, like
3486 @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
3487 ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
3488 changed by the conversion like in @code{abs (2.0)}. Warnings about
3489 conversions between signed and unsigned integers can be disabled by
3490 using @option{-Wno-sign-conversion}.
3492 For C++, also warn for conversions between @code{NULL} and non-pointer
3493 types; confusing overload resolution for user-defined conversions; and
3494 conversions that will never use a type conversion operator:
3495 conversions to @code{void}, the same type, a base class or a reference
3496 to them. Warnings about conversions between signed and unsigned
3497 integers are disabled by default in C++ unless
3498 @option{-Wsign-conversion} is explicitly enabled.
3501 @opindex Wempty-body
3502 Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do
3503 while} statement. Additionally, in C++, warn when an empty body occurs
3504 in a @samp{while} or @samp{for} statement with no whitespacing before
3505 the semicolon. This warning is also enabled by @option{-Wextra}.
3507 @item -Wsign-compare
3508 @opindex Wsign-compare
3509 @cindex warning for comparison of signed and unsigned values
3510 @cindex comparison of signed and unsigned values, warning
3511 @cindex signed and unsigned values, comparison warning
3512 Warn when a comparison between signed and unsigned values could produce
3513 an incorrect result when the signed value is converted to unsigned.
3514 This warning is also enabled by @option{-Wextra}; to get the other warnings
3515 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
3517 @item -Wsign-conversion
3518 @opindex Wsign-conversion
3519 @opindex Wno-sign-conversion
3520 Warn for implicit conversions that may change the sign of an integer
3521 value, like assigning a signed integer expression to an unsigned
3522 integer variable. An explicit cast silences the warning. In C, this
3523 option is enabled also by @option{-Wconversion}.
3527 @opindex Wno-address
3528 Warn about suspicious uses of memory addresses. These include using
3529 the address of a function in a conditional expression, such as
3530 @code{void func(void); if (func)}, and comparisons against the memory
3531 address of a string literal, such as @code{if (x == "abc")}. Such
3532 uses typically indicate a programmer error: the address of a function
3533 always evaluates to true, so their use in a conditional usually
3534 indicate that the programmer forgot the parentheses in a function
3535 call; and comparisons against string literals result in unspecified
3536 behavior and are not portable in C, so they usually indicate that the
3537 programmer intended to use @code{strcmp}. This warning is enabled by
3541 @opindex Wlogical-op
3542 @opindex Wno-logical-op
3543 Warn about suspicious uses of logical operators in expressions.
3544 This includes using logical operators in contexts where a
3545 bit-wise operator is likely to be expected.
3547 @item -Waggregate-return
3548 @opindex Waggregate-return
3549 Warn if any functions that return structures or unions are defined or
3550 called. (In languages where you can return an array, this also elicits
3553 @item -Wno-attributes
3554 @opindex Wno-attributes
3555 @opindex Wattributes
3556 Do not warn if an unexpected @code{__attribute__} is used, such as
3557 unrecognized attributes, function attributes applied to variables,
3558 etc. This will not stop errors for incorrect use of supported
3561 @item -Wstrict-prototypes @r{(C only)}
3562 @opindex Wstrict-prototypes
3563 Warn if a function is declared or defined without specifying the
3564 argument types. (An old-style function definition is permitted without
3565 a warning if preceded by a declaration which specifies the argument
3568 @item -Wold-style-declaration @r{(C only)}
3569 @opindex Wold-style-declaration
3570 Warn for obsolescent usages, according to the C Standard, in a
3571 declaration. For example, warn if storage-class specifiers like
3572 @code{static} are not the first things in a declaration. This warning
3573 is also enabled by @option{-Wextra}.
3575 @item -Wold-style-definition @r{(C only)}
3576 @opindex Wold-style-definition
3577 Warn if an old-style function definition is used. A warning is given
3578 even if there is a previous prototype.
3580 @item -Wmissing-parameter-type @r{(C only)}
3581 @opindex Wmissing-parameter-type
3582 A function parameter is declared without a type specifier in K&R-style
3589 This warning is also enabled by @option{-Wextra}.
3591 @item -Wmissing-prototypes @r{(C only)}
3592 @opindex Wmissing-prototypes
3593 Warn if a global function is defined without a previous prototype
3594 declaration. This warning is issued even if the definition itself
3595 provides a prototype. The aim is to detect global functions that fail
3596 to be declared in header files.
3598 @item -Wmissing-declarations @r{(C and C++ only)}
3599 @opindex Wmissing-declarations
3600 Warn if a global function is defined without a previous declaration.
3601 Do so even if the definition itself provides a prototype.
3602 Use this option to detect global functions that are not declared in
3603 header files. In C++, no warnings are issued for function templates,
3604 or for inline functions, or for functions in anonymous namespaces.
3606 @item -Wmissing-field-initializers
3607 @opindex Wmissing-field-initializers
3610 Warn if a structure's initializer has some fields missing. For
3611 example, the following code would cause such a warning, because
3612 @code{x.h} is implicitly zero:
3615 struct s @{ int f, g, h; @};
3616 struct s x = @{ 3, 4 @};
3619 This option does not warn about designated initializers, so the following
3620 modification would not trigger a warning:
3623 struct s @{ int f, g, h; @};
3624 struct s x = @{ .f = 3, .g = 4 @};
3627 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
3628 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
3630 @item -Wmissing-noreturn
3631 @opindex Wmissing-noreturn
3632 Warn about functions which might be candidates for attribute @code{noreturn}.
3633 Note these are only possible candidates, not absolute ones. Care should
3634 be taken to manually verify functions actually do not ever return before
3635 adding the @code{noreturn} attribute, otherwise subtle code generation
3636 bugs could be introduced. You will not get a warning for @code{main} in
3637 hosted C environments.
3639 @item -Wmissing-format-attribute
3640 @opindex Wmissing-format-attribute
3642 Warn about function pointers which might be candidates for @code{format}
3643 attributes. Note these are only possible candidates, not absolute ones.
3644 GCC will guess that function pointers with @code{format} attributes that
3645 are used in assignment, initialization, parameter passing or return
3646 statements should have a corresponding @code{format} attribute in the
3647 resulting type. I.e.@: the left-hand side of the assignment or
3648 initialization, the type of the parameter variable, or the return type
3649 of the containing function respectively should also have a @code{format}
3650 attribute to avoid the warning.
3652 GCC will also warn about function definitions which might be
3653 candidates for @code{format} attributes. Again, these are only
3654 possible candidates. GCC will guess that @code{format} attributes
3655 might be appropriate for any function that calls a function like
3656 @code{vprintf} or @code{vscanf}, but this might not always be the
3657 case, and some functions for which @code{format} attributes are
3658 appropriate may not be detected.
3660 @item -Wno-multichar
3661 @opindex Wno-multichar
3663 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3664 Usually they indicate a typo in the user's code, as they have
3665 implementation-defined values, and should not be used in portable code.
3667 @item -Wnormalized=<none|id|nfc|nfkc>
3668 @opindex Wnormalized
3671 @cindex character set, input normalization
3672 In ISO C and ISO C++, two identifiers are different if they are
3673 different sequences of characters. However, sometimes when characters
3674 outside the basic ASCII character set are used, you can have two
3675 different character sequences that look the same. To avoid confusion,
3676 the ISO 10646 standard sets out some @dfn{normalization rules} which
3677 when applied ensure that two sequences that look the same are turned into
3678 the same sequence. GCC can warn you if you are using identifiers which
3679 have not been normalized; this option controls that warning.
3681 There are four levels of warning that GCC supports. The default is
3682 @option{-Wnormalized=nfc}, which warns about any identifier which is
3683 not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
3684 recommended form for most uses.
3686 Unfortunately, there are some characters which ISO C and ISO C++ allow
3687 in identifiers that when turned into NFC aren't allowable as
3688 identifiers. That is, there's no way to use these symbols in portable
3689 ISO C or C++ and have all your identifiers in NFC.
3690 @option{-Wnormalized=id} suppresses the warning for these characters.
3691 It is hoped that future versions of the standards involved will correct
3692 this, which is why this option is not the default.
3694 You can switch the warning off for all characters by writing
3695 @option{-Wnormalized=none}. You would only want to do this if you
3696 were using some other normalization scheme (like ``D''), because
3697 otherwise you can easily create bugs that are literally impossible to see.
3699 Some characters in ISO 10646 have distinct meanings but look identical
3700 in some fonts or display methodologies, especially once formatting has
3701 been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
3702 LETTER N'', will display just like a regular @code{n} which has been
3703 placed in a superscript. ISO 10646 defines the @dfn{NFKC}
3704 normalization scheme to convert all these into a standard form as
3705 well, and GCC will warn if your code is not in NFKC if you use
3706 @option{-Wnormalized=nfkc}. This warning is comparable to warning
3707 about every identifier that contains the letter O because it might be
3708 confused with the digit 0, and so is not the default, but may be
3709 useful as a local coding convention if the programming environment is
3710 unable to be fixed to display these characters distinctly.
3712 @item -Wno-deprecated-declarations
3713 @opindex Wno-deprecated-declarations
3714 Do not warn about uses of functions (@pxref{Function Attributes}),
3715 variables (@pxref{Variable Attributes}), and types (@pxref{Type
3716 Attributes}) marked as deprecated by using the @code{deprecated}
3720 @opindex Wno-overflow
3721 Do not warn about compile-time overflow in constant expressions.
3723 @item -Woverride-init
3724 @opindex Woverride-init
3727 Warn if an initialized field without side effects is overridden when
3728 using designated initializers (@pxref{Designated Inits, , Designated
3731 This warning is included in @option{-Wextra}. To get other
3732 @option{-Wextra} warnings without this one, use @samp{-Wextra
3733 -Wno-override-init}.
3737 Warn if a structure is given the packed attribute, but the packed
3738 attribute has no effect on the layout or size of the structure.
3739 Such structures may be mis-aligned for little benefit. For
3740 instance, in this code, the variable @code{f.x} in @code{struct bar}
3741 will be misaligned even though @code{struct bar} does not itself
3742 have the packed attribute:
3749 @} __attribute__((packed));
3759 Warn if padding is included in a structure, either to align an element
3760 of the structure or to align the whole structure. Sometimes when this
3761 happens it is possible to rearrange the fields of the structure to
3762 reduce the padding and so make the structure smaller.
3764 @item -Wredundant-decls
3765 @opindex Wredundant-decls
3766 Warn if anything is declared more than once in the same scope, even in
3767 cases where multiple declaration is valid and changes nothing.
3769 @item -Wnested-externs @r{(C only)}
3770 @opindex Wnested-externs
3771 Warn if an @code{extern} declaration is encountered within a function.
3773 @item -Wunreachable-code
3774 @opindex Wunreachable-code
3775 Warn if the compiler detects that code will never be executed.
3777 This option is intended to warn when the compiler detects that at
3778 least a whole line of source code will never be executed, because
3779 some condition is never satisfied or because it is after a
3780 procedure that never returns.
3782 It is possible for this option to produce a warning even though there
3783 are circumstances under which part of the affected line can be executed,
3784 so care should be taken when removing apparently-unreachable code.
3786 For instance, when a function is inlined, a warning may mean that the
3787 line is unreachable in only one inlined copy of the function.
3789 This option is not made part of @option{-Wall} because in a debugging
3790 version of a program there is often substantial code which checks
3791 correct functioning of the program and is, hopefully, unreachable
3792 because the program does work. Another common use of unreachable
3793 code is to provide behavior which is selectable at compile-time.
3797 Warn if a function can not be inlined and it was declared as inline.
3798 Even with this option, the compiler will not warn about failures to
3799 inline functions declared in system headers.
3801 The compiler uses a variety of heuristics to determine whether or not
3802 to inline a function. For example, the compiler takes into account
3803 the size of the function being inlined and the amount of inlining
3804 that has already been done in the current function. Therefore,
3805 seemingly insignificant changes in the source program can cause the
3806 warnings produced by @option{-Winline} to appear or disappear.
3808 @item -Wno-invalid-offsetof @r{(C++ only)}
3809 @opindex Wno-invalid-offsetof
3810 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3811 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3812 to a non-POD type is undefined. In existing C++ implementations,
3813 however, @samp{offsetof} typically gives meaningful results even when
3814 applied to certain kinds of non-POD types. (Such as a simple
3815 @samp{struct} that fails to be a POD type only by virtue of having a
3816 constructor.) This flag is for users who are aware that they are
3817 writing nonportable code and who have deliberately chosen to ignore the
3820 The restrictions on @samp{offsetof} may be relaxed in a future version
3821 of the C++ standard.
3823 @item -Wno-int-to-pointer-cast @r{(C only)}
3824 @opindex Wno-int-to-pointer-cast
3825 Suppress warnings from casts to pointer type of an integer of a
3828 @item -Wno-pointer-to-int-cast @r{(C only)}
3829 @opindex Wno-pointer-to-int-cast
3830 Suppress warnings from casts from a pointer to an integer type of a
3834 @opindex Winvalid-pch
3835 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3836 the search path but can't be used.
3840 @opindex Wno-long-long
3841 Warn if @samp{long long} type is used. This is default. To inhibit
3842 the warning messages, use @option{-Wno-long-long}. Flags
3843 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3844 only when @option{-pedantic} flag is used.
3846 @item -Wvariadic-macros
3847 @opindex Wvariadic-macros
3848 @opindex Wno-variadic-macros
3849 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3850 alternate syntax when in pedantic ISO C99 mode. This is default.
3851 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3856 Warn if variable length array is used in the code.
3857 @option{-Wno-vla} will prevent the @option{-pedantic} warning of
3858 the variable length array.
3860 @item -Wvolatile-register-var
3861 @opindex Wvolatile-register-var
3862 @opindex Wno-volatile-register-var
3863 Warn if a register variable is declared volatile. The volatile
3864 modifier does not inhibit all optimizations that may eliminate reads
3865 and/or writes to register variables.
3867 @item -Wdisabled-optimization
3868 @opindex Wdisabled-optimization
3869 Warn if a requested optimization pass is disabled. This warning does
3870 not generally indicate that there is anything wrong with your code; it
3871 merely indicates that GCC's optimizers were unable to handle the code
3872 effectively. Often, the problem is that your code is too big or too
3873 complex; GCC will refuse to optimize programs when the optimization
3874 itself is likely to take inordinate amounts of time.
3876 @item -Wpointer-sign
3877 @opindex Wpointer-sign
3878 @opindex Wno-pointer-sign
3879 Warn for pointer argument passing or assignment with different signedness.
3880 This option is only supported for C and Objective-C@. It is implied by
3881 @option{-Wall} and by @option{-pedantic}, which can be disabled with
3882 @option{-Wno-pointer-sign}.
3886 Make all warnings into errors.
3890 Make the specified warning into an errors. The specifier for a
3891 warning is appended, for example @option{-Werror=switch} turns the
3892 warnings controlled by @option{-Wswitch} into errors. This switch
3893 takes a negative form, to be used to negate @option{-Werror} for
3894 specific warnings, for example @option{-Wno-error=switch} makes
3895 @option{-Wswitch} warnings not be errors, even when @option{-Werror}
3896 is in effect. You can use the @option{-fdiagnostics-show-option}
3897 option to have each controllable warning amended with the option which
3898 controls it, to determine what to use with this option.
3900 Note that specifying @option{-Werror=}@var{foo} automatically implies
3901 @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
3904 @item -Wstack-protector
3905 @opindex Wstack-protector
3906 This option is only active when @option{-fstack-protector} is active. It
3907 warns about functions that will not be protected against stack smashing.
3909 @item -Woverlength-strings
3910 @opindex Woverlength-strings
3911 Warn about string constants which are longer than the ``minimum
3912 maximum'' length specified in the C standard. Modern compilers
3913 generally allow string constants which are much longer than the
3914 standard's minimum limit, but very portable programs should avoid
3915 using longer strings.
3917 The limit applies @emph{after} string constant concatenation, and does
3918 not count the trailing NUL@. In C89, the limit was 509 characters; in
3919 C99, it was raised to 4095. C++98 does not specify a normative
3920 minimum maximum, so we do not diagnose overlength strings in C++@.
3922 This option is implied by @option{-pedantic}, and can be disabled with
3923 @option{-Wno-overlength-strings}.
3926 @node Debugging Options
3927 @section Options for Debugging Your Program or GCC
3928 @cindex options, debugging
3929 @cindex debugging information options
3931 GCC has various special options that are used for debugging
3932 either your program or GCC:
3937 Produce debugging information in the operating system's native format
3938 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3941 On most systems that use stabs format, @option{-g} enables use of extra
3942 debugging information that only GDB can use; this extra information
3943 makes debugging work better in GDB but will probably make other debuggers
3945 refuse to read the program. If you want to control for certain whether
3946 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3947 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3949 GCC allows you to use @option{-g} with
3950 @option{-O}. The shortcuts taken by optimized code may occasionally
3951 produce surprising results: some variables you declared may not exist
3952 at all; flow of control may briefly move where you did not expect it;
3953 some statements may not be executed because they compute constant
3954 results or their values were already at hand; some statements may
3955 execute in different places because they were moved out of loops.
3957 Nevertheless it proves possible to debug optimized output. This makes
3958 it reasonable to use the optimizer for programs that might have bugs.
3960 The following options are useful when GCC is generated with the
3961 capability for more than one debugging format.
3965 Produce debugging information for use by GDB@. This means to use the
3966 most expressive format available (DWARF 2, stabs, or the native format
3967 if neither of those are supported), including GDB extensions if at all
3972 Produce debugging information in stabs format (if that is supported),
3973 without GDB extensions. This is the format used by DBX on most BSD
3974 systems. On MIPS, Alpha and System V Release 4 systems this option
3975 produces stabs debugging output which is not understood by DBX or SDB@.
3976 On System V Release 4 systems this option requires the GNU assembler.
3978 @item -feliminate-unused-debug-symbols
3979 @opindex feliminate-unused-debug-symbols
3980 Produce debugging information in stabs format (if that is supported),
3981 for only symbols that are actually used.
3983 @item -femit-class-debug-always
3984 Instead of emitting debugging information for a C++ class in only one
3985 object file, emit it in all object files using the class. This option
3986 should be used only with debuggers that are unable to handle the way GCC
3987 normally emits debugging information for classes because using this
3988 option will increase the size of debugging information by as much as a
3993 Produce debugging information in stabs format (if that is supported),
3994 using GNU extensions understood only by the GNU debugger (GDB)@. The
3995 use of these extensions is likely to make other debuggers crash or
3996 refuse to read the program.
4000 Produce debugging information in COFF format (if that is supported).
4001 This is the format used by SDB on most System V systems prior to
4006 Produce debugging information in XCOFF format (if that is supported).
4007 This is the format used by the DBX debugger on IBM RS/6000 systems.
4011 Produce debugging information in XCOFF format (if that is supported),
4012 using GNU extensions understood only by the GNU debugger (GDB)@. The
4013 use of these extensions is likely to make other debuggers crash or
4014 refuse to read the program, and may cause assemblers other than the GNU
4015 assembler (GAS) to fail with an error.
4019 Produce debugging information in DWARF version 2 format (if that is
4020 supported). This is the format used by DBX on IRIX 6. With this
4021 option, GCC uses features of DWARF version 3 when they are useful;
4022 version 3 is upward compatible with version 2, but may still cause
4023 problems for older debuggers.
4027 Produce debugging information in VMS debug format (if that is
4028 supported). This is the format used by DEBUG on VMS systems.
4031 @itemx -ggdb@var{level}
4032 @itemx -gstabs@var{level}
4033 @itemx -gcoff@var{level}
4034 @itemx -gxcoff@var{level}
4035 @itemx -gvms@var{level}
4036 Request debugging information and also use @var{level} to specify how
4037 much information. The default level is 2.
4039 Level 0 produces no debug information at all. Thus, @option{-g0} negates
4042 Level 1 produces minimal information, enough for making backtraces in
4043 parts of the program that you don't plan to debug. This includes
4044 descriptions of functions and external variables, but no information
4045 about local variables and no line numbers.
4047 Level 3 includes extra information, such as all the macro definitions
4048 present in the program. Some debuggers support macro expansion when
4049 you use @option{-g3}.
4051 @option{-gdwarf-2} does not accept a concatenated debug level, because
4052 GCC used to support an option @option{-gdwarf} that meant to generate
4053 debug information in version 1 of the DWARF format (which is very
4054 different from version 2), and it would have been too confusing. That
4055 debug format is long obsolete, but the option cannot be changed now.
4056 Instead use an additional @option{-g@var{level}} option to change the
4057 debug level for DWARF2.
4059 @item -feliminate-dwarf2-dups
4060 @opindex feliminate-dwarf2-dups
4061 Compress DWARF2 debugging information by eliminating duplicated
4062 information about each symbol. This option only makes sense when
4063 generating DWARF2 debugging information with @option{-gdwarf-2}.
4065 @item -femit-struct-debug-baseonly
4066 Emit debug information for struct-like types
4067 only when the base name of the compilation source file
4068 matches the base name of file in which the struct was defined.
4070 This option substantially reduces the size of debugging information,
4071 but at significant potential loss in type information to the debugger.
4072 See @option{-femit-struct-debug-reduced} for a less aggressive option.
4073 See @option{-femit-struct-debug-detailed} for more detailed control.
4075 This option works only with DWARF 2.
4077 @item -femit-struct-debug-reduced
4078 Emit debug information for struct-like types
4079 only when the base name of the compilation source file
4080 matches the base name of file in which the type was defined,
4081 unless the struct is a template or defined in a system header.
4083 This option significantly reduces the size of debugging information,
4084 with some potential loss in type information to the debugger.
4085 See @option{-femit-struct-debug-baseonly} for a more aggressive option.
4086 See @option{-femit-struct-debug-detailed} for more detailed control.
4088 This option works only with DWARF 2.
4090 @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
4091 Specify the struct-like types
4092 for which the compiler will generate debug information.
4093 The intent is to reduce duplicate struct debug information
4094 between different object files within the same program.
4096 This option is a detailed version of
4097 @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
4098 which will serve for most needs.
4100 A specification has the syntax
4101 [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
4103 The optional first word limits the specification to
4104 structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
4105 A struct type is used directly when it is the type of a variable, member.
4106 Indirect uses arise through pointers to structs.
4107 That is, when use of an incomplete struct would be legal, the use is indirect.
4109 @samp{struct one direct; struct two * indirect;}.
4111 The optional second word limits the specification to
4112 ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
4113 Generic structs are a bit complicated to explain.
4114 For C++, these are non-explicit specializations of template classes,
4115 or non-template classes within the above.
4116 Other programming languages have generics,
4117 but @samp{-femit-struct-debug-detailed} does not yet implement them.
4119 The third word specifies the source files for those
4120 structs for which the compiler will emit debug information.
4121 The values @samp{none} and @samp{any} have the normal meaning.
4122 The value @samp{base} means that
4123 the base of name of the file in which the type declaration appears
4124 must match the base of the name of the main compilation file.
4125 In practice, this means that
4126 types declared in @file{foo.c} and @file{foo.h} will have debug information,
4127 but types declared in other header will not.
4128 The value @samp{sys} means those types satisfying @samp{base}
4129 or declared in system or compiler headers.
4131 You may need to experiment to determine the best settings for your application.
4133 The default is @samp{-femit-struct-debug-detailed=all}.
4135 This option works only with DWARF 2.
4137 @cindex @command{prof}
4140 Generate extra code to write profile information suitable for the
4141 analysis program @command{prof}. You must use this option when compiling
4142 the source files you want data about, and you must also use it when
4145 @cindex @command{gprof}
4148 Generate extra code to write profile information suitable for the
4149 analysis program @command{gprof}. You must use this option when compiling
4150 the source files you want data about, and you must also use it when
4155 Makes the compiler print out each function name as it is compiled, and
4156 print some statistics about each pass when it finishes.
4159 @opindex ftime-report
4160 Makes the compiler print some statistics about the time consumed by each
4161 pass when it finishes.
4164 @opindex fmem-report
4165 Makes the compiler print some statistics about permanent memory
4166 allocation when it finishes.
4168 @item -fpre-ipa-mem-report
4169 @opindex fpre-ipa-mem-report
4170 @item -fpost-ipa-mem-report
4171 @opindex fpost-ipa-mem-report
4172 Makes the compiler print some statistics about permanent memory
4173 allocation before or after interprocedural optimization.
4175 @item -fprofile-arcs
4176 @opindex fprofile-arcs
4177 Add code so that program flow @dfn{arcs} are instrumented. During
4178 execution the program records how many times each branch and call is
4179 executed and how many times it is taken or returns. When the compiled
4180 program exits it saves this data to a file called
4181 @file{@var{auxname}.gcda} for each source file. The data may be used for
4182 profile-directed optimizations (@option{-fbranch-probabilities}), or for
4183 test coverage analysis (@option{-ftest-coverage}). Each object file's
4184 @var{auxname} is generated from the name of the output file, if
4185 explicitly specified and it is not the final executable, otherwise it is
4186 the basename of the source file. In both cases any suffix is removed
4187 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
4188 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
4189 @xref{Cross-profiling}.
4191 @cindex @command{gcov}
4195 This option is used to compile and link code instrumented for coverage
4196 analysis. The option is a synonym for @option{-fprofile-arcs}
4197 @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
4198 linking). See the documentation for those options for more details.
4203 Compile the source files with @option{-fprofile-arcs} plus optimization
4204 and code generation options. For test coverage analysis, use the
4205 additional @option{-ftest-coverage} option. You do not need to profile
4206 every source file in a program.
4209 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
4210 (the latter implies the former).
4213 Run the program on a representative workload to generate the arc profile
4214 information. This may be repeated any number of times. You can run
4215 concurrent instances of your program, and provided that the file system
4216 supports locking, the data files will be correctly updated. Also
4217 @code{fork} calls are detected and correctly handled (double counting
4221 For profile-directed optimizations, compile the source files again with
4222 the same optimization and code generation options plus
4223 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
4224 Control Optimization}).
4227 For test coverage analysis, use @command{gcov} to produce human readable
4228 information from the @file{.gcno} and @file{.gcda} files. Refer to the
4229 @command{gcov} documentation for further information.
4233 With @option{-fprofile-arcs}, for each function of your program GCC
4234 creates a program flow graph, then finds a spanning tree for the graph.
4235 Only arcs that are not on the spanning tree have to be instrumented: the
4236 compiler adds code to count the number of times that these arcs are
4237 executed. When an arc is the only exit or only entrance to a block, the
4238 instrumentation code can be added to the block; otherwise, a new basic
4239 block must be created to hold the instrumentation code.
4242 @item -ftest-coverage
4243 @opindex ftest-coverage
4244 Produce a notes file that the @command{gcov} code-coverage utility
4245 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
4246 show program coverage. Each source file's note file is called
4247 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
4248 above for a description of @var{auxname} and instructions on how to
4249 generate test coverage data. Coverage data will match the source files
4250 more closely, if you do not optimize.
4252 @item -fdbg-cnt-list
4253 @opindex fdbg-cnt-list
4254 Print the name and the counter upperbound for all debug counters.
4256 @item -fdbg-cnt=@var{counter-value-list}
4258 Set the internal debug counter upperbound. @var{counter-value-list}
4259 is a comma-separated list of @var{name}:@var{value} pairs
4260 which sets the upperbound of each debug counter @var{name} to @var{value}.
4261 All debug counters have the initial upperbound of @var{UINT_MAX},
4262 thus dbg_cnt() returns true always unless the upperbound is set by this option.
4263 e.g. With -fdbg-cnt=dce:10,tail_call:0
4264 dbg_cnt(dce) will return true only for first 10 invocations
4265 and dbg_cnt(tail_call) will return false always.
4267 @item -d@var{letters}
4268 @item -fdump-rtl-@var{pass}
4270 Says to make debugging dumps during compilation at times specified by
4271 @var{letters}. This is used for debugging the RTL-based passes of the
4272 compiler. The file names for most of the dumps are made by appending a
4273 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
4274 from the name of the output file, if explicitly specified and it is not
4275 an executable, otherwise it is the basename of the source file. These
4276 switches may have different effects when @option{-E} is used for
4279 Most debug dumps can be enabled either passing a letter to the @option{-d}
4280 option, or with a long @option{-fdump-rtl} switch; here are the possible
4281 letters for use in @var{letters} and @var{pass}, and their meanings:
4286 Annotate the assembler output with miscellaneous debugging information.
4289 @itemx -fdump-rtl-bbro
4291 @opindex fdump-rtl-bbro
4292 Dump after block reordering, to @file{@var{file}.148r.bbro}.
4295 @itemx -fdump-rtl-combine
4297 @opindex fdump-rtl-combine
4298 Dump after the RTL instruction combination pass, to the file
4299 @file{@var{file}.129r.combine}.
4302 @itemx -fdump-rtl-ce1
4303 @itemx -fdump-rtl-ce2
4305 @opindex fdump-rtl-ce1
4306 @opindex fdump-rtl-ce2
4307 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
4308 first if conversion, to the file @file{@var{file}.117r.ce1}. @option{-dC}
4309 and @option{-fdump-rtl-ce2} enable dumping after the second if
4310 conversion, to the file @file{@var{file}.130r.ce2}.
4313 @itemx -fdump-rtl-btl
4314 @itemx -fdump-rtl-dbr
4316 @opindex fdump-rtl-btl
4317 @opindex fdump-rtl-dbr
4318 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
4319 target load optimization, to @file{@var{file}.31.btl}. @option{-dd}
4320 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
4321 scheduling, to @file{@var{file}.36.dbr}.
4325 Dump all macro definitions, at the end of preprocessing, in addition to
4329 @itemx -fdump-rtl-ce3
4331 @opindex fdump-rtl-ce3
4332 Dump after the third if conversion, to @file{@var{file}.146r.ce3}.
4335 @itemx -fdump-rtl-cfg
4336 @itemx -fdump-rtl-life
4338 @opindex fdump-rtl-cfg
4339 @opindex fdump-rtl-life
4340 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
4341 and data flow analysis, to @file{@var{file}.116r.cfg}. @option{-df}
4342 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
4343 to @file{@var{file}.128r.life1} and @file{@var{file}.135r.life2}.
4346 @itemx -fdump-rtl-greg
4348 @opindex fdump-rtl-greg
4349 Dump after global register allocation, to @file{@var{file}.139r.greg}.
4352 @itemx -fdump-rtl-gcse
4353 @itemx -fdump-rtl-bypass
4355 @opindex fdump-rtl-gcse
4356 @opindex fdump-rtl-bypass
4357 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
4358 @file{@var{file}.114r.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
4359 enable dumping after jump bypassing and control flow optimizations, to
4360 @file{@var{file}.115r.bypass}.
4363 @itemx -fdump-rtl-eh
4365 @opindex fdump-rtl-eh
4366 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
4369 @itemx -fdump-rtl-sibling
4371 @opindex fdump-rtl-sibling
4372 Dump after sibling call optimizations, to @file{@var{file}.106r.sibling}.
4375 @itemx -fdump-rtl-jump
4377 @opindex fdump-rtl-jump
4378 Dump after the first jump optimization, to @file{@var{file}.112r.jump}.
4381 @itemx -fdump-rtl-stack
4383 @opindex fdump-rtl-stack
4384 Dump after conversion from GCC's "flat register file" registers to the
4385 x87's stack-like registers, to @file{@var{file}.152r.stack}.
4388 @itemx -fdump-rtl-lreg
4390 @opindex fdump-rtl-lreg
4391 Dump after local register allocation, to @file{@var{file}.138r.lreg}.
4394 @itemx -fdump-rtl-loop2
4396 @opindex fdump-rtl-loop2
4397 @option{-dL} and @option{-fdump-rtl-loop2} enable dumping after the
4398 loop optimization pass, to @file{@var{file}.119r.loop2},
4399 @file{@var{file}.120r.loop2_init},
4400 @file{@var{file}.121r.loop2_invariant}, and
4401 @file{@var{file}.125r.loop2_done}.
4404 @itemx -fdump-rtl-sms
4406 @opindex fdump-rtl-sms
4407 Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
4410 @itemx -fdump-rtl-mach
4412 @opindex fdump-rtl-mach
4413 Dump after performing the machine dependent reorganization pass, to
4414 @file{@var{file}.155r.mach} if that pass exists.
4417 @itemx -fdump-rtl-rnreg
4419 @opindex fdump-rtl-rnreg
4420 Dump after register renumbering, to @file{@var{file}.147r.rnreg}.
4423 @itemx -fdump-rtl-regmove
4425 @opindex fdump-rtl-regmove
4426 Dump after the register move pass, to @file{@var{file}.132r.regmove}.
4429 @itemx -fdump-rtl-postreload
4431 @opindex fdump-rtl-postreload
4432 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
4435 @itemx -fdump-rtl-expand
4437 @opindex fdump-rtl-expand
4438 Dump after RTL generation, to @file{@var{file}.104r.expand}.
4441 @itemx -fdump-rtl-sched2
4443 @opindex fdump-rtl-sched2
4444 Dump after the second scheduling pass, to @file{@var{file}.149r.sched2}.
4447 @itemx -fdump-rtl-cse
4449 @opindex fdump-rtl-cse
4450 Dump after CSE (including the jump optimization that sometimes follows
4451 CSE), to @file{@var{file}.113r.cse}.
4454 @itemx -fdump-rtl-sched1
4456 @opindex fdump-rtl-sched1
4457 Dump after the first scheduling pass, to @file{@var{file}.136r.sched1}.
4460 @itemx -fdump-rtl-cse2
4462 @opindex fdump-rtl-cse2
4463 Dump after the second CSE pass (including the jump optimization that
4464 sometimes follows CSE), to @file{@var{file}.127r.cse2}.
4467 @itemx -fdump-rtl-tracer
4469 @opindex fdump-rtl-tracer
4470 Dump after running tracer, to @file{@var{file}.118r.tracer}.
4473 @itemx -fdump-rtl-vpt
4474 @itemx -fdump-rtl-vartrack
4476 @opindex fdump-rtl-vpt
4477 @opindex fdump-rtl-vartrack
4478 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
4479 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
4480 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
4481 to @file{@var{file}.154r.vartrack}.
4484 @itemx -fdump-rtl-flow2
4486 @opindex fdump-rtl-flow2
4487 Dump after the second flow pass, to @file{@var{file}.142r.flow2}.
4490 @itemx -fdump-rtl-peephole2
4492 @opindex fdump-rtl-peephole2
4493 Dump after the peephole pass, to @file{@var{file}.145r.peephole2}.
4496 @itemx -fdump-rtl-web
4498 @opindex fdump-rtl-web
4499 Dump after live range splitting, to @file{@var{file}.126r.web}.
4502 @itemx -fdump-rtl-all
4504 @opindex fdump-rtl-all
4505 Produce all the dumps listed above.
4509 Produce a core dump whenever an error occurs.
4513 Print statistics on memory usage, at the end of the run, to
4518 Annotate the assembler output with a comment indicating which
4519 pattern and alternative was used. The length of each instruction is
4524 Dump the RTL in the assembler output as a comment before each instruction.
4525 Also turns on @option{-dp} annotation.
4529 For each of the other indicated dump files (either with @option{-d} or
4530 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
4531 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
4535 Just generate RTL for a function instead of compiling it. Usually used
4536 with @samp{r} (@option{-fdump-rtl-expand}).
4540 Dump debugging information during parsing, to standard error.
4544 @opindex fdump-noaddr
4545 When doing debugging dumps (see @option{-d} option above), suppress
4546 address output. This makes it more feasible to use diff on debugging
4547 dumps for compiler invocations with different compiler binaries and/or
4548 different text / bss / data / heap / stack / dso start locations.
4550 @item -fdump-unnumbered
4551 @opindex fdump-unnumbered
4552 When doing debugging dumps (see @option{-d} option above), suppress instruction
4553 numbers and address output. This makes it more feasible to
4554 use diff on debugging dumps for compiler invocations with different
4555 options, in particular with and without @option{-g}.
4557 @item -fdump-translation-unit @r{(C++ only)}
4558 @itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
4559 @opindex fdump-translation-unit
4560 Dump a representation of the tree structure for the entire translation
4561 unit to a file. The file name is made by appending @file{.tu} to the
4562 source file name. If the @samp{-@var{options}} form is used, @var{options}
4563 controls the details of the dump as described for the
4564 @option{-fdump-tree} options.
4566 @item -fdump-class-hierarchy @r{(C++ only)}
4567 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
4568 @opindex fdump-class-hierarchy
4569 Dump a representation of each class's hierarchy and virtual function
4570 table layout to a file. The file name is made by appending @file{.class}
4571 to the source file name. If the @samp{-@var{options}} form is used,
4572 @var{options} controls the details of the dump as described for the
4573 @option{-fdump-tree} options.
4575 @item -fdump-ipa-@var{switch}
4577 Control the dumping at various stages of inter-procedural analysis
4578 language tree to a file. The file name is generated by appending a switch
4579 specific suffix to the source file name. The following dumps are possible:
4583 Enables all inter-procedural analysis dumps; currently the only produced
4584 dump is the @samp{cgraph} dump.
4587 Dumps information about call-graph optimization, unused function removal,
4588 and inlining decisions.
4591 @item -fdump-tree-@var{switch}
4592 @itemx -fdump-tree-@var{switch}-@var{options}
4594 Control the dumping at various stages of processing the intermediate
4595 language tree to a file. The file name is generated by appending a switch
4596 specific suffix to the source file name. If the @samp{-@var{options}}
4597 form is used, @var{options} is a list of @samp{-} separated options that
4598 control the details of the dump. Not all options are applicable to all
4599 dumps, those which are not meaningful will be ignored. The following
4600 options are available
4604 Print the address of each node. Usually this is not meaningful as it
4605 changes according to the environment and source file. Its primary use
4606 is for tying up a dump file with a debug environment.
4608 Inhibit dumping of members of a scope or body of a function merely
4609 because that scope has been reached. Only dump such items when they
4610 are directly reachable by some other path. When dumping pretty-printed
4611 trees, this option inhibits dumping the bodies of control structures.
4613 Print a raw representation of the tree. By default, trees are
4614 pretty-printed into a C-like representation.
4616 Enable more detailed dumps (not honored by every dump option).
4618 Enable dumping various statistics about the pass (not honored by every dump
4621 Enable showing basic block boundaries (disabled in raw dumps).
4623 Enable showing virtual operands for every statement.
4625 Enable showing line numbers for statements.
4627 Enable showing the unique ID (@code{DECL_UID}) for each variable.
4629 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
4632 The following tree dumps are possible:
4636 Dump before any tree based optimization, to @file{@var{file}.original}.
4639 Dump after all tree based optimization, to @file{@var{file}.optimized}.
4642 Dump after function inlining, to @file{@var{file}.inlined}.
4645 @opindex fdump-tree-gimple
4646 Dump each function before and after the gimplification pass to a file. The
4647 file name is made by appending @file{.gimple} to the source file name.
4650 @opindex fdump-tree-cfg
4651 Dump the control flow graph of each function to a file. The file name is
4652 made by appending @file{.cfg} to the source file name.
4655 @opindex fdump-tree-vcg
4656 Dump the control flow graph of each function to a file in VCG format. The
4657 file name is made by appending @file{.vcg} to the source file name. Note
4658 that if the file contains more than one function, the generated file cannot
4659 be used directly by VCG@. You will need to cut and paste each function's
4660 graph into its own separate file first.
4663 @opindex fdump-tree-ch
4664 Dump each function after copying loop headers. The file name is made by
4665 appending @file{.ch} to the source file name.
4668 @opindex fdump-tree-ssa
4669 Dump SSA related information to a file. The file name is made by appending
4670 @file{.ssa} to the source file name.
4673 @opindex fdump-tree-salias
4674 Dump structure aliasing variable information to a file. This file name
4675 is made by appending @file{.salias} to the source file name.
4678 @opindex fdump-tree-alias
4679 Dump aliasing information for each function. The file name is made by
4680 appending @file{.alias} to the source file name.
4683 @opindex fdump-tree-ccp
4684 Dump each function after CCP@. The file name is made by appending
4685 @file{.ccp} to the source file name.
4688 @opindex fdump-tree-storeccp
4689 Dump each function after STORE-CCP. The file name is made by appending
4690 @file{.storeccp} to the source file name.
4693 @opindex fdump-tree-pre
4694 Dump trees after partial redundancy elimination. The file name is made
4695 by appending @file{.pre} to the source file name.
4698 @opindex fdump-tree-fre
4699 Dump trees after full redundancy elimination. The file name is made
4700 by appending @file{.fre} to the source file name.
4703 @opindex fdump-tree-copyprop
4704 Dump trees after copy propagation. The file name is made
4705 by appending @file{.copyprop} to the source file name.
4707 @item store_copyprop
4708 @opindex fdump-tree-store_copyprop
4709 Dump trees after store copy-propagation. The file name is made
4710 by appending @file{.store_copyprop} to the source file name.
4713 @opindex fdump-tree-dce
4714 Dump each function after dead code elimination. The file name is made by
4715 appending @file{.dce} to the source file name.
4718 @opindex fdump-tree-mudflap
4719 Dump each function after adding mudflap instrumentation. The file name is
4720 made by appending @file{.mudflap} to the source file name.
4723 @opindex fdump-tree-sra
4724 Dump each function after performing scalar replacement of aggregates. The
4725 file name is made by appending @file{.sra} to the source file name.
4728 @opindex fdump-tree-sink
4729 Dump each function after performing code sinking. The file name is made
4730 by appending @file{.sink} to the source file name.
4733 @opindex fdump-tree-dom
4734 Dump each function after applying dominator tree optimizations. The file
4735 name is made by appending @file{.dom} to the source file name.
4738 @opindex fdump-tree-dse
4739 Dump each function after applying dead store elimination. The file
4740 name is made by appending @file{.dse} to the source file name.
4743 @opindex fdump-tree-phiopt
4744 Dump each function after optimizing PHI nodes into straightline code. The file
4745 name is made by appending @file{.phiopt} to the source file name.
4748 @opindex fdump-tree-forwprop
4749 Dump each function after forward propagating single use variables. The file
4750 name is made by appending @file{.forwprop} to the source file name.
4753 @opindex fdump-tree-copyrename
4754 Dump each function after applying the copy rename optimization. The file
4755 name is made by appending @file{.copyrename} to the source file name.
4758 @opindex fdump-tree-nrv
4759 Dump each function after applying the named return value optimization on
4760 generic trees. The file name is made by appending @file{.nrv} to the source
4764 @opindex fdump-tree-vect
4765 Dump each function after applying vectorization of loops. The file name is
4766 made by appending @file{.vect} to the source file name.
4769 @opindex fdump-tree-vrp
4770 Dump each function after Value Range Propagation (VRP). The file name
4771 is made by appending @file{.vrp} to the source file name.
4774 @opindex fdump-tree-all
4775 Enable all the available tree dumps with the flags provided in this option.
4778 @item -ftree-vectorizer-verbose=@var{n}
4779 @opindex ftree-vectorizer-verbose
4780 This option controls the amount of debugging output the vectorizer prints.
4781 This information is written to standard error, unless
4782 @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified,
4783 in which case it is output to the usual dump listing file, @file{.vect}.
4784 For @var{n}=0 no diagnostic information is reported.
4785 If @var{n}=1 the vectorizer reports each loop that got vectorized,
4786 and the total number of loops that got vectorized.
4787 If @var{n}=2 the vectorizer also reports non-vectorized loops that passed
4788 the first analysis phase (vect_analyze_loop_form) - i.e. countable,
4789 inner-most, single-bb, single-entry/exit loops. This is the same verbosity
4790 level that @option{-fdump-tree-vect-stats} uses.
4791 Higher verbosity levels mean either more information dumped for each
4792 reported loop, or same amount of information reported for more loops:
4793 If @var{n}=3, alignment related information is added to the reports.
4794 If @var{n}=4, data-references related information (e.g. memory dependences,
4795 memory access-patterns) is added to the reports.
4796 If @var{n}=5, the vectorizer reports also non-vectorized inner-most loops
4797 that did not pass the first analysis phase (i.e. may not be countable, or
4798 may have complicated control-flow).
4799 If @var{n}=6, the vectorizer reports also non-vectorized nested loops.
4800 For @var{n}=7, all the information the vectorizer generates during its
4801 analysis and transformation is reported. This is the same verbosity level
4802 that @option{-fdump-tree-vect-details} uses.
4804 @item -frandom-seed=@var{string}
4805 @opindex frandom-string
4806 This option provides a seed that GCC uses when it would otherwise use
4807 random numbers. It is used to generate certain symbol names
4808 that have to be different in every compiled file. It is also used to
4809 place unique stamps in coverage data files and the object files that
4810 produce them. You can use the @option{-frandom-seed} option to produce
4811 reproducibly identical object files.
4813 The @var{string} should be different for every file you compile.
4815 @item -fsched-verbose=@var{n}
4816 @opindex fsched-verbose
4817 On targets that use instruction scheduling, this option controls the
4818 amount of debugging output the scheduler prints. This information is
4819 written to standard error, unless @option{-dS} or @option{-dR} is
4820 specified, in which case it is output to the usual dump
4821 listing file, @file{.sched} or @file{.sched2} respectively. However
4822 for @var{n} greater than nine, the output is always printed to standard
4825 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
4826 same information as @option{-dRS}. For @var{n} greater than one, it
4827 also output basic block probabilities, detailed ready list information
4828 and unit/insn info. For @var{n} greater than two, it includes RTL
4829 at abort point, control-flow and regions info. And for @var{n} over
4830 four, @option{-fsched-verbose} also includes dependence info.
4834 Store the usual ``temporary'' intermediate files permanently; place them
4835 in the current directory and name them based on the source file. Thus,
4836 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
4837 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
4838 preprocessed @file{foo.i} output file even though the compiler now
4839 normally uses an integrated preprocessor.
4841 When used in combination with the @option{-x} command line option,
4842 @option{-save-temps} is sensible enough to avoid over writing an
4843 input source file with the same extension as an intermediate file.
4844 The corresponding intermediate file may be obtained by renaming the
4845 source file before using @option{-save-temps}.
4849 Report the CPU time taken by each subprocess in the compilation
4850 sequence. For C source files, this is the compiler proper and assembler
4851 (plus the linker if linking is done). The output looks like this:
4858 The first number on each line is the ``user time'', that is time spent
4859 executing the program itself. The second number is ``system time'',
4860 time spent executing operating system routines on behalf of the program.
4861 Both numbers are in seconds.
4863 @item -fvar-tracking
4864 @opindex fvar-tracking
4865 Run variable tracking pass. It computes where variables are stored at each
4866 position in code. Better debugging information is then generated
4867 (if the debugging information format supports this information).
4869 It is enabled by default when compiling with optimization (@option{-Os},
4870 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
4871 the debug info format supports it.
4873 @item -print-file-name=@var{library}
4874 @opindex print-file-name
4875 Print the full absolute name of the library file @var{library} that
4876 would be used when linking---and don't do anything else. With this
4877 option, GCC does not compile or link anything; it just prints the
4880 @item -print-multi-directory
4881 @opindex print-multi-directory
4882 Print the directory name corresponding to the multilib selected by any
4883 other switches present in the command line. This directory is supposed
4884 to exist in @env{GCC_EXEC_PREFIX}.
