1 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2 @c 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
8 Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
9 1998, 1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
11 Permission is granted to copy, distribute and/or modify this document
12 under the terms of the GNU Free Documentation License, Version 1.2 or
13 any later version published by the Free Software Foundation; with the
14 Invariant Sections being ``GNU General Public License'' and ``Funding
15 Free Software'', the Front-Cover texts being (a) (see below), and with
16 the Back-Cover Texts being (b) (see below). A copy of the license is
17 included in the gfdl(7) man page.
19 (a) The FSF's Front-Cover Text is:
23 (b) The FSF's Back-Cover Text is:
25 You have freedom to copy and modify this GNU Manual, like GNU
26 software. Copies published by the Free Software Foundation raise
27 funds for GNU development.
29 @c Set file name and title for the man page.
31 @settitle GNU project C and C++ compiler
33 gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
34 [@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
35 [@option{-W}@var{warn}@dots{}] [@option{-pedantic}]
36 [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
37 [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
38 [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
39 [@option{-o} @var{outfile}] @var{infile}@dots{}
41 Only the most useful options are listed here; see below for the
42 remainder. @samp{g++} accepts mostly the same options as @samp{gcc}.
45 gpl(7), gfdl(7), fsf-funding(7),
46 cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
47 and the Info entries for @file{gcc}, @file{cpp}, @file{as},
48 @file{ld}, @file{binutils} and @file{gdb}.
51 For instructions on reporting bugs, see
52 @w{@uref{http://gcc.gnu.org/bugs.html}}. Use of the @command{gccbug}
53 script to report bugs is recommended.
56 See the Info entry for @command{gcc}, or
57 @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
58 for contributors to GCC@.
63 @chapter GCC Command Options
64 @cindex GCC command options
65 @cindex command options
66 @cindex options, GCC command
68 @c man begin DESCRIPTION
69 When you invoke GCC, it normally does preprocessing, compilation,
70 assembly and linking. The ``overall options'' allow you to stop this
71 process at an intermediate stage. For example, the @option{-c} option
72 says not to run the linker. Then the output consists of object files
73 output by the assembler.
75 Other options are passed on to one stage of processing. Some options
76 control the preprocessor and others the compiler itself. Yet other
77 options control the assembler and linker; most of these are not
78 documented here, since you rarely need to use any of them.
80 @cindex C compilation options
81 Most of the command line options that you can use with GCC are useful
82 for C programs; when an option is only useful with another language
83 (usually C++), the explanation says so explicitly. If the description
84 for a particular option does not mention a source language, you can use
85 that option with all supported languages.
87 @cindex C++ compilation options
88 @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special
89 options for compiling C++ programs.
91 @cindex grouping options
92 @cindex options, grouping
93 The @command{gcc} program accepts options and file names as operands. Many
94 options have multi-letter names; therefore multiple single-letter options
95 may @emph{not} be grouped: @option{-dr} is very different from @w{@samp{-d
98 @cindex order of options
99 @cindex options, order
100 You can mix options and other arguments. For the most part, the order
101 you use doesn't matter. Order does matter when you use several options
102 of the same kind; for example, if you specify @option{-L} more than once,
103 the directories are searched in the order specified.
105 Many options have long names starting with @samp{-f} or with
106 @samp{-W}---for example, @option{-fforce-mem},
107 @option{-fstrength-reduce}, @option{-Wformat} and so on. Most of
108 these have both positive and negative forms; the negative form of
109 @option{-ffoo} would be @option{-fno-foo}. This manual documents
110 only one of these two forms, whichever one is not the default.
114 @xref{Option Index}, for an index to GCC's options.
117 * Option Summary:: Brief list of all options, without explanations.
118 * Overall Options:: Controlling the kind of output:
119 an executable, object files, assembler files,
120 or preprocessed source.
121 * Invoking G++:: Compiling C++ programs.
122 * C Dialect Options:: Controlling the variant of C language compiled.
123 * C++ Dialect Options:: Variations on C++.
124 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
126 * Language Independent Options:: Controlling how diagnostics should be
128 * Warning Options:: How picky should the compiler be?
129 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
130 * Optimize Options:: How much optimization?
131 * Preprocessor Options:: Controlling header files and macro definitions.
132 Also, getting dependency information for Make.
133 * Assembler Options:: Passing options to the assembler.
134 * Link Options:: Specifying libraries and so on.
135 * Directory Options:: Where to find header files and libraries.
136 Where to find the compiler executable files.
137 * Spec Files:: How to pass switches to sub-processes.
138 * Target Options:: Running a cross-compiler, or an old version of GCC.
139 * Submodel Options:: Specifying minor hardware or convention variations,
140 such as 68010 vs 68020.
141 * Code Gen Options:: Specifying conventions for function calls, data layout
143 * Environment Variables:: Env vars that affect GCC.
144 * Precompiled Headers:: Compiling a header once, and using it many times.
145 * Running Protoize:: Automatically adding or removing function prototypes.
151 @section Option Summary
153 Here is a summary of all the options, grouped by type. Explanations are
154 in the following sections.
157 @item Overall Options
158 @xref{Overall Options,,Options Controlling the Kind of Output}.
159 @gccoptlist{-c -S -E -o @var{file} -combine -pipe -pass-exit-codes @gol
160 -x @var{language} -v -### --help --target-help --version}
162 @item C Language Options
163 @xref{C Dialect Options,,Options Controlling C Dialect}.
164 @gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol
165 -fno-asm -fno-builtin -fno-builtin-@var{function} @gol
166 -fhosted -ffreestanding -fms-extensions @gol
167 -trigraphs -no-integrated-cpp -traditional -traditional-cpp @gol
168 -fallow-single-precision -fcond-mismatch @gol
169 -fsigned-bitfields -fsigned-char @gol
170 -funsigned-bitfields -funsigned-char}
172 @item C++ Language Options
173 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
174 @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol
175 -fconserve-space -fno-const-strings @gol
176 -fno-elide-constructors @gol
177 -fno-enforce-eh-specs @gol
178 -ffor-scope -fno-for-scope -fno-gnu-keywords @gol
179 -fno-implicit-templates @gol
180 -fno-implicit-inline-templates @gol
181 -fno-implement-inlines -fms-extensions @gol
182 -fno-nonansi-builtins -fno-operator-names @gol
183 -fno-optional-diags -fpermissive @gol
184 -frepo -fno-rtti -fstats -ftemplate-depth-@var{n} @gol
185 -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol
186 -fno-default-inline -fvisibility-inlines-hidden @gol
187 -Wabi -Wctor-dtor-privacy @gol
188 -Wnon-virtual-dtor -Wreorder @gol
189 -Weffc++ -Wno-deprecated @gol
190 -Wno-non-template-friend -Wold-style-cast @gol
191 -Woverloaded-virtual -Wno-pmf-conversions @gol
192 -Wsign-promo -Wsynth}
194 @item Objective-C and Objective-C++ Language Options
195 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
196 Objective-C and Objective-C++ Dialects}.
198 -fconstant-string-class=@var{class-name} @gol
199 -fgnu-runtime -fnext-runtime @gol
200 -fno-nil-receivers @gol
201 -fobjc-exceptions @gol
202 -freplace-objc-classes @gol
205 -Wno-protocol -Wselector -Wundeclared-selector}
207 @item Language Independent Options
208 @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}.
209 @gccoptlist{-fmessage-length=@var{n} @gol
210 -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]}}
212 @item Warning Options
213 @xref{Warning Options,,Options to Request or Suppress Warnings}.
214 @gccoptlist{-fsyntax-only -pedantic -pedantic-errors @gol
215 -w -Wextra -Wall -Waggregate-return @gol
216 -Wcast-align -Wcast-qual -Wchar-subscripts -Wcomment @gol
217 -Wconversion -Wno-deprecated-declarations @gol
218 -Wdisabled-optimization -Wno-div-by-zero -Wendif-labels @gol
219 -Werror -Werror-implicit-function-declaration @gol
220 -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
221 -Wno-format-extra-args -Wformat-nonliteral @gol
222 -Wformat-security -Wformat-y2k @gol
223 -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol
224 -Wimport -Wno-import -Winit-self -Winline @gol
225 -Wno-invalid-offsetof -Winvalid-pch @gol
226 -Wlarger-than-@var{len} -Wlong-long @gol
227 -Wmain -Wmissing-braces -Wmissing-field-initializers @gol
228 -Wmissing-format-attribute -Wmissing-include-dirs @gol
229 -Wmissing-noreturn @gol
230 -Wno-multichar -Wnonnull -Wpacked -Wpadded @gol
231 -Wparentheses -Wpointer-arith -Wredundant-decls @gol
232 -Wreturn-type -Wsequence-point -Wshadow @gol
233 -Wsign-compare -Wstrict-aliasing -Wstrict-aliasing=2 @gol
234 -Wswitch -Wswitch-default -Wswitch-enum @gol
235 -Wsystem-headers -Wtrigraphs -Wundef -Wuninitialized @gol
236 -Wunknown-pragmas -Wunreachable-code @gol
237 -Wunused -Wunused-function -Wunused-label -Wunused-parameter @gol
238 -Wunused-value -Wunused-variable -Wwrite-strings @gol
241 @item C-only Warning Options
242 @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
243 -Wmissing-prototypes -Wnested-externs -Wold-style-definition @gol
244 -Wstrict-prototypes -Wtraditional @gol
245 -Wdeclaration-after-statement}
247 @item Debugging Options
248 @xref{Debugging Options,,Options for Debugging Your Program or GCC}.
249 @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
250 -fdump-unnumbered -fdump-translation-unit@r{[}-@var{n}@r{]} @gol
251 -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
252 -fdump-ipa-all -fdump-ipa-cgraph @gol
254 -fdump-tree-original@r{[}-@var{n}@r{]} @gol
255 -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
256 -fdump-tree-inlined@r{[}-@var{n}@r{]} @gol
257 -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol
259 -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
260 -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
261 -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol
262 -fdump-tree-dom@r{[}-@var{n}@r{]} @gol
263 -fdump-tree-dse@r{[}-@var{n}@r{]} @gol
264 -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
265 -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
266 -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol
267 -fdump-tree-nrv -fdump-tree-vect @gol
268 -fdump-tree-sra@r{[}-@var{n}@r{]} @gol
269 -fdump-tree-fre@r{[}-@var{n}@r{]} @gol
270 -feliminate-dwarf2-dups -feliminate-unused-debug-types @gol
271 -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs -ftree-based-profiling @gol
272 -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
273 -ftest-coverage -ftime-report -fvar-tracking @gol
274 -g -g@var{level} -gcoff -gdwarf-2 @gol
275 -ggdb -gstabs -gstabs+ -gvms -gxcoff -gxcoff+ @gol
276 -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol
277 -print-multi-directory -print-multi-lib @gol
278 -print-prog-name=@var{program} -print-search-dirs -Q @gol
281 @item Optimization Options
282 @xref{Optimize Options,,Options that Control Optimization}.
283 @gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
284 -falign-labels=@var{n} -falign-loops=@var{n} @gol
285 -fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
286 -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
287 -fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
288 -fcaller-saves -fcprop-registers @gol
289 -fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
290 -fdelayed-branch -fdelete-null-pointer-checks @gol
291 -fexpensive-optimizations -ffast-math -ffloat-store @gol
292 -fforce-addr -fforce-mem -ffunction-sections @gol
293 -fgcse -fgcse-lm -fgcse-sm -fgcse-las -fgcse-after-reload @gol
294 -floop-optimize -fcrossjumping -fif-conversion -fif-conversion2 @gol
295 -finline-functions -finline-limit=@var{n} -fkeep-inline-functions @gol
296 -fkeep-static-consts -fmerge-constants -fmerge-all-constants @gol
297 -fmodulo-sched -fnew-ra -fno-branch-count-reg @gol
298 -fno-default-inline -fno-defer-pop -floop-optimize2 -fmove-loop-invariants @gol
299 -fno-function-cse -fno-guess-branch-probability @gol
300 -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol
301 -funsafe-math-optimizations -ffinite-math-only @gol
302 -fno-trapping-math -fno-zero-initialized-in-bss @gol
303 -fomit-frame-pointer -foptimize-register-move @gol
304 -foptimize-sibling-calls -fprefetch-loop-arrays @gol
305 -fprofile-generate -fprofile-use @gol
306 -fregmove -frename-registers @gol
307 -freorder-blocks -freorder-blocks-and-partition -freorder-functions @gol
308 -frerun-cse-after-loop -frerun-loop-opt @gol
309 -frounding-math -fschedule-insns -fschedule-insns2 @gol
310 -fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
311 -fsched-spec-load-dangerous @gol
312 -fsched-stalled-insns=@var{n} -sched-stalled-insns-dep=@var{n} @gol
313 -fsched2-use-superblocks @gol
314 -fsched2-use-traces -freschedule-modulo-scheduled-loops @gol
315 -fsignaling-nans -fsingle-precision-constant -fspeculative-prefetching @gol
316 -fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
317 -funroll-all-loops -funroll-loops -fpeel-loops @gol
318 -fsplit-ivs-in-unroller -funswitch-loops @gol
319 -fvariable-expansion-in-unroller @gol
320 -ftree-pre -ftree-ccp -ftree-dce -ftree-loop-optimize @gol
321 -ftree-loop-linear -ftree-loop-im -ftree-loop-ivcanon -fivopts @gol
322 -ftree-dominator-opts -ftree-dse -ftree-copyrename @gol
323 -ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
324 --param @var{name}=@var{value}
325 -O -O0 -O1 -O2 -O3 -Os}
327 @item Preprocessor Options
328 @xref{Preprocessor Options,,Options Controlling the Preprocessor}.
329 @gccoptlist{-A@var{question}=@var{answer} @gol
330 -A-@var{question}@r{[}=@var{answer}@r{]} @gol
331 -C -dD -dI -dM -dN @gol
332 -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol
333 -idirafter @var{dir} @gol
334 -include @var{file} -imacros @var{file} @gol
335 -iprefix @var{file} -iwithprefix @var{dir} @gol
336 -iwithprefixbefore @var{dir} -isystem @var{dir} @gol
337 -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol
338 -P -fworking-directory -remap @gol
339 -trigraphs -undef -U@var{macro} -Wp,@var{option} @gol
340 -Xpreprocessor @var{option}}
342 @item Assembler Option
343 @xref{Assembler Options,,Passing Options to the Assembler}.
344 @gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
347 @xref{Link Options,,Options for Linking}.
348 @gccoptlist{@var{object-file-name} -l@var{library} @gol
349 -nostartfiles -nodefaultlibs -nostdlib -pie @gol
350 -s -static -static-libgcc -shared -shared-libgcc -symbolic @gol
351 -Wl,@var{option} -Xlinker @var{option} @gol
354 @item Directory Options
355 @xref{Directory Options,,Options for Directory Search}.
356 @gccoptlist{-B@var{prefix} -I@var{dir} -iquote@var{dir} -L@var{dir} -specs=@var{file} -I-}
359 @c I wrote this xref this way to avoid overfull hbox. -- rms
360 @xref{Target Options}.
361 @gccoptlist{-V @var{version} -b @var{machine}}
363 @item Machine Dependent Options
364 @xref{Submodel Options,,Hardware Models and Configurations}.
365 @c This list is ordered alphanumerically by subsection name.
366 @c Try and put the significant identifier (CPU or system) first,
367 @c so users have a clue at guessing where the ones they want will be.
370 @gccoptlist{-EB -EL @gol
371 -mmangle-cpu -mcpu=@var{cpu} -mtext=@var{text-section} @gol
372 -mdata=@var{data-section} -mrodata=@var{readonly-data-section}}
375 @gccoptlist{-mapcs-frame -mno-apcs-frame @gol
376 -mabi=@var{name} @gol
377 -mapcs-stack-check -mno-apcs-stack-check @gol
378 -mapcs-float -mno-apcs-float @gol
379 -mapcs-reentrant -mno-apcs-reentrant @gol
380 -msched-prolog -mno-sched-prolog @gol
381 -mlittle-endian -mbig-endian -mwords-little-endian @gol
382 -mfloat-abi=@var{name} -msoft-float -mhard-float -mfpe @gol
383 -mthumb-interwork -mno-thumb-interwork @gol
384 -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
385 -mstructure-size-boundary=@var{n} @gol
386 -mabort-on-noreturn @gol
387 -mlong-calls -mno-long-calls @gol
388 -msingle-pic-base -mno-single-pic-base @gol
389 -mpic-register=@var{reg} @gol
390 -mnop-fun-dllimport @gol
391 -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol
392 -mpoke-function-name @gol
394 -mtpcs-frame -mtpcs-leaf-frame @gol
395 -mcaller-super-interworking -mcallee-super-interworking}
398 @gccoptlist{-mmcu=@var{mcu} -msize -minit-stack=@var{n} -mno-interrupts @gol
399 -mcall-prologues -mno-tablejump -mtiny-stack -mint8}
402 @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
403 -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
404 -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
405 -mstack-align -mdata-align -mconst-align @gol
406 -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
407 -melf -maout -melinux -mlinux -sim -sim2 @gol
408 -mmul-bug-workaround -mno-mul-bug-workaround}
410 @emph{Darwin Options}
411 @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
412 -arch_only -bind_at_load -bundle -bundle_loader @gol
413 -client_name -compatibility_version -current_version @gol
415 -dependency-file -dylib_file -dylinker_install_name @gol
416 -dynamic -dynamiclib -exported_symbols_list @gol
417 -filelist -flat_namespace -force_cpusubtype_ALL @gol
418 -force_flat_namespace -headerpad_max_install_names @gol
419 -image_base -init -install_name -keep_private_externs @gol
420 -multi_module -multiply_defined -multiply_defined_unused @gol
421 -noall_load -no_dead_strip_inits_and_terms @gol
422 -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
423 -pagezero_size -prebind -prebind_all_twolevel_modules @gol
424 -private_bundle -read_only_relocs -sectalign @gol
425 -sectobjectsymbols -whyload -seg1addr @gol
426 -sectcreate -sectobjectsymbols -sectorder @gol
427 -segaddr -segs_read_only_addr -segs_read_write_addr @gol
428 -seg_addr_table -seg_addr_table_filename -seglinkedit @gol
429 -segprot -segs_read_only_addr -segs_read_write_addr @gol
430 -single_module -static -sub_library -sub_umbrella @gol
431 -twolevel_namespace -umbrella -undefined @gol
432 -unexported_symbols_list -weak_reference_mismatches @gol
433 -whatsloaded -F -gused -gfull -mone-byte-bool}
435 @emph{DEC Alpha Options}
436 @gccoptlist{-mno-fp-regs -msoft-float -malpha-as -mgas @gol
437 -mieee -mieee-with-inexact -mieee-conformant @gol
438 -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
439 -mtrap-precision=@var{mode} -mbuild-constants @gol
440 -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
441 -mbwx -mmax -mfix -mcix @gol
442 -mfloat-vax -mfloat-ieee @gol
443 -mexplicit-relocs -msmall-data -mlarge-data @gol
444 -msmall-text -mlarge-text @gol
445 -mmemory-latency=@var{time}}
447 @emph{DEC Alpha/VMS Options}
448 @gccoptlist{-mvms-return-codes}
451 @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
452 -mhard-float -msoft-float @gol
453 -malloc-cc -mfixed-cc -mdword -mno-dword @gol
454 -mdouble -mno-double @gol
455 -mmedia -mno-media -mmuladd -mno-muladd @gol
456 -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
457 -mlinked-fp -mlong-calls -malign-labels @gol
458 -mlibrary-pic -macc-4 -macc-8 @gol
459 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
460 -mscc -mno-scc -mcond-exec -mno-cond-exec @gol
461 -mvliw-branch -mno-vliw-branch @gol
462 -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
463 -mno-nested-cond-exec -mtomcat-stats @gol
466 @emph{H8/300 Options}
467 @gccoptlist{-mrelax -mh -ms -mn -mint32 -malign-300}
470 @gccoptlist{-march=@var{architecture-type} @gol
471 -mbig-switch -mdisable-fpregs -mdisable-indexing @gol
472 -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
473 -mfixed-range=@var{register-range} @gol
474 -mjump-in-delay -mlinker-opt -mlong-calls @gol
475 -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol
476 -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
477 -mno-jump-in-delay -mno-long-load-store @gol
478 -mno-portable-runtime -mno-soft-float @gol
479 -mno-space-regs -msoft-float -mpa-risc-1-0 @gol
480 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
481 -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
482 -munix=@var{unix-std} -nolibdld -static -threads}
484 @emph{i386 and x86-64 Options}
485 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
486 -mfpmath=@var{unit} @gol
487 -masm=@var{dialect} -mno-fancy-math-387 @gol
488 -mno-fp-ret-in-387 -msoft-float -msvr3-shlib @gol
489 -mno-wide-multiply -mrtd -malign-double @gol
490 -mpreferred-stack-boundary=@var{num} @gol
491 -mmmx -msse -msse2 -msse3 -m3dnow @gol
492 -mthreads -mno-align-stringops -minline-all-stringops @gol
493 -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
494 -m96bit-long-double -mregparm=@var{num} -momit-leaf-frame-pointer @gol
495 -mno-red-zone -mno-tls-direct-seg-refs @gol
496 -mcmodel=@var{code-model} @gol
500 @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
501 -mvolatile-asm-stop -mb-step -mregister-names -mno-sdata @gol
502 -mconstant-gp -mauto-pic -minline-float-divide-min-latency @gol
503 -minline-float-divide-max-throughput @gol
504 -minline-int-divide-min-latency @gol
505 -minline-int-divide-max-throughput -mno-dwarf2-asm @gol
506 -mfixed-range=@var{register-range}}
508 @emph{M32R/D Options}
509 @gccoptlist{-m32r2 -m32rx -m32r @gol
511 -malign-loops -mno-align-loops @gol
512 -missue-rate=@var{number} @gol
513 -mbranch-cost=@var{number} @gol
514 -mmodel=@var{code-size-model-type} @gol
515 -msdata=@var{sdata-type} @gol
516 -mno-flush-func -mflush-func=@var{name} @gol
517 -mno-flush-trap -mflush-trap=@var{number} @gol
520 @emph{M680x0 Options}
521 @gccoptlist{-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
522 -m68060 -mcpu32 -m5200 -m68881 -mbitfield -mc68000 -mc68020 @gol
523 -mnobitfield -mrtd -mshort -msoft-float -mpcrel @gol
524 -malign-int -mstrict-align -msep-data -mno-sep-data @gol
525 -mshared-library-id=n -mid-shared-library -mno-id-shared-library}
527 @emph{M68hc1x Options}
528 @gccoptlist{-m6811 -m6812 -m68hc11 -m68hc12 -m68hcs12 @gol
529 -mauto-incdec -minmax -mlong-calls -mshort @gol
530 -msoft-reg-count=@var{count}}
533 @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
534 -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
535 -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
536 -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
537 -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
540 @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
541 -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips64 @gol
542 -mips16 -mno-mips16 -mabi=@var{abi} -mabicalls -mno-abicalls @gol
543 -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfp64 @gol
544 -mhard-float -msoft-float -msingle-float -mdouble-float @gol
545 -mpaired-single -mips3d @gol
546 -mint64 -mlong64 -mlong32 @gol
547 -G@var{num} -membedded-data -mno-embedded-data @gol
548 -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
549 -msplit-addresses -mno-split-addresses @gol
550 -mexplicit-relocs -mno-explicit-relocs @gol
551 -mcheck-zero-division -mno-check-zero-division @gol
552 -mdivide-traps -mdivide-breaks @gol
553 -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
554 -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol
555 -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
556 -mfix-vr4120 -mno-fix-vr4120 -mfix-sb1 -mno-fix-sb1 @gol
557 -mflush-func=@var{func} -mno-flush-func @gol
558 -mbranch-likely -mno-branch-likely @gol
559 -mfp-exceptions -mno-fp-exceptions @gol
560 -mvr4130-align -mno-vr4130-align}
563 @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
564 -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
565 -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
566 -mno-base-addresses -msingle-exit -mno-single-exit}
568 @emph{MN10300 Options}
569 @gccoptlist{-mmult-bug -mno-mult-bug @gol
570 -mam33 -mno-am33 @gol
571 -mam33-2 -mno-am33-2 @gol
575 @gccoptlist{-m32032 -m32332 -m32532 -m32081 -m32381 @gol
576 -mmult-add -mnomult-add -msoft-float -mrtd -mnortd @gol
577 -mregparam -mnoregparam -msb -mnosb @gol
578 -mbitfield -mnobitfield -mhimem -mnohimem}
580 @emph{PDP-11 Options}
581 @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
582 -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
583 -mint16 -mno-int32 -mfloat32 -mno-float64 @gol
584 -mfloat64 -mno-float32 -mabshi -mno-abshi @gol
585 -mbranch-expensive -mbranch-cheap @gol
586 -msplit -mno-split -munix-asm -mdec-asm}
588 @emph{PowerPC Options}
589 See RS/6000 and PowerPC Options.
591 @emph{RS/6000 and PowerPC Options}
592 @gccoptlist{-mcpu=@var{cpu-type} @gol
593 -mtune=@var{cpu-type} @gol
594 -mpower -mno-power -mpower2 -mno-power2 @gol
595 -mpowerpc -mpowerpc64 -mno-powerpc @gol
596 -maltivec -mno-altivec @gol
597 -mpowerpc-gpopt -mno-powerpc-gpopt @gol
598 -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
599 -mnew-mnemonics -mold-mnemonics @gol
600 -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
601 -m64 -m32 -mxl-call -mno-xl-call -mpe @gol
602 -malign-power -malign-natural @gol
603 -msoft-float -mhard-float -mmultiple -mno-multiple @gol
604 -mstring -mno-string -mupdate -mno-update @gol
605 -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
606 -mstrict-align -mno-strict-align -mrelocatable @gol
607 -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
608 -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
609 -mdynamic-no-pic @gol
610 -mprioritize-restricted-insns=@var{priority} @gol
611 -msched-costly-dep=@var{dependence_type} @gol
612 -minsert-sched-nops=@var{scheme} @gol
613 -mcall-sysv -mcall-netbsd @gol
614 -maix-struct-return -msvr4-struct-return @gol
615 -mabi=altivec -mabi=no-altivec @gol
616 -mabi=spe -mabi=no-spe @gol
617 -misel=yes -misel=no @gol
618 -mspe=yes -mspe=no @gol
619 -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
620 -mprototype -mno-prototype @gol
621 -msim -mmvme -mads -myellowknife -memb -msdata @gol
622 -msdata=@var{opt} -mvxworks -mwindiss -G @var{num} -pthread}
624 @emph{S/390 and zSeries Options}
625 @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
626 -mhard-float -msoft-float -mbackchain -mno-backchain -mkernel-backchain @gol
627 -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
628 -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
629 -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
630 -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard}
633 @gccoptlist{-m1 -m2 -m2e -m3 -m3e @gol
634 -m4-nofpu -m4-single-only -m4-single -m4 @gol
635 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
636 -m5-64media -m5-64media-nofpu @gol
637 -m5-32media -m5-32media-nofpu @gol
638 -m5-compact -m5-compact-nofpu @gol
639 -mb -ml -mdalign -mrelax @gol
640 -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol
641 -mieee -misize -mpadstruct -mspace @gol
642 -mprefergot -musermode}
645 @gccoptlist{-mcpu=@var{cpu-type} @gol
646 -mtune=@var{cpu-type} @gol
647 -mcmodel=@var{code-model} @gol
648 -m32 -m64 -mapp-regs -mno-app-regs @gol
649 -mfaster-structs -mno-faster-structs @gol
650 -mfpu -mno-fpu -mhard-float -msoft-float @gol
651 -mhard-quad-float -msoft-quad-float @gol
652 -mimpure-text -mno-impure-text -mlittle-endian @gol
653 -mstack-bias -mno-stack-bias @gol
654 -munaligned-doubles -mno-unaligned-doubles @gol
655 -mv8plus -mno-v8plus -mvis -mno-vis
658 @emph{System V Options}
659 @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
661 @emph{TMS320C3x/C4x Options}
662 @gccoptlist{-mcpu=@var{cpu} -mbig -msmall -mregparm -mmemparm @gol
663 -mfast-fix -mmpyi -mbk -mti -mdp-isr-reload @gol
664 -mrpts=@var{count} -mrptb -mdb -mloop-unsigned @gol
665 -mparallel-insns -mparallel-mpy -mpreserve-float}
668 @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
669 -mprolog-function -mno-prolog-function -mspace @gol
670 -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
671 -mapp-regs -mno-app-regs @gol
672 -mdisable-callt -mno-disable-callt @gol
678 @gccoptlist{-mg -mgnu -munix}
680 @emph{x86-64 Options}
681 See i386 and x86-64 Options.
683 @emph{Xstormy16 Options}
686 @emph{Xtensa Options}
687 @gccoptlist{-mconst16 -mno-const16 @gol
688 -mfused-madd -mno-fused-madd @gol
689 -mtext-section-literals -mno-text-section-literals @gol
690 -mtarget-align -mno-target-align @gol
691 -mlongcalls -mno-longcalls}
693 @emph{zSeries Options}
694 See S/390 and zSeries Options.
696 @item Code Generation Options
697 @xref{Code Gen Options,,Options for Code Generation Conventions}.
698 @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
699 -ffixed-@var{reg} -fexceptions @gol
700 -fnon-call-exceptions -funwind-tables @gol
701 -fasynchronous-unwind-tables @gol
702 -finhibit-size-directive -finstrument-functions @gol
703 -fno-common -fno-ident @gol
704 -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol
705 -freg-struct-return -fshared-data -fshort-enums @gol
706 -fshort-double -fshort-wchar @gol
707 -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
708 -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
709 -fargument-alias -fargument-noalias @gol
710 -fargument-noalias-global -fleading-underscore @gol
711 -ftls-model=@var{model} @gol
712 -ftrapv -fwrapv -fbounds-check @gol
717 * Overall Options:: Controlling the kind of output:
718 an executable, object files, assembler files,
719 or preprocessed source.
720 * C Dialect Options:: Controlling the variant of C language compiled.
721 * C++ Dialect Options:: Variations on C++.
722 * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
724 * Language Independent Options:: Controlling how diagnostics should be
726 * Warning Options:: How picky should the compiler be?
727 * Debugging Options:: Symbol tables, measurements, and debugging dumps.
728 * Optimize Options:: How much optimization?
729 * Preprocessor Options:: Controlling header files and macro definitions.
730 Also, getting dependency information for Make.
731 * Assembler Options:: Passing options to the assembler.
732 * Link Options:: Specifying libraries and so on.
733 * Directory Options:: Where to find header files and libraries.
734 Where to find the compiler executable files.
735 * Spec Files:: How to pass switches to sub-processes.
736 * Target Options:: Running a cross-compiler, or an old version of GCC.
739 @node Overall Options
740 @section Options Controlling the Kind of Output
742 Compilation can involve up to four stages: preprocessing, compilation
743 proper, assembly and linking, always in that order. GCC is capable of
744 preprocessing and compiling several files either into several
745 assembler input files, or into one assembler input file; then each
746 assembler input file produces an object file, and linking combines all
747 the object files (those newly compiled, and those specified as input)
748 into an executable file.
750 @cindex file name suffix
751 For any given input file, the file name suffix determines what kind of
756 C source code which must be preprocessed.
759 C source code which should not be preprocessed.
762 C++ source code which should not be preprocessed.
765 Objective-C source code. Note that you must link with the @file{libobjc}
766 library to make an Objective-C program work.
769 Objective-C source code which should not be preprocessed.
773 Objective-C++ source code. Note that you must link with the @file{libobjc}
774 library to make an Objective-C++ program work. Note that @samp{.M} refers
775 to a literal capital M@.
778 Objective-C++ source code which should not be preprocessed.
781 C, C++, Objective-C or Objective-C++ header file to be turned into a
786 @itemx @var{file}.cxx
787 @itemx @var{file}.cpp
788 @itemx @var{file}.CPP
789 @itemx @var{file}.c++
791 C++ source code which must be preprocessed. Note that in @samp{.cxx},
792 the last two letters must both be literally @samp{x}. Likewise,
793 @samp{.C} refers to a literal capital C@.
797 C++ header file to be turned into a precompiled header.
800 @itemx @var{file}.for
801 @itemx @var{file}.FOR
802 Fortran source code which should not be preprocessed.
805 @itemx @var{file}.fpp
806 @itemx @var{file}.FPP
807 Fortran source code which must be preprocessed (with the traditional
811 Fortran source code which must be preprocessed with a RATFOR
812 preprocessor (not included with GCC)@.
815 @itemx @var{file}.f95
816 Fortran 90/95 source code which should not be preprocessed.
818 @c FIXME: Descriptions of Java file types.
825 Ada source code file which contains a library unit declaration (a
826 declaration of a package, subprogram, or generic, or a generic
827 instantiation), or a library unit renaming declaration (a package,
828 generic, or subprogram renaming declaration). Such files are also
831 @itemx @var{file}.adb
832 Ada source code file containing a library unit body (a subprogram or
833 package body). Such files are also called @dfn{bodies}.
835 @c GCC also knows about some suffixes for languages not yet included:
844 Assembler code which must be preprocessed.
847 An object file to be fed straight into linking.
848 Any file name with no recognized suffix is treated this way.
852 You can specify the input language explicitly with the @option{-x} option:
855 @item -x @var{language}
856 Specify explicitly the @var{language} for the following input files
857 (rather than letting the compiler choose a default based on the file
858 name suffix). This option applies to all following input files until
859 the next @option{-x} option. Possible values for @var{language} are:
861 c c-header c-cpp-output
862 c++ c++-header c++-cpp-output
863 objective-c objective-c-header objective-c-cpp-output
864 objective-c++ objective-c++-header objective-c++-cpp-output
865 assembler assembler-with-cpp
867 f77 f77-cpp-input ratfor
874 Turn off any specification of a language, so that subsequent files are
875 handled according to their file name suffixes (as they are if @option{-x}
876 has not been used at all).
878 @item -pass-exit-codes
879 @opindex pass-exit-codes
880 Normally the @command{gcc} program will exit with the code of 1 if any
881 phase of the compiler returns a non-success return code. If you specify
882 @option{-pass-exit-codes}, the @command{gcc} program will instead return with
883 numerically highest error produced by any phase that returned an error
887 If you only want some of the stages of compilation, you can use
888 @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
889 one of the options @option{-c}, @option{-S}, or @option{-E} to say where
890 @command{gcc} is to stop. Note that some combinations (for example,
891 @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
896 Compile or assemble the source files, but do not link. The linking
897 stage simply is not done. The ultimate output is in the form of an
898 object file for each source file.
900 By default, the object file name for a source file is made by replacing
901 the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
903 Unrecognized input files, not requiring compilation or assembly, are
908 Stop after the stage of compilation proper; do not assemble. The output
909 is in the form of an assembler code file for each non-assembler input
912 By default, the assembler file name for a source file is made by
913 replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
915 Input files that don't require compilation are ignored.
919 Stop after the preprocessing stage; do not run the compiler proper. The
920 output is in the form of preprocessed source code, which is sent to the
923 Input files which don't require preprocessing are ignored.
925 @cindex output file option
928 Place output in file @var{file}. This applies regardless to whatever
929 sort of output is being produced, whether it be an executable file,
930 an object file, an assembler file or preprocessed C code.
932 If @option{-o} is not specified, the default is to put an executable
933 file in @file{a.out}, the object file for
934 @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
935 assembler file in @file{@var{source}.s}, a precompiled header file in
936 @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
941 Print (on standard error output) the commands executed to run the stages
942 of compilation. Also print the version number of the compiler driver
943 program and of the preprocessor and the compiler proper.
947 Like @option{-v} except the commands are not executed and all command
948 arguments are quoted. This is useful for shell scripts to capture the
949 driver-generated command lines.
953 Use pipes rather than temporary files for communication between the
954 various stages of compilation. This fails to work on some systems where
955 the assembler is unable to read from a pipe; but the GNU assembler has
960 If you are compiling multiple source files, this option tells the driver
961 to pass all the source files to the compiler at once (for those
962 languages for which the compiler can handle this). This will allow
963 intermodule analysis (IMA) to be performed by the compiler. Currently the only
964 language for which this is supported is C. If you pass source files for
965 multiple languages to the driver, using this option, the driver will invoke
966 the compiler(s) that support IMA once each, passing each compiler all the
967 source files appropriate for it. For those languages that do not support
968 IMA this option will be ignored, and the compiler will be invoked once for
969 each source file in that language. If you use this option in conjunction
970 with -save-temps, the compiler will generate multiple pre-processed files
971 (one for each source file), but only one (combined) .o or .s file.
975 Print (on the standard output) a description of the command line options
976 understood by @command{gcc}. If the @option{-v} option is also specified
977 then @option{--help} will also be passed on to the various processes
978 invoked by @command{gcc}, so that they can display the command line options
979 they accept. If the @option{-Wextra} option is also specified then command
980 line options which have no documentation associated with them will also
985 Print (on the standard output) a description of target specific command
986 line options for each tool.
990 Display the version number and copyrights of the invoked GCC.
994 @section Compiling C++ Programs
996 @cindex suffixes for C++ source
997 @cindex C++ source file suffixes
998 C++ source files conventionally use one of the suffixes @samp{.C},
999 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1000 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1001 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1002 files with these names and compiles them as C++ programs even if you
1003 call the compiler the same way as for compiling C programs (usually
1004 with the name @command{gcc}).
1008 However, C++ programs often require class libraries as well as a
1009 compiler that understands the C++ language---and under some
1010 circumstances, you might want to compile programs or header files from
1011 standard input, or otherwise without a suffix that flags them as C++
1012 programs. You might also like to precompile a C header file with a
1013 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1014 program that calls GCC with the default language set to C++, and
1015 automatically specifies linking against the C++ library. On many
1016 systems, @command{g++} is also installed with the name @command{c++}.
1018 @cindex invoking @command{g++}
1019 When you compile C++ programs, you may specify many of the same
1020 command-line options that you use for compiling programs in any
1021 language; or command-line options meaningful for C and related
1022 languages; or options that are meaningful only for C++ programs.
1023 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1024 explanations of options for languages related to C@.
1025 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1026 explanations of options that are meaningful only for C++ programs.
1028 @node C Dialect Options
1029 @section Options Controlling C Dialect
1030 @cindex dialect options
1031 @cindex language dialect options
1032 @cindex options, dialect
1034 The following options control the dialect of C (or languages derived
1035 from C, such as C++, Objective-C and Objective-C++) that the compiler
1039 @cindex ANSI support
1043 In C mode, support all ISO C90 programs. In C++ mode,
1044 remove GNU extensions that conflict with ISO C++.
1046 This turns off certain features of GCC that are incompatible with ISO
1047 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1048 such as the @code{asm} and @code{typeof} keywords, and
1049 predefined macros such as @code{unix} and @code{vax} that identify the
1050 type of system you are using. It also enables the undesirable and
1051 rarely used ISO trigraph feature. For the C compiler,
1052 it disables recognition of C++ style @samp{//} comments as well as
1053 the @code{inline} keyword.
1055 The alternate keywords @code{__asm__}, @code{__extension__},
1056 @code{__inline__} and @code{__typeof__} continue to work despite
1057 @option{-ansi}. You would not want to use them in an ISO C program, of
1058 course, but it is useful to put them in header files that might be included
1059 in compilations done with @option{-ansi}. Alternate predefined macros
1060 such as @code{__unix__} and @code{__vax__} are also available, with or
1061 without @option{-ansi}.
1063 The @option{-ansi} option does not cause non-ISO programs to be
1064 rejected gratuitously. For that, @option{-pedantic} is required in
1065 addition to @option{-ansi}. @xref{Warning Options}.
1067 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1068 option is used. Some header files may notice this macro and refrain
1069 from declaring certain functions or defining certain macros that the
1070 ISO standard doesn't call for; this is to avoid interfering with any
1071 programs that might use these names for other things.
1073 Functions which would normally be built in but do not have semantics
1074 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1075 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1076 built-in functions provided by GCC}, for details of the functions
1081 Determine the language standard. This option is currently only
1082 supported when compiling C or C++. A value for this option must be
1083 provided; possible values are
1088 ISO C90 (same as @option{-ansi}).
1090 @item iso9899:199409
1091 ISO C90 as modified in amendment 1.
1097 ISO C99. Note that this standard is not yet fully supported; see
1098 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1099 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1102 Default, ISO C90 plus GNU extensions (including some C99 features).
1106 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1107 this will become the default. The name @samp{gnu9x} is deprecated.
1110 The 1998 ISO C++ standard plus amendments.
1113 The same as @option{-std=c++98} plus GNU extensions. This is the
1114 default for C++ code.
1117 Even when this option is not specified, you can still use some of the
1118 features of newer standards in so far as they do not conflict with
1119 previous C standards. For example, you may use @code{__restrict__} even
1120 when @option{-std=c99} is not specified.
1122 The @option{-std} options specifying some version of ISO C have the same
1123 effects as @option{-ansi}, except that features that were not in ISO C90
1124 but are in the specified version (for example, @samp{//} comments and
1125 the @code{inline} keyword in ISO C99) are not disabled.
1127 @xref{Standards,,Language Standards Supported by GCC}, for details of
1128 these standard versions.
1130 @item -aux-info @var{filename}
1132 Output to the given filename prototyped declarations for all functions
1133 declared and/or defined in a translation unit, including those in header
1134 files. This option is silently ignored in any language other than C@.
1136 Besides declarations, the file indicates, in comments, the origin of
1137 each declaration (source file and line), whether the declaration was
1138 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1139 @samp{O} for old, respectively, in the first character after the line
1140 number and the colon), and whether it came from a declaration or a
1141 definition (@samp{C} or @samp{F}, respectively, in the following
1142 character). In the case of function definitions, a K&R-style list of
1143 arguments followed by their declarations is also provided, inside
1144 comments, after the declaration.
1148 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1149 keyword, so that code can use these words as identifiers. You can use
1150 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1151 instead. @option{-ansi} implies @option{-fno-asm}.