4886 @item -print-multi-lib
4887 @opindex print-multi-lib
4888 Print the mapping from multilib directory names to compiler switches
4889 that enable them. The directory name is separated from the switches by
4890 @samp{;}, and each switch starts with an @samp{@@} instead of the
4891 @samp{-}, without spaces between multiple switches. This is supposed to
4892 ease shell-processing.
4894 @item -print-prog-name=@var{program}
4895 @opindex print-prog-name
4896 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
4898 @item -print-libgcc-file-name
4899 @opindex print-libgcc-file-name
4900 Same as @option{-print-file-name=libgcc.a}.
4902 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
4903 but you do want to link with @file{libgcc.a}. You can do
4906 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
4909 @item -print-search-dirs
4910 @opindex print-search-dirs
4911 Print the name of the configured installation directory and a list of
4912 program and library directories @command{gcc} will search---and don't do anything else.
4914 This is useful when @command{gcc} prints the error message
4915 @samp{installation problem, cannot exec cpp0: No such file or directory}.
4916 To resolve this you either need to put @file{cpp0} and the other compiler
4917 components where @command{gcc} expects to find them, or you can set the environment
4918 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
4919 Don't forget the trailing @samp{/}.
4920 @xref{Environment Variables}.
4922 @item -print-sysroot-headers-suffix
4923 @opindex print-sysroot-headers-suffix
4924 Print the suffix added to the target sysroot when searching for
4925 headers, or give an error if the compiler is not configured with such
4926 a suffix---and don't do anything else.
4929 @opindex dumpmachine
4930 Print the compiler's target machine (for example,
4931 @samp{i686-pc-linux-gnu})---and don't do anything else.
4934 @opindex dumpversion
4935 Print the compiler version (for example, @samp{3.0})---and don't do
4940 Print the compiler's built-in specs---and don't do anything else. (This
4941 is used when GCC itself is being built.) @xref{Spec Files}.
4943 @item -feliminate-unused-debug-types
4944 @opindex feliminate-unused-debug-types
4945 Normally, when producing DWARF2 output, GCC will emit debugging
4946 information for all types declared in a compilation
4947 unit, regardless of whether or not they are actually used
4948 in that compilation unit. Sometimes this is useful, such as
4949 if, in the debugger, you want to cast a value to a type that is
4950 not actually used in your program (but is declared). More often,
4951 however, this results in a significant amount of wasted space.
4952 With this option, GCC will avoid producing debug symbol output
4953 for types that are nowhere used in the source file being compiled.
4956 @node Optimize Options
4957 @section Options That Control Optimization
4958 @cindex optimize options
4959 @cindex options, optimization
4961 These options control various sorts of optimizations.
4963 Without any optimization option, the compiler's goal is to reduce the
4964 cost of compilation and to make debugging produce the expected
4965 results. Statements are independent: if you stop the program with a
4966 breakpoint between statements, you can then assign a new value to any
4967 variable or change the program counter to any other statement in the
4968 function and get exactly the results you would expect from the source
4971 Turning on optimization flags makes the compiler attempt to improve
4972 the performance and/or code size at the expense of compilation time
4973 and possibly the ability to debug the program.
4975 The compiler performs optimization based on the knowledge it has of
4976 the program. Optimization levels @option{-O} and above, in
4977 particular, enable @emph{unit-at-a-time} mode, which allows the
4978 compiler to consider information gained from later functions in
4979 the file when compiling a function. Compiling multiple files at
4980 once to a single output file in @emph{unit-at-a-time} mode allows
4981 the compiler to use information gained from all of the files when
4982 compiling each of them.
4984 Not all optimizations are controlled directly by a flag. Only
4985 optimizations that have a flag are listed.
4992 Optimize. Optimizing compilation takes somewhat more time, and a lot
4993 more memory for a large function.
4995 With @option{-O}, the compiler tries to reduce code size and execution
4996 time, without performing any optimizations that take a great deal of
4999 @option{-O} turns on the following optimization flags:
5000 @gccoptlist{-fdefer-pop @gol
5001 -fdelayed-branch @gol
5002 -fguess-branch-probability @gol
5003 -fcprop-registers @gol
5004 -fif-conversion @gol
5005 -fif-conversion2 @gol
5006 -fsplit-wide-types @gol
5009 -ftree-dominator-opts @gol
5013 -ftree-copyrename @gol
5016 -funit-at-a-time @gol
5019 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
5020 where doing so does not interfere with debugging.
5024 Optimize even more. GCC performs nearly all supported optimizations
5025 that do not involve a space-speed tradeoff. The compiler does not
5026 perform loop unrolling or function inlining when you specify @option{-O2}.
5027 As compared to @option{-O}, this option increases both compilation time
5028 and the performance of the generated code.
5030 @option{-O2} turns on all optimization flags specified by @option{-O}. It
5031 also turns on the following optimization flags:
5032 @gccoptlist{-fthread-jumps @gol
5034 -foptimize-sibling-calls @gol
5035 -fcse-follow-jumps -fcse-skip-blocks @gol
5036 -fgcse -fgcse-lm @gol
5037 -fexpensive-optimizations @gol
5038 -frerun-cse-after-loop @gol
5041 -fschedule-insns -fschedule-insns2 @gol
5042 -fsched-interblock -fsched-spec @gol
5044 -fstrict-aliasing -fstrict-overflow @gol
5045 -fdelete-null-pointer-checks @gol
5046 -freorder-blocks -freorder-functions @gol
5047 -falign-functions -falign-jumps @gol
5048 -falign-loops -falign-labels @gol
5052 Please note the warning under @option{-fgcse} about
5053 invoking @option{-O2} on programs that use computed gotos.
5057 Optimize yet more. @option{-O3} turns on all optimizations specified by
5058 @option{-O2} and also turns on the @option{-finline-functions},
5059 @option{-funswitch-loops}, @option{-fpredictive-commoning} and
5060 @option{-fgcse-after-reload} options.
5064 Reduce compilation time and make debugging produce the expected
5065 results. This is the default.
5069 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
5070 do not typically increase code size. It also performs further
5071 optimizations designed to reduce code size.
5073 @option{-Os} disables the following optimization flags:
5074 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
5075 -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol
5076 -fprefetch-loop-arrays -ftree-vect-loop-version}
5078 If you use multiple @option{-O} options, with or without level numbers,
5079 the last such option is the one that is effective.
5082 Options of the form @option{-f@var{flag}} specify machine-independent
5083 flags. Most flags have both positive and negative forms; the negative
5084 form of @option{-ffoo} would be @option{-fno-foo}. In the table
5085 below, only one of the forms is listed---the one you typically will
5086 use. You can figure out the other form by either removing @samp{no-}
5089 The following options control specific optimizations. They are either
5090 activated by @option{-O} options or are related to ones that are. You
5091 can use the following flags in the rare cases when ``fine-tuning'' of
5092 optimizations to be performed is desired.
5095 @item -fno-default-inline
5096 @opindex fno-default-inline
5097 Do not make member functions inline by default merely because they are
5098 defined inside the class scope (C++ only). Otherwise, when you specify
5099 @w{@option{-O}}, member functions defined inside class scope are compiled
5100 inline by default; i.e., you don't need to add @samp{inline} in front of
5101 the member function name.
5103 @item -fno-defer-pop
5104 @opindex fno-defer-pop
5105 Always pop the arguments to each function call as soon as that function
5106 returns. For machines which must pop arguments after a function call,
5107 the compiler normally lets arguments accumulate on the stack for several
5108 function calls and pops them all at once.
5110 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5113 @opindex fforce-addr
5114 Force memory address constants to be copied into registers before
5115 doing arithmetic on them.
5117 @item -fforward-propagate
5118 @opindex fforward-propagate
5119 Perform a forward propagation pass on RTL. The pass tries to combine two
5120 instructions and checks if the result can be simplified. If loop unrolling
5121 is active, two passes are performed and the second is scheduled after
5124 This option is enabled by default at optimization levels @option{-O2},
5125 @option{-O3}, @option{-Os}.
5127 @item -fomit-frame-pointer
5128 @opindex fomit-frame-pointer
5129 Don't keep the frame pointer in a register for functions that
5130 don't need one. This avoids the instructions to save, set up and
5131 restore frame pointers; it also makes an extra register available
5132 in many functions. @strong{It also makes debugging impossible on
5135 On some machines, such as the VAX, this flag has no effect, because
5136 the standard calling sequence automatically handles the frame pointer
5137 and nothing is saved by pretending it doesn't exist. The
5138 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
5139 whether a target machine supports this flag. @xref{Registers,,Register
5140 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
5142 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5144 @item -foptimize-sibling-calls
5145 @opindex foptimize-sibling-calls
5146 Optimize sibling and tail recursive calls.
5148 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5152 Don't pay attention to the @code{inline} keyword. Normally this option
5153 is used to keep the compiler from expanding any functions inline.
5154 Note that if you are not optimizing, no functions can be expanded inline.
5156 @item -finline-functions
5157 @opindex finline-functions
5158 Integrate all simple functions into their callers. The compiler
5159 heuristically decides which functions are simple enough to be worth
5160 integrating in this way.
5162 If all calls to a given function are integrated, and the function is
5163 declared @code{static}, then the function is normally not output as
5164 assembler code in its own right.
5166 Enabled at level @option{-O3}.
5168 @item -finline-functions-called-once
5169 @opindex finline-functions-called-once
5170 Consider all @code{static} functions called once for inlining into their
5171 caller even if they are not marked @code{inline}. If a call to a given
5172 function is integrated, then the function is not output as assembler code
5175 Enabled if @option{-funit-at-a-time} is enabled.
5177 @item -fearly-inlining
5178 @opindex fearly-inlining
5179 Inline functions marked by @code{always_inline} and functions whose body seems
5180 smaller than the function call overhead early before doing
5181 @option{-fprofile-generate} instrumentation and real inlining pass. Doing so
5182 makes profiling significantly cheaper and usually inlining faster on programs
5183 having large chains of nested wrapper functions.
5187 @item -finline-limit=@var{n}
5188 @opindex finline-limit
5189 By default, GCC limits the size of functions that can be inlined. This flag
5190 allows the control of this limit for functions that are explicitly marked as
5191 inline (i.e., marked with the inline keyword or defined within the class
5192 definition in c++). @var{n} is the size of functions that can be inlined in
5193 number of pseudo instructions (not counting parameter handling). The default
5194 value of @var{n} is 600.
5195 Increasing this value can result in more inlined code at
5196 the cost of compilation time and memory consumption. Decreasing usually makes
5197 the compilation faster and less code will be inlined (which presumably
5198 means slower programs). This option is particularly useful for programs that
5199 use inlining heavily such as those based on recursive templates with C++.
5201 Inlining is actually controlled by a number of parameters, which may be
5202 specified individually by using @option{--param @var{name}=@var{value}}.
5203 The @option{-finline-limit=@var{n}} option sets some of these parameters
5207 @item max-inline-insns-single
5208 is set to @var{n}/2.
5209 @item max-inline-insns-auto
5210 is set to @var{n}/2.
5211 @item min-inline-insns
5212 is set to 130 or @var{n}/4, whichever is smaller.
5213 @item max-inline-insns-rtl
5217 See below for a documentation of the individual
5218 parameters controlling inlining.
5220 @emph{Note:} pseudo instruction represents, in this particular context, an
5221 abstract measurement of function's size. In no way does it represent a count
5222 of assembly instructions and as such its exact meaning might change from one
5223 release to an another.
5225 @item -fkeep-inline-functions
5226 @opindex fkeep-inline-functions
5227 In C, emit @code{static} functions that are declared @code{inline}
5228 into the object file, even if the function has been inlined into all
5229 of its callers. This switch does not affect functions using the
5230 @code{extern inline} extension in GNU C89@. In C++, emit any and all
5231 inline functions into the object file.
5233 @item -fkeep-static-consts
5234 @opindex fkeep-static-consts
5235 Emit variables declared @code{static const} when optimization isn't turned
5236 on, even if the variables aren't referenced.
5238 GCC enables this option by default. If you want to force the compiler to
5239 check if the variable was referenced, regardless of whether or not
5240 optimization is turned on, use the @option{-fno-keep-static-consts} option.
5242 @item -fmerge-constants
5243 Attempt to merge identical constants (string constants and floating point
5244 constants) across compilation units.
5246 This option is the default for optimized compilation if the assembler and
5247 linker support it. Use @option{-fno-merge-constants} to inhibit this
5250 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5252 @item -fmerge-all-constants
5253 Attempt to merge identical constants and identical variables.
5255 This option implies @option{-fmerge-constants}. In addition to
5256 @option{-fmerge-constants} this considers e.g.@: even constant initialized
5257 arrays or initialized constant variables with integral or floating point
5258 types. Languages like C or C++ require each non-automatic variable to
5259 have distinct location, so using this option will result in non-conforming
5262 @item -fmodulo-sched
5263 @opindex fmodulo-sched
5264 Perform swing modulo scheduling immediately before the first scheduling
5265 pass. This pass looks at innermost loops and reorders their
5266 instructions by overlapping different iterations.
5268 @item -fno-branch-count-reg
5269 @opindex fno-branch-count-reg
5270 Do not use ``decrement and branch'' instructions on a count register,
5271 but instead generate a sequence of instructions that decrement a
5272 register, compare it against zero, then branch based upon the result.
5273 This option is only meaningful on architectures that support such
5274 instructions, which include x86, PowerPC, IA-64 and S/390.
5276 The default is @option{-fbranch-count-reg}.
5278 @item -fno-function-cse
5279 @opindex fno-function-cse
5280 Do not put function addresses in registers; make each instruction that
5281 calls a constant function contain the function's address explicitly.
5283 This option results in less efficient code, but some strange hacks
5284 that alter the assembler output may be confused by the optimizations
5285 performed when this option is not used.
5287 The default is @option{-ffunction-cse}
5289 @item -fno-zero-initialized-in-bss
5290 @opindex fno-zero-initialized-in-bss
5291 If the target supports a BSS section, GCC by default puts variables that
5292 are initialized to zero into BSS@. This can save space in the resulting
5295 This option turns off this behavior because some programs explicitly
5296 rely on variables going to the data section. E.g., so that the
5297 resulting executable can find the beginning of that section and/or make
5298 assumptions based on that.
5300 The default is @option{-fzero-initialized-in-bss}.
5302 @item -fbounds-check
5303 @opindex fbounds-check
5304 For front-ends that support it, generate additional code to check that
5305 indices used to access arrays are within the declared range. This is
5306 currently only supported by the Java and Fortran front-ends, where
5307 this option defaults to true and false respectively.
5309 @item -fmudflap -fmudflapth -fmudflapir
5313 @cindex bounds checking
5315 For front-ends that support it (C and C++), instrument all risky
5316 pointer/array dereferencing operations, some standard library
5317 string/heap functions, and some other associated constructs with
5318 range/validity tests. Modules so instrumented should be immune to
5319 buffer overflows, invalid heap use, and some other classes of C/C++
5320 programming errors. The instrumentation relies on a separate runtime
5321 library (@file{libmudflap}), which will be linked into a program if
5322 @option{-fmudflap} is given at link time. Run-time behavior of the
5323 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
5324 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
5327 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
5328 link if your program is multi-threaded. Use @option{-fmudflapir}, in
5329 addition to @option{-fmudflap} or @option{-fmudflapth}, if
5330 instrumentation should ignore pointer reads. This produces less
5331 instrumentation (and therefore faster execution) and still provides
5332 some protection against outright memory corrupting writes, but allows
5333 erroneously read data to propagate within a program.
5335 @item -fthread-jumps
5336 @opindex fthread-jumps
5337 Perform optimizations where we check to see if a jump branches to a
5338 location where another comparison subsumed by the first is found. If
5339 so, the first branch is redirected to either the destination of the
5340 second branch or a point immediately following it, depending on whether
5341 the condition is known to be true or false.
5343 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5345 @item -fsplit-wide-types
5346 @opindex fsplit-wide-types
5347 When using a type that occupies multiple registers, such as @code{long
5348 long} on a 32-bit system, split the registers apart and allocate them
5349 independently. This normally generates better code for those types,
5350 but may make debugging more difficult.
5352 Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
5355 @item -fcse-follow-jumps
5356 @opindex fcse-follow-jumps
5357 In common subexpression elimination, scan through jump instructions
5358 when the target of the jump is not reached by any other path. For
5359 example, when CSE encounters an @code{if} statement with an
5360 @code{else} clause, CSE will follow the jump when the condition
5363 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5365 @item -fcse-skip-blocks
5366 @opindex fcse-skip-blocks
5367 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
5368 follow jumps which conditionally skip over blocks. When CSE
5369 encounters a simple @code{if} statement with no else clause,
5370 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
5371 body of the @code{if}.
5373 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5375 @item -frerun-cse-after-loop
5376 @opindex frerun-cse-after-loop
5377 Re-run common subexpression elimination after loop optimizations has been
5380 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5384 Perform a global common subexpression elimination pass.
5385 This pass also performs global constant and copy propagation.
5387 @emph{Note:} When compiling a program using computed gotos, a GCC
5388 extension, you may get better runtime performance if you disable
5389 the global common subexpression elimination pass by adding
5390 @option{-fno-gcse} to the command line.
5392 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5396 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
5397 attempt to move loads which are only killed by stores into themselves. This
5398 allows a loop containing a load/store sequence to be changed to a load outside
5399 the loop, and a copy/store within the loop.
5401 Enabled by default when gcse is enabled.
5405 When @option{-fgcse-sm} is enabled, a store motion pass is run after
5406 global common subexpression elimination. This pass will attempt to move
5407 stores out of loops. When used in conjunction with @option{-fgcse-lm},
5408 loops containing a load/store sequence can be changed to a load before
5409 the loop and a store after the loop.
5411 Not enabled at any optimization level.
5415 When @option{-fgcse-las} is enabled, the global common subexpression
5416 elimination pass eliminates redundant loads that come after stores to the
5417 same memory location (both partial and full redundancies).
5419 Not enabled at any optimization level.
5421 @item -fgcse-after-reload
5422 @opindex fgcse-after-reload
5423 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
5424 pass is performed after reload. The purpose of this pass is to cleanup
5427 @item -funsafe-loop-optimizations
5428 @opindex funsafe-loop-optimizations
5429 If given, the loop optimizer will assume that loop indices do not
5430 overflow, and that the loops with nontrivial exit condition are not
5431 infinite. This enables a wider range of loop optimizations even if
5432 the loop optimizer itself cannot prove that these assumptions are valid.
5433 Using @option{-Wunsafe-loop-optimizations}, the compiler will warn you
5434 if it finds this kind of loop.
5436 @item -fcrossjumping
5437 @opindex crossjumping
5438 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
5439 resulting code may or may not perform better than without cross-jumping.
5441 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5443 @item -fif-conversion
5444 @opindex if-conversion
5445 Attempt to transform conditional jumps into branch-less equivalents. This
5446 include use of conditional moves, min, max, set flags and abs instructions, and
5447 some tricks doable by standard arithmetics. The use of conditional execution
5448 on chips where it is available is controlled by @code{if-conversion2}.
5450 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5452 @item -fif-conversion2
5453 @opindex if-conversion2
5454 Use conditional execution (where available) to transform conditional jumps into
5455 branch-less equivalents.
5457 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5459 @item -fdelete-null-pointer-checks
5460 @opindex fdelete-null-pointer-checks
5461 Use global dataflow analysis to identify and eliminate useless checks
5462 for null pointers. The compiler assumes that dereferencing a null
5463 pointer would have halted the program. If a pointer is checked after
5464 it has already been dereferenced, it cannot be null.
5466 In some environments, this assumption is not true, and programs can
5467 safely dereference null pointers. Use
5468 @option{-fno-delete-null-pointer-checks} to disable this optimization
5469 for programs which depend on that behavior.
5471 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5473 @item -fexpensive-optimizations
5474 @opindex fexpensive-optimizations
5475 Perform a number of minor optimizations that are relatively expensive.
5477 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5479 @item -foptimize-register-move
5481 @opindex foptimize-register-move
5483 Attempt to reassign register numbers in move instructions and as
5484 operands of other simple instructions in order to maximize the amount of
5485 register tying. This is especially helpful on machines with two-operand
5488 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
5491 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5493 @item -fdelayed-branch
5494 @opindex fdelayed-branch
5495 If supported for the target machine, attempt to reorder instructions
5496 to exploit instruction slots available after delayed branch
5499 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5501 @item -fschedule-insns
5502 @opindex fschedule-insns
5503 If supported for the target machine, attempt to reorder instructions to
5504 eliminate execution stalls due to required data being unavailable. This
5505 helps machines that have slow floating point or memory load instructions
5506 by allowing other instructions to be issued until the result of the load
5507 or floating point instruction is required.
5509 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5511 @item -fschedule-insns2
5512 @opindex fschedule-insns2
5513 Similar to @option{-fschedule-insns}, but requests an additional pass of
5514 instruction scheduling after register allocation has been done. This is
5515 especially useful on machines with a relatively small number of
5516 registers and where memory load instructions take more than one cycle.
5518 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5520 @item -fno-sched-interblock
5521 @opindex fno-sched-interblock
5522 Don't schedule instructions across basic blocks. This is normally
5523 enabled by default when scheduling before register allocation, i.e.@:
5524 with @option{-fschedule-insns} or at @option{-O2} or higher.
5526 @item -fno-sched-spec
5527 @opindex fno-sched-spec
5528 Don't allow speculative motion of non-load instructions. This is normally
5529 enabled by default when scheduling before register allocation, i.e.@:
5530 with @option{-fschedule-insns} or at @option{-O2} or higher.
5532 @item -fsched-spec-load
5533 @opindex fsched-spec-load
5534 Allow speculative motion of some load instructions. This only makes
5535 sense when scheduling before register allocation, i.e.@: with
5536 @option{-fschedule-insns} or at @option{-O2} or higher.
5538 @item -fsched-spec-load-dangerous
5539 @opindex fsched-spec-load-dangerous
5540 Allow speculative motion of more load instructions. This only makes
5541 sense when scheduling before register allocation, i.e.@: with
5542 @option{-fschedule-insns} or at @option{-O2} or higher.
5544 @item -fsched-stalled-insns=@var{n}
5545 @opindex fsched-stalled-insns
5546 Define how many insns (if any) can be moved prematurely from the queue
5547 of stalled insns into the ready list, during the second scheduling pass.
5549 @item -fsched-stalled-insns-dep=@var{n}
5550 @opindex fsched-stalled-insns-dep
5551 Define how many insn groups (cycles) will be examined for a dependency
5552 on a stalled insn that is candidate for premature removal from the queue
5553 of stalled insns. Has an effect only during the second scheduling pass,
5554 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
5556 @item -fsched2-use-superblocks
5557 @opindex fsched2-use-superblocks
5558 When scheduling after register allocation, do use superblock scheduling
5559 algorithm. Superblock scheduling allows motion across basic block boundaries
5560 resulting on faster schedules. This option is experimental, as not all machine
5561 descriptions used by GCC model the CPU closely enough to avoid unreliable
5562 results from the algorithm.
5564 This only makes sense when scheduling after register allocation, i.e.@: with
5565 @option{-fschedule-insns2} or at @option{-O2} or higher.
5567 @item -fsched2-use-traces
5568 @opindex fsched2-use-traces
5569 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
5570 allocation and additionally perform code duplication in order to increase the
5571 size of superblocks using tracer pass. See @option{-ftracer} for details on
5574 This mode should produce faster but significantly longer programs. Also
5575 without @option{-fbranch-probabilities} the traces constructed may not
5576 match the reality and hurt the performance. This only makes
5577 sense when scheduling after register allocation, i.e.@: with
5578 @option{-fschedule-insns2} or at @option{-O2} or higher.
5582 Eliminates redundant extension instructions and move the non redundant
5583 ones to optimal placement using LCM.
5585 @item -freschedule-modulo-scheduled-loops
5586 @opindex fscheduling-in-modulo-scheduled-loops
5587 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
5588 we may want to prevent the later scheduling passes from changing its schedule, we use this
5589 option to control that.
5591 @item -fcaller-saves
5592 @opindex fcaller-saves
5593 Enable values to be allocated in registers that will be clobbered by
5594 function calls, by emitting extra instructions to save and restore the
5595 registers around such calls. Such allocation is done only when it
5596 seems to result in better code than would otherwise be produced.
5598 This option is always enabled by default on certain machines, usually
5599 those which have no call-preserved registers to use instead.
5601 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5604 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
5605 enabled by default at @option{-O2} and @option{-O3}.
5608 Perform Full Redundancy Elimination (FRE) on trees. The difference
5609 between FRE and PRE is that FRE only considers expressions
5610 that are computed on all paths leading to the redundant computation.
5611 This analysis is faster than PRE, though it exposes fewer redundancies.
5612 This flag is enabled by default at @option{-O} and higher.
5614 @item -ftree-copy-prop
5615 Perform copy propagation on trees. This pass eliminates unnecessary
5616 copy operations. This flag is enabled by default at @option{-O} and
5619 @item -ftree-store-copy-prop
5620 Perform copy propagation of memory loads and stores. This pass
5621 eliminates unnecessary copy operations in memory references
5622 (structures, global variables, arrays, etc). This flag is enabled by
5623 default at @option{-O2} and higher.
5626 Perform structural alias analysis on trees. This flag
5627 is enabled by default at @option{-O} and higher.
5630 Perform interprocedural pointer analysis.
5633 Perform forward store motion on trees. This flag is
5634 enabled by default at @option{-O} and higher.
5637 Perform sparse conditional constant propagation (CCP) on trees. This
5638 pass only operates on local scalar variables and is enabled by default
5639 at @option{-O} and higher.
5641 @item -ftree-store-ccp
5642 Perform sparse conditional constant propagation (CCP) on trees. This
5643 pass operates on both local scalar variables and memory stores and
5644 loads (global variables, structures, arrays, etc). This flag is
5645 enabled by default at @option{-O2} and higher.
5648 Perform dead code elimination (DCE) on trees. This flag is enabled by
5649 default at @option{-O} and higher.
5651 @item -ftree-dominator-opts
5652 Perform a variety of simple scalar cleanups (constant/copy
5653 propagation, redundancy elimination, range propagation and expression
5654 simplification) based on a dominator tree traversal. This also
5655 performs jump threading (to reduce jumps to jumps). This flag is
5656 enabled by default at @option{-O} and higher.
5659 Perform loop header copying on trees. This is beneficial since it increases
5660 effectiveness of code motion optimizations. It also saves one jump. This flag
5661 is enabled by default at @option{-O} and higher. It is not enabled
5662 for @option{-Os}, since it usually increases code size.
5664 @item -ftree-loop-optimize
5665 Perform loop optimizations on trees. This flag is enabled by default
5666 at @option{-O} and higher.
5668 @item -ftree-loop-linear
5669 Perform linear loop transformations on tree. This flag can improve cache
5670 performance and allow further loop optimizations to take place.
5672 @item -fcheck-data-deps
5673 Compare the results of several data dependence analyzers. This option
5674 is used for debugging the data dependence analyzers.
5676 @item -ftree-loop-im
5677 Perform loop invariant motion on trees. This pass moves only invariants that
5678 would be hard to handle at RTL level (function calls, operations that expand to
5679 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
5680 operands of conditions that are invariant out of the loop, so that we can use
5681 just trivial invariantness analysis in loop unswitching. The pass also includes
5684 @item -ftree-loop-ivcanon
5685 Create a canonical counter for number of iterations in the loop for that
5686 determining number of iterations requires complicated analysis. Later
5687 optimizations then may determine the number easily. Useful especially
5688 in connection with unrolling.
5691 Perform induction variable optimizations (strength reduction, induction
5692 variable merging and induction variable elimination) on trees.
5695 Perform scalar replacement of aggregates. This pass replaces structure
5696 references with scalars to prevent committing structures to memory too
5697 early. This flag is enabled by default at @option{-O} and higher.
5699 @item -ftree-copyrename
5700 Perform copy renaming on trees. This pass attempts to rename compiler
5701 temporaries to other variables at copy locations, usually resulting in
5702 variable names which more closely resemble the original variables. This flag
5703 is enabled by default at @option{-O} and higher.
5706 Perform temporary expression replacement during the SSA->normal phase. Single
5707 use/single def temporaries are replaced at their use location with their
5708 defining expression. This results in non-GIMPLE code, but gives the expanders
5709 much more complex trees to work on resulting in better RTL generation. This is
5710 enabled by default at @option{-O} and higher.
5712 @item -ftree-vectorize
5713 Perform loop vectorization on trees.
5715 @item -ftree-vect-loop-version
5716 @opindex ftree-vect-loop-version
5717 Perform loop versioning when doing loop vectorization on trees. When a loop
5718 appears to be vectorizable except that data alignment or data dependence cannot
5719 be determined at compile time then vectorized and non-vectorized versions of
5720 the loop are generated along with runtime checks for alignment or dependence
5721 to control which version is executed. This option is enabled by default
5722 except at level @option{-Os} where it is disabled.
5724 @item -fvect-cost-model
5725 Enable cost model for vectorization.
5728 Perform Value Range Propagation on trees. This is similar to the
5729 constant propagation pass, but instead of values, ranges of values are
5730 propagated. This allows the optimizers to remove unnecessary range
5731 checks like array bound checks and null pointer checks. This is
5732 enabled by default at @option{-O2} and higher. Null pointer check
5733 elimination is only done if @option{-fdelete-null-pointer-checks} is
5738 Perform tail duplication to enlarge superblock size. This transformation
5739 simplifies the control flow of the function allowing other optimizations to do
5742 @item -funroll-loops
5743 @opindex funroll-loops
5744 Unroll loops whose number of iterations can be determined at compile
5745 time or upon entry to the loop. @option{-funroll-loops} implies
5746 @option{-frerun-cse-after-loop}. This option makes code larger,
5747 and may or may not make it run faster.
5749 @item -funroll-all-loops
5750 @opindex funroll-all-loops
5751 Unroll all loops, even if their number of iterations is uncertain when
5752 the loop is entered. This usually makes programs run more slowly.
5753 @option{-funroll-all-loops} implies the same options as
5754 @option{-funroll-loops},
5756 @item -fsplit-ivs-in-unroller
5757 @opindex fsplit-ivs-in-unroller
5758 Enables expressing of values of induction variables in later iterations
5759 of the unrolled loop using the value in the first iteration. This breaks
5760 long dependency chains, thus improving efficiency of the scheduling passes.
5762 Combination of @option{-fweb} and CSE is often sufficient to obtain the
5763 same effect. However in cases the loop body is more complicated than
5764 a single basic block, this is not reliable. It also does not work at all
5765 on some of the architectures due to restrictions in the CSE pass.
5767 This optimization is enabled by default.
5769 @item -fvariable-expansion-in-unroller
5770 @opindex fvariable-expansion-in-unroller
5771 With this option, the compiler will create multiple copies of some
5772 local variables when unrolling a loop which can result in superior code.
5774 @item -fpredictive-commoning
5775 @opindex fpredictive-commoning
5776 Perform predictive commoning optimization, i.e., reusing computations
5777 (especially memory loads and stores) performed in previous
5778 iterations of loops.
5780 This option is enabled at level @option{-O3}.
5782 @item -fprefetch-loop-arrays
5783 @opindex fprefetch-loop-arrays
5784 If supported by the target machine, generate instructions to prefetch
5785 memory to improve the performance of loops that access large arrays.
5787 This option may generate better or worse code; results are highly
5788 dependent on the structure of loops within the source code.
5790 Disabled at level @option{-Os}.
5793 @itemx -fno-peephole2
5794 @opindex fno-peephole
5795 @opindex fno-peephole2
5796 Disable any machine-specific peephole optimizations. The difference
5797 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
5798 are implemented in the compiler; some targets use one, some use the
5799 other, a few use both.
5801 @option{-fpeephole} is enabled by default.
5802 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5804 @item -fno-guess-branch-probability
5805 @opindex fno-guess-branch-probability
5806 Do not guess branch probabilities using heuristics.
5808 GCC will use heuristics to guess branch probabilities if they are
5809 not provided by profiling feedback (@option{-fprofile-arcs}). These
5810 heuristics are based on the control flow graph. If some branch probabilities
5811 are specified by @samp{__builtin_expect}, then the heuristics will be
5812 used to guess branch probabilities for the rest of the control flow graph,
5813 taking the @samp{__builtin_expect} info into account. The interactions
5814 between the heuristics and @samp{__builtin_expect} can be complex, and in
5815 some cases, it may be useful to disable the heuristics so that the effects
5816 of @samp{__builtin_expect} are easier to understand.
5818 The default is @option{-fguess-branch-probability} at levels
5819 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
5821 @item -freorder-blocks
5822 @opindex freorder-blocks
5823 Reorder basic blocks in the compiled function in order to reduce number of
5824 taken branches and improve code locality.
5826 Enabled at levels @option{-O2}, @option{-O3}.
5828 @item -freorder-blocks-and-partition
5829 @opindex freorder-blocks-and-partition
5830 In addition to reordering basic blocks in the compiled function, in order
5831 to reduce number of taken branches, partitions hot and cold basic blocks
5832 into separate sections of the assembly and .o files, to improve
5833 paging and cache locality performance.
5835 This optimization is automatically turned off in the presence of
5836 exception handling, for linkonce sections, for functions with a user-defined
5837 section attribute and on any architecture that does not support named
5840 @item -freorder-functions
5841 @opindex freorder-functions
5842 Reorder functions in the object file in order to
5843 improve code locality. This is implemented by using special
5844 subsections @code{.text.hot} for most frequently executed functions and
5845 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
5846 the linker so object file format must support named sections and linker must
5847 place them in a reasonable way.
5849 Also profile feedback must be available in to make this option effective. See
5850 @option{-fprofile-arcs} for details.
5852 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5854 @item -fstrict-aliasing
5855 @opindex fstrict-aliasing
5856 Allows the compiler to assume the strictest aliasing rules applicable to
5857 the language being compiled. For C (and C++), this activates
5858 optimizations based on the type of expressions. In particular, an
5859 object of one type is assumed never to reside at the same address as an
5860 object of a different type, unless the types are almost the same. For
5861 example, an @code{unsigned int} can alias an @code{int}, but not a
5862 @code{void*} or a @code{double}. A character type may alias any other
5865 Pay special attention to code like this:
5878 The practice of reading from a different union member than the one most
5879 recently written to (called ``type-punning'') is common. Even with
5880 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
5881 is accessed through the union type. So, the code above will work as
5882 expected. However, this code might not:
5893 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
5895 @item -fstrict-overflow
5896 @opindex fstrict-overflow
5897 Allow the compiler to assume strict signed overflow rules, depending
5898 on the language being compiled. For C (and C++) this means that
5899 overflow when doing arithmetic with signed numbers is undefined, which
5900 means that the compiler may assume that it will not happen. This
5901 permits various optimizations. For example, the compiler will assume
5902 that an expression like @code{i + 10 > i} will always be true for
5903 signed @code{i}. This assumption is only valid if signed overflow is
5904 undefined, as the expression is false if @code{i + 10} overflows when
5905 using twos complement arithmetic. When this option is in effect any
5906 attempt to determine whether an operation on signed numbers will
5907 overflow must be written carefully to not actually involve overflow.
5909 See also the @option{-fwrapv} option. Using @option{-fwrapv} means
5910 that signed overflow is fully defined: it wraps. When
5911 @option{-fwrapv} is used, there is no difference between
5912 @option{-fstrict-overflow} and @option{-fno-strict-overflow}. With
5913 @option{-fwrapv} certain types of overflow are permitted. For
5914 example, if the compiler gets an overflow when doing arithmetic on
5915 constants, the overflowed value can still be used with
5916 @option{-fwrapv}, but not otherwise.
5918 The @option{-fstrict-overflow} option is enabled at levels
5919 @option{-O2}, @option{-O3}, @option{-Os}.
5921 @item -falign-functions
5922 @itemx -falign-functions=@var{n}
5923 @opindex falign-functions
5924 Align the start of functions to the next power-of-two greater than
5925 @var{n}, skipping up to @var{n} bytes. For instance,
5926 @option{-falign-functions=32} aligns functions to the next 32-byte
5927 boundary, but @option{-falign-functions=24} would align to the next
5928 32-byte boundary only if this can be done by skipping 23 bytes or less.
5930 @option{-fno-align-functions} and @option{-falign-functions=1} are
5931 equivalent and mean that functions will not be aligned.
5933 Some assemblers only support this flag when @var{n} is a power of two;
5934 in that case, it is rounded up.
5936 If @var{n} is not specified or is zero, use a machine-dependent default.
5938 Enabled at levels @option{-O2}, @option{-O3}.
5940 @item -falign-labels
5941 @itemx -falign-labels=@var{n}
5942 @opindex falign-labels
5943 Align all branch targets to a power-of-two boundary, skipping up to
5944 @var{n} bytes like @option{-falign-functions}. This option can easily
5945 make code slower, because it must insert dummy operations for when the
5946 branch target is reached in the usual flow of the code.
5948 @option{-fno-align-labels} and @option{-falign-labels=1} are
5949 equivalent and mean that labels will not be aligned.
5951 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
5952 are greater than this value, then their values are used instead.
5954 If @var{n} is not specified or is zero, use a machine-dependent default
5955 which is very likely to be @samp{1}, meaning no alignment.
5957 Enabled at levels @option{-O2}, @option{-O3}.
5960 @itemx -falign-loops=@var{n}
5961 @opindex falign-loops
5962 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
5963 like @option{-falign-functions}. The hope is that the loop will be
5964 executed many times, which will make up for any execution of the dummy
5967 @option{-fno-align-loops} and @option{-falign-loops=1} are
5968 equivalent and mean that loops will not be aligned.
5970 If @var{n} is not specified or is zero, use a machine-dependent default.
5972 Enabled at levels @option{-O2}, @option{-O3}.
5975 @itemx -falign-jumps=@var{n}
5976 @opindex falign-jumps
5977 Align branch targets to a power-of-two boundary, for branch targets
5978 where the targets can only be reached by jumping, skipping up to @var{n}
5979 bytes like @option{-falign-functions}. In this case, no dummy operations
5982 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
5983 equivalent and mean that loops will not be aligned.
5985 If @var{n} is not specified or is zero, use a machine-dependent default.
5987 Enabled at levels @option{-O2}, @option{-O3}.
5989 @item -funit-at-a-time
5990 @opindex funit-at-a-time
5991 Parse the whole compilation unit before starting to produce code.
5992 This allows some extra optimizations to take place but consumes
5993 more memory (in general). There are some compatibility issues
5994 with @emph{unit-at-a-time} mode:
5997 enabling @emph{unit-at-a-time} mode may change the order
5998 in which functions, variables, and top-level @code{asm} statements
5999 are emitted, and will likely break code relying on some particular
6000 ordering. The majority of such top-level @code{asm} statements,
6001 though, can be replaced by @code{section} attributes. The
6002 @option{fno-toplevel-reorder} option may be used to keep the ordering
6003 used in the input file, at the cost of some optimizations.
6006 @emph{unit-at-a-time} mode removes unreferenced static variables
6007 and functions. This may result in undefined references
6008 when an @code{asm} statement refers directly to variables or functions
6009 that are otherwise unused. In that case either the variable/function
6010 shall be listed as an operand of the @code{asm} statement operand or,
6011 in the case of top-level @code{asm} statements the attribute @code{used}
6012 shall be used on the declaration.
6015 Static functions now can use non-standard passing conventions that
6016 may break @code{asm} statements calling functions directly. Again,
6017 attribute @code{used} will prevent this behavior.
6020 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
6021 but this scheme may not be supported by future releases of GCC@.
6023 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6025 @item -fno-toplevel-reorder
6026 Do not reorder top-level functions, variables, and @code{asm}
6027 statements. Output them in the same order that they appear in the
6028 input file. When this option is used, unreferenced static variables
6029 will not be removed. This option is intended to support existing code
6030 which relies on a particular ordering. For new code, it is better to
6035 Constructs webs as commonly used for register allocation purposes and assign
6036 each web individual pseudo register. This allows the register allocation pass
6037 to operate on pseudos directly, but also strengthens several other optimization
6038 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
6039 however, make debugging impossible, since variables will no longer stay in a
6042 Enabled by default with @option{-funroll-loops}.
6044 @item -fwhole-program
6045 @opindex fwhole-program
6046 Assume that the current compilation unit represents whole program being
6047 compiled. All public functions and variables with the exception of @code{main}
6048 and those merged by attribute @code{externally_visible} become static functions
6049 and in a affect gets more aggressively optimized by interprocedural optimizers.
6050 While this option is equivalent to proper use of @code{static} keyword for
6051 programs consisting of single file, in combination with option
6052 @option{--combine} this flag can be used to compile most of smaller scale C
6053 programs since the functions and variables become local for the whole combined
6054 compilation unit, not for the single source file itself.
6057 @item -fno-cprop-registers
6058 @opindex fno-cprop-registers
6059 After register allocation and post-register allocation instruction splitting,
6060 we perform a copy-propagation pass to try to reduce scheduling dependencies
6061 and occasionally eliminate the copy.
6063 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
6065 @item -fprofile-generate
6066 @opindex fprofile-generate
6068 Enable options usually used for instrumenting application to produce
6069 profile useful for later recompilation with profile feedback based
6070 optimization. You must use @option{-fprofile-generate} both when
6071 compiling and when linking your program.
6073 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
6076 @opindex fprofile-use
6077 Enable profile feedback directed optimizations, and optimizations
6078 generally profitable only with profile feedback available.
6080 The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt},
6081 @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}
6083 By default, GCC emits an error message if the feedback profiles do not
6084 match the source code. This error can be turned into a warning by using
6085 @option{-Wcoverage-mismatch}. Note this may result in poorly optimized
6089 The following options control compiler behavior regarding floating
6090 point arithmetic. These options trade off between speed and
6091 correctness. All must be specifically enabled.
6095 @opindex ffloat-store
6096 Do not store floating point variables in registers, and inhibit other
6097 options that might change whether a floating point value is taken from a
6100 @cindex floating point precision
6101 This option prevents undesirable excess precision on machines such as
6102 the 68000 where the floating registers (of the 68881) keep more
6103 precision than a @code{double} is supposed to have. Similarly for the
6104 x86 architecture. For most programs, the excess precision does only
6105 good, but a few programs rely on the precise definition of IEEE floating
6106 point. Use @option{-ffloat-store} for such programs, after modifying
6107 them to store all pertinent intermediate computations into variables.
6111 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
6112 @option{-fno-trapping-math}, @option{-ffinite-math-only},
6113 @option{-fno-rounding-math}, @option{-fno-signaling-nans},
6114 @option{-fno-signed-zeros} and @option{fcx-limited-range}.
6116 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
6118 This option is not turned on by any @option{-O} option since
6119 it can result in incorrect output for programs which depend on
6120 an exact implementation of IEEE or ISO rules/specifications for
6121 math functions. It may, however, yield faster code for programs
6122 that do not require the guarantees of these specifications.
6124 @item -fno-math-errno
6125 @opindex fno-math-errno
6126 Do not set ERRNO after calling math functions that are executed
6127 with a single instruction, e.g., sqrt. A program that relies on
6128 IEEE exceptions for math error handling may want to use this flag
6129 for speed while maintaining IEEE arithmetic compatibility.
6131 This option is not turned on by any @option{-O} option since
6132 it can result in incorrect output for programs which depend on
6133 an exact implementation of IEEE or ISO rules/specifications for
6134 math functions. It may, however, yield faster code for programs
6135 that do not require the guarantees of these specifications.
6137 The default is @option{-fmath-errno}.
6139 On Darwin systems, the math library never sets @code{errno}. There is
6140 therefore no reason for the compiler to consider the possibility that
6141 it might, and @option{-fno-math-errno} is the default.
6143 @item -funsafe-math-optimizations
6144 @opindex funsafe-math-optimizations
6145 Allow optimizations for floating-point arithmetic that (a) assume
6146 that arguments and results are valid and (b) may violate IEEE or
6147 ANSI standards. When used at link-time, it may include libraries
6148 or startup files that change the default FPU control word or other
6149 similar optimizations.
6151 This option is not turned on by any @option{-O} option since
6152 it can result in incorrect output for programs which depend on
6153 an exact implementation of IEEE or ISO rules/specifications for
6154 math functions. It may, however, yield faster code for programs
6155 that do not require the guarantees of these specifications.
6157 The default is @option{-fno-unsafe-math-optimizations}.
6159 @item -ffinite-math-only
6160 @opindex ffinite-math-only
6161 Allow optimizations for floating-point arithmetic that assume
6162 that arguments and results are not NaNs or +-Infs.
6164 This option is not turned on by any @option{-O} option since
6165 it can result in incorrect output for programs which depend on
6166 an exact implementation of IEEE or ISO rules/specifications for
6167 math functions. It may, however, yield faster code for programs
6168 that do not require the guarantees of these specifications.
6170 The default is @option{-fno-finite-math-only}.
6172 @item -fno-signed-zeros
6173 @opindex fno-signed-zeros
6174 Allow optimizations for floating point arithmetic that ignore the
6175 signedness of zero. IEEE arithmetic specifies the behavior of
6176 distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
6177 of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
6178 This option implies that the sign of a zero result isn't significant.
6180 The default is @option{-fsigned-zeros}.
6182 @item -fno-trapping-math
6183 @opindex fno-trapping-math
6184 Compile code assuming that floating-point operations cannot generate
6185 user-visible traps. These traps include division by zero, overflow,
6186 underflow, inexact result and invalid operation. This option implies
6187 @option{-fno-signaling-nans}. Setting this option may allow faster
6188 code if one relies on ``non-stop'' IEEE arithmetic, for example.
6190 This option should never be turned on by any @option{-O} option since
6191 it can result in incorrect output for programs which depend on
6192 an exact implementation of IEEE or ISO rules/specifications for
6195 The default is @option{-ftrapping-math}.
6197 @item -frounding-math
6198 @opindex frounding-math
6199 Disable transformations and optimizations that assume default floating
6200 point rounding behavior. This is round-to-zero for all floating point
6201 to integer conversions, and round-to-nearest for all other arithmetic
6202 truncations. This option should be specified for programs that change
6203 the FP rounding mode dynamically, or that may be executed with a
6204 non-default rounding mode. This option disables constant folding of
6205 floating point expressions at compile-time (which may be affected by
6206 rounding mode) and arithmetic transformations that are unsafe in the
6207 presence of sign-dependent rounding modes.
6209 The default is @option{-fno-rounding-math}.
6211 This option is experimental and does not currently guarantee to
6212 disable all GCC optimizations that are affected by rounding mode.
6213 Future versions of GCC may provide finer control of this setting
6214 using C99's @code{FENV_ACCESS} pragma. This command line option
6215 will be used to specify the default state for @code{FENV_ACCESS}.
6217 @item -frtl-abstract-sequences
6218 @opindex frtl-abstract-sequences
6219 It is a size optimization method. This option is to find identical
6220 sequences of code, which can be turned into pseudo-procedures and
6221 then replace all occurrences with calls to the newly created
6222 subroutine. It is kind of an opposite of @option{-finline-functions}.
6223 This optimization runs at RTL level.
6225 @item -fsignaling-nans
6226 @opindex fsignaling-nans
6227 Compile code assuming that IEEE signaling NaNs may generate user-visible
6228 traps during floating-point operations. Setting this option disables
6229 optimizations that may change the number of exceptions visible with
6230 signaling NaNs. This option implies @option{-ftrapping-math}.
6232 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
6235 The default is @option{-fno-signaling-nans}.
6237 This option is experimental and does not currently guarantee to
6238 disable all GCC optimizations that affect signaling NaN behavior.
6240 @item -fsingle-precision-constant
6241 @opindex fsingle-precision-constant
6242 Treat floating point constant as single precision constant instead of
6243 implicitly converting it to double precision constant.
6245 @item -fcx-limited-range
6246 @itemx -fno-cx-limited-range
6247 @opindex fcx-limited-range
6248 @opindex fno-cx-limited-range
6249 When enabled, this option states that a range reduction step is not
6250 needed when performing complex division. The default is
6251 @option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
6253 This option controls the default setting of the ISO C99
6254 @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
6259 The following options control optimizations that may improve
6260 performance, but are not enabled by any @option{-O} options. This
6261 section includes experimental options that may produce broken code.
6264 @item -fbranch-probabilities
6265 @opindex fbranch-probabilities
6266 After running a program compiled with @option{-fprofile-arcs}
6267 (@pxref{Debugging Options,, Options for Debugging Your Program or
6268 @command{gcc}}), you can compile it a second time using
6269 @option{-fbranch-probabilities}, to improve optimizations based on
6270 the number of times each branch was taken. When the program
6271 compiled with @option{-fprofile-arcs} exits it saves arc execution
6272 counts to a file called @file{@var{sourcename}.gcda} for each source
6273 file. The information in this data file is very dependent on the
6274 structure of the generated code, so you must use the same source code
6275 and the same optimization options for both compilations.
6277 With @option{-fbranch-probabilities}, GCC puts a
6278 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
6279 These can be used to improve optimization. Currently, they are only
6280 used in one place: in @file{reorg.c}, instead of guessing which path a
6281 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
6282 exactly determine which path is taken more often.
6284 @item -fprofile-values
6285 @opindex fprofile-values
6286 If combined with @option{-fprofile-arcs}, it adds code so that some
6287 data about values of expressions in the program is gathered.
6289 With @option{-fbranch-probabilities}, it reads back the data gathered
6290 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
6291 notes to instructions for their later usage in optimizations.
6293 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
6297 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
6298 a code to gather information about values of expressions.
6300 With @option{-fbranch-probabilities}, it reads back the data gathered
6301 and actually performs the optimizations based on them.
6302 Currently the optimizations include specialization of division operation
6303 using the knowledge about the value of the denominator.
6305 @item -frename-registers
6306 @opindex frename-registers
6307 Attempt to avoid false dependencies in scheduled code by making use
6308 of registers left over after register allocation. This optimization
6309 will most benefit processors with lots of registers. Depending on the
6310 debug information format adopted by the target, however, it can
6311 make debugging impossible, since variables will no longer stay in
6312 a ``home register''.
6314 Enabled by default with @option{-funroll-loops}.
6318 Perform tail duplication to enlarge superblock size. This transformation
6319 simplifies the control flow of the function allowing other optimizations to do
6322 Enabled with @option{-fprofile-use}.
6324 @item -funroll-loops
6325 @opindex funroll-loops
6326 Unroll loops whose number of iterations can be determined at compile time or
6327 upon entry to the loop. @option{-funroll-loops} implies
6328 @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
6329 It also turns on complete loop peeling (i.e.@: complete removal of loops with
6330 small constant number of iterations). This option makes code larger, and may
6331 or may not make it run faster.
6333 Enabled with @option{-fprofile-use}.
6335 @item -funroll-all-loops
6336 @opindex funroll-all-loops
6337 Unroll all loops, even if their number of iterations is uncertain when
6338 the loop is entered. This usually makes programs run more slowly.
6339 @option{-funroll-all-loops} implies the same options as
6340 @option{-funroll-loops}.
6343 @opindex fpeel-loops
6344 Peels the loops for that there is enough information that they do not
6345 roll much (from profile feedback). It also turns on complete loop peeling
6346 (i.e.@: complete removal of loops with small constant number of iterations).
6348 Enabled with @option{-fprofile-use}.
6350 @item -fmove-loop-invariants
6351 @opindex fmove-loop-invariants
6352 Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
6353 at level @option{-O1}
6355 @item -funswitch-loops
6356 @opindex funswitch-loops
6357 Move branches with loop invariant conditions out of the loop, with duplicates
6358 of the loop on both branches (modified according to result of the condition).
6360 @item -ffunction-sections
6361 @itemx -fdata-sections
6362 @opindex ffunction-sections
6363 @opindex fdata-sections
6364 Place each function or data item into its own section in the output
6365 file if the target supports arbitrary sections. The name of the
6366 function or the name of the data item determines the section's name
6369 Use these options on systems where the linker can perform optimizations
6370 to improve locality of reference in the instruction space. Most systems
6371 using the ELF object format and SPARC processors running Solaris 2 have
6372 linkers with such optimizations. AIX may have these optimizations in
6375 Only use these options when there are significant benefits from doing
6376 so. When you specify these options, the assembler and linker will
6377 create larger object and executable files and will also be slower.
6378 You will not be able to use @code{gprof} on all systems if you
6379 specify this option and you may have problems with debugging if
6380 you specify both this option and @option{-g}.
6382 @item -fbranch-target-load-optimize
6383 @opindex fbranch-target-load-optimize
6384 Perform branch target register load optimization before prologue / epilogue
6386 The use of target registers can typically be exposed only during reload,
6387 thus hoisting loads out of loops and doing inter-block scheduling needs
6388 a separate optimization pass.
6390 @item -fbranch-target-load-optimize2
6391 @opindex fbranch-target-load-optimize2
6392 Perform branch target register load optimization after prologue / epilogue
6395 @item -fbtr-bb-exclusive
6396 @opindex fbtr-bb-exclusive
6397 When performing branch target register load optimization, don't reuse
6398 branch target registers in within any basic block.
6400 @item -fstack-protector
6401 Emit extra code to check for buffer overflows, such as stack smashing
6402 attacks. This is done by adding a guard variable to functions with
6403 vulnerable objects. This includes functions that call alloca, and
6404 functions with buffers larger than 8 bytes. The guards are initialized
6405 when a function is entered and then checked when the function exits.
6406 If a guard check fails, an error message is printed and the program exits.
6408 @item -fstack-protector-all
6409 Like @option{-fstack-protector} except that all functions are protected.
6411 @item -fsection-anchors
6412 @opindex fsection-anchors
6413 Try to reduce the number of symbolic address calculations by using
6414 shared ``anchor'' symbols to address nearby objects. This transformation
6415 can help to reduce the number of GOT entries and GOT accesses on some
6418 For example, the implementation of the following function @code{foo}:
6422 int foo (void) @{ return a + b + c; @}
6425 would usually calculate the addresses of all three variables, but if you
6426 compile it with @option{-fsection-anchors}, it will access the variables
6427 from a common anchor point instead. The effect is similar to the
6428 following pseudocode (which isn't valid C):
6433 register int *xr = &x;
6434 return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
6438 Not all targets support this option.
6440 @item --param @var{name}=@var{value}
6442 In some places, GCC uses various constants to control the amount of
6443 optimization that is done. For example, GCC will not inline functions
6444 that contain more that a certain number of instructions. You can
6445 control some of these constants on the command-line using the
6446 @option{--param} option.
6448 The names of specific parameters, and the meaning of the values, are
6449 tied to the internals of the compiler, and are subject to change
6450 without notice in future releases.
6452 In each case, the @var{value} is an integer. The allowable choices for
6453 @var{name} are given in the following table:
6456 @item salias-max-implicit-fields
6457 The maximum number of fields in a variable without direct
6458 structure accesses for which structure aliasing will consider trying
6459 to track each field. The default is 5
6461 @item salias-max-array-elements
6462 The maximum number of elements an array can have and its elements
6463 still be tracked individually by structure aliasing. The default is 4
6465 @item sra-max-structure-size
6466 The maximum structure size, in bytes, at which the scalar replacement
6467 of aggregates (SRA) optimization will perform block copies. The
6468 default value, 0, implies that GCC will select the most appropriate
6471 @item sra-field-structure-ratio
6472 The threshold ratio (as a percentage) between instantiated fields and
6473 the complete structure size. We say that if the ratio of the number
6474 of bytes in instantiated fields to the number of bytes in the complete
6475 structure exceeds this parameter, then block copies are not used. The
6478 @item max-crossjump-edges
6479 The maximum number of incoming edges to consider for crossjumping.
6480 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
6481 the number of edges incoming to each block. Increasing values mean
6482 more aggressive optimization, making the compile time increase with
6483 probably small improvement in executable size.
6485 @item min-crossjump-insns
6486 The minimum number of instructions which must be matched at the end
6487 of two blocks before crossjumping will be performed on them. This
6488 value is ignored in the case where all instructions in the block being
6489 crossjumped from are matched. The default value is 5.
6491 @item max-grow-copy-bb-insns
6492 The maximum code size expansion factor when copying basic blocks
6493 instead of jumping. The expansion is relative to a jump instruction.
6494 The default value is 8.
6496 @item max-goto-duplication-insns
6497 The maximum number of instructions to duplicate to a block that jumps
6498 to a computed goto. To avoid @math{O(N^2)} behavior in a number of
6499 passes, GCC factors computed gotos early in the compilation process,
6500 and unfactors them as late as possible. Only computed jumps at the
6501 end of a basic blocks with no more than max-goto-duplication-insns are
6502 unfactored. The default value is 8.
6504 @item max-delay-slot-insn-search
6505 The maximum number of instructions to consider when looking for an
6506 instruction to fill a delay slot. If more than this arbitrary number of
6507 instructions is searched, the time savings from filling the delay slot
6508 will be minimal so stop searching. Increasing values mean more
6509 aggressive optimization, making the compile time increase with probably
6510 small improvement in executable run time.
6512 @item max-delay-slot-live-search
6513 When trying to fill delay slots, the maximum number of instructions to
6514 consider when searching for a block with valid live register
6515 information. Increasing this arbitrarily chosen value means more
6516 aggressive optimization, increasing the compile time. This parameter
6517 should be removed when the delay slot code is rewritten to maintain the
6520 @item max-gcse-memory
6521 The approximate maximum amount of memory that will be allocated in
6522 order to perform the global common subexpression elimination
6523 optimization. If more memory than specified is required, the
6524 optimization will not be done.
6526 @item max-gcse-passes
6527 The maximum number of passes of GCSE to run. The default is 1.
6529 @item max-pending-list-length
6530 The maximum number of pending dependencies scheduling will allow
6531 before flushing the current state and starting over. Large functions
6532 with few branches or calls can create excessively large lists which
6533 needlessly consume memory and resources.
6535 @item max-inline-insns-single
6536 Several parameters control the tree inliner used in gcc.
6537 This number sets the maximum number of instructions (counted in GCC's
6538 internal representation) in a single function that the tree inliner
6539 will consider for inlining. This only affects functions declared
6540 inline and methods implemented in a class declaration (C++).
6541 The default value is 450.
6543 @item max-inline-insns-auto
6544 When you use @option{-finline-functions} (included in @option{-O3}),
6545 a lot of functions that would otherwise not be considered for inlining
6546 by the compiler will be investigated. To those functions, a different
6547 (more restrictive) limit compared to functions declared inline can
6549 The default value is 90.
6551 @item large-function-insns
6552 The limit specifying really large functions. For functions larger than this
6553 limit after inlining inlining is constrained by
6554 @option{--param large-function-growth}. This parameter is useful primarily
6555 to avoid extreme compilation time caused by non-linear algorithms used by the
6557 This parameter is ignored when @option{-funit-at-a-time} is not used.
6558 The default value is 2700.
6560 @item large-function-growth
6561 Specifies maximal growth of large function caused by inlining in percents.
6562 This parameter is ignored when @option{-funit-at-a-time} is not used.
6563 The default value is 100 which limits large function growth to 2.0 times
6566 @item large-unit-insns
6567 The limit specifying large translation unit. Growth caused by inlining of
6568 units larger than this limit is limited by @option{--param inline-unit-growth}.
6569 For small units this might be too tight (consider unit consisting of function A
6570 that is inline and B that just calls A three time. If B is small relative to
6571 A, the growth of unit is 300\% and yet such inlining is very sane. For very
6572 large units consisting of small inlininable functions however the overall unit
6573 growth limit is needed to avoid exponential explosion of code size. Thus for
6574 smaller units, the size is increased to @option{--param large-unit-insns}
6575 before applying @option{--param inline-unit-growth}. The default is 10000
6577 @item inline-unit-growth
6578 Specifies maximal overall growth of the compilation unit caused by inlining.
6579 This parameter is ignored when @option{-funit-at-a-time} is not used.
6580 The default value is 30 which limits unit growth to 1.3 times the original
6583 @item large-stack-frame
6584 The limit specifying large stack frames. While inlining the algorithm is trying
6585 to not grow past this limit too much. Default value is 256 bytes.
6587 @item large-stack-frame-growth
6588 Specifies maximal growth of large stack frames caused by inlining in percents.
6589 The default value is 1000 which limits large stack frame growth to 11 times
6592 @item max-inline-insns-recursive
6593 @itemx max-inline-insns-recursive-auto
6594 Specifies maximum number of instructions out-of-line copy of self recursive inline
6595 function can grow into by performing recursive inlining.
6597 For functions declared inline @option{--param max-inline-insns-recursive} is
6598 taken into account. For function not declared inline, recursive inlining
6599 happens only when @option{-finline-functions} (included in @option{-O3}) is
6600 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
6601 default value is 450.
6603 @item max-inline-recursive-depth
6604 @itemx max-inline-recursive-depth-auto
6605 Specifies maximum recursion depth used by the recursive inlining.
6607 For functions declared inline @option{--param max-inline-recursive-depth} is
6608 taken into account. For function not declared inline, recursive inlining
6609 happens only when @option{-finline-functions} (included in @option{-O3}) is
6610 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
6611 default value is 450.
6613 @item min-inline-recursive-probability
6614 Recursive inlining is profitable only for function having deep recursion
6615 in average and can hurt for function having little recursion depth by
6616 increasing the prologue size or complexity of function body to other
6619 When profile feedback is available (see @option{-fprofile-generate}) the actual
6620 recursion depth can be guessed from probability that function will recurse via
6621 given call expression. This parameter limits inlining only to call expression
6622 whose probability exceeds given threshold (in percents). The default value is
6625 @item inline-call-cost
6626 Specify cost of call instruction relative to simple arithmetics operations
6627 (having cost of 1). Increasing this cost disqualifies inlining of non-leaf
6628 functions and at the same time increases size of leaf function that is believed to
6629 reduce function size by being inlined. In effect it increases amount of
6630 inlining for code having large abstraction penalty (many functions that just
6631 pass the arguments to other functions) and decrease inlining for code with low
6632 abstraction penalty. The default value is 16.
6634 @item min-vect-loop-bound
6635 The minimum number of iterations under which a loop will not get vectorized
6636 when @option{-ftree-vectorize} is used. The number of iterations after
6637 vectorization needs to be greater than the value specified by this option
6638 to allow vectorization. The default value is 0.
6640 @item max-unrolled-insns
6641 The maximum number of instructions that a loop should have if that loop
6642 is unrolled, and if the loop is unrolled, it determines how many times
6643 the loop code is unrolled.
6645 @item max-average-unrolled-insns
6646 The maximum number of instructions biased by probabilities of their execution
6647 that a loop should have if that loop is unrolled, and if the loop is unrolled,
6648 it determines how many times the loop code is unrolled.
6650 @item max-unroll-times
6651 The maximum number of unrollings of a single loop.
6653 @item max-peeled-insns
6654 The maximum number of instructions that a loop should have if that loop
6655 is peeled, and if the loop is peeled, it determines how many times
6656 the loop code is peeled.
6658 @item max-peel-times
6659 The maximum number of peelings of a single loop.
6661 @item max-completely-peeled-insns
6662 The maximum number of insns of a completely peeled loop.
6664 @item max-completely-peel-times
6665 The maximum number of iterations of a loop to be suitable for complete peeling.
6667 @item max-unswitch-insns
6668 The maximum number of insns of an unswitched loop.
6670 @item max-unswitch-level
6671 The maximum number of branches unswitched in a single loop.
6674 The minimum cost of an expensive expression in the loop invariant motion.
6676 @item iv-consider-all-candidates-bound
6677 Bound on number of candidates for induction variables below that
6678 all candidates are considered for each use in induction variable
6679 optimizations. Only the most relevant candidates are considered
6680 if there are more candidates, to avoid quadratic time complexity.
6682 @item iv-max-considered-uses
6683 The induction variable optimizations give up on loops that contain more
6684 induction variable uses.
6686 @item iv-always-prune-cand-set-bound
6687 If number of candidates in the set is smaller than this value,
6688 we always try to remove unnecessary ivs from the set during its
6689 optimization when a new iv is added to the set.
6691 @item scev-max-expr-size
6692 Bound on size of expressions used in the scalar evolutions analyzer.
6693 Large expressions slow the analyzer.
6695 @item omega-max-vars
6696 The maximum number of variables in an Omega constraint system.
6697 The default value is 128.
6699 @item omega-max-geqs
6700 The maximum number of inequalities in an Omega constraint system.
6701 The default value is 256.
6704 The maximum number of equalities in an Omega constraint system.
6705 The default value is 128.
6707 @item omega-max-wild-cards
6708 The maximum number of wildcard variables that the Omega solver will
6709 be able to insert. The default value is 18.
6711 @item omega-hash-table-size
6712 The size of the hash table in the Omega solver. The default value is
6715 @item omega-max-keys
6716 The maximal number of keys used by the Omega solver. The default
6719 @item omega-eliminate-redundant-constraints
6720 When set to 1, use expensive methods to eliminate all redundant
6721 constraints. The default value is 0.
6723 @item vect-max-version-checks
6724 The maximum number of runtime checks that can be performed when doing
6725 loop versioning in the vectorizer. See option ftree-vect-loop-version
6726 for more information.
6728 @item max-iterations-to-track
6730 The maximum number of iterations of a loop the brute force algorithm
6731 for analysis of # of iterations of the loop tries to evaluate.
6733 @item hot-bb-count-fraction
6734 Select fraction of the maximal count of repetitions of basic block in program
6735 given basic block needs to have to be considered hot.
6737 @item hot-bb-frequency-fraction
6738 Select fraction of the maximal frequency of executions of basic block in
6739 function given basic block needs to have to be considered hot
6741 @item max-predicted-iterations
6742 The maximum number of loop iterations we predict statically. This is useful
6743 in cases where function contain single loop with known bound and other loop
6744 with unknown. We predict the known number of iterations correctly, while
6745 the unknown number of iterations average to roughly 10. This means that the
6746 loop without bounds would appear artificially cold relative to the other one.
6748 @item tracer-dynamic-coverage
6749 @itemx tracer-dynamic-coverage-feedback
6751 This value is used to limit superblock formation once the given percentage of
6752 executed instructions is covered. This limits unnecessary code size
6755 The @option{tracer-dynamic-coverage-feedback} is used only when profile
6756 feedback is available. The real profiles (as opposed to statically estimated
6757 ones) are much less balanced allowing the threshold to be larger value.
6759 @item tracer-max-code-growth
6760 Stop tail duplication once code growth has reached given percentage. This is
6761 rather hokey argument, as most of the duplicates will be eliminated later in
6762 cross jumping, so it may be set to much higher values than is the desired code
6765 @item tracer-min-branch-ratio
6767 Stop reverse growth when the reverse probability of best edge is less than this
6768 threshold (in percent).
6770 @item tracer-min-branch-ratio
6771 @itemx tracer-min-branch-ratio-feedback
6773 Stop forward growth if the best edge do have probability lower than this
6776 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
6777 compilation for profile feedback and one for compilation without. The value
6778 for compilation with profile feedback needs to be more conservative (higher) in
6779 order to make tracer effective.
6781 @item max-cse-path-length
6783 Maximum number of basic blocks on path that cse considers. The default is 10.
6786 The maximum instructions CSE process before flushing. The default is 1000.
6788 @item max-aliased-vops
6790 Maximum number of virtual operands per function allowed to represent
6791 aliases before triggering the alias partitioning heuristic. Alias
6792 partitioning reduces compile times and memory consumption needed for
6793 aliasing at the expense of precision loss in alias information. The
6794 default value for this parameter is 100 for -O1, 500 for -O2 and 1000
6797 Notice that if a function contains more memory statements than the
6798 value of this parameter, it is not really possible to achieve this
6799 reduction. In this case, the compiler will use the number of memory
6800 statements as the value for @option{max-aliased-vops}.
6802 @item avg-aliased-vops
6804 Average number of virtual operands per statement allowed to represent
6805 aliases before triggering the alias partitioning heuristic. This
6806 works in conjunction with @option{max-aliased-vops}. If a function
6807 contains more than @option{max-aliased-vops} virtual operators, then
6808 memory symbols will be grouped into memory partitions until either the
6809 total number of virtual operators is below @option{max-aliased-vops}
6810 or the average number of virtual operators per memory statement is
6811 below @option{avg-aliased-vops}. The default value for this parameter
6812 is 1 for -O1 and -O2, and 3 for -O3.
6814 @item ggc-min-expand
6816 GCC uses a garbage collector to manage its own memory allocation. This
6817 parameter specifies the minimum percentage by which the garbage
6818 collector's heap should be allowed to expand between collections.
6819 Tuning this may improve compilation speed; it has no effect on code
6822 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
6823 RAM >= 1GB@. If @code{getrlimit} is available, the notion of "RAM" is
6824 the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
6825 GCC is not able to calculate RAM on a particular platform, the lower
6826 bound of 30% is used. Setting this parameter and
6827 @option{ggc-min-heapsize} to zero causes a full collection to occur at
6828 every opportunity. This is extremely slow, but can be useful for
6831 @item ggc-min-heapsize
6833 Minimum size of the garbage collector's heap before it begins bothering
6834 to collect garbage. The first collection occurs after the heap expands
6835 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
6836 tuning this may improve compilation speed, and has no effect on code
6839 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
6840 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
6841 with a lower bound of 4096 (four megabytes) and an upper bound of
6842 131072 (128 megabytes). If GCC is not able to calculate RAM on a
6843 particular platform, the lower bound is used. Setting this parameter
6844 very large effectively disables garbage collection. Setting this
6845 parameter and @option{ggc-min-expand} to zero causes a full collection
6846 to occur at every opportunity.
6848 @item max-reload-search-insns
6849 The maximum number of instruction reload should look backward for equivalent
6850 register. Increasing values mean more aggressive optimization, making the
6851 compile time increase with probably slightly better performance. The default
6854 @item max-cselib-memory-locations
6855 The maximum number of memory locations cselib should take into account.
6856 Increasing values mean more aggressive optimization, making the compile time
6857 increase with probably slightly better performance. The default value is 500.
6859 @item max-flow-memory-locations
6860 Similar as @option{max-cselib-memory-locations} but for dataflow liveness.
6861 The default value is 100.
6863 @item reorder-blocks-duplicate
6864 @itemx reorder-blocks-duplicate-feedback
6866 Used by basic block reordering pass to decide whether to use unconditional
6867 branch or duplicate the code on its destination. Code is duplicated when its
6868 estimated size is smaller than this value multiplied by the estimated size of
6869 unconditional jump in the hot spots of the program.
6871 The @option{reorder-block-duplicate-feedback} is used only when profile
6872 feedback is available and may be set to higher values than
6873 @option{reorder-block-duplicate} since information about the hot spots is more
6876 @item max-sched-ready-insns
6877 The maximum number of instructions ready to be issued the scheduler should
6878 consider at any given time during the first scheduling pass. Increasing
6879 values mean more thorough searches, making the compilation time increase
6880 with probably little benefit. The default value is 100.
6882 @item max-sched-region-blocks
6883 The maximum number of blocks in a region to be considered for
6884 interblock scheduling. The default value is 10.
6886 @item max-sched-region-insns
6887 The maximum number of insns in a region to be considered for
6888 interblock scheduling. The default value is 100.
6891 The minimum probability (in percents) of reaching a source block
6892 for interblock speculative scheduling. The default value is 40.
6894 @item max-sched-extend-regions-iters
6895 The maximum number of iterations through CFG to extend regions.
6896 0 - disable region extension,
6897 N - do at most N iterations.
6898 The default value is 0.
6900 @item max-sched-insn-conflict-delay
6901 The maximum conflict delay for an insn to be considered for speculative motion.
6902 The default value is 3.
6904 @item sched-spec-prob-cutoff
6905 The minimal probability of speculation success (in percents), so that
6906 speculative insn will be scheduled.
6907 The default value is 40.
6909 @item max-last-value-rtl
6911 The maximum size measured as number of RTLs that can be recorded in an expression
6912 in combiner for a pseudo register as last known value of that register. The default
6915 @item integer-share-limit
6916 Small integer constants can use a shared data structure, reducing the
6917 compiler's memory usage and increasing its speed. This sets the maximum
6918 value of a shared integer constant's. The default value is 256.
6920 @item min-virtual-mappings
6921 Specifies the minimum number of virtual mappings in the incremental
6922 SSA updater that should be registered to trigger the virtual mappings
6923 heuristic defined by virtual-mappings-ratio. The default value is
6926 @item virtual-mappings-ratio
6927 If the number of virtual mappings is virtual-mappings-ratio bigger
6928 than the number of virtual symbols to be updated, then the incremental
6929 SSA updater switches to a full update for those symbols. The default
6932 @item ssp-buffer-size
6933 The minimum size of buffers (i.e. arrays) that will receive stack smashing
6934 protection when @option{-fstack-protection} is used.
6936 @item max-jump-thread-duplication-stmts
6937 Maximum number of statements allowed in a block that needs to be
6938 duplicated when threading jumps.
6940 @item max-fields-for-field-sensitive
6941 Maximum number of fields in a structure we will treat in
6942 a field sensitive manner during pointer analysis.
6944 @item prefetch-latency
6945 Estimate on average number of instructions that are executed before
6946 prefetch finishes. The distance we prefetch ahead is proportional
6947 to this constant. Increasing this number may also lead to less
6948 streams being prefetched (see @option{simultaneous-prefetches}).
6950 @item simultaneous-prefetches
6951 Maximum number of prefetches that can run at the same time.
6953 @item l1-cache-line-size
6954 The size of cache line in L1 cache, in bytes.
6957 The number of cache lines in L1 cache.
6959 @item verify-canonical-types
6960 Whether the compiler should verify the ``canonical'' types used for
6961 type equality comparisons within the C++ and Objective-C++ front
6962 ends. Set to 1 (the default when GCC is configured with
6963 --enable-checking) to enable verification, 0 to disable verification
6964 (the default when GCC is configured with --disable-checking).
6969 @node Preprocessor Options
6970 @section Options Controlling the Preprocessor
6971 @cindex preprocessor options
6972 @cindex options, preprocessor
6974 These options control the C preprocessor, which is run on each C source
6975 file before actual compilation.
6977 If you use the @option{-E} option, nothing is done except preprocessing.
6978 Some of these options make sense only together with @option{-E} because
6979 they cause the preprocessor output to be unsuitable for actual
6984 You can use @option{-Wp,@var{option}} to bypass the compiler driver
6985 and pass @var{option} directly through to the preprocessor. If
6986 @var{option} contains commas, it is split into multiple options at the
6987 commas. However, many options are modified, translated or interpreted
6988 by the compiler driver before being passed to the preprocessor, and
6989 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
6990 interface is undocumented and subject to change, so whenever possible
6991 you should avoid using @option{-Wp} and let the driver handle the
6994 @item -Xpreprocessor @var{option}
6995 @opindex preprocessor
6996 Pass @var{option} as an option to the preprocessor. You can use this to
6997 supply system-specific preprocessor options which GCC does not know how to
7000 If you want to pass an option that takes an argument, you must use
7001 @option{-Xpreprocessor} twice, once for the option and once for the argument.
7004 @include cppopts.texi
7006 @node Assembler Options
7007 @section Passing Options to the Assembler
7009 @c prevent bad page break with this line
7010 You can pass options to the assembler.
7013 @item -Wa,@var{option}
7015 Pass @var{option} as an option to the assembler. If @var{option}
7016 contains commas, it is split into multiple options at the commas.
7018 @item -Xassembler @var{option}
7020 Pass @var{option} as an option to the assembler. You can use this to
7021 supply system-specific assembler options which GCC does not know how to
7024 If you want to pass an option that takes an argument, you must use
7025 @option{-Xassembler} twice, once for the option and once for the argument.
7030 @section Options for Linking
7031 @cindex link options
7032 @cindex options, linking
7034 These options come into play when the compiler links object files into
7035 an executable output file. They are meaningless if the compiler is
7036 not doing a link step.
7040 @item @var{object-file-name}
7041 A file name that does not end in a special recognized suffix is
7042 considered to name an object file or library. (Object files are
7043 distinguished from libraries by the linker according to the file
7044 contents.) If linking is done, these object files are used as input
7053 If any of these options is used, then the linker is not run, and
7054 object file names should not be used as arguments. @xref{Overall
7058 @item -l@var{library}
7059 @itemx -l @var{library}
7061 Search the library named @var{library} when linking. (The second
7062 alternative with the library as a separate argument is only for
7063 POSIX compliance and is not recommended.)
7065 It makes a difference where in the command you write this option; the
7066 linker searches and processes libraries and object files in the order they
7067 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
7068 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
7069 to functions in @samp{z}, those functions may not be loaded.
7071 The linker searches a standard list of directories for the library,
7072 which is actually a file named @file{lib@var{library}.a}. The linker
7073 then uses this file as if it had been specified precisely by name.
7075 The directories searched include several standard system directories
7076 plus any that you specify with @option{-L}.
7078 Normally the files found this way are library files---archive files
7079 whose members are object files. The linker handles an archive file by
7080 scanning through it for members which define symbols that have so far
7081 been referenced but not defined. But if the file that is found is an
7082 ordinary object file, it is linked in the usual fashion. The only
7083 difference between using an @option{-l} option and specifying a file name
7084 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
7085 and searches several directories.
7089 You need this special case of the @option{-l} option in order to
7090 link an Objective-C or Objective-C++ program.
7093 @opindex nostartfiles
7094 Do not use the standard system startup files when linking.
7095 The standard system libraries are used normally, unless @option{-nostdlib}
7096 or @option{-nodefaultlibs} is used.
7098 @item -nodefaultlibs
7099 @opindex nodefaultlibs
7100 Do not use the standard system libraries when linking.
7101 Only the libraries you specify will be passed to the linker.
7102 The standard startup files are used normally, unless @option{-nostartfiles}
7103 is used. The compiler may generate calls to @code{memcmp},
7104 @code{memset}, @code{memcpy} and @code{memmove}.
7105 These entries are usually resolved by entries in
7106 libc. These entry points should be supplied through some other
7107 mechanism when this option is specified.
7111 Do not use the standard system startup files or libraries when linking.
7112 No startup files and only the libraries you specify will be passed to
7113 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
7114 @code{memcpy} and @code{memmove}.
7115 These entries are usually resolved by entries in
7116 libc. These entry points should be supplied through some other
7117 mechanism when this option is specified.
7119 @cindex @option{-lgcc}, use with @option{-nostdlib}
7120 @cindex @option{-nostdlib} and unresolved references
7121 @cindex unresolved references and @option{-nostdlib}
7122 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
7123 @cindex @option{-nodefaultlibs} and unresolved references
7124 @cindex unresolved references and @option{-nodefaultlibs}
7125 One of the standard libraries bypassed by @option{-nostdlib} and
7126 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
7127 that GCC uses to overcome shortcomings of particular machines, or special
7128 needs for some languages.
7129 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
7130 Collection (GCC) Internals},
7131 for more discussion of @file{libgcc.a}.)
7132 In most cases, you need @file{libgcc.a} even when you want to avoid
7133 other standard libraries. In other words, when you specify @option{-nostdlib}
7134 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
7135 This ensures that you have no unresolved references to internal GCC
7136 library subroutines. (For example, @samp{__main}, used to ensure C++
7137 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
7138 GNU Compiler Collection (GCC) Internals}.)
7142 Produce a position independent executable on targets which support it.
7143 For predictable results, you must also specify the same set of options
7144 that were used to generate code (@option{-fpie}, @option{-fPIE},
7145 or model suboptions) when you specify this option.
7149 Pass the flag @option{-export-dynamic} to the ELF linker, on targets
7150 that support it. This instructs the linker to add all symbols, not
7151 only used ones, to the dynamic symbol table. This option is needed
7152 for some uses of @code{dlopen} or to allow obtaining backtraces
7153 from within a program.
7157 Remove all symbol table and relocation information from the executable.
7161 On systems that support dynamic linking, this prevents linking with the shared
7162 libraries. On other systems, this option has no effect.
7166 Produce a shared object which can then be linked with other objects to
7167 form an executable. Not all systems support this option. For predictable
7168 results, you must also specify the same set of options that were used to
7169 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
7170 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
7171 needs to build supplementary stub code for constructors to work. On
7172 multi-libbed systems, @samp{gcc -shared} must select the correct support
7173 libraries to link against. Failing to supply the correct flags may lead
7174 to subtle defects. Supplying them in cases where they are not necessary
7177 @item -shared-libgcc
7178 @itemx -static-libgcc
7179 @opindex shared-libgcc
7180 @opindex static-libgcc
7181 On systems that provide @file{libgcc} as a shared library, these options
7182 force the use of either the shared or static version respectively.
7183 If no shared version of @file{libgcc} was built when the compiler was
7184 configured, these options have no effect.
7186 There are several situations in which an application should use the
7187 shared @file{libgcc} instead of the static version. The most common
7188 of these is when the application wishes to throw and catch exceptions
7189 across different shared libraries. In that case, each of the libraries
7190 as well as the application itself should use the shared @file{libgcc}.
7192 Therefore, the G++ and GCJ drivers automatically add
7193 @option{-shared-libgcc} whenever you build a shared library or a main
7194 executable, because C++ and Java programs typically use exceptions, so
7195 this is the right thing to do.
7197 If, instead, you use the GCC driver to create shared libraries, you may
7198 find that they will not always be linked with the shared @file{libgcc}.
7199 If GCC finds, at its configuration time, that you have a non-GNU linker
7200 or a GNU linker that does not support option @option{--eh-frame-hdr},
7201 it will link the shared version of @file{libgcc} into shared libraries
7202 by default. Otherwise, it will take advantage of the linker and optimize
7203 away the linking with the shared version of @file{libgcc}, linking with
7204 the static version of libgcc by default. This allows exceptions to
7205 propagate through such shared libraries, without incurring relocation
7206 costs at library load time.
7208 However, if a library or main executable is supposed to throw or catch
7209 exceptions, you must link it using the G++ or GCJ driver, as appropriate
7210 for the languages used in the program, or using the option
7211 @option{-shared-libgcc}, such that it is linked with the shared
7216 Bind references to global symbols when building a shared object. Warn
7217 about any unresolved references (unless overridden by the link editor
7218 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
7221 @item -Xlinker @var{option}
7223 Pass @var{option} as an option to the linker. You can use this to
7224 supply system-specific linker options which GCC does not know how to
7227 If you want to pass an option that takes an argument, you must use
7228 @option{-Xlinker} twice, once for the option and once for the argument.
7229 For example, to pass @option{-assert definitions}, you must write
7230 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
7231 @option{-Xlinker "-assert definitions"}, because this passes the entire
7232 string as a single argument, which is not what the linker expects.
7234 @item -Wl,@var{option}
7236 Pass @var{option} as an option to the linker. If @var{option} contains
7237 commas, it is split into multiple options at the commas.
7239 @item -u @var{symbol}
7241 Pretend the symbol @var{symbol} is undefined, to force linking of
7242 library modules to define it. You can use @option{-u} multiple times with
7243 different symbols to force loading of additional library modules.
7246 @node Directory Options
7247 @section Options for Directory Search
7248 @cindex directory options
7249 @cindex options, directory search
7252 These options specify directories to search for header files, for
7253 libraries and for parts of the compiler:
7258 Add the directory @var{dir} to the head of the list of directories to be
7259 searched for header files. This can be used to override a system header
7260 file, substituting your own version, since these directories are
7261 searched before the system header file directories. However, you should
7262 not use this option to add directories that contain vendor-supplied
7263 system header files (use @option{-isystem} for that). If you use more than
7264 one @option{-I} option, the directories are scanned in left-to-right
7265 order; the standard system directories come after.
7267 If a standard system include directory, or a directory specified with
7268 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
7269 option will be ignored. The directory will still be searched but as a
7270 system directory at its normal position in the system include chain.
7271 This is to ensure that GCC's procedure to fix buggy system headers and
7272 the ordering for the include_next directive are not inadvertently changed.
7273 If you really need to change the search order for system directories,
7274 use the @option{-nostdinc} and/or @option{-isystem} options.
7276 @item -iquote@var{dir}
7278 Add the directory @var{dir} to the head of the list of directories to
7279 be searched for header files only for the case of @samp{#include
7280 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
7281 otherwise just like @option{-I}.
7285 Add directory @var{dir} to the list of directories to be searched
7288 @item -B@var{prefix}
7290 This option specifies where to find the executables, libraries,
7291 include files, and data files of the compiler itself.
7293 The compiler driver program runs one or more of the subprograms
7294 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
7295 @var{prefix} as a prefix for each program it tries to run, both with and
7296 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
7298 For each subprogram to be run, the compiler driver first tries the
7299 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
7300 was not specified, the driver tries two standard prefixes, which are
7301 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
7302 those results in a file name that is found, the unmodified program
7303 name is searched for using the directories specified in your
7304 @env{PATH} environment variable.
7306 The compiler will check to see if the path provided by the @option{-B}
7307 refers to a directory, and if necessary it will add a directory
7308 separator character at the end of the path.
7310 @option{-B} prefixes that effectively specify directory names also apply
7311 to libraries in the linker, because the compiler translates these
7312 options into @option{-L} options for the linker. They also apply to
7313 includes files in the preprocessor, because the compiler translates these
7314 options into @option{-isystem} options for the preprocessor. In this case,
7315 the compiler appends @samp{include} to the prefix.
7317 The run-time support file @file{libgcc.a} can also be searched for using
7318 the @option{-B} prefix, if needed. If it is not found there, the two
7319 standard prefixes above are tried, and that is all. The file is left
7320 out of the link if it is not found by those means.
7322 Another way to specify a prefix much like the @option{-B} prefix is to use
7323 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
7326 As a special kludge, if the path provided by @option{-B} is
7327 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
7328 9, then it will be replaced by @file{[dir/]include}. This is to help
7329 with boot-strapping the compiler.
7331 @item -specs=@var{file}
7333 Process @var{file} after the compiler reads in the standard @file{specs}
7334 file, in order to override the defaults that the @file{gcc} driver
7335 program uses when determining what switches to pass to @file{cc1},
7336 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
7337 @option{-specs=@var{file}} can be specified on the command line, and they
7338 are processed in order, from left to right.
7340 @item --sysroot=@var{dir}
7342 Use @var{dir} as the logical root directory for headers and libraries.
7343 For example, if the compiler would normally search for headers in
7344 @file{/usr/include} and libraries in @file{/usr/lib}, it will instead
7345 search @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
7347 If you use both this option and the @option{-isysroot} option, then
7348 the @option{--sysroot} option will apply to libraries, but the
7349 @option{-isysroot} option will apply to header files.
7351 The GNU linker (beginning with version 2.16) has the necessary support
7352 for this option. If your linker does not support this option, the
7353 header file aspect of @option{--sysroot} will still work, but the
7354 library aspect will not.
7358 This option has been deprecated. Please use @option{-iquote} instead for
7359 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
7360 Any directories you specify with @option{-I} options before the @option{-I-}
7361 option are searched only for the case of @samp{#include "@var{file}"};
7362 they are not searched for @samp{#include <@var{file}>}.
7364 If additional directories are specified with @option{-I} options after
7365 the @option{-I-}, these directories are searched for all @samp{#include}
7366 directives. (Ordinarily @emph{all} @option{-I} directories are used
7369 In addition, the @option{-I-} option inhibits the use of the current
7370 directory (where the current input file came from) as the first search
7371 directory for @samp{#include "@var{file}"}. There is no way to
7372 override this effect of @option{-I-}. With @option{-I.} you can specify
7373 searching the directory which was current when the compiler was
7374 invoked. That is not exactly the same as what the preprocessor does
7375 by default, but it is often satisfactory.
7377 @option{-I-} does not inhibit the use of the standard system directories
7378 for header files. Thus, @option{-I-} and @option{-nostdinc} are
7385 @section Specifying subprocesses and the switches to pass to them
7388 @command{gcc} is a driver program. It performs its job by invoking a
7389 sequence of other programs to do the work of compiling, assembling and
7390 linking. GCC interprets its command-line parameters and uses these to
7391 deduce which programs it should invoke, and which command-line options
7392 it ought to place on their command lines. This behavior is controlled
7393 by @dfn{spec strings}. In most cases there is one spec string for each
7394 program that GCC can invoke, but a few programs have multiple spec
7395 strings to control their behavior. The spec strings built into GCC can
7396 be overridden by using the @option{-specs=} command-line switch to specify
7399 @dfn{Spec files} are plaintext files that are used to construct spec
7400 strings. They consist of a sequence of directives separated by blank
7401 lines. The type of directive is determined by the first non-whitespace
7402 character on the line and it can be one of the following:
7405 @item %@var{command}
7406 Issues a @var{command} to the spec file processor. The commands that can
7410 @item %include <@var{file}>
7412 Search for @var{file} and insert its text at the current point in the
7415 @item %include_noerr <@var{file}>
7416 @cindex %include_noerr
7417 Just like @samp{%include}, but do not generate an error message if the include
7418 file cannot be found.
7420 @item %rename @var{old_name} @var{new_name}
7422 Rename the spec string @var{old_name} to @var{new_name}.
7426 @item *[@var{spec_name}]:
7427 This tells the compiler to create, override or delete the named spec
7428 string. All lines after this directive up to the next directive or
7429 blank line are considered to be the text for the spec string. If this
7430 results in an empty string then the spec will be deleted. (Or, if the
7431 spec did not exist, then nothing will happened.) Otherwise, if the spec
7432 does not currently exist a new spec will be created. If the spec does
7433 exist then its contents will be overridden by the text of this
7434 directive, unless the first character of that text is the @samp{+}
7435 character, in which case the text will be appended to the spec.
7437 @item [@var{suffix}]:
7438 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
7439 and up to the next directive or blank line are considered to make up the
7440 spec string for the indicated suffix. When the compiler encounters an
7441 input file with the named suffix, it will processes the spec string in
7442 order to work out how to compile that file. For example:
7449 This says that any input file whose name ends in @samp{.ZZ} should be
7450 passed to the program @samp{z-compile}, which should be invoked with the
7451 command-line switch @option{-input} and with the result of performing the
7452 @samp{%i} substitution. (See below.)
7454 As an alternative to providing a spec string, the text that follows a
7455 suffix directive can be one of the following:
7458 @item @@@var{language}
7459 This says that the suffix is an alias for a known @var{language}. This is
7460 similar to using the @option{-x} command-line switch to GCC to specify a
7461 language explicitly. For example:
7468 Says that .ZZ files are, in fact, C++ source files.
7471 This causes an error messages saying:
7474 @var{name} compiler not installed on this system.
7478 GCC already has an extensive list of suffixes built into it.
7479 This directive will add an entry to the end of the list of suffixes, but
7480 since the list is searched from the end backwards, it is effectively
7481 possible to override earlier entries using this technique.
7485 GCC has the following spec strings built into it. Spec files can
7486 override these strings or create their own. Note that individual
7487 targets can also add their own spec strings to this list.
7490 asm Options to pass to the assembler
7491 asm_final Options to pass to the assembler post-processor
7492 cpp Options to pass to the C preprocessor
7493 cc1 Options to pass to the C compiler
7494 cc1plus Options to pass to the C++ compiler
7495 endfile Object files to include at the end of the link
7496 link Options to pass to the linker
7497 lib Libraries to include on the command line to the linker
7498 libgcc Decides which GCC support library to pass to the linker
7499 linker Sets the name of the linker
7500 predefines Defines to be passed to the C preprocessor
7501 signed_char Defines to pass to CPP to say whether @code{char} is signed
7503 startfile Object files to include at the start of the link
7506 Here is a small example of a spec file:
7512 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
7515 This example renames the spec called @samp{lib} to @samp{old_lib} and
7516 then overrides the previous definition of @samp{lib} with a new one.
7517 The new definition adds in some extra command-line options before
7518 including the text of the old definition.
7520 @dfn{Spec strings} are a list of command-line options to be passed to their
7521 corresponding program. In addition, the spec strings can contain
7522 @samp{%}-prefixed sequences to substitute variable text or to
7523 conditionally insert text into the command line. Using these constructs
7524 it is possible to generate quite complex command lines.
7526 Here is a table of all defined @samp{%}-sequences for spec
7527 strings. Note that spaces are not generated automatically around the
7528 results of expanding these sequences. Therefore you can concatenate them
7529 together or combine them with constant text in a single argument.
7533 Substitute one @samp{%} into the program name or argument.
7536 Substitute the name of the input file being processed.
7539 Substitute the basename of the input file being processed.
7540 This is the substring up to (and not including) the last period
7541 and not including the directory.
7544 This is the same as @samp{%b}, but include the file suffix (text after
7548 Marks the argument containing or following the @samp{%d} as a
7549 temporary file name, so that that file will be deleted if GCC exits
7550 successfully. Unlike @samp{%g}, this contributes no text to the
7553 @item %g@var{suffix}
7554 Substitute a file name that has suffix @var{suffix} and is chosen
7555 once per compilation, and mark the argument in the same way as
7556 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
7557 name is now chosen in a way that is hard to predict even when previously
7558 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
7559 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
7560 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
7561 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
7562 was simply substituted with a file name chosen once per compilation,
7563 without regard to any appended suffix (which was therefore treated
7564 just like ordinary text), making such attacks more likely to succeed.
7566 @item %u@var{suffix}
7567 Like @samp{%g}, but generates a new temporary file name even if
7568 @samp{%u@var{suffix}} was already seen.
7570 @item %U@var{suffix}
7571 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
7572 new one if there is no such last file name. In the absence of any
7573 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
7574 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
7575 would involve the generation of two distinct file names, one
7576 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
7577 simply substituted with a file name chosen for the previous @samp{%u},
7578 without regard to any appended suffix.
7580 @item %j@var{suffix}
7581 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
7582 writable, and if save-temps is off; otherwise, substitute the name
7583 of a temporary file, just like @samp{%u}. This temporary file is not
7584 meant for communication between processes, but rather as a junk
7587 @item %|@var{suffix}
7588 @itemx %m@var{suffix}
7589 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
7590 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
7591 all. These are the two most common ways to instruct a program that it
7592 should read from standard input or write to standard output. If you
7593 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
7594 construct: see for example @file{f/lang-specs.h}.
7596 @item %.@var{SUFFIX}
7597 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
7598 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
7599 terminated by the next space or %.