1153 In C++, this switch only affects the @code{typeof} keyword, since
1154 @code{asm} and @code{inline} are standard keywords. You may want to
1155 use the @option{-fno-gnu-keywords} flag instead, which has the same
1156 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1157 switch only affects the @code{asm} and @code{typeof} keywords, since
1158 @code{inline} is a standard keyword in ISO C99.
1161 @itemx -fno-builtin-@var{function}
1162 @opindex fno-builtin
1163 @cindex built-in functions
1164 Don't recognize built-in functions that do not begin with
1165 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1166 functions provided by GCC}, for details of the functions affected,
1167 including those which are not built-in functions when @option{-ansi} or
1168 @option{-std} options for strict ISO C conformance are used because they
1169 do not have an ISO standard meaning.
1171 GCC normally generates special code to handle certain built-in functions
1172 more efficiently; for instance, calls to @code{alloca} may become single
1173 instructions that adjust the stack directly, and calls to @code{memcpy}
1174 may become inline copy loops. The resulting code is often both smaller
1175 and faster, but since the function calls no longer appear as such, you
1176 cannot set a breakpoint on those calls, nor can you change the behavior
1177 of the functions by linking with a different library. In addition,
1178 when a function is recognized as a built-in function, GCC may use
1179 information about that function to warn about problems with calls to
1180 that function, or to generate more efficient code, even if the
1181 resulting code still contains calls to that function. For example,
1182 warnings are given with @option{-Wformat} for bad calls to
1183 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1184 known not to modify global memory.
1186 With the @option{-fno-builtin-@var{function}} option
1187 only the built-in function @var{function} is
1188 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1189 function is named this is not built-in in this version of GCC, this
1190 option is ignored. There is no corresponding
1191 @option{-fbuiltin-@var{function}} option; if you wish to enable
1192 built-in functions selectively when using @option{-fno-builtin} or
1193 @option{-ffreestanding}, you may define macros such as:
1196 #define abs(n) __builtin_abs ((n))
1197 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1202 @cindex hosted environment
1204 Assert that compilation takes place in a hosted environment. This implies
1205 @option{-fbuiltin}. A hosted environment is one in which the
1206 entire standard library is available, and in which @code{main} has a return
1207 type of @code{int}. Examples are nearly everything except a kernel.
1208 This is equivalent to @option{-fno-freestanding}.
1210 @item -ffreestanding
1211 @opindex ffreestanding
1212 @cindex hosted environment
1214 Assert that compilation takes place in a freestanding environment. This
1215 implies @option{-fno-builtin}. A freestanding environment
1216 is one in which the standard library may not exist, and program startup may
1217 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1218 This is equivalent to @option{-fno-hosted}.
1220 @xref{Standards,,Language Standards Supported by GCC}, for details of
1221 freestanding and hosted environments.
1223 @item -fms-extensions
1224 @opindex fms-extensions
1225 Accept some non-standard constructs used in Microsoft header files.
1227 Some cases of unnamed fields in structures and unions are only
1228 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1229 fields within structs/unions}, for details.
1233 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1234 options for strict ISO C conformance) implies @option{-trigraphs}.
1236 @item -no-integrated-cpp
1237 @opindex no-integrated-cpp
1238 Performs a compilation in two passes: preprocessing and compiling. This
1239 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1240 @option{-B} option. The user supplied compilation step can then add in
1241 an additional preprocessing step after normal preprocessing but before
1242 compiling. The default is to use the integrated cpp (internal cpp)
1244 The semantics of this option will change if "cc1", "cc1plus", and
1245 "cc1obj" are merged.
1247 @cindex traditional C language
1248 @cindex C language, traditional
1250 @itemx -traditional-cpp
1251 @opindex traditional-cpp
1252 @opindex traditional
1253 Formerly, these options caused GCC to attempt to emulate a pre-standard
1254 C compiler. They are now only supported with the @option{-E} switch.
1255 The preprocessor continues to support a pre-standard mode. See the GNU
1256 CPP manual for details.
1258 @item -fcond-mismatch
1259 @opindex fcond-mismatch
1260 Allow conditional expressions with mismatched types in the second and
1261 third arguments. The value of such an expression is void. This option
1262 is not supported for C++.
1264 @item -funsigned-char
1265 @opindex funsigned-char
1266 Let the type @code{char} be unsigned, like @code{unsigned char}.
1268 Each kind of machine has a default for what @code{char} should
1269 be. It is either like @code{unsigned char} by default or like
1270 @code{signed char} by default.
1272 Ideally, a portable program should always use @code{signed char} or
1273 @code{unsigned char} when it depends on the signedness of an object.
1274 But many programs have been written to use plain @code{char} and
1275 expect it to be signed, or expect it to be unsigned, depending on the
1276 machines they were written for. This option, and its inverse, let you
1277 make such a program work with the opposite default.
1279 The type @code{char} is always a distinct type from each of
1280 @code{signed char} or @code{unsigned char}, even though its behavior
1281 is always just like one of those two.
1284 @opindex fsigned-char
1285 Let the type @code{char} be signed, like @code{signed char}.
1287 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1288 the negative form of @option{-funsigned-char}. Likewise, the option
1289 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1291 @item -fsigned-bitfields
1292 @itemx -funsigned-bitfields
1293 @itemx -fno-signed-bitfields
1294 @itemx -fno-unsigned-bitfields
1295 @opindex fsigned-bitfields
1296 @opindex funsigned-bitfields
1297 @opindex fno-signed-bitfields
1298 @opindex fno-unsigned-bitfields
1299 These options control whether a bit-field is signed or unsigned, when the
1300 declaration does not use either @code{signed} or @code{unsigned}. By
1301 default, such a bit-field is signed, because this is consistent: the
1302 basic integer types such as @code{int} are signed types.
1305 @node C++ Dialect Options
1306 @section Options Controlling C++ Dialect
1308 @cindex compiler options, C++
1309 @cindex C++ options, command line
1310 @cindex options, C++
1311 This section describes the command-line options that are only meaningful
1312 for C++ programs; but you can also use most of the GNU compiler options
1313 regardless of what language your program is in. For example, you
1314 might compile a file @code{firstClass.C} like this:
1317 g++ -g -frepo -O -c firstClass.C
1321 In this example, only @option{-frepo} is an option meant
1322 only for C++ programs; you can use the other options with any
1323 language supported by GCC@.
1325 Here is a list of options that are @emph{only} for compiling C++ programs:
1329 @item -fabi-version=@var{n}
1330 @opindex fabi-version
1331 Use version @var{n} of the C++ ABI. Version 2 is the version of the
1332 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1333 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1334 the version that conforms most closely to the C++ ABI specification.
1335 Therefore, the ABI obtained using version 0 will change as ABI bugs
1338 The default is version 2.
1340 @item -fno-access-control
1341 @opindex fno-access-control
1342 Turn off all access checking. This switch is mainly useful for working
1343 around bugs in the access control code.
1347 Check that the pointer returned by @code{operator new} is non-null
1348 before attempting to modify the storage allocated. This check is
1349 normally unnecessary because the C++ standard specifies that
1350 @code{operator new} will only return @code{0} if it is declared
1351 @samp{throw()}, in which case the compiler will always check the
1352 return value even without this option. In all other cases, when
1353 @code{operator new} has a non-empty exception specification, memory
1354 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1355 @samp{new (nothrow)}.
1357 @item -fconserve-space
1358 @opindex fconserve-space
1359 Put uninitialized or runtime-initialized global variables into the
1360 common segment, as C does. This saves space in the executable at the
1361 cost of not diagnosing duplicate definitions. If you compile with this
1362 flag and your program mysteriously crashes after @code{main()} has
1363 completed, you may have an object that is being destroyed twice because
1364 two definitions were merged.
1366 This option is no longer useful on most targets, now that support has
1367 been added for putting variables into BSS without making them common.
1369 @item -fno-const-strings
1370 @opindex fno-const-strings
1371 Give string constants type @code{char *} instead of type @code{const
1372 char *}. By default, G++ uses type @code{const char *} as required by
1373 the standard. Even if you use @option{-fno-const-strings}, you cannot
1374 actually modify the value of a string constant.
1376 This option might be removed in a future release of G++. For maximum
1377 portability, you should structure your code so that it works with
1378 string constants that have type @code{const char *}.
1380 @item -fno-elide-constructors
1381 @opindex fno-elide-constructors
1382 The C++ standard allows an implementation to omit creating a temporary
1383 which is only used to initialize another object of the same type.
1384 Specifying this option disables that optimization, and forces G++ to
1385 call the copy constructor in all cases.
1387 @item -fno-enforce-eh-specs
1388 @opindex fno-enforce-eh-specs
1389 Don't check for violation of exception specifications at runtime. This
1390 option violates the C++ standard, but may be useful for reducing code
1391 size in production builds, much like defining @samp{NDEBUG}. The compiler
1392 will still optimize based on the exception specifications.
1395 @itemx -fno-for-scope
1397 @opindex fno-for-scope
1398 If @option{-ffor-scope} is specified, the scope of variables declared in
1399 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1400 as specified by the C++ standard.
1401 If @option{-fno-for-scope} is specified, the scope of variables declared in
1402 a @i{for-init-statement} extends to the end of the enclosing scope,
1403 as was the case in old versions of G++, and other (traditional)
1404 implementations of C++.
1406 The default if neither flag is given to follow the standard,
1407 but to allow and give a warning for old-style code that would
1408 otherwise be invalid, or have different behavior.
1410 @item -fno-gnu-keywords
1411 @opindex fno-gnu-keywords
1412 Do not recognize @code{typeof} as a keyword, so that code can use this
1413 word as an identifier. You can use the keyword @code{__typeof__} instead.
1414 @option{-ansi} implies @option{-fno-gnu-keywords}.
1416 @item -fno-implicit-templates
1417 @opindex fno-implicit-templates
1418 Never emit code for non-inline templates which are instantiated
1419 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1420 @xref{Template Instantiation}, for more information.
1422 @item -fno-implicit-inline-templates
1423 @opindex fno-implicit-inline-templates
1424 Don't emit code for implicit instantiations of inline templates, either.
1425 The default is to handle inlines differently so that compiles with and
1426 without optimization will need the same set of explicit instantiations.
1428 @item -fno-implement-inlines
1429 @opindex fno-implement-inlines
1430 To save space, do not emit out-of-line copies of inline functions
1431 controlled by @samp{#pragma implementation}. This will cause linker
1432 errors if these functions are not inlined everywhere they are called.
1434 @item -fms-extensions
1435 @opindex fms-extensions
1436 Disable pedantic warnings about constructs used in MFC, such as implicit
1437 int and getting a pointer to member function via non-standard syntax.
1439 @item -fno-nonansi-builtins
1440 @opindex fno-nonansi-builtins
1441 Disable built-in declarations of functions that are not mandated by
1442 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1443 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1445 @item -fno-operator-names
1446 @opindex fno-operator-names
1447 Do not treat the operator name keywords @code{and}, @code{bitand},
1448 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1449 synonyms as keywords.
1451 @item -fno-optional-diags
1452 @opindex fno-optional-diags
1453 Disable diagnostics that the standard says a compiler does not need to
1454 issue. Currently, the only such diagnostic issued by G++ is the one for
1455 a name having multiple meanings within a class.
1458 @opindex fpermissive
1459 Downgrade some diagnostics about nonconformant code from errors to
1460 warnings. Thus, using @option{-fpermissive} will allow some
1461 nonconforming code to compile.
1465 Enable automatic template instantiation at link time. This option also
1466 implies @option{-fno-implicit-templates}. @xref{Template
1467 Instantiation}, for more information.
1471 Disable generation of information about every class with virtual
1472 functions for use by the C++ runtime type identification features
1473 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1474 of the language, you can save some space by using this flag. Note that
1475 exception handling uses the same information, but it will generate it as
1480 Emit statistics about front-end processing at the end of the compilation.
1481 This information is generally only useful to the G++ development team.
1483 @item -ftemplate-depth-@var{n}
1484 @opindex ftemplate-depth
1485 Set the maximum instantiation depth for template classes to @var{n}.
1486 A limit on the template instantiation depth is needed to detect
1487 endless recursions during template class instantiation. ANSI/ISO C++
1488 conforming programs must not rely on a maximum depth greater than 17.
1490 @item -fno-threadsafe-statics
1491 @opindex fno-threadsafe-statics
1492 Do not emit the extra code to use the routines specified in the C++
1493 ABI for thread-safe initialization of local statics. You can use this
1494 option to reduce code size slightly in code that doesn't need to be
1497 @item -fuse-cxa-atexit
1498 @opindex fuse-cxa-atexit
1499 Register destructors for objects with static storage duration with the
1500 @code{__cxa_atexit} function rather than the @code{atexit} function.
1501 This option is required for fully standards-compliant handling of static
1502 destructors, but will only work if your C library supports
1503 @code{__cxa_atexit}.
1505 @item -fvisibility-inlines-hidden
1506 @opindex fvisibility-inlines-hidden
1507 Causes all inlined methods to be marked with
1508 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1509 appear in the export table of a DSO and do not require a PLT indirection
1510 when used within the DSO. Enabling this option can have a dramatic effect
1511 on load and link times of a DSO as it massively reduces the size of the
1512 dynamic export table when the library makes heavy use of templates. While
1513 it can cause bloating through duplication of code within each DSO where
1514 it is used, often the wastage is less than the considerable space occupied
1515 by a long symbol name in the export table which is typical when using
1516 templates and namespaces. For even more savings, combine with the
1517 @option{-fvisibility=hidden} switch.
1521 Do not use weak symbol support, even if it is provided by the linker.
1522 By default, G++ will use weak symbols if they are available. This
1523 option exists only for testing, and should not be used by end-users;
1524 it will result in inferior code and has no benefits. This option may
1525 be removed in a future release of G++.
1529 Do not search for header files in the standard directories specific to
1530 C++, but do still search the other standard directories. (This option
1531 is used when building the C++ library.)
1534 In addition, these optimization, warning, and code generation options
1535 have meanings only for C++ programs:
1538 @item -fno-default-inline
1539 @opindex fno-default-inline
1540 Do not assume @samp{inline} for functions defined inside a class scope.
1541 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1542 functions will have linkage like inline functions; they just won't be
1545 @item -Wabi @r{(C++ only)}
1547 Warn when G++ generates code that is probably not compatible with the
1548 vendor-neutral C++ ABI. Although an effort has been made to warn about
1549 all such cases, there are probably some cases that are not warned about,
1550 even though G++ is generating incompatible code. There may also be
1551 cases where warnings are emitted even though the code that is generated
1554 You should rewrite your code to avoid these warnings if you are
1555 concerned about the fact that code generated by G++ may not be binary
1556 compatible with code generated by other compilers.
1558 The known incompatibilities at this point include:
1563 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1564 pack data into the same byte as a base class. For example:
1567 struct A @{ virtual void f(); int f1 : 1; @};
1568 struct B : public A @{ int f2 : 1; @};
1572 In this case, G++ will place @code{B::f2} into the same byte
1573 as@code{A::f1}; other compilers will not. You can avoid this problem
1574 by explicitly padding @code{A} so that its size is a multiple of the
1575 byte size on your platform; that will cause G++ and other compilers to
1576 layout @code{B} identically.
1579 Incorrect handling of tail-padding for virtual bases. G++ does not use
1580 tail padding when laying out virtual bases. For example:
1583 struct A @{ virtual void f(); char c1; @};
1584 struct B @{ B(); char c2; @};
1585 struct C : public A, public virtual B @{@};
1589 In this case, G++ will not place @code{B} into the tail-padding for
1590 @code{A}; other compilers will. You can avoid this problem by
1591 explicitly padding @code{A} so that its size is a multiple of its
1592 alignment (ignoring virtual base classes); that will cause G++ and other
1593 compilers to layout @code{C} identically.
1596 Incorrect handling of bit-fields with declared widths greater than that
1597 of their underlying types, when the bit-fields appear in a union. For
1601 union U @{ int i : 4096; @};
1605 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1606 union too small by the number of bits in an @code{int}.
1609 Empty classes can be placed at incorrect offsets. For example:
1619 struct C : public B, public A @{@};
1623 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1624 it should be placed at offset zero. G++ mistakenly believes that the
1625 @code{A} data member of @code{B} is already at offset zero.
1628 Names of template functions whose types involve @code{typename} or
1629 template template parameters can be mangled incorrectly.
1632 template <typename Q>
1633 void f(typename Q::X) @{@}
1635 template <template <typename> class Q>
1636 void f(typename Q<int>::X) @{@}
1640 Instantiations of these templates may be mangled incorrectly.
1644 @item -Wctor-dtor-privacy @r{(C++ only)}
1645 @opindex Wctor-dtor-privacy
1646 Warn when a class seems unusable because all the constructors or
1647 destructors in that class are private, and it has neither friends nor
1648 public static member functions.
1650 @item -Wnon-virtual-dtor @r{(C++ only)}
1651 @opindex Wnon-virtual-dtor
1652 Warn when a class appears to be polymorphic, thereby requiring a virtual
1653 destructor, yet it declares a non-virtual one.
1654 This warning is enabled by @option{-Wall}.
1656 @item -Wreorder @r{(C++ only)}
1658 @cindex reordering, warning
1659 @cindex warning for reordering of member initializers
1660 Warn when the order of member initializers given in the code does not
1661 match the order in which they must be executed. For instance:
1667 A(): j (0), i (1) @{ @}
1671 The compiler will rearrange the member initializers for @samp{i}
1672 and @samp{j} to match the declaration order of the members, emitting
1673 a warning to that effect. This warning is enabled by @option{-Wall}.
1676 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1679 @item -Weffc++ @r{(C++ only)}
1681 Warn about violations of the following style guidelines from Scott Meyers'
1682 @cite{Effective C++} book:
1686 Item 11: Define a copy constructor and an assignment operator for classes
1687 with dynamically allocated memory.
1690 Item 12: Prefer initialization to assignment in constructors.
1693 Item 14: Make destructors virtual in base classes.
1696 Item 15: Have @code{operator=} return a reference to @code{*this}.
1699 Item 23: Don't try to return a reference when you must return an object.
1703 Also warn about violations of the following style guidelines from
1704 Scott Meyers' @cite{More Effective C++} book:
1708 Item 6: Distinguish between prefix and postfix forms of increment and
1709 decrement operators.
1712 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1716 When selecting this option, be aware that the standard library
1717 headers do not obey all of these guidelines; use @samp{grep -v}
1718 to filter out those warnings.
1720 @item -Wno-deprecated @r{(C++ only)}
1721 @opindex Wno-deprecated
1722 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1724 @item -Wno-non-template-friend @r{(C++ only)}
1725 @opindex Wno-non-template-friend
1726 Disable warnings when non-templatized friend functions are declared
1727 within a template. Since the advent of explicit template specification
1728 support in G++, if the name of the friend is an unqualified-id (i.e.,
1729 @samp{friend foo(int)}), the C++ language specification demands that the
1730 friend declare or define an ordinary, nontemplate function. (Section
1731 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1732 could be interpreted as a particular specialization of a templatized
1733 function. Because this non-conforming behavior is no longer the default
1734 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1735 check existing code for potential trouble spots and is on by default.
1736 This new compiler behavior can be turned off with
1737 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1738 but disables the helpful warning.
1740 @item -Wold-style-cast @r{(C++ only)}
1741 @opindex Wold-style-cast
1742 Warn if an old-style (C-style) cast to a non-void type is used within
1743 a C++ program. The new-style casts (@samp{static_cast},
1744 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1745 unintended effects and much easier to search for.
1747 @item -Woverloaded-virtual @r{(C++ only)}
1748 @opindex Woverloaded-virtual
1749 @cindex overloaded virtual fn, warning
1750 @cindex warning for overloaded virtual fn
1751 Warn when a function declaration hides virtual functions from a
1752 base class. For example, in:
1759 struct B: public A @{
1764 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1772 will fail to compile.
1774 @item -Wno-pmf-conversions @r{(C++ only)}
1775 @opindex Wno-pmf-conversions
1776 Disable the diagnostic for converting a bound pointer to member function
1779 @item -Wsign-promo @r{(C++ only)}
1780 @opindex Wsign-promo
1781 Warn when overload resolution chooses a promotion from unsigned or
1782 enumerated type to a signed type, over a conversion to an unsigned type of
1783 the same size. Previous versions of G++ would try to preserve
1784 unsignedness, but the standard mandates the current behavior.
1786 @item -Wsynth @r{(C++ only)}
1788 @cindex warning for synthesized methods
1789 @cindex synthesized methods, warning
1790 Warn when G++'s synthesis behavior does not match that of cfront. For
1796 A& operator = (int);
1806 In this example, G++ will synthesize a default @samp{A& operator =
1807 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1810 @node Objective-C and Objective-C++ Dialect Options
1811 @section Options Controlling Objective-C and Objective-C++ Dialects
1813 @cindex compiler options, Objective-C and Objective-C++
1814 @cindex Objective-C and Objective-C++ options, command line
1815 @cindex options, Objective-C and Objective-C++
1816 (NOTE: This manual does not describe the Objective-C and Objective-C++
1817 languages themselves. See @xref{Standards,,Language Standards
1818 Supported by GCC}, for references.)
1820 This section describes the command-line options that are only meaningful
1821 for Objective-C and Objective-C++ programs, but you can also use most of
1822 the language-independent GNU compiler options.
1823 For example, you might compile a file @code{some_class.m} like this:
1826 gcc -g -fgnu-runtime -O -c some_class.m
1830 In this example, @option{-fgnu-runtime} is an option meant only for
1831 Objective-C and Objective-C++ programs; you can use the other options with
1832 any language supported by GCC@.
1834 Note that since Objective-C is an extension of the C language, Objective-C
1835 compilations may also use options specific to the C front-end (e.g.,
1836 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1837 C++-specific options (e.g., @option{-Wabi}).
1839 Here is a list of options that are @emph{only} for compiling Objective-C
1840 and Objective-C++ programs:
1843 @item -fconstant-string-class=@var{class-name}
1844 @opindex fconstant-string-class
1845 Use @var{class-name} as the name of the class to instantiate for each
1846 literal string specified with the syntax @code{@@"@dots{}"}. The default
1847 class name is @code{NXConstantString} if the GNU runtime is being used, and
1848 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1849 @option{-fconstant-cfstrings} option, if also present, will override the
1850 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1851 to be laid out as constant CoreFoundation strings.
1854 @opindex fgnu-runtime
1855 Generate object code compatible with the standard GNU Objective-C
1856 runtime. This is the default for most types of systems.
1858 @item -fnext-runtime
1859 @opindex fnext-runtime
1860 Generate output compatible with the NeXT runtime. This is the default
1861 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1862 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1865 @item -fno-nil-receivers
1866 @opindex fno-nil-receivers
1867 Assume that all Objective-C message dispatches (e.g.,
1868 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1869 is not @code{nil}. This allows for more efficient entry points in the runtime
1870 to be used. Currently, this option is only available in conjunction with
1871 the NeXT runtime on Mac OS X 10.3 and later.
1873 @item -fobjc-exceptions
1874 @opindex fobjc-exceptions
1875 Enable syntactic support for structured exception handling in Objective-C,
1876 similar to what is offered by C++ and Java. Currently, this option is only
1877 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1885 @@catch (AnObjCClass *exc) @{
1892 @@catch (AnotherClass *exc) @{
1895 @@catch (id allOthers) @{
1905 The @code{@@throw} statement may appear anywhere in an Objective-C or
1906 Objective-C++ program; when used inside of a @code{@@catch} block, the
1907 @code{@@throw} may appear without an argument (as shown above), in which case
1908 the object caught by the @code{@@catch} will be rethrown.
1910 Note that only (pointers to) Objective-C objects may be thrown and
1911 caught using this scheme. When an object is thrown, it will be caught
1912 by the nearest @code{@@catch} clause capable of handling objects of that type,
1913 analogously to how @code{catch} blocks work in C++ and Java. A
1914 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1915 any and all Objective-C exceptions not caught by previous @code{@@catch}
1918 The @code{@@finally} clause, if present, will be executed upon exit from the
1919 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1920 regardless of whether any exceptions are thrown, caught or rethrown
1921 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1922 of the @code{finally} clause in Java.
1924 There are several caveats to using the new exception mechanism:
1928 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1929 idioms provided by the @code{NSException} class, the new
1930 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1931 systems, due to additional functionality needed in the (NeXT) Objective-C
1935 As mentioned above, the new exceptions do not support handling
1936 types other than Objective-C objects. Furthermore, when used from
1937 Objective-C++, the Objective-C exception model does not interoperate with C++
1938 exceptions at this time. This means you cannot @code{@@throw} an exception
1939 from Objective-C and @code{catch} it in C++, or vice versa
1940 (i.e., @code{throw @dots{} @@catch}).
1943 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1944 blocks for thread-safe execution:
1947 @@synchronized (ObjCClass *guard) @{
1952 Upon entering the @code{@@synchronized} block, a thread of execution shall
1953 first check whether a lock has been placed on the corresponding @code{guard}
1954 object by another thread. If it has, the current thread shall wait until
1955 the other thread relinquishes its lock. Once @code{guard} becomes available,
1956 the current thread will place its own lock on it, execute the code contained in
1957 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1958 making @code{guard} available to other threads).
1960 Unlike Java, Objective-C does not allow for entire methods to be marked
1961 @code{@@synchronized}. Note that throwing exceptions out of
1962 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1963 to be unlocked properly.
1965 @item -freplace-objc-classes
1966 @opindex freplace-objc-classes
1967 Emit a special marker instructing @command{ld(1)} not to statically link in
1968 the resulting object file, and allow @command{dyld(1)} to load it in at
1969 run time instead. This is used in conjunction with the Fix-and-Continue
1970 debugging mode, where the object file in question may be recompiled and
1971 dynamically reloaded in the course of program execution, without the need
1972 to restart the program itself. Currently, Fix-and-Continue functionality
1973 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
1978 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1979 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1980 compile time) with static class references that get initialized at load time,
1981 which improves run-time performance. Specifying the @option{-fzero-link} flag
1982 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1983 to be retained. This is useful in Zero-Link debugging mode, since it allows
1984 for individual class implementations to be modified during program execution.
1988 Dump interface declarations for all classes seen in the source file to a
1989 file named @file{@var{sourcename}.decl}.
1992 @opindex Wno-protocol
1993 If a class is declared to implement a protocol, a warning is issued for
1994 every method in the protocol that is not implemented by the class. The
1995 default behavior is to issue a warning for every method not explicitly
1996 implemented in the class, even if a method implementation is inherited
1997 from the superclass. If you use the @option{-Wno-protocol} option, then
1998 methods inherited from the superclass are considered to be implemented,
1999 and no warning is issued for them.
2003 Warn if multiple methods of different types for the same selector are
2004 found during compilation. The check is performed on the list of methods
2005 in the final stage of compilation. Additionally, a check is performed
2006 for each selector appearing in a @code{@@selector(@dots{})}
2007 expression, and a corresponding method for that selector has been found
2008 during compilation. Because these checks scan the method table only at
2009 the end of compilation, these warnings are not produced if the final
2010 stage of compilation is not reached, for example because an error is
2011 found during compilation, or because the @option{-fsyntax-only} option is
2014 @item -Wundeclared-selector
2015 @opindex Wundeclared-selector
2016 Warn if a @code{@@selector(@dots{})} expression referring to an
2017 undeclared selector is found. A selector is considered undeclared if no
2018 method with that name has been declared before the
2019 @code{@@selector(@dots{})} expression, either explicitly in an
2020 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2021 an @code{@@implementation} section. This option always performs its
2022 checks as soon as a @code{@@selector(@dots{})} expression is found,
2023 while @option{-Wselector} only performs its checks in the final stage of
2024 compilation. This also enforces the coding style convention
2025 that methods and selectors must be declared before being used.
2027 @item -print-objc-runtime-info
2028 @opindex print-objc-runtime-info
2029 Generate C header describing the largest structure that is passed by
2034 @node Language Independent Options
2035 @section Options to Control Diagnostic Messages Formatting
2036 @cindex options to control diagnostics formatting
2037 @cindex diagnostic messages
2038 @cindex message formatting
2040 Traditionally, diagnostic messages have been formatted irrespective of
2041 the output device's aspect (e.g.@: its width, @dots{}). The options described
2042 below can be used to control the diagnostic messages formatting
2043 algorithm, e.g.@: how many characters per line, how often source location
2044 information should be reported. Right now, only the C++ front end can
2045 honor these options. However it is expected, in the near future, that
2046 the remaining front ends would be able to digest them correctly.
2049 @item -fmessage-length=@var{n}
2050 @opindex fmessage-length
2051 Try to format error messages so that they fit on lines of about @var{n}
2052 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2053 the front ends supported by GCC@. If @var{n} is zero, then no
2054 line-wrapping will be done; each error message will appear on a single
2057 @opindex fdiagnostics-show-location
2058 @item -fdiagnostics-show-location=once
2059 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2060 reporter to emit @emph{once} source location information; that is, in
2061 case the message is too long to fit on a single physical line and has to
2062 be wrapped, the source location won't be emitted (as prefix) again,
2063 over and over, in subsequent continuation lines. This is the default
2066 @item -fdiagnostics-show-location=every-line
2067 Only meaningful in line-wrapping mode. Instructs the diagnostic
2068 messages reporter to emit the same source location information (as
2069 prefix) for physical lines that result from the process of breaking
2070 a message which is too long to fit on a single line.
2074 @node Warning Options
2075 @section Options to Request or Suppress Warnings
2076 @cindex options to control warnings
2077 @cindex warning messages
2078 @cindex messages, warning
2079 @cindex suppressing warnings
2081 Warnings are diagnostic messages that report constructions which
2082 are not inherently erroneous but which are risky or suggest there
2083 may have been an error.
2085 You can request many specific warnings with options beginning @samp{-W},
2086 for example @option{-Wimplicit} to request warnings on implicit
2087 declarations. Each of these specific warning options also has a
2088 negative form beginning @samp{-Wno-} to turn off warnings;
2089 for example, @option{-Wno-implicit}. This manual lists only one of the
2090 two forms, whichever is not the default.
2092 The following options control the amount and kinds of warnings produced
2093 by GCC; for further, language-specific options also refer to
2094 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2098 @cindex syntax checking
2100 @opindex fsyntax-only
2101 Check the code for syntax errors, but don't do anything beyond that.
2105 Issue all the warnings demanded by strict ISO C and ISO C++;
2106 reject all programs that use forbidden extensions, and some other
2107 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2108 version of the ISO C standard specified by any @option{-std} option used.
2110 Valid ISO C and ISO C++ programs should compile properly with or without
2111 this option (though a rare few will require @option{-ansi} or a
2112 @option{-std} option specifying the required version of ISO C)@. However,
2113 without this option, certain GNU extensions and traditional C and C++
2114 features are supported as well. With this option, they are rejected.
2116 @option{-pedantic} does not cause warning messages for use of the
2117 alternate keywords whose names begin and end with @samp{__}. Pedantic
2118 warnings are also disabled in the expression that follows
2119 @code{__extension__}. However, only system header files should use
2120 these escape routes; application programs should avoid them.
2121 @xref{Alternate Keywords}.
2123 Some users try to use @option{-pedantic} to check programs for strict ISO
2124 C conformance. They soon find that it does not do quite what they want:
2125 it finds some non-ISO practices, but not all---only those for which
2126 ISO C @emph{requires} a diagnostic, and some others for which
2127 diagnostics have been added.
2129 A feature to report any failure to conform to ISO C might be useful in
2130 some instances, but would require considerable additional work and would
2131 be quite different from @option{-pedantic}. We don't have plans to
2132 support such a feature in the near future.
2134 Where the standard specified with @option{-std} represents a GNU
2135 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2136 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2137 extended dialect is based. Warnings from @option{-pedantic} are given
2138 where they are required by the base standard. (It would not make sense
2139 for such warnings to be given only for features not in the specified GNU
2140 C dialect, since by definition the GNU dialects of C include all
2141 features the compiler supports with the given option, and there would be
2142 nothing to warn about.)
2144 @item -pedantic-errors
2145 @opindex pedantic-errors
2146 Like @option{-pedantic}, except that errors are produced rather than
2151 Inhibit all warning messages.
2155 Inhibit warning messages about the use of @samp{#import}.
2157 @item -Wchar-subscripts
2158 @opindex Wchar-subscripts
2159 Warn if an array subscript has type @code{char}. This is a common cause
2160 of error, as programmers often forget that this type is signed on some
2165 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2166 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2168 @item -Wfatal-errors
2169 @opindex Wfatal-errors
2170 This option causes the compiler to abort compilation on the first error
2171 occurred rather than trying to keep going and printing further error
2176 @opindex ffreestanding
2177 @opindex fno-builtin
2178 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2179 the arguments supplied have types appropriate to the format string
2180 specified, and that the conversions specified in the format string make
2181 sense. This includes standard functions, and others specified by format
2182 attributes (@pxref{Function Attributes}), in the @code{printf},
2183 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2184 not in the C standard) families (or other target-specific families).
2185 Which functions are checked without format attributes having been
2186 specified depends on the standard version selected, and such checks of
2187 functions without the attribute specified are disabled by
2188 @option{-ffreestanding} or @option{-fno-builtin}.
2190 The formats are checked against the format features supported by GNU
2191 libc version 2.2. These include all ISO C90 and C99 features, as well
2192 as features from the Single Unix Specification and some BSD and GNU
2193 extensions. Other library implementations may not support all these
2194 features; GCC does not support warning about features that go beyond a
2195 particular library's limitations. However, if @option{-pedantic} is used
2196 with @option{-Wformat}, warnings will be given about format features not
2197 in the selected standard version (but not for @code{strfmon} formats,
2198 since those are not in any version of the C standard). @xref{C Dialect
2199 Options,,Options Controlling C Dialect}.
2201 Since @option{-Wformat} also checks for null format arguments for
2202 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2204 @option{-Wformat} is included in @option{-Wall}. For more control over some
2205 aspects of format checking, the options @option{-Wformat-y2k},
2206 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2207 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2208 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2211 @opindex Wformat-y2k
2212 If @option{-Wformat} is specified, also warn about @code{strftime}
2213 formats which may yield only a two-digit year.
2215 @item -Wno-format-extra-args
2216 @opindex Wno-format-extra-args
2217 If @option{-Wformat} is specified, do not warn about excess arguments to a
2218 @code{printf} or @code{scanf} format function. The C standard specifies
2219 that such arguments are ignored.
2221 Where the unused arguments lie between used arguments that are
2222 specified with @samp{$} operand number specifications, normally
2223 warnings are still given, since the implementation could not know what
2224 type to pass to @code{va_arg} to skip the unused arguments. However,
2225 in the case of @code{scanf} formats, this option will suppress the
2226 warning if the unused arguments are all pointers, since the Single
2227 Unix Specification says that such unused arguments are allowed.
2229 @item -Wno-format-zero-length
2230 @opindex Wno-format-zero-length
2231 If @option{-Wformat} is specified, do not warn about zero-length formats.
2232 The C standard specifies that zero-length formats are allowed.
2234 @item -Wformat-nonliteral
2235 @opindex Wformat-nonliteral
2236 If @option{-Wformat} is specified, also warn if the format string is not a
2237 string literal and so cannot be checked, unless the format function
2238 takes its format arguments as a @code{va_list}.
2240 @item -Wformat-security
2241 @opindex Wformat-security
2242 If @option{-Wformat} is specified, also warn about uses of format
2243 functions that represent possible security problems. At present, this
2244 warns about calls to @code{printf} and @code{scanf} functions where the
2245 format string is not a string literal and there are no format arguments,
2246 as in @code{printf (foo);}. This may be a security hole if the format
2247 string came from untrusted input and contains @samp{%n}. (This is
2248 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2249 in future warnings may be added to @option{-Wformat-security} that are not
2250 included in @option{-Wformat-nonliteral}.)
2254 Enable @option{-Wformat} plus format checks not included in
2255 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2256 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2260 Warn about passing a null pointer for arguments marked as
2261 requiring a non-null value by the @code{nonnull} function attribute.
2263 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2264 can be disabled with the @option{-Wno-nonnull} option.
2266 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2268 Warn about uninitialized variables which are initialized with themselves.
2269 Note this option can only be used with the @option{-Wuninitialized} option,
2270 which in turn only works with @option{-O1} and above.
2272 For example, GCC will warn about @code{i} being uninitialized in the
2273 following snippet only when @option{-Winit-self} has been specified:
2284 @item -Wimplicit-int
2285 @opindex Wimplicit-int
2286 Warn when a declaration does not specify a type.
2288 @item -Wimplicit-function-declaration
2289 @itemx -Werror-implicit-function-declaration
2290 @opindex Wimplicit-function-declaration
2291 @opindex Werror-implicit-function-declaration
2292 Give a warning (or error) whenever a function is used before being
2293 declared. The form @option{-Wno-error-implicit-function-declaration}
2298 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2302 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2303 function with external linkage, returning int, taking either zero
2304 arguments, two, or three arguments of appropriate types.
2306 @item -Wmissing-braces
2307 @opindex Wmissing-braces
2308 Warn if an aggregate or union initializer is not fully bracketed. In
2309 the following example, the initializer for @samp{a} is not fully
2310 bracketed, but that for @samp{b} is fully bracketed.
2313 int a[2][2] = @{ 0, 1, 2, 3 @};
2314 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2317 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2318 @opindex Wmissing-include-dirs
2319 Warn if a user-supplied include directory does not exist.
2322 @opindex Wparentheses
2323 Warn if parentheses are omitted in certain contexts, such
2324 as when there is an assignment in a context where a truth value
2325 is expected, or when operators are nested whose precedence people
2326 often get confused about. Only the warning for an assignment used as
2327 a truth value is supported when compiling C++; the other warnings are
2328 only supported when compiling C@.
2330 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2331 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2332 interpretation from that of ordinary mathematical notation.
2334 Also warn about constructions where there may be confusion to which
2335 @code{if} statement an @code{else} branch belongs. Here is an example of
2350 In C, every @code{else} branch belongs to the innermost possible @code{if}
2351 statement, which in this example is @code{if (b)}. This is often not
2352 what the programmer expected, as illustrated in the above example by
2353 indentation the programmer chose. When there is the potential for this
2354 confusion, GCC will issue a warning when this flag is specified.
2355 To eliminate the warning, add explicit braces around the innermost
2356 @code{if} statement so there is no way the @code{else} could belong to
2357 the enclosing @code{if}. The resulting code would look like this:
2373 @item -Wsequence-point
2374 @opindex Wsequence-point
2375 Warn about code that may have undefined semantics because of violations
2376 of sequence point rules in the C standard.
2378 The C standard defines the order in which expressions in a C program are
2379 evaluated in terms of @dfn{sequence points}, which represent a partial
2380 ordering between the execution of parts of the program: those executed
2381 before the sequence point, and those executed after it. These occur
2382 after the evaluation of a full expression (one which is not part of a
2383 larger expression), after the evaluation of the first operand of a
2384 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2385 function is called (but after the evaluation of its arguments and the
2386 expression denoting the called function), and in certain other places.
2387 Other than as expressed by the sequence point rules, the order of
2388 evaluation of subexpressions of an expression is not specified. All
2389 these rules describe only a partial order rather than a total order,
2390 since, for example, if two functions are called within one expression
2391 with no sequence point between them, the order in which the functions
2392 are called is not specified. However, the standards committee have
2393 ruled that function calls do not overlap.
2395 It is not specified when between sequence points modifications to the
2396 values of objects take effect. Programs whose behavior depends on this
2397 have undefined behavior; the C standard specifies that ``Between the
2398 previous and next sequence point an object shall have its stored value
2399 modified at most once by the evaluation of an expression. Furthermore,
2400 the prior value shall be read only to determine the value to be
2401 stored.''. If a program breaks these rules, the results on any
2402 particular implementation are entirely unpredictable.
2404 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2405 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2406 diagnosed by this option, and it may give an occasional false positive
2407 result, but in general it has been found fairly effective at detecting
2408 this sort of problem in programs.
2410 The present implementation of this option only works for C programs. A
2411 future implementation may also work for C++ programs.
2413 The C standard is worded confusingly, therefore there is some debate
2414 over the precise meaning of the sequence point rules in subtle cases.
2415 Links to discussions of the problem, including proposed formal
2416 definitions, may be found on the GCC readings page, at
2417 @w{@uref{http://gcc.gnu.org/readings.html}}.
2420 @opindex Wreturn-type
2421 Warn whenever a function is defined with a return-type that defaults to
2422 @code{int}. Also warn about any @code{return} statement with no
2423 return-value in a function whose return-type is not @code{void}.
2425 For C, also warn if the return type of a function has a type qualifier
2426 such as @code{const}. Such a type qualifier has no effect, since the
2427 value returned by a function is not an lvalue. ISO C prohibits
2428 qualified @code{void} return types on function definitions, so such
2429 return types always receive a warning even without this option.
2431 For C++, a function without return type always produces a diagnostic
2432 message, even when @option{-Wno-return-type} is specified. The only
2433 exceptions are @samp{main} and functions defined in system headers.
2437 Warn whenever a @code{switch} statement has an index of enumerated type
2438 and lacks a @code{case} for one or more of the named codes of that
2439 enumeration. (The presence of a @code{default} label prevents this
2440 warning.) @code{case} labels outside the enumeration range also
2441 provoke warnings when this option is used.
2443 @item -Wswitch-default
2444 @opindex Wswitch-switch
2445 Warn whenever a @code{switch} statement does not have a @code{default}
2449 @opindex Wswitch-enum
2450 Warn whenever a @code{switch} statement has an index of enumerated type
2451 and lacks a @code{case} for one or more of the named codes of that
2452 enumeration. @code{case} labels outside the enumeration range also
2453 provoke warnings when this option is used.
2457 Warn if any trigraphs are encountered that might change the meaning of
2458 the program (trigraphs within comments are not warned about).
2460 @item -Wunused-function
2461 @opindex Wunused-function
2462 Warn whenever a static function is declared but not defined or a
2463 non\-inline static function is unused.
2465 @item -Wunused-label
2466 @opindex Wunused-label
2467 Warn whenever a label is declared but not used.
2469 To suppress this warning use the @samp{unused} attribute
2470 (@pxref{Variable Attributes}).