7602 Marks the argument containing or following the @samp{%w} as the
7603 designated output file of this compilation. This puts the argument
7604 into the sequence of arguments that @samp{%o} will substitute later.
7607 Substitutes the names of all the output files, with spaces
7608 automatically placed around them. You should write spaces
7609 around the @samp{%o} as well or the results are undefined.
7610 @samp{%o} is for use in the specs for running the linker.
7611 Input files whose names have no recognized suffix are not compiled
7612 at all, but they are included among the output files, so they will
7616 Substitutes the suffix for object files. Note that this is
7617 handled specially when it immediately follows @samp{%g, %u, or %U},
7618 because of the need for those to form complete file names. The
7619 handling is such that @samp{%O} is treated exactly as if it had already
7620 been substituted, except that @samp{%g, %u, and %U} do not currently
7621 support additional @var{suffix} characters following @samp{%O} as they would
7622 following, for example, @samp{.o}.
7625 Substitutes the standard macro predefinitions for the
7626 current target machine. Use this when running @code{cpp}.
7629 Like @samp{%p}, but puts @samp{__} before and after the name of each
7630 predefined macro, except for macros that start with @samp{__} or with
7631 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
7635 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
7636 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
7637 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
7638 and @option{-imultilib} as necessary.
7641 Current argument is the name of a library or startup file of some sort.
7642 Search for that file in a standard list of directories and substitute
7643 the full name found.
7646 Print @var{str} as an error message. @var{str} is terminated by a newline.
7647 Use this when inconsistent options are detected.
7650 Substitute the contents of spec string @var{name} at this point.
7653 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
7655 @item %x@{@var{option}@}
7656 Accumulate an option for @samp{%X}.
7659 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
7663 Output the accumulated assembler options specified by @option{-Wa}.
7666 Output the accumulated preprocessor options specified by @option{-Wp}.
7669 Process the @code{asm} spec. This is used to compute the
7670 switches to be passed to the assembler.
7673 Process the @code{asm_final} spec. This is a spec string for
7674 passing switches to an assembler post-processor, if such a program is
7678 Process the @code{link} spec. This is the spec for computing the
7679 command line passed to the linker. Typically it will make use of the
7680 @samp{%L %G %S %D and %E} sequences.
7683 Dump out a @option{-L} option for each directory that GCC believes might
7684 contain startup files. If the target supports multilibs then the
7685 current multilib directory will be prepended to each of these paths.
7688 Process the @code{lib} spec. This is a spec string for deciding which
7689 libraries should be included on the command line to the linker.
7692 Process the @code{libgcc} spec. This is a spec string for deciding
7693 which GCC support library should be included on the command line to the linker.
7696 Process the @code{startfile} spec. This is a spec for deciding which
7697 object files should be the first ones passed to the linker. Typically
7698 this might be a file named @file{crt0.o}.
7701 Process the @code{endfile} spec. This is a spec string that specifies
7702 the last object files that will be passed to the linker.
7705 Process the @code{cpp} spec. This is used to construct the arguments
7706 to be passed to the C preprocessor.
7709 Process the @code{cc1} spec. This is used to construct the options to be
7710 passed to the actual C compiler (@samp{cc1}).
7713 Process the @code{cc1plus} spec. This is used to construct the options to be
7714 passed to the actual C++ compiler (@samp{cc1plus}).
7717 Substitute the variable part of a matched option. See below.
7718 Note that each comma in the substituted string is replaced by
7722 Remove all occurrences of @code{-S} from the command line. Note---this
7723 command is position dependent. @samp{%} commands in the spec string
7724 before this one will see @code{-S}, @samp{%} commands in the spec string
7725 after this one will not.
7727 @item %:@var{function}(@var{args})
7728 Call the named function @var{function}, passing it @var{args}.
7729 @var{args} is first processed as a nested spec string, then split
7730 into an argument vector in the usual fashion. The function returns
7731 a string which is processed as if it had appeared literally as part
7732 of the current spec.
7734 The following built-in spec functions are provided:
7738 The @code{getenv} spec function takes two arguments: an environment
7739 variable name and a string. If the environment variable is not
7740 defined, a fatal error is issued. Otherwise, the return value is the
7741 value of the environment variable concatenated with the string. For
7742 example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
7745 %:getenv(TOPDIR /include)
7748 expands to @file{/path/to/top/include}.
7750 @item @code{if-exists}
7751 The @code{if-exists} spec function takes one argument, an absolute
7752 pathname to a file. If the file exists, @code{if-exists} returns the
7753 pathname. Here is a small example of its usage:
7757 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
7760 @item @code{if-exists-else}
7761 The @code{if-exists-else} spec function is similar to the @code{if-exists}
7762 spec function, except that it takes two arguments. The first argument is
7763 an absolute pathname to a file. If the file exists, @code{if-exists-else}
7764 returns the pathname. If it does not exist, it returns the second argument.
7765 This way, @code{if-exists-else} can be used to select one file or another,
7766 based on the existence of the first. Here is a small example of its usage:
7770 crt0%O%s %:if-exists(crti%O%s) \
7771 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
7774 @item @code{replace-outfile}
7775 The @code{replace-outfile} spec function takes two arguments. It looks for the
7776 first argument in the outfiles array and replaces it with the second argument. Here
7777 is a small example of its usage:
7780 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
7783 @item @code{print-asm-header}
7784 The @code{print-asm-header} function takes no arguments and simply
7785 prints a banner like:
7791 Use "-Wa,OPTION" to pass "OPTION" to the assembler.
7794 It is used to separate compiler options from assembler options
7795 in the @option{--target-help} output.
7799 Substitutes the @code{-S} switch, if that switch was given to GCC@.
7800 If that switch was not specified, this substitutes nothing. Note that
7801 the leading dash is omitted when specifying this option, and it is
7802 automatically inserted if the substitution is performed. Thus the spec
7803 string @samp{%@{foo@}} would match the command-line option @option{-foo}
7804 and would output the command line option @option{-foo}.
7806 @item %W@{@code{S}@}
7807 Like %@{@code{S}@} but mark last argument supplied within as a file to be
7810 @item %@{@code{S}*@}
7811 Substitutes all the switches specified to GCC whose names start
7812 with @code{-S}, but which also take an argument. This is used for
7813 switches like @option{-o}, @option{-D}, @option{-I}, etc.
7814 GCC considers @option{-o foo} as being
7815 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
7816 text, including the space. Thus two arguments would be generated.
7818 @item %@{@code{S}*&@code{T}*@}
7819 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
7820 (the order of @code{S} and @code{T} in the spec is not significant).
7821 There can be any number of ampersand-separated variables; for each the
7822 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
7824 @item %@{@code{S}:@code{X}@}
7825 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
7827 @item %@{!@code{S}:@code{X}@}
7828 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
7830 @item %@{@code{S}*:@code{X}@}
7831 Substitutes @code{X} if one or more switches whose names start with
7832 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
7833 once, no matter how many such switches appeared. However, if @code{%*}
7834 appears somewhere in @code{X}, then @code{X} will be substituted once
7835 for each matching switch, with the @code{%*} replaced by the part of
7836 that switch that matched the @code{*}.
7838 @item %@{.@code{S}:@code{X}@}
7839 Substitutes @code{X}, if processing a file with suffix @code{S}.
7841 @item %@{!.@code{S}:@code{X}@}
7842 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
7844 @item %@{,@code{S}:@code{X}@}
7845 Substitutes @code{X}, if processing a file for language @code{S}.
7847 @item %@{!,@code{S}:@code{X}@}
7848 Substitutes @code{X}, if not processing a file for language @code{S}.
7850 @item %@{@code{S}|@code{P}:@code{X}@}
7851 Substitutes @code{X} if either @code{-S} or @code{-P} was given to
7852 GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
7853 @code{*} sequences as well, although they have a stronger binding than
7854 the @samp{|}. If @code{%*} appears in @code{X}, all of the
7855 alternatives must be starred, and only the first matching alternative
7858 For example, a spec string like this:
7861 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
7864 will output the following command-line options from the following input
7865 command-line options:
7870 -d fred.c -foo -baz -boggle
7871 -d jim.d -bar -baz -boggle
7874 @item %@{S:X; T:Y; :D@}
7876 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
7877 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
7878 be as many clauses as you need. This may be combined with @code{.},
7879 @code{,}, @code{!}, @code{|}, and @code{*} as needed.
7884 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
7885 construct may contain other nested @samp{%} constructs or spaces, or
7886 even newlines. They are processed as usual, as described above.
7887 Trailing white space in @code{X} is ignored. White space may also
7888 appear anywhere on the left side of the colon in these constructs,
7889 except between @code{.} or @code{*} and the corresponding word.
7891 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
7892 handled specifically in these constructs. If another value of
7893 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
7894 @option{-W} switch is found later in the command line, the earlier
7895 switch value is ignored, except with @{@code{S}*@} where @code{S} is
7896 just one letter, which passes all matching options.
7898 The character @samp{|} at the beginning of the predicate text is used to
7899 indicate that a command should be piped to the following command, but
7900 only if @option{-pipe} is specified.
7902 It is built into GCC which switches take arguments and which do not.
7903 (You might think it would be useful to generalize this to allow each
7904 compiler's spec to say which switches take arguments. But this cannot
7905 be done in a consistent fashion. GCC cannot even decide which input
7906 files have been specified without knowing which switches take arguments,
7907 and it must know which input files to compile in order to tell which
7910 GCC also knows implicitly that arguments starting in @option{-l} are to be
7911 treated as compiler output files, and passed to the linker in their
7912 proper position among the other output files.
7914 @c man begin OPTIONS
7916 @node Target Options
7917 @section Specifying Target Machine and Compiler Version
7918 @cindex target options
7919 @cindex cross compiling
7920 @cindex specifying machine version
7921 @cindex specifying compiler version and target machine
7922 @cindex compiler version, specifying
7923 @cindex target machine, specifying
7925 The usual way to run GCC is to run the executable called @file{gcc}, or
7926 @file{<machine>-gcc} when cross-compiling, or
7927 @file{<machine>-gcc-<version>} to run a version other than the one that
7928 was installed last. Sometimes this is inconvenient, so GCC provides
7929 options that will switch to another cross-compiler or version.
7932 @item -b @var{machine}
7934 The argument @var{machine} specifies the target machine for compilation.
7936 The value to use for @var{machine} is the same as was specified as the
7937 machine type when configuring GCC as a cross-compiler. For
7938 example, if a cross-compiler was configured with @samp{configure
7939 arm-elf}, meaning to compile for an arm processor with elf binaries,
7940 then you would specify @option{-b arm-elf} to run that cross compiler.
7941 Because there are other options beginning with @option{-b}, the
7942 configuration must contain a hyphen.
7944 @item -V @var{version}
7946 The argument @var{version} specifies which version of GCC to run.
7947 This is useful when multiple versions are installed. For example,
7948 @var{version} might be @samp{4.0}, meaning to run GCC version 4.0.
7951 The @option{-V} and @option{-b} options work by running the
7952 @file{<machine>-gcc-<version>} executable, so there's no real reason to
7953 use them if you can just run that directly.
7955 @node Submodel Options
7956 @section Hardware Models and Configurations
7957 @cindex submodel options
7958 @cindex specifying hardware config
7959 @cindex hardware models and configurations, specifying
7960 @cindex machine dependent options
7962 Earlier we discussed the standard option @option{-b} which chooses among
7963 different installed compilers for completely different target
7964 machines, such as VAX vs.@: 68000 vs.@: 80386.
7966 In addition, each of these target machine types can have its own
7967 special options, starting with @samp{-m}, to choose among various
7968 hardware models or configurations---for example, 68010 vs 68020,
7969 floating coprocessor or none. A single installed version of the
7970 compiler can compile for any model or configuration, according to the
7973 Some configurations of the compiler also support additional special
7974 options, usually for compatibility with other compilers on the same
7977 @c This list is ordered alphanumerically by subsection name.
7978 @c It should be the same order and spelling as these options are listed
7979 @c in Machine Dependent Options
7985 * Blackfin Options::
7989 * DEC Alpha Options::
7990 * DEC Alpha/VMS Options::
7992 * GNU/Linux Options::
7995 * i386 and x86-64 Options::
8008 * RS/6000 and PowerPC Options::
8009 * S/390 and zSeries Options::
8014 * System V Options::
8015 * TMS320C3x/C4x Options::
8020 * Xstormy16 Options::
8026 @subsection ARC Options
8029 These options are defined for ARC implementations:
8034 Compile code for little endian mode. This is the default.
8038 Compile code for big endian mode.
8041 @opindex mmangle-cpu
8042 Prepend the name of the cpu to all public symbol names.
8043 In multiple-processor systems, there are many ARC variants with different
8044 instruction and register set characteristics. This flag prevents code
8045 compiled for one cpu to be linked with code compiled for another.
8046 No facility exists for handling variants that are ``almost identical''.
8047 This is an all or nothing option.
8049 @item -mcpu=@var{cpu}
8051 Compile code for ARC variant @var{cpu}.
8052 Which variants are supported depend on the configuration.
8053 All variants support @option{-mcpu=base}, this is the default.
8055 @item -mtext=@var{text-section}
8056 @itemx -mdata=@var{data-section}
8057 @itemx -mrodata=@var{readonly-data-section}
8061 Put functions, data, and readonly data in @var{text-section},
8062 @var{data-section}, and @var{readonly-data-section} respectively
8063 by default. This can be overridden with the @code{section} attribute.
8064 @xref{Variable Attributes}.
8069 @subsection ARM Options
8072 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
8076 @item -mabi=@var{name}
8078 Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
8079 @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
8082 @opindex mapcs-frame
8083 Generate a stack frame that is compliant with the ARM Procedure Call
8084 Standard for all functions, even if this is not strictly necessary for
8085 correct execution of the code. Specifying @option{-fomit-frame-pointer}
8086 with this option will cause the stack frames not to be generated for
8087 leaf functions. The default is @option{-mno-apcs-frame}.
8091 This is a synonym for @option{-mapcs-frame}.
8094 @c not currently implemented
8095 @item -mapcs-stack-check
8096 @opindex mapcs-stack-check
8097 Generate code to check the amount of stack space available upon entry to
8098 every function (that actually uses some stack space). If there is
8099 insufficient space available then either the function
8100 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
8101 called, depending upon the amount of stack space required. The run time
8102 system is required to provide these functions. The default is
8103 @option{-mno-apcs-stack-check}, since this produces smaller code.
8105 @c not currently implemented
8107 @opindex mapcs-float
8108 Pass floating point arguments using the float point registers. This is
8109 one of the variants of the APCS@. This option is recommended if the
8110 target hardware has a floating point unit or if a lot of floating point
8111 arithmetic is going to be performed by the code. The default is
8112 @option{-mno-apcs-float}, since integer only code is slightly increased in
8113 size if @option{-mapcs-float} is used.
8115 @c not currently implemented
8116 @item -mapcs-reentrant
8117 @opindex mapcs-reentrant
8118 Generate reentrant, position independent code. The default is
8119 @option{-mno-apcs-reentrant}.
8122 @item -mthumb-interwork
8123 @opindex mthumb-interwork
8124 Generate code which supports calling between the ARM and Thumb
8125 instruction sets. Without this option the two instruction sets cannot
8126 be reliably used inside one program. The default is
8127 @option{-mno-thumb-interwork}, since slightly larger code is generated
8128 when @option{-mthumb-interwork} is specified.
8130 @item -mno-sched-prolog
8131 @opindex mno-sched-prolog
8132 Prevent the reordering of instructions in the function prolog, or the
8133 merging of those instruction with the instructions in the function's
8134 body. This means that all functions will start with a recognizable set
8135 of instructions (or in fact one of a choice from a small set of
8136 different function prologues), and this information can be used to
8137 locate the start if functions inside an executable piece of code. The
8138 default is @option{-msched-prolog}.
8141 @opindex mhard-float
8142 Generate output containing floating point instructions. This is the
8146 @opindex msoft-float
8147 Generate output containing library calls for floating point.
8148 @strong{Warning:} the requisite libraries are not available for all ARM
8149 targets. Normally the facilities of the machine's usual C compiler are
8150 used, but this cannot be done directly in cross-compilation. You must make
8151 your own arrangements to provide suitable library functions for
8154 @option{-msoft-float} changes the calling convention in the output file;
8155 therefore, it is only useful if you compile @emph{all} of a program with
8156 this option. In particular, you need to compile @file{libgcc.a}, the
8157 library that comes with GCC, with @option{-msoft-float} in order for
8160 @item -mfloat-abi=@var{name}
8162 Specifies which ABI to use for floating point values. Permissible values
8163 are: @samp{soft}, @samp{softfp} and @samp{hard}.
8165 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
8166 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
8167 of floating point instructions, but still uses the soft-float calling
8170 @item -mlittle-endian
8171 @opindex mlittle-endian
8172 Generate code for a processor running in little-endian mode. This is
8173 the default for all standard configurations.
8176 @opindex mbig-endian
8177 Generate code for a processor running in big-endian mode; the default is
8178 to compile code for a little-endian processor.
8180 @item -mwords-little-endian
8181 @opindex mwords-little-endian
8182 This option only applies when generating code for big-endian processors.
8183 Generate code for a little-endian word order but a big-endian byte
8184 order. That is, a byte order of the form @samp{32107654}. Note: this
8185 option should only be used if you require compatibility with code for
8186 big-endian ARM processors generated by versions of the compiler prior to
8189 @item -mcpu=@var{name}
8191 This specifies the name of the target ARM processor. GCC uses this name
8192 to determine what kind of instructions it can emit when generating
8193 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
8194 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
8195 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
8196 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
8197 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
8198 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
8199 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
8200 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
8201 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
8202 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
8203 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
8204 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
8205 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
8206 @samp{arm1156t2-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
8207 @samp{cortex-a8}, @samp{cortex-r4}, @samp{cortex-m3},
8208 @samp{xscale}, @samp{iwmmxt}, @samp{ep9312}.
8210 @itemx -mtune=@var{name}
8212 This option is very similar to the @option{-mcpu=} option, except that
8213 instead of specifying the actual target processor type, and hence
8214 restricting which instructions can be used, it specifies that GCC should
8215 tune the performance of the code as if the target were of the type
8216 specified in this option, but still choosing the instructions that it
8217 will generate based on the cpu specified by a @option{-mcpu=} option.
8218 For some ARM implementations better performance can be obtained by using
8221 @item -march=@var{name}
8223 This specifies the name of the target ARM architecture. GCC uses this
8224 name to determine what kind of instructions it can emit when generating
8225 assembly code. This option can be used in conjunction with or instead
8226 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
8227 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
8228 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
8229 @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv7}, @samp{armv7-a},
8230 @samp{armv7-r}, @samp{armv7-m}, @samp{iwmmxt}, @samp{ep9312}.
8232 @item -mfpu=@var{name}
8233 @itemx -mfpe=@var{number}
8234 @itemx -mfp=@var{number}
8238 This specifies what floating point hardware (or hardware emulation) is
8239 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
8240 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
8241 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
8242 with older versions of GCC@.
8244 If @option{-msoft-float} is specified this specifies the format of
8245 floating point values.
8247 @item -mstructure-size-boundary=@var{n}
8248 @opindex mstructure-size-boundary
8249 The size of all structures and unions will be rounded up to a multiple
8250 of the number of bits set by this option. Permissible values are 8, 32
8251 and 64. The default value varies for different toolchains. For the COFF
8252 targeted toolchain the default value is 8. A value of 64 is only allowed
8253 if the underlying ABI supports it.
8255 Specifying the larger number can produce faster, more efficient code, but
8256 can also increase the size of the program. Different values are potentially
8257 incompatible. Code compiled with one value cannot necessarily expect to
8258 work with code or libraries compiled with another value, if they exchange
8259 information using structures or unions.
8261 @item -mabort-on-noreturn
8262 @opindex mabort-on-noreturn
8263 Generate a call to the function @code{abort} at the end of a
8264 @code{noreturn} function. It will be executed if the function tries to
8268 @itemx -mno-long-calls
8269 @opindex mlong-calls
8270 @opindex mno-long-calls
8271 Tells the compiler to perform function calls by first loading the
8272 address of the function into a register and then performing a subroutine
8273 call on this register. This switch is needed if the target function
8274 will lie outside of the 64 megabyte addressing range of the offset based
8275 version of subroutine call instruction.
8277 Even if this switch is enabled, not all function calls will be turned
8278 into long calls. The heuristic is that static functions, functions
8279 which have the @samp{short-call} attribute, functions that are inside
8280 the scope of a @samp{#pragma no_long_calls} directive and functions whose
8281 definitions have already been compiled within the current compilation
8282 unit, will not be turned into long calls. The exception to this rule is
8283 that weak function definitions, functions with the @samp{long-call}
8284 attribute or the @samp{section} attribute, and functions that are within
8285 the scope of a @samp{#pragma long_calls} directive, will always be
8286 turned into long calls.
8288 This feature is not enabled by default. Specifying
8289 @option{-mno-long-calls} will restore the default behavior, as will
8290 placing the function calls within the scope of a @samp{#pragma
8291 long_calls_off} directive. Note these switches have no effect on how
8292 the compiler generates code to handle function calls via function
8295 @item -mnop-fun-dllimport
8296 @opindex mnop-fun-dllimport
8297 Disable support for the @code{dllimport} attribute.
8299 @item -msingle-pic-base
8300 @opindex msingle-pic-base
8301 Treat the register used for PIC addressing as read-only, rather than
8302 loading it in the prologue for each function. The run-time system is
8303 responsible for initializing this register with an appropriate value
8304 before execution begins.
8306 @item -mpic-register=@var{reg}
8307 @opindex mpic-register
8308 Specify the register to be used for PIC addressing. The default is R10
8309 unless stack-checking is enabled, when R9 is used.
8311 @item -mcirrus-fix-invalid-insns
8312 @opindex mcirrus-fix-invalid-insns
8313 @opindex mno-cirrus-fix-invalid-insns
8314 Insert NOPs into the instruction stream to in order to work around
8315 problems with invalid Maverick instruction combinations. This option
8316 is only valid if the @option{-mcpu=ep9312} option has been used to
8317 enable generation of instructions for the Cirrus Maverick floating
8318 point co-processor. This option is not enabled by default, since the
8319 problem is only present in older Maverick implementations. The default
8320 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
8323 @item -mpoke-function-name
8324 @opindex mpoke-function-name
8325 Write the name of each function into the text section, directly
8326 preceding the function prologue. The generated code is similar to this:
8330 .ascii "arm_poke_function_name", 0
8333 .word 0xff000000 + (t1 - t0)
8334 arm_poke_function_name
8336 stmfd sp!, @{fp, ip, lr, pc@}
8340 When performing a stack backtrace, code can inspect the value of
8341 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
8342 location @code{pc - 12} and the top 8 bits are set, then we know that
8343 there is a function name embedded immediately preceding this location
8344 and has length @code{((pc[-3]) & 0xff000000)}.
8348 Generate code for the Thumb instruction set. The default is to
8349 use the 32-bit ARM instruction set.
8350 This option automatically enables either 16-bit Thumb-1 or
8351 mixed 16/32-bit Thumb-2 instructions based on the @option{-mcpu=@var{name}}
8352 and @option{-march=@var{name}} options.
8355 @opindex mtpcs-frame
8356 Generate a stack frame that is compliant with the Thumb Procedure Call
8357 Standard for all non-leaf functions. (A leaf function is one that does
8358 not call any other functions.) The default is @option{-mno-tpcs-frame}.
8360 @item -mtpcs-leaf-frame
8361 @opindex mtpcs-leaf-frame
8362 Generate a stack frame that is compliant with the Thumb Procedure Call
8363 Standard for all leaf functions. (A leaf function is one that does
8364 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
8366 @item -mcallee-super-interworking
8367 @opindex mcallee-super-interworking
8368 Gives all externally visible functions in the file being compiled an ARM
8369 instruction set header which switches to Thumb mode before executing the
8370 rest of the function. This allows these functions to be called from
8371 non-interworking code.
8373 @item -mcaller-super-interworking
8374 @opindex mcaller-super-interworking
8375 Allows calls via function pointers (including virtual functions) to
8376 execute correctly regardless of whether the target code has been
8377 compiled for interworking or not. There is a small overhead in the cost
8378 of executing a function pointer if this option is enabled.
8380 @item -mtp=@var{name}
8382 Specify the access model for the thread local storage pointer. The valid
8383 models are @option{soft}, which generates calls to @code{__aeabi_read_tp},
8384 @option{cp15}, which fetches the thread pointer from @code{cp15} directly
8385 (supported in the arm6k architecture), and @option{auto}, which uses the
8386 best available method for the selected processor. The default setting is
8392 @subsection AVR Options
8395 These options are defined for AVR implementations:
8398 @item -mmcu=@var{mcu}
8400 Specify ATMEL AVR instruction set or MCU type.
8402 Instruction set avr1 is for the minimal AVR core, not supported by the C
8403 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
8404 attiny11, attiny12, attiny15, attiny28).
8406 Instruction set avr2 (default) is for the classic AVR core with up to
8407 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
8408 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
8409 at90c8534, at90s8535).
8411 Instruction set avr3 is for the classic AVR core with up to 128K program
8412 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
8414 Instruction set avr4 is for the enhanced AVR core with up to 8K program
8415 memory space (MCU types: atmega8, atmega83, atmega85).
8417 Instruction set avr5 is for the enhanced AVR core with up to 128K program
8418 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
8419 atmega64, atmega128, at43usb355, at94k).
8423 Output instruction sizes to the asm file.
8425 @item -minit-stack=@var{N}
8426 @opindex minit-stack
8427 Specify the initial stack address, which may be a symbol or numeric value,
8428 @samp{__stack} is the default.
8430 @item -mno-interrupts
8431 @opindex mno-interrupts
8432 Generated code is not compatible with hardware interrupts.
8433 Code size will be smaller.
8435 @item -mcall-prologues
8436 @opindex mcall-prologues
8437 Functions prologues/epilogues expanded as call to appropriate
8438 subroutines. Code size will be smaller.
8440 @item -mno-tablejump
8441 @opindex mno-tablejump
8442 Do not generate tablejump insns which sometimes increase code size.
8445 @opindex mtiny-stack
8446 Change only the low 8 bits of the stack pointer.
8450 Assume int to be 8 bit integer. This affects the sizes of all types: A
8451 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
8452 and long long will be 4 bytes. Please note that this option does not
8453 comply to the C standards, but it will provide you with smaller code
8457 @node Blackfin Options
8458 @subsection Blackfin Options
8459 @cindex Blackfin Options
8462 @item -mcpu=@var{cpu}
8464 Specifies the name of the target Blackfin processor. Currently, @var{cpu}
8465 can be one of @samp{bf531}, @samp{bf532}, @samp{bf533},
8466 @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf561}.
8467 Without this option, @samp{bf532} is used as the processor by default.
8468 The corresponding predefined processor macros for @var{cpu} is to
8469 be defined. For the @samp{bfin-elf} toolchain, this causes the hardware
8470 BSP provided by libgloss to be linked in if @samp{-msim} is not given.
8471 Support for @samp{bf561} is incomplete; only the processor macro is defined.
8475 Specifies that the program will be run on the simulator. This causes
8476 the simulator BSP provided by libgloss to be linked in. This option
8477 has effect only for @samp{bfin-elf} toolchain.
8479 @item -momit-leaf-frame-pointer
8480 @opindex momit-leaf-frame-pointer
8481 Don't keep the frame pointer in a register for leaf functions. This
8482 avoids the instructions to save, set up and restore frame pointers and
8483 makes an extra register available in leaf functions. The option
8484 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8485 which might make debugging harder.
8487 @item -mspecld-anomaly
8488 @opindex mspecld-anomaly
8489 When enabled, the compiler will ensure that the generated code does not
8490 contain speculative loads after jump instructions. This option is enabled
8493 @item -mno-specld-anomaly
8494 @opindex mno-specld-anomaly
8495 Don't generate extra code to prevent speculative loads from occurring.
8497 @item -mcsync-anomaly
8498 @opindex mcsync-anomaly
8499 When enabled, the compiler will ensure that the generated code does not
8500 contain CSYNC or SSYNC instructions too soon after conditional branches.
8501 This option is enabled by default.
8503 @item -mno-csync-anomaly
8504 @opindex mno-csync-anomaly
8505 Don't generate extra code to prevent CSYNC or SSYNC instructions from
8506 occurring too soon after a conditional branch.
8510 When enabled, the compiler is free to take advantage of the knowledge that
8511 the entire program fits into the low 64k of memory.
8514 @opindex mno-low-64k
8515 Assume that the program is arbitrarily large. This is the default.
8517 @item -mstack-check-l1
8518 @opindex mstack-check-l1
8519 Do stack checking using information placed into L1 scratchpad memory by the
8522 @item -mid-shared-library
8523 @opindex mid-shared-library
8524 Generate code that supports shared libraries via the library ID method.
8525 This allows for execute in place and shared libraries in an environment
8526 without virtual memory management. This option implies @option{-fPIC}.
8528 @item -mno-id-shared-library
8529 @opindex mno-id-shared-library
8530 Generate code that doesn't assume ID based shared libraries are being used.
8531 This is the default.
8533 @item -mleaf-id-shared-library
8534 @opindex mleaf-id-shared-library
8535 Generate code that supports shared libraries via the library ID method,
8536 but assumes that this library or executable won't link against any other
8537 ID shared libraries. That allows the compiler to use faster code for jumps
8540 @item -mno-leaf-id-shared-library
8541 @opindex mno-leaf-id-shared-library
8542 Do not assume that the code being compiled won't link against any ID shared
8543 libraries. Slower code will be generated for jump and call insns.
8545 @item -mshared-library-id=n
8546 @opindex mshared-library-id
8547 Specified the identification number of the ID based shared library being
8548 compiled. Specifying a value of 0 will generate more compact code, specifying
8549 other values will force the allocation of that number to the current
8550 library but is no more space or time efficient than omitting this option.
8554 Generate code that allows the data segment to be located in a different
8555 area of memory from the text segment. This allows for execute in place in
8556 an environment without virtual memory management by eliminating relocations
8557 against the text section.
8560 @opindex mno-sep-data
8561 Generate code that assumes that the data segment follows the text segment.
8562 This is the default.
8565 @itemx -mno-long-calls
8566 @opindex mlong-calls
8567 @opindex mno-long-calls
8568 Tells the compiler to perform function calls by first loading the
8569 address of the function into a register and then performing a subroutine
8570 call on this register. This switch is needed if the target function
8571 will lie outside of the 24 bit addressing range of the offset based
8572 version of subroutine call instruction.
8574 This feature is not enabled by default. Specifying
8575 @option{-mno-long-calls} will restore the default behavior. Note these
8576 switches have no effect on how the compiler generates code to handle
8577 function calls via function pointers.
8581 @subsection CRIS Options
8582 @cindex CRIS Options
8584 These options are defined specifically for the CRIS ports.
8587 @item -march=@var{architecture-type}
8588 @itemx -mcpu=@var{architecture-type}
8591 Generate code for the specified architecture. The choices for
8592 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
8593 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
8594 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
8597 @item -mtune=@var{architecture-type}
8599 Tune to @var{architecture-type} everything applicable about the generated
8600 code, except for the ABI and the set of available instructions. The
8601 choices for @var{architecture-type} are the same as for
8602 @option{-march=@var{architecture-type}}.
8604 @item -mmax-stack-frame=@var{n}
8605 @opindex mmax-stack-frame
8606 Warn when the stack frame of a function exceeds @var{n} bytes.
8608 @item -melinux-stacksize=@var{n}
8609 @opindex melinux-stacksize
8610 Only available with the @samp{cris-axis-aout} target. Arranges for
8611 indications in the program to the kernel loader that the stack of the
8612 program should be set to @var{n} bytes.
8618 The options @option{-metrax4} and @option{-metrax100} are synonyms for
8619 @option{-march=v3} and @option{-march=v8} respectively.
8621 @item -mmul-bug-workaround
8622 @itemx -mno-mul-bug-workaround
8623 @opindex mmul-bug-workaround
8624 @opindex mno-mul-bug-workaround
8625 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
8626 models where it applies. This option is active by default.
8630 Enable CRIS-specific verbose debug-related information in the assembly
8631 code. This option also has the effect to turn off the @samp{#NO_APP}
8632 formatted-code indicator to the assembler at the beginning of the
8637 Do not use condition-code results from previous instruction; always emit
8638 compare and test instructions before use of condition codes.
8640 @item -mno-side-effects
8641 @opindex mno-side-effects
8642 Do not emit instructions with side-effects in addressing modes other than
8646 @itemx -mno-stack-align
8648 @itemx -mno-data-align
8649 @itemx -mconst-align
8650 @itemx -mno-const-align
8651 @opindex mstack-align
8652 @opindex mno-stack-align
8653 @opindex mdata-align
8654 @opindex mno-data-align
8655 @opindex mconst-align
8656 @opindex mno-const-align
8657 These options (no-options) arranges (eliminate arrangements) for the
8658 stack-frame, individual data and constants to be aligned for the maximum
8659 single data access size for the chosen CPU model. The default is to
8660 arrange for 32-bit alignment. ABI details such as structure layout are
8661 not affected by these options.
8669 Similar to the stack- data- and const-align options above, these options
8670 arrange for stack-frame, writable data and constants to all be 32-bit,
8671 16-bit or 8-bit aligned. The default is 32-bit alignment.
8673 @item -mno-prologue-epilogue
8674 @itemx -mprologue-epilogue
8675 @opindex mno-prologue-epilogue
8676 @opindex mprologue-epilogue
8677 With @option{-mno-prologue-epilogue}, the normal function prologue and
8678 epilogue that sets up the stack-frame are omitted and no return
8679 instructions or return sequences are generated in the code. Use this
8680 option only together with visual inspection of the compiled code: no
8681 warnings or errors are generated when call-saved registers must be saved,
8682 or storage for local variable needs to be allocated.
8688 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
8689 instruction sequences that load addresses for functions from the PLT part
8690 of the GOT rather than (traditional on other architectures) calls to the
8691 PLT@. The default is @option{-mgotplt}.
8695 Legacy no-op option only recognized with the cris-axis-aout target.
8699 Legacy no-op option only recognized with the cris-axis-elf and
8700 cris-axis-linux-gnu targets.
8704 Only recognized with the cris-axis-aout target, where it selects a
8705 GNU/linux-like multilib, include files and instruction set for
8710 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
8714 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
8715 to link with input-output functions from a simulator library. Code,
8716 initialized data and zero-initialized data are allocated consecutively.
8720 Like @option{-sim}, but pass linker options to locate initialized data at
8721 0x40000000 and zero-initialized data at 0x80000000.
8725 @subsection CRX Options
8728 These options are defined specifically for the CRX ports.
8734 Enable the use of multiply-accumulate instructions. Disabled by default.
8738 Push instructions will be used to pass outgoing arguments when functions
8739 are called. Enabled by default.
8742 @node Darwin Options
8743 @subsection Darwin Options
8744 @cindex Darwin options
8746 These options are defined for all architectures running the Darwin operating
8749 FSF GCC on Darwin does not create ``fat'' object files; it will create
8750 an object file for the single architecture that it was built to
8751 target. Apple's GCC on Darwin does create ``fat'' files if multiple
8752 @option{-arch} options are used; it does so by running the compiler or
8753 linker multiple times and joining the results together with
8756 The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
8757 @samp{i686}) is determined by the flags that specify the ISA
8758 that GCC is targetting, like @option{-mcpu} or @option{-march}. The
8759 @option{-force_cpusubtype_ALL} option can be used to override this.
8761 The Darwin tools vary in their behavior when presented with an ISA
8762 mismatch. The assembler, @file{as}, will only permit instructions to
8763 be used that are valid for the subtype of the file it is generating,
8764 so you cannot put 64-bit instructions in an @samp{ppc750} object file.
8765 The linker for shared libraries, @file{/usr/bin/libtool}, will fail
8766 and print an error if asked to create a shared library with a less
8767 restrictive subtype than its input files (for instance, trying to put
8768 a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
8769 for executables, @file{ld}, will quietly give the executable the most
8770 restrictive subtype of any of its input files.
8775 Add the framework directory @var{dir} to the head of the list of
8776 directories to be searched for header files. These directories are
8777 interleaved with those specified by @option{-I} options and are
8778 scanned in a left-to-right order.
8780 A framework directory is a directory with frameworks in it. A
8781 framework is a directory with a @samp{"Headers"} and/or
8782 @samp{"PrivateHeaders"} directory contained directly in it that ends
8783 in @samp{".framework"}. The name of a framework is the name of this
8784 directory excluding the @samp{".framework"}. Headers associated with
8785 the framework are found in one of those two directories, with
8786 @samp{"Headers"} being searched first. A subframework is a framework
8787 directory that is in a framework's @samp{"Frameworks"} directory.
8788 Includes of subframework headers can only appear in a header of a
8789 framework that contains the subframework, or in a sibling subframework
8790 header. Two subframeworks are siblings if they occur in the same
8791 framework. A subframework should not have the same name as a
8792 framework, a warning will be issued if this is violated. Currently a
8793 subframework cannot have subframeworks, in the future, the mechanism
8794 may be extended to support this. The standard frameworks can be found
8795 in @samp{"/System/Library/Frameworks"} and
8796 @samp{"/Library/Frameworks"}. An example include looks like
8797 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
8798 the name of the framework and header.h is found in the
8799 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
8801 @item -iframework@var{dir}
8803 Like @option{-F} except the directory is a treated as a system
8804 directory. The main difference between this @option{-iframework} and
8805 @option{-F} is that with @option{-iframework} the compiler does not
8806 warn about constructs contained within header files found via
8807 @var{dir}. This option is valid only for the C family of languages.
8811 Emit debugging information for symbols that are used. For STABS
8812 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
8813 This is by default ON@.
8817 Emit debugging information for all symbols and types.
8819 @item -mmacosx-version-min=@var{version}
8820 The earliest version of MacOS X that this executable will run on
8821 is @var{version}. Typical values of @var{version} include @code{10.1},
8822 @code{10.2}, and @code{10.3.9}.
8824 If the compiler was built to use the system's headers by default,
8825 then the default for this option is the system version on which the
8826 compiler is running, otherwise the default is to make choices which
8827 are compatible with as many systems and code bases as possible.
8831 Enable kernel development mode. The @option{-mkernel} option sets
8832 @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit},
8833 @option{-fno-exceptions}, @option{-fno-non-call-exceptions},
8834 @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
8835 applicable. This mode also sets @option{-mno-altivec},
8836 @option{-msoft-float}, @option{-fno-builtin} and
8837 @option{-mlong-branch} for PowerPC targets.
8839 @item -mone-byte-bool
8840 @opindex mone-byte-bool
8841 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
8842 By default @samp{sizeof(bool)} is @samp{4} when compiling for
8843 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
8844 option has no effect on x86.
8846 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
8847 to generate code that is not binary compatible with code generated
8848 without that switch. Using this switch may require recompiling all
8849 other modules in a program, including system libraries. Use this
8850 switch to conform to a non-default data model.
8852 @item -mfix-and-continue
8853 @itemx -ffix-and-continue
8854 @itemx -findirect-data
8855 @opindex mfix-and-continue
8856 @opindex ffix-and-continue
8857 @opindex findirect-data
8858 Generate code suitable for fast turn around development. Needed to
8859 enable gdb to dynamically load @code{.o} files into already running
8860 programs. @option{-findirect-data} and @option{-ffix-and-continue}
8861 are provided for backwards compatibility.
8865 Loads all members of static archive libraries.
8866 See man ld(1) for more information.
8868 @item -arch_errors_fatal
8869 @opindex arch_errors_fatal
8870 Cause the errors having to do with files that have the wrong architecture
8874 @opindex bind_at_load
8875 Causes the output file to be marked such that the dynamic linker will
8876 bind all undefined references when the file is loaded or launched.
8880 Produce a Mach-o bundle format file.
8881 See man ld(1) for more information.
8883 @item -bundle_loader @var{executable}
8884 @opindex bundle_loader
8885 This option specifies the @var{executable} that will be loading the build
8886 output file being linked. See man ld(1) for more information.
8890 When passed this option, GCC will produce a dynamic library instead of
8891 an executable when linking, using the Darwin @file{libtool} command.
8893 @item -force_cpusubtype_ALL
8894 @opindex force_cpusubtype_ALL
8895 This causes GCC's output file to have the @var{ALL} subtype, instead of
8896 one controlled by the @option{-mcpu} or @option{-march} option.
8898 @item -allowable_client @var{client_name}
8900 @itemx -compatibility_version
8901 @itemx -current_version
8903 @itemx -dependency-file
8905 @itemx -dylinker_install_name
8907 @itemx -exported_symbols_list
8909 @itemx -flat_namespace
8910 @itemx -force_flat_namespace
8911 @itemx -headerpad_max_install_names
8914 @itemx -install_name
8915 @itemx -keep_private_externs
8916 @itemx -multi_module
8917 @itemx -multiply_defined
8918 @itemx -multiply_defined_unused
8920 @itemx -no_dead_strip_inits_and_terms
8921 @itemx -nofixprebinding
8924 @itemx -noseglinkedit
8925 @itemx -pagezero_size
8927 @itemx -prebind_all_twolevel_modules
8928 @itemx -private_bundle
8929 @itemx -read_only_relocs
8931 @itemx -sectobjectsymbols
8935 @itemx -sectobjectsymbols
8938 @itemx -segs_read_only_addr
8939 @itemx -segs_read_write_addr
8940 @itemx -seg_addr_table
8941 @itemx -seg_addr_table_filename
8944 @itemx -segs_read_only_addr
8945 @itemx -segs_read_write_addr
8946 @itemx -single_module
8949 @itemx -sub_umbrella
8950 @itemx -twolevel_namespace
8953 @itemx -unexported_symbols_list
8954 @itemx -weak_reference_mismatches
8957 @opindex allowable_client
8958 @opindex client_name
8959 @opindex compatibility_version
8960 @opindex current_version
8962 @opindex dependency-file
8964 @opindex dylinker_install_name
8966 @opindex exported_symbols_list
8968 @opindex flat_namespace
8969 @opindex force_flat_namespace
8970 @opindex headerpad_max_install_names
8973 @opindex install_name
8974 @opindex keep_private_externs
8975 @opindex multi_module
8976 @opindex multiply_defined
8977 @opindex multiply_defined_unused
8979 @opindex no_dead_strip_inits_and_terms
8980 @opindex nofixprebinding
8981 @opindex nomultidefs
8983 @opindex noseglinkedit
8984 @opindex pagezero_size
8986 @opindex prebind_all_twolevel_modules
8987 @opindex private_bundle
8988 @opindex read_only_relocs
8990 @opindex sectobjectsymbols
8994 @opindex sectobjectsymbols
8997 @opindex segs_read_only_addr
8998 @opindex segs_read_write_addr
8999 @opindex seg_addr_table
9000 @opindex seg_addr_table_filename
9001 @opindex seglinkedit
9003 @opindex segs_read_only_addr
9004 @opindex segs_read_write_addr
9005 @opindex single_module
9007 @opindex sub_library
9008 @opindex sub_umbrella
9009 @opindex twolevel_namespace
9012 @opindex unexported_symbols_list
9013 @opindex weak_reference_mismatches
9014 @opindex whatsloaded
9016 These options are passed to the Darwin linker. The Darwin linker man page
9017 describes them in detail.
9020 @node DEC Alpha Options
9021 @subsection DEC Alpha Options
9023 These @samp{-m} options are defined for the DEC Alpha implementations:
9026 @item -mno-soft-float
9028 @opindex mno-soft-float
9029 @opindex msoft-float
9030 Use (do not use) the hardware floating-point instructions for
9031 floating-point operations. When @option{-msoft-float} is specified,
9032 functions in @file{libgcc.a} will be used to perform floating-point
9033 operations. Unless they are replaced by routines that emulate the
9034 floating-point operations, or compiled in such a way as to call such
9035 emulations routines, these routines will issue floating-point
9036 operations. If you are compiling for an Alpha without floating-point
9037 operations, you must ensure that the library is built so as not to call
9040 Note that Alpha implementations without floating-point operations are
9041 required to have floating-point registers.
9046 @opindex mno-fp-regs
9047 Generate code that uses (does not use) the floating-point register set.
9048 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
9049 register set is not used, floating point operands are passed in integer
9050 registers as if they were integers and floating-point results are passed
9051 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
9052 so any function with a floating-point argument or return value called by code
9053 compiled with @option{-mno-fp-regs} must also be compiled with that
9056 A typical use of this option is building a kernel that does not use,
9057 and hence need not save and restore, any floating-point registers.
9061 The Alpha architecture implements floating-point hardware optimized for
9062 maximum performance. It is mostly compliant with the IEEE floating
9063 point standard. However, for full compliance, software assistance is
9064 required. This option generates code fully IEEE compliant code
9065 @emph{except} that the @var{inexact-flag} is not maintained (see below).
9066 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
9067 defined during compilation. The resulting code is less efficient but is
9068 able to correctly support denormalized numbers and exceptional IEEE
9069 values such as not-a-number and plus/minus infinity. Other Alpha
9070 compilers call this option @option{-ieee_with_no_inexact}.
9072 @item -mieee-with-inexact
9073 @opindex mieee-with-inexact
9074 This is like @option{-mieee} except the generated code also maintains
9075 the IEEE @var{inexact-flag}. Turning on this option causes the
9076 generated code to implement fully-compliant IEEE math. In addition to
9077 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
9078 macro. On some Alpha implementations the resulting code may execute
9079 significantly slower than the code generated by default. Since there is
9080 very little code that depends on the @var{inexact-flag}, you should
9081 normally not specify this option. Other Alpha compilers call this
9082 option @option{-ieee_with_inexact}.
9084 @item -mfp-trap-mode=@var{trap-mode}
9085 @opindex mfp-trap-mode
9086 This option controls what floating-point related traps are enabled.
9087 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
9088 The trap mode can be set to one of four values:
9092 This is the default (normal) setting. The only traps that are enabled
9093 are the ones that cannot be disabled in software (e.g., division by zero
9097 In addition to the traps enabled by @samp{n}, underflow traps are enabled
9101 Like @samp{u}, but the instructions are marked to be safe for software
9102 completion (see Alpha architecture manual for details).
9105 Like @samp{su}, but inexact traps are enabled as well.
9108 @item -mfp-rounding-mode=@var{rounding-mode}
9109 @opindex mfp-rounding-mode
9110 Selects the IEEE rounding mode. Other Alpha compilers call this option
9111 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
9116 Normal IEEE rounding mode. Floating point numbers are rounded towards
9117 the nearest machine number or towards the even machine number in case
9121 Round towards minus infinity.
9124 Chopped rounding mode. Floating point numbers are rounded towards zero.
9127 Dynamic rounding mode. A field in the floating point control register
9128 (@var{fpcr}, see Alpha architecture reference manual) controls the
9129 rounding mode in effect. The C library initializes this register for
9130 rounding towards plus infinity. Thus, unless your program modifies the
9131 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
9134 @item -mtrap-precision=@var{trap-precision}
9135 @opindex mtrap-precision
9136 In the Alpha architecture, floating point traps are imprecise. This
9137 means without software assistance it is impossible to recover from a
9138 floating trap and program execution normally needs to be terminated.