2472 @item -Wunused-parameter
2473 @opindex Wunused-parameter
2474 Warn whenever a function parameter is unused aside from its declaration.
2476 To suppress this warning use the @samp{unused} attribute
2477 (@pxref{Variable Attributes}).
2479 @item -Wunused-variable
2480 @opindex Wunused-variable
2481 Warn whenever a local variable or non-constant static variable is unused
2482 aside from its declaration
2484 To suppress this warning use the @samp{unused} attribute
2485 (@pxref{Variable Attributes}).
2487 @item -Wunused-value
2488 @opindex Wunused-value
2489 Warn whenever a statement computes a result that is explicitly not used.
2491 To suppress this warning cast the expression to @samp{void}.
2495 All the above @option{-Wunused} options combined.
2497 In order to get a warning about an unused function parameter, you must
2498 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2499 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2501 @item -Wuninitialized
2502 @opindex Wuninitialized
2503 Warn if an automatic variable is used without first being initialized or
2504 if a variable may be clobbered by a @code{setjmp} call.
2506 These warnings are possible only in optimizing compilation,
2507 because they require data flow information that is computed only
2508 when optimizing. If you don't specify @option{-O}, you simply won't
2511 If you want to warn about code which uses the uninitialized value of the
2512 variable in its own initializer, use the @option{-Winit-self} option.
2514 These warnings occur only for variables that are candidates for
2515 register allocation. Therefore, they do not occur for a variable that
2516 is declared @code{volatile}, or whose address is taken, or whose size
2517 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2518 structures, unions or arrays, even when they are in registers.
2520 Note that there may be no warning about a variable that is used only
2521 to compute a value that itself is never used, because such
2522 computations may be deleted by data flow analysis before the warnings
2525 These warnings are made optional because GCC is not smart
2526 enough to see all the reasons why the code might be correct
2527 despite appearing to have an error. Here is one example of how
2548 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2549 always initialized, but GCC doesn't know this. Here is
2550 another common case:
2555 if (change_y) save_y = y, y = new_y;
2557 if (change_y) y = save_y;
2562 This has no bug because @code{save_y} is used only if it is set.
2564 @cindex @code{longjmp} warnings
2565 This option also warns when a non-volatile automatic variable might be
2566 changed by a call to @code{longjmp}. These warnings as well are possible
2567 only in optimizing compilation.
2569 The compiler sees only the calls to @code{setjmp}. It cannot know
2570 where @code{longjmp} will be called; in fact, a signal handler could
2571 call it at any point in the code. As a result, you may get a warning
2572 even when there is in fact no problem because @code{longjmp} cannot
2573 in fact be called at the place which would cause a problem.
2575 Some spurious warnings can be avoided if you declare all the functions
2576 you use that never return as @code{noreturn}. @xref{Function
2579 @item -Wunknown-pragmas
2580 @opindex Wunknown-pragmas
2581 @cindex warning for unknown pragmas
2582 @cindex unknown pragmas, warning
2583 @cindex pragmas, warning of unknown
2584 Warn when a #pragma directive is encountered which is not understood by
2585 GCC@. If this command line option is used, warnings will even be issued
2586 for unknown pragmas in system header files. This is not the case if
2587 the warnings were only enabled by the @option{-Wall} command line option.
2589 @item -Wstrict-aliasing
2590 @opindex Wstrict-aliasing
2591 This option is only active when @option{-fstrict-aliasing} is active.
2592 It warns about code which might break the strict aliasing rules that the
2593 compiler is using for optimization. The warning does not catch all
2594 cases, but does attempt to catch the more common pitfalls. It is
2595 included in @option{-Wall}.
2597 @item -Wstrict-aliasing=2
2598 @opindex Wstrict-aliasing=2
2599 This option is only active when @option{-fstrict-aliasing} is active.
2600 It warns about all code which might break the strict aliasing rules that the
2601 compiler is using for optimization. This warning catches all cases, but
2602 it will also give a warning for some ambiguous cases that are safe.
2606 All of the above @samp{-W} options combined. This enables all the
2607 warnings about constructions that some users consider questionable, and
2608 that are easy to avoid (or modify to prevent the warning), even in
2609 conjunction with macros. This also enables some language-specific
2610 warnings described in @ref{C++ Dialect Options} and
2611 @ref{Objective-C and Objective-C++ Dialect Options}.
2614 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2615 Some of them warn about constructions that users generally do not
2616 consider questionable, but which occasionally you might wish to check
2617 for; others warn about constructions that are necessary or hard to avoid
2618 in some cases, and there is no simple way to modify the code to suppress
2625 (This option used to be called @option{-W}. The older name is still
2626 supported, but the newer name is more descriptive.) Print extra warning
2627 messages for these events:
2631 A function can return either with or without a value. (Falling
2632 off the end of the function body is considered returning without
2633 a value.) For example, this function would evoke such a
2647 An expression-statement or the left-hand side of a comma expression
2648 contains no side effects.
2649 To suppress the warning, cast the unused expression to void.
2650 For example, an expression such as @samp{x[i,j]} will cause a warning,
2651 but @samp{x[(void)i,j]} will not.
2654 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2657 Storage-class specifiers like @code{static} are not the first things in
2658 a declaration. According to the C Standard, this usage is obsolescent.
2661 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2665 A comparison between signed and unsigned values could produce an
2666 incorrect result when the signed value is converted to unsigned.
2667 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2670 An aggregate has an initializer which does not initialize all members.
2671 This warning can be independently controlled by
2672 @option{-Wmissing-field-initializers}.
2675 A function parameter is declared without a type specifier in K&R-style
2683 An empty body occurs in an @samp{if} or @samp{else} statement.
2686 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2687 @samp{>}, or @samp{>=}.
2690 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2693 Any of several floating-point events that often indicate errors, such as
2694 overflow, underflow, loss of precision, etc.
2696 @item @r{(C++ only)}
2697 An enumerator and a non-enumerator both appear in a conditional expression.
2699 @item @r{(C++ only)}
2700 A non-static reference or non-static @samp{const} member appears in a
2701 class without constructors.
2703 @item @r{(C++ only)}
2704 Ambiguous virtual bases.
2706 @item @r{(C++ only)}
2707 Subscripting an array which has been declared @samp{register}.
2709 @item @r{(C++ only)}
2710 Taking the address of a variable which has been declared @samp{register}.
2712 @item @r{(C++ only)}
2713 A base class is not initialized in a derived class' copy constructor.
2716 @item -Wno-div-by-zero
2717 @opindex Wno-div-by-zero
2718 @opindex Wdiv-by-zero
2719 Do not warn about compile-time integer division by zero. Floating point
2720 division by zero is not warned about, as it can be a legitimate way of
2721 obtaining infinities and NaNs.
2723 @item -Wsystem-headers
2724 @opindex Wsystem-headers
2725 @cindex warnings from system headers
2726 @cindex system headers, warnings from
2727 Print warning messages for constructs found in system header files.
2728 Warnings from system headers are normally suppressed, on the assumption
2729 that they usually do not indicate real problems and would only make the
2730 compiler output harder to read. Using this command line option tells
2731 GCC to emit warnings from system headers as if they occurred in user
2732 code. However, note that using @option{-Wall} in conjunction with this
2733 option will @emph{not} warn about unknown pragmas in system
2734 headers---for that, @option{-Wunknown-pragmas} must also be used.
2737 @opindex Wfloat-equal
2738 Warn if floating point values are used in equality comparisons.
2740 The idea behind this is that sometimes it is convenient (for the
2741 programmer) to consider floating-point values as approximations to
2742 infinitely precise real numbers. If you are doing this, then you need
2743 to compute (by analyzing the code, or in some other way) the maximum or
2744 likely maximum error that the computation introduces, and allow for it
2745 when performing comparisons (and when producing output, but that's a
2746 different problem). In particular, instead of testing for equality, you
2747 would check to see whether the two values have ranges that overlap; and
2748 this is done with the relational operators, so equality comparisons are
2751 @item -Wtraditional @r{(C only)}
2752 @opindex Wtraditional
2753 Warn about certain constructs that behave differently in traditional and
2754 ISO C@. Also warn about ISO C constructs that have no traditional C
2755 equivalent, and/or problematic constructs which should be avoided.
2759 Macro parameters that appear within string literals in the macro body.
2760 In traditional C macro replacement takes place within string literals,
2761 but does not in ISO C@.
2764 In traditional C, some preprocessor directives did not exist.
2765 Traditional preprocessors would only consider a line to be a directive
2766 if the @samp{#} appeared in column 1 on the line. Therefore
2767 @option{-Wtraditional} warns about directives that traditional C
2768 understands but would ignore because the @samp{#} does not appear as the
2769 first character on the line. It also suggests you hide directives like
2770 @samp{#pragma} not understood by traditional C by indenting them. Some
2771 traditional implementations would not recognize @samp{#elif}, so it
2772 suggests avoiding it altogether.
2775 A function-like macro that appears without arguments.
2778 The unary plus operator.
2781 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2782 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2783 constants.) Note, these suffixes appear in macros defined in the system
2784 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2785 Use of these macros in user code might normally lead to spurious
2786 warnings, however GCC's integrated preprocessor has enough context to
2787 avoid warning in these cases.
2790 A function declared external in one block and then used after the end of
2794 A @code{switch} statement has an operand of type @code{long}.
2797 A non-@code{static} function declaration follows a @code{static} one.
2798 This construct is not accepted by some traditional C compilers.
2801 The ISO type of an integer constant has a different width or
2802 signedness from its traditional type. This warning is only issued if
2803 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2804 typically represent bit patterns, are not warned about.
2807 Usage of ISO string concatenation is detected.
2810 Initialization of automatic aggregates.
2813 Identifier conflicts with labels. Traditional C lacks a separate
2814 namespace for labels.
2817 Initialization of unions. If the initializer is zero, the warning is
2818 omitted. This is done under the assumption that the zero initializer in
2819 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2820 initializer warnings and relies on default initialization to zero in the
2824 Conversions by prototypes between fixed/floating point values and vice
2825 versa. The absence of these prototypes when compiling with traditional
2826 C would cause serious problems. This is a subset of the possible
2827 conversion warnings, for the full set use @option{-Wconversion}.
2830 Use of ISO C style function definitions. This warning intentionally is
2831 @emph{not} issued for prototype declarations or variadic functions
2832 because these ISO C features will appear in your code when using
2833 libiberty's traditional C compatibility macros, @code{PARAMS} and
2834 @code{VPARAMS}. This warning is also bypassed for nested functions
2835 because that feature is already a GCC extension and thus not relevant to
2836 traditional C compatibility.
2839 @item -Wdeclaration-after-statement @r{(C only)}
2840 @opindex Wdeclaration-after-statement
2841 Warn when a declaration is found after a statement in a block. This
2842 construct, known from C++, was introduced with ISO C99 and is by default
2843 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2844 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2848 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2850 @item -Wendif-labels
2851 @opindex Wendif-labels
2852 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2856 Warn whenever a local variable shadows another local variable, parameter or
2857 global variable or whenever a built-in function is shadowed.
2859 @item -Wlarger-than-@var{len}
2860 @opindex Wlarger-than
2861 Warn whenever an object of larger than @var{len} bytes is defined.
2863 @item -Wpointer-arith
2864 @opindex Wpointer-arith
2865 Warn about anything that depends on the ``size of'' a function type or
2866 of @code{void}. GNU C assigns these types a size of 1, for
2867 convenience in calculations with @code{void *} pointers and pointers
2870 @item -Wbad-function-cast @r{(C only)}
2871 @opindex Wbad-function-cast
2872 Warn whenever a function call is cast to a non-matching type.
2873 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2877 Warn whenever a pointer is cast so as to remove a type qualifier from
2878 the target type. For example, warn if a @code{const char *} is cast
2879 to an ordinary @code{char *}.
2882 @opindex Wcast-align
2883 Warn whenever a pointer is cast such that the required alignment of the
2884 target is increased. For example, warn if a @code{char *} is cast to
2885 an @code{int *} on machines where integers can only be accessed at
2886 two- or four-byte boundaries.
2888 @item -Wwrite-strings
2889 @opindex Wwrite-strings
2890 When compiling C, give string constants the type @code{const
2891 char[@var{length}]} so that
2892 copying the address of one into a non-@code{const} @code{char *}
2893 pointer will get a warning; when compiling C++, warn about the
2894 deprecated conversion from string constants to @code{char *}.
2895 These warnings will help you find at
2896 compile time code that can try to write into a string constant, but
2897 only if you have been very careful about using @code{const} in
2898 declarations and prototypes. Otherwise, it will just be a nuisance;
2899 this is why we did not make @option{-Wall} request these warnings.
2902 @opindex Wconversion
2903 Warn if a prototype causes a type conversion that is different from what
2904 would happen to the same argument in the absence of a prototype. This
2905 includes conversions of fixed point to floating and vice versa, and
2906 conversions changing the width or signedness of a fixed point argument
2907 except when the same as the default promotion.
2909 Also, warn if a negative integer constant expression is implicitly
2910 converted to an unsigned type. For example, warn about the assignment
2911 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2912 casts like @code{(unsigned) -1}.
2914 @item -Wsign-compare
2915 @opindex Wsign-compare
2916 @cindex warning for comparison of signed and unsigned values
2917 @cindex comparison of signed and unsigned values, warning
2918 @cindex signed and unsigned values, comparison warning
2919 Warn when a comparison between signed and unsigned values could produce
2920 an incorrect result when the signed value is converted to unsigned.
2921 This warning is also enabled by @option{-Wextra}; to get the other warnings
2922 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2924 @item -Waggregate-return
2925 @opindex Waggregate-return
2926 Warn if any functions that return structures or unions are defined or
2927 called. (In languages where you can return an array, this also elicits
2930 @item -Wstrict-prototypes @r{(C only)}
2931 @opindex Wstrict-prototypes
2932 Warn if a function is declared or defined without specifying the
2933 argument types. (An old-style function definition is permitted without
2934 a warning if preceded by a declaration which specifies the argument
2937 @item -Wold-style-definition @r{(C only)}
2938 @opindex Wold-style-definition
2939 Warn if an old-style function definition is used. A warning is given
2940 even if there is a previous prototype.
2942 @item -Wmissing-prototypes @r{(C only)}
2943 @opindex Wmissing-prototypes
2944 Warn if a global function is defined without a previous prototype
2945 declaration. This warning is issued even if the definition itself
2946 provides a prototype. The aim is to detect global functions that fail
2947 to be declared in header files.
2949 @item -Wmissing-declarations @r{(C only)}
2950 @opindex Wmissing-declarations
2951 Warn if a global function is defined without a previous declaration.
2952 Do so even if the definition itself provides a prototype.
2953 Use this option to detect global functions that are not declared in
2956 @item -Wmissing-field-initializers
2957 @opindex Wmissing-field-initializers
2960 Warn if a structure's initializer has some fields missing. For
2961 example, the following code would cause such a warning, because
2962 @code{x.h} is implicitly zero:
2965 struct s @{ int f, g, h; @};
2966 struct s x = @{ 3, 4 @};
2969 This option does not warn about designated initializers, so the following
2970 modification would not trigger a warning:
2973 struct s @{ int f, g, h; @};
2974 struct s x = @{ .f = 3, .g = 4 @};
2977 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
2978 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
2980 @item -Wmissing-noreturn
2981 @opindex Wmissing-noreturn
2982 Warn about functions which might be candidates for attribute @code{noreturn}.
2983 Note these are only possible candidates, not absolute ones. Care should
2984 be taken to manually verify functions actually do not ever return before
2985 adding the @code{noreturn} attribute, otherwise subtle code generation
2986 bugs could be introduced. You will not get a warning for @code{main} in
2987 hosted C environments.
2989 @item -Wmissing-format-attribute
2990 @opindex Wmissing-format-attribute
2992 If @option{-Wformat} is enabled, also warn about functions which might be
2993 candidates for @code{format} attributes. Note these are only possible
2994 candidates, not absolute ones. GCC will guess that @code{format}
2995 attributes might be appropriate for any function that calls a function
2996 like @code{vprintf} or @code{vscanf}, but this might not always be the
2997 case, and some functions for which @code{format} attributes are
2998 appropriate may not be detected. This option has no effect unless
2999 @option{-Wformat} is enabled (possibly by @option{-Wall}).
3001 @item -Wno-multichar
3002 @opindex Wno-multichar
3004 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3005 Usually they indicate a typo in the user's code, as they have
3006 implementation-defined values, and should not be used in portable code.
3008 @item -Wno-deprecated-declarations
3009 @opindex Wno-deprecated-declarations
3010 Do not warn about uses of functions, variables, and types marked as
3011 deprecated by using the @code{deprecated} attribute.
3012 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3013 @pxref{Type Attributes}.)
3017 Warn if a structure is given the packed attribute, but the packed
3018 attribute has no effect on the layout or size of the structure.
3019 Such structures may be mis-aligned for little benefit. For
3020 instance, in this code, the variable @code{f.x} in @code{struct bar}
3021 will be misaligned even though @code{struct bar} does not itself
3022 have the packed attribute:
3029 @} __attribute__((packed));
3039 Warn if padding is included in a structure, either to align an element
3040 of the structure or to align the whole structure. Sometimes when this
3041 happens it is possible to rearrange the fields of the structure to
3042 reduce the padding and so make the structure smaller.
3044 @item -Wredundant-decls
3045 @opindex Wredundant-decls
3046 Warn if anything is declared more than once in the same scope, even in
3047 cases where multiple declaration is valid and changes nothing.
3049 @item -Wnested-externs @r{(C only)}
3050 @opindex Wnested-externs
3051 Warn if an @code{extern} declaration is encountered within a function.
3053 @item -Wunreachable-code
3054 @opindex Wunreachable-code
3055 Warn if the compiler detects that code will never be executed.
3057 This option is intended to warn when the compiler detects that at
3058 least a whole line of source code will never be executed, because
3059 some condition is never satisfied or because it is after a
3060 procedure that never returns.
3062 It is possible for this option to produce a warning even though there
3063 are circumstances under which part of the affected line can be executed,
3064 so care should be taken when removing apparently-unreachable code.
3066 For instance, when a function is inlined, a warning may mean that the
3067 line is unreachable in only one inlined copy of the function.
3069 This option is not made part of @option{-Wall} because in a debugging
3070 version of a program there is often substantial code which checks
3071 correct functioning of the program and is, hopefully, unreachable
3072 because the program does work. Another common use of unreachable
3073 code is to provide behavior which is selectable at compile-time.
3077 Warn if a function can not be inlined and it was declared as inline.
3078 Even with this option, the compiler will not warn about failures to
3079 inline functions declared in system headers.
3081 The compiler uses a variety of heuristics to determine whether or not
3082 to inline a function. For example, the compiler takes into account
3083 the size of the function being inlined and the the amount of inlining
3084 that has already been done in the current function. Therefore,
3085 seemingly insignificant changes in the source program can cause the
3086 warnings produced by @option{-Winline} to appear or disappear.
3088 @item -Wno-invalid-offsetof @r{(C++ only)}
3089 @opindex Wno-invalid-offsetof
3090 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3091 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3092 to a non-POD type is undefined. In existing C++ implementations,
3093 however, @samp{offsetof} typically gives meaningful results even when
3094 applied to certain kinds of non-POD types. (Such as a simple
3095 @samp{struct} that fails to be a POD type only by virtue of having a
3096 constructor.) This flag is for users who are aware that they are
3097 writing nonportable code and who have deliberately chosen to ignore the
3100 The restrictions on @samp{offsetof} may be relaxed in a future version
3101 of the C++ standard.
3104 @opindex Winvalid-pch
3105 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3106 the search path but can't be used.
3110 @opindex Wno-long-long
3111 Warn if @samp{long long} type is used. This is default. To inhibit
3112 the warning messages, use @option{-Wno-long-long}. Flags
3113 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3114 only when @option{-pedantic} flag is used.
3116 @item -Wvariadic-macros
3117 @opindex Wvariadic-macros
3118 @opindex Wno-variadic-macros
3119 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3120 alternate syntax when in pedantic ISO C99 mode. This is default.
3121 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3123 @item -Wdisabled-optimization
3124 @opindex Wdisabled-optimization
3125 Warn if a requested optimization pass is disabled. This warning does
3126 not generally indicate that there is anything wrong with your code; it
3127 merely indicates that GCC's optimizers were unable to handle the code
3128 effectively. Often, the problem is that your code is too big or too
3129 complex; GCC will refuse to optimize programs when the optimization
3130 itself is likely to take inordinate amounts of time.
3134 Make all warnings into errors.
3137 @node Debugging Options
3138 @section Options for Debugging Your Program or GCC
3139 @cindex options, debugging
3140 @cindex debugging information options
3142 GCC has various special options that are used for debugging
3143 either your program or GCC:
3148 Produce debugging information in the operating system's native format
3149 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3152 On most systems that use stabs format, @option{-g} enables use of extra
3153 debugging information that only GDB can use; this extra information
3154 makes debugging work better in GDB but will probably make other debuggers
3156 refuse to read the program. If you want to control for certain whether
3157 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3158 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3160 GCC allows you to use @option{-g} with
3161 @option{-O}. The shortcuts taken by optimized code may occasionally
3162 produce surprising results: some variables you declared may not exist
3163 at all; flow of control may briefly move where you did not expect it;
3164 some statements may not be executed because they compute constant
3165 results or their values were already at hand; some statements may
3166 execute in different places because they were moved out of loops.
3168 Nevertheless it proves possible to debug optimized output. This makes
3169 it reasonable to use the optimizer for programs that might have bugs.
3171 The following options are useful when GCC is generated with the
3172 capability for more than one debugging format.
3176 Produce debugging information for use by GDB@. This means to use the
3177 most expressive format available (DWARF 2, stabs, or the native format
3178 if neither of those are supported), including GDB extensions if at all
3183 Produce debugging information in stabs format (if that is supported),
3184 without GDB extensions. This is the format used by DBX on most BSD
3185 systems. On MIPS, Alpha and System V Release 4 systems this option
3186 produces stabs debugging output which is not understood by DBX or SDB@.
3187 On System V Release 4 systems this option requires the GNU assembler.
3189 @item -feliminate-unused-debug-symbols
3190 @opindex feliminate-unused-debug-symbols
3191 Produce debugging information in stabs format (if that is supported),
3192 for only symbols that are actually used.
3196 Produce debugging information in stabs format (if that is supported),
3197 using GNU extensions understood only by the GNU debugger (GDB)@. The
3198 use of these extensions is likely to make other debuggers crash or
3199 refuse to read the program.
3203 Produce debugging information in COFF format (if that is supported).
3204 This is the format used by SDB on most System V systems prior to
3209 Produce debugging information in XCOFF format (if that is supported).
3210 This is the format used by the DBX debugger on IBM RS/6000 systems.
3214 Produce debugging information in XCOFF format (if that is supported),
3215 using GNU extensions understood only by the GNU debugger (GDB)@. The
3216 use of these extensions is likely to make other debuggers crash or
3217 refuse to read the program, and may cause assemblers other than the GNU
3218 assembler (GAS) to fail with an error.
3222 Produce debugging information in DWARF version 2 format (if that is
3223 supported). This is the format used by DBX on IRIX 6. With this
3224 option, GCC uses features of DWARF version 3 when they are useful;
3225 version 3 is upward compatible with version 2, but may still cause
3226 problems for older debuggers.
3230 Produce debugging information in VMS debug format (if that is
3231 supported). This is the format used by DEBUG on VMS systems.
3234 @itemx -ggdb@var{level}
3235 @itemx -gstabs@var{level}
3236 @itemx -gcoff@var{level}
3237 @itemx -gxcoff@var{level}
3238 @itemx -gvms@var{level}
3239 Request debugging information and also use @var{level} to specify how
3240 much information. The default level is 2.
3242 Level 1 produces minimal information, enough for making backtraces in
3243 parts of the program that you don't plan to debug. This includes
3244 descriptions of functions and external variables, but no information
3245 about local variables and no line numbers.
3247 Level 3 includes extra information, such as all the macro definitions
3248 present in the program. Some debuggers support macro expansion when
3249 you use @option{-g3}.
3251 @option{-gdwarf-2} does not accept a concatenated debug level, because
3252 GCC used to support an option @option{-gdwarf} that meant to generate
3253 debug information in version 1 of the DWARF format (which is very
3254 different from version 2), and it would have been too confusing. That
3255 debug format is long obsolete, but the option cannot be changed now.
3256 Instead use an additional @option{-g@var{level}} option to change the
3257 debug level for DWARF2.
3259 @item -feliminate-dwarf2-dups
3260 @opindex feliminate-dwarf2-dups
3261 Compress DWARF2 debugging information by eliminating duplicated
3262 information about each symbol. This option only makes sense when
3263 generating DWARF2 debugging information with @option{-gdwarf-2}.
3265 @cindex @command{prof}
3268 Generate extra code to write profile information suitable for the
3269 analysis program @command{prof}. You must use this option when compiling
3270 the source files you want data about, and you must also use it when
3273 @cindex @command{gprof}
3276 Generate extra code to write profile information suitable for the
3277 analysis program @command{gprof}. You must use this option when compiling
3278 the source files you want data about, and you must also use it when
3283 Makes the compiler print out each function name as it is compiled, and
3284 print some statistics about each pass when it finishes.
3287 @opindex ftime-report
3288 Makes the compiler print some statistics about the time consumed by each
3289 pass when it finishes.
3292 @opindex fmem-report
3293 Makes the compiler print some statistics about permanent memory
3294 allocation when it finishes.
3296 @item -fprofile-arcs
3297 @opindex fprofile-arcs
3298 Add code so that program flow @dfn{arcs} are instrumented. During
3299 execution the program records how many times each branch and call is
3300 executed and how many times it is taken or returns. When the compiled
3301 program exits it saves this data to a file called
3302 @file{@var{auxname}.gcda} for each source file. The data may be used for
3303 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3304 test coverage analysis (@option{-ftest-coverage}). Each object file's
3305 @var{auxname} is generated from the name of the output file, if
3306 explicitly specified and it is not the final executable, otherwise it is
3307 the basename of the source file. In both cases any suffix is removed
3308 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3309 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3314 Compile the source files with @option{-fprofile-arcs} plus optimization
3315 and code generation options. For test coverage analysis, use the
3316 additional @option{-ftest-coverage} option. You do not need to profile
3317 every source file in a program.
3320 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3321 (the latter implies the former).
3324 Run the program on a representative workload to generate the arc profile
3325 information. This may be repeated any number of times. You can run
3326 concurrent instances of your program, and provided that the file system
3327 supports locking, the data files will be correctly updated. Also
3328 @code{fork} calls are detected and correctly handled (double counting
3332 For profile-directed optimizations, compile the source files again with
3333 the same optimization and code generation options plus
3334 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3335 Control Optimization}).
3338 For test coverage analysis, use @command{gcov} to produce human readable
3339 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3340 @command{gcov} documentation for further information.
3344 With @option{-fprofile-arcs}, for each function of your program GCC
3345 creates a program flow graph, then finds a spanning tree for the graph.
3346 Only arcs that are not on the spanning tree have to be instrumented: the
3347 compiler adds code to count the number of times that these arcs are
3348 executed. When an arc is the only exit or only entrance to a block, the
3349 instrumentation code can be added to the block; otherwise, a new basic
3350 block must be created to hold the instrumentation code.
3352 @item -ftree-based-profiling
3353 @opindex ftree-based-profiling
3354 This option is used in addition to @option{-fprofile-arcs} or
3355 @option{-fbranch-probabilities} to control whether those optimizations
3356 are performed on a tree-based or rtl-based internal representation.
3357 If you use this option when compiling with @option{-fprofile-arcs},
3358 you must also use it when compiling later with @option{-fbranch-probabilities}.
3359 Currently the tree-based optimization is in an early stage of
3360 development, and this option is recommended only for those people
3361 working on improving it.
3364 @item -ftest-coverage
3365 @opindex ftest-coverage
3366 Produce a notes file that the @command{gcov} code-coverage utility
3367 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3368 show program coverage. Each source file's note file is called
3369 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3370 above for a description of @var{auxname} and instructions on how to
3371 generate test coverage data. Coverage data will match the source files
3372 more closely, if you do not optimize.
3374 @item -d@var{letters}
3375 @item -fdump-rtl-@var{pass}
3377 Says to make debugging dumps during compilation at times specified by
3378 @var{letters}. This is used for debugging the RTL-based passes of the
3379 compiler. The file names for most of the dumps are made by appending a
3380 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3381 from the name of the output file, if explicitly specified and it is not
3382 an executable, otherwise it is the basename of the source file.
3384 Most debug dumps can be enabled either passing a letter to the @option{-d}
3385 option, or with a long @option{-fdump-rtl} switch; here are the possible
3386 letters for use in @var{letters} and @var{pass}, and their meanings:
3391 Annotate the assembler output with miscellaneous debugging information.
3394 @itemx -fdump-rtl-bp
3396 @opindex fdump-rtl-bp
3397 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3400 @itemx -fdump-rtl-bbro
3402 @opindex fdump-rtl-bbro
3403 Dump after block reordering, to @file{@var{file}.30.bbro}.
3406 @itemx -fdump-rtl-combine
3408 @opindex fdump-rtl-combine
3409 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3412 @itemx -fdump-rtl-ce1
3413 @itemx -fdump-rtl-ce2
3415 @opindex fdump-rtl-ce1
3416 @opindex fdump-rtl-ce2
3417 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3418 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3419 and @option{-fdump-rtl-ce2} enable dumping after the second if
3420 conversion, to the file @file{@var{file}.18.ce2}.
3423 @itemx -fdump-rtl-btl
3424 @itemx -fdump-rtl-dbr
3426 @opindex fdump-rtl-btl
3427 @opindex fdump-rtl-dbr
3428 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3429 target load optimization, to to @file{@var{file}.31.btl}. @option{-dd}
3430 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3431 scheduling, to @file{@var{file}.36.dbr}.
3435 Dump all macro definitions, at the end of preprocessing, in addition to
3439 @itemx -fdump-rtl-ce3
3441 @opindex fdump-rtl-ce3
3442 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3445 @itemx -fdump-rtl-cfg
3446 @itemx -fdump-rtl-life
3448 @opindex fdump-rtl-cfg
3449 @opindex fdump-rtl-life
3450 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3451 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3452 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3453 to @file{@var{file}.16.life}.
3456 @itemx -fdump-rtl-greg
3458 @opindex fdump-rtl-greg
3459 Dump after global register allocation, to @file{@var{file}.23.greg}.
3462 @itemx -fdump-rtl-gcse
3463 @itemx -fdump-rtl-bypass
3465 @opindex fdump-rtl-gcse
3466 @opindex fdump-rtl-bypass
3467 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3468 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3469 enable dumping after jump bypassing and control flow optimizations, to
3470 @file{@var{file}.07.bypass}.
3473 @itemx -fdump-rtl-eh
3475 @opindex fdump-rtl-eh
3476 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3479 @itemx -fdump-rtl-sibling
3481 @opindex fdump-rtl-sibling
3482 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3485 @itemx -fdump-rtl-jump
3487 @opindex fdump-rtl-jump
3488 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3491 @itemx -fdump-rtl-stack
3493 @opindex fdump-rtl-stack
3494 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3497 @itemx -fdump-rtl-lreg
3499 @opindex fdump-rtl-lreg
3500 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3503 @itemx -fdump-rtl-loop
3504 @itemx -fdump-rtl-loop2
3506 @opindex fdump-rtl-loop
3507 @opindex fdump-rtl-loop2
3508 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3509 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3510 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3511 @file{@var{file}.13.loop2}.
3514 @itemx -fdump-rtl-sms
3516 @opindex fdump-rtl-sms
3517 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3520 @itemx -fdump-rtl-mach
3522 @opindex fdump-rtl-mach
3523 Dump after performing the machine dependent reorganization pass, to
3524 @file{@var{file}.35.mach}.
3527 @itemx -fdump-rtl-rnreg
3529 @opindex fdump-rtl-rnreg
3530 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3533 @itemx -fdump-rtl-regmove
3535 @opindex fdump-rtl-regmove
3536 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3539 @itemx -fdump-rtl-postreload
3541 @opindex fdump-rtl-postreload
3542 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3545 @itemx -fdump-rtl-expand
3547 @opindex fdump-rtl-expand
3548 Dump after RTL generation, to @file{@var{file}.00.expand}.
3551 @itemx -fdump-rtl-sched2
3553 @opindex fdump-rtl-sched2
3554 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3557 @itemx -fdump-rtl-cse
3559 @opindex fdump-rtl-cse
3560 Dump after CSE (including the jump optimization that sometimes follows
3561 CSE), to @file{@var{file}.04.cse}.
3564 @itemx -fdump-rtl-sched
3566 @opindex fdump-rtl-sched
3567 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3570 @itemx -fdump-rtl-cse2
3572 @opindex fdump-rtl-cse2
3573 Dump after the second CSE pass (including the jump optimization that
3574 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3577 @itemx -fdump-rtl-tracer
3579 @opindex fdump-rtl-tracer
3580 Dump after running tracer, to @file{@var{file}.12.tracer}.
3583 @itemx -fdump-rtl-vpt
3584 @itemx -fdump-rtl-vartrack
3586 @opindex fdump-rtl-vpt
3587 @opindex fdump-rtl-vartrack
3588 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3589 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3590 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3591 to @file{@var{file}.34.vartrack}.
3594 @itemx -fdump-rtl-flow2
3596 @opindex fdump-rtl-flow2
3597 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3600 @itemx -fdump-rtl-peephole2
3602 @opindex fdump-rtl-peephole2
3603 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3606 @itemx -fdump-rtl-web
3608 @opindex fdump-rtl-web
3609 Dump after live range splitting, to @file{@var{file}.14.web}.
3612 @itemx -fdump-rtl-all
3614 @opindex fdump-rtl-all
3615 Produce all the dumps listed above.
3619 Produce a core dump whenever an error occurs.
3623 Print statistics on memory usage, at the end of the run, to
3628 Annotate the assembler output with a comment indicating which
3629 pattern and alternative was used. The length of each instruction is
3634 Dump the RTL in the assembler output as a comment before each instruction.
3635 Also turns on @option{-dp} annotation.
3639 For each of the other indicated dump files (either with @option{-d} or
3640 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3641 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3645 Just generate RTL for a function instead of compiling it. Usually used
3646 with @samp{r} (@option{-fdump-rtl-expand}).
3650 Dump debugging information during parsing, to standard error.
3653 @item -fdump-unnumbered
3654 @opindex fdump-unnumbered
3655 When doing debugging dumps (see @option{-d} option above), suppress instruction
3656 numbers and line number note output. This makes it more feasible to
3657 use diff on debugging dumps for compiler invocations with different
3658 options, in particular with and without @option{-g}.
3660 @item -fdump-translation-unit @r{(C and C++ only)}
3661 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3662 @opindex fdump-translation-unit
3663 Dump a representation of the tree structure for the entire translation
3664 unit to a file. The file name is made by appending @file{.tu} to the
3665 source file name. If the @samp{-@var{options}} form is used, @var{options}
3666 controls the details of the dump as described for the
3667 @option{-fdump-tree} options.
3669 @item -fdump-class-hierarchy @r{(C++ only)}
3670 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3671 @opindex fdump-class-hierarchy
3672 Dump a representation of each class's hierarchy and virtual function
3673 table layout to a file. The file name is made by appending @file{.class}
3674 to the source file name. If the @samp{-@var{options}} form is used,
3675 @var{options} controls the details of the dump as described for the
3676 @option{-fdump-tree} options.
3678 @item -fdump-ipa-@var{switch}
3680 Control the dumping at various stages of inter-procedural analysis
3681 language tree to a file. The file name is generated by appending a switch
3682 specific suffix to the source file name. The following dumps are possible:
3686 Enables all inter-procedural analysis dumps; currently the only produced
3687 dump is the @samp{cgraph} dump.
3690 Dumps information about call-graph optimization, unused function removal,
3691 and inlining decisions.
3694 @item -fdump-tree-@var{switch} @r{(C and C++ only)}
3695 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C and C++ only)}
3697 Control the dumping at various stages of processing the intermediate
3698 language tree to a file. The file name is generated by appending a switch
3699 specific suffix to the source file name. If the @samp{-@var{options}}
3700 form is used, @var{options} is a list of @samp{-} separated options that
3701 control the details of the dump. Not all options are applicable to all
3702 dumps, those which are not meaningful will be ignored. The following
3703 options are available
3707 Print the address of each node. Usually this is not meaningful as it
3708 changes according to the environment and source file. Its primary use
3709 is for tying up a dump file with a debug environment.
3711 Inhibit dumping of members of a scope or body of a function merely
3712 because that scope has been reached. Only dump such items when they
3713 are directly reachable by some other path. When dumping pretty-printed
3714 trees, this option inhibits dumping the bodies of control structures.
3716 Print a raw representation of the tree. By default, trees are
3717 pretty-printed into a C-like representation.
3719 Enable more detailed dumps (not honored by every dump option).
3721 Enable dumping various statistics about the pass (not honored by every dump
3724 Enable showing basic block boundaries (disabled in raw dumps).
3726 Enable showing virtual operands for every statement.
3728 Enable showing line numbers for statements.
3730 Enable showing the unique ID (@code{DECL_UID}) for each variable.
3732 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
3735 The following tree dumps are possible:
3739 Dump before any tree based optimization, to @file{@var{file}.original}.
3742 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3745 Dump after function inlining, to @file{@var{file}.inlined}.
3748 @opindex fdump-tree-gimple
3749 Dump each function before and after the gimplification pass to a file. The
3750 file name is made by appending @file{.gimple} to the source file name.
3753 @opindex fdump-tree-cfg
3754 Dump the control flow graph of each function to a file. The file name is
3755 made by appending @file{.cfg} to the source file name.
3758 @opindex fdump-tree-vcg
3759 Dump the control flow graph of each function to a file in VCG format. The
3760 file name is made by appending @file{.vcg} to the source file name. Note
3761 that if the file contains more than one function, the generated file cannot
3762 be used directly by VCG. You will need to cut and paste each function's
3763 graph into its own separate file first.
3766 @opindex fdump-tree-ch
3767 Dump each function after copying loop headers. The file name is made by
3768 appending @file{.ch} to the source file name.
3771 @opindex fdump-tree-ssa
3772 Dump SSA related information to a file. The file name is made by appending
3773 @file{.ssa} to the source file name.
3776 @opindex fdump-tree-alias
3777 Dump aliasing information for each function. The file name is made by
3778 appending @file{.alias} to the source file name.
3781 @opindex fdump-tree-ccp
3782 Dump each function after CCP. The file name is made by appending
3783 @file{.ccp} to the source file name.
3786 @opindex fdump-tree-pre
3787 Dump trees after partial redundancy elimination. The file name is made
3788 by appending @file{.pre} to the source file name.
3791 @opindex fdump-tree-fre
3792 Dump trees after full redundancy elimination. The file name is made
3793 by appending @file{.fre} to the source file name.
3796 @opindex fdump-tree-dce
3797 Dump each function after dead code elimination. The file name is made by
3798 appending @file{.dce} to the source file name.
3801 @opindex fdump-tree-mudflap
3802 Dump each function after adding mudflap instrumentation. The file name is
3803 made by appending @file{.mudflap} to the source file name.
3806 @opindex fdump-tree-sra
3807 Dump each function after performing scalar replacement of aggregates. The
3808 file name is made by appending @file{.sra} to the source file name.
3811 @opindex fdump-tree-dom
3812 Dump each function after applying dominator tree optimizations. The file
3813 name is made by appending @file{.dom} to the source file name.
3816 @opindex fdump-tree-dse
3817 Dump each function after applying dead store elimination. The file
3818 name is made by appending @file{.dse} to the source file name.
3821 @opindex fdump-tree-phiopt
3822 Dump each function after optimizing PHI nodes into straightline code. The file
3823 name is made by appending @file{.phiopt} to the source file name.
3826 @opindex fdump-tree-forwprop
3827 Dump each function after forward propagating single use variables. The file
3828 name is made by appending @file{.forwprop} to the source file name.
3831 @opindex fdump-tree-copyrename
3832 Dump each function after applying the copy rename optimization. The file
3833 name is made by appending @file{.copyrename} to the source file name.
3836 @opindex fdump-tree-nrv
3837 Dump each function after applying the named return value optimization on
3838 generic trees. The file name is made by appending @file{.nrv} to the source
3842 @opindex fdump-tree-vect
3843 Dump each function after applying vectorization of loops. The file name is
3844 made by appending @file{.vect} to the source file name.
3847 @opindex fdump-tree-all
3848 Enable all the available tree dumps with the flags provided in this option.
3851 @item -frandom-seed=@var{string}
3852 @opindex frandom-string
3853 This option provides a seed that GCC uses when it would otherwise use
3854 random numbers. It is used to generate certain symbol names
3855 that have to be different in every compiled file. It is also used to
3856 place unique stamps in coverage data files and the object files that
3857 produce them. You can use the @option{-frandom-seed} option to produce
3858 reproducibly identical object files.
3860 The @var{string} should be different for every file you compile.
3862 @item -fsched-verbose=@var{n}
3863 @opindex fsched-verbose
3864 On targets that use instruction scheduling, this option controls the
3865 amount of debugging output the scheduler prints. This information is
3866 written to standard error, unless @option{-dS} or @option{-dR} is
3867 specified, in which case it is output to the usual dump
3868 listing file, @file{.sched} or @file{.sched2} respectively. However
3869 for @var{n} greater than nine, the output is always printed to standard
3872 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3873 same information as @option{-dRS}. For @var{n} greater than one, it
3874 also output basic block probabilities, detailed ready list information
3875 and unit/insn info. For @var{n} greater than two, it includes RTL
3876 at abort point, control-flow and regions info. And for @var{n} over
3877 four, @option{-fsched-verbose} also includes dependence info.
3881 Store the usual ``temporary'' intermediate files permanently; place them
3882 in the current directory and name them based on the source file. Thus,
3883 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3884 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3885 preprocessed @file{foo.i} output file even though the compiler now
3886 normally uses an integrated preprocessor.