9139 GCC can generate code that can assist operating system trap handlers
9140 in determining the exact location that caused a floating point trap.
9141 Depending on the requirements of an application, different levels of
9142 precisions can be selected:
9146 Program precision. This option is the default and means a trap handler
9147 can only identify which program caused a floating point exception.
9150 Function precision. The trap handler can determine the function that
9151 caused a floating point exception.
9154 Instruction precision. The trap handler can determine the exact
9155 instruction that caused a floating point exception.
9158 Other Alpha compilers provide the equivalent options called
9159 @option{-scope_safe} and @option{-resumption_safe}.
9161 @item -mieee-conformant
9162 @opindex mieee-conformant
9163 This option marks the generated code as IEEE conformant. You must not
9164 use this option unless you also specify @option{-mtrap-precision=i} and either
9165 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
9166 is to emit the line @samp{.eflag 48} in the function prologue of the
9167 generated assembly file. Under DEC Unix, this has the effect that
9168 IEEE-conformant math library routines will be linked in.
9170 @item -mbuild-constants
9171 @opindex mbuild-constants
9172 Normally GCC examines a 32- or 64-bit integer constant to
9173 see if it can construct it from smaller constants in two or three
9174 instructions. If it cannot, it will output the constant as a literal and
9175 generate code to load it from the data segment at runtime.
9177 Use this option to require GCC to construct @emph{all} integer constants
9178 using code, even if it takes more instructions (the maximum is six).
9180 You would typically use this option to build a shared library dynamic
9181 loader. Itself a shared library, it must relocate itself in memory
9182 before it can find the variables and constants in its own data segment.
9188 Select whether to generate code to be assembled by the vendor-supplied
9189 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
9207 Indicate whether GCC should generate code to use the optional BWX,
9208 CIX, FIX and MAX instruction sets. The default is to use the instruction
9209 sets supported by the CPU type specified via @option{-mcpu=} option or that
9210 of the CPU on which GCC was built if none was specified.
9215 @opindex mfloat-ieee
9216 Generate code that uses (does not use) VAX F and G floating point
9217 arithmetic instead of IEEE single and double precision.
9219 @item -mexplicit-relocs
9220 @itemx -mno-explicit-relocs
9221 @opindex mexplicit-relocs
9222 @opindex mno-explicit-relocs
9223 Older Alpha assemblers provided no way to generate symbol relocations
9224 except via assembler macros. Use of these macros does not allow
9225 optimal instruction scheduling. GNU binutils as of version 2.12
9226 supports a new syntax that allows the compiler to explicitly mark
9227 which relocations should apply to which instructions. This option
9228 is mostly useful for debugging, as GCC detects the capabilities of
9229 the assembler when it is built and sets the default accordingly.
9233 @opindex msmall-data
9234 @opindex mlarge-data
9235 When @option{-mexplicit-relocs} is in effect, static data is
9236 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
9237 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
9238 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
9239 16-bit relocations off of the @code{$gp} register. This limits the
9240 size of the small data area to 64KB, but allows the variables to be
9241 directly accessed via a single instruction.
9243 The default is @option{-mlarge-data}. With this option the data area
9244 is limited to just below 2GB@. Programs that require more than 2GB of
9245 data must use @code{malloc} or @code{mmap} to allocate the data in the
9246 heap instead of in the program's data segment.
9248 When generating code for shared libraries, @option{-fpic} implies
9249 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
9253 @opindex msmall-text
9254 @opindex mlarge-text
9255 When @option{-msmall-text} is used, the compiler assumes that the
9256 code of the entire program (or shared library) fits in 4MB, and is
9257 thus reachable with a branch instruction. When @option{-msmall-data}
9258 is used, the compiler can assume that all local symbols share the
9259 same @code{$gp} value, and thus reduce the number of instructions
9260 required for a function call from 4 to 1.
9262 The default is @option{-mlarge-text}.
9264 @item -mcpu=@var{cpu_type}
9266 Set the instruction set and instruction scheduling parameters for
9267 machine type @var{cpu_type}. You can specify either the @samp{EV}
9268 style name or the corresponding chip number. GCC supports scheduling
9269 parameters for the EV4, EV5 and EV6 family of processors and will
9270 choose the default values for the instruction set from the processor
9271 you specify. If you do not specify a processor type, GCC will default
9272 to the processor on which the compiler was built.
9274 Supported values for @var{cpu_type} are
9280 Schedules as an EV4 and has no instruction set extensions.
9284 Schedules as an EV5 and has no instruction set extensions.
9288 Schedules as an EV5 and supports the BWX extension.
9293 Schedules as an EV5 and supports the BWX and MAX extensions.
9297 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
9301 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
9304 @item -mtune=@var{cpu_type}
9306 Set only the instruction scheduling parameters for machine type
9307 @var{cpu_type}. The instruction set is not changed.
9309 @item -mmemory-latency=@var{time}
9310 @opindex mmemory-latency
9311 Sets the latency the scheduler should assume for typical memory
9312 references as seen by the application. This number is highly
9313 dependent on the memory access patterns used by the application
9314 and the size of the external cache on the machine.
9316 Valid options for @var{time} are
9320 A decimal number representing clock cycles.
9326 The compiler contains estimates of the number of clock cycles for
9327 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
9328 (also called Dcache, Scache, and Bcache), as well as to main memory.
9329 Note that L3 is only valid for EV5.
9334 @node DEC Alpha/VMS Options
9335 @subsection DEC Alpha/VMS Options
9337 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
9340 @item -mvms-return-codes
9341 @opindex mvms-return-codes
9342 Return VMS condition codes from main. The default is to return POSIX
9343 style condition (e.g.@: error) codes.
9347 @subsection FRV Options
9354 Only use the first 32 general purpose registers.
9359 Use all 64 general purpose registers.
9364 Use only the first 32 floating point registers.
9369 Use all 64 floating point registers
9372 @opindex mhard-float
9374 Use hardware instructions for floating point operations.
9377 @opindex msoft-float
9379 Use library routines for floating point operations.
9384 Dynamically allocate condition code registers.
9389 Do not try to dynamically allocate condition code registers, only
9390 use @code{icc0} and @code{fcc0}.
9395 Change ABI to use double word insns.
9400 Do not use double word instructions.
9405 Use floating point double instructions.
9410 Do not use floating point double instructions.
9415 Use media instructions.
9420 Do not use media instructions.
9425 Use multiply and add/subtract instructions.
9430 Do not use multiply and add/subtract instructions.
9435 Select the FDPIC ABI, that uses function descriptors to represent
9436 pointers to functions. Without any PIC/PIE-related options, it
9437 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
9438 assumes GOT entries and small data are within a 12-bit range from the
9439 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
9440 are computed with 32 bits.
9443 @opindex minline-plt
9445 Enable inlining of PLT entries in function calls to functions that are
9446 not known to bind locally. It has no effect without @option{-mfdpic}.
9447 It's enabled by default if optimizing for speed and compiling for
9448 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
9449 optimization option such as @option{-O3} or above is present in the
9455 Assume a large TLS segment when generating thread-local code.
9460 Do not assume a large TLS segment when generating thread-local code.
9465 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
9466 that is known to be in read-only sections. It's enabled by default,
9467 except for @option{-fpic} or @option{-fpie}: even though it may help
9468 make the global offset table smaller, it trades 1 instruction for 4.
9469 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
9470 one of which may be shared by multiple symbols, and it avoids the need
9471 for a GOT entry for the referenced symbol, so it's more likely to be a
9472 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
9474 @item -multilib-library-pic
9475 @opindex multilib-library-pic
9477 Link with the (library, not FD) pic libraries. It's implied by
9478 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
9479 @option{-fpic} without @option{-mfdpic}. You should never have to use
9485 Follow the EABI requirement of always creating a frame pointer whenever
9486 a stack frame is allocated. This option is enabled by default and can
9487 be disabled with @option{-mno-linked-fp}.
9490 @opindex mlong-calls
9492 Use indirect addressing to call functions outside the current
9493 compilation unit. This allows the functions to be placed anywhere
9494 within the 32-bit address space.
9496 @item -malign-labels
9497 @opindex malign-labels
9499 Try to align labels to an 8-byte boundary by inserting nops into the
9500 previous packet. This option only has an effect when VLIW packing
9501 is enabled. It doesn't create new packets; it merely adds nops to
9505 @opindex mlibrary-pic
9507 Generate position-independent EABI code.
9512 Use only the first four media accumulator registers.
9517 Use all eight media accumulator registers.
9522 Pack VLIW instructions.
9527 Do not pack VLIW instructions.
9532 Do not mark ABI switches in e_flags.
9537 Enable the use of conditional-move instructions (default).
9539 This switch is mainly for debugging the compiler and will likely be removed
9540 in a future version.
9542 @item -mno-cond-move
9543 @opindex mno-cond-move
9545 Disable the use of conditional-move instructions.
9547 This switch is mainly for debugging the compiler and will likely be removed
9548 in a future version.
9553 Enable the use of conditional set instructions (default).
9555 This switch is mainly for debugging the compiler and will likely be removed
9556 in a future version.
9561 Disable the use of conditional set instructions.
9563 This switch is mainly for debugging the compiler and will likely be removed
9564 in a future version.
9569 Enable the use of conditional execution (default).
9571 This switch is mainly for debugging the compiler and will likely be removed
9572 in a future version.
9574 @item -mno-cond-exec
9575 @opindex mno-cond-exec
9577 Disable the use of conditional execution.
9579 This switch is mainly for debugging the compiler and will likely be removed
9580 in a future version.
9583 @opindex mvliw-branch
9585 Run a pass to pack branches into VLIW instructions (default).
9587 This switch is mainly for debugging the compiler and will likely be removed
9588 in a future version.
9590 @item -mno-vliw-branch
9591 @opindex mno-vliw-branch
9593 Do not run a pass to pack branches into VLIW instructions.
9595 This switch is mainly for debugging the compiler and will likely be removed
9596 in a future version.
9598 @item -mmulti-cond-exec
9599 @opindex mmulti-cond-exec
9601 Enable optimization of @code{&&} and @code{||} in conditional execution
9604 This switch is mainly for debugging the compiler and will likely be removed
9605 in a future version.
9607 @item -mno-multi-cond-exec
9608 @opindex mno-multi-cond-exec
9610 Disable optimization of @code{&&} and @code{||} in conditional execution.
9612 This switch is mainly for debugging the compiler and will likely be removed
9613 in a future version.
9615 @item -mnested-cond-exec
9616 @opindex mnested-cond-exec
9618 Enable nested conditional execution optimizations (default).
9620 This switch is mainly for debugging the compiler and will likely be removed
9621 in a future version.
9623 @item -mno-nested-cond-exec
9624 @opindex mno-nested-cond-exec
9626 Disable nested conditional execution optimizations.
9628 This switch is mainly for debugging the compiler and will likely be removed
9629 in a future version.
9631 @item -moptimize-membar
9632 @opindex moptimize-membar
9634 This switch removes redundant @code{membar} instructions from the
9635 compiler generated code. It is enabled by default.
9637 @item -mno-optimize-membar
9638 @opindex mno-optimize-membar
9640 This switch disables the automatic removal of redundant @code{membar}
9641 instructions from the generated code.
9643 @item -mtomcat-stats
9644 @opindex mtomcat-stats
9646 Cause gas to print out tomcat statistics.
9648 @item -mcpu=@var{cpu}
9651 Select the processor type for which to generate code. Possible values are
9652 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
9653 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
9657 @node GNU/Linux Options
9658 @subsection GNU/Linux Options
9660 These @samp{-m} options are defined for GNU/Linux targets:
9665 Use the GNU C library instead of uClibc. This is the default except
9666 on @samp{*-*-linux-*uclibc*} targets.
9670 Use uClibc instead of the GNU C library. This is the default on
9671 @samp{*-*-linux-*uclibc*} targets.
9674 @node H8/300 Options
9675 @subsection H8/300 Options
9677 These @samp{-m} options are defined for the H8/300 implementations:
9682 Shorten some address references at link time, when possible; uses the
9683 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
9684 ld, Using ld}, for a fuller description.
9688 Generate code for the H8/300H@.
9692 Generate code for the H8S@.
9696 Generate code for the H8S and H8/300H in the normal mode. This switch
9697 must be used either with @option{-mh} or @option{-ms}.
9701 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
9705 Make @code{int} data 32 bits by default.
9709 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
9710 The default for the H8/300H and H8S is to align longs and floats on 4
9712 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
9713 This option has no effect on the H8/300.
9717 @subsection HPPA Options
9718 @cindex HPPA Options
9720 These @samp{-m} options are defined for the HPPA family of computers:
9723 @item -march=@var{architecture-type}
9725 Generate code for the specified architecture. The choices for
9726 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
9727 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
9728 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
9729 architecture option for your machine. Code compiled for lower numbered
9730 architectures will run on higher numbered architectures, but not the
9734 @itemx -mpa-risc-1-1
9735 @itemx -mpa-risc-2-0
9736 @opindex mpa-risc-1-0
9737 @opindex mpa-risc-1-1
9738 @opindex mpa-risc-2-0
9739 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
9742 @opindex mbig-switch
9743 Generate code suitable for big switch tables. Use this option only if
9744 the assembler/linker complain about out of range branches within a switch
9747 @item -mjump-in-delay
9748 @opindex mjump-in-delay
9749 Fill delay slots of function calls with unconditional jump instructions
9750 by modifying the return pointer for the function call to be the target
9751 of the conditional jump.
9753 @item -mdisable-fpregs
9754 @opindex mdisable-fpregs
9755 Prevent floating point registers from being used in any manner. This is
9756 necessary for compiling kernels which perform lazy context switching of
9757 floating point registers. If you use this option and attempt to perform
9758 floating point operations, the compiler will abort.
9760 @item -mdisable-indexing
9761 @opindex mdisable-indexing
9762 Prevent the compiler from using indexing address modes. This avoids some
9763 rather obscure problems when compiling MIG generated code under MACH@.
9765 @item -mno-space-regs
9766 @opindex mno-space-regs
9767 Generate code that assumes the target has no space registers. This allows
9768 GCC to generate faster indirect calls and use unscaled index address modes.
9770 Such code is suitable for level 0 PA systems and kernels.
9772 @item -mfast-indirect-calls
9773 @opindex mfast-indirect-calls
9774 Generate code that assumes calls never cross space boundaries. This
9775 allows GCC to emit code which performs faster indirect calls.
9777 This option will not work in the presence of shared libraries or nested
9780 @item -mfixed-range=@var{register-range}
9781 @opindex mfixed-range
9782 Generate code treating the given register range as fixed registers.
9783 A fixed register is one that the register allocator can not use. This is
9784 useful when compiling kernel code. A register range is specified as
9785 two registers separated by a dash. Multiple register ranges can be
9786 specified separated by a comma.
9788 @item -mlong-load-store
9789 @opindex mlong-load-store
9790 Generate 3-instruction load and store sequences as sometimes required by
9791 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
9794 @item -mportable-runtime
9795 @opindex mportable-runtime
9796 Use the portable calling conventions proposed by HP for ELF systems.
9800 Enable the use of assembler directives only GAS understands.
9802 @item -mschedule=@var{cpu-type}
9804 Schedule code according to the constraints for the machine type
9805 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
9806 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
9807 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
9808 proper scheduling option for your machine. The default scheduling is
9812 @opindex mlinker-opt
9813 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
9814 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
9815 linkers in which they give bogus error messages when linking some programs.
9818 @opindex msoft-float
9819 Generate output containing library calls for floating point.
9820 @strong{Warning:} the requisite libraries are not available for all HPPA
9821 targets. Normally the facilities of the machine's usual C compiler are
9822 used, but this cannot be done directly in cross-compilation. You must make
9823 your own arrangements to provide suitable library functions for
9824 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
9825 does provide software floating point support.
9827 @option{-msoft-float} changes the calling convention in the output file;
9828 therefore, it is only useful if you compile @emph{all} of a program with
9829 this option. In particular, you need to compile @file{libgcc.a}, the
9830 library that comes with GCC, with @option{-msoft-float} in order for
9835 Generate the predefine, @code{_SIO}, for server IO@. The default is
9836 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
9837 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
9838 options are available under HP-UX and HI-UX@.
9842 Use GNU ld specific options. This passes @option{-shared} to ld when
9843 building a shared library. It is the default when GCC is configured,
9844 explicitly or implicitly, with the GNU linker. This option does not
9845 have any affect on which ld is called, it only changes what parameters
9846 are passed to that ld. The ld that is called is determined by the
9847 @option{--with-ld} configure option, GCC's program search path, and
9848 finally by the user's @env{PATH}. The linker used by GCC can be printed
9849 using @samp{which `gcc -print-prog-name=ld`}. This option is only available
9850 on the 64 bit HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
9854 Use HP ld specific options. This passes @option{-b} to ld when building
9855 a shared library and passes @option{+Accept TypeMismatch} to ld on all
9856 links. It is the default when GCC is configured, explicitly or
9857 implicitly, with the HP linker. This option does not have any affect on
9858 which ld is called, it only changes what parameters are passed to that
9859 ld. The ld that is called is determined by the @option{--with-ld}
9860 configure option, GCC's program search path, and finally by the user's
9861 @env{PATH}. The linker used by GCC can be printed using @samp{which
9862 `gcc -print-prog-name=ld`}. This option is only available on the 64 bit
9863 HP-UX GCC, i.e. configured with @samp{hppa*64*-*-hpux*}.
9866 @opindex mno-long-calls
9867 Generate code that uses long call sequences. This ensures that a call
9868 is always able to reach linker generated stubs. The default is to generate
9869 long calls only when the distance from the call site to the beginning
9870 of the function or translation unit, as the case may be, exceeds a
9871 predefined limit set by the branch type being used. The limits for
9872 normal calls are 7,600,000 and 240,000 bytes, respectively for the
9873 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
9876 Distances are measured from the beginning of functions when using the
9877 @option{-ffunction-sections} option, or when using the @option{-mgas}
9878 and @option{-mno-portable-runtime} options together under HP-UX with
9881 It is normally not desirable to use this option as it will degrade
9882 performance. However, it may be useful in large applications,
9883 particularly when partial linking is used to build the application.
9885 The types of long calls used depends on the capabilities of the
9886 assembler and linker, and the type of code being generated. The
9887 impact on systems that support long absolute calls, and long pic
9888 symbol-difference or pc-relative calls should be relatively small.
9889 However, an indirect call is used on 32-bit ELF systems in pic code
9890 and it is quite long.
9892 @item -munix=@var{unix-std}
9894 Generate compiler predefines and select a startfile for the specified
9895 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
9896 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
9897 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
9898 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
9899 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
9902 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
9903 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
9904 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
9905 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
9906 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
9907 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
9909 It is @emph{important} to note that this option changes the interfaces
9910 for various library routines. It also affects the operational behavior
9911 of the C library. Thus, @emph{extreme} care is needed in using this
9914 Library code that is intended to operate with more than one UNIX
9915 standard must test, set and restore the variable @var{__xpg4_extended_mask}
9916 as appropriate. Most GNU software doesn't provide this capability.
9920 Suppress the generation of link options to search libdld.sl when the
9921 @option{-static} option is specified on HP-UX 10 and later.
9925 The HP-UX implementation of setlocale in libc has a dependency on
9926 libdld.sl. There isn't an archive version of libdld.sl. Thus,
9927 when the @option{-static} option is specified, special link options
9928 are needed to resolve this dependency.
9930 On HP-UX 10 and later, the GCC driver adds the necessary options to
9931 link with libdld.sl when the @option{-static} option is specified.
9932 This causes the resulting binary to be dynamic. On the 64-bit port,
9933 the linkers generate dynamic binaries by default in any case. The
9934 @option{-nolibdld} option can be used to prevent the GCC driver from
9935 adding these link options.
9939 Add support for multithreading with the @dfn{dce thread} library
9940 under HP-UX@. This option sets flags for both the preprocessor and
9944 @node i386 and x86-64 Options
9945 @subsection Intel 386 and AMD x86-64 Options
9946 @cindex i386 Options
9947 @cindex x86-64 Options
9948 @cindex Intel 386 Options
9949 @cindex AMD x86-64 Options
9951 These @samp{-m} options are defined for the i386 and x86-64 family of
9955 @item -mtune=@var{cpu-type}
9957 Tune to @var{cpu-type} everything applicable about the generated code, except
9958 for the ABI and the set of available instructions. The choices for
9962 Produce code optimized for the most common IA32/AMD64/EM64T processors.
9963 If you know the CPU on which your code will run, then you should use
9964 the corresponding @option{-mtune} option instead of
9965 @option{-mtune=generic}. But, if you do not know exactly what CPU users
9966 of your application will have, then you should use this option.
9968 As new processors are deployed in the marketplace, the behavior of this
9969 option will change. Therefore, if you upgrade to a newer version of
9970 GCC, the code generated option will change to reflect the processors
9971 that were most common when that version of GCC was released.
9973 There is no @option{-march=generic} option because @option{-march}
9974 indicates the instruction set the compiler can use, and there is no
9975 generic instruction set applicable to all processors. In contrast,
9976 @option{-mtune} indicates the processor (or, in this case, collection of
9977 processors) for which the code is optimized.
9979 This selects the CPU to tune for at compilation time by determining
9980 the processor type of the compiling machine. Using @option{-mtune=native}
9981 will produce code optimized for the local machine under the constraints
9982 of the selected instruction set. Using @option{-march=native} will
9983 enable all instruction subsets supported by the local machine (hence
9984 the result might not run on different machines).
9986 Original Intel's i386 CPU@.
9988 Intel's i486 CPU@. (No scheduling is implemented for this chip.)
9990 Intel Pentium CPU with no MMX support.
9992 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
9994 Intel PentiumPro CPU@.
9996 Same as @code{generic}, but when used as @code{march} option, PentiumPro
9997 instruction set will be used, so the code will run on all i686 family chips.
9999 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
10000 @item pentium3, pentium3m
10001 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
10004 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
10005 support. Used by Centrino notebooks.
10006 @item pentium4, pentium4m
10007 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
10009 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
10012 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
10013 SSE2 and SSE3 instruction set support.
10015 Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
10016 instruction set support.
10018 AMD K6 CPU with MMX instruction set support.
10020 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
10021 @item athlon, athlon-tbird
10022 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
10024 @item athlon-4, athlon-xp, athlon-mp
10025 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
10026 instruction set support.
10027 @item k8, opteron, athlon64, athlon-fx
10028 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
10029 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
10030 @item k8-sse3, opteron-sse3, athlon64-sse3
10031 Improved versions of k8, opteron and athlon64 with SSE3 instruction set support.
10032 @item amdfam10, barcelona
10033 AMD Family 10h core based CPUs with x86-64 instruction set support. (This
10034 supersets MMX, SSE, SSE2, SSE3, SSE4A, 3dNOW!, enhanced 3dNOW!, ABM and 64-bit
10035 instruction set extensions.)
10037 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
10040 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
10041 instruction set support.
10043 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
10044 implemented for this chip.)
10046 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
10047 implemented for this chip.)
10049 Embedded AMD CPU with MMX and 3dNOW! instruction set support.
10052 While picking a specific @var{cpu-type} will schedule things appropriately
10053 for that particular chip, the compiler will not generate any code that
10054 does not run on the i386 without the @option{-march=@var{cpu-type}} option
10057 @item -march=@var{cpu-type}
10059 Generate instructions for the machine type @var{cpu-type}. The choices
10060 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
10061 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
10063 @item -mcpu=@var{cpu-type}
10065 A deprecated synonym for @option{-mtune}.
10067 @item -mfpmath=@var{unit}
10069 Generate floating point arithmetics for selected unit @var{unit}. The choices
10070 for @var{unit} are:
10074 Use the standard 387 floating point coprocessor present majority of chips and
10075 emulated otherwise. Code compiled with this option will run almost everywhere.
10076 The temporary results are computed in 80bit precision instead of precision
10077 specified by the type resulting in slightly different results compared to most
10078 of other chips. See @option{-ffloat-store} for more detailed description.
10080 This is the default choice for i386 compiler.
10083 Use scalar floating point instructions present in the SSE instruction set.
10084 This instruction set is supported by Pentium3 and newer chips, in the AMD line
10085 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
10086 instruction set supports only single precision arithmetics, thus the double and
10087 extended precision arithmetics is still done using 387. Later version, present
10088 only in Pentium4 and the future AMD x86-64 chips supports double precision
10091 For the i386 compiler, you need to use @option{-march=@var{cpu-type}}, @option{-msse}
10092 or @option{-msse2} switches to enable SSE extensions and make this option
10093 effective. For the x86-64 compiler, these extensions are enabled by default.
10095 The resulting code should be considerably faster in the majority of cases and avoid
10096 the numerical instability problems of 387 code, but may break some existing
10097 code that expects temporaries to be 80bit.
10099 This is the default choice for the x86-64 compiler.
10102 Attempt to utilize both instruction sets at once. This effectively double the
10103 amount of available registers and on chips with separate execution units for
10104 387 and SSE the execution resources too. Use this option with care, as it is
10105 still experimental, because the GCC register allocator does not model separate
10106 functional units well resulting in instable performance.
10109 @item -masm=@var{dialect}
10110 @opindex masm=@var{dialect}
10111 Output asm instructions using selected @var{dialect}. Supported
10112 choices are @samp{intel} or @samp{att} (the default one). Darwin does
10113 not support @samp{intel}.
10116 @itemx -mno-ieee-fp
10118 @opindex mno-ieee-fp
10119 Control whether or not the compiler uses IEEE floating point
10120 comparisons. These handle correctly the case where the result of a
10121 comparison is unordered.
10124 @opindex msoft-float
10125 Generate output containing library calls for floating point.
10126 @strong{Warning:} the requisite libraries are not part of GCC@.
10127 Normally the facilities of the machine's usual C compiler are used, but
10128 this can't be done directly in cross-compilation. You must make your
10129 own arrangements to provide suitable library functions for
10132 On machines where a function returns floating point results in the 80387
10133 register stack, some floating point opcodes may be emitted even if
10134 @option{-msoft-float} is used.
10136 @item -mno-fp-ret-in-387
10137 @opindex mno-fp-ret-in-387
10138 Do not use the FPU registers for return values of functions.
10140 The usual calling convention has functions return values of types
10141 @code{float} and @code{double} in an FPU register, even if there
10142 is no FPU@. The idea is that the operating system should emulate
10145 The option @option{-mno-fp-ret-in-387} causes such values to be returned
10146 in ordinary CPU registers instead.
10148 @item -mno-fancy-math-387
10149 @opindex mno-fancy-math-387
10150 Some 387 emulators do not support the @code{sin}, @code{cos} and
10151 @code{sqrt} instructions for the 387. Specify this option to avoid
10152 generating those instructions. This option is the default on FreeBSD,
10153 OpenBSD and NetBSD@. This option is overridden when @option{-march}
10154 indicates that the target cpu will always have an FPU and so the
10155 instruction will not need emulation. As of revision 2.6.1, these
10156 instructions are not generated unless you also use the
10157 @option{-funsafe-math-optimizations} switch.
10159 @item -malign-double
10160 @itemx -mno-align-double
10161 @opindex malign-double
10162 @opindex mno-align-double
10163 Control whether GCC aligns @code{double}, @code{long double}, and
10164 @code{long long} variables on a two word boundary or a one word
10165 boundary. Aligning @code{double} variables on a two word boundary will
10166 produce code that runs somewhat faster on a @samp{Pentium} at the
10167 expense of more memory.
10169 On x86-64, @option{-malign-double} is enabled by default.
10171 @strong{Warning:} if you use the @option{-malign-double} switch,
10172 structures containing the above types will be aligned differently than
10173 the published application binary interface specifications for the 386
10174 and will not be binary compatible with structures in code compiled
10175 without that switch.
10177 @item -m96bit-long-double
10178 @itemx -m128bit-long-double
10179 @opindex m96bit-long-double
10180 @opindex m128bit-long-double
10181 These switches control the size of @code{long double} type. The i386
10182 application binary interface specifies the size to be 96 bits,
10183 so @option{-m96bit-long-double} is the default in 32 bit mode.
10185 Modern architectures (Pentium and newer) would prefer @code{long double}
10186 to be aligned to an 8 or 16 byte boundary. In arrays or structures
10187 conforming to the ABI, this would not be possible. So specifying a
10188 @option{-m128bit-long-double} will align @code{long double}
10189 to a 16 byte boundary by padding the @code{long double} with an additional
10192 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
10193 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
10195 Notice that neither of these options enable any extra precision over the x87
10196 standard of 80 bits for a @code{long double}.
10198 @strong{Warning:} if you override the default value for your target ABI, the
10199 structures and arrays containing @code{long double} variables will change
10200 their size as well as function calling convention for function taking
10201 @code{long double} will be modified. Hence they will not be binary
10202 compatible with arrays or structures in code compiled without that switch.
10204 @item -mmlarge-data-threshold=@var{number}
10205 @opindex mlarge-data-threshold=@var{number}
10206 When @option{-mcmodel=medium} is specified, the data greater than
10207 @var{threshold} are placed in large data section. This value must be the
10208 same across all object linked into the binary and defaults to 65535.
10212 Use a different function-calling convention, in which functions that
10213 take a fixed number of arguments return with the @code{ret} @var{num}
10214 instruction, which pops their arguments while returning. This saves one
10215 instruction in the caller since there is no need to pop the arguments
10218 You can specify that an individual function is called with this calling
10219 sequence with the function attribute @samp{stdcall}. You can also
10220 override the @option{-mrtd} option by using the function attribute
10221 @samp{cdecl}. @xref{Function Attributes}.
10223 @strong{Warning:} this calling convention is incompatible with the one
10224 normally used on Unix, so you cannot use it if you need to call
10225 libraries compiled with the Unix compiler.
10227 Also, you must provide function prototypes for all functions that
10228 take variable numbers of arguments (including @code{printf});
10229 otherwise incorrect code will be generated for calls to those
10232 In addition, seriously incorrect code will result if you call a
10233 function with too many arguments. (Normally, extra arguments are
10234 harmlessly ignored.)
10236 @item -mregparm=@var{num}
10238 Control how many registers are used to pass integer arguments. By
10239 default, no registers are used to pass arguments, and at most 3
10240 registers can be used. You can control this behavior for a specific
10241 function by using the function attribute @samp{regparm}.
10242 @xref{Function Attributes}.
10244 @strong{Warning:} if you use this switch, and
10245 @var{num} is nonzero, then you must build all modules with the same
10246 value, including any libraries. This includes the system libraries and
10250 @opindex msseregparm
10251 Use SSE register passing conventions for float and double arguments
10252 and return values. You can control this behavior for a specific
10253 function by using the function attribute @samp{sseregparm}.
10254 @xref{Function Attributes}.
10256 @strong{Warning:} if you use this switch then you must build all
10257 modules with the same value, including any libraries. This includes
10258 the system libraries and startup modules.
10267 Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
10268 is specified, the significands of results of floating-point operations are
10269 rounded to 24 bits (single precision); @option{-mpc64} rounds the the
10270 significands of results of floating-point operations to 53 bits (double
10271 precision) and @option{-mpc80} rounds the significands of results of
10272 floating-point operations to 64 bits (extended double precision), which is
10273 the default. When this option is used, floating-point operations in higher
10274 precisions are not available to the programmer without setting the FPU
10275 control word explicitly.
10277 Setting the rounding of floating-point operations to less than the default
10278 80 bits can speed some programs by 2% or more. Note that some mathematical
10279 libraries assume that extended precision (80 bit) floating-point operations
10280 are enabled by default; routines in such libraries could suffer significant
10281 loss of accuracy, typically through so-called "catastrophic cancellation",
10282 when this option is used to set the precision to less than extended precision.
10284 @item -mstackrealign
10285 @opindex mstackrealign
10286 Realign the stack at entry. On the Intel x86, the
10287 @option{-mstackrealign} option will generate an alternate prologue and
10288 epilogue that realigns the runtime stack. This supports mixing legacy
10289 codes that keep a 4-byte aligned stack with modern codes that keep a
10290 16-byte stack for SSE compatibility. The alternate prologue and
10291 epilogue are slower and bigger than the regular ones, and the
10292 alternate prologue requires an extra scratch register; this lowers the
10293 number of registers available if used in conjunction with the
10294 @code{regparm} attribute. The @option{-mstackrealign} option is
10295 incompatible with the nested function prologue; this is considered a
10296 hard error. See also the attribute @code{force_align_arg_pointer},
10297 applicable to individual functions.
10299 @item -mpreferred-stack-boundary=@var{num}
10300 @opindex mpreferred-stack-boundary
10301 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
10302 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
10303 the default is 4 (16 bytes or 128 bits).
10305 On Pentium and PentiumPro, @code{double} and @code{long double} values
10306 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
10307 suffer significant run time performance penalties. On Pentium III, the
10308 Streaming SIMD Extension (SSE) data type @code{__m128} may not work
10309 properly if it is not 16 byte aligned.
10311 To ensure proper alignment of this values on the stack, the stack boundary
10312 must be as aligned as that required by any value stored on the stack.
10313 Further, every function must be generated such that it keeps the stack
10314 aligned. Thus calling a function compiled with a higher preferred
10315 stack boundary from a function compiled with a lower preferred stack
10316 boundary will most likely misalign the stack. It is recommended that
10317 libraries that use callbacks always use the default setting.
10319 This extra alignment does consume extra stack space, and generally
10320 increases code size. Code that is sensitive to stack space usage, such
10321 as embedded systems and operating system kernels, may want to reduce the
10322 preferred alignment to @option{-mpreferred-stack-boundary=2}.
10354 These switches enable or disable the use of instructions in the MMX,
10355 SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4A, ABM or 3DNow! extended
10357 These extensions are also available as built-in functions: see
10358 @ref{X86 Built-in Functions}, for details of the functions enabled and
10359 disabled by these switches.
10361 To have SSE/SSE2 instructions generated automatically from floating-point
10362 code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
10364 These options will enable GCC to use these extended instructions in
10365 generated code, even without @option{-mfpmath=sse}. Applications which
10366 perform runtime CPU detection must compile separate files for each
10367 supported architecture, using the appropriate flags. In particular,
10368 the file containing the CPU detection code should be compiled without
10373 This option will enable GCC to use CMPXCHG16B instruction in generated code.
10374 CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword)
10375 data types. This is useful for high resolution counters that could be updated
10376 by multiple processors (or cores). This instruction is generated as part of
10377 atomic built-in functions: see @ref{Atomic Builtins} for details.
10381 This option will enable GCC to use SAHF instruction in generated 64-bit code.
10382 Early Intel CPUs with Intel 64 lacked LAHF and SAHF instructions supported
10383 by AMD64 until introduction of Pentium 4 G1 step in December 2005. LAHF and
10384 SAHF are load and store instructions, respectively, for certain status flags.
10385 In 64-bit mode, SAHF instruction is used to optimize @code{fmod}, @code{drem}
10386 or @code{remainder} built-in functions: see @ref{Other Builtins} for details.
10390 This option will enable GCC to use RCPSS and RSQRTSS instructions (and their
10391 vectorized variants RCPPS and RSQRTPS) instead of DIVSS and SQRTSS (and their
10392 vectorized variants). These instructions will be generated only when
10393 @option{-funsafe-math-optimizations} is enabled.
10396 @itemx -mno-push-args
10397 @opindex mpush-args
10398 @opindex mno-push-args
10399 Use PUSH operations to store outgoing parameters. This method is shorter
10400 and usually equally fast as method using SUB/MOV operations and is enabled
10401 by default. In some cases disabling it may improve performance because of
10402 improved scheduling and reduced dependencies.
10404 @item -maccumulate-outgoing-args
10405 @opindex maccumulate-outgoing-args
10406 If enabled, the maximum amount of space required for outgoing arguments will be
10407 computed in the function prologue. This is faster on most modern CPUs
10408 because of reduced dependencies, improved scheduling and reduced stack usage
10409 when preferred stack boundary is not equal to 2. The drawback is a notable
10410 increase in code size. This switch implies @option{-mno-push-args}.
10414 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
10415 on thread-safe exception handling must compile and link all code with the
10416 @option{-mthreads} option. When compiling, @option{-mthreads} defines
10417 @option{-D_MT}; when linking, it links in a special thread helper library
10418 @option{-lmingwthrd} which cleans up per thread exception handling data.
10420 @item -mno-align-stringops
10421 @opindex mno-align-stringops
10422 Do not align destination of inlined string operations. This switch reduces
10423 code size and improves performance in case the destination is already aligned,
10424 but GCC doesn't know about it.
10426 @item -minline-all-stringops
10427 @opindex minline-all-stringops
10428 By default GCC inlines string operations only when destination is known to be
10429 aligned at least to 4 byte boundary. This enables more inlining, increase code
10430 size, but may improve performance of code that depends on fast memcpy, strlen
10431 and memset for short lengths.
10433 @item -minline-stringops-dynamically
10434 @opindex minline-stringops-dynamically
10435 For string operation of unknown size, inline runtime checks so for small
10436 blocks inline code is used, while for large blocks library call is used.
10438 @item -mstringop-strategy=@var{alg}
10439 @opindex mstringop-strategy=@var{alg}
10440 Overwrite internal decision heuristic about particular algorithm to inline
10441 string operation with. The allowed values are @code{rep_byte},
10442 @code{rep_4byte}, @code{rep_8byte} for expanding using i386 @code{rep} prefix
10443 of specified size, @code{byte_loop}, @code{loop}, @code{unrolled_loop} for
10444 expanding inline loop, @code{libcall} for always expanding library call.
10446 @item -momit-leaf-frame-pointer
10447 @opindex momit-leaf-frame-pointer
10448 Don't keep the frame pointer in a register for leaf functions. This
10449 avoids the instructions to save, set up and restore frame pointers and
10450 makes an extra register available in leaf functions. The option
10451 @option{-fomit-frame-pointer} removes the frame pointer for all functions
10452 which might make debugging harder.
10454 @item -mtls-direct-seg-refs
10455 @itemx -mno-tls-direct-seg-refs
10456 @opindex mtls-direct-seg-refs
10457 Controls whether TLS variables may be accessed with offsets from the
10458 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
10459 or whether the thread base pointer must be added. Whether or not this
10460 is legal depends on the operating system, and whether it maps the
10461 segment to cover the entire TLS area.
10463 For systems that use GNU libc, the default is on.
10466 These @samp{-m} switches are supported in addition to the above
10467 on AMD x86-64 processors in 64-bit environments.
10474 Generate code for a 32-bit or 64-bit environment.
10475 The 32-bit environment sets int, long and pointer to 32 bits and
10476 generates code that runs on any i386 system.
10477 The 64-bit environment sets int to 32 bits and long and pointer
10478 to 64 bits and generates code for AMD's x86-64 architecture. For
10479 darwin only the -m64 option turns off the @option{-fno-pic} and
10480 @option{-mdynamic-no-pic} options.
10482 @item -mno-red-zone
10483 @opindex no-red-zone
10484 Do not use a so called red zone for x86-64 code. The red zone is mandated
10485 by the x86-64 ABI, it is a 128-byte area beyond the location of the
10486 stack pointer that will not be modified by signal or interrupt handlers
10487 and therefore can be used for temporary data without adjusting the stack
10488 pointer. The flag @option{-mno-red-zone} disables this red zone.
10490 @item -mcmodel=small
10491 @opindex mcmodel=small
10492 Generate code for the small code model: the program and its symbols must
10493 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
10494 Programs can be statically or dynamically linked. This is the default
10497 @item -mcmodel=kernel
10498 @opindex mcmodel=kernel
10499 Generate code for the kernel code model. The kernel runs in the
10500 negative 2 GB of the address space.
10501 This model has to be used for Linux kernel code.
10503 @item -mcmodel=medium
10504 @opindex mcmodel=medium
10505 Generate code for the medium model: The program is linked in the lower 2
10506 GB of the address space but symbols can be located anywhere in the
10507 address space. Programs can be statically or dynamically linked, but
10508 building of shared libraries are not supported with the medium model.
10510 @item -mcmodel=large
10511 @opindex mcmodel=large
10512 Generate code for the large model: This model makes no assumptions
10513 about addresses and sizes of sections.
10516 @node IA-64 Options
10517 @subsection IA-64 Options
10518 @cindex IA-64 Options
10520 These are the @samp{-m} options defined for the Intel IA-64 architecture.
10524 @opindex mbig-endian
10525 Generate code for a big endian target. This is the default for HP-UX@.
10527 @item -mlittle-endian
10528 @opindex mlittle-endian
10529 Generate code for a little endian target. This is the default for AIX5
10535 @opindex mno-gnu-as
10536 Generate (or don't) code for the GNU assembler. This is the default.
10537 @c Also, this is the default if the configure option @option{--with-gnu-as}
10543 @opindex mno-gnu-ld
10544 Generate (or don't) code for the GNU linker. This is the default.
10545 @c Also, this is the default if the configure option @option{--with-gnu-ld}
10550 Generate code that does not use a global pointer register. The result
10551 is not position independent code, and violates the IA-64 ABI@.
10553 @item -mvolatile-asm-stop
10554 @itemx -mno-volatile-asm-stop
10555 @opindex mvolatile-asm-stop
10556 @opindex mno-volatile-asm-stop
10557 Generate (or don't) a stop bit immediately before and after volatile asm
10560 @item -mregister-names
10561 @itemx -mno-register-names
10562 @opindex mregister-names
10563 @opindex mno-register-names
10564 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
10565 the stacked registers. This may make assembler output more readable.
10571 Disable (or enable) optimizations that use the small data section. This may
10572 be useful for working around optimizer bugs.
10574 @item -mconstant-gp
10575 @opindex mconstant-gp
10576 Generate code that uses a single constant global pointer value. This is
10577 useful when compiling kernel code.
10581 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
10582 This is useful when compiling firmware code.
10584 @item -minline-float-divide-min-latency
10585 @opindex minline-float-divide-min-latency
10586 Generate code for inline divides of floating point values
10587 using the minimum latency algorithm.
10589 @item -minline-float-divide-max-throughput
10590 @opindex minline-float-divide-max-throughput
10591 Generate code for inline divides of floating point values
10592 using the maximum throughput algorithm.
10594 @item -minline-int-divide-min-latency
10595 @opindex minline-int-divide-min-latency
10596 Generate code for inline divides of integer values
10597 using the minimum latency algorithm.
10599 @item -minline-int-divide-max-throughput
10600 @opindex minline-int-divide-max-throughput
10601 Generate code for inline divides of integer values
10602 using the maximum throughput algorithm.
10604 @item -minline-sqrt-min-latency
10605 @opindex minline-sqrt-min-latency
10606 Generate code for inline square roots
10607 using the minimum latency algorithm.
10609 @item -minline-sqrt-max-throughput
10610 @opindex minline-sqrt-max-throughput
10611 Generate code for inline square roots
10612 using the maximum throughput algorithm.
10614 @item -mno-dwarf2-asm
10615 @itemx -mdwarf2-asm
10616 @opindex mno-dwarf2-asm
10617 @opindex mdwarf2-asm
10618 Don't (or do) generate assembler code for the DWARF2 line number debugging
10619 info. This may be useful when not using the GNU assembler.
10621 @item -mearly-stop-bits
10622 @itemx -mno-early-stop-bits
10623 @opindex mearly-stop-bits
10624 @opindex mno-early-stop-bits
10625 Allow stop bits to be placed earlier than immediately preceding the
10626 instruction that triggered the stop bit. This can improve instruction
10627 scheduling, but does not always do so.
10629 @item -mfixed-range=@var{register-range}
10630 @opindex mfixed-range
10631 Generate code treating the given register range as fixed registers.
10632 A fixed register is one that the register allocator can not use. This is
10633 useful when compiling kernel code. A register range is specified as
10634 two registers separated by a dash. Multiple register ranges can be
10635 specified separated by a comma.
10637 @item -mtls-size=@var{tls-size}
10639 Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
10642 @item -mtune=@var{cpu-type}
10644 Tune the instruction scheduling for a particular CPU, Valid values are
10645 itanium, itanium1, merced, itanium2, and mckinley.
10651 Add support for multithreading using the POSIX threads library. This
10652 option sets flags for both the preprocessor and linker. It does
10653 not affect the thread safety of object code produced by the compiler or
10654 that of libraries supplied with it. These are HP-UX specific flags.
10660 Generate code for a 32-bit or 64-bit environment.
10661 The 32-bit environment sets int, long and pointer to 32 bits.
10662 The 64-bit environment sets int to 32 bits and long and pointer
10663 to 64 bits. These are HP-UX specific flags.
10665 @item -mno-sched-br-data-spec
10666 @itemx -msched-br-data-spec
10667 @opindex mno-sched-br-data-spec
10668 @opindex msched-br-data-spec
10669 (Dis/En)able data speculative scheduling before reload.
10670 This will result in generation of the ld.a instructions and
10671 the corresponding check instructions (ld.c / chk.a).
10672 The default is 'disable'.
10674 @item -msched-ar-data-spec
10675 @itemx -mno-sched-ar-data-spec
10676 @opindex msched-ar-data-spec
10677 @opindex mno-sched-ar-data-spec
10678 (En/Dis)able data speculative scheduling after reload.
10679 This will result in generation of the ld.a instructions and
10680 the corresponding check instructions (ld.c / chk.a).
10681 The default is 'enable'.
10683 @item -mno-sched-control-spec
10684 @itemx -msched-control-spec
10685 @opindex mno-sched-control-spec
10686 @opindex msched-control-spec
10687 (Dis/En)able control speculative scheduling. This feature is
10688 available only during region scheduling (i.e. before reload).
10689 This will result in generation of the ld.s instructions and
10690 the corresponding check instructions chk.s .
10691 The default is 'disable'.
10693 @item -msched-br-in-data-spec
10694 @itemx -mno-sched-br-in-data-spec
10695 @opindex msched-br-in-data-spec
10696 @opindex mno-sched-br-in-data-spec
10697 (En/Dis)able speculative scheduling of the instructions that
10698 are dependent on the data speculative loads before reload.
10699 This is effective only with @option{-msched-br-data-spec} enabled.
10700 The default is 'enable'.
10702 @item -msched-ar-in-data-spec
10703 @itemx -mno-sched-ar-in-data-spec
10704 @opindex msched-ar-in-data-spec
10705 @opindex mno-sched-ar-in-data-spec
10706 (En/Dis)able speculative scheduling of the instructions that
10707 are dependent on the data speculative loads after reload.
10708 This is effective only with @option{-msched-ar-data-spec} enabled.
10709 The default is 'enable'.
10711 @item -msched-in-control-spec
10712 @itemx -mno-sched-in-control-spec
10713 @opindex msched-in-control-spec
10714 @opindex mno-sched-in-control-spec
10715 (En/Dis)able speculative scheduling of the instructions that
10716 are dependent on the control speculative loads.
10717 This is effective only with @option{-msched-control-spec} enabled.
10718 The default is 'enable'.
10721 @itemx -mno-sched-ldc
10722 @opindex msched-ldc
10723 @opindex mno-sched-ldc
10724 (En/Dis)able use of simple data speculation checks ld.c .
10725 If disabled, only chk.a instructions will be emitted to check
10726 data speculative loads.