3890 Report the CPU time taken by each subprocess in the compilation
3891 sequence. For C source files, this is the compiler proper and assembler
3892 (plus the linker if linking is done). The output looks like this:
3899 The first number on each line is the ``user time'', that is time spent
3900 executing the program itself. The second number is ``system time'',
3901 time spent executing operating system routines on behalf of the program.
3902 Both numbers are in seconds.
3904 @item -fvar-tracking
3905 @opindex fvar-tracking
3906 Run variable tracking pass. It computes where variables are stored at each
3907 position in code. Better debugging information is then generated
3908 (if the debugging information format supports this information).
3910 It is enabled by default when compiling with optimization (@option{-Os},
3911 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
3912 the debug info format supports it.
3914 @item -print-file-name=@var{library}
3915 @opindex print-file-name
3916 Print the full absolute name of the library file @var{library} that
3917 would be used when linking---and don't do anything else. With this
3918 option, GCC does not compile or link anything; it just prints the
3921 @item -print-multi-directory
3922 @opindex print-multi-directory
3923 Print the directory name corresponding to the multilib selected by any
3924 other switches present in the command line. This directory is supposed
3925 to exist in @env{GCC_EXEC_PREFIX}.
3927 @item -print-multi-lib
3928 @opindex print-multi-lib
3929 Print the mapping from multilib directory names to compiler switches
3930 that enable them. The directory name is separated from the switches by
3931 @samp{;}, and each switch starts with an @samp{@@} instead of the
3932 @samp{-}, without spaces between multiple switches. This is supposed to
3933 ease shell-processing.
3935 @item -print-prog-name=@var{program}
3936 @opindex print-prog-name
3937 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3939 @item -print-libgcc-file-name
3940 @opindex print-libgcc-file-name
3941 Same as @option{-print-file-name=libgcc.a}.
3943 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3944 but you do want to link with @file{libgcc.a}. You can do
3947 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3950 @item -print-search-dirs
3951 @opindex print-search-dirs
3952 Print the name of the configured installation directory and a list of
3953 program and library directories @command{gcc} will search---and don't do anything else.
3955 This is useful when @command{gcc} prints the error message
3956 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3957 To resolve this you either need to put @file{cpp0} and the other compiler
3958 components where @command{gcc} expects to find them, or you can set the environment
3959 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3960 Don't forget the trailing '/'.
3961 @xref{Environment Variables}.
3964 @opindex dumpmachine
3965 Print the compiler's target machine (for example,
3966 @samp{i686-pc-linux-gnu})---and don't do anything else.
3969 @opindex dumpversion
3970 Print the compiler version (for example, @samp{3.0})---and don't do
3975 Print the compiler's built-in specs---and don't do anything else. (This
3976 is used when GCC itself is being built.) @xref{Spec Files}.
3978 @item -feliminate-unused-debug-types
3979 @opindex feliminate-unused-debug-types
3980 Normally, when producing DWARF2 output, GCC will emit debugging
3981 information for all types declared in a compilation
3982 unit, regardless of whether or not they are actually used
3983 in that compilation unit. Sometimes this is useful, such as
3984 if, in the debugger, you want to cast a value to a type that is
3985 not actually used in your program (but is declared). More often,
3986 however, this results in a significant amount of wasted space.
3987 With this option, GCC will avoid producing debug symbol output
3988 for types that are nowhere used in the source file being compiled.
3991 @node Optimize Options
3992 @section Options That Control Optimization
3993 @cindex optimize options
3994 @cindex options, optimization
3996 These options control various sorts of optimizations.
3998 Without any optimization option, the compiler's goal is to reduce the
3999 cost of compilation and to make debugging produce the expected
4000 results. Statements are independent: if you stop the program with a
4001 breakpoint between statements, you can then assign a new value to any
4002 variable or change the program counter to any other statement in the
4003 function and get exactly the results you would expect from the source
4006 Turning on optimization flags makes the compiler attempt to improve
4007 the performance and/or code size at the expense of compilation time
4008 and possibly the ability to debug the program.
4010 The compiler performs optimization based on the knowledge it has of
4011 the program. Optimization levels @option{-O2} and above, in
4012 particular, enable @emph{unit-at-a-time} mode, which allows the
4013 compiler to consider information gained from later functions in
4014 the file when compiling a function. Compiling multiple files at
4015 once to a single output file in @emph{unit-at-a-time} mode allows
4016 the compiler to use information gained from all of the files when
4017 compiling each of them.
4019 Not all optimizations are controlled directly by a flag. Only
4020 optimizations that have a flag are listed.
4027 Optimize. Optimizing compilation takes somewhat more time, and a lot
4028 more memory for a large function.
4030 With @option{-O}, the compiler tries to reduce code size and execution
4031 time, without performing any optimizations that take a great deal of
4034 @option{-O} turns on the following optimization flags:
4035 @gccoptlist{-fdefer-pop @gol
4036 -fmerge-constants @gol
4038 -floop-optimize @gol
4039 -fif-conversion @gol
4040 -fif-conversion2 @gol
4041 -fdelayed-branch @gol
4042 -fguess-branch-probability @gol
4045 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4046 where doing so does not interfere with debugging.
4050 Optimize even more. GCC performs nearly all supported optimizations
4051 that do not involve a space-speed tradeoff. The compiler does not
4052 perform loop unrolling or function inlining when you specify @option{-O2}.
4053 As compared to @option{-O}, this option increases both compilation time
4054 and the performance of the generated code.
4056 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4057 also turns on the following optimization flags:
4058 @gccoptlist{-fforce-mem @gol
4059 -foptimize-sibling-calls @gol
4060 -fstrength-reduce @gol
4061 -fcse-follow-jumps -fcse-skip-blocks @gol
4062 -frerun-cse-after-loop -frerun-loop-opt @gol
4063 -fgcse -fgcse-lm -fgcse-sm -fgcse-las @gol
4064 -fdelete-null-pointer-checks @gol
4065 -fexpensive-optimizations @gol
4067 -fschedule-insns -fschedule-insns2 @gol
4068 -fsched-interblock -fsched-spec @gol
4071 -freorder-blocks -freorder-functions @gol
4072 -fstrict-aliasing @gol
4073 -funit-at-a-time @gol
4074 -falign-functions -falign-jumps @gol
4075 -falign-loops -falign-labels @gol
4078 Please note the warning under @option{-fgcse} about
4079 invoking @option{-O2} on programs that use computed gotos.
4083 Optimize yet more. @option{-O3} turns on all optimizations specified by
4084 @option{-O2} and also turns on the @option{-finline-functions},
4085 @option{-fweb} and @option{-fgcse-after-reload} options.
4089 Do not optimize. This is the default.
4093 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4094 do not typically increase code size. It also performs further
4095 optimizations designed to reduce code size.
4097 @option{-Os} disables the following optimization flags:
4098 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4099 -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays}
4101 If you use multiple @option{-O} options, with or without level numbers,
4102 the last such option is the one that is effective.
4105 Options of the form @option{-f@var{flag}} specify machine-independent
4106 flags. Most flags have both positive and negative forms; the negative
4107 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4108 below, only one of the forms is listed---the one you typically will
4109 use. You can figure out the other form by either removing @samp{no-}
4112 The following options control specific optimizations. They are either
4113 activated by @option{-O} options or are related to ones that are. You
4114 can use the following flags in the rare cases when ``fine-tuning'' of
4115 optimizations to be performed is desired.
4118 @item -fno-default-inline
4119 @opindex fno-default-inline
4120 Do not make member functions inline by default merely because they are
4121 defined inside the class scope (C++ only). Otherwise, when you specify
4122 @w{@option{-O}}, member functions defined inside class scope are compiled
4123 inline by default; i.e., you don't need to add @samp{inline} in front of
4124 the member function name.
4126 @item -fno-defer-pop
4127 @opindex fno-defer-pop
4128 Always pop the arguments to each function call as soon as that function
4129 returns. For machines which must pop arguments after a function call,
4130 the compiler normally lets arguments accumulate on the stack for several
4131 function calls and pops them all at once.
4133 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4137 Force memory operands to be copied into registers before doing
4138 arithmetic on them. This produces better code by making all memory
4139 references potential common subexpressions. When they are not common
4140 subexpressions, instruction combination should eliminate the separate
4143 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4146 @opindex fforce-addr
4147 Force memory address constants to be copied into registers before
4148 doing arithmetic on them. This may produce better code just as
4149 @option{-fforce-mem} may.
4151 @item -fomit-frame-pointer
4152 @opindex fomit-frame-pointer
4153 Don't keep the frame pointer in a register for functions that
4154 don't need one. This avoids the instructions to save, set up and
4155 restore frame pointers; it also makes an extra register available
4156 in many functions. @strong{It also makes debugging impossible on
4159 On some machines, such as the VAX, this flag has no effect, because
4160 the standard calling sequence automatically handles the frame pointer
4161 and nothing is saved by pretending it doesn't exist. The
4162 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4163 whether a target machine supports this flag. @xref{Registers,,Register
4164 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4166 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4168 @item -foptimize-sibling-calls
4169 @opindex foptimize-sibling-calls
4170 Optimize sibling and tail recursive calls.
4172 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4176 Don't pay attention to the @code{inline} keyword. Normally this option
4177 is used to keep the compiler from expanding any functions inline.
4178 Note that if you are not optimizing, no functions can be expanded inline.
4180 @item -finline-functions
4181 @opindex finline-functions
4182 Integrate all simple functions into their callers. The compiler
4183 heuristically decides which functions are simple enough to be worth
4184 integrating in this way.
4186 If all calls to a given function are integrated, and the function is
4187 declared @code{static}, then the function is normally not output as
4188 assembler code in its own right.
4190 Enabled at level @option{-O3}.
4192 @item -finline-limit=@var{n}
4193 @opindex finline-limit
4194 By default, GCC limits the size of functions that can be inlined. This flag
4195 allows the control of this limit for functions that are explicitly marked as
4196 inline (i.e., marked with the inline keyword or defined within the class
4197 definition in c++). @var{n} is the size of functions that can be inlined in
4198 number of pseudo instructions (not counting parameter handling). The default
4199 value of @var{n} is 600.
4200 Increasing this value can result in more inlined code at
4201 the cost of compilation time and memory consumption. Decreasing usually makes
4202 the compilation faster and less code will be inlined (which presumably
4203 means slower programs). This option is particularly useful for programs that
4204 use inlining heavily such as those based on recursive templates with C++.
4206 Inlining is actually controlled by a number of parameters, which may be
4207 specified individually by using @option{--param @var{name}=@var{value}}.
4208 The @option{-finline-limit=@var{n}} option sets some of these parameters
4212 @item max-inline-insns-single
4213 is set to @var{n}/2.
4214 @item max-inline-insns-auto
4215 is set to @var{n}/2.
4216 @item min-inline-insns
4217 is set to 130 or @var{n}/4, whichever is smaller.
4218 @item max-inline-insns-rtl
4222 See below for a documentation of the individual
4223 parameters controlling inlining.
4225 @emph{Note:} pseudo instruction represents, in this particular context, an
4226 abstract measurement of function's size. In no way, it represents a count
4227 of assembly instructions and as such its exact meaning might change from one
4228 release to an another.
4230 @item -fkeep-inline-functions
4231 @opindex fkeep-inline-functions
4232 In C, emit @code{static} functions that are declared @code{inline}
4233 into the object file, even if the function has been inlined into all
4234 of its callers. This switch does not affect functions using the
4235 @code{extern inline} extension in GNU C. In C++, emit any and all
4236 inline functions into the object file.
4238 @item -fkeep-static-consts
4239 @opindex fkeep-static-consts
4240 Emit variables declared @code{static const} when optimization isn't turned
4241 on, even if the variables aren't referenced.
4243 GCC enables this option by default. If you want to force the compiler to
4244 check if the variable was referenced, regardless of whether or not
4245 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4247 @item -fmerge-constants
4248 Attempt to merge identical constants (string constants and floating point
4249 constants) across compilation units.
4251 This option is the default for optimized compilation if the assembler and
4252 linker support it. Use @option{-fno-merge-constants} to inhibit this
4255 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4257 @item -fmerge-all-constants
4258 Attempt to merge identical constants and identical variables.
4260 This option implies @option{-fmerge-constants}. In addition to
4261 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4262 arrays or initialized constant variables with integral or floating point
4263 types. Languages like C or C++ require each non-automatic variable to
4264 have distinct location, so using this option will result in non-conforming
4267 @item -fmodulo-sched
4268 @opindex fmodulo-sched
4269 Perform swing modulo scheduling immediately before the first scheduling
4270 pass. This pass looks at innermost loops and reorders their
4271 instructions by overlapping different iterations.
4275 Use a graph coloring register allocator. Currently this option is meant
4276 only for testing. Users should not specify this option, since it is not
4277 yet ready for production use.
4279 @item -fno-branch-count-reg
4280 @opindex fno-branch-count-reg
4281 Do not use ``decrement and branch'' instructions on a count register,
4282 but instead generate a sequence of instructions that decrement a
4283 register, compare it against zero, then branch based upon the result.
4284 This option is only meaningful on architectures that support such
4285 instructions, which include x86, PowerPC, IA-64 and S/390.
4287 The default is @option{-fbranch-count-reg}, enabled when
4288 @option{-fstrength-reduce} is enabled.
4290 @item -fno-function-cse
4291 @opindex fno-function-cse
4292 Do not put function addresses in registers; make each instruction that
4293 calls a constant function contain the function's address explicitly.
4295 This option results in less efficient code, but some strange hacks
4296 that alter the assembler output may be confused by the optimizations
4297 performed when this option is not used.
4299 The default is @option{-ffunction-cse}
4301 @item -fno-zero-initialized-in-bss
4302 @opindex fno-zero-initialized-in-bss
4303 If the target supports a BSS section, GCC by default puts variables that
4304 are initialized to zero into BSS@. This can save space in the resulting
4307 This option turns off this behavior because some programs explicitly
4308 rely on variables going to the data section. E.g., so that the
4309 resulting executable can find the beginning of that section and/or make
4310 assumptions based on that.
4312 The default is @option{-fzero-initialized-in-bss}.
4314 @item -fbounds-check
4315 @opindex fbounds-check
4316 For front-ends that support it, generate additional code to check that
4317 indices used to access arrays are within the declared range. This is
4318 currently only supported by the Java and Fortran front-ends, where
4319 this option defaults to true and false respectively.
4321 @item -fmudflap -fmudflapth -fmudflapir
4325 @cindex bounds checking
4327 For front-ends that support it (C and C++), instrument all risky
4328 pointer/array dereferencing operations, some standard library
4329 string/heap functions, and some other associated constructs with
4330 range/validity tests. Modules so instrumented should be immune to
4331 buffer overflows, invalid heap use, and some other classes of C/C++
4332 programming errors. The instrumentation relies on a separate runtime
4333 library (@file{libmudflap}), which will be linked into a program if
4334 @option{-fmudflap} is given at link time. Run-time behavior of the
4335 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4336 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4339 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4340 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4341 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4342 instrumentation should ignore pointer reads. This produces less
4343 instrumentation (and therefore faster execution) and still provides
4344 some protection against outright memory corrupting writes, but allows
4345 erroneously read data to propagate within a program.
4347 @item -fstrength-reduce
4348 @opindex fstrength-reduce
4349 Perform the optimizations of loop strength reduction and
4350 elimination of iteration variables.
4352 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4354 @item -fthread-jumps
4355 @opindex fthread-jumps
4356 Perform optimizations where we check to see if a jump branches to a
4357 location where another comparison subsumed by the first is found. If
4358 so, the first branch is redirected to either the destination of the
4359 second branch or a point immediately following it, depending on whether
4360 the condition is known to be true or false.
4362 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4364 @item -fcse-follow-jumps
4365 @opindex fcse-follow-jumps
4366 In common subexpression elimination, scan through jump instructions
4367 when the target of the jump is not reached by any other path. For
4368 example, when CSE encounters an @code{if} statement with an
4369 @code{else} clause, CSE will follow the jump when the condition
4372 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4374 @item -fcse-skip-blocks
4375 @opindex fcse-skip-blocks
4376 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4377 follow jumps which conditionally skip over blocks. When CSE
4378 encounters a simple @code{if} statement with no else clause,
4379 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4380 body of the @code{if}.
4382 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4384 @item -frerun-cse-after-loop
4385 @opindex frerun-cse-after-loop
4386 Re-run common subexpression elimination after loop optimizations has been
4389 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4391 @item -frerun-loop-opt
4392 @opindex frerun-loop-opt
4393 Run the loop optimizer twice.
4395 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4399 Perform a global common subexpression elimination pass.
4400 This pass also performs global constant and copy propagation.
4402 @emph{Note:} When compiling a program using computed gotos, a GCC
4403 extension, you may get better runtime performance if you disable
4404 the global common subexpression elimination pass by adding
4405 @option{-fno-gcse} to the command line.
4407 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4411 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4412 attempt to move loads which are only killed by stores into themselves. This
4413 allows a loop containing a load/store sequence to be changed to a load outside
4414 the loop, and a copy/store within the loop.
4416 Enabled by default when gcse is enabled.
4420 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4421 global common subexpression elimination. This pass will attempt to move
4422 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4423 loops containing a load/store sequence can be changed to a load before
4424 the loop and a store after the loop.
4426 Enabled by default when gcse is enabled.
4430 When @option{-fgcse-las} is enabled, the global common subexpression
4431 elimination pass eliminates redundant loads that come after stores to the
4432 same memory location (both partial and full redundancies).
4434 Enabled by default when gcse is enabled.
4436 @item -fgcse-after-reload
4437 @opindex fgcse-after-reload
4438 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4439 pass is performed after reload. The purpose of this pass is to cleanup
4442 @item -floop-optimize
4443 @opindex floop-optimize
4444 Perform loop optimizations: move constant expressions out of loops, simplify
4445 exit test conditions and optionally do strength-reduction as well.
4447 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4449 @item -floop-optimize2
4450 @opindex floop-optimize2
4451 Perform loop optimizations using the new loop optimizer. The optimizations
4452 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4455 @item -fcrossjumping
4456 @opindex crossjumping
4457 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4458 resulting code may or may not perform better than without cross-jumping.
4460 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4462 @item -fif-conversion
4463 @opindex if-conversion
4464 Attempt to transform conditional jumps into branch-less equivalents. This
4465 include use of conditional moves, min, max, set flags and abs instructions, and
4466 some tricks doable by standard arithmetics. The use of conditional execution
4467 on chips where it is available is controlled by @code{if-conversion2}.
4469 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4471 @item -fif-conversion2
4472 @opindex if-conversion2
4473 Use conditional execution (where available) to transform conditional jumps into
4474 branch-less equivalents.
4476 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4478 @item -fdelete-null-pointer-checks
4479 @opindex fdelete-null-pointer-checks
4480 Use global dataflow analysis to identify and eliminate useless checks
4481 for null pointers. The compiler assumes that dereferencing a null
4482 pointer would have halted the program. If a pointer is checked after
4483 it has already been dereferenced, it cannot be null.
4485 In some environments, this assumption is not true, and programs can
4486 safely dereference null pointers. Use
4487 @option{-fno-delete-null-pointer-checks} to disable this optimization
4488 for programs which depend on that behavior.
4490 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4492 @item -fexpensive-optimizations
4493 @opindex fexpensive-optimizations
4494 Perform a number of minor optimizations that are relatively expensive.
4496 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4498 @item -foptimize-register-move
4500 @opindex foptimize-register-move
4502 Attempt to reassign register numbers in move instructions and as
4503 operands of other simple instructions in order to maximize the amount of
4504 register tying. This is especially helpful on machines with two-operand
4507 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4510 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4512 @item -fdelayed-branch
4513 @opindex fdelayed-branch
4514 If supported for the target machine, attempt to reorder instructions
4515 to exploit instruction slots available after delayed branch
4518 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4520 @item -fschedule-insns
4521 @opindex fschedule-insns
4522 If supported for the target machine, attempt to reorder instructions to
4523 eliminate execution stalls due to required data being unavailable. This
4524 helps machines that have slow floating point or memory load instructions
4525 by allowing other instructions to be issued until the result of the load
4526 or floating point instruction is required.
4528 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4530 @item -fschedule-insns2
4531 @opindex fschedule-insns2
4532 Similar to @option{-fschedule-insns}, but requests an additional pass of
4533 instruction scheduling after register allocation has been done. This is
4534 especially useful on machines with a relatively small number of
4535 registers and where memory load instructions take more than one cycle.
4537 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4539 @item -fno-sched-interblock
4540 @opindex fno-sched-interblock
4541 Don't schedule instructions across basic blocks. This is normally
4542 enabled by default when scheduling before register allocation, i.e.@:
4543 with @option{-fschedule-insns} or at @option{-O2} or higher.
4545 @item -fno-sched-spec
4546 @opindex fno-sched-spec
4547 Don't allow speculative motion of non-load instructions. This is normally
4548 enabled by default when scheduling before register allocation, i.e.@:
4549 with @option{-fschedule-insns} or at @option{-O2} or higher.
4551 @item -fsched-spec-load
4552 @opindex fsched-spec-load
4553 Allow speculative motion of some load instructions. This only makes
4554 sense when scheduling before register allocation, i.e.@: with
4555 @option{-fschedule-insns} or at @option{-O2} or higher.
4557 @item -fsched-spec-load-dangerous
4558 @opindex fsched-spec-load-dangerous
4559 Allow speculative motion of more load instructions. This only makes
4560 sense when scheduling before register allocation, i.e.@: with
4561 @option{-fschedule-insns} or at @option{-O2} or higher.
4563 @item -fsched-stalled-insns=@var{n}
4564 @opindex fsched-stalled-insns
4565 Define how many insns (if any) can be moved prematurely from the queue
4566 of stalled insns into the ready list, during the second scheduling pass.
4568 @item -fsched-stalled-insns-dep=@var{n}
4569 @opindex fsched-stalled-insns-dep
4570 Define how many insn groups (cycles) will be examined for a dependency
4571 on a stalled insn that is candidate for premature removal from the queue
4572 of stalled insns. Has an effect only during the second scheduling pass,
4573 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4575 @item -fsched2-use-superblocks
4576 @opindex fsched2-use-superblocks
4577 When scheduling after register allocation, do use superblock scheduling
4578 algorithm. Superblock scheduling allows motion across basic block boundaries
4579 resulting on faster schedules. This option is experimental, as not all machine
4580 descriptions used by GCC model the CPU closely enough to avoid unreliable
4581 results from the algorithm.
4583 This only makes sense when scheduling after register allocation, i.e.@: with
4584 @option{-fschedule-insns2} or at @option{-O2} or higher.
4586 @item -fsched2-use-traces
4587 @opindex fsched2-use-traces
4588 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4589 allocation and additionally perform code duplication in order to increase the
4590 size of superblocks using tracer pass. See @option{-ftracer} for details on
4593 This mode should produce faster but significantly longer programs. Also
4594 without @option{-fbranch-probabilities} the traces constructed may not
4595 match the reality and hurt the performance. This only makes
4596 sense when scheduling after register allocation, i.e.@: with
4597 @option{-fschedule-insns2} or at @option{-O2} or higher.
4599 @item -freschedule-modulo-scheduled-loops
4600 @opindex fscheduling-in-modulo-scheduled-loops
4601 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4602 we may want to prevent the later scheduling passes from changing its schedule, we use this
4603 option to control that.
4605 @item -fcaller-saves
4606 @opindex fcaller-saves
4607 Enable values to be allocated in registers that will be clobbered by
4608 function calls, by emitting extra instructions to save and restore the
4609 registers around such calls. Such allocation is done only when it
4610 seems to result in better code than would otherwise be produced.
4612 This option is always enabled by default on certain machines, usually
4613 those which have no call-preserved registers to use instead.
4615 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4618 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4619 enabled by default at @option{-O} and higher.
4622 Perform Full Redundancy Elimination (FRE) on trees. The difference
4623 between FRE and PRE is that FRE only considers expressions
4624 that are computed on all paths leading to the redundant computation.
4625 This analysis faster than PRE, though it exposes fewer redundancies.
4626 This flag is enabled by default at @option{-O} and higher.
4629 Perform sparse conditional constant propagation (CCP) on trees. This flag
4630 is enabled by default at @option{-O} and higher.
4633 Perform dead code elimination (DCE) on trees. This flag is enabled by
4634 default at @option{-O} and higher.
4636 @item -ftree-dominator-opts
4637 Perform dead code elimination (DCE) on trees. This flag is enabled by
4638 default at @option{-O} and higher.
4641 Perform loop header copying on trees. This is beneficial since it increases
4642 effectiveness of code motion optimizations. It also saves one jump. This flag
4643 is enabled by default at @option{-O} and higher. It is not enabled
4644 for @option{-Os}, since it usually increases code size.
4646 @item -ftree-loop-optimize
4647 Perform loop optimizations on trees. This flag is enabled by default
4648 at @option{-O} and higher.
4650 @item -ftree-loop-linear
4651 Perform linear loop transformations on tree. This flag can improve cache
4652 performance and allow further loop optimizations to take place.
4655 Perform loop invariant motion on trees. This pass moves only invartiants that
4656 would be hard to handle on rtl level (function calls, operations that expand to
4657 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
4658 operands of conditions that are invariant out of the loop, so that we can use
4659 just trivial invariantness analysis in loop unswitching. The pass also includes
4663 Create a canonical counter for number of iterations in the loop for that
4664 determining number of iterations requires complicated analysis. Later
4665 optimizations then may determine the number easily. Useful especially
4666 in connection with unrolling.
4669 Perform induction variable optimizations (strength reduction, induction
4670 variable merging and induction variable elimination) on trees.
4673 Perform scalar replacement of aggregates. This pass replaces structure
4674 references with scalars to prevent committing structures to memory too
4675 early. This flag is enabled by default at @option{-O} and higher.
4677 @item -ftree-copyrename
4678 Perform copy renaming on trees. This pass attempts to rename compiler
4679 temporaries to other variables at copy locations, usually resulting in
4680 variable names which more closely resemble the original variables. This flag
4681 is enabled by default at @option{-O} and higher.
4684 Perform temporary expression replacement during the SSA->normal phase. Single
4685 use/single def temporaries are replaced at their use location with their
4686 defining expression. This results in non-GIMPLE code, but gives the expanders
4687 much more complex trees to work on resulting in better RTL generation. This is
4688 enabled by default at @option{-O} and higher.
4691 Perform live range splitting during the SSA->normal phase. Distinct live
4692 ranges of a variable are split into unique variables, allowing for better
4693 optimization later. This is enabled by default at @option{-O} and higher.
4695 @item -ftree-vectorize
4696 Perform loop vectorization on trees.
4700 Perform tail duplication to enlarge superblock size. This transformation
4701 simplifies the control flow of the function allowing other optimizations to do
4704 @item -funroll-loops
4705 @opindex funroll-loops
4706 Unroll loops whose number of iterations can be determined at compile
4707 time or upon entry to the loop. @option{-funroll-loops} implies both
4708 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4709 option makes code larger, and may or may not make it run faster.
4711 @item -funroll-all-loops
4712 @opindex funroll-all-loops
4713 Unroll all loops, even if their number of iterations is uncertain when
4714 the loop is entered. This usually makes programs run more slowly.
4715 @option{-funroll-all-loops} implies the same options as
4716 @option{-funroll-loops},
4718 @item -fsplit-ivs-in-unroller
4719 @opindex -fsplit-ivs-in-unroller
4720 Enables expressing of values of induction variables in later iterations
4721 of the unrolled loop using the value in the first iteration. This breaks
4722 long dependency chains, thus improving efficiency of the scheduling passes
4723 (for best results, @option{-fweb} should be used as well).
4725 Combination of @option{-fweb} and CSE is often sufficient to obtain the
4726 same effect. However in cases the loop body is more complicated than
4727 a single basic block, this is not reliable. It also does not work at all
4728 on some of the architectures due to restrictions in the CSE pass.
4730 This optimization is enabled by default.
4732 @item -fvariable-expansion-in-unroller
4733 @opindex -fvariable-expansion-in-unroller
4734 With this option, the compiler will create multiple copies of some
4735 local variables when unrolling a loop which can result in superior code.
4737 @item -fprefetch-loop-arrays
4738 @opindex fprefetch-loop-arrays
4739 If supported by the target machine, generate instructions to prefetch
4740 memory to improve the performance of loops that access large arrays.
4742 These options may generate better or worse code; results are highly
4743 dependent on the structure of loops within the source code.
4746 @itemx -fno-peephole2
4747 @opindex fno-peephole
4748 @opindex fno-peephole2
4749 Disable any machine-specific peephole optimizations. The difference
4750 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4751 are implemented in the compiler; some targets use one, some use the
4752 other, a few use both.
4754 @option{-fpeephole} is enabled by default.
4755 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4757 @item -fno-guess-branch-probability
4758 @opindex fno-guess-branch-probability
4759 Do not guess branch probabilities using a randomized model.
4761 Sometimes GCC will opt to use a randomized model to guess branch
4762 probabilities, when none are available from either profiling feedback
4763 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4764 different runs of the compiler on the same program may produce different
4767 In a hard real-time system, people don't want different runs of the
4768 compiler to produce code that has different behavior; minimizing
4769 non-determinism is of paramount import. This switch allows users to
4770 reduce non-determinism, possibly at the expense of inferior
4773 The default is @option{-fguess-branch-probability} at levels
4774 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4776 @item -freorder-blocks
4777 @opindex freorder-blocks
4778 Reorder basic blocks in the compiled function in order to reduce number of
4779 taken branches and improve code locality.
4781 Enabled at levels @option{-O2}, @option{-O3}.
4783 @item -freorder-blocks-and-partition
4784 @opindex freorder-blocks-and-partition
4785 In addition to reordering basic blocks in the compiled function, in order
4786 to reduce number of taken branches, partitions hot and cold basic blocks
4787 into separate sections of the assembly and .o files, to improve
4788 paging and cache locality performance.
4790 This optimization is automatically turned off in the presence of
4791 exception handling, for linkonce sections, for functions with a user-defined
4792 section attribute and on any architecture that does not support named
4795 @item -freorder-functions
4796 @opindex freorder-functions
4797 Reorder basic blocks in the compiled function in order to reduce number of
4798 taken branches and improve code locality. This is implemented by using special
4799 subsections @code{.text.hot} for most frequently executed functions and
4800 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
4801 the linker so object file format must support named sections and linker must
4802 place them in a reasonable way.
4804 Also profile feedback must be available in to make this option effective. See
4805 @option{-fprofile-arcs} for details.
4807 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4809 @item -fstrict-aliasing
4810 @opindex fstrict-aliasing
4811 Allows the compiler to assume the strictest aliasing rules applicable to
4812 the language being compiled. For C (and C++), this activates
4813 optimizations based on the type of expressions. In particular, an
4814 object of one type is assumed never to reside at the same address as an
4815 object of a different type, unless the types are almost the same. For
4816 example, an @code{unsigned int} can alias an @code{int}, but not a
4817 @code{void*} or a @code{double}. A character type may alias any other
4820 Pay special attention to code like this:
4833 The practice of reading from a different union member than the one most
4834 recently written to (called ``type-punning'') is common. Even with
4835 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4836 is accessed through the union type. So, the code above will work as
4837 expected. However, this code might not:
4848 Every language that wishes to perform language-specific alias analysis
4849 should define a function that computes, given an @code{tree}
4850 node, an alias set for the node. Nodes in different alias sets are not
4851 allowed to alias. For an example, see the C front-end function
4852 @code{c_get_alias_set}.
4854 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4856 @item -falign-functions
4857 @itemx -falign-functions=@var{n}
4858 @opindex falign-functions
4859 Align the start of functions to the next power-of-two greater than
4860 @var{n}, skipping up to @var{n} bytes. For instance,
4861 @option{-falign-functions=32} aligns functions to the next 32-byte
4862 boundary, but @option{-falign-functions=24} would align to the next
4863 32-byte boundary only if this can be done by skipping 23 bytes or less.
4865 @option{-fno-align-functions} and @option{-falign-functions=1} are
4866 equivalent and mean that functions will not be aligned.
4868 Some assemblers only support this flag when @var{n} is a power of two;
4869 in that case, it is rounded up.
4871 If @var{n} is not specified or is zero, use a machine-dependent default.
4873 Enabled at levels @option{-O2}, @option{-O3}.
4875 @item -falign-labels
4876 @itemx -falign-labels=@var{n}
4877 @opindex falign-labels
4878 Align all branch targets to a power-of-two boundary, skipping up to
4879 @var{n} bytes like @option{-falign-functions}. This option can easily
4880 make code slower, because it must insert dummy operations for when the
4881 branch target is reached in the usual flow of the code.
4883 @option{-fno-align-labels} and @option{-falign-labels=1} are
4884 equivalent and mean that labels will not be aligned.
4886 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4887 are greater than this value, then their values are used instead.
4889 If @var{n} is not specified or is zero, use a machine-dependent default
4890 which is very likely to be @samp{1}, meaning no alignment.
4892 Enabled at levels @option{-O2}, @option{-O3}.
4895 @itemx -falign-loops=@var{n}
4896 @opindex falign-loops
4897 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4898 like @option{-falign-functions}. The hope is that the loop will be
4899 executed many times, which will make up for any execution of the dummy
4902 @option{-fno-align-loops} and @option{-falign-loops=1} are
4903 equivalent and mean that loops will not be aligned.
4905 If @var{n} is not specified or is zero, use a machine-dependent default.
4907 Enabled at levels @option{-O2}, @option{-O3}.
4910 @itemx -falign-jumps=@var{n}
4911 @opindex falign-jumps
4912 Align branch targets to a power-of-two boundary, for branch targets
4913 where the targets can only be reached by jumping, skipping up to @var{n}
4914 bytes like @option{-falign-functions}. In this case, no dummy operations
4917 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4918 equivalent and mean that loops will not be aligned.
4920 If @var{n} is not specified or is zero, use a machine-dependent default.
4922 Enabled at levels @option{-O2}, @option{-O3}.
4924 @item -funit-at-a-time
4925 @opindex funit-at-a-time
4926 Parse the whole compilation unit before starting to produce code.
4927 This allows some extra optimizations to take place but consumes
4928 more memory (in general). There are some compatibility issues
4929 with @emph{unit-at-at-time} mode:
4932 enabling @emph{unit-at-a-time} mode may change the order
4933 in which functions, variables, and top-level @code{asm} statements
4934 are emitted, and will likely break code relying on some particular
4935 ordering. The majority of such top-level @code{asm} statements,
4936 though, can be replaced by @code{section} attributes.
4939 @emph{unit-at-a-time} mode removes unreferenced static variables
4940 and functions are removed. This may result in undefined references
4941 when an @code{asm} statement refers directly to variables or functions
4942 that are otherwise unused. In that case either the variable/function
4943 shall be listed as an operand of the @code{asm} statement operand or,
4944 in the case of top-level @code{asm} statements the attribute @code{used}
4945 shall be used on the declaration.
4948 Static functions now can use non-standard passing conventions that
4949 may break @code{asm} statements calling functions directly. Again,
4950 attribute @code{used} will prevent this behavior.
4953 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
4954 but this scheme may not be supported by future releases of GCC.
4956 Enabled at levels @option{-O2}, @option{-O3}.
4960 Constructs webs as commonly used for register allocation purposes and assign
4961 each web individual pseudo register. This allows the register allocation pass
4962 to operate on pseudos directly, but also strengthens several other optimization
4963 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
4964 however, make debugging impossible, since variables will no longer stay in a
4967 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os},
4968 on targets where the default format for debugging information supports
4971 @item -fno-cprop-registers
4972 @opindex fno-cprop-registers
4973 After register allocation and post-register allocation instruction splitting,
4974 we perform a copy-propagation pass to try to reduce scheduling dependencies
4975 and occasionally eliminate the copy.
4977 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4979 @item -fprofile-generate
4980 @opindex fprofile-generate
4982 Enable options usually used for instrumenting application to produce
4983 profile useful for later recompilation with profile feedback based
4984 optimization. You must use @option{-fprofile-generate} both when
4985 compiling and when linking your program.
4987 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
4990 @opindex fprofile-use
4991 Enable profile feedback directed optimizations, and optimizations
4992 generally profitable only with profile feedback available.
4994 The following options are enabled: @code{-fbranch-probabilities},
4995 @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}.
4999 The following options control compiler behavior regarding floating
5000 point arithmetic. These options trade off between speed and
5001 correctness. All must be specifically enabled.
5005 @opindex ffloat-store
5006 Do not store floating point variables in registers, and inhibit other
5007 options that might change whether a floating point value is taken from a
5010 @cindex floating point precision
5011 This option prevents undesirable excess precision on machines such as
5012 the 68000 where the floating registers (of the 68881) keep more
5013 precision than a @code{double} is supposed to have. Similarly for the
5014 x86 architecture. For most programs, the excess precision does only
5015 good, but a few programs rely on the precise definition of IEEE floating
5016 point. Use @option{-ffloat-store} for such programs, after modifying
5017 them to store all pertinent intermediate computations into variables.
5021 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5022 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5023 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
5025 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5027 This option should never be turned on by any @option{-O} option since
5028 it can result in incorrect output for programs which depend on
5029 an exact implementation of IEEE or ISO rules/specifications for
5032 @item -fno-math-errno
5033 @opindex fno-math-errno
5034 Do not set ERRNO after calling math functions that are executed
5035 with a single instruction, e.g., sqrt. A program that relies on
5036 IEEE exceptions for math error handling may want to use this flag
5037 for speed while maintaining IEEE arithmetic compatibility.
5039 This option should never be turned on by any @option{-O} option since
5040 it can result in incorrect output for programs which depend on
5041 an exact implementation of IEEE or ISO rules/specifications for
5044 The default is @option{-fmath-errno}.
5046 @item -funsafe-math-optimizations
5047 @opindex funsafe-math-optimizations
5048 Allow optimizations for floating-point arithmetic that (a) assume
5049 that arguments and results are valid and (b) may violate IEEE or
5050 ANSI standards. When used at link-time, it may include libraries
5051 or startup files that change the default FPU control word or other
5052 similar optimizations.
5054 This option should never be turned on by any @option{-O} option since
5055 it can result in incorrect output for programs which depend on
5056 an exact implementation of IEEE or ISO rules/specifications for
5059 The default is @option{-fno-unsafe-math-optimizations}.
5061 @item -ffinite-math-only
5062 @opindex ffinite-math-only
5063 Allow optimizations for floating-point arithmetic that assume
5064 that arguments and results are not NaNs or +-Infs.
5066 This option should never be turned on by any @option{-O} option since
5067 it can result in incorrect output for programs which depend on
5068 an exact implementation of IEEE or ISO rules/specifications.
5070 The default is @option{-fno-finite-math-only}.
5072 @item -fno-trapping-math
5073 @opindex fno-trapping-math
5074 Compile code assuming that floating-point operations cannot generate
5075 user-visible traps. These traps include division by zero, overflow,
5076 underflow, inexact result and invalid operation. This option implies
5077 @option{-fno-signaling-nans}. Setting this option may allow faster
5078 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5080 This option should never be turned on by any @option{-O} option since
5081 it can result in incorrect output for programs which depend on
5082 an exact implementation of IEEE or ISO rules/specifications for
5085 The default is @option{-ftrapping-math}.
5087 @item -frounding-math
5088 @opindex frounding-math
5089 Disable transformations and optimizations that assume default floating
5090 point rounding behavior. This is round-to-zero for all floating point
5091 to integer conversions, and round-to-nearest for all other arithmetic
5092 truncations. This option should be specified for programs that change
5093 the FP rounding mode dynamically, or that may be executed with a
5094 non-default rounding mode. This option disables constant folding of
5095 floating point expressions at compile-time (which may be affected by
5096 rounding mode) and arithmetic transformations that are unsafe in the
5097 presence of sign-dependent rounding modes.
5099 The default is @option{-fno-rounding-math}.
5101 This option is experimental and does not currently guarantee to
5102 disable all GCC optimizations that are affected by rounding mode.
5103 Future versions of GCC may provide finer control of this setting
5104 using C99's @code{FENV_ACCESS} pragma. This command line option
5105 will be used to specify the default state for @code{FENV_ACCESS}.
5107 @item -fsignaling-nans
5108 @opindex fsignaling-nans
5109 Compile code assuming that IEEE signaling NaNs may generate user-visible
5110 traps during floating-point operations. Setting this option disables
5111 optimizations that may change the number of exceptions visible with
5112 signaling NaNs. This option implies @option{-ftrapping-math}.
5114 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5117 The default is @option{-fno-signaling-nans}.
5119 This option is experimental and does not currently guarantee to
5120 disable all GCC optimizations that affect signaling NaN behavior.
5122 @item -fsingle-precision-constant
5123 @opindex fsingle-precision-constant
5124 Treat floating point constant as single precision constant instead of
5125 implicitly converting it to double precision constant.
5130 The following options control optimizations that may improve
5131 performance, but are not enabled by any @option{-O} options. This
5132 section includes experimental options that may produce broken code.
5135 @item -fbranch-probabilities
5136 @opindex fbranch-probabilities
5137 After running a program compiled with @option{-fprofile-arcs}
5138 (@pxref{Debugging Options,, Options for Debugging Your Program or
5139 @command{gcc}}), you can compile it a second time using
5140 @option{-fbranch-probabilities}, to improve optimizations based on
5141 the number of times each branch was taken. When the program
5142 compiled with @option{-fprofile-arcs} exits it saves arc execution
5143 counts to a file called @file{@var{sourcename}.gcda} for each source
5144 file The information in this data file is very dependent on the
5145 structure of the generated code, so you must use the same source code
5146 and the same optimization options for both compilations.
5148 With @option{-fbranch-probabilities}, GCC puts a
5149 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5150 These can be used to improve optimization. Currently, they are only
5151 used in one place: in @file{reorg.c}, instead of guessing which path a
5152 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5153 exactly determine which path is taken more often.
5155 @item -fprofile-values
5156 @opindex fprofile-values
5157 If combined with @option{-fprofile-arcs}, it adds code so that some
5158 data about values of expressions in the program is gathered.
5160 With @option{-fbranch-probabilities}, it reads back the data gathered
5161 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5162 notes to instructions for their later usage in optimizations.