10727 The default is 'enable'.
10729 @item -mno-sched-control-ldc
10730 @itemx -msched-control-ldc
10731 @opindex mno-sched-control-ldc
10732 @opindex msched-control-ldc
10733 (Dis/En)able use of ld.c instructions to check control speculative loads.
10734 If enabled, in case of control speculative load with no speculatively
10735 scheduled dependent instructions this load will be emitted as ld.sa and
10736 ld.c will be used to check it.
10737 The default is 'disable'.
10739 @item -mno-sched-spec-verbose
10740 @itemx -msched-spec-verbose
10741 @opindex mno-sched-spec-verbose
10742 @opindex msched-spec-verbose
10743 (Dis/En)able printing of the information about speculative motions.
10745 @item -mno-sched-prefer-non-data-spec-insns
10746 @itemx -msched-prefer-non-data-spec-insns
10747 @opindex mno-sched-prefer-non-data-spec-insns
10748 @opindex msched-prefer-non-data-spec-insns
10749 If enabled, data speculative instructions will be chosen for schedule
10750 only if there are no other choices at the moment. This will make
10751 the use of the data speculation much more conservative.
10752 The default is 'disable'.
10754 @item -mno-sched-prefer-non-control-spec-insns
10755 @itemx -msched-prefer-non-control-spec-insns
10756 @opindex mno-sched-prefer-non-control-spec-insns
10757 @opindex msched-prefer-non-control-spec-insns
10758 If enabled, control speculative instructions will be chosen for schedule
10759 only if there are no other choices at the moment. This will make
10760 the use of the control speculation much more conservative.
10761 The default is 'disable'.
10763 @item -mno-sched-count-spec-in-critical-path
10764 @itemx -msched-count-spec-in-critical-path
10765 @opindex mno-sched-count-spec-in-critical-path
10766 @opindex msched-count-spec-in-critical-path
10767 If enabled, speculative dependencies will be considered during
10768 computation of the instructions priorities. This will make the use of the
10769 speculation a bit more conservative.
10770 The default is 'disable'.
10775 @subsection M32C Options
10776 @cindex M32C options
10779 @item -mcpu=@var{name}
10781 Select the CPU for which code is generated. @var{name} may be one of
10782 @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
10783 /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
10784 the M32C/80 series.
10788 Specifies that the program will be run on the simulator. This causes
10789 an alternate runtime library to be linked in which supports, for
10790 example, file I/O. You must not use this option when generating
10791 programs that will run on real hardware; you must provide your own
10792 runtime library for whatever I/O functions are needed.
10794 @item -memregs=@var{number}
10796 Specifies the number of memory-based pseudo-registers GCC will use
10797 during code generation. These pseudo-registers will be used like real
10798 registers, so there is a tradeoff between GCC's ability to fit the
10799 code into available registers, and the performance penalty of using
10800 memory instead of registers. Note that all modules in a program must
10801 be compiled with the same value for this option. Because of that, you
10802 must not use this option with the default runtime libraries gcc
10807 @node M32R/D Options
10808 @subsection M32R/D Options
10809 @cindex M32R/D options
10811 These @option{-m} options are defined for Renesas M32R/D architectures:
10816 Generate code for the M32R/2@.
10820 Generate code for the M32R/X@.
10824 Generate code for the M32R@. This is the default.
10826 @item -mmodel=small
10827 @opindex mmodel=small
10828 Assume all objects live in the lower 16MB of memory (so that their addresses
10829 can be loaded with the @code{ld24} instruction), and assume all subroutines
10830 are reachable with the @code{bl} instruction.
10831 This is the default.
10833 The addressability of a particular object can be set with the
10834 @code{model} attribute.
10836 @item -mmodel=medium
10837 @opindex mmodel=medium
10838 Assume objects may be anywhere in the 32-bit address space (the compiler
10839 will generate @code{seth/add3} instructions to load their addresses), and
10840 assume all subroutines are reachable with the @code{bl} instruction.
10842 @item -mmodel=large
10843 @opindex mmodel=large
10844 Assume objects may be anywhere in the 32-bit address space (the compiler
10845 will generate @code{seth/add3} instructions to load their addresses), and
10846 assume subroutines may not be reachable with the @code{bl} instruction
10847 (the compiler will generate the much slower @code{seth/add3/jl}
10848 instruction sequence).
10851 @opindex msdata=none
10852 Disable use of the small data area. Variables will be put into
10853 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
10854 @code{section} attribute has been specified).
10855 This is the default.
10857 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
10858 Objects may be explicitly put in the small data area with the
10859 @code{section} attribute using one of these sections.
10861 @item -msdata=sdata
10862 @opindex msdata=sdata
10863 Put small global and static data in the small data area, but do not
10864 generate special code to reference them.
10867 @opindex msdata=use
10868 Put small global and static data in the small data area, and generate
10869 special instructions to reference them.
10873 @cindex smaller data references
10874 Put global and static objects less than or equal to @var{num} bytes
10875 into the small data or bss sections instead of the normal data or bss
10876 sections. The default value of @var{num} is 8.
10877 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
10878 for this option to have any effect.
10880 All modules should be compiled with the same @option{-G @var{num}} value.
10881 Compiling with different values of @var{num} may or may not work; if it
10882 doesn't the linker will give an error message---incorrect code will not be
10887 Makes the M32R specific code in the compiler display some statistics
10888 that might help in debugging programs.
10890 @item -malign-loops
10891 @opindex malign-loops
10892 Align all loops to a 32-byte boundary.
10894 @item -mno-align-loops
10895 @opindex mno-align-loops
10896 Do not enforce a 32-byte alignment for loops. This is the default.
10898 @item -missue-rate=@var{number}
10899 @opindex missue-rate=@var{number}
10900 Issue @var{number} instructions per cycle. @var{number} can only be 1
10903 @item -mbranch-cost=@var{number}
10904 @opindex mbranch-cost=@var{number}
10905 @var{number} can only be 1 or 2. If it is 1 then branches will be
10906 preferred over conditional code, if it is 2, then the opposite will
10909 @item -mflush-trap=@var{number}
10910 @opindex mflush-trap=@var{number}
10911 Specifies the trap number to use to flush the cache. The default is
10912 12. Valid numbers are between 0 and 15 inclusive.
10914 @item -mno-flush-trap
10915 @opindex mno-flush-trap
10916 Specifies that the cache cannot be flushed by using a trap.
10918 @item -mflush-func=@var{name}
10919 @opindex mflush-func=@var{name}
10920 Specifies the name of the operating system function to call to flush
10921 the cache. The default is @emph{_flush_cache}, but a function call
10922 will only be used if a trap is not available.
10924 @item -mno-flush-func
10925 @opindex mno-flush-func
10926 Indicates that there is no OS function for flushing the cache.
10930 @node M680x0 Options
10931 @subsection M680x0 Options
10932 @cindex M680x0 options
10934 These are the @samp{-m} options defined for M680x0 and ColdFire processors.
10935 The default settings depend on which architecture was selected when
10936 the compiler was configured; the defaults for the most common choices
10940 @item -march=@var{arch}
10942 Generate code for a specific M680x0 or ColdFire instruction set
10943 architecture. Permissible values of @var{arch} for M680x0
10944 architectures are: @samp{68000}, @samp{68010}, @samp{68020},
10945 @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
10946 architectures are selected according to Freescale's ISA classification
10947 and the permissible values are: @samp{isaa}, @samp{isaaplus},
10948 @samp{isab} and @samp{isac}.
10950 gcc defines a macro @samp{__mcf@var{arch}__} whenever it is generating
10951 code for a ColdFire target. The @var{arch} in this macro is one of the
10952 @option{-march} arguments given above.
10954 When used together, @option{-march} and @option{-mtune} select code
10955 that runs on a family of similar processors but that is optimized
10956 for a particular microarchitecture.
10958 @item -mcpu=@var{cpu}
10960 Generate code for a specific M680x0 or ColdFire processor.
10961 The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
10962 @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
10963 and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
10964 below, which also classifies the CPUs into families:
10966 @multitable @columnfractions 0.20 0.80
10967 @item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
10968 @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
10969 @item @samp{5206e} @tab @samp{5206e}
10970 @item @samp{5208} @tab @samp{5207} @samp{5208}
10971 @item @samp{5211a} @tab @samp{5210a} @samp{5211a}
10972 @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
10973 @item @samp{5216} @tab @samp{5214} @samp{5216}
10974 @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
10975 @item @samp{5225} @tab @samp{5224} @samp{5225}
10976 @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
10977 @item @samp{5249} @tab @samp{5249}
10978 @item @samp{5250} @tab @samp{5250}
10979 @item @samp{5271} @tab @samp{5270} @samp{5271}
10980 @item @samp{5272} @tab @samp{5272}
10981 @item @samp{5275} @tab @samp{5274} @samp{5275}
10982 @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
10983 @item @samp{5307} @tab @samp{5307}
10984 @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
10985 @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
10986 @item @samp{5407} @tab @samp{5407}
10987 @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}
10990 @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
10991 @var{arch} is compatible with @var{cpu}. Other combinations of
10992 @option{-mcpu} and @option{-march} are rejected.
10994 gcc defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target
10995 @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}},
10996 where the value of @var{family} is given by the table above.
10998 @item -mtune=@var{tune}
11000 Tune the code for a particular microarchitecture, within the
11001 constraints set by @option{-march} and @option{-mcpu}.
11002 The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
11003 @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
11004 and @samp{cpu32}. The ColdFire microarchitectures
11005 are: @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
11007 You can also use @option{-mtune=68020-40} for code that needs
11008 to run relatively well on 68020, 68030 and 68040 targets.
11009 @option{-mtune=68020-60} is similar but includes 68060 targets
11010 as well. These two options select the same tuning decisions as
11011 @option{-m68020-40} and @option{-m68020-60} respectively.
11013 gcc defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__}
11014 when tuning for 680x0 architecture @var{arch}. It also defines
11015 @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
11016 option is used. If gcc is tuning for a range of architectures,
11017 as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
11018 it defines the macros for every architecture in the range.
11020 gcc also defines the macro @samp{__m@var{uarch}__} when tuning for
11021 ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
11022 of the arguments given above.
11028 Generate output for a 68000. This is the default
11029 when the compiler is configured for 68000-based systems.
11030 It is equivalent to @option{-march=68000}.
11032 Use this option for microcontrollers with a 68000 or EC000 core,
11033 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
11037 Generate output for a 68010. This is the default
11038 when the compiler is configured for 68010-based systems.
11039 It is equivalent to @option{-march=68010}.
11045 Generate output for a 68020. This is the default
11046 when the compiler is configured for 68020-based systems.
11047 It is equivalent to @option{-march=68020}.
11051 Generate output for a 68030. This is the default when the compiler is
11052 configured for 68030-based systems. It is equivalent to
11053 @option{-march=68030}.
11057 Generate output for a 68040. This is the default when the compiler is
11058 configured for 68040-based systems. It is equivalent to
11059 @option{-march=68040}.
11061 This option inhibits the use of 68881/68882 instructions that have to be
11062 emulated by software on the 68040. Use this option if your 68040 does not
11063 have code to emulate those instructions.
11067 Generate output for a 68060. This is the default when the compiler is
11068 configured for 68060-based systems. It is equivalent to
11069 @option{-march=68060}.
11071 This option inhibits the use of 68020 and 68881/68882 instructions that
11072 have to be emulated by software on the 68060. Use this option if your 68060
11073 does not have code to emulate those instructions.
11077 Generate output for a CPU32. This is the default
11078 when the compiler is configured for CPU32-based systems.
11079 It is equivalent to @option{-march=cpu32}.
11081 Use this option for microcontrollers with a
11082 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
11083 68336, 68340, 68341, 68349 and 68360.
11087 Generate output for a 520X ColdFire CPU. This is the default
11088 when the compiler is configured for 520X-based systems.
11089 It is equivalent to @option{-mcpu=5206}, and is now deprecated
11090 in favor of that option.
11092 Use this option for microcontroller with a 5200 core, including
11093 the MCF5202, MCF5203, MCF5204 and MCF5206.
11097 Generate output for a 5206e ColdFire CPU. The option is now
11098 deprecated in favor of the equivalent @option{-mcpu=5206e}.
11102 Generate output for a member of the ColdFire 528X family.
11103 The option is now deprecated in favor of the equivalent
11104 @option{-mcpu=528x}.
11108 Generate output for a ColdFire 5307 CPU. The option is now deprecated
11109 in favor of the equivalent @option{-mcpu=5307}.
11113 Generate output for a ColdFire 5407 CPU. The option is now deprecated
11114 in favor of the equivalent @option{-mcpu=5407}.
11118 Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
11119 This includes use of hardware floating point instructions.
11120 The option is equivalent to @option{-mcpu=547x}, and is now
11121 deprecated in favor of that option.
11125 Generate output for a 68040, without using any of the new instructions.
11126 This results in code which can run relatively efficiently on either a
11127 68020/68881 or a 68030 or a 68040. The generated code does use the
11128 68881 instructions that are emulated on the 68040.
11130 The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
11134 Generate output for a 68060, without using any of the new instructions.
11135 This results in code which can run relatively efficiently on either a
11136 68020/68881 or a 68030 or a 68040. The generated code does use the
11137 68881 instructions that are emulated on the 68060.
11139 The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
11143 @opindex mhard-float
11145 Generate floating-point instructions. This is the default for 68020
11146 and above, and for ColdFire devices that have an FPU. It defines the
11147 macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__}
11148 on ColdFire targets.
11151 @opindex msoft-float
11152 Do not generate floating-point instructions; use library calls instead.
11153 This is the default for 68000, 68010, and 68832 targets. It is also
11154 the default for ColdFire devices that have no FPU.
11160 Generate (do not generate) ColdFire hardware divide and remainder
11161 instructions. If @option{-march} is used without @option{-mcpu},
11162 the default is ``on'' for ColdFire architectures and ``off'' for M680x0
11163 architectures. Otherwise, the default is taken from the target CPU
11164 (either the default CPU, or the one specified by @option{-mcpu}). For
11165 example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
11166 @option{-mcpu=5206e}.
11168 gcc defines the macro @samp{__mcfhwdiv__} when this option is enabled.
11172 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11173 Additionally, parameters passed on the stack are also aligned to a
11174 16-bit boundary even on targets whose API mandates promotion to 32-bit.
11178 Do not consider type @code{int} to be 16 bits wide. This is the default.
11181 @itemx -mno-bitfield
11182 @opindex mnobitfield
11183 @opindex mno-bitfield
11184 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
11185 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
11189 Do use the bit-field instructions. The @option{-m68020} option implies
11190 @option{-mbitfield}. This is the default if you use a configuration
11191 designed for a 68020.
11195 Use a different function-calling convention, in which functions
11196 that take a fixed number of arguments return with the @code{rtd}
11197 instruction, which pops their arguments while returning. This
11198 saves one instruction in the caller since there is no need to pop
11199 the arguments there.
11201 This calling convention is incompatible with the one normally
11202 used on Unix, so you cannot use it if you need to call libraries
11203 compiled with the Unix compiler.
11205 Also, you must provide function prototypes for all functions that
11206 take variable numbers of arguments (including @code{printf});
11207 otherwise incorrect code will be generated for calls to those
11210 In addition, seriously incorrect code will result if you call a
11211 function with too many arguments. (Normally, extra arguments are
11212 harmlessly ignored.)
11214 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
11215 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
11219 Do not use the calling conventions selected by @option{-mrtd}.
11220 This is the default.
11223 @itemx -mno-align-int
11224 @opindex malign-int
11225 @opindex mno-align-int
11226 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
11227 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
11228 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
11229 Aligning variables on 32-bit boundaries produces code that runs somewhat
11230 faster on processors with 32-bit busses at the expense of more memory.
11232 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
11233 align structures containing the above types differently than
11234 most published application binary interface specifications for the m68k.
11238 Use the pc-relative addressing mode of the 68000 directly, instead of
11239 using a global offset table. At present, this option implies @option{-fpic},
11240 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
11241 not presently supported with @option{-mpcrel}, though this could be supported for
11242 68020 and higher processors.
11244 @item -mno-strict-align
11245 @itemx -mstrict-align
11246 @opindex mno-strict-align
11247 @opindex mstrict-align
11248 Do not (do) assume that unaligned memory references will be handled by
11252 Generate code that allows the data segment to be located in a different
11253 area of memory from the text segment. This allows for execute in place in
11254 an environment without virtual memory management. This option implies
11257 @item -mno-sep-data
11258 Generate code that assumes that the data segment follows the text segment.
11259 This is the default.
11261 @item -mid-shared-library
11262 Generate code that supports shared libraries via the library ID method.
11263 This allows for execute in place and shared libraries in an environment
11264 without virtual memory management. This option implies @option{-fPIC}.
11266 @item -mno-id-shared-library
11267 Generate code that doesn't assume ID based shared libraries are being used.
11268 This is the default.
11270 @item -mshared-library-id=n
11271 Specified the identification number of the ID based shared library being
11272 compiled. Specifying a value of 0 will generate more compact code, specifying
11273 other values will force the allocation of that number to the current
11274 library but is no more space or time efficient than omitting this option.
11278 @node M68hc1x Options
11279 @subsection M68hc1x Options
11280 @cindex M68hc1x options
11282 These are the @samp{-m} options defined for the 68hc11 and 68hc12
11283 microcontrollers. The default values for these options depends on
11284 which style of microcontroller was selected when the compiler was configured;
11285 the defaults for the most common choices are given below.
11292 Generate output for a 68HC11. This is the default
11293 when the compiler is configured for 68HC11-based systems.
11299 Generate output for a 68HC12. This is the default
11300 when the compiler is configured for 68HC12-based systems.
11306 Generate output for a 68HCS12.
11308 @item -mauto-incdec
11309 @opindex mauto-incdec
11310 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
11317 Enable the use of 68HC12 min and max instructions.
11320 @itemx -mno-long-calls
11321 @opindex mlong-calls
11322 @opindex mno-long-calls
11323 Treat all calls as being far away (near). If calls are assumed to be
11324 far away, the compiler will use the @code{call} instruction to
11325 call a function and the @code{rtc} instruction for returning.
11329 Consider type @code{int} to be 16 bits wide, like @code{short int}.
11331 @item -msoft-reg-count=@var{count}
11332 @opindex msoft-reg-count
11333 Specify the number of pseudo-soft registers which are used for the
11334 code generation. The maximum number is 32. Using more pseudo-soft
11335 register may or may not result in better code depending on the program.
11336 The default is 4 for 68HC11 and 2 for 68HC12.
11340 @node MCore Options
11341 @subsection MCore Options
11342 @cindex MCore options
11344 These are the @samp{-m} options defined for the Motorola M*Core
11350 @itemx -mno-hardlit
11352 @opindex mno-hardlit
11353 Inline constants into the code stream if it can be done in two
11354 instructions or less.
11360 Use the divide instruction. (Enabled by default).
11362 @item -mrelax-immediate
11363 @itemx -mno-relax-immediate
11364 @opindex mrelax-immediate
11365 @opindex mno-relax-immediate
11366 Allow arbitrary sized immediates in bit operations.
11368 @item -mwide-bitfields
11369 @itemx -mno-wide-bitfields
11370 @opindex mwide-bitfields
11371 @opindex mno-wide-bitfields
11372 Always treat bit-fields as int-sized.
11374 @item -m4byte-functions
11375 @itemx -mno-4byte-functions
11376 @opindex m4byte-functions
11377 @opindex mno-4byte-functions
11378 Force all functions to be aligned to a four byte boundary.
11380 @item -mcallgraph-data
11381 @itemx -mno-callgraph-data
11382 @opindex mcallgraph-data
11383 @opindex mno-callgraph-data
11384 Emit callgraph information.
11387 @itemx -mno-slow-bytes
11388 @opindex mslow-bytes
11389 @opindex mno-slow-bytes
11390 Prefer word access when reading byte quantities.
11392 @item -mlittle-endian
11393 @itemx -mbig-endian
11394 @opindex mlittle-endian
11395 @opindex mbig-endian
11396 Generate code for a little endian target.
11402 Generate code for the 210 processor.
11406 @subsection MIPS Options
11407 @cindex MIPS options
11413 Generate big-endian code.
11417 Generate little-endian code. This is the default for @samp{mips*el-*-*}
11420 @item -march=@var{arch}
11422 Generate code that will run on @var{arch}, which can be the name of a
11423 generic MIPS ISA, or the name of a particular processor.
11425 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
11426 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
11427 The processor names are:
11428 @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
11429 @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
11430 @samp{5kc}, @samp{5kf},
11432 @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
11433 @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
11434 @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1},
11435 @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
11438 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
11439 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000},
11440 @samp{rm7000}, @samp{rm9000},
11443 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
11444 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
11445 The special value @samp{from-abi} selects the
11446 most compatible architecture for the selected ABI (that is,
11447 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
11449 In processor names, a final @samp{000} can be abbreviated as @samp{k}
11450 (for example, @samp{-march=r2k}). Prefixes are optional, and
11451 @samp{vr} may be written @samp{r}.
11453 Names of the form @samp{@var{n}f2_1} refer to processors with
11454 FPUs clocked at half the rate of the core, names of the form
11455 @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
11456 rate as the core, and names of the form @samp{@var{n}f3_2} refer to
11457 processors with FPUs clocked a ratio of 3:2 with respect to the core.
11458 For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
11459 for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
11460 accepted as synonyms for @samp{@var{n}f1_1}.
11462 GCC defines two macros based on the value of this option. The first
11463 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
11464 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
11465 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
11466 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
11467 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
11469 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
11470 above. In other words, it will have the full prefix and will not
11471 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
11472 the macro names the resolved architecture (either @samp{"mips1"} or
11473 @samp{"mips3"}). It names the default architecture when no
11474 @option{-march} option is given.
11476 @item -mtune=@var{arch}
11478 Optimize for @var{arch}. Among other things, this option controls
11479 the way instructions are scheduled, and the perceived cost of arithmetic
11480 operations. The list of @var{arch} values is the same as for
11483 When this option is not used, GCC will optimize for the processor
11484 specified by @option{-march}. By using @option{-march} and
11485 @option{-mtune} together, it is possible to generate code that will
11486 run on a family of processors, but optimize the code for one
11487 particular member of that family.
11489 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
11490 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
11491 @samp{-march} ones described above.
11495 Equivalent to @samp{-march=mips1}.
11499 Equivalent to @samp{-march=mips2}.
11503 Equivalent to @samp{-march=mips3}.
11507 Equivalent to @samp{-march=mips4}.
11511 Equivalent to @samp{-march=mips32}.
11515 Equivalent to @samp{-march=mips32r2}.
11519 Equivalent to @samp{-march=mips64}.
11524 @opindex mno-mips16
11525 Generate (do not generate) MIPS16 code. If GCC is targetting a
11526 MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE@.
11538 Generate code for the given ABI@.
11540 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
11541 generates 64-bit code when you select a 64-bit architecture, but you
11542 can use @option{-mgp32} to get 32-bit code instead.
11544 For information about the O64 ABI, see
11545 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
11547 GCC supports a variant of the o32 ABI in which floating-point registers
11548 are 64 rather than 32 bits wide. You can select this combination with
11549 @option{-mabi=32} @option{-mfp64}. This ABI relies on the @samp{mthc1}
11550 and @samp{mfhc1} instructions and is therefore only supported for
11551 MIPS32R2 processors.
11553 The register assignments for arguments and return values remain the
11554 same, but each scalar value is passed in a single 64-bit register
11555 rather than a pair of 32-bit registers. For example, scalar
11556 floating-point values are returned in @samp{$f0} only, not a
11557 @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
11558 remains the same, but all 64 bits are saved.
11561 @itemx -mno-abicalls
11563 @opindex mno-abicalls
11564 Generate (do not generate) code that is suitable for SVR4-style
11565 dynamic objects. @option{-mabicalls} is the default for SVR4-based
11570 Generate (do not generate) code that is fully position-independent,
11571 and that can therefore be linked into shared libraries. This option
11572 only affects @option{-mabicalls}.
11574 All @option{-mabicalls} code has traditionally been position-independent,
11575 regardless of options like @option{-fPIC} and @option{-fpic}. However,
11576 as an extension, the GNU toolchain allows executables to use absolute
11577 accesses for locally-binding symbols. It can also use shorter GP
11578 initialization sequences and generate direct calls to locally-defined
11579 functions. This mode is selected by @option{-mno-shared}.
11581 @option{-mno-shared} depends on binutils 2.16 or higher and generates
11582 objects that can only be linked by the GNU linker. However, the option
11583 does not affect the ABI of the final executable; it only affects the ABI
11584 of relocatable objects. Using @option{-mno-shared} will generally make
11585 executables both smaller and quicker.
11587 @option{-mshared} is the default.
11593 Lift (do not lift) the usual restrictions on the size of the global
11596 GCC normally uses a single instruction to load values from the GOT@.
11597 While this is relatively efficient, it will only work if the GOT
11598 is smaller than about 64k. Anything larger will cause the linker
11599 to report an error such as:
11601 @cindex relocation truncated to fit (MIPS)
11603 relocation truncated to fit: R_MIPS_GOT16 foobar
11606 If this happens, you should recompile your code with @option{-mxgot}.
11607 It should then work with very large GOTs, although it will also be
11608 less efficient, since it will take three instructions to fetch the
11609 value of a global symbol.
11611 Note that some linkers can create multiple GOTs. If you have such a
11612 linker, you should only need to use @option{-mxgot} when a single object
11613 file accesses more than 64k's worth of GOT entries. Very few do.
11615 These options have no effect unless GCC is generating position
11620 Assume that general-purpose registers are 32 bits wide.
11624 Assume that general-purpose registers are 64 bits wide.
11628 Assume that floating-point registers are 32 bits wide.
11632 Assume that floating-point registers are 64 bits wide.
11635 @opindex mhard-float
11636 Use floating-point coprocessor instructions.
11639 @opindex msoft-float
11640 Do not use floating-point coprocessor instructions. Implement
11641 floating-point calculations using library calls instead.
11643 @item -msingle-float
11644 @opindex msingle-float
11645 Assume that the floating-point coprocessor only supports single-precision
11648 @item -mdouble-float
11649 @opindex mdouble-float
11650 Assume that the floating-point coprocessor supports double-precision
11651 operations. This is the default.
11657 Use (do not use) the MIPS DSP ASE. @xref{MIPS DSP Built-in Functions}.
11663 Use (do not use) the MIPS DSP ASE REV 2. @xref{MIPS DSP Built-in Functions}.
11664 The option @option{-mdspr2} implies @option{-mdsp}.
11667 @itemx -mno-smartmips
11668 @opindex msmartmips
11669 @opindex mno-smartmips
11670 Use (do not use) the MIPS SmartMIPS ASE.
11672 @item -mpaired-single
11673 @itemx -mno-paired-single
11674 @opindex mpaired-single
11675 @opindex mno-paired-single
11676 Use (do not use) paired-single floating-point instructions.
11677 @xref{MIPS Paired-Single Support}. This option can only be used
11678 when generating 64-bit code and requires hardware floating-point
11679 support to be enabled.
11685 Use (do not use) MIPS Digital Media Extension instructions.
11686 This option can only be used when generating 64-bit code and requires
11687 hardware floating-point support to be enabled.
11692 @opindex mno-mips3d
11693 Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
11694 The option @option{-mips3d} implies @option{-mpaired-single}.
11700 Use (do not use) MT Multithreading instructions.
11704 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
11705 an explanation of the default and the way that the pointer size is
11710 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
11712 The default size of @code{int}s, @code{long}s and pointers depends on
11713 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
11714 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
11715 32-bit @code{long}s. Pointers are the same size as @code{long}s,
11716 or the same size as integer registers, whichever is smaller.
11722 Assume (do not assume) that all symbols have 32-bit values, regardless
11723 of the selected ABI@. This option is useful in combination with
11724 @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
11725 to generate shorter and faster references to symbolic addresses.
11729 @cindex smaller data references (MIPS)
11730 @cindex gp-relative references (MIPS)
11731 Put global and static items less than or equal to @var{num} bytes into
11732 the small data or bss section instead of the normal data or bss section.
11733 This allows the data to be accessed using a single instruction.
11735 All modules should be compiled with the same @option{-G @var{num}}
11738 @item -membedded-data
11739 @itemx -mno-embedded-data
11740 @opindex membedded-data
11741 @opindex mno-embedded-data
11742 Allocate variables to the read-only data section first if possible, then
11743 next in the small data section if possible, otherwise in data. This gives
11744 slightly slower code than the default, but reduces the amount of RAM required
11745 when executing, and thus may be preferred for some embedded systems.
11747 @item -muninit-const-in-rodata
11748 @itemx -mno-uninit-const-in-rodata
11749 @opindex muninit-const-in-rodata
11750 @opindex mno-uninit-const-in-rodata
11751 Put uninitialized @code{const} variables in the read-only data section.
11752 This option is only meaningful in conjunction with @option{-membedded-data}.
11754 @item -msplit-addresses
11755 @itemx -mno-split-addresses
11756 @opindex msplit-addresses
11757 @opindex mno-split-addresses
11758 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
11759 relocation operators. This option has been superseded by
11760 @option{-mexplicit-relocs} but is retained for backwards compatibility.
11762 @item -mexplicit-relocs
11763 @itemx -mno-explicit-relocs
11764 @opindex mexplicit-relocs
11765 @opindex mno-explicit-relocs
11766 Use (do not use) assembler relocation operators when dealing with symbolic
11767 addresses. The alternative, selected by @option{-mno-explicit-relocs},
11768 is to use assembler macros instead.
11770 @option{-mexplicit-relocs} is the default if GCC was configured
11771 to use an assembler that supports relocation operators.
11773 @item -mcheck-zero-division
11774 @itemx -mno-check-zero-division
11775 @opindex mcheck-zero-division
11776 @opindex mno-check-zero-division
11777 Trap (do not trap) on integer division by zero.
11779 The default is @option{-mcheck-zero-division}.
11781 @item -mdivide-traps
11782 @itemx -mdivide-breaks
11783 @opindex mdivide-traps
11784 @opindex mdivide-breaks
11785 MIPS systems check for division by zero by generating either a
11786 conditional trap or a break instruction. Using traps results in
11787 smaller code, but is only supported on MIPS II and later. Also, some
11788 versions of the Linux kernel have a bug that prevents trap from
11789 generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
11790 allow conditional traps on architectures that support them and
11791 @option{-mdivide-breaks} to force the use of breaks.
11793 The default is usually @option{-mdivide-traps}, but this can be
11794 overridden at configure time using @option{--with-divide=breaks}.
11795 Divide-by-zero checks can be completely disabled using
11796 @option{-mno-check-zero-division}.
11801 @opindex mno-memcpy
11802 Force (do not force) the use of @code{memcpy()} for non-trivial block
11803 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
11804 most constant-sized copies.
11807 @itemx -mno-long-calls
11808 @opindex mlong-calls
11809 @opindex mno-long-calls
11810 Disable (do not disable) use of the @code{jal} instruction. Calling
11811 functions using @code{jal} is more efficient but requires the caller
11812 and callee to be in the same 256 megabyte segment.
11814 This option has no effect on abicalls code. The default is
11815 @option{-mno-long-calls}.
11821 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
11822 instructions, as provided by the R4650 ISA@.
11825 @itemx -mno-fused-madd
11826 @opindex mfused-madd
11827 @opindex mno-fused-madd
11828 Enable (disable) use of the floating point multiply-accumulate
11829 instructions, when they are available. The default is
11830 @option{-mfused-madd}.
11832 When multiply-accumulate instructions are used, the intermediate
11833 product is calculated to infinite precision and is not subject to
11834 the FCSR Flush to Zero bit. This may be undesirable in some
11839 Tell the MIPS assembler to not run its preprocessor over user
11840 assembler files (with a @samp{.s} suffix) when assembling them.
11843 @itemx -mno-fix-r4000
11844 @opindex mfix-r4000
11845 @opindex mno-fix-r4000
11846 Work around certain R4000 CPU errata:
11849 A double-word or a variable shift may give an incorrect result if executed
11850 immediately after starting an integer division.
11852 A double-word or a variable shift may give an incorrect result if executed
11853 while an integer multiplication is in progress.
11855 An integer division may give an incorrect result if started in a delay slot
11856 of a taken branch or a jump.
11860 @itemx -mno-fix-r4400
11861 @opindex mfix-r4400
11862 @opindex mno-fix-r4400
11863 Work around certain R4400 CPU errata:
11866 A double-word or a variable shift may give an incorrect result if executed
11867 immediately after starting an integer division.
11871 @itemx -mno-fix-vr4120
11872 @opindex mfix-vr4120
11873 Work around certain VR4120 errata:
11876 @code{dmultu} does not always produce the correct result.
11878 @code{div} and @code{ddiv} do not always produce the correct result if one
11879 of the operands is negative.
11881 The workarounds for the division errata rely on special functions in
11882 @file{libgcc.a}. At present, these functions are only provided by
11883 the @code{mips64vr*-elf} configurations.
11885 Other VR4120 errata require a nop to be inserted between certain pairs of
11886 instructions. These errata are handled by the assembler, not by GCC itself.
11889 @opindex mfix-vr4130
11890 Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
11891 workarounds are implemented by the assembler rather than by GCC,
11892 although GCC will avoid using @code{mflo} and @code{mfhi} if the
11893 VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
11894 instructions are available instead.
11897 @itemx -mno-fix-sb1
11899 Work around certain SB-1 CPU core errata.
11900 (This flag currently works around the SB-1 revision 2
11901 ``F1'' and ``F2'' floating point errata.)
11903 @item -mflush-func=@var{func}
11904 @itemx -mno-flush-func
11905 @opindex mflush-func
11906 Specifies the function to call to flush the I and D caches, or to not
11907 call any such function. If called, the function must take the same
11908 arguments as the common @code{_flush_func()}, that is, the address of the
11909 memory range for which the cache is being flushed, the size of the
11910 memory range, and the number 3 (to flush both caches). The default
11911 depends on the target GCC was configured for, but commonly is either
11912 @samp{_flush_func} or @samp{__cpu_flush}.
11914 @item -mbranch-likely
11915 @itemx -mno-branch-likely
11916 @opindex mbranch-likely
11917 @opindex mno-branch-likely
11918 Enable or disable use of Branch Likely instructions, regardless of the
11919 default for the selected architecture. By default, Branch Likely
11920 instructions may be generated if they are supported by the selected
11921 architecture. An exception is for the MIPS32 and MIPS64 architectures
11922 and processors which implement those architectures; for those, Branch
11923 Likely instructions will not be generated by default because the MIPS32
11924 and MIPS64 architectures specifically deprecate their use.
11926 @item -mfp-exceptions
11927 @itemx -mno-fp-exceptions
11928 @opindex mfp-exceptions
11929 Specifies whether FP exceptions are enabled. This affects how we schedule
11930 FP instructions for some processors. The default is that FP exceptions are
11933 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
11934 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
11937 @item -mvr4130-align
11938 @itemx -mno-vr4130-align
11939 @opindex mvr4130-align
11940 The VR4130 pipeline is two-way superscalar, but can only issue two
11941 instructions together if the first one is 8-byte aligned. When this
11942 option is enabled, GCC will align pairs of instructions that it
11943 thinks should execute in parallel.
11945 This option only has an effect when optimizing for the VR4130.
11946 It normally makes code faster, but at the expense of making it bigger.
11947 It is enabled by default at optimization level @option{-O3}.
11951 @subsection MMIX Options
11952 @cindex MMIX Options
11954 These options are defined for the MMIX:
11958 @itemx -mno-libfuncs
11960 @opindex mno-libfuncs
11961 Specify that intrinsic library functions are being compiled, passing all
11962 values in registers, no matter the size.
11965 @itemx -mno-epsilon
11967 @opindex mno-epsilon
11968 Generate floating-point comparison instructions that compare with respect
11969 to the @code{rE} epsilon register.
11971 @item -mabi=mmixware
11973 @opindex mabi-mmixware
11975 Generate code that passes function parameters and return values that (in
11976 the called function) are seen as registers @code{$0} and up, as opposed to
11977 the GNU ABI which uses global registers @code{$231} and up.
11979 @item -mzero-extend
11980 @itemx -mno-zero-extend
11981 @opindex mzero-extend
11982 @opindex mno-zero-extend
11983 When reading data from memory in sizes shorter than 64 bits, use (do not
11984 use) zero-extending load instructions by default, rather than
11985 sign-extending ones.
11988 @itemx -mno-knuthdiv
11990 @opindex mno-knuthdiv
11991 Make the result of a division yielding a remainder have the same sign as
11992 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
11993 remainder follows the sign of the dividend. Both methods are
11994 arithmetically valid, the latter being almost exclusively used.
11996 @item -mtoplevel-symbols
11997 @itemx -mno-toplevel-symbols
11998 @opindex mtoplevel-symbols
11999 @opindex mno-toplevel-symbols
12000 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
12001 code can be used with the @code{PREFIX} assembly directive.
12005 Generate an executable in the ELF format, rather than the default
12006 @samp{mmo} format used by the @command{mmix} simulator.
12008 @item -mbranch-predict
12009 @itemx -mno-branch-predict
12010 @opindex mbranch-predict
12011 @opindex mno-branch-predict
12012 Use (do not use) the probable-branch instructions, when static branch
12013 prediction indicates a probable branch.
12015 @item -mbase-addresses
12016 @itemx -mno-base-addresses
12017 @opindex mbase-addresses
12018 @opindex mno-base-addresses
12019 Generate (do not generate) code that uses @emph{base addresses}. Using a
12020 base address automatically generates a request (handled by the assembler
12021 and the linker) for a constant to be set up in a global register. The
12022 register is used for one or more base address requests within the range 0
12023 to 255 from the value held in the register. The generally leads to short
12024 and fast code, but the number of different data items that can be
12025 addressed is limited. This means that a program that uses lots of static
12026 data may require @option{-mno-base-addresses}.
12028 @item -msingle-exit
12029 @itemx -mno-single-exit
12030 @opindex msingle-exit
12031 @opindex mno-single-exit
12032 Force (do not force) generated code to have a single exit point in each
12036 @node MN10300 Options
12037 @subsection MN10300 Options
12038 @cindex MN10300 options
12040 These @option{-m} options are defined for Matsushita MN10300 architectures:
12045 Generate code to avoid bugs in the multiply instructions for the MN10300
12046 processors. This is the default.
12048 @item -mno-mult-bug
12049 @opindex mno-mult-bug
12050 Do not generate code to avoid bugs in the multiply instructions for the
12051 MN10300 processors.
12055 Generate code which uses features specific to the AM33 processor.
12059 Do not generate code which uses features specific to the AM33 processor. This
12062 @item -mreturn-pointer-on-d0
12063 @opindex mreturn-pointer-on-d0
12064 When generating a function which returns a pointer, return the pointer
12065 in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
12066 only in a0, and attempts to call such functions without a prototype
12067 would result in errors. Note that this option is on by default; use
12068 @option{-mno-return-pointer-on-d0} to disable it.
12072 Do not link in the C run-time initialization object file.
12076 Indicate to the linker that it should perform a relaxation optimization pass
12077 to shorten branches, calls and absolute memory addresses. This option only
12078 has an effect when used on the command line for the final link step.
12080 This option makes symbolic debugging impossible.
12084 @subsection MT Options
12087 These @option{-m} options are defined for Morpho MT architectures:
12091 @item -march=@var{cpu-type}
12093 Generate code that will run on @var{cpu-type}, which is the name of a system
12094 representing a certain processor type. Possible values for
12095 @var{cpu-type} are @samp{ms1-64-001}, @samp{ms1-16-002},
12096 @samp{ms1-16-003} and @samp{ms2}.
12098 When this option is not used, the default is @option{-march=ms1-16-002}.
12102 Use byte loads and stores when generating code.
12106 Do not use byte loads and stores when generating code.
12110 Use simulator runtime
12114 Do not link in the C run-time initialization object file
12115 @file{crti.o}. Other run-time initialization and termination files
12116 such as @file{startup.o} and @file{exit.o} are still included on the
12117 linker command line.
12121 @node PDP-11 Options
12122 @subsection PDP-11 Options
12123 @cindex PDP-11 Options
12125 These options are defined for the PDP-11:
12130 Use hardware FPP floating point. This is the default. (FIS floating
12131 point on the PDP-11/40 is not supported.)
12134 @opindex msoft-float
12135 Do not use hardware floating point.
12139 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
12143 Return floating-point results in memory. This is the default.
12147 Generate code for a PDP-11/40.
12151 Generate code for a PDP-11/45. This is the default.
12155 Generate code for a PDP-11/10.
12157 @item -mbcopy-builtin
12158 @opindex bcopy-builtin
12159 Use inline @code{movmemhi} patterns for copying memory. This is the
12164 Do not use inline @code{movmemhi} patterns for copying memory.
12170 Use 16-bit @code{int}. This is the default.
12176 Use 32-bit @code{int}.
12179 @itemx -mno-float32
12181 @opindex mno-float32
12182 Use 64-bit @code{float}. This is the default.
12185 @itemx -mno-float64
12187 @opindex mno-float64
12188 Use 32-bit @code{float}.
12192 Use @code{abshi2} pattern. This is the default.
12196 Do not use @code{abshi2} pattern.
12198 @item -mbranch-expensive
12199 @opindex mbranch-expensive
12200 Pretend that branches are expensive. This is for experimenting with
12201 code generation only.
12203 @item -mbranch-cheap
12204 @opindex mbranch-cheap
12205 Do not pretend that branches are expensive. This is the default.
12209 Generate code for a system with split I&D@.
12213 Generate code for a system without split I&D@. This is the default.
12217 Use Unix assembler syntax. This is the default when configured for
12218 @samp{pdp11-*-bsd}.
12222 Use DEC assembler syntax. This is the default when configured for any
12223 PDP-11 target other than @samp{pdp11-*-bsd}.
12226 @node PowerPC Options
12227 @subsection PowerPC Options
12228 @cindex PowerPC options
12230 These are listed under @xref{RS/6000 and PowerPC Options}.
12232 @node RS/6000 and PowerPC Options
12233 @subsection IBM RS/6000 and PowerPC Options
12234 @cindex RS/6000 and PowerPC Options
12235 @cindex IBM RS/6000 and PowerPC Options
12237 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
12244 @itemx -mno-powerpc
12245 @itemx -mpowerpc-gpopt
12246 @itemx -mno-powerpc-gpopt
12247 @itemx -mpowerpc-gfxopt
12248 @itemx -mno-powerpc-gfxopt
12250 @itemx -mno-powerpc64
12254 @itemx -mno-popcntb
12266 @opindex mno-power2
12268 @opindex mno-powerpc
12269 @opindex mpowerpc-gpopt
12270 @opindex mno-powerpc-gpopt
12271 @opindex mpowerpc-gfxopt
12272 @opindex mno-powerpc-gfxopt
12273 @opindex mpowerpc64
12274 @opindex mno-powerpc64
12278 @opindex mno-popcntb
12284 @opindex mno-mfpgpr
12287 GCC supports two related instruction set architectures for the
12288 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
12289 instructions supported by the @samp{rios} chip set used in the original
12290 RS/6000 systems and the @dfn{PowerPC} instruction set is the
12291 architecture of the Freescale MPC5xx, MPC6xx, MPC8xx microprocessors, and
12292 the IBM 4xx, 6xx, and follow-on microprocessors.
12294 Neither architecture is a subset of the other. However there is a
12295 large common subset of instructions supported by both. An MQ
12296 register is included in processors supporting the POWER architecture.
12298 You use these options to specify which instructions are available on the
12299 processor you are using. The default value of these options is
12300 determined when configuring GCC@. Specifying the
12301 @option{-mcpu=@var{cpu_type}} overrides the specification of these
12302 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
12303 rather than the options listed above.
12305 The @option{-mpower} option allows GCC to generate instructions that
12306 are found only in the POWER architecture and to use the MQ register.
12307 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
12308 to generate instructions that are present in the POWER2 architecture but
12309 not the original POWER architecture.
12311 The @option{-mpowerpc} option allows GCC to generate instructions that
12312 are found only in the 32-bit subset of the PowerPC architecture.
12313 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
12314 GCC to use the optional PowerPC architecture instructions in the
12315 General Purpose group, including floating-point square root. Specifying
12316 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
12317 use the optional PowerPC architecture instructions in the Graphics
12318 group, including floating-point select.
12320 The @option{-mmfcrf} option allows GCC to generate the move from
12321 condition register field instruction implemented on the POWER4
12322 processor and other processors that support the PowerPC V2.01
12324 The @option{-mpopcntb} option allows GCC to generate the popcount and
12325 double precision FP reciprocal estimate instruction implemented on the
12326 POWER5 processor and other processors that support the PowerPC V2.02
12328 The @option{-mfprnd} option allows GCC to generate the FP round to
12329 integer instructions implemented on the POWER5+ processor and other
12330 processors that support the PowerPC V2.03 architecture.
12331 The @option{-mcmpb} option allows GCC to generate the compare bytes
12332 instruction implemented on the POWER6 processor and other processors
12333 that support the PowerPC V2.05 architecture.
12334 The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
12335 general purpose register instructions implemented on the POWER6X
12336 processor and other processors that support the extended PowerPC V2.05
12338 The @option{-mdfp} option allows GCC to generate the decimal floating
12339 point instructions implemented on some POWER processors.
12341 The @option{-mpowerpc64} option allows GCC to generate the additional
12342 64-bit instructions that are found in the full PowerPC64 architecture
12343 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
12344 @option{-mno-powerpc64}.
12346 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
12347 will use only the instructions in the common subset of both
12348 architectures plus some special AIX common-mode calls, and will not use
12349 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
12350 permits GCC to use any instruction from either architecture and to
12351 allow use of the MQ register; specify this for the Motorola MPC601.
12353 @item -mnew-mnemonics
12354 @itemx -mold-mnemonics
12355 @opindex mnew-mnemonics
12356 @opindex mold-mnemonics
12357 Select which mnemonics to use in the generated assembler code. With
12358 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
12359 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
12360 assembler mnemonics defined for the POWER architecture. Instructions
12361 defined in only one architecture have only one mnemonic; GCC uses that
12362 mnemonic irrespective of which of these options is specified.
12364 GCC defaults to the mnemonics appropriate for the architecture in
12365 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
12366 value of these option. Unless you are building a cross-compiler, you
12367 should normally not specify either @option{-mnew-mnemonics} or
12368 @option{-mold-mnemonics}, but should instead accept the default.
12370 @item -mcpu=@var{cpu_type}
12372 Set architecture type, register usage, choice of mnemonics, and
12373 instruction scheduling parameters for machine type @var{cpu_type}.
12374 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
12375 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
12376 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
12377 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
12378 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
12379 @samp{860}, @samp{970}, @samp{8540}, @samp{ec603e}, @samp{G3},
12380 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
12381 @samp{power4}, @samp{power5}, @samp{power5+}, @samp{power6},
12382 @samp{power6x}, @samp{common}, @samp{powerpc}, @samp{powerpc64},
12383 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64}.
12385 @option{-mcpu=common} selects a completely generic processor. Code
12386 generated under this option will run on any POWER or PowerPC processor.