5164 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5168 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5169 a code to gather information about values of expressions.
5171 With @option{-fbranch-probabilities}, it reads back the data gathered
5172 and actually performs the optimizations based on them.
5173 Currently the optimizations include specialization of division operation
5174 using the knowledge about the value of the denominator.
5176 @item -fspeculative-prefetching
5177 @opindex fspeculative-prefetching
5178 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5179 a code to gather information about addresses of memory references in the
5182 With @option{-fbranch-probabilities}, it reads back the data gathered
5183 and issues prefetch instructions according to them. In addition to the opportunities
5184 noticed by @option{-fprefetch-loop-arrays}, it also notices more complicated
5185 memory access patterns -- for example accesses to the data stored in linked
5186 list whose elements are usually allocated sequentially.
5188 In order to prevent issuing double prefetches, usage of
5189 @option{-fspeculative-prefetching} implies @option{-fno-prefetch-loop-arrays}.
5191 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5193 @item -frename-registers
5194 @opindex frename-registers
5195 Attempt to avoid false dependencies in scheduled code by making use
5196 of registers left over after register allocation. This optimization
5197 will most benefit processors with lots of registers. Depending on the
5198 debug information format adopted by the target, however, it can
5199 make debugging impossible, since variables will no longer stay in
5200 a ``home register''.
5202 Not enabled by default at any level because it has known bugs.
5206 Use a graph coloring register allocator. Currently this option is meant
5207 for testing, so we are interested to hear about miscompilations with
5212 Perform tail duplication to enlarge superblock size. This transformation
5213 simplifies the control flow of the function allowing other optimizations to do
5216 Enabled with @option{-fprofile-use}.
5218 @item -funroll-loops
5219 @opindex funroll-loops
5220 Unroll loops whose number of iterations can be determined at compile time or
5221 upon entry to the loop. @option{-funroll-loops} implies
5222 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
5223 (i.e.@: complete removal of loops with small constant number of iterations).
5224 This option makes code larger, and may or may not make it run faster.
5226 Enabled with @option{-fprofile-use}.
5228 @item -funroll-all-loops
5229 @opindex funroll-all-loops
5230 Unroll all loops, even if their number of iterations is uncertain when
5231 the loop is entered. This usually makes programs run more slowly.
5232 @option{-funroll-all-loops} implies the same options as
5233 @option{-funroll-loops}.
5236 @opindex fpeel-loops
5237 Peels the loops for that there is enough information that they do not
5238 roll much (from profile feedback). It also turns on complete loop peeling
5239 (i.e.@: complete removal of loops with small constant number of iterations).
5241 Enabled with @option{-fprofile-use}.
5243 @item -fmove-loop-invariants
5244 @opindex fmove-loop-invariants
5245 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5246 at level @option{-O1}
5248 @item -funswitch-loops
5249 @opindex funswitch-loops
5250 Move branches with loop invariant conditions out of the loop, with duplicates
5251 of the loop on both branches (modified according to result of the condition).
5253 @item -fprefetch-loop-arrays
5254 @opindex fprefetch-loop-arrays
5255 If supported by the target machine, generate instructions to prefetch
5256 memory to improve the performance of loops that access large arrays.
5258 Disabled at level @option{-Os}.
5260 @item -ffunction-sections
5261 @itemx -fdata-sections
5262 @opindex ffunction-sections
5263 @opindex fdata-sections
5264 Place each function or data item into its own section in the output
5265 file if the target supports arbitrary sections. The name of the
5266 function or the name of the data item determines the section's name
5269 Use these options on systems where the linker can perform optimizations
5270 to improve locality of reference in the instruction space. Most systems
5271 using the ELF object format and SPARC processors running Solaris 2 have
5272 linkers with such optimizations. AIX may have these optimizations in
5275 Only use these options when there are significant benefits from doing
5276 so. When you specify these options, the assembler and linker will
5277 create larger object and executable files and will also be slower.
5278 You will not be able to use @code{gprof} on all systems if you
5279 specify this option and you may have problems with debugging if
5280 you specify both this option and @option{-g}.
5282 @item -fbranch-target-load-optimize
5283 @opindex fbranch-target-load-optimize
5284 Perform branch target register load optimization before prologue / epilogue
5286 The use of target registers can typically be exposed only during reload,
5287 thus hoisting loads out of loops and doing inter-block scheduling needs
5288 a separate optimization pass.
5290 @item -fbranch-target-load-optimize2
5291 @opindex fbranch-target-load-optimize2
5292 Perform branch target register load optimization after prologue / epilogue
5295 @item -fbtr-bb-exclusive
5296 @opindex fbtr-bb-exclusive
5297 When performing branch target register load optimization, don't reuse
5298 branch target registers in within any basic block.
5300 @item --param @var{name}=@var{value}
5302 In some places, GCC uses various constants to control the amount of
5303 optimization that is done. For example, GCC will not inline functions
5304 that contain more that a certain number of instructions. You can
5305 control some of these constants on the command-line using the
5306 @option{--param} option.
5308 The names of specific parameters, and the meaning of the values, are
5309 tied to the internals of the compiler, and are subject to change
5310 without notice in future releases.
5312 In each case, the @var{value} is an integer. The allowable choices for
5313 @var{name} are given in the following table:
5316 @item sra-max-structure-size
5317 The maximum structure size, in bytes, at which the scalar replacement
5318 of aggregates (SRA) optimization will perform block copies. The
5319 default value, 0, implies that GCC will select the most appropriate
5322 @item sra-field-structure-ratio
5323 The treshold ratio (as a percentage) between instantiated fields and
5324 the complete structure size. We say that if the ratio of the number
5325 of bytes in instantiated fields to the number of bytes in the complete
5326 structure exceeds this parameter, then block copies are not used. The
5329 @item max-crossjump-edges
5330 The maximum number of incoming edges to consider for crossjumping.
5331 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5332 the number of edges incoming to each block. Increasing values mean
5333 more aggressive optimization, making the compile time increase with
5334 probably small improvement in executable size.
5336 @item min-crossjump-insns
5337 The minimum number of instructions which must be matched at the end
5338 of two blocks before crossjumping will be performed on them. This
5339 value is ignored in the case where all instructions in the block being
5340 crossjumped from are matched. The default value is 5.
5342 @item max-delay-slot-insn-search
5343 The maximum number of instructions to consider when looking for an
5344 instruction to fill a delay slot. If more than this arbitrary number of
5345 instructions is searched, the time savings from filling the delay slot
5346 will be minimal so stop searching. Increasing values mean more
5347 aggressive optimization, making the compile time increase with probably
5348 small improvement in executable run time.
5350 @item max-delay-slot-live-search
5351 When trying to fill delay slots, the maximum number of instructions to
5352 consider when searching for a block with valid live register
5353 information. Increasing this arbitrarily chosen value means more
5354 aggressive optimization, increasing the compile time. This parameter
5355 should be removed when the delay slot code is rewritten to maintain the
5358 @item max-gcse-memory
5359 The approximate maximum amount of memory that will be allocated in
5360 order to perform the global common subexpression elimination
5361 optimization. If more memory than specified is required, the
5362 optimization will not be done.
5364 @item max-gcse-passes
5365 The maximum number of passes of GCSE to run. The default is 1.
5367 @item max-pending-list-length
5368 The maximum number of pending dependencies scheduling will allow
5369 before flushing the current state and starting over. Large functions
5370 with few branches or calls can create excessively large lists which
5371 needlessly consume memory and resources.
5373 @item max-inline-insns-single
5374 Several parameters control the tree inliner used in gcc.
5375 This number sets the maximum number of instructions (counted in GCC's
5376 internal representation) in a single function that the tree inliner
5377 will consider for inlining. This only affects functions declared
5378 inline and methods implemented in a class declaration (C++).
5379 The default value is 500.
5381 @item max-inline-insns-auto
5382 When you use @option{-finline-functions} (included in @option{-O3}),
5383 a lot of functions that would otherwise not be considered for inlining
5384 by the compiler will be investigated. To those functions, a different
5385 (more restrictive) limit compared to functions declared inline can
5387 The default value is 120.
5389 @item large-function-insns
5390 The limit specifying really large functions. For functions greater than this
5391 limit inlining is constrained by @option{--param large-function-growth}.
5392 This parameter is useful primarily to avoid extreme compilation time caused by non-linear
5393 algorithms used by the backend.
5394 This parameter is ignored when @option{-funit-at-a-time} is not used.
5395 The default value is 3000.
5397 @item large-function-growth
5398 Specifies maximal growth of large function caused by inlining in percents.
5399 This parameter is ignored when @option{-funit-at-a-time} is not used.
5400 The default value is 200.
5402 @item inline-unit-growth
5403 Specifies maximal overall growth of the compilation unit caused by inlining.
5404 This parameter is ignored when @option{-funit-at-a-time} is not used.
5405 The default value is 150.
5407 @item max-inline-insns-recursive
5408 @itemx max-inline-insns-recursive-auto
5409 Specifies maximum number of instructions out-of-line copy of self recursive inline
5410 function can grow into by performing recursive inlining.
5412 For functions declared inline @option{--param max-inline-insns-recursive} is
5413 taken into acount. For function not declared inline, recursive inlining
5414 happens only when @option{-finline-functions} (included in @option{-O3}) is
5415 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5416 default value is 500.
5418 @item max-inline-recursive-depth
5419 @itemx max-inline-recursive-depth-auto
5420 Specifies maximum recursion depth used by the recursive inlining.
5422 For functions declared inline @option{--param max-inline-recursive-depth} is
5423 taken into acount. For function not declared inline, recursive inlining
5424 happens only when @option{-finline-functions} (included in @option{-O3}) is
5425 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5426 default value is 500.
5428 @item max-inline-insns-rtl
5429 For languages that use the RTL inliner (this happens at a later stage
5430 than tree inlining), you can set the maximum allowable size (counted
5431 in RTL instructions) for the RTL inliner with this parameter.
5432 The default value is 600.
5434 @item max-unrolled-insns
5435 The maximum number of instructions that a loop should have if that loop
5436 is unrolled, and if the loop is unrolled, it determines how many times
5437 the loop code is unrolled.
5439 @item max-average-unrolled-insns
5440 The maximum number of instructions biased by probabilities of their execution
5441 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5442 it determines how many times the loop code is unrolled.
5444 @item max-unroll-times
5445 The maximum number of unrollings of a single loop.
5447 @item max-peeled-insns
5448 The maximum number of instructions that a loop should have if that loop
5449 is peeled, and if the loop is peeled, it determines how many times
5450 the loop code is peeled.
5452 @item max-peel-times
5453 The maximum number of peelings of a single loop.
5455 @item max-completely-peeled-insns
5456 The maximum number of insns of a completely peeled loop.
5458 @item max-completely-peel-times
5459 The maximum number of iterations of a loop to be suitable for complete peeling.
5461 @item max-unswitch-insns
5462 The maximum number of insns of an unswitched loop.
5464 @item max-unswitch-level
5465 The maximum number of branches unswitched in a single loop.
5468 The minimum cost of an expensive expression in the loop invariant motion.
5470 @item iv-consider-all-candidates-bound
5471 Bound on number of candidates for induction variables below that
5472 all candidates are considered for each use in induction variable
5473 optimizations. Only the most relevant candidates are considered
5474 if there are more candidates, to avoid quadratic time complexity.
5476 @item iv-max-considered-uses
5477 The induction variable optimizations give up on loops that contain more
5478 induction variable uses.
5480 @item max-iterations-to-track
5482 The maximum number of iterations of a loop the brute force algorithm
5483 for analysis of # of iterations of the loop tries to evaluate.
5485 @item hot-bb-count-fraction
5486 Select fraction of the maximal count of repetitions of basic block in program
5487 given basic block needs to have to be considered hot.
5489 @item hot-bb-frequency-fraction
5490 Select fraction of the maximal frequency of executions of basic block in
5491 function given basic block needs to have to be considered hot
5493 @item tracer-dynamic-coverage
5494 @itemx tracer-dynamic-coverage-feedback
5496 This value is used to limit superblock formation once the given percentage of
5497 executed instructions is covered. This limits unnecessary code size
5500 The @option{tracer-dynamic-coverage-feedback} is used only when profile
5501 feedback is available. The real profiles (as opposed to statically estimated
5502 ones) are much less balanced allowing the threshold to be larger value.
5504 @item tracer-max-code-growth
5505 Stop tail duplication once code growth has reached given percentage. This is
5506 rather hokey argument, as most of the duplicates will be eliminated later in
5507 cross jumping, so it may be set to much higher values than is the desired code
5510 @item tracer-min-branch-ratio
5512 Stop reverse growth when the reverse probability of best edge is less than this
5513 threshold (in percent).
5515 @item tracer-min-branch-ratio
5516 @itemx tracer-min-branch-ratio-feedback
5518 Stop forward growth if the best edge do have probability lower than this
5521 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
5522 compilation for profile feedback and one for compilation without. The value
5523 for compilation with profile feedback needs to be more conservative (higher) in
5524 order to make tracer effective.
5526 @item max-cse-path-length
5528 Maximum number of basic blocks on path that cse considers. The default is 10.
5530 @item global-var-threshold
5532 Counts the number of function calls (N) and the number of
5533 call-clobbered variables (V). If NxV is larger than this limit, a
5534 single artificial variable will be created to represent all the
5535 call-clobbered variables at function call sites. This artificial
5536 variable will then be made to alias every call-clobbered variable.
5537 (done as int * size_t on the host machine; beware overflow).
5539 @item max-aliased-vops
5541 Maximum number of virtual operands allowed to represent aliases
5542 before triggering the alias grouping heuristic. Alias grouping
5543 reduces compile times and memory consumption needed for aliasing at
5544 the expense of precision loss in alias information.
5546 @item ggc-min-expand
5548 GCC uses a garbage collector to manage its own memory allocation. This
5549 parameter specifies the minimum percentage by which the garbage
5550 collector's heap should be allowed to expand between collections.
5551 Tuning this may improve compilation speed; it has no effect on code
5554 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
5555 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
5556 the smallest of actual RAM and RLIMIT_DATA or RLIMIT_AS. If
5557 GCC is not able to calculate RAM on a particular platform, the lower
5558 bound of 30% is used. Setting this parameter and
5559 @option{ggc-min-heapsize} to zero causes a full collection to occur at
5560 every opportunity. This is extremely slow, but can be useful for
5563 @item ggc-min-heapsize
5565 Minimum size of the garbage collector's heap before it begins bothering
5566 to collect garbage. The first collection occurs after the heap expands
5567 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
5568 tuning this may improve compilation speed, and has no effect on code
5571 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
5572 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
5573 with a lower bound of 4096 (four megabytes) and an upper bound of
5574 131072 (128 megabytes). If GCC is not able to calculate RAM on a
5575 particular platform, the lower bound is used. Setting this parameter
5576 very large effectively disables garbage collection. Setting this
5577 parameter and @option{ggc-min-expand} to zero causes a full collection
5578 to occur at every opportunity.
5580 @item max-reload-search-insns
5581 The maximum number of instruction reload should look backward for equivalent
5582 register. Increasing values mean more aggressive optimization, making the
5583 compile time increase with probably slightly better performance. The default
5586 @item max-cselib-memory-location
5587 The maximum number of memory locations cselib should take into acount.
5588 Increasing values mean more aggressive optimization, making the compile time
5589 increase with probably slightly better performance. The default value is 500.
5591 @item reorder-blocks-duplicate
5592 @itemx reorder-blocks-duplicate-feedback
5594 Used by basic block reordering pass to decide whether to use unconditional
5595 branch or duplicate the code on its destination. Code is duplicated when its
5596 estimated size is smaller than this value multiplied by the estimated size of
5597 unconditional jump in the hot spots of the program.
5599 The @option{reorder-block-duplicate-feedback} is used only when profile
5600 feedback is available and may be set to higher values than
5601 @option{reorder-block-duplicate} since information about the hot spots is more
5604 @item max-sched-region-blocks
5605 The maximum number of blocks in a region to be considered for
5606 interblock scheduling. The default value is 10.
5608 @item max-sched-region-insns
5609 The maximum number of insns in a region to be considered for
5610 interblock scheduling. The default value is 100.
5612 @item integer-share-limit
5613 Small integer constants can use a shared data structure, reducing the
5614 compiler's memory usage and increasing its speed. This sets the maximum
5615 value of a shared integer constant's. The default value is 256.
5620 @node Preprocessor Options
5621 @section Options Controlling the Preprocessor
5622 @cindex preprocessor options
5623 @cindex options, preprocessor
5625 These options control the C preprocessor, which is run on each C source
5626 file before actual compilation.
5628 If you use the @option{-E} option, nothing is done except preprocessing.
5629 Some of these options make sense only together with @option{-E} because
5630 they cause the preprocessor output to be unsuitable for actual
5635 You can use @option{-Wp,@var{option}} to bypass the compiler driver
5636 and pass @var{option} directly through to the preprocessor. If
5637 @var{option} contains commas, it is split into multiple options at the
5638 commas. However, many options are modified, translated or interpreted
5639 by the compiler driver before being passed to the preprocessor, and
5640 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
5641 interface is undocumented and subject to change, so whenever possible
5642 you should avoid using @option{-Wp} and let the driver handle the
5645 @item -Xpreprocessor @var{option}
5646 @opindex preprocessor
5647 Pass @var{option} as an option to the preprocessor. You can use this to
5648 supply system-specific preprocessor options which GCC does not know how to
5651 If you want to pass an option that takes an argument, you must use
5652 @option{-Xpreprocessor} twice, once for the option and once for the argument.
5655 @include cppopts.texi
5657 @node Assembler Options
5658 @section Passing Options to the Assembler
5660 @c prevent bad page break with this line
5661 You can pass options to the assembler.
5664 @item -Wa,@var{option}
5666 Pass @var{option} as an option to the assembler. If @var{option}
5667 contains commas, it is split into multiple options at the commas.
5669 @item -Xassembler @var{option}
5671 Pass @var{option} as an option to the assembler. You can use this to
5672 supply system-specific assembler options which GCC does not know how to
5675 If you want to pass an option that takes an argument, you must use
5676 @option{-Xassembler} twice, once for the option and once for the argument.
5681 @section Options for Linking
5682 @cindex link options
5683 @cindex options, linking
5685 These options come into play when the compiler links object files into
5686 an executable output file. They are meaningless if the compiler is
5687 not doing a link step.
5691 @item @var{object-file-name}
5692 A file name that does not end in a special recognized suffix is
5693 considered to name an object file or library. (Object files are
5694 distinguished from libraries by the linker according to the file
5695 contents.) If linking is done, these object files are used as input
5704 If any of these options is used, then the linker is not run, and
5705 object file names should not be used as arguments. @xref{Overall
5709 @item -l@var{library}
5710 @itemx -l @var{library}
5712 Search the library named @var{library} when linking. (The second
5713 alternative with the library as a separate argument is only for
5714 POSIX compliance and is not recommended.)
5716 It makes a difference where in the command you write this option; the
5717 linker searches and processes libraries and object files in the order they
5718 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
5719 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
5720 to functions in @samp{z}, those functions may not be loaded.
5722 The linker searches a standard list of directories for the library,
5723 which is actually a file named @file{lib@var{library}.a}. The linker
5724 then uses this file as if it had been specified precisely by name.
5726 The directories searched include several standard system directories
5727 plus any that you specify with @option{-L}.
5729 Normally the files found this way are library files---archive files
5730 whose members are object files. The linker handles an archive file by
5731 scanning through it for members which define symbols that have so far
5732 been referenced but not defined. But if the file that is found is an
5733 ordinary object file, it is linked in the usual fashion. The only
5734 difference between using an @option{-l} option and specifying a file name
5735 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5736 and searches several directories.
5740 You need this special case of the @option{-l} option in order to
5741 link an Objective-C or Objective-C++ program.
5744 @opindex nostartfiles
5745 Do not use the standard system startup files when linking.
5746 The standard system libraries are used normally, unless @option{-nostdlib}
5747 or @option{-nodefaultlibs} is used.
5749 @item -nodefaultlibs
5750 @opindex nodefaultlibs
5751 Do not use the standard system libraries when linking.
5752 Only the libraries you specify will be passed to the linker.
5753 The standard startup files are used normally, unless @option{-nostartfiles}
5754 is used. The compiler may generate calls to @code{memcmp},
5755 @code{memset}, @code{memcpy} and @code{memmove}.
5756 These entries are usually resolved by entries in
5757 libc. These entry points should be supplied through some other
5758 mechanism when this option is specified.
5762 Do not use the standard system startup files or libraries when linking.
5763 No startup files and only the libraries you specify will be passed to
5764 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
5765 @code{memcpy} and @code{memmove}.
5766 These entries are usually resolved by entries in
5767 libc. These entry points should be supplied through some other
5768 mechanism when this option is specified.
5770 @cindex @option{-lgcc}, use with @option{-nostdlib}
5771 @cindex @option{-nostdlib} and unresolved references
5772 @cindex unresolved references and @option{-nostdlib}
5773 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5774 @cindex @option{-nodefaultlibs} and unresolved references
5775 @cindex unresolved references and @option{-nodefaultlibs}
5776 One of the standard libraries bypassed by @option{-nostdlib} and
5777 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5778 that GCC uses to overcome shortcomings of particular machines, or special
5779 needs for some languages.
5780 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5781 Collection (GCC) Internals},
5782 for more discussion of @file{libgcc.a}.)
5783 In most cases, you need @file{libgcc.a} even when you want to avoid
5784 other standard libraries. In other words, when you specify @option{-nostdlib}
5785 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5786 This ensures that you have no unresolved references to internal GCC
5787 library subroutines. (For example, @samp{__main}, used to ensure C++
5788 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5789 GNU Compiler Collection (GCC) Internals}.)
5793 Produce a position independent executable on targets which support it.
5794 For predictable results, you must also specify the same set of options
5795 that were used to generate code (@option{-fpie}, @option{-fPIE},
5796 or model suboptions) when you specify this option.
5800 Remove all symbol table and relocation information from the executable.
5804 On systems that support dynamic linking, this prevents linking with the shared
5805 libraries. On other systems, this option has no effect.
5809 Produce a shared object which can then be linked with other objects to
5810 form an executable. Not all systems support this option. For predictable
5811 results, you must also specify the same set of options that were used to
5812 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5813 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5814 needs to build supplementary stub code for constructors to work. On
5815 multi-libbed systems, @samp{gcc -shared} must select the correct support
5816 libraries to link against. Failing to supply the correct flags may lead
5817 to subtle defects. Supplying them in cases where they are not necessary
5820 @item -shared-libgcc
5821 @itemx -static-libgcc
5822 @opindex shared-libgcc
5823 @opindex static-libgcc
5824 On systems that provide @file{libgcc} as a shared library, these options
5825 force the use of either the shared or static version respectively.
5826 If no shared version of @file{libgcc} was built when the compiler was
5827 configured, these options have no effect.
5829 There are several situations in which an application should use the
5830 shared @file{libgcc} instead of the static version. The most common
5831 of these is when the application wishes to throw and catch exceptions
5832 across different shared libraries. In that case, each of the libraries
5833 as well as the application itself should use the shared @file{libgcc}.
5835 Therefore, the G++ and GCJ drivers automatically add
5836 @option{-shared-libgcc} whenever you build a shared library or a main
5837 executable, because C++ and Java programs typically use exceptions, so
5838 this is the right thing to do.
5840 If, instead, you use the GCC driver to create shared libraries, you may
5841 find that they will not always be linked with the shared @file{libgcc}.
5842 If GCC finds, at its configuration time, that you have a non-GNU linker
5843 or a GNU linker that does not support option @option{--eh-frame-hdr},
5844 it will link the shared version of @file{libgcc} into shared libraries
5845 by default. Otherwise, it will take advantage of the linker and optimize
5846 away the linking with the shared version of @file{libgcc}, linking with
5847 the static version of libgcc by default. This allows exceptions to
5848 propagate through such shared libraries, without incurring relocation
5849 costs at library load time.
5851 However, if a library or main executable is supposed to throw or catch
5852 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5853 for the languages used in the program, or using the option
5854 @option{-shared-libgcc}, such that it is linked with the shared
5859 Bind references to global symbols when building a shared object. Warn
5860 about any unresolved references (unless overridden by the link editor
5861 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5864 @item -Xlinker @var{option}
5866 Pass @var{option} as an option to the linker. You can use this to
5867 supply system-specific linker options which GCC does not know how to
5870 If you want to pass an option that takes an argument, you must use
5871 @option{-Xlinker} twice, once for the option and once for the argument.
5872 For example, to pass @option{-assert definitions}, you must write
5873 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5874 @option{-Xlinker "-assert definitions"}, because this passes the entire
5875 string as a single argument, which is not what the linker expects.
5877 @item -Wl,@var{option}
5879 Pass @var{option} as an option to the linker. If @var{option} contains
5880 commas, it is split into multiple options at the commas.
5882 @item -u @var{symbol}
5884 Pretend the symbol @var{symbol} is undefined, to force linking of
5885 library modules to define it. You can use @option{-u} multiple times with
5886 different symbols to force loading of additional library modules.
5889 @node Directory Options
5890 @section Options for Directory Search
5891 @cindex directory options
5892 @cindex options, directory search
5895 These options specify directories to search for header files, for
5896 libraries and for parts of the compiler:
5901 Add the directory @var{dir} to the head of the list of directories to be
5902 searched for header files. This can be used to override a system header
5903 file, substituting your own version, since these directories are
5904 searched before the system header file directories. However, you should
5905 not use this option to add directories that contain vendor-supplied
5906 system header files (use @option{-isystem} for that). If you use more than
5907 one @option{-I} option, the directories are scanned in left-to-right
5908 order; the standard system directories come after.
5910 If a standard system include directory, or a directory specified with
5911 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5912 option will be ignored. The directory will still be searched but as a
5913 system directory at its normal position in the system include chain.
5914 This is to ensure that GCC's procedure to fix buggy system headers and
5915 the ordering for the include_next directive are not inadvertently changed.
5916 If you really need to change the search order for system directories,
5917 use the @option{-nostdinc} and/or @option{-isystem} options.
5919 @item -iquote@var{dir}
5921 Add the directory @var{dir} to the head of the list of directories to
5922 be searched for header files only for the case of @samp{#include
5923 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
5924 otherwise just like @option{-I}.
5928 Add directory @var{dir} to the list of directories to be searched
5931 @item -B@var{prefix}
5933 This option specifies where to find the executables, libraries,
5934 include files, and data files of the compiler itself.
5936 The compiler driver program runs one or more of the subprograms
5937 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5938 @var{prefix} as a prefix for each program it tries to run, both with and
5939 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5941 For each subprogram to be run, the compiler driver first tries the
5942 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5943 was not specified, the driver tries two standard prefixes, which are
5944 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5945 those results in a file name that is found, the unmodified program
5946 name is searched for using the directories specified in your
5947 @env{PATH} environment variable.
5949 The compiler will check to see if the path provided by the @option{-B}
5950 refers to a directory, and if necessary it will add a directory
5951 separator character at the end of the path.
5953 @option{-B} prefixes that effectively specify directory names also apply
5954 to libraries in the linker, because the compiler translates these
5955 options into @option{-L} options for the linker. They also apply to
5956 includes files in the preprocessor, because the compiler translates these
5957 options into @option{-isystem} options for the preprocessor. In this case,
5958 the compiler appends @samp{include} to the prefix.
5960 The run-time support file @file{libgcc.a} can also be searched for using
5961 the @option{-B} prefix, if needed. If it is not found there, the two
5962 standard prefixes above are tried, and that is all. The file is left
5963 out of the link if it is not found by those means.
5965 Another way to specify a prefix much like the @option{-B} prefix is to use
5966 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5969 As a special kludge, if the path provided by @option{-B} is
5970 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5971 9, then it will be replaced by @file{[dir/]include}. This is to help
5972 with boot-strapping the compiler.
5974 @item -specs=@var{file}
5976 Process @var{file} after the compiler reads in the standard @file{specs}
5977 file, in order to override the defaults that the @file{gcc} driver
5978 program uses when determining what switches to pass to @file{cc1},
5979 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5980 @option{-specs=@var{file}} can be specified on the command line, and they
5981 are processed in order, from left to right.
5985 This option has been deprecated. Please use @option{-iquote} instead for
5986 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
5987 Any directories you specify with @option{-I} options before the @option{-I-}
5988 option are searched only for the case of @samp{#include "@var{file}"};
5989 they are not searched for @samp{#include <@var{file}>}.
5991 If additional directories are specified with @option{-I} options after
5992 the @option{-I-}, these directories are searched for all @samp{#include}
5993 directives. (Ordinarily @emph{all} @option{-I} directories are used
5996 In addition, the @option{-I-} option inhibits the use of the current
5997 directory (where the current input file came from) as the first search
5998 directory for @samp{#include "@var{file}"}. There is no way to
5999 override this effect of @option{-I-}. With @option{-I.} you can specify
6000 searching the directory which was current when the compiler was
6001 invoked. That is not exactly the same as what the preprocessor does
6002 by default, but it is often satisfactory.
6004 @option{-I-} does not inhibit the use of the standard system directories
6005 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6012 @section Specifying subprocesses and the switches to pass to them
6015 @command{gcc} is a driver program. It performs its job by invoking a
6016 sequence of other programs to do the work of compiling, assembling and
6017 linking. GCC interprets its command-line parameters and uses these to
6018 deduce which programs it should invoke, and which command-line options
6019 it ought to place on their command lines. This behavior is controlled
6020 by @dfn{spec strings}. In most cases there is one spec string for each
6021 program that GCC can invoke, but a few programs have multiple spec
6022 strings to control their behavior. The spec strings built into GCC can
6023 be overridden by using the @option{-specs=} command-line switch to specify
6026 @dfn{Spec files} are plaintext files that are used to construct spec
6027 strings. They consist of a sequence of directives separated by blank
6028 lines. The type of directive is determined by the first non-whitespace
6029 character on the line and it can be one of the following:
6032 @item %@var{command}
6033 Issues a @var{command} to the spec file processor. The commands that can
6037 @item %include <@var{file}>
6039 Search for @var{file} and insert its text at the current point in the
6042 @item %include_noerr <@var{file}>
6043 @cindex %include_noerr
6044 Just like @samp{%include}, but do not generate an error message if the include
6045 file cannot be found.
6047 @item %rename @var{old_name} @var{new_name}
6049 Rename the spec string @var{old_name} to @var{new_name}.
6053 @item *[@var{spec_name}]:
6054 This tells the compiler to create, override or delete the named spec
6055 string. All lines after this directive up to the next directive or
6056 blank line are considered to be the text for the spec string. If this
6057 results in an empty string then the spec will be deleted. (Or, if the
6058 spec did not exist, then nothing will happened.) Otherwise, if the spec
6059 does not currently exist a new spec will be created. If the spec does
6060 exist then its contents will be overridden by the text of this
6061 directive, unless the first character of that text is the @samp{+}
6062 character, in which case the text will be appended to the spec.
6064 @item [@var{suffix}]:
6065 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6066 and up to the next directive or blank line are considered to make up the
6067 spec string for the indicated suffix. When the compiler encounters an
6068 input file with the named suffix, it will processes the spec string in
6069 order to work out how to compile that file. For example:
6076 This says that any input file whose name ends in @samp{.ZZ} should be
6077 passed to the program @samp{z-compile}, which should be invoked with the
6078 command-line switch @option{-input} and with the result of performing the
6079 @samp{%i} substitution. (See below.)
6081 As an alternative to providing a spec string, the text that follows a
6082 suffix directive can be one of the following:
6085 @item @@@var{language}
6086 This says that the suffix is an alias for a known @var{language}. This is
6087 similar to using the @option{-x} command-line switch to GCC to specify a
6088 language explicitly. For example:
6095 Says that .ZZ files are, in fact, C++ source files.
6098 This causes an error messages saying:
6101 @var{name} compiler not installed on this system.
6105 GCC already has an extensive list of suffixes built into it.
6106 This directive will add an entry to the end of the list of suffixes, but
6107 since the list is searched from the end backwards, it is effectively
6108 possible to override earlier entries using this technique.
6112 GCC has the following spec strings built into it. Spec files can
6113 override these strings or create their own. Note that individual
6114 targets can also add their own spec strings to this list.
6117 asm Options to pass to the assembler
6118 asm_final Options to pass to the assembler post-processor
6119 cpp Options to pass to the C preprocessor
6120 cc1 Options to pass to the C compiler
6121 cc1plus Options to pass to the C++ compiler
6122 endfile Object files to include at the end of the link
6123 link Options to pass to the linker
6124 lib Libraries to include on the command line to the linker
6125 libgcc Decides which GCC support library to pass to the linker
6126 linker Sets the name of the linker
6127 predefines Defines to be passed to the C preprocessor
6128 signed_char Defines to pass to CPP to say whether @code{char} is signed
6130 startfile Object files to include at the start of the link
6133 Here is a small example of a spec file:
6139 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6142 This example renames the spec called @samp{lib} to @samp{old_lib} and
6143 then overrides the previous definition of @samp{lib} with a new one.
6144 The new definition adds in some extra command-line options before
6145 including the text of the old definition.
6147 @dfn{Spec strings} are a list of command-line options to be passed to their
6148 corresponding program. In addition, the spec strings can contain
6149 @samp{%}-prefixed sequences to substitute variable text or to
6150 conditionally insert text into the command line. Using these constructs
6151 it is possible to generate quite complex command lines.
6153 Here is a table of all defined @samp{%}-sequences for spec
6154 strings. Note that spaces are not generated automatically around the
6155 results of expanding these sequences. Therefore you can concatenate them
6156 together or combine them with constant text in a single argument.
6160 Substitute one @samp{%} into the program name or argument.
6163 Substitute the name of the input file being processed.
6166 Substitute the basename of the input file being processed.
6167 This is the substring up to (and not including) the last period
6168 and not including the directory.
6171 This is the same as @samp{%b}, but include the file suffix (text after
6175 Marks the argument containing or following the @samp{%d} as a
6176 temporary file name, so that that file will be deleted if GCC exits
6177 successfully. Unlike @samp{%g}, this contributes no text to the
6180 @item %g@var{suffix}
6181 Substitute a file name that has suffix @var{suffix} and is chosen
6182 once per compilation, and mark the argument in the same way as
6183 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6184 name is now chosen in a way that is hard to predict even when previously
6185 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6186 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6187 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6188 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6189 was simply substituted with a file name chosen once per compilation,
6190 without regard to any appended suffix (which was therefore treated
6191 just like ordinary text), making such attacks more likely to succeed.
6193 @item %u@var{suffix}
6194 Like @samp{%g}, but generates a new temporary file name even if
6195 @samp{%u@var{suffix}} was already seen.
6197 @item %U@var{suffix}
6198 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6199 new one if there is no such last file name. In the absence of any
6200 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6201 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6202 would involve the generation of two distinct file names, one
6203 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6204 simply substituted with a file name chosen for the previous @samp{%u},
6205 without regard to any appended suffix.
6207 @item %j@var{suffix}
6208 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6209 writable, and if save-temps is off; otherwise, substitute the name
6210 of a temporary file, just like @samp{%u}. This temporary file is not
6211 meant for communication between processes, but rather as a junk
6214 @item %|@var{suffix}
6215 @itemx %m@var{suffix}
6216 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6217 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6218 all. These are the two most common ways to instruct a program that it
6219 should read from standard input or write to standard output. If you
6220 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6221 construct: see for example @file{f/lang-specs.h}.
6223 @item %.@var{SUFFIX}
6224 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6225 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6226 terminated by the next space or %.
6229 Marks the argument containing or following the @samp{%w} as the
6230 designated output file of this compilation. This puts the argument
6231 into the sequence of arguments that @samp{%o} will substitute later.
6234 Substitutes the names of all the output files, with spaces
6235 automatically placed around them. You should write spaces
6236 around the @samp{%o} as well or the results are undefined.
6237 @samp{%o} is for use in the specs for running the linker.
6238 Input files whose names have no recognized suffix are not compiled
6239 at all, but they are included among the output files, so they will
6243 Substitutes the suffix for object files. Note that this is
6244 handled specially when it immediately follows @samp{%g, %u, or %U},
6245 because of the need for those to form complete file names. The
6246 handling is such that @samp{%O} is treated exactly as if it had already
6247 been substituted, except that @samp{%g, %u, and %U} do not currently
6248 support additional @var{suffix} characters following @samp{%O} as they would
6249 following, for example, @samp{.o}.
6252 Substitutes the standard macro predefinitions for the
6253 current target machine. Use this when running @code{cpp}.
6256 Like @samp{%p}, but puts @samp{__} before and after the name of each
6257 predefined macro, except for macros that start with @samp{__} or with
6258 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6262 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6263 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
6264 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6268 Current argument is the name of a library or startup file of some sort.
6269 Search for that file in a standard list of directories and substitute
6270 the full name found.
6273 Print @var{str} as an error message. @var{str} is terminated by a newline.
6274 Use this when inconsistent options are detected.
6277 Substitute the contents of spec string @var{name} at this point.
6280 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6282 @item %x@{@var{option}@}
6283 Accumulate an option for @samp{%X}.
6286 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6290 Output the accumulated assembler options specified by @option{-Wa}.
6293 Output the accumulated preprocessor options specified by @option{-Wp}.
6296 Process the @code{asm} spec. This is used to compute the
6297 switches to be passed to the assembler.
6300 Process the @code{asm_final} spec. This is a spec string for
6301 passing switches to an assembler post-processor, if such a program is
6305 Process the @code{link} spec. This is the spec for computing the
6306 command line passed to the linker. Typically it will make use of the
6307 @samp{%L %G %S %D and %E} sequences.
6310 Dump out a @option{-L} option for each directory that GCC believes might
6311 contain startup files. If the target supports multilibs then the
6312 current multilib directory will be prepended to each of these paths.
6315 Output the multilib directory with directory separators replaced with
6316 @samp{_}. If multilib directories are not set, or the multilib directory is
6317 @file{.} then this option emits nothing.
6320 Process the @code{lib} spec. This is a spec string for deciding which
6321 libraries should be included on the command line to the linker.
6324 Process the @code{libgcc} spec. This is a spec string for deciding
6325 which GCC support library should be included on the command line to the linker.
6328 Process the @code{startfile} spec. This is a spec for deciding which
6329 object files should be the first ones passed to the linker. Typically
6330 this might be a file named @file{crt0.o}.
6333 Process the @code{endfile} spec. This is a spec string that specifies
6334 the last object files that will be passed to the linker.
6337 Process the @code{cpp} spec. This is used to construct the arguments
6338 to be passed to the C preprocessor.
6341 Process the @code{cc1} spec. This is used to construct the options to be
6342 passed to the actual C compiler (@samp{cc1}).
6345 Process the @code{cc1plus} spec. This is used to construct the options to be
6346 passed to the actual C++ compiler (@samp{cc1plus}).
6349 Substitute the variable part of a matched option. See below.
6350 Note that each comma in the substituted string is replaced by
6354 Remove all occurrences of @code{-S} from the command line. Note---this
6355 command is position dependent. @samp{%} commands in the spec string
6356 before this one will see @code{-S}, @samp{%} commands in the spec string
6357 after this one will not.
6359 @item %:@var{function}(@var{args})
6360 Call the named function @var{function}, passing it @var{args}.
6361 @var{args} is first processed as a nested spec string, then split
6362 into an argument vector in the usual fashion. The function returns
6363 a string which is processed as if it had appeared literally as part
6364 of the current spec.
6366 The following built-in spec functions are provided:
6369 @item @code{if-exists}
6370 The @code{if-exists} spec function takes one argument, an absolute
6371 pathname to a file. If the file exists, @code{if-exists} returns the
6372 pathname. Here is a small example of its usage:
6376 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6379 @item @code{if-exists-else}
6380 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6381 spec function, except that it takes two arguments. The first argument is
6382 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6383 returns the pathname. If it does not exist, it returns the second argument.
6384 This way, @code{if-exists-else} can be used to select one file or another,
6385 based on the existence of the first. Here is a small example of its usage:
6389 crt0%O%s %:if-exists(crti%O%s) \
6390 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6393 @item @code{replace-outfile}
6394 The @code{replace-outfile} spec function takes two arguments. It looks for the
6395 first argument in the outfiles array and replaces it with the second argument. Here
6396 is a small example of its usage:
6399 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
6405 Substitutes the @code{-S} switch, if that switch was given to GCC@.
6406 If that switch was not specified, this substitutes nothing. Note that
6407 the leading dash is omitted when specifying this option, and it is
6408 automatically inserted if the substitution is performed. Thus the spec
6409 string @samp{%@{foo@}} would match the command-line option @option{-foo}
6410 and would output the command line option @option{-foo}.
6412 @item %W@{@code{S}@}
6413 Like %@{@code{S}@} but mark last argument supplied within as a file to be
6416 @item %@{@code{S}*@}
6417 Substitutes all the switches specified to GCC whose names start
6418 with @code{-S}, but which also take an argument. This is used for
6419 switches like @option{-o}, @option{-D}, @option{-I}, etc.
6420 GCC considers @option{-o foo} as being
6421 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
6422 text, including the space. Thus two arguments would be generated.
6424 @item %@{@code{S}*&@code{T}*@}
6425 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
6426 (the order of @code{S} and @code{T} in the spec is not significant).
6427 There can be any number of ampersand-separated variables; for each the
6428 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
6430 @item %@{@code{S}:@code{X}@}
6431 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
6433 @item %@{!@code{S}:@code{X}@}
6434 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
6436 @item %@{@code{S}*:@code{X}@}
6437 Substitutes @code{X} if one or more switches whose names start with
6438 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
6439 once, no matter how many such switches appeared. However, if @code{%*}
6440 appears somewhere in @code{X}, then @code{X} will be substituted once
6441 for each matching switch, with the @code{%*} replaced by the part of
6442 that switch that matched the @code{*}.
6444 @item %@{.@code{S}:@code{X}@}
6445 Substitutes @code{X}, if processing a file with suffix @code{S}.
6447 @item %@{!.@code{S}:@code{X}@}
6448 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
6450 @item %@{@code{S}|@code{P}:@code{X}@}
6451 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
6452 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
6453 although they have a stronger binding than the @samp{|}. If @code{%*}
6454 appears in @code{X}, all of the alternatives must be starred, and only
6455 the first matching alternative is substituted.
6457 For example, a spec string like this:
6460 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
6463 will output the following command-line options from the following input
6464 command-line options:
6469 -d fred.c -foo -baz -boggle
6470 -d jim.d -bar -baz -boggle
6473 @item %@{S:X; T:Y; :D@}
6475 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
6476 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
6477 be as many clauses as you need. This may be combined with @code{.},
6478 @code{!}, @code{|}, and @code{*} as needed.
6483 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
6484 construct may contain other nested @samp{%} constructs or spaces, or
6485 even newlines. They are processed as usual, as described above.
6486 Trailing white space in @code{X} is ignored. White space may also
6487 appear anywhere on the left side of the colon in these constructs,
6488 except between @code{.} or @code{*} and the corresponding word.
6490 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
6491 handled specifically in these constructs. If another value of
6492 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
6493 @option{-W} switch is found later in the command line, the earlier
6494 switch value is ignored, except with @{@code{S}*@} where @code{S} is
6495 just one letter, which passes all matching options.
6497 The character @samp{|} at the beginning of the predicate text is used to
6498 indicate that a command should be piped to the following command, but
6499 only if @option{-pipe} is specified.
6501 It is built into GCC which switches take arguments and which do not.
6502 (You might think it would be useful to generalize this to allow each
6503 compiler's spec to say which switches take arguments. But this cannot
6504 be done in a consistent fashion. GCC cannot even decide which input
6505 files have been specified without knowing which switches take arguments,
6506 and it must know which input files to compile in order to tell which
6509 GCC also knows implicitly that arguments starting in @option{-l} are to be
6510 treated as compiler output files, and passed to the linker in their
6511 proper position among the other output files.
6513 @c man begin OPTIONS
6515 @node Target Options
6516 @section Specifying Target Machine and Compiler Version
6517 @cindex target options
6518 @cindex cross compiling
6519 @cindex specifying machine version
6520 @cindex specifying compiler version and target machine
6521 @cindex compiler version, specifying
6522 @cindex target machine, specifying
6524 The usual way to run GCC is to run the executable called @file{gcc}, or
6525 @file{<machine>-gcc} when cross-compiling, or
6526 @file{<machine>-gcc-<version>} to run a version other than the one that
6527 was installed last. Sometimes this is inconvenient, so GCC provides
6528 options that will switch to another cross-compiler or version.
6531 @item -b @var{machine}
6533 The argument @var{machine} specifies the target machine for compilation.
6535 The value to use for @var{machine} is the same as was specified as the
6536 machine type when configuring GCC as a cross-compiler. For
6537 example, if a cross-compiler was configured with @samp{configure
6538 i386v}, meaning to compile for an 80386 running System V, then you
6539 would specify @option{-b i386v} to run that cross compiler.
6541 @item -V @var{version}
6543 The argument @var{version} specifies which version of GCC to run.
6544 This is useful when multiple versions are installed. For example,
6545 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
6548 The @option{-V} and @option{-b} options work by running the
6549 @file{<machine>-gcc-<version>} executable, so there's no real reason to
6550 use them if you can just run that directly.
6552 @node Submodel Options
6553 @section Hardware Models and Configurations
6554 @cindex submodel options
6555 @cindex specifying hardware config
6556 @cindex hardware models and configurations, specifying
6557 @cindex machine dependent options
6559 Earlier we discussed the standard option @option{-b} which chooses among
6560 different installed compilers for completely different target
6561 machines, such as VAX vs.@: 68000 vs.@: 80386.
6563 In addition, each of these target machine types can have its own
6564 special options, starting with @samp{-m}, to choose among various
6565 hardware models or configurations---for example, 68010 vs 68020,
6566 floating coprocessor or none. A single installed version of the
6567 compiler can compile for any model or configuration, according to the
6570 Some configurations of the compiler also support additional special
6571 options, usually for compatibility with other compilers on the same
6574 These options are defined by the macro @code{TARGET_SWITCHES} in the
6575 machine description. The default for the options is also defined by
6576 that macro, which enables you to change the defaults.
6578 @c This list is ordered alphanumerically by subsection name.
6579 @c It should be the same order and spelling as these options are listed
6580 @c in Machine Dependent Options
6588 * DEC Alpha Options::
6589 * DEC Alpha/VMS Options::
6593 * i386 and x86-64 Options::
6605 * RS/6000 and PowerPC Options::
6606 * S/390 and zSeries Options::
6609 * System V Options::
6610 * TMS320C3x/C4x Options::
6614 * Xstormy16 Options::
6620 @subsection ARC Options
6623 These options are defined for ARC implementations:
6628 Compile code for little endian mode. This is the default.
6632 Compile code for big endian mode.
6635 @opindex mmangle-cpu
6636 Prepend the name of the cpu to all public symbol names.
6637 In multiple-processor systems, there are many ARC variants with different
6638 instruction and register set characteristics. This flag prevents code
6639 compiled for one cpu to be linked with code compiled for another.
6640 No facility exists for handling variants that are ``almost identical''.
6641 This is an all or nothing option.
6643 @item -mcpu=@var{cpu}
6645 Compile code for ARC variant @var{cpu}.
6646 Which variants are supported depend on the configuration.
6647 All variants support @option{-mcpu=base}, this is the default.
6649 @item -mtext=@var{text-section}
6650 @itemx -mdata=@var{data-section}
6651 @itemx -mrodata=@var{readonly-data-section}
6655 Put functions, data, and readonly data in @var{text-section},
6656 @var{data-section}, and @var{readonly-data-section} respectively
6657 by default. This can be overridden with the @code{section} attribute.
6658 @xref{Variable Attributes}.
6663 @subsection ARM Options
6666 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6670 @item -mabi=@var{name}
6672 Generate code for the specified ABI. Permissible values are: @samp{apcs-gnu},
6673 @samp{atpcs}, @samp{aapcs} and @samp{iwmmxt}.
6676 @opindex mapcs-frame
6677 Generate a stack frame that is compliant with the ARM Procedure Call
6678 Standard for all functions, even if this is not strictly necessary for
6679 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6680 with this option will cause the stack frames not to be generated for
6681 leaf functions. The default is @option{-mno-apcs-frame}.
6685 This is a synonym for @option{-mapcs-frame}.
6688 @c not currently implemented
6689 @item -mapcs-stack-check
6690 @opindex mapcs-stack-check
6691 Generate code to check the amount of stack space available upon entry to
6692 every function (that actually uses some stack space). If there is
6693 insufficient space available then either the function
6694 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6695 called, depending upon the amount of stack space required. The run time
6696 system is required to provide these functions. The default is
6697 @option{-mno-apcs-stack-check}, since this produces smaller code.
6699 @c not currently implemented
6701 @opindex mapcs-float
6702 Pass floating point arguments using the float point registers. This is
6703 one of the variants of the APCS@. This option is recommended if the
6704 target hardware has a floating point unit or if a lot of floating point
6705 arithmetic is going to be performed by the code. The default is
6706 @option{-mno-apcs-float}, since integer only code is slightly increased in
6707 size if @option{-mapcs-float} is used.
6709 @c not currently implemented
6710 @item -mapcs-reentrant
6711 @opindex mapcs-reentrant
6712 Generate reentrant, position independent code. The default is
6713 @option{-mno-apcs-reentrant}.
6716 @item -mthumb-interwork
6717 @opindex mthumb-interwork
6718 Generate code which supports calling between the ARM and Thumb
6719 instruction sets. Without this option the two instruction sets cannot
6720 be reliably used inside one program. The default is
6721 @option{-mno-thumb-interwork}, since slightly larger code is generated
6722 when @option{-mthumb-interwork} is specified.
6724 @item -mno-sched-prolog
6725 @opindex mno-sched-prolog
6726 Prevent the reordering of instructions in the function prolog, or the
6727 merging of those instruction with the instructions in the function's
6728 body. This means that all functions will start with a recognizable set
6729 of instructions (or in fact one of a choice from a small set of
6730 different function prologues), and this information can be used to
6731 locate the start if functions inside an executable piece of code. The
6732 default is @option{-msched-prolog}.
6735 @opindex mhard-float
6736 Generate output containing floating point instructions. This is the
6740 @opindex msoft-float
6741 Generate output containing library calls for floating point.
6742 @strong{Warning:} the requisite libraries are not available for all ARM
6743 targets. Normally the facilities of the machine's usual C compiler are
6744 used, but this cannot be done directly in cross-compilation. You must make
6745 your own arrangements to provide suitable library functions for
6748 @option{-msoft-float} changes the calling convention in the output file;
6749 therefore, it is only useful if you compile @emph{all} of a program with
6750 this option. In particular, you need to compile @file{libgcc.a}, the
6751 library that comes with GCC, with @option{-msoft-float} in order for
6754 @item -mfloat-abi=@var{name}
6756 Specifies which ABI to use for floating point values. Permissible values
6757 are: @samp{soft}, @samp{softfp} and @samp{hard}.
6759 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
6760 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
6761 of floating point instructions, but still uses the soft-float calling
6764 @item -mlittle-endian
6765 @opindex mlittle-endian
6766 Generate code for a processor running in little-endian mode. This is
6767 the default for all standard configurations.
6770 @opindex mbig-endian
6771 Generate code for a processor running in big-endian mode; the default is
6772 to compile code for a little-endian processor.
6774 @item -mwords-little-endian
6775 @opindex mwords-little-endian
6776 This option only applies when generating code for big-endian processors.
6777 Generate code for a little-endian word order but a big-endian byte
6778 order. That is, a byte order of the form @samp{32107654}. Note: this
6779 option should only be used if you require compatibility with code for
6780 big-endian ARM processors generated by versions of the compiler prior to
6783 @item -mcpu=@var{name}
6785 This specifies the name of the target ARM processor. GCC uses this name
6786 to determine what kind of instructions it can emit when generating
6787 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6788 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6789 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6790 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6791 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6792 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
6793 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6794 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6795 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
6796 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
6797 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
6798 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
6799 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
6800 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
6803 @itemx -mtune=@var{name}
6805 This option is very similar to the @option{-mcpu=} option, except that
6806 instead of specifying the actual target processor type, and hence
6807 restricting which instructions can be used, it specifies that GCC should
6808 tune the performance of the code as if the target were of the type
6809 specified in this option, but still choosing the instructions that it
6810 will generate based on the cpu specified by a @option{-mcpu=} option.
6811 For some ARM implementations better performance can be obtained by using
6814 @item -march=@var{name}
6816 This specifies the name of the target ARM architecture. GCC uses this
6817 name to determine what kind of instructions it can emit when generating
6818 assembly code. This option can be used in conjunction with or instead
6819 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6820 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6821 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
6822 @samp{iwmmxt}, @samp{ep9312}.
6824 @item -mfpu=@var{name}
6825 @itemx -mfpe=@var{number}
6826 @itemx -mfp=@var{number}
6830 This specifies what floating point hardware (or hardware emulation) is
6831 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
6832 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
6833 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
6834 with older versions of GCC@.
6836 If @option{-msoft-float} is specified this specifies the format of
6837 floating point values.
6839 @item -mstructure-size-boundary=@var{n}
6840 @opindex mstructure-size-boundary
6841 The size of all structures and unions will be rounded up to a multiple
6842 of the number of bits set by this option. Permissible values are 8, 32
6843 and 64. The default value varies for different toolchains. For the COFF
6844 targeted toolchain the default value is 8. A value of 64 is only allowed
6845 if the underlying ABI supports it.
6847 Specifying the larger number can produce faster, more efficient code, but
6848 can also increase the size of the program. Different values are potentially
6849 incompatible. Code compiled with one value cannot necessarily expect to
6850 work with code or libraries compiled with another value, if they exchange
6851 information using structures or unions.
6853 @item -mabort-on-noreturn
6854 @opindex mabort-on-noreturn
6855 Generate a call to the function @code{abort} at the end of a
6856 @code{noreturn} function. It will be executed if the function tries to
6860 @itemx -mno-long-calls
6861 @opindex mlong-calls
6862 @opindex mno-long-calls
6863 Tells the compiler to perform function calls by first loading the
6864 address of the function into a register and then performing a subroutine
6865 call on this register. This switch is needed if the target function
6866 will lie outside of the 64 megabyte addressing range of the offset based
6867 version of subroutine call instruction.
6869 Even if this switch is enabled, not all function calls will be turned
6870 into long calls. The heuristic is that static functions, functions
6871 which have the @samp{short-call} attribute, functions that are inside
6872 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6873 definitions have already been compiled within the current compilation
6874 unit, will not be turned into long calls. The exception to this rule is
6875 that weak function definitions, functions with the @samp{long-call}
6876 attribute or the @samp{section} attribute, and functions that are within
6877 the scope of a @samp{#pragma long_calls} directive, will always be
6878 turned into long calls.
6880 This feature is not enabled by default. Specifying
6881 @option{-mno-long-calls} will restore the default behavior, as will
6882 placing the function calls within the scope of a @samp{#pragma
6883 long_calls_off} directive. Note these switches have no effect on how
6884 the compiler generates code to handle function calls via function
6887 @item -mnop-fun-dllimport
6888 @opindex mnop-fun-dllimport
6889 Disable support for the @code{dllimport} attribute.
6891 @item -msingle-pic-base
6892 @opindex msingle-pic-base
6893 Treat the register used for PIC addressing as read-only, rather than
6894 loading it in the prologue for each function. The run-time system is
6895 responsible for initializing this register with an appropriate value
6896 before execution begins.
6898 @item -mpic-register=@var{reg}
6899 @opindex mpic-register
6900 Specify the register to be used for PIC addressing. The default is R10
6901 unless stack-checking is enabled, when R9 is used.
6903 @item -mcirrus-fix-invalid-insns
6904 @opindex mcirrus-fix-invalid-insns
6905 @opindex mno-cirrus-fix-invalid-insns
6906 Insert NOPs into the instruction stream to in order to work around
6907 problems with invalid Maverick instruction combinations. This option
6908 is only valid if the @option{-mcpu=ep9312} option has been used to
6909 enable generation of instructions for the Cirrus Maverick floating
6910 point co-processor. This option is not enabled by default, since the
6911 problem is only present in older Maverick implementations. The default
6912 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6915 @item -mpoke-function-name
6916 @opindex mpoke-function-name
6917 Write the name of each function into the text section, directly
6918 preceding the function prologue. The generated code is similar to this:
6922 .ascii "arm_poke_function_name", 0
6925 .word 0xff000000 + (t1 - t0)
6926 arm_poke_function_name
6928 stmfd sp!, @{fp, ip, lr, pc@}
6932 When performing a stack backtrace, code can inspect the value of
6933 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6934 location @code{pc - 12} and the top 8 bits are set, then we know that
6935 there is a function name embedded immediately preceding this location
6936 and has length @code{((pc[-3]) & 0xff000000)}.
6940 Generate code for the 16-bit Thumb instruction set. The default is to
6941 use the 32-bit ARM instruction set.
6944 @opindex mtpcs-frame
6945 Generate a stack frame that is compliant with the Thumb Procedure Call
6946 Standard for all non-leaf functions. (A leaf function is one that does
6947 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6949 @item -mtpcs-leaf-frame
6950 @opindex mtpcs-leaf-frame
6951 Generate a stack frame that is compliant with the Thumb Procedure Call
6952 Standard for all leaf functions. (A leaf function is one that does
6953 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6955 @item -mcallee-super-interworking
6956 @opindex mcallee-super-interworking
6957 Gives all externally visible functions in the file being compiled an ARM
6958 instruction set header which switches to Thumb mode before executing the
6959 rest of the function. This allows these functions to be called from
6960 non-interworking code.
6962 @item -mcaller-super-interworking
6963 @opindex mcaller-super-interworking
6964 Allows calls via function pointers (including virtual functions) to
6965 execute correctly regardless of whether the target code has been
6966 compiled for interworking or not. There is a small overhead in the cost
6967 of executing a function pointer if this option is enabled.
6972 @subsection AVR Options
6975 These options are defined for AVR implementations:
6978 @item -mmcu=@var{mcu}
6980 Specify ATMEL AVR instruction set or MCU type.
6982 Instruction set avr1 is for the minimal AVR core, not supported by the C
6983 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
6984 attiny11, attiny12, attiny15, attiny28).
6986 Instruction set avr2 (default) is for the classic AVR core with up to
6987 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
6988 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
6989 at90c8534, at90s8535).
6991 Instruction set avr3 is for the classic AVR core with up to 128K program
6992 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
6994 Instruction set avr4 is for the enhanced AVR core with up to 8K program
6995 memory space (MCU types: atmega8, atmega83, atmega85).
6997 Instruction set avr5 is for the enhanced AVR core with up to 128K program
6998 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
6999 atmega64, atmega128, at43usb355, at94k).
7003 Output instruction sizes to the asm file.
7005 @item -minit-stack=@var{N}
7006 @opindex minit-stack
7007 Specify the initial stack address, which may be a symbol or numeric value,
7008 @samp{__stack} is the default.
7010 @item -mno-interrupts
7011 @opindex mno-interrupts
7012 Generated code is not compatible with hardware interrupts.
7013 Code size will be smaller.
7015 @item -mcall-prologues
7016 @opindex mcall-prologues
7017 Functions prologues/epilogues expanded as call to appropriate
7018 subroutines. Code size will be smaller.
7020 @item -mno-tablejump
7021 @opindex mno-tablejump
7022 Do not generate tablejump insns which sometimes increase code size.
7025 @opindex mtiny-stack
7026 Change only the low 8 bits of the stack pointer.
7030 Assume int to be 8 bit integer. This affects the sizes of all types: A
7031 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7032 and long long will be 4 bytes. Please note that this option does not
7033 comply to the C standards, but it will provide you with smaller code
7038 @subsection CRIS Options
7039 @cindex CRIS Options
7041 These options are defined specifically for the CRIS ports.
7044 @item -march=@var{architecture-type}
7045 @itemx -mcpu=@var{architecture-type}
7048 Generate code for the specified architecture. The choices for
7049 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7050 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
7051 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7054 @item -mtune=@var{architecture-type}
7056 Tune to @var{architecture-type} everything applicable about the generated
7057 code, except for the ABI and the set of available instructions. The
7058 choices for @var{architecture-type} are the same as for
7059 @option{-march=@var{architecture-type}}.
7061 @item -mmax-stack-frame=@var{n}
7062 @opindex mmax-stack-frame
7063 Warn when the stack frame of a function exceeds @var{n} bytes.
7065 @item -melinux-stacksize=@var{n}
7066 @opindex melinux-stacksize
7067 Only available with the @samp{cris-axis-aout} target. Arranges for
7068 indications in the program to the kernel loader that the stack of the
7069 program should be set to @var{n} bytes.
7075 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7076 @option{-march=v3} and @option{-march=v8} respectively.
7078 @item -mmul-bug-workaround
7079 @itemx -mno-mul-bug-workaround
7080 @opindex mmul-bug-workaround
7081 @opindex mno-mul-bug-workaround
7082 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7083 models where it applies. This option is active by default.
7087 Enable CRIS-specific verbose debug-related information in the assembly
7088 code. This option also has the effect to turn off the @samp{#NO_APP}
7089 formatted-code indicator to the assembler at the beginning of the
7094 Do not use condition-code results from previous instruction; always emit
7095 compare and test instructions before use of condition codes.
7097 @item -mno-side-effects
7098 @opindex mno-side-effects
7099 Do not emit instructions with side-effects in addressing modes other than
7103 @itemx -mno-stack-align
7105 @itemx -mno-data-align
7106 @itemx -mconst-align
7107 @itemx -mno-const-align
7108 @opindex mstack-align
7109 @opindex mno-stack-align
7110 @opindex mdata-align
7111 @opindex mno-data-align
7112 @opindex mconst-align
7113 @opindex mno-const-align
7114 These options (no-options) arranges (eliminate arrangements) for the
7115 stack-frame, individual data and constants to be aligned for the maximum
7116 single data access size for the chosen CPU model. The default is to
7117 arrange for 32-bit alignment. ABI details such as structure layout are
7118 not affected by these options.
7126 Similar to the stack- data- and const-align options above, these options
7127 arrange for stack-frame, writable data and constants to all be 32-bit,
7128 16-bit or 8-bit aligned. The default is 32-bit alignment.
7130 @item -mno-prologue-epilogue
7131 @itemx -mprologue-epilogue
7132 @opindex mno-prologue-epilogue
7133 @opindex mprologue-epilogue
7134 With @option{-mno-prologue-epilogue}, the normal function prologue and
7135 epilogue that sets up the stack-frame are omitted and no return
7136 instructions or return sequences are generated in the code. Use this
7137 option only together with visual inspection of the compiled code: no
7138 warnings or errors are generated when call-saved registers must be saved,
7139 or storage for local variable needs to be allocated.
7145 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7146 instruction sequences that load addresses for functions from the PLT part
7147 of the GOT rather than (traditional on other architectures) calls to the
7148 PLT. The default is @option{-mgotplt}.
7152 Legacy no-op option only recognized with the cris-axis-aout target.
7156 Legacy no-op option only recognized with the cris-axis-elf and
7157 cris-axis-linux-gnu targets.
7161 Only recognized with the cris-axis-aout target, where it selects a
7162 GNU/linux-like multilib, include files and instruction set for
7167 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7171 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7172 to link with input-output functions from a simulator library. Code,
7173 initialized data and zero-initialized data are allocated consecutively.
7177 Like @option{-sim}, but pass linker options to locate initialized data at
7178 0x40000000 and zero-initialized data at 0x80000000.
7181 @node Darwin Options
7182 @subsection Darwin Options
7183 @cindex Darwin options
7185 These options are defined for all architectures running the Darwin operating
7186 system. They are useful for compatibility with other Mac OS compilers.
7191 Add the framework directory @var{dir} to the head of the list of
7192 directories to be searched for header files. These directories are
7193 interleaved with those specified by @option{-I} options and are
7194 scanned in a left-to-right order.
7196 A framework directory is a directory with frameworks in it. A
7197 framework is a directory with a @samp{"Headers"} and/or
7198 @samp{"PrivateHeaders"} directory contained directly in it that ends
7199 in @samp{".framework"}. The name of a framework is the name of this
7200 directory excluding the @samp{".framework"}. Headers associated with
7201 the framework are found in one of those two directories, with
7202 @samp{"Headers"} being searched first. A subframework is a framework
7203 directory that is in a framework's @samp{"Frameworks"} directory.
7204 Includes of subframework headers can only appear in a header of a
7205 framework that contains the subframework, or in a sibling subframework
7206 header. Two subframeworks are siblings if they occur in the same
7207 framework. A subframework should not have the same name as a
7208 framework, a warning will be issued if this is violated. Currently a
7209 subframework cannot have subframeworks, in the future, the mechanism
7210 may be extended to support this. The standard frameworks can be found
7211 in @samp{"/System/Library/Frameworks"} and
7212 @samp{"/Library/Frameworks"}. An example include looks like
7213 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7214 the name of the framework and header.h is found in the
7215 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7219 Emit debugging information for symbols that are used. For STABS
7220 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7221 This is by default ON.
7225 Emit debugging information for all symbols and types.
7227 @item -mone-byte-bool
7228 @opindex -mone-byte-bool
7229 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7230 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7231 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7232 option has no effect on x86.
7234 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7235 to generate code that is not binary compatible with code generated
7236 without that switch. Using this switch may require recompiling all
7237 other modules in a program, including system libraries. Use this
7238 switch to conform to a non-default data model.
7240 @item -mfix-and-continue
7241 @itemx -ffix-and-continue
7242 @itemx -findirect-data
7243 @opindex mfix-and-continue
7244 @opindex ffix-and-continue
7245 @opindex findirect-data
7246 Generate code suitable for fast turn around development. Needed to
7247 enable gdb to dynamically load @code{.o} files into already running
7248 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7249 are provided for backwards compatibility.
7253 Loads all members of static archive libraries.
7254 See man ld(1) for more information.
7256 @item -arch_errors_fatal
7257 @opindex arch_errors_fatal
7258 Cause the errors having to do with files that have the wrong architecture
7262 @opindex bind_at_load
7263 Causes the output file to be marked such that the dynamic linker will
7264 bind all undefined references when the file is loaded or launched.
7268 Produce a Mach-o bundle format file.
7269 See man ld(1) for more information.
7271 @item -bundle_loader @var{executable}
7272 @opindex bundle_loader
7273 This specifies the @var{executable} that will be loading the build
7274 output file being linked. See man ld(1) for more information.
7276 @item -allowable_client @var{client_name}
7280 @itemx -compatibility_version
7281 @itemx -current_version
7283 @itemx -dependency-file
7285 @itemx -dylinker_install_name
7288 @itemx -exported_symbols_list
7290 @itemx -flat_namespace
7291 @itemx -force_cpusubtype_ALL
7292 @itemx -force_flat_namespace
7293 @itemx -headerpad_max_install_names
7296 @itemx -install_name
7297 @itemx -keep_private_externs
7298 @itemx -multi_module
7299 @itemx -multiply_defined
7300 @itemx -multiply_defined_unused
7302 @itemx -no_dead_strip_inits_and_terms
7303 @itemx -nofixprebinding
7306 @itemx -noseglinkedit
7307 @itemx -pagezero_size
7309 @itemx -prebind_all_twolevel_modules
7310 @itemx -private_bundle
7311 @itemx -read_only_relocs
7313 @itemx -sectobjectsymbols
7317 @itemx -sectobjectsymbols
7320 @itemx -segs_read_only_addr
7321 @itemx -segs_read_write_addr
7322 @itemx -seg_addr_table
7323 @itemx -seg_addr_table_filename
7326 @itemx -segs_read_only_addr
7327 @itemx -segs_read_write_addr
7328 @itemx -single_module
7331 @itemx -sub_umbrella
7332 @itemx -twolevel_namespace
7335 @itemx -unexported_symbols_list
7336 @itemx -weak_reference_mismatches
7339 @opindex allowable_client
7341 @opindex client_name
7342 @opindex compatibility_version
7343 @opindex current_version
7345 @opindex dependency-file
7347 @opindex dylinker_install_name
7350 @opindex exported_symbols_list
7352 @opindex flat_namespace
7353 @opindex force_cpusubtype_ALL
7354 @opindex force_flat_namespace
7355 @opindex headerpad_max_install_names
7358 @opindex install_name
7359 @opindex keep_private_externs
7360 @opindex multi_module
7361 @opindex multiply_defined
7362 @opindex multiply_defined_unused
7364 @opindex no_dead_strip_inits_and_terms
7365 @opindex nofixprebinding
7366 @opindex nomultidefs
7368 @opindex noseglinkedit
7369 @opindex pagezero_size
7371 @opindex prebind_all_twolevel_modules
7372 @opindex private_bundle
7373 @opindex read_only_relocs
7375 @opindex sectobjectsymbols
7379 @opindex sectobjectsymbols
7382 @opindex segs_read_only_addr
7383 @opindex segs_read_write_addr
7384 @opindex seg_addr_table
7385 @opindex seg_addr_table_filename
7386 @opindex seglinkedit
7388 @opindex segs_read_only_addr
7389 @opindex segs_read_write_addr
7390 @opindex single_module
7392 @opindex sub_library
7393 @opindex sub_umbrella
7394 @opindex twolevel_namespace
7397 @opindex unexported_symbols_list
7398 @opindex weak_reference_mismatches
7399 @opindex whatsloaded
7401 These options are available for Darwin linker. Darwin linker man page
7402 describes them in detail.
7405 @node DEC Alpha Options
7406 @subsection DEC Alpha Options
7408 These @samp{-m} options are defined for the DEC Alpha implementations:
7411 @item -mno-soft-float
7413 @opindex mno-soft-float
7414 @opindex msoft-float
7415 Use (do not use) the hardware floating-point instructions for
7416 floating-point operations. When @option{-msoft-float} is specified,
7417 functions in @file{libgcc.a} will be used to perform floating-point
7418 operations. Unless they are replaced by routines that emulate the
7419 floating-point operations, or compiled in such a way as to call such
7420 emulations routines, these routines will issue floating-point
7421 operations. If you are compiling for an Alpha without floating-point
7422 operations, you must ensure that the library is built so as not to call
7425 Note that Alpha implementations without floating-point operations are
7426 required to have floating-point registers.
7431 @opindex mno-fp-regs
7432 Generate code that uses (does not use) the floating-point register set.
7433 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
7434 register set is not used, floating point operands are passed in integer
7435 registers as if they were integers and floating-point results are passed
7436 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
7437 so any function with a floating-point argument or return value called by code
7438 compiled with @option{-mno-fp-regs} must also be compiled with that
7441 A typical use of this option is building a kernel that does not use,
7442 and hence need not save and restore, any floating-point registers.
7446 The Alpha architecture implements floating-point hardware optimized for
7447 maximum performance. It is mostly compliant with the IEEE floating
7448 point standard. However, for full compliance, software assistance is
7449 required. This option generates code fully IEEE compliant code
7450 @emph{except} that the @var{inexact-flag} is not maintained (see below).
7451 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
7452 defined during compilation. The resulting code is less efficient but is
7453 able to correctly support denormalized numbers and exceptional IEEE
7454 values such as not-a-number and plus/minus infinity. Other Alpha
7455 compilers call this option @option{-ieee_with_no_inexact}.
7457 @item -mieee-with-inexact
7458 @opindex mieee-with-inexact
7459 This is like @option{-mieee} except the generated code also maintains
7460 the IEEE @var{inexact-flag}. Turning on this option causes the
7461 generated code to implement fully-compliant IEEE math. In addition to
7462 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
7463 macro. On some Alpha implementations the resulting code may execute
7464 significantly slower than the code generated by default. Since there is
7465 very little code that depends on the @var{inexact-flag}, you should
7466 normally not specify this option. Other Alpha compilers call this
7467 option @option{-ieee_with_inexact}.
7469 @item -mfp-trap-mode=@var{trap-mode}
7470 @opindex mfp-trap-mode
7471 This option controls what floating-point related traps are enabled.
7472 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
7473 The trap mode can be set to one of four values:
7477 This is the default (normal) setting. The only traps that are enabled
7478 are the ones that cannot be disabled in software (e.g., division by zero
7482 In addition to the traps enabled by @samp{n}, underflow traps are enabled
7486 Like @samp{su}, but the instructions are marked to be safe for software
7487 completion (see Alpha architecture manual for details).
7490 Like @samp{su}, but inexact traps are enabled as well.
7493 @item -mfp-rounding-mode=@var{rounding-mode}
7494 @opindex mfp-rounding-mode
7495 Selects the IEEE rounding mode. Other Alpha compilers call this option
7496 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
7501 Normal IEEE rounding mode. Floating point numbers are rounded towards
7502 the nearest machine number or towards the even machine number in case
7506 Round towards minus infinity.
7509 Chopped rounding mode. Floating point numbers are rounded towards zero.
7512 Dynamic rounding mode. A field in the floating point control register
7513 (@var{fpcr}, see Alpha architecture reference manual) controls the
7514 rounding mode in effect. The C library initializes this register for
7515 rounding towards plus infinity. Thus, unless your program modifies the
7516 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
7519 @item -mtrap-precision=@var{trap-precision}
7520 @opindex mtrap-precision
7521 In the Alpha architecture, floating point traps are imprecise. This
7522 means without software assistance it is impossible to recover from a
7523 floating trap and program execution normally needs to be terminated.
7524 GCC can generate code that can assist operating system trap handlers
7525 in determining the exact location that caused a floating point trap.
7526 Depending on the requirements of an application, different levels of
7527 precisions can be selected:
7531 Program precision. This option is the default and means a trap handler
7532 can only identify which program caused a floating point exception.
7535 Function precision. The trap handler can determine the function that
7536 caused a floating point exception.
7539 Instruction precision. The trap handler can determine the exact
7540 instruction that caused a floating point exception.
7543 Other Alpha compilers provide the equivalent options called
7544 @option{-scope_safe} and @option{-resumption_safe}.
7546 @item -mieee-conformant
7547 @opindex mieee-conformant
7548 This option marks the generated code as IEEE conformant. You must not
7549 use this option unless you also specify @option{-mtrap-precision=i} and either
7550 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
7551 is to emit the line @samp{.eflag 48} in the function prologue of the
7552 generated assembly file. Under DEC Unix, this has the effect that
7553 IEEE-conformant math library routines will be linked in.
7555 @item -mbuild-constants
7556 @opindex mbuild-constants
7557 Normally GCC examines a 32- or 64-bit integer constant to
7558 see if it can construct it from smaller constants in two or three
7559 instructions. If it cannot, it will output the constant as a literal and
7560 generate code to load it from the data segment at runtime.
7562 Use this option to require GCC to construct @emph{all} integer constants
7563 using code, even if it takes more instructions (the maximum is six).
7565 You would typically use this option to build a shared library dynamic
7566 loader. Itself a shared library, it must relocate itself in memory
7567 before it can find the variables and constants in its own data segment.
7573 Select whether to generate code to be assembled by the vendor-supplied
7574 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
7592 Indicate whether GCC should generate code to use the optional BWX,
7593 CIX, FIX and MAX instruction sets. The default is to use the instruction
7594 sets supported by the CPU type specified via @option{-mcpu=} option or that
7595 of the CPU on which GCC was built if none was specified.
7600 @opindex mfloat-ieee
7601 Generate code that uses (does not use) VAX F and G floating point
7602 arithmetic instead of IEEE single and double precision.
7604 @item -mexplicit-relocs
7605 @itemx -mno-explicit-relocs
7606 @opindex mexplicit-relocs
7607 @opindex mno-explicit-relocs
7608 Older Alpha assemblers provided no way to generate symbol relocations
7609 except via assembler macros. Use of these macros does not allow
7610 optimal instruction scheduling. GNU binutils as of version 2.12
7611 supports a new syntax that allows the compiler to explicitly mark
7612 which relocations should apply to which instructions. This option
7613 is mostly useful for debugging, as GCC detects the capabilities of
7614 the assembler when it is built and sets the default accordingly.
7618 @opindex msmall-data
7619 @opindex mlarge-data
7620 When @option{-mexplicit-relocs} is in effect, static data is
7621 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
7622 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
7623 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
7624 16-bit relocations off of the @code{$gp} register. This limits the
7625 size of the small data area to 64KB, but allows the variables to be
7626 directly accessed via a single instruction.
7628 The default is @option{-mlarge-data}. With this option the data area
7629 is limited to just below 2GB. Programs that require more than 2GB of
7630 data must use @code{malloc} or @code{mmap} to allocate the data in the
7631 heap instead of in the program's data segment.
7633 When generating code for shared libraries, @option{-fpic} implies
7634 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
7638 @opindex msmall-text
7639 @opindex mlarge-text
7640 When @option{-msmall-text} is used, the compiler assumes that the
7641 code of the entire program (or shared library) fits in 4MB, and is
7642 thus reachable with a branch instruction. When @option{-msmall-data}
7643 is used, the compiler can assume that all local symbols share the
7644 same @code{$gp} value, and thus reduce the number of instructions
7645 required for a function call from 4 to 1.
7647 The default is @option{-mlarge-text}.
7649 @item -mcpu=@var{cpu_type}
7651 Set the instruction set and instruction scheduling parameters for
7652 machine type @var{cpu_type}. You can specify either the @samp{EV}
7653 style name or the corresponding chip number. GCC supports scheduling
7654 parameters for the EV4, EV5 and EV6 family of processors and will
7655 choose the default values for the instruction set from the processor
7656 you specify. If you do not specify a processor type, GCC will default
7657 to the processor on which the compiler was built.
7659 Supported values for @var{cpu_type} are
7665 Schedules as an EV4 and has no instruction set extensions.
7669 Schedules as an EV5 and has no instruction set extensions.
7673 Schedules as an EV5 and supports the BWX extension.
7678 Schedules as an EV5 and supports the BWX and MAX extensions.
7682 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
7686 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
7689 @item -mtune=@var{cpu_type}
7691 Set only the instruction scheduling parameters for machine type
7692 @var{cpu_type}. The instruction set is not changed.
7694 @item -mmemory-latency=@var{time}
7695 @opindex mmemory-latency
7696 Sets the latency the scheduler should assume for typical memory
7697 references as seen by the application. This number is highly
7698 dependent on the memory access patterns used by the application
7699 and the size of the external cache on the machine.
7701 Valid options for @var{time} are
7705 A decimal number representing clock cycles.
7711 The compiler contains estimates of the number of clock cycles for
7712 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
7713 (also called Dcache, Scache, and Bcache), as well as to main memory.
7714 Note that L3 is only valid for EV5.
7719 @node DEC Alpha/VMS Options
7720 @subsection DEC Alpha/VMS Options
7722 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
7725 @item -mvms-return-codes
7726 @opindex mvms-return-codes
7727 Return VMS condition codes from main. The default is to return POSIX
7728 style condition (e.g.@ error) codes.
7732 @subsection FRV Options
7739 Only use the first 32 general purpose registers.
7744 Use all 64 general purpose registers.
7749 Use only the first 32 floating point registers.
7754 Use all 64 floating point registers
7757 @opindex mhard-float
7759 Use hardware instructions for floating point operations.
7762 @opindex msoft-float
7764 Use library routines for floating point operations.
7769 Dynamically allocate condition code registers.
7774 Do not try to dynamically allocate condition code registers, only
7775 use @code{icc0} and @code{fcc0}.
7780 Change ABI to use double word insns.
7785 Do not use double word instructions.
7790 Use floating point double instructions.
7795 Do not use floating point double instructions.
7800 Use media instructions.
7805 Do not use media instructions.
7810 Use multiply and add/subtract instructions.
7815 Do not use multiply and add/subtract instructions.
7820 Select the FDPIC ABI, that uses function descriptors to represent
7821 pointers to functions. Without any PIC/PIE-related options, it
7822 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
7823 assumes GOT entries and small data are within a 12-bit range from the
7824 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
7825 are computed with 32 bits.
7828 @opindex minline-plt
7830 Enable inlining of PLT entries in function calls to functions that are
7831 not known to bind locally. It has no effect without @option{-mfdpic}.
7832 It's enabled by default if optimizing for speed and compiling for
7833 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
7834 optimization option such as @option{-O3} or above is present in the
7840 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
7841 that is known to be in read-only sections. It's enabled by default,
7842 except for @option{-fpic} or @option{-fpie}: even though it may help
7843 make the global offset table smaller, it trades 1 instruction for 4.
7844 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
7845 one of which may be shared by multiple symbols, and it avoids the need
7846 for a GOT entry for the referenced symbol, so it's more likely to be a
7847 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
7849 @item -multilib-library-pic
7850 @opindex multilib-library-pic
7852 Link with the (library, not FD) pic libraries. It's implied by
7853 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
7854 @option{-fpic} without @option{-mfdpic}. You should never have to use
7860 Follow the EABI requirement of always creating a frame pointer whenever
7861 a stack frame is allocated. This option is enabled by default and can
7862 be disabled with @option{-mno-linked-fp}.
7865 @opindex mlong-calls
7867 Use indirect addressing to call functions outside the current
7868 compilation unit. This allows the functions to be placed anywhere
7869 within the 32-bit address space.
7871 @item -malign-labels
7872 @opindex malign-labels
7874 Try to align labels to an 8-byte boundary by inserting nops into the
7875 previous packet. This option only has an effect when VLIW packing
7876 is enabled. It doesn't create new packets; it merely adds nops to
7880 @opindex mlibrary-pic
7882 Generate position-independent EABI code.
7887 Use only the first four media accumulator registers.
7892 Use all eight media accumulator registers.
7897 Pack VLIW instructions.
7902 Do not pack VLIW instructions.
7907 Do not mark ABI switches in e_flags.
7912 Enable the use of conditional-move instructions (default).
7914 This switch is mainly for debugging the compiler and will likely be removed
7915 in a future version.
7917 @item -mno-cond-move
7918 @opindex mno-cond-move
7920 Disable the use of conditional-move instructions.
7922 This switch is mainly for debugging the compiler and will likely be removed
7923 in a future version.
7928 Enable the use of conditional set instructions (default).
7930 This switch is mainly for debugging the compiler and will likely be removed
7931 in a future version.
7936 Disable the use of conditional set instructions.
7938 This switch is mainly for debugging the compiler and will likely be removed
7939 in a future version.
7944 Enable the use of conditional execution (default).
7946 This switch is mainly for debugging the compiler and will likely be removed
7947 in a future version.
7949 @item -mno-cond-exec
7950 @opindex mno-cond-exec
7952 Disable the use of conditional execution.
7954 This switch is mainly for debugging the compiler and will likely be removed
7955 in a future version.
7958 @opindex mvliw-branch
7960 Run a pass to pack branches into VLIW instructions (default).
7962 This switch is mainly for debugging the compiler and will likely be removed
7963 in a future version.
7965 @item -mno-vliw-branch
7966 @opindex mno-vliw-branch
7968 Do not run a pass to pack branches into VLIW instructions.
7970 This switch is mainly for debugging the compiler and will likely be removed
7971 in a future version.
7973 @item -mmulti-cond-exec
7974 @opindex mmulti-cond-exec
7976 Enable optimization of @code{&&} and @code{||} in conditional execution
7979 This switch is mainly for debugging the compiler and will likely be removed
7980 in a future version.
7982 @item -mno-multi-cond-exec
7983 @opindex mno-multi-cond-exec
7985 Disable optimization of @code{&&} and @code{||} in conditional execution.
7987 This switch is mainly for debugging the compiler and will likely be removed
7988 in a future version.
7990 @item -mnested-cond-exec
7991 @opindex mnested-cond-exec
7993 Enable nested conditional execution optimizations (default).
7995 This switch is mainly for debugging the compiler and will likely be removed
7996 in a future version.
7998 @item -mno-nested-cond-exec
7999 @opindex mno-nested-cond-exec
8001 Disable nested conditional execution optimizations.
8003 This switch is mainly for debugging the compiler and will likely be removed
8004 in a future version.