12387 GCC will use only the instructions in the common subset of both
12388 architectures, and will not use the MQ register. GCC assumes a generic
12389 processor model for scheduling purposes.
12391 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
12392 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
12393 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
12394 types, with an appropriate, generic processor model assumed for
12395 scheduling purposes.
12397 The other options specify a specific processor. Code generated under
12398 those options will run best on that processor, and may not run at all on
12401 The @option{-mcpu} options automatically enable or disable the
12404 @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
12405 -mnew-mnemonics -mpopcntb -mpower -mpower2 -mpowerpc64 @gol
12406 -mpowerpc-gpopt -mpowerpc-gfxopt -mstring -mmulhw -mdlmzb -mmfpgpr}
12408 The particular options set for any particular CPU will vary between
12409 compiler versions, depending on what setting seems to produce optimal
12410 code for that CPU; it doesn't necessarily reflect the actual hardware's
12411 capabilities. If you wish to set an individual option to a particular
12412 value, you may specify it after the @option{-mcpu} option, like
12413 @samp{-mcpu=970 -mno-altivec}.
12415 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
12416 not enabled or disabled by the @option{-mcpu} option at present because
12417 AIX does not have full support for these options. You may still
12418 enable or disable them individually if you're sure it'll work in your
12421 @item -mtune=@var{cpu_type}
12423 Set the instruction scheduling parameters for machine type
12424 @var{cpu_type}, but do not set the architecture type, register usage, or
12425 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
12426 values for @var{cpu_type} are used for @option{-mtune} as for
12427 @option{-mcpu}. If both are specified, the code generated will use the
12428 architecture, registers, and mnemonics set by @option{-mcpu}, but the
12429 scheduling parameters set by @option{-mtune}.
12435 Generate code to compute division as reciprocal estimate and iterative
12436 refinement, creating opportunities for increased throughput. This
12437 feature requires: optional PowerPC Graphics instruction set for single
12438 precision and FRE instruction for double precision, assuming divides
12439 cannot generate user-visible traps, and the domain values not include
12440 Infinities, denormals or zero denominator.
12443 @itemx -mno-altivec
12445 @opindex mno-altivec
12446 Generate code that uses (does not use) AltiVec instructions, and also
12447 enable the use of built-in functions that allow more direct access to
12448 the AltiVec instruction set. You may also need to set
12449 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
12455 @opindex mno-vrsave
12456 Generate VRSAVE instructions when generating AltiVec code.
12459 @opindex msecure-plt
12460 Generate code that allows ld and ld.so to build executables and shared
12461 libraries with non-exec .plt and .got sections. This is a PowerPC
12462 32-bit SYSV ABI option.
12466 Generate code that uses a BSS .plt section that ld.so fills in, and
12467 requires .plt and .got sections that are both writable and executable.
12468 This is a PowerPC 32-bit SYSV ABI option.
12474 This switch enables or disables the generation of ISEL instructions.
12476 @item -misel=@var{yes/no}
12477 This switch has been deprecated. Use @option{-misel} and
12478 @option{-mno-isel} instead.
12484 This switch enables or disables the generation of SPE simd
12487 @item -mspe=@var{yes/no}
12488 This option has been deprecated. Use @option{-mspe} and
12489 @option{-mno-spe} instead.
12491 @item -mfloat-gprs=@var{yes/single/double/no}
12492 @itemx -mfloat-gprs
12493 @opindex mfloat-gprs
12494 This switch enables or disables the generation of floating point
12495 operations on the general purpose registers for architectures that
12498 The argument @var{yes} or @var{single} enables the use of
12499 single-precision floating point operations.
12501 The argument @var{double} enables the use of single and
12502 double-precision floating point operations.
12504 The argument @var{no} disables floating point operations on the
12505 general purpose registers.
12507 This option is currently only available on the MPC854x.
12513 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
12514 targets (including GNU/Linux). The 32-bit environment sets int, long
12515 and pointer to 32 bits and generates code that runs on any PowerPC
12516 variant. The 64-bit environment sets int to 32 bits and long and
12517 pointer to 64 bits, and generates code for PowerPC64, as for
12518 @option{-mpowerpc64}.
12521 @itemx -mno-fp-in-toc
12522 @itemx -mno-sum-in-toc
12523 @itemx -mminimal-toc
12525 @opindex mno-fp-in-toc
12526 @opindex mno-sum-in-toc
12527 @opindex mminimal-toc
12528 Modify generation of the TOC (Table Of Contents), which is created for
12529 every executable file. The @option{-mfull-toc} option is selected by
12530 default. In that case, GCC will allocate at least one TOC entry for
12531 each unique non-automatic variable reference in your program. GCC
12532 will also place floating-point constants in the TOC@. However, only
12533 16,384 entries are available in the TOC@.
12535 If you receive a linker error message that saying you have overflowed
12536 the available TOC space, you can reduce the amount of TOC space used
12537 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
12538 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
12539 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
12540 generate code to calculate the sum of an address and a constant at
12541 run-time instead of putting that sum into the TOC@. You may specify one
12542 or both of these options. Each causes GCC to produce very slightly
12543 slower and larger code at the expense of conserving TOC space.
12545 If you still run out of space in the TOC even when you specify both of
12546 these options, specify @option{-mminimal-toc} instead. This option causes
12547 GCC to make only one TOC entry for every file. When you specify this
12548 option, GCC will produce code that is slower and larger but which
12549 uses extremely little TOC space. You may wish to use this option
12550 only on files that contain less frequently executed code.
12556 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
12557 @code{long} type, and the infrastructure needed to support them.
12558 Specifying @option{-maix64} implies @option{-mpowerpc64} and
12559 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
12560 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
12563 @itemx -mno-xl-compat
12564 @opindex mxl-compat
12565 @opindex mno-xl-compat
12566 Produce code that conforms more closely to IBM XL compiler semantics
12567 when using AIX-compatible ABI. Pass floating-point arguments to
12568 prototyped functions beyond the register save area (RSA) on the stack
12569 in addition to argument FPRs. Do not assume that most significant
12570 double in 128-bit long double value is properly rounded when comparing
12571 values and converting to double. Use XL symbol names for long double
12574 The AIX calling convention was extended but not initially documented to
12575 handle an obscure K&R C case of calling a function that takes the
12576 address of its arguments with fewer arguments than declared. IBM XL
12577 compilers access floating point arguments which do not fit in the
12578 RSA from the stack when a subroutine is compiled without
12579 optimization. Because always storing floating-point arguments on the
12580 stack is inefficient and rarely needed, this option is not enabled by
12581 default and only is necessary when calling subroutines compiled by IBM
12582 XL compilers without optimization.
12586 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
12587 application written to use message passing with special startup code to
12588 enable the application to run. The system must have PE installed in the
12589 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
12590 must be overridden with the @option{-specs=} option to specify the
12591 appropriate directory location. The Parallel Environment does not
12592 support threads, so the @option{-mpe} option and the @option{-pthread}
12593 option are incompatible.
12595 @item -malign-natural
12596 @itemx -malign-power
12597 @opindex malign-natural
12598 @opindex malign-power
12599 On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
12600 @option{-malign-natural} overrides the ABI-defined alignment of larger
12601 types, such as floating-point doubles, on their natural size-based boundary.
12602 The option @option{-malign-power} instructs GCC to follow the ABI-specified
12603 alignment rules. GCC defaults to the standard alignment defined in the ABI@.
12605 On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
12609 @itemx -mhard-float
12610 @opindex msoft-float
12611 @opindex mhard-float
12612 Generate code that does not use (uses) the floating-point register set.
12613 Software floating point emulation is provided if you use the
12614 @option{-msoft-float} option, and pass the option to GCC when linking.
12617 @itemx -mno-multiple
12619 @opindex mno-multiple
12620 Generate code that uses (does not use) the load multiple word
12621 instructions and the store multiple word instructions. These
12622 instructions are generated by default on POWER systems, and not
12623 generated on PowerPC systems. Do not use @option{-mmultiple} on little
12624 endian PowerPC systems, since those instructions do not work when the
12625 processor is in little endian mode. The exceptions are PPC740 and
12626 PPC750 which permit the instructions usage in little endian mode.
12631 @opindex mno-string
12632 Generate code that uses (does not use) the load string instructions
12633 and the store string word instructions to save multiple registers and
12634 do small block moves. These instructions are generated by default on
12635 POWER systems, and not generated on PowerPC systems. Do not use
12636 @option{-mstring} on little endian PowerPC systems, since those
12637 instructions do not work when the processor is in little endian mode.
12638 The exceptions are PPC740 and PPC750 which permit the instructions
12639 usage in little endian mode.
12644 @opindex mno-update
12645 Generate code that uses (does not use) the load or store instructions
12646 that update the base register to the address of the calculated memory
12647 location. These instructions are generated by default. If you use
12648 @option{-mno-update}, there is a small window between the time that the
12649 stack pointer is updated and the address of the previous frame is
12650 stored, which means code that walks the stack frame across interrupts or
12651 signals may get corrupted data.
12654 @itemx -mno-fused-madd
12655 @opindex mfused-madd
12656 @opindex mno-fused-madd
12657 Generate code that uses (does not use) the floating point multiply and
12658 accumulate instructions. These instructions are generated by default if
12659 hardware floating is used.
12665 Generate code that uses (does not use) the half-word multiply and
12666 multiply-accumulate instructions on the IBM 405 and 440 processors.
12667 These instructions are generated by default when targetting those
12674 Generate code that uses (does not use) the string-search @samp{dlmzb}
12675 instruction on the IBM 405 and 440 processors. This instruction is
12676 generated by default when targetting those processors.
12678 @item -mno-bit-align
12680 @opindex mno-bit-align
12681 @opindex mbit-align
12682 On System V.4 and embedded PowerPC systems do not (do) force structures
12683 and unions that contain bit-fields to be aligned to the base type of the
12686 For example, by default a structure containing nothing but 8
12687 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
12688 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
12689 the structure would be aligned to a 1 byte boundary and be one byte in
12692 @item -mno-strict-align
12693 @itemx -mstrict-align
12694 @opindex mno-strict-align
12695 @opindex mstrict-align
12696 On System V.4 and embedded PowerPC systems do not (do) assume that
12697 unaligned memory references will be handled by the system.
12699 @item -mrelocatable
12700 @itemx -mno-relocatable
12701 @opindex mrelocatable
12702 @opindex mno-relocatable
12703 On embedded PowerPC systems generate code that allows (does not allow)
12704 the program to be relocated to a different address at runtime. If you
12705 use @option{-mrelocatable} on any module, all objects linked together must
12706 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
12708 @item -mrelocatable-lib
12709 @itemx -mno-relocatable-lib
12710 @opindex mrelocatable-lib
12711 @opindex mno-relocatable-lib
12712 On embedded PowerPC systems generate code that allows (does not allow)
12713 the program to be relocated to a different address at runtime. Modules
12714 compiled with @option{-mrelocatable-lib} can be linked with either modules
12715 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
12716 with modules compiled with the @option{-mrelocatable} options.
12722 On System V.4 and embedded PowerPC systems do not (do) assume that
12723 register 2 contains a pointer to a global area pointing to the addresses
12724 used in the program.
12727 @itemx -mlittle-endian
12729 @opindex mlittle-endian
12730 On System V.4 and embedded PowerPC systems compile code for the
12731 processor in little endian mode. The @option{-mlittle-endian} option is
12732 the same as @option{-mlittle}.
12735 @itemx -mbig-endian
12737 @opindex mbig-endian
12738 On System V.4 and embedded PowerPC systems compile code for the
12739 processor in big endian mode. The @option{-mbig-endian} option is
12740 the same as @option{-mbig}.
12742 @item -mdynamic-no-pic
12743 @opindex mdynamic-no-pic
12744 On Darwin and Mac OS X systems, compile code so that it is not
12745 relocatable, but that its external references are relocatable. The
12746 resulting code is suitable for applications, but not shared
12749 @item -mprioritize-restricted-insns=@var{priority}
12750 @opindex mprioritize-restricted-insns
12751 This option controls the priority that is assigned to
12752 dispatch-slot restricted instructions during the second scheduling
12753 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
12754 @var{no/highest/second-highest} priority to dispatch slot restricted
12757 @item -msched-costly-dep=@var{dependence_type}
12758 @opindex msched-costly-dep
12759 This option controls which dependences are considered costly
12760 by the target during instruction scheduling. The argument
12761 @var{dependence_type} takes one of the following values:
12762 @var{no}: no dependence is costly,
12763 @var{all}: all dependences are costly,
12764 @var{true_store_to_load}: a true dependence from store to load is costly,
12765 @var{store_to_load}: any dependence from store to load is costly,
12766 @var{number}: any dependence which latency >= @var{number} is costly.
12768 @item -minsert-sched-nops=@var{scheme}
12769 @opindex minsert-sched-nops
12770 This option controls which nop insertion scheme will be used during
12771 the second scheduling pass. The argument @var{scheme} takes one of the
12773 @var{no}: Don't insert nops.
12774 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
12775 according to the scheduler's grouping.
12776 @var{regroup_exact}: Insert nops to force costly dependent insns into
12777 separate groups. Insert exactly as many nops as needed to force an insn
12778 to a new group, according to the estimated processor grouping.
12779 @var{number}: Insert nops to force costly dependent insns into
12780 separate groups. Insert @var{number} nops to force an insn to a new group.
12783 @opindex mcall-sysv
12784 On System V.4 and embedded PowerPC systems compile code using calling
12785 conventions that adheres to the March 1995 draft of the System V
12786 Application Binary Interface, PowerPC processor supplement. This is the
12787 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
12789 @item -mcall-sysv-eabi
12790 @opindex mcall-sysv-eabi
12791 Specify both @option{-mcall-sysv} and @option{-meabi} options.
12793 @item -mcall-sysv-noeabi
12794 @opindex mcall-sysv-noeabi
12795 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
12797 @item -mcall-solaris
12798 @opindex mcall-solaris
12799 On System V.4 and embedded PowerPC systems compile code for the Solaris
12803 @opindex mcall-linux
12804 On System V.4 and embedded PowerPC systems compile code for the
12805 Linux-based GNU system.
12809 On System V.4 and embedded PowerPC systems compile code for the
12810 Hurd-based GNU system.
12812 @item -mcall-netbsd
12813 @opindex mcall-netbsd
12814 On System V.4 and embedded PowerPC systems compile code for the
12815 NetBSD operating system.
12817 @item -maix-struct-return
12818 @opindex maix-struct-return
12819 Return all structures in memory (as specified by the AIX ABI)@.
12821 @item -msvr4-struct-return
12822 @opindex msvr4-struct-return
12823 Return structures smaller than 8 bytes in registers (as specified by the
12826 @item -mabi=@var{abi-type}
12828 Extend the current ABI with a particular extension, or remove such extension.
12829 Valid values are @var{altivec}, @var{no-altivec}, @var{spe},
12830 @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@.
12834 Extend the current ABI with SPE ABI extensions. This does not change
12835 the default ABI, instead it adds the SPE ABI extensions to the current
12839 @opindex mabi=no-spe
12840 Disable Booke SPE ABI extensions for the current ABI@.
12842 @item -mabi=ibmlongdouble
12843 @opindex mabi=ibmlongdouble
12844 Change the current ABI to use IBM extended precision long double.
12845 This is a PowerPC 32-bit SYSV ABI option.
12847 @item -mabi=ieeelongdouble
12848 @opindex mabi=ieeelongdouble
12849 Change the current ABI to use IEEE extended precision long double.
12850 This is a PowerPC 32-bit Linux ABI option.
12853 @itemx -mno-prototype
12854 @opindex mprototype
12855 @opindex mno-prototype
12856 On System V.4 and embedded PowerPC systems assume that all calls to
12857 variable argument functions are properly prototyped. Otherwise, the
12858 compiler must insert an instruction before every non prototyped call to
12859 set or clear bit 6 of the condition code register (@var{CR}) to
12860 indicate whether floating point values were passed in the floating point
12861 registers in case the function takes a variable arguments. With
12862 @option{-mprototype}, only calls to prototyped variable argument functions
12863 will set or clear the bit.
12867 On embedded PowerPC systems, assume that the startup module is called
12868 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
12869 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
12874 On embedded PowerPC systems, assume that the startup module is called
12875 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
12880 On embedded PowerPC systems, assume that the startup module is called
12881 @file{crt0.o} and the standard C libraries are @file{libads.a} and
12884 @item -myellowknife
12885 @opindex myellowknife
12886 On embedded PowerPC systems, assume that the startup module is called
12887 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
12892 On System V.4 and embedded PowerPC systems, specify that you are
12893 compiling for a VxWorks system.
12897 Specify that you are compiling for the WindISS simulation environment.
12901 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
12902 header to indicate that @samp{eabi} extended relocations are used.
12908 On System V.4 and embedded PowerPC systems do (do not) adhere to the
12909 Embedded Applications Binary Interface (eabi) which is a set of
12910 modifications to the System V.4 specifications. Selecting @option{-meabi}
12911 means that the stack is aligned to an 8 byte boundary, a function
12912 @code{__eabi} is called to from @code{main} to set up the eabi
12913 environment, and the @option{-msdata} option can use both @code{r2} and
12914 @code{r13} to point to two separate small data areas. Selecting
12915 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
12916 do not call an initialization function from @code{main}, and the
12917 @option{-msdata} option will only use @code{r13} to point to a single
12918 small data area. The @option{-meabi} option is on by default if you
12919 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
12922 @opindex msdata=eabi
12923 On System V.4 and embedded PowerPC systems, put small initialized
12924 @code{const} global and static data in the @samp{.sdata2} section, which
12925 is pointed to by register @code{r2}. Put small initialized
12926 non-@code{const} global and static data in the @samp{.sdata} section,
12927 which is pointed to by register @code{r13}. Put small uninitialized
12928 global and static data in the @samp{.sbss} section, which is adjacent to
12929 the @samp{.sdata} section. The @option{-msdata=eabi} option is
12930 incompatible with the @option{-mrelocatable} option. The
12931 @option{-msdata=eabi} option also sets the @option{-memb} option.
12934 @opindex msdata=sysv
12935 On System V.4 and embedded PowerPC systems, put small global and static
12936 data in the @samp{.sdata} section, which is pointed to by register
12937 @code{r13}. Put small uninitialized global and static data in the
12938 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
12939 The @option{-msdata=sysv} option is incompatible with the
12940 @option{-mrelocatable} option.
12942 @item -msdata=default
12944 @opindex msdata=default
12946 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
12947 compile code the same as @option{-msdata=eabi}, otherwise compile code the
12948 same as @option{-msdata=sysv}.
12951 @opindex msdata-data
12952 On System V.4 and embedded PowerPC systems, put small global
12953 data in the @samp{.sdata} section. Put small uninitialized global
12954 data in the @samp{.sbss} section. Do not use register @code{r13}
12955 to address small data however. This is the default behavior unless
12956 other @option{-msdata} options are used.
12960 @opindex msdata=none
12962 On embedded PowerPC systems, put all initialized global and static data
12963 in the @samp{.data} section, and all uninitialized data in the
12964 @samp{.bss} section.
12968 @cindex smaller data references (PowerPC)
12969 @cindex .sdata/.sdata2 references (PowerPC)
12970 On embedded PowerPC systems, put global and static items less than or
12971 equal to @var{num} bytes into the small data or bss sections instead of
12972 the normal data or bss section. By default, @var{num} is 8. The
12973 @option{-G @var{num}} switch is also passed to the linker.
12974 All modules should be compiled with the same @option{-G @var{num}} value.
12977 @itemx -mno-regnames
12979 @opindex mno-regnames
12980 On System V.4 and embedded PowerPC systems do (do not) emit register
12981 names in the assembly language output using symbolic forms.
12984 @itemx -mno-longcall
12986 @opindex mno-longcall
12987 By default assume that all calls are far away so that a longer more
12988 expensive calling sequence is required. This is required for calls
12989 further than 32 megabytes (33,554,432 bytes) from the current location.
12990 A short call will be generated if the compiler knows
12991 the call cannot be that far away. This setting can be overridden by
12992 the @code{shortcall} function attribute, or by @code{#pragma
12995 Some linkers are capable of detecting out-of-range calls and generating
12996 glue code on the fly. On these systems, long calls are unnecessary and
12997 generate slower code. As of this writing, the AIX linker can do this,
12998 as can the GNU linker for PowerPC/64. It is planned to add this feature
12999 to the GNU linker for 32-bit PowerPC systems as well.
13001 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
13002 callee, L42'', plus a ``branch island'' (glue code). The two target
13003 addresses represent the callee and the ``branch island''. The
13004 Darwin/PPC linker will prefer the first address and generate a ``bl
13005 callee'' if the PPC ``bl'' instruction will reach the callee directly;
13006 otherwise, the linker will generate ``bl L42'' to call the ``branch
13007 island''. The ``branch island'' is appended to the body of the
13008 calling function; it computes the full 32-bit address of the callee
13011 On Mach-O (Darwin) systems, this option directs the compiler emit to
13012 the glue for every direct call, and the Darwin linker decides whether
13013 to use or discard it.
13015 In the future, we may cause GCC to ignore all longcall specifications
13016 when the linker is known to generate glue.
13020 Adds support for multithreading with the @dfn{pthreads} library.
13021 This option sets flags for both the preprocessor and linker.
13025 @node S/390 and zSeries Options
13026 @subsection S/390 and zSeries Options
13027 @cindex S/390 and zSeries Options
13029 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
13033 @itemx -msoft-float
13034 @opindex mhard-float
13035 @opindex msoft-float
13036 Use (do not use) the hardware floating-point instructions and registers
13037 for floating-point operations. When @option{-msoft-float} is specified,
13038 functions in @file{libgcc.a} will be used to perform floating-point
13039 operations. When @option{-mhard-float} is specified, the compiler
13040 generates IEEE floating-point instructions. This is the default.
13042 @item -mlong-double-64
13043 @itemx -mlong-double-128
13044 @opindex mlong-double-64
13045 @opindex mlong-double-128
13046 These switches control the size of @code{long double} type. A size
13047 of 64bit makes the @code{long double} type equivalent to the @code{double}
13048 type. This is the default.
13051 @itemx -mno-backchain
13052 @opindex mbackchain
13053 @opindex mno-backchain
13054 Store (do not store) the address of the caller's frame as backchain pointer
13055 into the callee's stack frame.
13056 A backchain may be needed to allow debugging using tools that do not understand
13057 DWARF-2 call frame information.
13058 When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
13059 at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
13060 the backchain is placed into the topmost word of the 96/160 byte register
13063 In general, code compiled with @option{-mbackchain} is call-compatible with
13064 code compiled with @option{-mmo-backchain}; however, use of the backchain
13065 for debugging purposes usually requires that the whole binary is built with
13066 @option{-mbackchain}. Note that the combination of @option{-mbackchain},
13067 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13068 to build a linux kernel use @option{-msoft-float}.
13070 The default is to not maintain the backchain.
13072 @item -mpacked-stack
13073 @item -mno-packed-stack
13074 @opindex mpacked-stack
13075 @opindex mno-packed-stack
13076 Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
13077 specified, the compiler uses the all fields of the 96/160 byte register save
13078 area only for their default purpose; unused fields still take up stack space.
13079 When @option{-mpacked-stack} is specified, register save slots are densely
13080 packed at the top of the register save area; unused space is reused for other
13081 purposes, allowing for more efficient use of the available stack space.
13082 However, when @option{-mbackchain} is also in effect, the topmost word of
13083 the save area is always used to store the backchain, and the return address
13084 register is always saved two words below the backchain.
13086 As long as the stack frame backchain is not used, code generated with
13087 @option{-mpacked-stack} is call-compatible with code generated with
13088 @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
13089 S/390 or zSeries generated code that uses the stack frame backchain at run
13090 time, not just for debugging purposes. Such code is not call-compatible
13091 with code compiled with @option{-mpacked-stack}. Also, note that the
13092 combination of @option{-mbackchain},
13093 @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
13094 to build a linux kernel use @option{-msoft-float}.
13096 The default is to not use the packed stack layout.
13099 @itemx -mno-small-exec
13100 @opindex msmall-exec
13101 @opindex mno-small-exec
13102 Generate (or do not generate) code using the @code{bras} instruction
13103 to do subroutine calls.
13104 This only works reliably if the total executable size does not
13105 exceed 64k. The default is to use the @code{basr} instruction instead,
13106 which does not have this limitation.
13112 When @option{-m31} is specified, generate code compliant to the
13113 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
13114 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
13115 particular to generate 64-bit instructions. For the @samp{s390}
13116 targets, the default is @option{-m31}, while the @samp{s390x}
13117 targets default to @option{-m64}.
13123 When @option{-mzarch} is specified, generate code using the
13124 instructions available on z/Architecture.
13125 When @option{-mesa} is specified, generate code using the
13126 instructions available on ESA/390. Note that @option{-mesa} is
13127 not possible with @option{-m64}.
13128 When generating code compliant to the GNU/Linux for S/390 ABI,
13129 the default is @option{-mesa}. When generating code compliant
13130 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
13136 Generate (or do not generate) code using the @code{mvcle} instruction
13137 to perform block moves. When @option{-mno-mvcle} is specified,
13138 use a @code{mvc} loop instead. This is the default unless optimizing for
13145 Print (or do not print) additional debug information when compiling.
13146 The default is to not print debug information.
13148 @item -march=@var{cpu-type}
13150 Generate code that will run on @var{cpu-type}, which is the name of a system
13151 representing a certain processor type. Possible values for
13152 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
13153 When generating code using the instructions available on z/Architecture,
13154 the default is @option{-march=z900}. Otherwise, the default is
13155 @option{-march=g5}.
13157 @item -mtune=@var{cpu-type}
13159 Tune to @var{cpu-type} everything applicable about the generated code,
13160 except for the ABI and the set of available instructions.
13161 The list of @var{cpu-type} values is the same as for @option{-march}.
13162 The default is the value used for @option{-march}.
13165 @itemx -mno-tpf-trace
13166 @opindex mtpf-trace
13167 @opindex mno-tpf-trace
13168 Generate code that adds (does not add) in TPF OS specific branches to trace
13169 routines in the operating system. This option is off by default, even
13170 when compiling for the TPF OS@.
13173 @itemx -mno-fused-madd
13174 @opindex mfused-madd
13175 @opindex mno-fused-madd
13176 Generate code that uses (does not use) the floating point multiply and
13177 accumulate instructions. These instructions are generated by default if
13178 hardware floating point is used.
13180 @item -mwarn-framesize=@var{framesize}
13181 @opindex mwarn-framesize
13182 Emit a warning if the current function exceeds the given frame size. Because
13183 this is a compile time check it doesn't need to be a real problem when the program
13184 runs. It is intended to identify functions which most probably cause
13185 a stack overflow. It is useful to be used in an environment with limited stack
13186 size e.g.@: the linux kernel.
13188 @item -mwarn-dynamicstack
13189 @opindex mwarn-dynamicstack
13190 Emit a warning if the function calls alloca or uses dynamically
13191 sized arrays. This is generally a bad idea with a limited stack size.
13193 @item -mstack-guard=@var{stack-guard}
13194 @item -mstack-size=@var{stack-size}
13195 @opindex mstack-guard
13196 @opindex mstack-size
13197 If these options are provided the s390 back end emits additional instructions in
13198 the function prologue which trigger a trap if the stack size is @var{stack-guard}
13199 bytes above the @var{stack-size} (remember that the stack on s390 grows downward).
13200 If the @var{stack-guard} option is omitted the smallest power of 2 larger than
13201 the frame size of the compiled function is chosen.
13202 These options are intended to be used to help debugging stack overflow problems.
13203 The additionally emitted code causes only little overhead and hence can also be
13204 used in production like systems without greater performance degradation. The given
13205 values have to be exact powers of 2 and @var{stack-size} has to be greater than
13206 @var{stack-guard} without exceeding 64k.
13207 In order to be efficient the extra code makes the assumption that the stack starts
13208 at an address aligned to the value given by @var{stack-size}.
13209 The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
13212 @node Score Options
13213 @subsection Score Options
13214 @cindex Score Options
13216 These options are defined for Score implementations:
13221 Compile code for big endian mode. This is the default.
13225 Compile code for little endian mode.
13229 Disable generate bcnz instruction.
13233 Enable generate unaligned load and store instruction.
13237 Enable the use of multiply-accumulate instructions. Disabled by default.
13241 Specify the SCORE5 as the target architecture.
13245 Specify the SCORE5U of the target architecture.
13249 Specify the SCORE7 as the target architecture. This is the default.
13253 Specify the SCORE7D as the target architecture.
13257 @subsection SH Options
13259 These @samp{-m} options are defined for the SH implementations:
13264 Generate code for the SH1.
13268 Generate code for the SH2.
13271 Generate code for the SH2e.
13275 Generate code for the SH3.
13279 Generate code for the SH3e.
13283 Generate code for the SH4 without a floating-point unit.
13285 @item -m4-single-only
13286 @opindex m4-single-only
13287 Generate code for the SH4 with a floating-point unit that only
13288 supports single-precision arithmetic.
13292 Generate code for the SH4 assuming the floating-point unit is in
13293 single-precision mode by default.
13297 Generate code for the SH4.
13301 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
13302 floating-point unit is not used.
13304 @item -m4a-single-only
13305 @opindex m4a-single-only
13306 Generate code for the SH4a, in such a way that no double-precision
13307 floating point operations are used.
13310 @opindex m4a-single
13311 Generate code for the SH4a assuming the floating-point unit is in
13312 single-precision mode by default.
13316 Generate code for the SH4a.
13320 Same as @option{-m4a-nofpu}, except that it implicitly passes
13321 @option{-dsp} to the assembler. GCC doesn't generate any DSP
13322 instructions at the moment.
13326 Compile code for the processor in big endian mode.
13330 Compile code for the processor in little endian mode.
13334 Align doubles at 64-bit boundaries. Note that this changes the calling
13335 conventions, and thus some functions from the standard C library will
13336 not work unless you recompile it first with @option{-mdalign}.
13340 Shorten some address references at link time, when possible; uses the
13341 linker option @option{-relax}.
13345 Use 32-bit offsets in @code{switch} tables. The default is to use
13350 Enable the use of the instruction @code{fmovd}.
13354 Comply with the calling conventions defined by Renesas.
13358 Comply with the calling conventions defined by Renesas.
13362 Comply with the calling conventions defined for GCC before the Renesas
13363 conventions were available. This option is the default for all
13364 targets of the SH toolchain except for @samp{sh-symbianelf}.
13367 @opindex mnomacsave
13368 Mark the @code{MAC} register as call-clobbered, even if
13369 @option{-mhitachi} is given.
13373 Increase IEEE-compliance of floating-point code.
13374 At the moment, this is equivalent to @option{-fno-finite-math-only}.
13375 When generating 16 bit SH opcodes, getting IEEE-conforming results for
13376 comparisons of NANs / infinities incurs extra overhead in every
13377 floating point comparison, therefore the default is set to
13378 @option{-ffinite-math-only}.
13380 @item -minline-ic_invalidate
13381 @opindex minline-ic_invalidate
13382 Inline code to invalidate instruction cache entries after setting up
13383 nested function trampolines.
13384 This option has no effect if -musermode is in effect and the selected
13385 code generation option (e.g. -m4) does not allow the use of the icbi
13387 If the selected code generation option does not allow the use of the icbi
13388 instruction, and -musermode is not in effect, the inlined code will
13389 manipulate the instruction cache address array directly with an associative
13390 write. This not only requires privileged mode, but it will also
13391 fail if the cache line had been mapped via the TLB and has become unmapped.
13395 Dump instruction size and location in the assembly code.
13398 @opindex mpadstruct
13399 This option is deprecated. It pads structures to multiple of 4 bytes,
13400 which is incompatible with the SH ABI@.
13404 Optimize for space instead of speed. Implied by @option{-Os}.
13407 @opindex mprefergot
13408 When generating position-independent code, emit function calls using
13409 the Global Offset Table instead of the Procedure Linkage Table.
13413 Don't generate privileged mode only code; implies -mno-inline-ic_invalidate
13414 if the inlined code would not work in user mode.
13415 This is the default when the target is @code{sh-*-linux*}.
13417 @item -multcost=@var{number}
13418 @opindex multcost=@var{number}
13419 Set the cost to assume for a multiply insn.
13421 @item -mdiv=@var{strategy}
13422 @opindex mdiv=@var{strategy}
13423 Set the division strategy to use for SHmedia code. @var{strategy} must be
13424 one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l, inv:call,
13425 inv:call2, inv:fp .
13426 "fp" performs the operation in floating point. This has a very high latency,
13427 but needs only a few instructions, so it might be a good choice if
13428 your code has enough easily exploitable ILP to allow the compiler to
13429 schedule the floating point instructions together with other instructions.
13430 Division by zero causes a floating point exception.
13431 "inv" uses integer operations to calculate the inverse of the divisor,
13432 and then multiplies the dividend with the inverse. This strategy allows
13433 cse and hoisting of the inverse calculation. Division by zero calculates
13434 an unspecified result, but does not trap.
13435 "inv:minlat" is a variant of "inv" where if no cse / hoisting opportunities
13436 have been found, or if the entire operation has been hoisted to the same
13437 place, the last stages of the inverse calculation are intertwined with the
13438 final multiply to reduce the overall latency, at the expense of using a few
13439 more instructions, and thus offering fewer scheduling opportunities with
13441 "call" calls a library function that usually implements the inv:minlat
13443 This gives high code density for m5-*media-nofpu compilations.
13444 "call2" uses a different entry point of the same library function, where it
13445 assumes that a pointer to a lookup table has already been set up, which
13446 exposes the pointer load to cse / code hoisting optimizations.
13447 "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm for initial
13448 code generation, but if the code stays unoptimized, revert to the "call",
13449 "call2", or "fp" strategies, respectively. Note that the
13450 potentially-trapping side effect of division by zero is carried by a
13451 separate instruction, so it is possible that all the integer instructions
13452 are hoisted out, but the marker for the side effect stays where it is.
13453 A recombination to fp operations or a call is not possible in that case.
13454 "inv20u" and "inv20l" are variants of the "inv:minlat" strategy. In the case
13455 that the inverse calculation was nor separated from the multiply, they speed
13456 up division where the dividend fits into 20 bits (plus sign where applicable),
13457 by inserting a test to skip a number of operations in this case; this test
13458 slows down the case of larger dividends. inv20u assumes the case of a such
13459 a small dividend to be unlikely, and inv20l assumes it to be likely.
13461 @item -mdivsi3_libfunc=@var{name}
13462 @opindex mdivsi3_libfunc=@var{name}
13463 Set the name of the library function used for 32 bit signed division to
13464 @var{name}. This only affect the name used in the call and inv:call
13465 division strategies, and the compiler will still expect the same
13466 sets of input/output/clobbered registers as if this option was not present.
13468 @item -madjust-unroll
13469 @opindex madjust-unroll
13470 Throttle unrolling to avoid thrashing target registers.
13471 This option only has an effect if the gcc code base supports the
13472 TARGET_ADJUST_UNROLL_MAX target hook.
13474 @item -mindexed-addressing
13475 @opindex mindexed-addressing
13476 Enable the use of the indexed addressing mode for SHmedia32/SHcompact.
13477 This is only safe if the hardware and/or OS implement 32 bit wrap-around
13478 semantics for the indexed addressing mode. The architecture allows the
13479 implementation of processors with 64 bit MMU, which the OS could use to
13480 get 32 bit addressing, but since no current hardware implementation supports
13481 this or any other way to make the indexed addressing mode safe to use in
13482 the 32 bit ABI, the default is -mno-indexed-addressing.
13484 @item -mgettrcost=@var{number}
13485 @opindex mgettrcost=@var{number}
13486 Set the cost assumed for the gettr instruction to @var{number}.
13487 The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise.
13491 Assume pt* instructions won't trap. This will generally generate better
13492 scheduled code, but is unsafe on current hardware. The current architecture
13493 definition says that ptabs and ptrel trap when the target anded with 3 is 3.
13494 This has the unintentional effect of making it unsafe to schedule ptabs /
13495 ptrel before a branch, or hoist it out of a loop. For example,
13496 __do_global_ctors, a part of libgcc that runs constructors at program
13497 startup, calls functions in a list which is delimited by @minus{}1. With the
13498 -mpt-fixed option, the ptabs will be done before testing against @minus{}1.
13499 That means that all the constructors will be run a bit quicker, but when
13500 the loop comes to the end of the list, the program crashes because ptabs
13501 loads @minus{}1 into a target register. Since this option is unsafe for any
13502 hardware implementing the current architecture specification, the default
13503 is -mno-pt-fixed. Unless the user specifies a specific cost with
13504 @option{-mgettrcost}, -mno-pt-fixed also implies @option{-mgettrcost=100};
13505 this deters register allocation using target registers for storing
13508 @item -minvalid-symbols
13509 @opindex minvalid-symbols
13510 Assume symbols might be invalid. Ordinary function symbols generated by
13511 the compiler will always be valid to load with movi/shori/ptabs or
13512 movi/shori/ptrel, but with assembler and/or linker tricks it is possible
13513 to generate symbols that will cause ptabs / ptrel to trap.
13514 This option is only meaningful when @option{-mno-pt-fixed} is in effect.
13515 It will then prevent cross-basic-block cse, hoisting and most scheduling
13516 of symbol loads. The default is @option{-mno-invalid-symbols}.
13519 @node SPARC Options
13520 @subsection SPARC Options
13521 @cindex SPARC options
13523 These @samp{-m} options are supported on the SPARC:
13526 @item -mno-app-regs
13528 @opindex mno-app-regs
13530 Specify @option{-mapp-regs} to generate output using the global registers
13531 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
13534 To be fully SVR4 ABI compliant at the cost of some performance loss,
13535 specify @option{-mno-app-regs}. You should compile libraries and system
13536 software with this option.
13539 @itemx -mhard-float
13541 @opindex mhard-float
13542 Generate output containing floating point instructions. This is the
13546 @itemx -msoft-float
13548 @opindex msoft-float
13549 Generate output containing library calls for floating point.
13550 @strong{Warning:} the requisite libraries are not available for all SPARC
13551 targets. Normally the facilities of the machine's usual C compiler are
13552 used, but this cannot be done directly in cross-compilation. You must make
13553 your own arrangements to provide suitable library functions for
13554 cross-compilation. The embedded targets @samp{sparc-*-aout} and
13555 @samp{sparclite-*-*} do provide software floating point support.
13557 @option{-msoft-float} changes the calling convention in the output file;
13558 therefore, it is only useful if you compile @emph{all} of a program with
13559 this option. In particular, you need to compile @file{libgcc.a}, the
13560 library that comes with GCC, with @option{-msoft-float} in order for
13563 @item -mhard-quad-float
13564 @opindex mhard-quad-float
13565 Generate output containing quad-word (long double) floating point
13568 @item -msoft-quad-float
13569 @opindex msoft-quad-float
13570 Generate output containing library calls for quad-word (long double)
13571 floating point instructions. The functions called are those specified
13572 in the SPARC ABI@. This is the default.
13574 As of this writing, there are no SPARC implementations that have hardware
13575 support for the quad-word floating point instructions. They all invoke
13576 a trap handler for one of these instructions, and then the trap handler
13577 emulates the effect of the instruction. Because of the trap handler overhead,
13578 this is much slower than calling the ABI library routines. Thus the
13579 @option{-msoft-quad-float} option is the default.
13581 @item -mno-unaligned-doubles
13582 @itemx -munaligned-doubles
13583 @opindex mno-unaligned-doubles
13584 @opindex munaligned-doubles
13585 Assume that doubles have 8 byte alignment. This is the default.
13587 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
13588 alignment only if they are contained in another type, or if they have an
13589 absolute address. Otherwise, it assumes they have 4 byte alignment.
13590 Specifying this option avoids some rare compatibility problems with code
13591 generated by other compilers. It is not the default because it results
13592 in a performance loss, especially for floating point code.
13594 @item -mno-faster-structs
13595 @itemx -mfaster-structs
13596 @opindex mno-faster-structs
13597 @opindex mfaster-structs
13598 With @option{-mfaster-structs}, the compiler assumes that structures
13599 should have 8 byte alignment. This enables the use of pairs of
13600 @code{ldd} and @code{std} instructions for copies in structure
13601 assignment, in place of twice as many @code{ld} and @code{st} pairs.
13602 However, the use of this changed alignment directly violates the SPARC
13603 ABI@. Thus, it's intended only for use on targets where the developer
13604 acknowledges that their resulting code will not be directly in line with
13605 the rules of the ABI@.
13607 @item -mimpure-text
13608 @opindex mimpure-text
13609 @option{-mimpure-text}, used in addition to @option{-shared}, tells
13610 the compiler to not pass @option{-z text} to the linker when linking a
13611 shared object. Using this option, you can link position-dependent
13612 code into a shared object.
13614 @option{-mimpure-text} suppresses the ``relocations remain against
13615 allocatable but non-writable sections'' linker error message.
13616 However, the necessary relocations will trigger copy-on-write, and the
13617 shared object is not actually shared across processes. Instead of
13618 using @option{-mimpure-text}, you should compile all source code with
13619 @option{-fpic} or @option{-fPIC}.
13621 This option is only available on SunOS and Solaris.
13623 @item -mcpu=@var{cpu_type}
13625 Set the instruction set, register set, and instruction scheduling parameters
13626 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
13627 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
13628 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
13629 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc},
13630 @samp{ultrasparc3}, and @samp{niagara}.
13632 Default instruction scheduling parameters are used for values that select
13633 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
13634 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
13636 Here is a list of each supported architecture and their supported
13641 v8: supersparc, hypersparc
13642 sparclite: f930, f934, sparclite86x
13644 v9: ultrasparc, ultrasparc3, niagara
13647 By default (unless configured otherwise), GCC generates code for the V7
13648 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
13649 additionally optimizes it for the Cypress CY7C602 chip, as used in the
13650 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
13651 SPARCStation 1, 2, IPX etc.
13653 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
13654 architecture. The only difference from V7 code is that the compiler emits
13655 the integer multiply and integer divide instructions which exist in SPARC-V8
13656 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
13657 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
13660 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
13661 the SPARC architecture. This adds the integer multiply, integer divide step
13662 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
13663 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
13664 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
13665 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
13666 MB86934 chip, which is the more recent SPARClite with FPU@.
13668 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
13669 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
13670 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
13671 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
13672 optimizes it for the TEMIC SPARClet chip.
13674 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
13675 architecture. This adds 64-bit integer and floating-point move instructions,
13676 3 additional floating-point condition code registers and conditional move
13677 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
13678 optimizes it for the Sun UltraSPARC I/II/IIi chips. With
13679 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
13680 Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
13681 @option{-mcpu=niagara}, the compiler additionally optimizes it for
13682 Sun UltraSPARC T1 chips.
13684 @item -mtune=@var{cpu_type}
13686 Set the instruction scheduling parameters for machine type
13687 @var{cpu_type}, but do not set the instruction set or register set that the
13688 option @option{-mcpu=@var{cpu_type}} would.
13690 The same values for @option{-mcpu=@var{cpu_type}} can be used for
13691 @option{-mtune=@var{cpu_type}}, but the only useful values are those
13692 that select a particular cpu implementation. Those are @samp{cypress},
13693 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
13694 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
13695 @samp{ultrasparc3}, and @samp{niagara}.
13700 @opindex mno-v8plus
13701 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
13702 difference from the V8 ABI is that the global and out registers are
13703 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
13704 mode for all SPARC-V9 processors.
13710 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
13711 Visual Instruction Set extensions. The default is @option{-mno-vis}.
13714 These @samp{-m} options are supported in addition to the above
13715 on SPARC-V9 processors in 64-bit environments:
13718 @item -mlittle-endian
13719 @opindex mlittle-endian
13720 Generate code for a processor running in little-endian mode. It is only
13721 available for a few configurations and most notably not on Solaris and Linux.
13727 Generate code for a 32-bit or 64-bit environment.
13728 The 32-bit environment sets int, long and pointer to 32 bits.
13729 The 64-bit environment sets int to 32 bits and long and pointer
13732 @item -mcmodel=medlow
13733 @opindex mcmodel=medlow
13734 Generate code for the Medium/Low code model: 64-bit addresses, programs
13735 must be linked in the low 32 bits of memory. Programs can be statically
13736 or dynamically linked.
13738 @item -mcmodel=medmid
13739 @opindex mcmodel=medmid
13740 Generate code for the Medium/Middle code model: 64-bit addresses, programs
13741 must be linked in the low 44 bits of memory, the text and data segments must
13742 be less than 2GB in size and the data segment must be located within 2GB of
13745 @item -mcmodel=medany
13746 @opindex mcmodel=medany
13747 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
13748 may be linked anywhere in memory, the text and data segments must be less
13749 than 2GB in size and the data segment must be located within 2GB of the
13752 @item -mcmodel=embmedany
13753 @opindex mcmodel=embmedany
13754 Generate code for the Medium/Anywhere code model for embedded systems:
13755 64-bit addresses, the text and data segments must be less than 2GB in
13756 size, both starting anywhere in memory (determined at link time). The
13757 global register %g4 points to the base of the data segment. Programs
13758 are statically linked and PIC is not supported.
13761 @itemx -mno-stack-bias
13762 @opindex mstack-bias
13763 @opindex mno-stack-bias
13764 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
13765 frame pointer if present, are offset by @minus{}2047 which must be added back
13766 when making stack frame references. This is the default in 64-bit mode.
13767 Otherwise, assume no such offset is present.
13770 These switches are supported in addition to the above on Solaris:
13775 Add support for multithreading using the Solaris threads library. This
13776 option sets flags for both the preprocessor and linker. This option does
13777 not affect the thread safety of object code produced by the compiler or
13778 that of libraries supplied with it.
13782 Add support for multithreading using the POSIX threads library. This
13783 option sets flags for both the preprocessor and linker. This option does
13784 not affect the thread safety of object code produced by the compiler or
13785 that of libraries supplied with it.
13789 This is a synonym for @option{-pthreads}.
13793 @subsection SPU Options
13794 @cindex SPU options
13796 These @samp{-m} options are supported on the SPU:
13800 @itemx -merror-reloc
13801 @opindex mwarn-reloc
13802 @opindex merror-reloc
13804 The loader for SPU does not handle dynamic relocations. By default, GCC
13805 will give an error when it generates code that requires a dynamic
13806 relocation. @option{-mno-error-reloc} disables the error,
13807 @option{-mwarn-reloc} will generate a warning instead.
13810 @itemx -munsafe-dma
13812 @opindex munsafe-dma
13814 Instructions which initiate or test completion of DMA must not be
13815 reordered with respect to loads and stores of the memory which is being
13816 accessed. Users typically address this problem using the volatile
13817 keyword, but that can lead to inefficient code in places where the
13818 memory is known to not change. Rather than mark the memory as volatile
13819 we treat the DMA instructions as potentially effecting all memory. With
13820 @option{-munsafe-dma} users must use the volatile keyword to protect
13823 @item -mbranch-hints
13824 @opindex mbranch-hints
13826 By default, GCC will generate a branch hint instruction to avoid
13827 pipeline stalls for always taken or probably taken branches. A hint
13828 will not be generated closer than 8 instructions away from its branch.