8006 @item -mtomcat-stats
8007 @opindex mtomcat-stats
8009 Cause gas to print out tomcat statistics.
8011 @item -mcpu=@var{cpu}
8014 Select the processor type for which to generate code. Possible values are
8015 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8016 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8020 @node H8/300 Options
8021 @subsection H8/300 Options
8023 These @samp{-m} options are defined for the H8/300 implementations:
8028 Shorten some address references at link time, when possible; uses the
8029 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8030 ld, Using ld}, for a fuller description.
8034 Generate code for the H8/300H@.
8038 Generate code for the H8S@.
8042 Generate code for the H8S and H8/300H in the normal mode. This switch
8043 must be used either with @option{-mh} or @option{-ms}.
8047 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8051 Make @code{int} data 32 bits by default.
8055 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8056 The default for the H8/300H and H8S is to align longs and floats on 4
8058 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8059 This option has no effect on the H8/300.
8063 @subsection HPPA Options
8064 @cindex HPPA Options
8066 These @samp{-m} options are defined for the HPPA family of computers:
8069 @item -march=@var{architecture-type}
8071 Generate code for the specified architecture. The choices for
8072 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8073 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8074 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8075 architecture option for your machine. Code compiled for lower numbered
8076 architectures will run on higher numbered architectures, but not the
8080 @itemx -mpa-risc-1-1
8081 @itemx -mpa-risc-2-0
8082 @opindex mpa-risc-1-0
8083 @opindex mpa-risc-1-1
8084 @opindex mpa-risc-2-0
8085 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8088 @opindex mbig-switch
8089 Generate code suitable for big switch tables. Use this option only if
8090 the assembler/linker complain about out of range branches within a switch
8093 @item -mjump-in-delay
8094 @opindex mjump-in-delay
8095 Fill delay slots of function calls with unconditional jump instructions
8096 by modifying the return pointer for the function call to be the target
8097 of the conditional jump.
8099 @item -mdisable-fpregs
8100 @opindex mdisable-fpregs
8101 Prevent floating point registers from being used in any manner. This is
8102 necessary for compiling kernels which perform lazy context switching of
8103 floating point registers. If you use this option and attempt to perform
8104 floating point operations, the compiler will abort.
8106 @item -mdisable-indexing
8107 @opindex mdisable-indexing
8108 Prevent the compiler from using indexing address modes. This avoids some
8109 rather obscure problems when compiling MIG generated code under MACH@.
8111 @item -mno-space-regs
8112 @opindex mno-space-regs
8113 Generate code that assumes the target has no space registers. This allows
8114 GCC to generate faster indirect calls and use unscaled index address modes.
8116 Such code is suitable for level 0 PA systems and kernels.
8118 @item -mfast-indirect-calls
8119 @opindex mfast-indirect-calls
8120 Generate code that assumes calls never cross space boundaries. This
8121 allows GCC to emit code which performs faster indirect calls.
8123 This option will not work in the presence of shared libraries or nested
8126 @item -mfixed-range=@var{register-range}
8127 @opindex mfixed-range
8128 Generate code treating the given register range as fixed registers.
8129 A fixed register is one that the register allocator can not use. This is
8130 useful when compiling kernel code. A register range is specified as
8131 two registers separated by a dash. Multiple register ranges can be
8132 specified separated by a comma.
8134 @item -mlong-load-store
8135 @opindex mlong-load-store
8136 Generate 3-instruction load and store sequences as sometimes required by
8137 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8140 @item -mportable-runtime
8141 @opindex mportable-runtime
8142 Use the portable calling conventions proposed by HP for ELF systems.
8146 Enable the use of assembler directives only GAS understands.
8148 @item -mschedule=@var{cpu-type}
8150 Schedule code according to the constraints for the machine type
8151 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8152 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8153 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8154 proper scheduling option for your machine. The default scheduling is
8158 @opindex mlinker-opt
8159 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8160 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8161 linkers in which they give bogus error messages when linking some programs.
8164 @opindex msoft-float
8165 Generate output containing library calls for floating point.
8166 @strong{Warning:} the requisite libraries are not available for all HPPA
8167 targets. Normally the facilities of the machine's usual C compiler are
8168 used, but this cannot be done directly in cross-compilation. You must make
8169 your own arrangements to provide suitable library functions for
8170 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8171 does provide software floating point support.
8173 @option{-msoft-float} changes the calling convention in the output file;
8174 therefore, it is only useful if you compile @emph{all} of a program with
8175 this option. In particular, you need to compile @file{libgcc.a}, the
8176 library that comes with GCC, with @option{-msoft-float} in order for
8181 Generate the predefine, @code{_SIO}, for server IO. The default is
8182 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8183 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8184 options are available under HP-UX and HI-UX.
8188 Use GNU ld specific options. This passes @option{-shared} to ld when
8189 building a shared library. It is the default when GCC is configured,
8190 explicitly or implicitly, with the GNU linker. This option does not
8191 have any affect on which ld is called, it only changes what parameters
8192 are passed to that ld. The ld that is called is determined by the
8193 @option{--with-ld} configure option, GCC's program search path, and
8194 finally by the user's @env{PATH}. The linker used by GCC can be printed
8195 using @samp{which `gcc -print-prog-name=ld`}.
8199 Use HP ld specific options. This passes @option{-b} to ld when building
8200 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8201 links. It is the default when GCC is configured, explicitly or
8202 implicitly, with the HP linker. This option does not have any affect on
8203 which ld is called, it only changes what parameters are passed to that
8204 ld. The ld that is called is determined by the @option{--with-ld}
8205 configure option, GCC's program search path, and finally by the user's
8206 @env{PATH}. The linker used by GCC can be printed using @samp{which
8207 `gcc -print-prog-name=ld`}.
8210 @opindex mno-long-calls
8211 Generate code that uses long call sequences. This ensures that a call
8212 is always able to reach linker generated stubs. The default is to generate
8213 long calls only when the distance from the call site to the beginning
8214 of the function or translation unit, as the case may be, exceeds a
8215 predefined limit set by the branch type being used. The limits for
8216 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8217 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8220 Distances are measured from the beginning of functions when using the
8221 @option{-ffunction-sections} option, or when using the @option{-mgas}
8222 and @option{-mno-portable-runtime} options together under HP-UX with
8225 It is normally not desirable to use this option as it will degrade
8226 performance. However, it may be useful in large applications,
8227 particularly when partial linking is used to build the application.
8229 The types of long calls used depends on the capabilities of the
8230 assembler and linker, and the type of code being generated. The
8231 impact on systems that support long absolute calls, and long pic
8232 symbol-difference or pc-relative calls should be relatively small.
8233 However, an indirect call is used on 32-bit ELF systems in pic code
8234 and it is quite long.
8236 @item -munix=@var{unix-std}
8238 Generate compiler predefines and select a startfile for the specified
8239 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
8240 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
8241 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
8242 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
8243 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
8246 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
8247 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
8248 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
8249 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
8250 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
8251 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
8253 It is @emph{important} to note that this option changes the interfaces
8254 for various library routines. It also affects the operational behavior
8255 of the C library. Thus, @emph{extreme} care is needed in using this
8258 Library code that is intended to operate with more than one UNIX
8259 standard must test, set and restore the variable @var{__xpg4_extended_mask}
8260 as appropriate. Most GNU software doesn't provide this capability.
8264 Suppress the generation of link options to search libdld.sl when the
8265 @option{-static} option is specified on HP-UX 10 and later.
8269 The HP-UX implementation of setlocale in libc has a dependency on
8270 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8271 when the @option{-static} option is specified, special link options
8272 are needed to resolve this dependency.
8274 On HP-UX 10 and later, the GCC driver adds the necessary options to
8275 link with libdld.sl when the @option{-static} option is specified.
8276 This causes the resulting binary to be dynamic. On the 64-bit port,
8277 the linkers generate dynamic binaries by default in any case. The
8278 @option{-nolibdld} option can be used to prevent the GCC driver from
8279 adding these link options.
8283 Add support for multithreading with the @dfn{dce thread} library
8284 under HP-UX. This option sets flags for both the preprocessor and
8288 @node i386 and x86-64 Options
8289 @subsection Intel 386 and AMD x86-64 Options
8290 @cindex i386 Options
8291 @cindex x86-64 Options
8292 @cindex Intel 386 Options
8293 @cindex AMD x86-64 Options
8295 These @samp{-m} options are defined for the i386 and x86-64 family of
8299 @item -mtune=@var{cpu-type}
8301 Tune to @var{cpu-type} everything applicable about the generated code, except
8302 for the ABI and the set of available instructions. The choices for
8306 Original Intel's i386 CPU.
8308 Intel's i486 CPU. (No scheduling is implemented for this chip.)
8310 Intel Pentium CPU with no MMX support.
8312 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
8313 @item i686, pentiumpro
8314 Intel PentiumPro CPU.
8316 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
8317 @item pentium3, pentium3m
8318 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
8321 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
8322 support. Used by Centrino notebooks.
8323 @item pentium4, pentium4m
8324 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
8326 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
8329 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
8330 SSE2 and SSE3 instruction set support.
8332 AMD K6 CPU with MMX instruction set support.
8334 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
8335 @item athlon, athlon-tbird
8336 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
8338 @item athlon-4, athlon-xp, athlon-mp
8339 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
8340 instruction set support.
8341 @item k8, opteron, athlon64, athlon-fx
8342 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
8343 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
8345 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
8348 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
8349 instruction set support.
8351 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
8352 implemented for this chip.)
8354 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
8355 implemented for this chip.)
8358 While picking a specific @var{cpu-type} will schedule things appropriately
8359 for that particular chip, the compiler will not generate any code that
8360 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8363 @item -march=@var{cpu-type}
8365 Generate instructions for the machine type @var{cpu-type}. The choices
8366 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8367 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8369 @item -mcpu=@var{cpu-type}
8371 A deprecated synonym for @option{-mtune}.
8380 @opindex mpentiumpro
8381 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8382 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8383 These synonyms are deprecated.
8385 @item -mfpmath=@var{unit}
8387 Generate floating point arithmetics for selected unit @var{unit}. The choices
8392 Use the standard 387 floating point coprocessor present majority of chips and
8393 emulated otherwise. Code compiled with this option will run almost everywhere.
8394 The temporary results are computed in 80bit precision instead of precision
8395 specified by the type resulting in slightly different results compared to most
8396 of other chips. See @option{-ffloat-store} for more detailed description.
8398 This is the default choice for i386 compiler.
8401 Use scalar floating point instructions present in the SSE instruction set.
8402 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8403 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8404 instruction set supports only single precision arithmetics, thus the double and
8405 extended precision arithmetics is still done using 387. Later version, present
8406 only in Pentium4 and the future AMD x86-64 chips supports double precision
8409 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8410 @option{-msse2} switches to enable SSE extensions and make this option
8411 effective. For x86-64 compiler, these extensions are enabled by default.
8413 The resulting code should be considerably faster in the majority of cases and avoid
8414 the numerical instability problems of 387 code, but may break some existing
8415 code that expects temporaries to be 80bit.
8417 This is the default choice for the x86-64 compiler.
8420 Attempt to utilize both instruction sets at once. This effectively double the
8421 amount of available registers and on chips with separate execution units for
8422 387 and SSE the execution resources too. Use this option with care, as it is
8423 still experimental, because the GCC register allocator does not model separate
8424 functional units well resulting in instable performance.
8427 @item -masm=@var{dialect}
8428 @opindex masm=@var{dialect}
8429 Output asm instructions using selected @var{dialect}. Supported choices are
8430 @samp{intel} or @samp{att} (the default one).
8435 @opindex mno-ieee-fp
8436 Control whether or not the compiler uses IEEE floating point
8437 comparisons. These handle correctly the case where the result of a
8438 comparison is unordered.
8441 @opindex msoft-float
8442 Generate output containing library calls for floating point.
8443 @strong{Warning:} the requisite libraries are not part of GCC@.
8444 Normally the facilities of the machine's usual C compiler are used, but
8445 this can't be done directly in cross-compilation. You must make your
8446 own arrangements to provide suitable library functions for
8449 On machines where a function returns floating point results in the 80387
8450 register stack, some floating point opcodes may be emitted even if
8451 @option{-msoft-float} is used.
8453 @item -mno-fp-ret-in-387
8454 @opindex mno-fp-ret-in-387
8455 Do not use the FPU registers for return values of functions.
8457 The usual calling convention has functions return values of types
8458 @code{float} and @code{double} in an FPU register, even if there
8459 is no FPU@. The idea is that the operating system should emulate
8462 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8463 in ordinary CPU registers instead.
8465 @item -mno-fancy-math-387
8466 @opindex mno-fancy-math-387
8467 Some 387 emulators do not support the @code{sin}, @code{cos} and
8468 @code{sqrt} instructions for the 387. Specify this option to avoid
8469 generating those instructions. This option is the default on FreeBSD,
8470 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8471 indicates that the target cpu will always have an FPU and so the
8472 instruction will not need emulation. As of revision 2.6.1, these
8473 instructions are not generated unless you also use the
8474 @option{-funsafe-math-optimizations} switch.
8476 @item -malign-double
8477 @itemx -mno-align-double
8478 @opindex malign-double
8479 @opindex mno-align-double
8480 Control whether GCC aligns @code{double}, @code{long double}, and
8481 @code{long long} variables on a two word boundary or a one word
8482 boundary. Aligning @code{double} variables on a two word boundary will
8483 produce code that runs somewhat faster on a @samp{Pentium} at the
8484 expense of more memory.
8486 @strong{Warning:} if you use the @option{-malign-double} switch,
8487 structures containing the above types will be aligned differently than
8488 the published application binary interface specifications for the 386
8489 and will not be binary compatible with structures in code compiled
8490 without that switch.
8492 @item -m96bit-long-double
8493 @itemx -m128bit-long-double
8494 @opindex m96bit-long-double
8495 @opindex m128bit-long-double
8496 These switches control the size of @code{long double} type. The i386
8497 application binary interface specifies the size to be 96 bits,
8498 so @option{-m96bit-long-double} is the default in 32 bit mode.
8500 Modern architectures (Pentium and newer) would prefer @code{long double}
8501 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8502 conforming to the ABI, this would not be possible. So specifying a
8503 @option{-m128bit-long-double} will align @code{long double}
8504 to a 16 byte boundary by padding the @code{long double} with an additional
8507 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8508 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8510 Notice that neither of these options enable any extra precision over the x87
8511 standard of 80 bits for a @code{long double}.
8513 @strong{Warning:} if you override the default value for your target ABI, the
8514 structures and arrays containing @code{long double} variables will change
8515 their size as well as function calling convention for function taking
8516 @code{long double} will be modified. Hence they will not be binary
8517 compatible with arrays or structures in code compiled without that switch.
8521 @itemx -mno-svr3-shlib
8522 @opindex msvr3-shlib
8523 @opindex mno-svr3-shlib
8524 Control whether GCC places uninitialized local variables into the
8525 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8526 into @code{bss}. These options are meaningful only on System V Release 3.
8530 Use a different function-calling convention, in which functions that
8531 take a fixed number of arguments return with the @code{ret} @var{num}
8532 instruction, which pops their arguments while returning. This saves one
8533 instruction in the caller since there is no need to pop the arguments
8536 You can specify that an individual function is called with this calling
8537 sequence with the function attribute @samp{stdcall}. You can also
8538 override the @option{-mrtd} option by using the function attribute
8539 @samp{cdecl}. @xref{Function Attributes}.
8541 @strong{Warning:} this calling convention is incompatible with the one
8542 normally used on Unix, so you cannot use it if you need to call
8543 libraries compiled with the Unix compiler.
8545 Also, you must provide function prototypes for all functions that
8546 take variable numbers of arguments (including @code{printf});
8547 otherwise incorrect code will be generated for calls to those
8550 In addition, seriously incorrect code will result if you call a
8551 function with too many arguments. (Normally, extra arguments are
8552 harmlessly ignored.)
8554 @item -mregparm=@var{num}
8556 Control how many registers are used to pass integer arguments. By
8557 default, no registers are used to pass arguments, and at most 3
8558 registers can be used. You can control this behavior for a specific
8559 function by using the function attribute @samp{regparm}.
8560 @xref{Function Attributes}.
8562 @strong{Warning:} if you use this switch, and
8563 @var{num} is nonzero, then you must build all modules with the same
8564 value, including any libraries. This includes the system libraries and
8567 @item -mpreferred-stack-boundary=@var{num}
8568 @opindex mpreferred-stack-boundary
8569 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8570 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8571 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8572 size (@option{-Os}), in which case the default is the minimum correct
8573 alignment (4 bytes for x86, and 8 bytes for x86-64).
8575 On Pentium and PentiumPro, @code{double} and @code{long double} values
8576 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8577 suffer significant run time performance penalties. On Pentium III, the
8578 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8579 penalties if it is not 16 byte aligned.
8581 To ensure proper alignment of this values on the stack, the stack boundary
8582 must be as aligned as that required by any value stored on the stack.
8583 Further, every function must be generated such that it keeps the stack
8584 aligned. Thus calling a function compiled with a higher preferred
8585 stack boundary from a function compiled with a lower preferred stack
8586 boundary will most likely misalign the stack. It is recommended that
8587 libraries that use callbacks always use the default setting.
8589 This extra alignment does consume extra stack space, and generally
8590 increases code size. Code that is sensitive to stack space usage, such
8591 as embedded systems and operating system kernels, may want to reduce the
8592 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8610 These switches enable or disable the use of built-in functions that allow
8611 direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
8614 @xref{X86 Built-in Functions}, for details of the functions enabled
8615 and disabled by these switches.
8617 To have SSE/SSE2 instructions generated automatically from floating-point
8618 code, see @option{-mfpmath=sse}.
8621 @itemx -mno-push-args
8623 @opindex mno-push-args
8624 Use PUSH operations to store outgoing parameters. This method is shorter
8625 and usually equally fast as method using SUB/MOV operations and is enabled
8626 by default. In some cases disabling it may improve performance because of
8627 improved scheduling and reduced dependencies.
8629 @item -maccumulate-outgoing-args
8630 @opindex maccumulate-outgoing-args
8631 If enabled, the maximum amount of space required for outgoing arguments will be
8632 computed in the function prologue. This is faster on most modern CPUs
8633 because of reduced dependencies, improved scheduling and reduced stack usage
8634 when preferred stack boundary is not equal to 2. The drawback is a notable
8635 increase in code size. This switch implies @option{-mno-push-args}.
8639 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8640 on thread-safe exception handling must compile and link all code with the
8641 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8642 @option{-D_MT}; when linking, it links in a special thread helper library
8643 @option{-lmingwthrd} which cleans up per thread exception handling data.
8645 @item -mno-align-stringops
8646 @opindex mno-align-stringops
8647 Do not align destination of inlined string operations. This switch reduces
8648 code size and improves performance in case the destination is already aligned,
8649 but GCC doesn't know about it.
8651 @item -minline-all-stringops
8652 @opindex minline-all-stringops
8653 By default GCC inlines string operations only when destination is known to be
8654 aligned at least to 4 byte boundary. This enables more inlining, increase code
8655 size, but may improve performance of code that depends on fast memcpy, strlen
8656 and memset for short lengths.
8658 @item -momit-leaf-frame-pointer
8659 @opindex momit-leaf-frame-pointer
8660 Don't keep the frame pointer in a register for leaf functions. This
8661 avoids the instructions to save, set up and restore frame pointers and
8662 makes an extra register available in leaf functions. The option
8663 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8664 which might make debugging harder.
8666 @item -mtls-direct-seg-refs
8667 @itemx -mno-tls-direct-seg-refs
8668 @opindex mtls-direct-seg-refs
8669 Controls whether TLS variables may be accessed with offsets from the
8670 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8671 or whether the thread base pointer must be added. Whether or not this
8672 is legal depends on the operating system, and whether it maps the
8673 segment to cover the entire TLS area.
8675 For systems that use GNU libc, the default is on.
8678 These @samp{-m} switches are supported in addition to the above
8679 on AMD x86-64 processors in 64-bit environments.
8686 Generate code for a 32-bit or 64-bit environment.
8687 The 32-bit environment sets int, long and pointer to 32 bits and
8688 generates code that runs on any i386 system.
8689 The 64-bit environment sets int to 32 bits and long and pointer
8690 to 64 bits and generates code for AMD's x86-64 architecture.
8693 @opindex no-red-zone
8694 Do not use a so called red zone for x86-64 code. The red zone is mandated
8695 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8696 stack pointer that will not be modified by signal or interrupt handlers
8697 and therefore can be used for temporary data without adjusting the stack
8698 pointer. The flag @option{-mno-red-zone} disables this red zone.
8700 @item -mcmodel=small
8701 @opindex mcmodel=small
8702 Generate code for the small code model: the program and its symbols must
8703 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8704 Programs can be statically or dynamically linked. This is the default
8707 @item -mcmodel=kernel
8708 @opindex mcmodel=kernel
8709 Generate code for the kernel code model. The kernel runs in the
8710 negative 2 GB of the address space.
8711 This model has to be used for Linux kernel code.
8713 @item -mcmodel=medium
8714 @opindex mcmodel=medium
8715 Generate code for the medium model: The program is linked in the lower 2
8716 GB of the address space but symbols can be located anywhere in the
8717 address space. Programs can be statically or dynamically linked, but
8718 building of shared libraries are not supported with the medium model.
8720 @item -mcmodel=large
8721 @opindex mcmodel=large
8722 Generate code for the large model: This model makes no assumptions
8723 about addresses and sizes of sections. Currently GCC does not implement
8728 @subsection IA-64 Options
8729 @cindex IA-64 Options
8731 These are the @samp{-m} options defined for the Intel IA-64 architecture.
8735 @opindex mbig-endian
8736 Generate code for a big endian target. This is the default for HP-UX@.
8738 @item -mlittle-endian
8739 @opindex mlittle-endian
8740 Generate code for a little endian target. This is the default for AIX5
8747 Generate (or don't) code for the GNU assembler. This is the default.
8748 @c Also, this is the default if the configure option @option{--with-gnu-as}
8755 Generate (or don't) code for the GNU linker. This is the default.
8756 @c Also, this is the default if the configure option @option{--with-gnu-ld}
8761 Generate code that does not use a global pointer register. The result
8762 is not position independent code, and violates the IA-64 ABI@.
8764 @item -mvolatile-asm-stop
8765 @itemx -mno-volatile-asm-stop
8766 @opindex mvolatile-asm-stop
8767 @opindex mno-volatile-asm-stop
8768 Generate (or don't) a stop bit immediately before and after volatile asm
8773 Generate code that works around Itanium B step errata.
8775 @item -mregister-names
8776 @itemx -mno-register-names
8777 @opindex mregister-names
8778 @opindex mno-register-names
8779 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
8780 the stacked registers. This may make assembler output more readable.
8786 Disable (or enable) optimizations that use the small data section. This may
8787 be useful for working around optimizer bugs.
8790 @opindex mconstant-gp
8791 Generate code that uses a single constant global pointer value. This is
8792 useful when compiling kernel code.
8796 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
8797 This is useful when compiling firmware code.
8799 @item -minline-float-divide-min-latency
8800 @opindex minline-float-divide-min-latency
8801 Generate code for inline divides of floating point values
8802 using the minimum latency algorithm.
8804 @item -minline-float-divide-max-throughput
8805 @opindex minline-float-divide-max-throughput
8806 Generate code for inline divides of floating point values
8807 using the maximum throughput algorithm.
8809 @item -minline-int-divide-min-latency
8810 @opindex minline-int-divide-min-latency
8811 Generate code for inline divides of integer values
8812 using the minimum latency algorithm.
8814 @item -minline-int-divide-max-throughput
8815 @opindex minline-int-divide-max-throughput
8816 Generate code for inline divides of integer values
8817 using the maximum throughput algorithm.
8819 @item -mno-dwarf2-asm
8821 @opindex mno-dwarf2-asm
8822 @opindex mdwarf2-asm
8823 Don't (or do) generate assembler code for the DWARF2 line number debugging
8824 info. This may be useful when not using the GNU assembler.
8826 @item -mfixed-range=@var{register-range}
8827 @opindex mfixed-range
8828 Generate code treating the given register range as fixed registers.
8829 A fixed register is one that the register allocator can not use. This is
8830 useful when compiling kernel code. A register range is specified as
8831 two registers separated by a dash. Multiple register ranges can be
8832 specified separated by a comma.
8834 @item -mearly-stop-bits
8835 @itemx -mno-early-stop-bits
8836 @opindex mearly-stop-bits
8837 @opindex mno-early-stop-bits
8838 Allow stop bits to be placed earlier than immediately preceding the
8839 instruction that triggered the stop bit. This can improve instruction
8840 scheduling, but does not always do so.
8843 @node M32R/D Options
8844 @subsection M32R/D Options
8845 @cindex M32R/D options
8847 These @option{-m} options are defined for Renesas M32R/D architectures:
8852 Generate code for the M32R/2@.
8856 Generate code for the M32R/X@.
8860 Generate code for the M32R@. This is the default.
8863 @opindex mmodel=small
8864 Assume all objects live in the lower 16MB of memory (so that their addresses
8865 can be loaded with the @code{ld24} instruction), and assume all subroutines
8866 are reachable with the @code{bl} instruction.
8867 This is the default.
8869 The addressability of a particular object can be set with the
8870 @code{model} attribute.
8872 @item -mmodel=medium
8873 @opindex mmodel=medium
8874 Assume objects may be anywhere in the 32-bit address space (the compiler
8875 will generate @code{seth/add3} instructions to load their addresses), and
8876 assume all subroutines are reachable with the @code{bl} instruction.
8879 @opindex mmodel=large
8880 Assume objects may be anywhere in the 32-bit address space (the compiler
8881 will generate @code{seth/add3} instructions to load their addresses), and
8882 assume subroutines may not be reachable with the @code{bl} instruction
8883 (the compiler will generate the much slower @code{seth/add3/jl}
8884 instruction sequence).
8887 @opindex msdata=none
8888 Disable use of the small data area. Variables will be put into
8889 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
8890 @code{section} attribute has been specified).
8891 This is the default.
8893 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
8894 Objects may be explicitly put in the small data area with the
8895 @code{section} attribute using one of these sections.
8898 @opindex msdata=sdata
8899 Put small global and static data in the small data area, but do not
8900 generate special code to reference them.
8904 Put small global and static data in the small data area, and generate
8905 special instructions to reference them.
8909 @cindex smaller data references
8910 Put global and static objects less than or equal to @var{num} bytes
8911 into the small data or bss sections instead of the normal data or bss
8912 sections. The default value of @var{num} is 8.
8913 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
8914 for this option to have any effect.
8916 All modules should be compiled with the same @option{-G @var{num}} value.
8917 Compiling with different values of @var{num} may or may not work; if it
8918 doesn't the linker will give an error message---incorrect code will not be
8923 Makes the M32R specific code in the compiler display some statistics
8924 that might help in debugging programs.
8927 @opindex malign-loops
8928 Align all loops to a 32-byte boundary.
8930 @item -mno-align-loops
8931 @opindex mno-align-loops
8932 Do not enforce a 32-byte alignment for loops. This is the default.
8934 @item -missue-rate=@var{number}
8935 @opindex missue-rate=@var{number}
8936 Issue @var{number} instructions per cycle. @var{number} can only be 1
8939 @item -mbranch-cost=@var{number}
8940 @opindex mbranch-cost=@var{number}
8941 @var{number} can only be 1 or 2. If it is 1 then branches will be
8942 preferred over conditional code, if it is 2, then the opposite will
8945 @item -mflush-trap=@var{number}
8946 @opindex mflush-trap=@var{number}
8947 Specifies the trap number to use to flush the cache. The default is
8948 12. Valid numbers are between 0 and 15 inclusive.
8950 @item -mno-flush-trap
8951 @opindex mno-flush-trap
8952 Specifies that the cache cannot be flushed by using a trap.
8954 @item -mflush-func=@var{name}
8955 @opindex mflush-func=@var{name}
8956 Specifies the name of the operating system function to call to flush
8957 the cache. The default is @emph{_flush_cache}, but a function call
8958 will only be used if a trap is not available.
8960 @item -mno-flush-func
8961 @opindex mno-flush-func
8962 Indicates that there is no OS function for flushing the cache.
8966 @node M680x0 Options
8967 @subsection M680x0 Options
8968 @cindex M680x0 options
8970 These are the @samp{-m} options defined for the 68000 series. The default
8971 values for these options depends on which style of 68000 was selected when
8972 the compiler was configured; the defaults for the most common choices are
8980 Generate output for a 68000. This is the default
8981 when the compiler is configured for 68000-based systems.
8983 Use this option for microcontrollers with a 68000 or EC000 core,
8984 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
8990 Generate output for a 68020. This is the default
8991 when the compiler is configured for 68020-based systems.
8995 Generate output containing 68881 instructions for floating point.
8996 This is the default for most 68020 systems unless @option{--nfp} was
8997 specified when the compiler was configured.
9001 Generate output for a 68030. This is the default when the compiler is
9002 configured for 68030-based systems.
9006 Generate output for a 68040. This is the default when the compiler is
9007 configured for 68040-based systems.
9009 This option inhibits the use of 68881/68882 instructions that have to be
9010 emulated by software on the 68040. Use this option if your 68040 does not
9011 have code to emulate those instructions.
9015 Generate output for a 68060. This is the default when the compiler is
9016 configured for 68060-based systems.
9018 This option inhibits the use of 68020 and 68881/68882 instructions that
9019 have to be emulated by software on the 68060. Use this option if your 68060
9020 does not have code to emulate those instructions.
9024 Generate output for a CPU32. This is the default
9025 when the compiler is configured for CPU32-based systems.
9027 Use this option for microcontrollers with a
9028 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9029 68336, 68340, 68341, 68349 and 68360.
9033 Generate output for a 520X ``coldfire'' family cpu. This is the default
9034 when the compiler is configured for 520X-based systems.
9036 Use this option for microcontroller with a 5200 core, including
9037 the MCF5202, MCF5203, MCF5204 and MCF5202.
9042 Generate output for a 68040, without using any of the new instructions.
9043 This results in code which can run relatively efficiently on either a
9044 68020/68881 or a 68030 or a 68040. The generated code does use the
9045 68881 instructions that are emulated on the 68040.
9049 Generate output for a 68060, without using any of the new instructions.
9050 This results in code which can run relatively efficiently on either a
9051 68020/68881 or a 68030 or a 68040. The generated code does use the
9052 68881 instructions that are emulated on the 68060.
9055 @opindex msoft-float
9056 Generate output containing library calls for floating point.
9057 @strong{Warning:} the requisite libraries are not available for all m68k
9058 targets. Normally the facilities of the machine's usual C compiler are
9059 used, but this can't be done directly in cross-compilation. You must
9060 make your own arrangements to provide suitable library functions for
9061 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9062 @samp{m68k-*-coff} do provide software floating point support.
9066 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9067 Additionally, parameters passed on the stack are also aligned to a
9068 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9071 @opindex mnobitfield
9072 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9073 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9077 Do use the bit-field instructions. The @option{-m68020} option implies
9078 @option{-mbitfield}. This is the default if you use a configuration
9079 designed for a 68020.
9083 Use a different function-calling convention, in which functions
9084 that take a fixed number of arguments return with the @code{rtd}
9085 instruction, which pops their arguments while returning. This
9086 saves one instruction in the caller since there is no need to pop
9087 the arguments there.
9089 This calling convention is incompatible with the one normally
9090 used on Unix, so you cannot use it if you need to call libraries
9091 compiled with the Unix compiler.
9093 Also, you must provide function prototypes for all functions that
9094 take variable numbers of arguments (including @code{printf});
9095 otherwise incorrect code will be generated for calls to those
9098 In addition, seriously incorrect code will result if you call a
9099 function with too many arguments. (Normally, extra arguments are
9100 harmlessly ignored.)
9102 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9103 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9106 @itemx -mno-align-int
9108 @opindex mno-align-int
9109 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9110 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9111 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9112 Aligning variables on 32-bit boundaries produces code that runs somewhat
9113 faster on processors with 32-bit busses at the expense of more memory.
9115 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9116 align structures containing the above types differently than
9117 most published application binary interface specifications for the m68k.
9121 Use the pc-relative addressing mode of the 68000 directly, instead of
9122 using a global offset table. At present, this option implies @option{-fpic},
9123 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9124 not presently supported with @option{-mpcrel}, though this could be supported for
9125 68020 and higher processors.
9127 @item -mno-strict-align
9128 @itemx -mstrict-align
9129 @opindex mno-strict-align
9130 @opindex mstrict-align
9131 Do not (do) assume that unaligned memory references will be handled by
9135 Generate code that allows the data segment to be located in a different
9136 area of memory from the text segment. This allows for execute in place in
9137 an environment without virtual memory management. This option implies
9141 Generate code that assumes that the data segment follows the text segment.
9142 This is the default.
9144 @item -mid-shared-library
9145 Generate code that supports shared libraries via the library ID method.
9146 This allows for execute in place and shared libraries in an environment
9147 without virtual memory management. This option implies @option{-fPIC}.
9149 @item -mno-id-shared-library
9150 Generate code that doesn't assume ID based shared libraries are being used.
9151 This is the default.
9153 @item -mshared-library-id=n
9154 Specified the identification number of the ID based shared library being
9155 compiled. Specifying a value of 0 will generate more compact code, specifying
9156 other values will force the allocation of that number to the current
9157 library but is no more space or time efficient than omitting this option.
9161 @node M68hc1x Options
9162 @subsection M68hc1x Options
9163 @cindex M68hc1x options
9165 These are the @samp{-m} options defined for the 68hc11 and 68hc12
9166 microcontrollers. The default values for these options depends on
9167 which style of microcontroller was selected when the compiler was configured;
9168 the defaults for the most common choices are given below.
9175 Generate output for a 68HC11. This is the default
9176 when the compiler is configured for 68HC11-based systems.
9182 Generate output for a 68HC12. This is the default
9183 when the compiler is configured for 68HC12-based systems.
9189 Generate output for a 68HCS12.
9192 @opindex mauto-incdec
9193 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
9200 Enable the use of 68HC12 min and max instructions.
9203 @itemx -mno-long-calls
9204 @opindex mlong-calls
9205 @opindex mno-long-calls
9206 Treat all calls as being far away (near). If calls are assumed to be
9207 far away, the compiler will use the @code{call} instruction to
9208 call a function and the @code{rtc} instruction for returning.
9212 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9214 @item -msoft-reg-count=@var{count}
9215 @opindex msoft-reg-count
9216 Specify the number of pseudo-soft registers which are used for the
9217 code generation. The maximum number is 32. Using more pseudo-soft
9218 register may or may not result in better code depending on the program.
9219 The default is 4 for 68HC11 and 2 for 68HC12.
9224 @subsection MCore Options
9225 @cindex MCore options
9227 These are the @samp{-m} options defined for the Motorola M*Core
9235 @opindex mno-hardlit
9236 Inline constants into the code stream if it can be done in two
9237 instructions or less.
9243 Use the divide instruction. (Enabled by default).
9245 @item -mrelax-immediate
9246 @itemx -mno-relax-immediate
9247 @opindex mrelax-immediate
9248 @opindex mno-relax-immediate
9249 Allow arbitrary sized immediates in bit operations.
9251 @item -mwide-bitfields
9252 @itemx -mno-wide-bitfields
9253 @opindex mwide-bitfields
9254 @opindex mno-wide-bitfields
9255 Always treat bit-fields as int-sized.
9257 @item -m4byte-functions
9258 @itemx -mno-4byte-functions
9259 @opindex m4byte-functions
9260 @opindex mno-4byte-functions
9261 Force all functions to be aligned to a four byte boundary.
9263 @item -mcallgraph-data
9264 @itemx -mno-callgraph-data
9265 @opindex mcallgraph-data
9266 @opindex mno-callgraph-data
9267 Emit callgraph information.
9270 @itemx -mno-slow-bytes
9271 @opindex mslow-bytes
9272 @opindex mno-slow-bytes
9273 Prefer word access when reading byte quantities.
9275 @item -mlittle-endian
9277 @opindex mlittle-endian
9278 @opindex mbig-endian
9279 Generate code for a little endian target.
9285 Generate code for the 210 processor.
9289 @subsection MIPS Options
9290 @cindex MIPS options
9296 Generate big-endian code.
9300 Generate little-endian code. This is the default for @samp{mips*el-*-*}
9303 @item -march=@var{arch}
9305 Generate code that will run on @var{arch}, which can be the name of a
9306 generic MIPS ISA, or the name of a particular processor.
9308 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
9309 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
9310 The processor names are:
9311 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
9313 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
9314 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
9318 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
9319 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
9320 The special value @samp{from-abi} selects the
9321 most compatible architecture for the selected ABI (that is,
9322 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
9324 In processor names, a final @samp{000} can be abbreviated as @samp{k}
9325 (for example, @samp{-march=r2k}). Prefixes are optional, and
9326 @samp{vr} may be written @samp{r}.
9328 GCC defines two macros based on the value of this option. The first
9329 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
9330 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
9331 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
9332 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
9333 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
9335 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
9336 above. In other words, it will have the full prefix and will not
9337 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
9338 the macro names the resolved architecture (either @samp{"mips1"} or
9339 @samp{"mips3"}). It names the default architecture when no
9340 @option{-march} option is given.
9342 @item -mtune=@var{arch}
9344 Optimize for @var{arch}. Among other things, this option controls
9345 the way instructions are scheduled, and the perceived cost of arithmetic
9346 operations. The list of @var{arch} values is the same as for
9349 When this option is not used, GCC will optimize for the processor
9350 specified by @option{-march}. By using @option{-march} and
9351 @option{-mtune} together, it is possible to generate code that will
9352 run on a family of processors, but optimize the code for one
9353 particular member of that family.
9355 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
9356 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
9357 @samp{-march} ones described above.
9361 Equivalent to @samp{-march=mips1}.
9365 Equivalent to @samp{-march=mips2}.
9369 Equivalent to @samp{-march=mips3}.
9373 Equivalent to @samp{-march=mips4}.
9377 Equivalent to @samp{-march=mips32}.
9381 Equivalent to @samp{-march=mips32r2}.
9385 Equivalent to @samp{-march=mips64}.
9391 Use (do not use) the MIPS16 ISA.
9403 Generate code for the given ABI@.
9405 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
9406 generates 64-bit code when you select a 64-bit architecture, but you
9407 can use @option{-mgp32} to get 32-bit code instead.
9409 For information about the O64 ABI, see
9410 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
9413 @itemx -mno-abicalls
9415 @opindex mno-abicalls
9416 Generate (do not generate) SVR4-style position-independent code.
9417 @option{-mabicalls} is the default for SVR4-based systems.
9423 Lift (do not lift) the usual restrictions on the size of the global
9426 GCC normally uses a single instruction to load values from the GOT.
9427 While this is relatively efficient, it will only work if the GOT
9428 is smaller than about 64k. Anything larger will cause the linker
9429 to report an error such as:
9431 @cindex relocation truncated to fit (MIPS)
9433 relocation truncated to fit: R_MIPS_GOT16 foobar
9436 If this happens, you should recompile your code with @option{-mxgot}.
9437 It should then work with very large GOTs, although it will also be
9438 less efficient, since it will take three instructions to fetch the
9439 value of a global symbol.
9441 Note that some linkers can create multiple GOTs. If you have such a
9442 linker, you should only need to use @option{-mxgot} when a single object
9443 file accesses more than 64k's worth of GOT entries. Very few do.
9445 These options have no effect unless GCC is generating position
9450 Assume that general-purpose registers are 32 bits wide.
9454 Assume that general-purpose registers are 64 bits wide.
9458 Assume that floating-point registers are 32 bits wide.
9462 Assume that floating-point registers are 64 bits wide.
9465 @opindex mhard-float
9466 Use floating-point coprocessor instructions.
9469 @opindex msoft-float
9470 Do not use floating-point coprocessor instructions. Implement
9471 floating-point calculations using library calls instead.
9473 @item -msingle-float
9474 @opindex msingle-float
9475 Assume that the floating-point coprocessor only supports single-precision
9478 @itemx -mdouble-float
9479 @opindex mdouble-float
9480 Assume that the floating-point coprocessor supports double-precision
9481 operations. This is the default.
9483 @itemx -mpaired-single
9484 @itemx -mno-paired-single
9485 @opindex mpaired-single
9486 @opindex mno-paired-single
9487 Use (do not use) paired-single floating-point instructions.
9488 @xref{MIPS Paired-Single Support}. This option can only be used
9489 when generating 64-bit code and requires hardware floating-point
9490 support to be enabled.
9496 Use (do not use) the MIPS-3D ASE. @xref{MIPS-3D Built-in Functions}.
9497 The option @option{-mips3d} implies @option{-mpaired-single}.
9501 Force @code{int} and @code{long} types to be 64 bits wide. See
9502 @option{-mlong32} for an explanation of the default and the way
9503 that the pointer size is determined.
9507 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
9508 an explanation of the default and the way that the pointer size is
9513 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
9515 The default size of @code{int}s, @code{long}s and pointers depends on
9516 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
9517 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
9518 32-bit @code{long}s. Pointers are the same size as @code{long}s,
9519 or the same size as integer registers, whichever is smaller.
9523 @cindex smaller data references (MIPS)
9524 @cindex gp-relative references (MIPS)
9525 Put global and static items less than or equal to @var{num} bytes into
9526 the small data or bss section instead of the normal data or bss section.
9527 This allows the data to be accessed using a single instruction.
9529 All modules should be compiled with the same @option{-G @var{num}}
9532 @item -membedded-data
9533 @itemx -mno-embedded-data
9534 @opindex membedded-data
9535 @opindex mno-embedded-data
9536 Allocate variables to the read-only data section first if possible, then
9537 next in the small data section if possible, otherwise in data. This gives
9538 slightly slower code than the default, but reduces the amount of RAM required
9539 when executing, and thus may be preferred for some embedded systems.
9541 @item -muninit-const-in-rodata
9542 @itemx -mno-uninit-const-in-rodata
9543 @opindex muninit-const-in-rodata
9544 @opindex mno-uninit-const-in-rodata
9545 Put uninitialized @code{const} variables in the read-only data section.
9546 This option is only meaningful in conjunction with @option{-membedded-data}.
9548 @item -msplit-addresses
9549 @itemx -mno-split-addresses
9550 @opindex msplit-addresses
9551 @opindex mno-split-addresses
9552 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
9553 relocation operators. This option has been superceded by
9554 @option{-mexplicit-relocs} but is retained for backwards compatibility.