13829 There is little reason to disable them, except for debugging purposes,
13830 or to make an object a little bit smaller.
13834 @opindex msmall-mem
13835 @opindex mlarge-mem
13837 By default, GCC generates code assuming that addresses are never larger
13838 than 18 bits. With @option{-mlarge-mem} code is generated that assumes
13839 a full 32 bit address.
13844 By default, GCC links against startup code that assumes the SPU-style
13845 main function interface (which has an unconventional parameter list).
13846 With @option{-mstdmain}, GCC will link your program against startup
13847 code that assumes a C99-style interface to @code{main}, including a
13848 local copy of @code{argv} strings.
13850 @item -mfixed-range=@var{register-range}
13851 @opindex mfixed-range
13852 Generate code treating the given register range as fixed registers.
13853 A fixed register is one that the register allocator can not use. This is
13854 useful when compiling kernel code. A register range is specified as
13855 two registers separated by a dash. Multiple register ranges can be
13856 specified separated by a comma.
13860 @node System V Options
13861 @subsection Options for System V
13863 These additional options are available on System V Release 4 for
13864 compatibility with other compilers on those systems:
13869 Create a shared object.
13870 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
13874 Identify the versions of each tool used by the compiler, in a
13875 @code{.ident} assembler directive in the output.
13879 Refrain from adding @code{.ident} directives to the output file (this is
13882 @item -YP,@var{dirs}
13884 Search the directories @var{dirs}, and no others, for libraries
13885 specified with @option{-l}.
13887 @item -Ym,@var{dir}
13889 Look in the directory @var{dir} to find the M4 preprocessor.
13890 The assembler uses this option.
13891 @c This is supposed to go with a -Yd for predefined M4 macro files, but
13892 @c the generic assembler that comes with Solaris takes just -Ym.
13895 @node TMS320C3x/C4x Options
13896 @subsection TMS320C3x/C4x Options
13897 @cindex TMS320C3x/C4x Options
13899 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
13903 @item -mcpu=@var{cpu_type}
13905 Set the instruction set, register set, and instruction scheduling
13906 parameters for machine type @var{cpu_type}. Supported values for
13907 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
13908 @samp{c44}. The default is @samp{c40} to generate code for the
13913 @itemx -msmall-memory
13915 @opindex mbig-memory
13917 @opindex msmall-memory
13919 Generates code for the big or small memory model. The small memory
13920 model assumed that all data fits into one 64K word page. At run-time
13921 the data page (DP) register must be set to point to the 64K page
13922 containing the .bss and .data program sections. The big memory model is
13923 the default and requires reloading of the DP register for every direct
13930 Allow (disallow) allocation of general integer operands into the block
13931 count register BK@.
13937 Enable (disable) generation of code using decrement and branch,
13938 DBcond(D), instructions. This is enabled by default for the C4x. To be
13939 on the safe side, this is disabled for the C3x, since the maximum
13940 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
13941 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
13942 that it can utilize the decrement and branch instruction, but will give
13943 up if there is more than one memory reference in the loop. Thus a loop
13944 where the loop counter is decremented can generate slightly more
13945 efficient code, in cases where the RPTB instruction cannot be utilized.
13947 @item -mdp-isr-reload
13949 @opindex mdp-isr-reload
13951 Force the DP register to be saved on entry to an interrupt service
13952 routine (ISR), reloaded to point to the data section, and restored on
13953 exit from the ISR@. This should not be required unless someone has
13954 violated the small memory model by modifying the DP register, say within
13961 For the C3x use the 24-bit MPYI instruction for integer multiplies
13962 instead of a library call to guarantee 32-bit results. Note that if one
13963 of the operands is a constant, then the multiplication will be performed
13964 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
13965 then squaring operations are performed inline instead of a library call.
13968 @itemx -mno-fast-fix
13970 @opindex mno-fast-fix
13971 The C3x/C4x FIX instruction to convert a floating point value to an
13972 integer value chooses the nearest integer less than or equal to the
13973 floating point value rather than to the nearest integer. Thus if the
13974 floating point number is negative, the result will be incorrectly
13975 truncated an additional code is necessary to detect and correct this
13976 case. This option can be used to disable generation of the additional
13977 code required to correct the result.
13983 Enable (disable) generation of repeat block sequences using the RPTB
13984 instruction for zero overhead looping. The RPTB construct is only used
13985 for innermost loops that do not call functions or jump across the loop
13986 boundaries. There is no advantage having nested RPTB loops due to the
13987 overhead required to save and restore the RC, RS, and RE registers.
13988 This is enabled by default with @option{-O2}.
13990 @item -mrpts=@var{count}
13994 Enable (disable) the use of the single instruction repeat instruction
13995 RPTS@. If a repeat block contains a single instruction, and the loop
13996 count can be guaranteed to be less than the value @var{count}, GCC will
13997 emit a RPTS instruction instead of a RPTB@. If no value is specified,
13998 then a RPTS will be emitted even if the loop count cannot be determined
13999 at compile time. Note that the repeated instruction following RPTS does
14000 not have to be reloaded from memory each iteration, thus freeing up the
14001 CPU buses for operands. However, since interrupts are blocked by this
14002 instruction, it is disabled by default.
14004 @item -mloop-unsigned
14005 @itemx -mno-loop-unsigned
14006 @opindex mloop-unsigned
14007 @opindex mno-loop-unsigned
14008 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
14009 is @math{2^{31} + 1} since these instructions test if the iteration count is
14010 negative to terminate the loop. If the iteration count is unsigned
14011 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
14012 exceeded. This switch allows an unsigned iteration count.
14016 Try to emit an assembler syntax that the TI assembler (asm30) is happy
14017 with. This also enforces compatibility with the API employed by the TI
14018 C3x C compiler. For example, long doubles are passed as structures
14019 rather than in floating point registers.
14025 Generate code that uses registers (stack) for passing arguments to functions.
14026 By default, arguments are passed in registers where possible rather
14027 than by pushing arguments on to the stack.
14029 @item -mparallel-insns
14030 @itemx -mno-parallel-insns
14031 @opindex mparallel-insns
14032 @opindex mno-parallel-insns
14033 Allow the generation of parallel instructions. This is enabled by
14034 default with @option{-O2}.
14036 @item -mparallel-mpy
14037 @itemx -mno-parallel-mpy
14038 @opindex mparallel-mpy
14039 @opindex mno-parallel-mpy
14040 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
14041 provided @option{-mparallel-insns} is also specified. These instructions have
14042 tight register constraints which can pessimize the code generation
14043 of large functions.
14048 @subsection V850 Options
14049 @cindex V850 Options
14051 These @samp{-m} options are defined for V850 implementations:
14055 @itemx -mno-long-calls
14056 @opindex mlong-calls
14057 @opindex mno-long-calls
14058 Treat all calls as being far away (near). If calls are assumed to be
14059 far away, the compiler will always load the functions address up into a
14060 register, and call indirect through the pointer.
14066 Do not optimize (do optimize) basic blocks that use the same index
14067 pointer 4 or more times to copy pointer into the @code{ep} register, and
14068 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
14069 option is on by default if you optimize.
14071 @item -mno-prolog-function
14072 @itemx -mprolog-function
14073 @opindex mno-prolog-function
14074 @opindex mprolog-function
14075 Do not use (do use) external functions to save and restore registers
14076 at the prologue and epilogue of a function. The external functions
14077 are slower, but use less code space if more than one function saves
14078 the same number of registers. The @option{-mprolog-function} option
14079 is on by default if you optimize.
14083 Try to make the code as small as possible. At present, this just turns
14084 on the @option{-mep} and @option{-mprolog-function} options.
14086 @item -mtda=@var{n}
14088 Put static or global variables whose size is @var{n} bytes or less into
14089 the tiny data area that register @code{ep} points to. The tiny data
14090 area can hold up to 256 bytes in total (128 bytes for byte references).
14092 @item -msda=@var{n}
14094 Put static or global variables whose size is @var{n} bytes or less into
14095 the small data area that register @code{gp} points to. The small data
14096 area can hold up to 64 kilobytes.
14098 @item -mzda=@var{n}
14100 Put static or global variables whose size is @var{n} bytes or less into
14101 the first 32 kilobytes of memory.
14105 Specify that the target processor is the V850.
14108 @opindex mbig-switch
14109 Generate code suitable for big switch tables. Use this option only if
14110 the assembler/linker complain about out of range branches within a switch
14115 This option will cause r2 and r5 to be used in the code generated by
14116 the compiler. This setting is the default.
14118 @item -mno-app-regs
14119 @opindex mno-app-regs
14120 This option will cause r2 and r5 to be treated as fixed registers.
14124 Specify that the target processor is the V850E1. The preprocessor
14125 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
14126 this option is used.
14130 Specify that the target processor is the V850E@. The preprocessor
14131 constant @samp{__v850e__} will be defined if this option is used.
14133 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
14134 are defined then a default target processor will be chosen and the
14135 relevant @samp{__v850*__} preprocessor constant will be defined.
14137 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
14138 defined, regardless of which processor variant is the target.
14140 @item -mdisable-callt
14141 @opindex mdisable-callt
14142 This option will suppress generation of the CALLT instruction for the
14143 v850e and v850e1 flavors of the v850 architecture. The default is
14144 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
14149 @subsection VAX Options
14150 @cindex VAX options
14152 These @samp{-m} options are defined for the VAX:
14157 Do not output certain jump instructions (@code{aobleq} and so on)
14158 that the Unix assembler for the VAX cannot handle across long
14163 Do output those jump instructions, on the assumption that you
14164 will assemble with the GNU assembler.
14168 Output code for g-format floating point numbers instead of d-format.
14171 @node VxWorks Options
14172 @subsection VxWorks Options
14173 @cindex VxWorks Options
14175 The options in this section are defined for all VxWorks targets.
14176 Options specific to the target hardware are listed with the other
14177 options for that target.
14182 GCC can generate code for both VxWorks kernels and real time processes
14183 (RTPs). This option switches from the former to the latter. It also
14184 defines the preprocessor macro @code{__RTP__}.
14187 @opindex non-static
14188 Link an RTP executable against shared libraries rather than static
14189 libraries. The options @option{-static} and @option{-shared} can
14190 also be used for RTPs (@pxref{Link Options}); @option{-static}
14197 These options are passed down to the linker. They are defined for
14198 compatibility with Diab.
14201 @opindex Xbind-lazy
14202 Enable lazy binding of function calls. This option is equivalent to
14203 @option{-Wl,-z,now} and is defined for compatibility with Diab.
14207 Disable lazy binding of function calls. This option is the default and
14208 is defined for compatibility with Diab.
14211 @node x86-64 Options
14212 @subsection x86-64 Options
14213 @cindex x86-64 options
14215 These are listed under @xref{i386 and x86-64 Options}.
14217 @node Xstormy16 Options
14218 @subsection Xstormy16 Options
14219 @cindex Xstormy16 Options
14221 These options are defined for Xstormy16:
14226 Choose startup files and linker script suitable for the simulator.
14229 @node Xtensa Options
14230 @subsection Xtensa Options
14231 @cindex Xtensa Options
14233 These options are supported for Xtensa targets:
14237 @itemx -mno-const16
14239 @opindex mno-const16
14240 Enable or disable use of @code{CONST16} instructions for loading
14241 constant values. The @code{CONST16} instruction is currently not a
14242 standard option from Tensilica. When enabled, @code{CONST16}
14243 instructions are always used in place of the standard @code{L32R}
14244 instructions. The use of @code{CONST16} is enabled by default only if
14245 the @code{L32R} instruction is not available.
14248 @itemx -mno-fused-madd
14249 @opindex mfused-madd
14250 @opindex mno-fused-madd
14251 Enable or disable use of fused multiply/add and multiply/subtract
14252 instructions in the floating-point option. This has no effect if the
14253 floating-point option is not also enabled. Disabling fused multiply/add
14254 and multiply/subtract instructions forces the compiler to use separate
14255 instructions for the multiply and add/subtract operations. This may be
14256 desirable in some cases where strict IEEE 754-compliant results are
14257 required: the fused multiply add/subtract instructions do not round the
14258 intermediate result, thereby producing results with @emph{more} bits of
14259 precision than specified by the IEEE standard. Disabling fused multiply
14260 add/subtract instructions also ensures that the program output is not
14261 sensitive to the compiler's ability to combine multiply and add/subtract
14264 @item -mtext-section-literals
14265 @itemx -mno-text-section-literals
14266 @opindex mtext-section-literals
14267 @opindex mno-text-section-literals
14268 Control the treatment of literal pools. The default is
14269 @option{-mno-text-section-literals}, which places literals in a separate
14270 section in the output file. This allows the literal pool to be placed
14271 in a data RAM/ROM, and it also allows the linker to combine literal
14272 pools from separate object files to remove redundant literals and
14273 improve code size. With @option{-mtext-section-literals}, the literals
14274 are interspersed in the text section in order to keep them as close as
14275 possible to their references. This may be necessary for large assembly
14278 @item -mtarget-align
14279 @itemx -mno-target-align
14280 @opindex mtarget-align
14281 @opindex mno-target-align
14282 When this option is enabled, GCC instructs the assembler to
14283 automatically align instructions to reduce branch penalties at the
14284 expense of some code density. The assembler attempts to widen density
14285 instructions to align branch targets and the instructions following call
14286 instructions. If there are not enough preceding safe density
14287 instructions to align a target, no widening will be performed. The
14288 default is @option{-mtarget-align}. These options do not affect the
14289 treatment of auto-aligned instructions like @code{LOOP}, which the
14290 assembler will always align, either by widening density instructions or
14291 by inserting no-op instructions.
14294 @itemx -mno-longcalls
14295 @opindex mlongcalls
14296 @opindex mno-longcalls
14297 When this option is enabled, GCC instructs the assembler to translate
14298 direct calls to indirect calls unless it can determine that the target
14299 of a direct call is in the range allowed by the call instruction. This
14300 translation typically occurs for calls to functions in other source
14301 files. Specifically, the assembler translates a direct @code{CALL}
14302 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
14303 The default is @option{-mno-longcalls}. This option should be used in
14304 programs where the call target can potentially be out of range. This
14305 option is implemented in the assembler, not the compiler, so the
14306 assembly code generated by GCC will still show direct call
14307 instructions---look at the disassembled object code to see the actual
14308 instructions. Note that the assembler will use an indirect call for
14309 every cross-file call, not just those that really will be out of range.
14312 @node zSeries Options
14313 @subsection zSeries Options
14314 @cindex zSeries options
14316 These are listed under @xref{S/390 and zSeries Options}.
14318 @node Code Gen Options
14319 @section Options for Code Generation Conventions
14320 @cindex code generation conventions
14321 @cindex options, code generation
14322 @cindex run-time options
14324 These machine-independent options control the interface conventions
14325 used in code generation.
14327 Most of them have both positive and negative forms; the negative form
14328 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
14329 one of the forms is listed---the one which is not the default. You
14330 can figure out the other form by either removing @samp{no-} or adding
14334 @item -fbounds-check
14335 @opindex fbounds-check
14336 For front-ends that support it, generate additional code to check that
14337 indices used to access arrays are within the declared range. This is
14338 currently only supported by the Java and Fortran front-ends, where
14339 this option defaults to true and false respectively.
14343 This option generates traps for signed overflow on addition, subtraction,
14344 multiplication operations.
14348 This option instructs the compiler to assume that signed arithmetic
14349 overflow of addition, subtraction and multiplication wraps around
14350 using twos-complement representation. This flag enables some optimizations
14351 and disables others. This option is enabled by default for the Java
14352 front-end, as required by the Java language specification.
14355 @opindex fexceptions
14356 Enable exception handling. Generates extra code needed to propagate
14357 exceptions. For some targets, this implies GCC will generate frame
14358 unwind information for all functions, which can produce significant data
14359 size overhead, although it does not affect execution. If you do not
14360 specify this option, GCC will enable it by default for languages like
14361 C++ which normally require exception handling, and disable it for
14362 languages like C that do not normally require it. However, you may need
14363 to enable this option when compiling C code that needs to interoperate
14364 properly with exception handlers written in C++. You may also wish to
14365 disable this option if you are compiling older C++ programs that don't
14366 use exception handling.
14368 @item -fnon-call-exceptions
14369 @opindex fnon-call-exceptions
14370 Generate code that allows trapping instructions to throw exceptions.
14371 Note that this requires platform-specific runtime support that does
14372 not exist everywhere. Moreover, it only allows @emph{trapping}
14373 instructions to throw exceptions, i.e.@: memory references or floating
14374 point instructions. It does not allow exceptions to be thrown from
14375 arbitrary signal handlers such as @code{SIGALRM}.
14377 @item -funwind-tables
14378 @opindex funwind-tables
14379 Similar to @option{-fexceptions}, except that it will just generate any needed
14380 static data, but will not affect the generated code in any other way.
14381 You will normally not enable this option; instead, a language processor
14382 that needs this handling would enable it on your behalf.
14384 @item -fasynchronous-unwind-tables
14385 @opindex fasynchronous-unwind-tables
14386 Generate unwind table in dwarf2 format, if supported by target machine. The
14387 table is exact at each instruction boundary, so it can be used for stack
14388 unwinding from asynchronous events (such as debugger or garbage collector).
14390 @item -fpcc-struct-return
14391 @opindex fpcc-struct-return
14392 Return ``short'' @code{struct} and @code{union} values in memory like
14393 longer ones, rather than in registers. This convention is less
14394 efficient, but it has the advantage of allowing intercallability between
14395 GCC-compiled files and files compiled with other compilers, particularly
14396 the Portable C Compiler (pcc).
14398 The precise convention for returning structures in memory depends
14399 on the target configuration macros.
14401 Short structures and unions are those whose size and alignment match
14402 that of some integer type.
14404 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
14405 switch is not binary compatible with code compiled with the
14406 @option{-freg-struct-return} switch.
14407 Use it to conform to a non-default application binary interface.
14409 @item -freg-struct-return
14410 @opindex freg-struct-return
14411 Return @code{struct} and @code{union} values in registers when possible.
14412 This is more efficient for small structures than
14413 @option{-fpcc-struct-return}.
14415 If you specify neither @option{-fpcc-struct-return} nor
14416 @option{-freg-struct-return}, GCC defaults to whichever convention is
14417 standard for the target. If there is no standard convention, GCC
14418 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
14419 the principal compiler. In those cases, we can choose the standard, and
14420 we chose the more efficient register return alternative.
14422 @strong{Warning:} code compiled with the @option{-freg-struct-return}
14423 switch is not binary compatible with code compiled with the
14424 @option{-fpcc-struct-return} switch.
14425 Use it to conform to a non-default application binary interface.
14427 @item -fshort-enums
14428 @opindex fshort-enums
14429 Allocate to an @code{enum} type only as many bytes as it needs for the
14430 declared range of possible values. Specifically, the @code{enum} type
14431 will be equivalent to the smallest integer type which has enough room.
14433 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
14434 code that is not binary compatible with code generated without that switch.
14435 Use it to conform to a non-default application binary interface.
14437 @item -fshort-double
14438 @opindex fshort-double
14439 Use the same size for @code{double} as for @code{float}.
14441 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
14442 code that is not binary compatible with code generated without that switch.
14443 Use it to conform to a non-default application binary interface.
14445 @item -fshort-wchar
14446 @opindex fshort-wchar
14447 Override the underlying type for @samp{wchar_t} to be @samp{short
14448 unsigned int} instead of the default for the target. This option is
14449 useful for building programs to run under WINE@.
14451 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
14452 code that is not binary compatible with code generated without that switch.
14453 Use it to conform to a non-default application binary interface.
14456 @opindex fno-common
14457 In C, allocate even uninitialized global variables in the data section of the
14458 object file, rather than generating them as common blocks. This has the
14459 effect that if the same variable is declared (without @code{extern}) in
14460 two different compilations, you will get an error when you link them.
14461 The only reason this might be useful is if you wish to verify that the
14462 program will work on other systems which always work this way.
14466 Ignore the @samp{#ident} directive.
14468 @item -finhibit-size-directive
14469 @opindex finhibit-size-directive
14470 Don't output a @code{.size} assembler directive, or anything else that
14471 would cause trouble if the function is split in the middle, and the
14472 two halves are placed at locations far apart in memory. This option is
14473 used when compiling @file{crtstuff.c}; you should not need to use it
14476 @item -fverbose-asm
14477 @opindex fverbose-asm
14478 Put extra commentary information in the generated assembly code to
14479 make it more readable. This option is generally only of use to those
14480 who actually need to read the generated assembly code (perhaps while
14481 debugging the compiler itself).
14483 @option{-fno-verbose-asm}, the default, causes the
14484 extra information to be omitted and is useful when comparing two assembler
14487 @item -frecord-gcc-switches
14488 @opindex frecord-gcc-switches
14489 This switch causes the command line that was used to invoke the
14490 compiler to be recorded into the object file that is being created.
14491 This switch is only implemented on some targets and the exact format
14492 of the recording is target and binary file format dependent, but it
14493 usually takes the form of a section containing ASCII text. This
14494 switch is related to the @option{-fverbose-asm} switch, but that
14495 switch only records information in the assembler output file as
14496 comments, so it never reaches the object file.
14500 @cindex global offset table
14502 Generate position-independent code (PIC) suitable for use in a shared
14503 library, if supported for the target machine. Such code accesses all
14504 constant addresses through a global offset table (GOT)@. The dynamic
14505 loader resolves the GOT entries when the program starts (the dynamic
14506 loader is not part of GCC; it is part of the operating system). If
14507 the GOT size for the linked executable exceeds a machine-specific
14508 maximum size, you get an error message from the linker indicating that
14509 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
14510 instead. (These maximums are 8k on the SPARC and 32k
14511 on the m68k and RS/6000. The 386 has no such limit.)
14513 Position-independent code requires special support, and therefore works
14514 only on certain machines. For the 386, GCC supports PIC for System V
14515 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
14516 position-independent.
14518 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
14523 If supported for the target machine, emit position-independent code,
14524 suitable for dynamic linking and avoiding any limit on the size of the
14525 global offset table. This option makes a difference on the m68k,
14526 PowerPC and SPARC@.
14528 Position-independent code requires special support, and therefore works
14529 only on certain machines.
14531 When this flag is set, the macros @code{__pic__} and @code{__PIC__}
14538 These options are similar to @option{-fpic} and @option{-fPIC}, but
14539 generated position independent code can be only linked into executables.
14540 Usually these options are used when @option{-pie} GCC option will be
14541 used during linking.
14543 @option{-fpie} and @option{-fPIE} both define the macros
14544 @code{__pie__} and @code{__PIE__}. The macros have the value 1
14545 for @option{-fpie} and 2 for @option{-fPIE}.
14547 @item -fno-jump-tables
14548 @opindex fno-jump-tables
14549 Do not use jump tables for switch statements even where it would be
14550 more efficient than other code generation strategies. This option is
14551 of use in conjunction with @option{-fpic} or @option{-fPIC} for
14552 building code which forms part of a dynamic linker and cannot
14553 reference the address of a jump table. On some targets, jump tables
14554 do not require a GOT and this option is not needed.
14556 @item -ffixed-@var{reg}
14558 Treat the register named @var{reg} as a fixed register; generated code
14559 should never refer to it (except perhaps as a stack pointer, frame
14560 pointer or in some other fixed role).
14562 @var{reg} must be the name of a register. The register names accepted
14563 are machine-specific and are defined in the @code{REGISTER_NAMES}
14564 macro in the machine description macro file.
14566 This flag does not have a negative form, because it specifies a
14569 @item -fcall-used-@var{reg}
14570 @opindex fcall-used
14571 Treat the register named @var{reg} as an allocable register that is
14572 clobbered by function calls. It may be allocated for temporaries or
14573 variables that do not live across a call. Functions compiled this way
14574 will not save and restore the register @var{reg}.
14576 It is an error to used this flag with the frame pointer or stack pointer.
14577 Use of this flag for other registers that have fixed pervasive roles in
14578 the machine's execution model will produce disastrous results.
14580 This flag does not have a negative form, because it specifies a
14583 @item -fcall-saved-@var{reg}
14584 @opindex fcall-saved
14585 Treat the register named @var{reg} as an allocable register saved by
14586 functions. It may be allocated even for temporaries or variables that
14587 live across a call. Functions compiled this way will save and restore
14588 the register @var{reg} if they use it.
14590 It is an error to used this flag with the frame pointer or stack pointer.
14591 Use of this flag for other registers that have fixed pervasive roles in
14592 the machine's execution model will produce disastrous results.
14594 A different sort of disaster will result from the use of this flag for
14595 a register in which function values may be returned.
14597 This flag does not have a negative form, because it specifies a
14600 @item -fpack-struct[=@var{n}]
14601 @opindex fpack-struct
14602 Without a value specified, pack all structure members together without
14603 holes. When a value is specified (which must be a small power of two), pack
14604 structure members according to this value, representing the maximum
14605 alignment (that is, objects with default alignment requirements larger than
14606 this will be output potentially unaligned at the next fitting location.
14608 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
14609 code that is not binary compatible with code generated without that switch.
14610 Additionally, it makes the code suboptimal.
14611 Use it to conform to a non-default application binary interface.
14613 @item -finstrument-functions
14614 @opindex finstrument-functions
14615 Generate instrumentation calls for entry and exit to functions. Just
14616 after function entry and just before function exit, the following
14617 profiling functions will be called with the address of the current
14618 function and its call site. (On some platforms,
14619 @code{__builtin_return_address} does not work beyond the current
14620 function, so the call site information may not be available to the
14621 profiling functions otherwise.)
14624 void __cyg_profile_func_enter (void *this_fn,
14626 void __cyg_profile_func_exit (void *this_fn,
14630 The first argument is the address of the start of the current function,
14631 which may be looked up exactly in the symbol table.
14633 This instrumentation is also done for functions expanded inline in other
14634 functions. The profiling calls will indicate where, conceptually, the
14635 inline function is entered and exited. This means that addressable
14636 versions of such functions must be available. If all your uses of a
14637 function are expanded inline, this may mean an additional expansion of
14638 code size. If you use @samp{extern inline} in your C code, an
14639 addressable version of such functions must be provided. (This is
14640 normally the case anyways, but if you get lucky and the optimizer always
14641 expands the functions inline, you might have gotten away without
14642 providing static copies.)
14644 A function may be given the attribute @code{no_instrument_function}, in
14645 which case this instrumentation will not be done. This can be used, for
14646 example, for the profiling functions listed above, high-priority
14647 interrupt routines, and any functions from which the profiling functions
14648 cannot safely be called (perhaps signal handlers, if the profiling
14649 routines generate output or allocate memory).
14651 @item -fstack-check
14652 @opindex fstack-check
14653 Generate code to verify that you do not go beyond the boundary of the
14654 stack. You should specify this flag if you are running in an
14655 environment with multiple threads, but only rarely need to specify it in
14656 a single-threaded environment since stack overflow is automatically
14657 detected on nearly all systems if there is only one stack.
14659 Note that this switch does not actually cause checking to be done; the
14660 operating system must do that. The switch causes generation of code
14661 to ensure that the operating system sees the stack being extended.
14663 @item -fstack-limit-register=@var{reg}
14664 @itemx -fstack-limit-symbol=@var{sym}
14665 @itemx -fno-stack-limit
14666 @opindex fstack-limit-register
14667 @opindex fstack-limit-symbol
14668 @opindex fno-stack-limit
14669 Generate code to ensure that the stack does not grow beyond a certain value,
14670 either the value of a register or the address of a symbol. If the stack
14671 would grow beyond the value, a signal is raised. For most targets,
14672 the signal is raised before the stack overruns the boundary, so
14673 it is possible to catch the signal without taking special precautions.
14675 For instance, if the stack starts at absolute address @samp{0x80000000}
14676 and grows downwards, you can use the flags
14677 @option{-fstack-limit-symbol=__stack_limit} and
14678 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
14679 of 128KB@. Note that this may only work with the GNU linker.
14681 @cindex aliasing of parameters
14682 @cindex parameters, aliased
14683 @item -fargument-alias
14684 @itemx -fargument-noalias
14685 @itemx -fargument-noalias-global
14686 @itemx -fargument-noalias-anything
14687 @opindex fargument-alias
14688 @opindex fargument-noalias
14689 @opindex fargument-noalias-global
14690 @opindex fargument-noalias-anything
14691 Specify the possible relationships among parameters and between
14692 parameters and global data.
14694 @option{-fargument-alias} specifies that arguments (parameters) may
14695 alias each other and may alias global storage.@*
14696 @option{-fargument-noalias} specifies that arguments do not alias
14697 each other, but may alias global storage.@*
14698 @option{-fargument-noalias-global} specifies that arguments do not
14699 alias each other and do not alias global storage.
14700 @option{-fargument-noalias-anything} specifies that arguments do not
14701 alias any other storage.
14703 Each language will automatically use whatever option is required by
14704 the language standard. You should not need to use these options yourself.
14706 @item -fleading-underscore
14707 @opindex fleading-underscore
14708 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
14709 change the way C symbols are represented in the object file. One use
14710 is to help link with legacy assembly code.
14712 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
14713 generate code that is not binary compatible with code generated without that
14714 switch. Use it to conform to a non-default application binary interface.
14715 Not all targets provide complete support for this switch.
14717 @item -ftls-model=@var{model}
14718 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
14719 The @var{model} argument should be one of @code{global-dynamic},
14720 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
14722 The default without @option{-fpic} is @code{initial-exec}; with
14723 @option{-fpic} the default is @code{global-dynamic}.
14725 @item -fvisibility=@var{default|internal|hidden|protected}
14726 @opindex fvisibility
14727 Set the default ELF image symbol visibility to the specified option---all
14728 symbols will be marked with this unless overridden within the code.
14729 Using this feature can very substantially improve linking and
14730 load times of shared object libraries, produce more optimized
14731 code, provide near-perfect API export and prevent symbol clashes.
14732 It is @strong{strongly} recommended that you use this in any shared objects
14735 Despite the nomenclature, @code{default} always means public ie;
14736 available to be linked against from outside the shared object.
14737 @code{protected} and @code{internal} are pretty useless in real-world
14738 usage so the only other commonly used option will be @code{hidden}.
14739 The default if @option{-fvisibility} isn't specified is
14740 @code{default}, i.e., make every
14741 symbol public---this causes the same behavior as previous versions of
14744 A good explanation of the benefits offered by ensuring ELF
14745 symbols have the correct visibility is given by ``How To Write
14746 Shared Libraries'' by Ulrich Drepper (which can be found at
14747 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
14748 solution made possible by this option to marking things hidden when
14749 the default is public is to make the default hidden and mark things
14750 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
14751 and @code{__attribute__ ((visibility("default")))} instead of
14752 @code{__declspec(dllexport)} you get almost identical semantics with
14753 identical syntax. This is a great boon to those working with
14754 cross-platform projects.
14756 For those adding visibility support to existing code, you may find
14757 @samp{#pragma GCC visibility} of use. This works by you enclosing
14758 the declarations you wish to set visibility for with (for example)
14759 @samp{#pragma GCC visibility push(hidden)} and
14760 @samp{#pragma GCC visibility pop}.
14761 Bear in mind that symbol visibility should be viewed @strong{as
14762 part of the API interface contract} and thus all new code should
14763 always specify visibility when it is not the default ie; declarations
14764 only for use within the local DSO should @strong{always} be marked explicitly
14765 as hidden as so to avoid PLT indirection overheads---making this
14766 abundantly clear also aids readability and self-documentation of the code.
14767 Note that due to ISO C++ specification requirements, operator new and
14768 operator delete must always be of default visibility.
14770 Be aware that headers from outside your project, in particular system
14771 headers and headers from any other library you use, may not be
14772 expecting to be compiled with visibility other than the default. You
14773 may need to explicitly say @samp{#pragma GCC visibility push(default)}
14774 before including any such headers.
14776 @samp{extern} declarations are not affected by @samp{-fvisibility}, so
14777 a lot of code can be recompiled with @samp{-fvisibility=hidden} with
14778 no modifications. However, this means that calls to @samp{extern}
14779 functions with no explicit visibility will use the PLT, so it is more
14780 effective to use @samp{__attribute ((visibility))} and/or
14781 @samp{#pragma GCC visibility} to tell the compiler which @samp{extern}
14782 declarations should be treated as hidden.
14784 Note that @samp{-fvisibility} does affect C++ vague linkage
14785 entities. This means that, for instance, an exception class that will
14786 be thrown between DSOs must be explicitly marked with default
14787 visibility so that the @samp{type_info} nodes will be unified between
14790 An overview of these techniques, their benefits and how to use them
14791 is at @w{@uref{http://gcc.gnu.org/wiki/Visibility}}.
14797 @node Environment Variables
14798 @section Environment Variables Affecting GCC
14799 @cindex environment variables
14801 @c man begin ENVIRONMENT
14802 This section describes several environment variables that affect how GCC
14803 operates. Some of them work by specifying directories or prefixes to use
14804 when searching for various kinds of files. Some are used to specify other
14805 aspects of the compilation environment.
14807 Note that you can also specify places to search using options such as
14808 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
14809 take precedence over places specified using environment variables, which
14810 in turn take precedence over those specified by the configuration of GCC@.
14811 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
14812 GNU Compiler Collection (GCC) Internals}.
14817 @c @itemx LC_COLLATE
14819 @c @itemx LC_MONETARY
14820 @c @itemx LC_NUMERIC
14825 @c @findex LC_COLLATE
14826 @findex LC_MESSAGES
14827 @c @findex LC_MONETARY
14828 @c @findex LC_NUMERIC
14832 These environment variables control the way that GCC uses
14833 localization information that allow GCC to work with different
14834 national conventions. GCC inspects the locale categories
14835 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
14836 so. These locale categories can be set to any value supported by your
14837 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
14838 Kingdom encoded in UTF-8.
14840 The @env{LC_CTYPE} environment variable specifies character
14841 classification. GCC uses it to determine the character boundaries in
14842 a string; this is needed for some multibyte encodings that contain quote
14843 and escape characters that would otherwise be interpreted as a string
14846 The @env{LC_MESSAGES} environment variable specifies the language to
14847 use in diagnostic messages.
14849 If the @env{LC_ALL} environment variable is set, it overrides the value
14850 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
14851 and @env{LC_MESSAGES} default to the value of the @env{LANG}
14852 environment variable. If none of these variables are set, GCC
14853 defaults to traditional C English behavior.
14857 If @env{TMPDIR} is set, it specifies the directory to use for temporary
14858 files. GCC uses temporary files to hold the output of one stage of
14859 compilation which is to be used as input to the next stage: for example,
14860 the output of the preprocessor, which is the input to the compiler
14863 @item GCC_EXEC_PREFIX
14864 @findex GCC_EXEC_PREFIX
14865 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
14866 names of the subprograms executed by the compiler. No slash is added
14867 when this prefix is combined with the name of a subprogram, but you can
14868 specify a prefix that ends with a slash if you wish.
14870 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
14871 an appropriate prefix to use based on the pathname it was invoked with.
14873 If GCC cannot find the subprogram using the specified prefix, it
14874 tries looking in the usual places for the subprogram.
14876 The default value of @env{GCC_EXEC_PREFIX} is
14877 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
14878 the installed compiler. In many cases @var{prefix} is the value
14879 of @code{prefix} when you ran the @file{configure} script.
14881 Other prefixes specified with @option{-B} take precedence over this prefix.
14883 This prefix is also used for finding files such as @file{crt0.o} that are
14886 In addition, the prefix is used in an unusual way in finding the
14887 directories to search for header files. For each of the standard
14888 directories whose name normally begins with @samp{/usr/local/lib/gcc}
14889 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
14890 replacing that beginning with the specified prefix to produce an
14891 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
14892 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
14893 These alternate directories are searched first; the standard directories
14894 come next. If a standard directory begins with the configured
14895 @var{prefix} then the value of @var{prefix} is replaced by
14896 @env{GCC_EXEC_PREFIX} when looking for header files.
14898 @item COMPILER_PATH
14899 @findex COMPILER_PATH
14900 The value of @env{COMPILER_PATH} is a colon-separated list of
14901 directories, much like @env{PATH}. GCC tries the directories thus
14902 specified when searching for subprograms, if it can't find the
14903 subprograms using @env{GCC_EXEC_PREFIX}.
14906 @findex LIBRARY_PATH
14907 The value of @env{LIBRARY_PATH} is a colon-separated list of
14908 directories, much like @env{PATH}. When configured as a native compiler,
14909 GCC tries the directories thus specified when searching for special
14910 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
14911 using GCC also uses these directories when searching for ordinary
14912 libraries for the @option{-l} option (but directories specified with
14913 @option{-L} come first).
14917 @cindex locale definition
14918 This variable is used to pass locale information to the compiler. One way in
14919 which this information is used is to determine the character set to be used
14920 when character literals, string literals and comments are parsed in C and C++.
14921 When the compiler is configured to allow multibyte characters,
14922 the following values for @env{LANG} are recognized:
14926 Recognize JIS characters.
14928 Recognize SJIS characters.
14930 Recognize EUCJP characters.
14933 If @env{LANG} is not defined, or if it has some other value, then the
14934 compiler will use mblen and mbtowc as defined by the default locale to
14935 recognize and translate multibyte characters.
14939 Some additional environments variables affect the behavior of the
14942 @include cppenv.texi
14946 @node Precompiled Headers
14947 @section Using Precompiled Headers
14948 @cindex precompiled headers
14949 @cindex speed of compilation
14951 Often large projects have many header files that are included in every
14952 source file. The time the compiler takes to process these header files
14953 over and over again can account for nearly all of the time required to
14954 build the project. To make builds faster, GCC allows users to
14955 `precompile' a header file; then, if builds can use the precompiled
14956 header file they will be much faster.
14958 To create a precompiled header file, simply compile it as you would any
14959 other file, if necessary using the @option{-x} option to make the driver
14960 treat it as a C or C++ header file. You will probably want to use a
14961 tool like @command{make} to keep the precompiled header up-to-date when
14962 the headers it contains change.
14964 A precompiled header file will be searched for when @code{#include} is
14965 seen in the compilation. As it searches for the included file
14966 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
14967 compiler looks for a precompiled header in each directory just before it
14968 looks for the include file in that directory. The name searched for is
14969 the name specified in the @code{#include} with @samp{.gch} appended. If
14970 the precompiled header file can't be used, it is ignored.
14972 For instance, if you have @code{#include "all.h"}, and you have
14973 @file{all.h.gch} in the same directory as @file{all.h}, then the
14974 precompiled header file will be used if possible, and the original
14975 header will be used otherwise.
14977 Alternatively, you might decide to put the precompiled header file in a
14978 directory and use @option{-I} to ensure that directory is searched
14979 before (or instead of) the directory containing the original header.
14980 Then, if you want to check that the precompiled header file is always
14981 used, you can put a file of the same name as the original header in this
14982 directory containing an @code{#error} command.
14984 This also works with @option{-include}. So yet another way to use
14985 precompiled headers, good for projects not designed with precompiled
14986 header files in mind, is to simply take most of the header files used by
14987 a project, include them from another header file, precompile that header
14988 file, and @option{-include} the precompiled header. If the header files
14989 have guards against multiple inclusion, they will be skipped because
14990 they've already been included (in the precompiled header).
14992 If you need to precompile the same header file for different
14993 languages, targets, or compiler options, you can instead make a
14994 @emph{directory} named like @file{all.h.gch}, and put each precompiled
14995 header in the directory, perhaps using @option{-o}. It doesn't matter
14996 what you call the files in the directory, every precompiled header in
14997 the directory will be considered. The first precompiled header
14998 encountered in the directory that is valid for this compilation will
14999 be used; they're searched in no particular order.
15001 There are many other possibilities, limited only by your imagination,
15002 good sense, and the constraints of your build system.
15004 A precompiled header file can be used only when these conditions apply:
15008 Only one precompiled header can be used in a particular compilation.
15011 A precompiled header can't be used once the first C token is seen. You
15012 can have preprocessor directives before a precompiled header; you can
15013 even include a precompiled header from inside another header, so long as
15014 there are no C tokens before the @code{#include}.
15017 The precompiled header file must be produced for the same language as
15018 the current compilation. You can't use a C precompiled header for a C++
15022 The precompiled header file must have been produced by the same compiler
15023 binary as the current compilation is using.
15026 Any macros defined before the precompiled header is included must
15027 either be defined in the same way as when the precompiled header was
15028 generated, or must not affect the precompiled header, which usually
15029 means that they don't appear in the precompiled header at all.
15031 The @option{-D} option is one way to define a macro before a
15032 precompiled header is included; using a @code{#define} can also do it.
15033 There are also some options that define macros implicitly, like
15034 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
15037 @item If debugging information is output when using the precompiled
15038 header, using @option{-g} or similar, the same kind of debugging information
15039 must have been output when building the precompiled header. However,
15040 a precompiled header built using @option{-g} can be used in a compilation
15041 when no debugging information is being output.
15043 @item The same @option{-m} options must generally be used when building
15044 and using the precompiled header. @xref{Submodel Options},
15045 for any cases where this rule is relaxed.
15047 @item Each of the following options must be the same when building and using
15048 the precompiled header:
15050 @gccoptlist{-fexceptions -funit-at-a-time}
15053 Some other command-line options starting with @option{-f},
15054 @option{-p}, or @option{-O} must be defined in the same way as when
15055 the precompiled header was generated. At present, it's not clear
15056 which options are safe to change and which are not; the safest choice
15057 is to use exactly the same options when generating and using the
15058 precompiled header. The following are known to be safe:
15060 @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
15061 -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
15062 -fsched-verbose=<number> -fschedule-insns -fvisibility= @gol
15067 For all of these except the last, the compiler will automatically
15068 ignore the precompiled header if the conditions aren't met. If you
15069 find an option combination that doesn't work and doesn't cause the
15070 precompiled header to be ignored, please consider filing a bug report,
15073 If you do use differing options when generating and using the
15074 precompiled header, the actual behavior will be a mixture of the
15075 behavior for the options. For instance, if you use @option{-g} to
15076 generate the precompiled header but not when using it, you may or may
15077 not get debugging information for routines in the precompiled header.
15079 @node Running Protoize
15080 @section Running Protoize
15082 The program @code{protoize} is an optional part of GCC@. You can use
15083 it to add prototypes to a program, thus converting the program to ISO
15084 C in one respect. The companion program @code{unprotoize} does the
15085 reverse: it removes argument types from any prototypes that are found.
15087 When you run these programs, you must specify a set of source files as
15088 command line arguments. The conversion programs start out by compiling
15089 these files to see what functions they define. The information gathered
15090 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
15092 After scanning comes actual conversion. The specified files are all
15093 eligible to be converted; any files they include (whether sources or
15094 just headers) are eligible as well.
15096 But not all the eligible files are converted. By default,
15097 @code{protoize} and @code{unprotoize} convert only source and header
15098 files in the current directory. You can specify additional directories
15099 whose files should be converted with the @option{-d @var{directory}}
15100 option. You can also specify particular files to exclude with the
15101 @option{-x @var{file}} option. A file is converted if it is eligible, its
15102 directory name matches one of the specified directory names, and its
15103 name within the directory has not been excluded.
15105 Basic conversion with @code{protoize} consists of rewriting most
15106 function definitions and function declarations to specify the types of
15107 the arguments. The only ones not rewritten are those for varargs
15110 @code{protoize} optionally inserts prototype declarations at the
15111 beginning of the source file, to make them available for any calls that
15112 precede the function's definition. Or it can insert prototype
15113 declarations with block scope in the blocks where undeclared functions
15116 Basic conversion with @code{unprotoize} consists of rewriting most
15117 function declarations to remove any argument types, and rewriting
15118 function definitions to the old-style pre-ISO form.
15120 Both conversion programs print a warning for any function declaration or
15121 definition that they can't convert. You can suppress these warnings
15124 The output from @code{protoize} or @code{unprotoize} replaces the
15125 original source file. The original file is renamed to a name ending
15126 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
15127 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
15128 for DOS) file already exists, then the source file is simply discarded.
15130 @code{protoize} and @code{unprotoize} both depend on GCC itself to
15131 scan the program and collect information about the functions it uses.
15132 So neither of these programs will work until GCC is installed.
15134 Here is a table of the options you can use with @code{protoize} and
15135 @code{unprotoize}. Each option works with both programs unless
15139 @item -B @var{directory}
15140 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
15141 usual directory (normally @file{/usr/local/lib}). This file contains
15142 prototype information about standard system functions. This option
15143 applies only to @code{protoize}.
15145 @item -c @var{compilation-options}
15146 Use @var{compilation-options} as the options when running @command{gcc} to
15147 produce the @samp{.X} files. The special option @option{-aux-info} is
15148 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
15150 Note that the compilation options must be given as a single argument to
15151 @code{protoize} or @code{unprotoize}. If you want to specify several
15152 @command{gcc} options, you must quote the entire set of compilation options
15153 to make them a single word in the shell.
15155 There are certain @command{gcc} arguments that you cannot use, because they
15156 would produce the wrong kind of output. These include @option{-g},
15157 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
15158 the @var{compilation-options}, they are ignored.
15161 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
15162 systems) instead of @samp{.c}. This is convenient if you are converting
15163 a C program to C++. This option applies only to @code{protoize}.
15166 Add explicit global declarations. This means inserting explicit
15167 declarations at the beginning of each source file for each function
15168 that is called in the file and was not declared. These declarations
15169 precede the first function definition that contains a call to an
15170 undeclared function. This option applies only to @code{protoize}.
15172 @item -i @var{string}
15173 Indent old-style parameter declarations with the string @var{string}.
15174 This option applies only to @code{protoize}.
15176 @code{unprotoize} converts prototyped function definitions to old-style
15177 function definitions, where the arguments are declared between the
15178 argument list and the initial @samp{@{}. By default, @code{unprotoize}
15179 uses five spaces as the indentation. If you want to indent with just
15180 one space instead, use @option{-i " "}.
15183 Keep the @samp{.X} files. Normally, they are deleted after conversion
15187 Add explicit local declarations. @code{protoize} with @option{-l} inserts
15188 a prototype declaration for each function in each block which calls the
15189 function without any declaration. This option applies only to
15193 Make no real changes. This mode just prints information about the conversions
15194 that would have been done without @option{-n}.
15197 Make no @samp{.save} files. The original files are simply deleted.
15198 Use this option with caution.
15200 @item -p @var{program}
15201 Use the program @var{program} as the compiler. Normally, the name
15202 @file{gcc} is used.
15205 Work quietly. Most warnings are suppressed.
15208 Print the version number, just like @option{-v} for @command{gcc}.
15211 If you need special compiler options to compile one of your program's
15212 source files, then you should generate that file's @samp{.X} file
15213 specially, by running @command{gcc} on that source file with the
15214 appropriate options and the option @option{-aux-info}. Then run
15215 @code{protoize} on the entire set of files. @code{protoize} will use
15216 the existing @samp{.X} file because it is newer than the source file.
15220 gcc -Dfoo=bar file1.c -aux-info file1.X
15225 You need to include the special files along with the rest in the
15226 @code{protoize} command, even though their @samp{.X} files already
15227 exist, because otherwise they won't get converted.
15229 @xref{Protoize Caveats}, for more information on how to use
15230 @code{protoize} successfully.