9556 @item -mexplicit-relocs
9557 @itemx -mno-explicit-relocs
9558 @opindex mexplicit-relocs
9559 @opindex mno-explicit-relocs
9560 Use (do not use) assembler relocation operators when dealing with symbolic
9561 addresses. The alternative, selected by @option{-mno-explicit-relocs},
9562 is to use assembler macros instead.
9564 @option{-mexplicit-relocs} is the default if GCC was configured
9565 to use an assembler that supports relocation operators.
9567 @item -mcheck-zero-division
9568 @itemx -mno-check-zero-division
9569 @opindex mcheck-zero-division
9570 @opindex mno-check-zero-division
9571 Trap (do not trap) on integer division by zero. The default is
9572 @option{-mcheck-zero-division}.
9574 @item -mdivide-traps
9575 @itemx -mdivide-breaks
9576 @opindex mdivide-traps
9577 @opindex mdivide-breaks
9578 MIPS systems check for division by zero by generating either a
9579 conditional trap or a break instruction. Using traps results in
9580 smaller code, but is only supported on MIPS II and later. Also, some
9581 versions of the Linux kernel have a bug that prevents trap from
9582 generating the proper signal (SIGFPE). Use @option{-mdivide-traps} to
9583 allow conditional traps on architectures that support them and
9584 @option{-mdivide-breaks} to force the use of breaks.
9586 The default is usually @option{-mdivide-traps}, but this can be
9587 overridden at configure time using @option{--with-divide=breaks}.
9588 Divide-by-zero checks can be completely disabled using
9589 @option{-mno-check-zero-division}.
9595 Force (do not force) the use of @code{memcpy()} for non-trivial block
9596 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
9597 most constant-sized copies.
9600 @itemx -mno-long-calls
9601 @opindex mlong-calls
9602 @opindex mno-long-calls
9603 Disable (do not disable) use of the @code{jal} instruction. Calling
9604 functions using @code{jal} is more efficient but requires the caller
9605 and callee to be in the same 256 megabyte segment.
9607 This option has no effect on abicalls code. The default is
9608 @option{-mno-long-calls}.
9614 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
9615 instructions, as provided by the R4650 ISA.
9618 @itemx -mno-fused-madd
9619 @opindex mfused-madd
9620 @opindex mno-fused-madd
9621 Enable (disable) use of the floating point multiply-accumulate
9622 instructions, when they are available. The default is
9623 @option{-mfused-madd}.
9625 When multiply-accumulate instructions are used, the intermediate
9626 product is calculated to infinite precision and is not subject to
9627 the FCSR Flush to Zero bit. This may be undesirable in some
9632 Tell the MIPS assembler to not run its preprocessor over user
9633 assembler files (with a @samp{.s} suffix) when assembling them.
9636 @itemx -mno-fix-r4000
9638 @opindex mno-fix-r4000
9639 Work around certain R4000 CPU errata:
9642 A double-word or a variable shift may give an incorrect result if executed
9643 immediately after starting an integer division.
9645 A double-word or a variable shift may give an incorrect result if executed
9646 while an integer multiplication is in progress.
9648 An integer division may give an incorrect result if started in a delay slot
9649 of a taken branch or a jump.
9653 @itemx -mno-fix-r4400
9655 @opindex mno-fix-r4400
9656 Work around certain R4400 CPU errata:
9659 A double-word or a variable shift may give an incorrect result if executed
9660 immediately after starting an integer division.
9664 @itemx -mno-fix-vr4120
9665 @opindex mfix-vr4120
9666 Work around certain VR4120 errata:
9669 @code{dmultu} does not always produce the correct result.
9671 @code{div} and @code{ddiv} do not always produce the correct result if one
9672 of the operands is negative.
9674 The workarounds for the division errata rely on special functions in
9675 @file{libgcc.a}. At present, these functions are only provided by
9676 the @code{mips64vr*-elf} configurations.
9678 Other VR4120 errata require a nop to be inserted between certain pairs of
9679 instructions. These errata are handled by the assembler, not by GCC itself.
9684 Work around certain SB-1 CPU core errata.
9685 (This flag currently works around the SB-1 revision 2
9686 ``F1'' and ``F2'' floating point errata.)
9688 @item -mflush-func=@var{func}
9689 @itemx -mno-flush-func
9690 @opindex mflush-func
9691 Specifies the function to call to flush the I and D caches, or to not
9692 call any such function. If called, the function must take the same
9693 arguments as the common @code{_flush_func()}, that is, the address of the
9694 memory range for which the cache is being flushed, the size of the
9695 memory range, and the number 3 (to flush both caches). The default
9696 depends on the target GCC was configured for, but commonly is either
9697 @samp{_flush_func} or @samp{__cpu_flush}.
9699 @item -mbranch-likely
9700 @itemx -mno-branch-likely
9701 @opindex mbranch-likely
9702 @opindex mno-branch-likely
9703 Enable or disable use of Branch Likely instructions, regardless of the
9704 default for the selected architecture. By default, Branch Likely
9705 instructions may be generated if they are supported by the selected
9706 architecture. An exception is for the MIPS32 and MIPS64 architectures
9707 and processors which implement those architectures; for those, Branch
9708 Likely instructions will not be generated by default because the MIPS32
9709 and MIPS64 architectures specifically deprecate their use.
9711 @item -mfp-exceptions
9712 @itemx -mno-fp-exceptions
9713 @opindex mfp-exceptions
9714 Specifies whether FP exceptions are enabled. This affects how we schedule
9715 FP instructions for some processors. The default is that FP exceptions are
9718 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
9719 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
9722 @item -mvr4130-align
9723 @itemx -mno-vr4130-align
9724 @opindex mvr4130-align
9725 The VR4130 pipeline is two-way superscalar, but can only issue two
9726 instructions together if the first one is 8-byte aligned. When this
9727 option is enabled, GCC will align pairs of instructions that it
9728 thinks should execute in parallel.
9730 This option only has an effect when optimizing for the VR4130.
9731 It normally makes code faster, but at the expense of making it bigger.
9732 It is enabled by default at optimization level @option{-O3}.
9736 @subsection MMIX Options
9737 @cindex MMIX Options
9739 These options are defined for the MMIX:
9743 @itemx -mno-libfuncs
9745 @opindex mno-libfuncs
9746 Specify that intrinsic library functions are being compiled, passing all
9747 values in registers, no matter the size.
9752 @opindex mno-epsilon
9753 Generate floating-point comparison instructions that compare with respect
9754 to the @code{rE} epsilon register.
9756 @item -mabi=mmixware
9758 @opindex mabi-mmixware
9760 Generate code that passes function parameters and return values that (in
9761 the called function) are seen as registers @code{$0} and up, as opposed to
9762 the GNU ABI which uses global registers @code{$231} and up.
9765 @itemx -mno-zero-extend
9766 @opindex mzero-extend
9767 @opindex mno-zero-extend
9768 When reading data from memory in sizes shorter than 64 bits, use (do not
9769 use) zero-extending load instructions by default, rather than
9770 sign-extending ones.
9773 @itemx -mno-knuthdiv
9775 @opindex mno-knuthdiv
9776 Make the result of a division yielding a remainder have the same sign as
9777 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9778 remainder follows the sign of the dividend. Both methods are
9779 arithmetically valid, the latter being almost exclusively used.
9781 @item -mtoplevel-symbols
9782 @itemx -mno-toplevel-symbols
9783 @opindex mtoplevel-symbols
9784 @opindex mno-toplevel-symbols
9785 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9786 code can be used with the @code{PREFIX} assembly directive.
9790 Generate an executable in the ELF format, rather than the default
9791 @samp{mmo} format used by the @command{mmix} simulator.
9793 @item -mbranch-predict
9794 @itemx -mno-branch-predict
9795 @opindex mbranch-predict
9796 @opindex mno-branch-predict
9797 Use (do not use) the probable-branch instructions, when static branch
9798 prediction indicates a probable branch.
9800 @item -mbase-addresses
9801 @itemx -mno-base-addresses
9802 @opindex mbase-addresses
9803 @opindex mno-base-addresses
9804 Generate (do not generate) code that uses @emph{base addresses}. Using a
9805 base address automatically generates a request (handled by the assembler
9806 and the linker) for a constant to be set up in a global register. The
9807 register is used for one or more base address requests within the range 0
9808 to 255 from the value held in the register. The generally leads to short
9809 and fast code, but the number of different data items that can be
9810 addressed is limited. This means that a program that uses lots of static
9811 data may require @option{-mno-base-addresses}.
9814 @itemx -mno-single-exit
9815 @opindex msingle-exit
9816 @opindex mno-single-exit
9817 Force (do not force) generated code to have a single exit point in each
9821 @node MN10300 Options
9822 @subsection MN10300 Options
9823 @cindex MN10300 options
9825 These @option{-m} options are defined for Matsushita MN10300 architectures:
9830 Generate code to avoid bugs in the multiply instructions for the MN10300
9831 processors. This is the default.
9834 @opindex mno-mult-bug
9835 Do not generate code to avoid bugs in the multiply instructions for the
9840 Generate code which uses features specific to the AM33 processor.
9844 Do not generate code which uses features specific to the AM33 processor. This
9849 Do not link in the C run-time initialization object file.
9853 Indicate to the linker that it should perform a relaxation optimization pass
9854 to shorten branches, calls and absolute memory addresses. This option only
9855 has an effect when used on the command line for the final link step.
9857 This option makes symbolic debugging impossible.
9861 @subsection NS32K Options
9862 @cindex NS32K options
9864 These are the @samp{-m} options defined for the 32000 series. The default
9865 values for these options depends on which style of 32000 was selected when
9866 the compiler was configured; the defaults for the most common choices are
9874 Generate output for a 32032. This is the default
9875 when the compiler is configured for 32032 and 32016 based systems.
9881 Generate output for a 32332. This is the default
9882 when the compiler is configured for 32332-based systems.
9888 Generate output for a 32532. This is the default
9889 when the compiler is configured for 32532-based systems.
9893 Generate output containing 32081 instructions for floating point.
9894 This is the default for all systems.
9898 Generate output containing 32381 instructions for floating point. This
9899 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9900 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9904 Try and generate multiply-add floating point instructions @code{polyF}
9905 and @code{dotF}. This option is only available if the @option{-m32381}
9906 option is in effect. Using these instructions requires changes to
9907 register allocation which generally has a negative impact on
9908 performance. This option should only be enabled when compiling code
9909 particularly likely to make heavy use of multiply-add instructions.
9912 @opindex mnomulti-add
9913 Do not try and generate multiply-add floating point instructions
9914 @code{polyF} and @code{dotF}. This is the default on all platforms.
9917 @opindex msoft-float
9918 Generate output containing library calls for floating point.
9919 @strong{Warning:} the requisite libraries may not be available.
9921 @item -mieee-compare
9922 @itemx -mno-ieee-compare
9923 @opindex mieee-compare
9924 @opindex mno-ieee-compare
9925 Control whether or not the compiler uses IEEE floating point
9926 comparisons. These handle correctly the case where the result of a
9927 comparison is unordered.
9928 @strong{Warning:} the requisite kernel support may not be available.
9931 @opindex mnobitfield
9932 Do not use the bit-field instructions. On some machines it is faster to
9933 use shifting and masking operations. This is the default for the pc532.
9937 Do use the bit-field instructions. This is the default for all platforms
9942 Use a different function-calling convention, in which functions
9943 that take a fixed number of arguments return pop their
9944 arguments on return with the @code{ret} instruction.
9946 This calling convention is incompatible with the one normally
9947 used on Unix, so you cannot use it if you need to call libraries
9948 compiled with the Unix compiler.
9950 Also, you must provide function prototypes for all functions that
9951 take variable numbers of arguments (including @code{printf});
9952 otherwise incorrect code will be generated for calls to those
9955 In addition, seriously incorrect code will result if you call a
9956 function with too many arguments. (Normally, extra arguments are
9957 harmlessly ignored.)
9959 This option takes its name from the 680x0 @code{rtd} instruction.
9964 Use a different function-calling convention where the first two arguments
9965 are passed in registers.
9967 This calling convention is incompatible with the one normally
9968 used on Unix, so you cannot use it if you need to call libraries
9969 compiled with the Unix compiler.
9972 @opindex mnoregparam
9973 Do not pass any arguments in registers. This is the default for all
9978 It is OK to use the sb as an index register which is always loaded with
9979 zero. This is the default for the pc532-netbsd target.
9983 The sb register is not available for use or has not been initialized to
9984 zero by the run time system. This is the default for all targets except
9985 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9986 @option{-fpic} is set.
9990 Many ns32000 series addressing modes use displacements of up to 512MB@.
9991 If an address is above 512MB then displacements from zero can not be used.
9992 This option causes code to be generated which can be loaded above 512MB@.
9993 This may be useful for operating systems or ROM code.
9997 Assume code will be loaded in the first 512MB of virtual address space.
9998 This is the default for all platforms.
10002 @node PDP-11 Options
10003 @subsection PDP-11 Options
10004 @cindex PDP-11 Options
10006 These options are defined for the PDP-11:
10011 Use hardware FPP floating point. This is the default. (FIS floating
10012 point on the PDP-11/40 is not supported.)
10015 @opindex msoft-float
10016 Do not use hardware floating point.
10020 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10024 Return floating-point results in memory. This is the default.
10028 Generate code for a PDP-11/40.
10032 Generate code for a PDP-11/45. This is the default.
10036 Generate code for a PDP-11/10.
10038 @item -mbcopy-builtin
10039 @opindex bcopy-builtin
10040 Use inline @code{movmemhi} patterns for copying memory. This is the
10045 Do not use inline @code{movmemhi} patterns for copying memory.
10051 Use 16-bit @code{int}. This is the default.
10057 Use 32-bit @code{int}.
10060 @itemx -mno-float32
10062 @opindex mno-float32
10063 Use 64-bit @code{float}. This is the default.
10066 @itemx -mno-float64
10068 @opindex mno-float64
10069 Use 32-bit @code{float}.
10073 Use @code{abshi2} pattern. This is the default.
10077 Do not use @code{abshi2} pattern.
10079 @item -mbranch-expensive
10080 @opindex mbranch-expensive
10081 Pretend that branches are expensive. This is for experimenting with
10082 code generation only.
10084 @item -mbranch-cheap
10085 @opindex mbranch-cheap
10086 Do not pretend that branches are expensive. This is the default.
10090 Generate code for a system with split I&D.
10094 Generate code for a system without split I&D. This is the default.
10098 Use Unix assembler syntax. This is the default when configured for
10099 @samp{pdp11-*-bsd}.
10103 Use DEC assembler syntax. This is the default when configured for any
10104 PDP-11 target other than @samp{pdp11-*-bsd}.
10107 @node PowerPC Options
10108 @subsection PowerPC Options
10109 @cindex PowerPC options
10111 These are listed under @xref{RS/6000 and PowerPC Options}.
10113 @node RS/6000 and PowerPC Options
10114 @subsection IBM RS/6000 and PowerPC Options
10115 @cindex RS/6000 and PowerPC Options
10116 @cindex IBM RS/6000 and PowerPC Options
10118 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10125 @itemx -mno-powerpc
10126 @itemx -mpowerpc-gpopt
10127 @itemx -mno-powerpc-gpopt
10128 @itemx -mpowerpc-gfxopt
10129 @itemx -mno-powerpc-gfxopt
10131 @itemx -mno-powerpc64
10135 @opindex mno-power2
10137 @opindex mno-powerpc
10138 @opindex mpowerpc-gpopt
10139 @opindex mno-powerpc-gpopt
10140 @opindex mpowerpc-gfxopt
10141 @opindex mno-powerpc-gfxopt
10142 @opindex mpowerpc64
10143 @opindex mno-powerpc64
10144 GCC supports two related instruction set architectures for the
10145 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10146 instructions supported by the @samp{rios} chip set used in the original
10147 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10148 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
10149 the IBM 4xx microprocessors.
10151 Neither architecture is a subset of the other. However there is a
10152 large common subset of instructions supported by both. An MQ
10153 register is included in processors supporting the POWER architecture.
10155 You use these options to specify which instructions are available on the
10156 processor you are using. The default value of these options is
10157 determined when configuring GCC@. Specifying the
10158 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10159 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10160 rather than the options listed above.
10162 The @option{-mpower} option allows GCC to generate instructions that
10163 are found only in the POWER architecture and to use the MQ register.
10164 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10165 to generate instructions that are present in the POWER2 architecture but
10166 not the original POWER architecture.
10168 The @option{-mpowerpc} option allows GCC to generate instructions that
10169 are found only in the 32-bit subset of the PowerPC architecture.
10170 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10171 GCC to use the optional PowerPC architecture instructions in the
10172 General Purpose group, including floating-point square root. Specifying
10173 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10174 use the optional PowerPC architecture instructions in the Graphics
10175 group, including floating-point select.
10177 The @option{-mpowerpc64} option allows GCC to generate the additional
10178 64-bit instructions that are found in the full PowerPC64 architecture
10179 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
10180 @option{-mno-powerpc64}.
10182 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
10183 will use only the instructions in the common subset of both
10184 architectures plus some special AIX common-mode calls, and will not use
10185 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
10186 permits GCC to use any instruction from either architecture and to
10187 allow use of the MQ register; specify this for the Motorola MPC601.
10189 @item -mnew-mnemonics
10190 @itemx -mold-mnemonics
10191 @opindex mnew-mnemonics
10192 @opindex mold-mnemonics
10193 Select which mnemonics to use in the generated assembler code. With
10194 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
10195 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
10196 assembler mnemonics defined for the POWER architecture. Instructions
10197 defined in only one architecture have only one mnemonic; GCC uses that
10198 mnemonic irrespective of which of these options is specified.
10200 GCC defaults to the mnemonics appropriate for the architecture in
10201 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
10202 value of these option. Unless you are building a cross-compiler, you
10203 should normally not specify either @option{-mnew-mnemonics} or
10204 @option{-mold-mnemonics}, but should instead accept the default.
10206 @item -mcpu=@var{cpu_type}
10208 Set architecture type, register usage, choice of mnemonics, and
10209 instruction scheduling parameters for machine type @var{cpu_type}.
10210 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
10211 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
10212 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
10213 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
10214 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
10215 @samp{860}, @samp{970}, @samp{common}, @samp{ec603e}, @samp{G3},
10216 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
10217 @samp{power4}, @samp{power5}, @samp{powerpc}, @samp{powerpc64},
10218 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64a}.
10220 @option{-mcpu=common} selects a completely generic processor. Code
10221 generated under this option will run on any POWER or PowerPC processor.
10222 GCC will use only the instructions in the common subset of both
10223 architectures, and will not use the MQ register. GCC assumes a generic
10224 processor model for scheduling purposes.
10226 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
10227 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
10228 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
10229 types, with an appropriate, generic processor model assumed for
10230 scheduling purposes.
10232 The other options specify a specific processor. Code generated under
10233 those options will run best on that processor, and may not run at all on
10236 The @option{-mcpu} options automatically enable or disable the
10237 following options: @option{-maltivec}, @option{-mhard-float},
10238 @option{-mmfcrf}, @option{-mmultiple}, @option{-mnew-mnemonics},
10239 @option{-mpower}, @option{-mpower2}, @option{-mpowerpc64},
10240 @option{-mpowerpc-gpopt}, @option{-mpowerpc-gfxopt},
10241 @option{-mstring}. The particular options set for any particular CPU
10242 will vary between compiler versions, depending on what setting seems
10243 to produce optimal code for that CPU; it doesn't necessarily reflect
10244 the actual hardware's capabilities. If you wish to set an individual
10245 option to a particular value, you may specify it after the
10246 @option{-mcpu} option, like @samp{-mcpu=970 -mno-altivec}.
10248 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
10249 not enabled or disabled by the @option{-mcpu} option at present, since
10250 AIX does not have full support for these options. You may still
10251 enable or disable them individually if you're sure it'll work in your
10254 @item -mtune=@var{cpu_type}
10256 Set the instruction scheduling parameters for machine type
10257 @var{cpu_type}, but do not set the architecture type, register usage, or
10258 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
10259 values for @var{cpu_type} are used for @option{-mtune} as for
10260 @option{-mcpu}. If both are specified, the code generated will use the
10261 architecture, registers, and mnemonics set by @option{-mcpu}, but the
10262 scheduling parameters set by @option{-mtune}.
10265 @itemx -mno-altivec
10267 @opindex mno-altivec
10268 Generate code that uses (does not use) AltiVec instructions, and also
10269 enable the use of built-in functions that allow more direct access to
10270 the AltiVec instruction set. You may also need to set
10271 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
10276 Extend the current ABI with SPE ABI extensions. This does not change
10277 the default ABI, instead it adds the SPE ABI extensions to the current
10281 @opindex mabi=no-spe
10282 Disable Booke SPE ABI extensions for the current ABI.
10284 @item -misel=@var{yes/no}
10287 This switch enables or disables the generation of ISEL instructions.
10289 @item -mspe=@var{yes/no}
10292 This switch enables or disables the generation of SPE simd
10295 @item -mfloat-gprs=@var{yes/single/double/no}
10296 @itemx -mfloat-gprs
10297 @opindex mfloat-gprs
10298 This switch enables or disables the generation of floating point
10299 operations on the general purpose registers for architectures that
10302 The argument @var{yes} or @var{single} enables the use of
10303 single-precision floating point operations.
10305 The argument @var{double} enables the use of single and
10306 double-precision floating point operations.
10308 The argument @var{no} disables floating point operations on the
10309 general purpose registers.
10311 This option is currently only available on the MPC854x.
10317 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
10318 targets (including GNU/Linux). The 32-bit environment sets int, long
10319 and pointer to 32 bits and generates code that runs on any PowerPC
10320 variant. The 64-bit environment sets int to 32 bits and long and
10321 pointer to 64 bits, and generates code for PowerPC64, as for
10322 @option{-mpowerpc64}.
10325 @itemx -mno-fp-in-toc
10326 @itemx -mno-sum-in-toc
10327 @itemx -mminimal-toc
10329 @opindex mno-fp-in-toc
10330 @opindex mno-sum-in-toc
10331 @opindex mminimal-toc
10332 Modify generation of the TOC (Table Of Contents), which is created for
10333 every executable file. The @option{-mfull-toc} option is selected by
10334 default. In that case, GCC will allocate at least one TOC entry for
10335 each unique non-automatic variable reference in your program. GCC
10336 will also place floating-point constants in the TOC@. However, only
10337 16,384 entries are available in the TOC@.
10339 If you receive a linker error message that saying you have overflowed
10340 the available TOC space, you can reduce the amount of TOC space used
10341 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
10342 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
10343 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
10344 generate code to calculate the sum of an address and a constant at
10345 run-time instead of putting that sum into the TOC@. You may specify one
10346 or both of these options. Each causes GCC to produce very slightly
10347 slower and larger code at the expense of conserving TOC space.
10349 If you still run out of space in the TOC even when you specify both of
10350 these options, specify @option{-mminimal-toc} instead. This option causes
10351 GCC to make only one TOC entry for every file. When you specify this
10352 option, GCC will produce code that is slower and larger but which
10353 uses extremely little TOC space. You may wish to use this option
10354 only on files that contain less frequently executed code.
10360 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
10361 @code{long} type, and the infrastructure needed to support them.
10362 Specifying @option{-maix64} implies @option{-mpowerpc64} and
10363 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
10364 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
10367 @itemx -mno-xl-call
10369 @opindex mno-xl-call
10370 On AIX, pass floating-point arguments to prototyped functions beyond the
10371 register save area (RSA) on the stack in addition to argument FPRs. The
10372 AIX calling convention was extended but not initially documented to
10373 handle an obscure K&R C case of calling a function that takes the
10374 address of its arguments with fewer arguments than declared. AIX XL
10375 compilers access floating point arguments which do not fit in the
10376 RSA from the stack when a subroutine is compiled without
10377 optimization. Because always storing floating-point arguments on the
10378 stack is inefficient and rarely needed, this option is not enabled by
10379 default and only is necessary when calling subroutines compiled by AIX
10380 XL compilers without optimization.
10384 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
10385 application written to use message passing with special startup code to
10386 enable the application to run. The system must have PE installed in the
10387 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
10388 must be overridden with the @option{-specs=} option to specify the
10389 appropriate directory location. The Parallel Environment does not
10390 support threads, so the @option{-mpe} option and the @option{-pthread}
10391 option are incompatible.
10393 @item -malign-natural
10394 @itemx -malign-power
10395 @opindex malign-natural
10396 @opindex malign-power
10397 On AIX, Darwin, and 64-bit PowerPC GNU/Linux, the option
10398 @option{-malign-natural} overrides the ABI-defined alignment of larger
10399 types, such as floating-point doubles, on their natural size-based boundary.
10400 The option @option{-malign-power} instructs GCC to follow the ABI-specified
10401 alignment rules. GCC defaults to the standard alignment defined in the ABI.
10404 @itemx -mhard-float
10405 @opindex msoft-float
10406 @opindex mhard-float
10407 Generate code that does not use (uses) the floating-point register set.
10408 Software floating point emulation is provided if you use the
10409 @option{-msoft-float} option, and pass the option to GCC when linking.
10412 @itemx -mno-multiple
10414 @opindex mno-multiple
10415 Generate code that uses (does not use) the load multiple word
10416 instructions and the store multiple word instructions. These
10417 instructions are generated by default on POWER systems, and not
10418 generated on PowerPC systems. Do not use @option{-mmultiple} on little
10419 endian PowerPC systems, since those instructions do not work when the
10420 processor is in little endian mode. The exceptions are PPC740 and
10421 PPC750 which permit the instructions usage in little endian mode.
10426 @opindex mno-string
10427 Generate code that uses (does not use) the load string instructions
10428 and the store string word instructions to save multiple registers and
10429 do small block moves. These instructions are generated by default on
10430 POWER systems, and not generated on PowerPC systems. Do not use
10431 @option{-mstring} on little endian PowerPC systems, since those
10432 instructions do not work when the processor is in little endian mode.
10433 The exceptions are PPC740 and PPC750 which permit the instructions
10434 usage in little endian mode.
10439 @opindex mno-update
10440 Generate code that uses (does not use) the load or store instructions
10441 that update the base register to the address of the calculated memory
10442 location. These instructions are generated by default. If you use
10443 @option{-mno-update}, there is a small window between the time that the
10444 stack pointer is updated and the address of the previous frame is
10445 stored, which means code that walks the stack frame across interrupts or
10446 signals may get corrupted data.
10449 @itemx -mno-fused-madd
10450 @opindex mfused-madd
10451 @opindex mno-fused-madd
10452 Generate code that uses (does not use) the floating point multiply and
10453 accumulate instructions. These instructions are generated by default if
10454 hardware floating is used.
10456 @item -mno-bit-align
10458 @opindex mno-bit-align
10459 @opindex mbit-align
10460 On System V.4 and embedded PowerPC systems do not (do) force structures
10461 and unions that contain bit-fields to be aligned to the base type of the
10464 For example, by default a structure containing nothing but 8
10465 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
10466 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
10467 the structure would be aligned to a 1 byte boundary and be one byte in
10470 @item -mno-strict-align
10471 @itemx -mstrict-align
10472 @opindex mno-strict-align
10473 @opindex mstrict-align
10474 On System V.4 and embedded PowerPC systems do not (do) assume that
10475 unaligned memory references will be handled by the system.
10477 @item -mrelocatable
10478 @itemx -mno-relocatable
10479 @opindex mrelocatable
10480 @opindex mno-relocatable
10481 On embedded PowerPC systems generate code that allows (does not allow)
10482 the program to be relocated to a different address at runtime. If you
10483 use @option{-mrelocatable} on any module, all objects linked together must
10484 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
10486 @item -mrelocatable-lib
10487 @itemx -mno-relocatable-lib
10488 @opindex mrelocatable-lib
10489 @opindex mno-relocatable-lib
10490 On embedded PowerPC systems generate code that allows (does not allow)
10491 the program to be relocated to a different address at runtime. Modules
10492 compiled with @option{-mrelocatable-lib} can be linked with either modules
10493 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
10494 with modules compiled with the @option{-mrelocatable} options.
10500 On System V.4 and embedded PowerPC systems do not (do) assume that
10501 register 2 contains a pointer to a global area pointing to the addresses
10502 used in the program.
10505 @itemx -mlittle-endian
10507 @opindex mlittle-endian
10508 On System V.4 and embedded PowerPC systems compile code for the
10509 processor in little endian mode. The @option{-mlittle-endian} option is
10510 the same as @option{-mlittle}.
10513 @itemx -mbig-endian
10515 @opindex mbig-endian
10516 On System V.4 and embedded PowerPC systems compile code for the
10517 processor in big endian mode. The @option{-mbig-endian} option is
10518 the same as @option{-mbig}.
10520 @item -mdynamic-no-pic
10521 @opindex mdynamic-no-pic
10522 On Darwin and Mac OS X systems, compile code so that it is not
10523 relocatable, but that its external references are relocatable. The
10524 resulting code is suitable for applications, but not shared
10527 @item -mprioritize-restricted-insns=@var{priority}
10528 @opindex mprioritize-restricted-insns
10529 This option controls the priority that is assigned to
10530 dispatch-slot restricted instructions during the second scheduling
10531 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
10532 @var{no/highest/second-highest} priority to dispatch slot restricted
10535 @item -msched-costly-dep=@var{dependence_type}
10536 @opindex msched-costly-dep
10537 This option controls which dependences are considered costly
10538 by the target during instruction scheduling. The argument
10539 @var{dependence_type} takes one of the following values:
10540 @var{no}: no dependence is costly,
10541 @var{all}: all dependences are costly,
10542 @var{true_store_to_load}: a true dependence from store to load is costly,
10543 @var{store_to_load}: any dependence from store to load is costly,
10544 @var{number}: any dependence which latency >= @var{number} is costly.
10546 @item -minsert-sched-nops=@var{scheme}
10547 @opindex minsert-sched-nops
10548 This option controls which nop insertion scheme will be used during
10549 the second scheduling pass. The argument @var{scheme} takes one of the
10551 @var{no}: Don't insert nops.
10552 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
10553 according to the scheduler's grouping.
10554 @var{regroup_exact}: Insert nops to force costly dependent insns into
10555 separate groups. Insert exactly as many nops as needed to force an insn
10556 to a new group, according to the estimated processor grouping.
10557 @var{number}: Insert nops to force costly dependent insns into
10558 separate groups. Insert @var{number} nops to force an insn to a new group.
10561 @opindex mcall-sysv
10562 On System V.4 and embedded PowerPC systems compile code using calling
10563 conventions that adheres to the March 1995 draft of the System V
10564 Application Binary Interface, PowerPC processor supplement. This is the
10565 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
10567 @item -mcall-sysv-eabi
10568 @opindex mcall-sysv-eabi
10569 Specify both @option{-mcall-sysv} and @option{-meabi} options.
10571 @item -mcall-sysv-noeabi
10572 @opindex mcall-sysv-noeabi
10573 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
10575 @item -mcall-solaris
10576 @opindex mcall-solaris
10577 On System V.4 and embedded PowerPC systems compile code for the Solaris
10581 @opindex mcall-linux
10582 On System V.4 and embedded PowerPC systems compile code for the
10583 Linux-based GNU system.
10587 On System V.4 and embedded PowerPC systems compile code for the
10588 Hurd-based GNU system.
10590 @item -mcall-netbsd
10591 @opindex mcall-netbsd
10592 On System V.4 and embedded PowerPC systems compile code for the
10593 NetBSD operating system.
10595 @item -maix-struct-return
10596 @opindex maix-struct-return
10597 Return all structures in memory (as specified by the AIX ABI)@.
10599 @item -msvr4-struct-return
10600 @opindex msvr4-struct-return
10601 Return structures smaller than 8 bytes in registers (as specified by the
10604 @item -mabi=altivec
10605 @opindex mabi=altivec
10606 Extend the current ABI with AltiVec ABI extensions. This does not
10607 change the default ABI, instead it adds the AltiVec ABI extensions to
10610 @item -mabi=no-altivec
10611 @opindex mabi=no-altivec
10612 Disable AltiVec ABI extensions for the current ABI.
10615 @itemx -mno-prototype
10616 @opindex mprototype
10617 @opindex mno-prototype
10618 On System V.4 and embedded PowerPC systems assume that all calls to
10619 variable argument functions are properly prototyped. Otherwise, the
10620 compiler must insert an instruction before every non prototyped call to
10621 set or clear bit 6 of the condition code register (@var{CR}) to
10622 indicate whether floating point values were passed in the floating point
10623 registers in case the function takes a variable arguments. With
10624 @option{-mprototype}, only calls to prototyped variable argument functions
10625 will set or clear the bit.
10629 On embedded PowerPC systems, assume that the startup module is called
10630 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
10631 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
10636 On embedded PowerPC systems, assume that the startup module is called
10637 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
10642 On embedded PowerPC systems, assume that the startup module is called
10643 @file{crt0.o} and the standard C libraries are @file{libads.a} and
10646 @item -myellowknife
10647 @opindex myellowknife
10648 On embedded PowerPC systems, assume that the startup module is called
10649 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
10654 On System V.4 and embedded PowerPC systems, specify that you are
10655 compiling for a VxWorks system.
10659 Specify that you are compiling for the WindISS simulation environment.
10663 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
10664 header to indicate that @samp{eabi} extended relocations are used.
10670 On System V.4 and embedded PowerPC systems do (do not) adhere to the
10671 Embedded Applications Binary Interface (eabi) which is a set of
10672 modifications to the System V.4 specifications. Selecting @option{-meabi}
10673 means that the stack is aligned to an 8 byte boundary, a function
10674 @code{__eabi} is called to from @code{main} to set up the eabi
10675 environment, and the @option{-msdata} option can use both @code{r2} and
10676 @code{r13} to point to two separate small data areas. Selecting
10677 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
10678 do not call an initialization function from @code{main}, and the
10679 @option{-msdata} option will only use @code{r13} to point to a single
10680 small data area. The @option{-meabi} option is on by default if you
10681 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
10684 @opindex msdata=eabi
10685 On System V.4 and embedded PowerPC systems, put small initialized
10686 @code{const} global and static data in the @samp{.sdata2} section, which
10687 is pointed to by register @code{r2}. Put small initialized
10688 non-@code{const} global and static data in the @samp{.sdata} section,
10689 which is pointed to by register @code{r13}. Put small uninitialized
10690 global and static data in the @samp{.sbss} section, which is adjacent to
10691 the @samp{.sdata} section. The @option{-msdata=eabi} option is
10692 incompatible with the @option{-mrelocatable} option. The
10693 @option{-msdata=eabi} option also sets the @option{-memb} option.
10696 @opindex msdata=sysv
10697 On System V.4 and embedded PowerPC systems, put small global and static
10698 data in the @samp{.sdata} section, which is pointed to by register
10699 @code{r13}. Put small uninitialized global and static data in the
10700 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
10701 The @option{-msdata=sysv} option is incompatible with the
10702 @option{-mrelocatable} option.
10704 @item -msdata=default
10706 @opindex msdata=default
10708 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
10709 compile code the same as @option{-msdata=eabi}, otherwise compile code the
10710 same as @option{-msdata=sysv}.
10713 @opindex msdata-data
10714 On System V.4 and embedded PowerPC systems, put small global and static
10715 data in the @samp{.sdata} section. Put small uninitialized global and
10716 static data in the @samp{.sbss} section. Do not use register @code{r13}
10717 to address small data however. This is the default behavior unless
10718 other @option{-msdata} options are used.
10722 @opindex msdata=none
10724 On embedded PowerPC systems, put all initialized global and static data
10725 in the @samp{.data} section, and all uninitialized data in the
10726 @samp{.bss} section.
10730 @cindex smaller data references (PowerPC)
10731 @cindex .sdata/.sdata2 references (PowerPC)
10732 On embedded PowerPC systems, put global and static items less than or
10733 equal to @var{num} bytes into the small data or bss sections instead of
10734 the normal data or bss section. By default, @var{num} is 8. The
10735 @option{-G @var{num}} switch is also passed to the linker.
10736 All modules should be compiled with the same @option{-G @var{num}} value.
10739 @itemx -mno-regnames
10741 @opindex mno-regnames
10742 On System V.4 and embedded PowerPC systems do (do not) emit register
10743 names in the assembly language output using symbolic forms.
10746 @itemx -mno-longcall
10748 @opindex mno-longcall
10749 Default to making all function calls indirectly, using a register, so
10750 that functions which reside further than 32 megabytes (33,554,432
10751 bytes) from the current location can be called. This setting can be
10752 overridden by the @code{shortcall} function attribute, or by
10753 @code{#pragma longcall(0)}.
10755 Some linkers are capable of detecting out-of-range calls and generating
10756 glue code on the fly. On these systems, long calls are unnecessary and
10757 generate slower code. As of this writing, the AIX linker can do this,
10758 as can the GNU linker for PowerPC/64. It is planned to add this feature
10759 to the GNU linker for 32-bit PowerPC systems as well.
10761 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
10762 callee, L42'', plus a ``branch island'' (glue code). The two target
10763 addresses represent the callee and the ``branch island''. The
10764 Darwin/PPC linker will prefer the first address and generate a ``bl
10765 callee'' if the PPC ``bl'' instruction will reach the callee directly;
10766 otherwise, the linker will generate ``bl L42'' to call the ``branch
10767 island''. The ``branch island'' is appended to the body of the
10768 calling function; it computes the full 32-bit address of the callee
10771 On Mach-O (Darwin) systems, this option directs the compiler emit to
10772 the glue for every direct call, and the Darwin linker decides whether
10773 to use or discard it.
10775 In the future, we may cause GCC to ignore all longcall specifications
10776 when the linker is known to generate glue.
10780 Adds support for multithreading with the @dfn{pthreads} library.
10781 This option sets flags for both the preprocessor and linker.
10785 @node S/390 and zSeries Options
10786 @subsection S/390 and zSeries Options
10787 @cindex S/390 and zSeries Options
10789 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10793 @itemx -msoft-float
10794 @opindex mhard-float
10795 @opindex msoft-float
10796 Use (do not use) the hardware floating-point instructions and registers
10797 for floating-point operations. When @option{-msoft-float} is specified,
10798 functions in @file{libgcc.a} will be used to perform floating-point
10799 operations. When @option{-mhard-float} is specified, the compiler
10800 generates IEEE floating-point instructions. This is the default.
10803 @itemx -mno-backchain
10804 @itemx -mkernel-backchain
10805 @opindex mbackchain
10806 @opindex mno-backchain
10807 @opindex mkernel-backchain
10808 In order to provide a backchain the address of the caller's frame
10809 is stored within the callee's stack frame.
10810 A backchain may be needed to allow debugging using tools that do not understand
10811 DWARF-2 call frame information.
10812 For @option{-mno-backchain} no backchain is maintained at all which is the
10814 If one of the other options is present the backchain pointer is placed either
10815 on top of the stack frame (@option{-mkernel-backchain}) or on
10816 the bottom (@option{-mbackchain}).
10817 Beside the different backchain location @option{-mkernel-backchain}
10818 also changes stack frame layout breaking the ABI. This option
10819 is intended to be used for code which internally needs a backchain but has
10820 to get by with a limited stack size e.g.@: the linux kernel.
10821 Internal unwinding code not using DWARF-2 info has to be able to locate the
10822 return address of a function. That will be eased be the fact that
10823 the return address of a function is placed two words below the backchain
10827 @itemx -mno-small-exec
10828 @opindex msmall-exec
10829 @opindex mno-small-exec
10830 Generate (or do not generate) code using the @code{bras} instruction
10831 to do subroutine calls.
10832 This only works reliably if the total executable size does not
10833 exceed 64k. The default is to use the @code{basr} instruction instead,
10834 which does not have this limitation.
10840 When @option{-m31} is specified, generate code compliant to the
10841 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
10842 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
10843 particular to generate 64-bit instructions. For the @samp{s390}
10844 targets, the default is @option{-m31}, while the @samp{s390x}
10845 targets default to @option{-m64}.
10851 When @option{-mzarch} is specified, generate code using the
10852 instructions available on z/Architecture.
10853 When @option{-mesa} is specified, generate code using the
10854 instructions available on ESA/390. Note that @option{-mesa} is
10855 not possible with @option{-m64}.
10856 When generating code compliant to the GNU/Linux for S/390 ABI,
10857 the default is @option{-mesa}. When generating code compliant
10858 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
10864 Generate (or do not generate) code using the @code{mvcle} instruction
10865 to perform block moves. When @option{-mno-mvcle} is specified,
10866 use a @code{mvc} loop instead. This is the default.
10872 Print (or do not print) additional debug information when compiling.
10873 The default is to not print debug information.
10875 @item -march=@var{cpu-type}
10877 Generate code that will run on @var{cpu-type}, which is the name of a system
10878 representing a certain processor type. Possible values for
10879 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10880 When generating code using the instructions available on z/Architecture,
10881 the default is @option{-march=z900}. Otherwise, the default is
10882 @option{-march=g5}.
10884 @item -mtune=@var{cpu-type}
10886 Tune to @var{cpu-type} everything applicable about the generated code,
10887 except for the ABI and the set of available instructions.
10888 The list of @var{cpu-type} values is the same as for @option{-march}.
10889 The default is the value used for @option{-march}.
10892 @itemx -mno-tpf-trace
10893 @opindex mtpf-trace
10894 @opindex mno-tpf-trace
10895 Generate code that adds (does not add) in TPF OS specific branches to trace
10896 routines in the operating system. This option is off by default, even
10897 when compiling for the TPF OS.
10900 @itemx -mno-fused-madd
10901 @opindex mfused-madd
10902 @opindex mno-fused-madd
10903 Generate code that uses (does not use) the floating point multiply and
10904 accumulate instructions. These instructions are generated by default if
10905 hardware floating point is used.
10907 @item -mwarn-framesize=@var{framesize}
10908 @opindex mwarn-framesize
10909 Emit a warning if the current function exceeds the given frame size. Because
10910 this is a compile time check it doesn't need to be a real problem when the program
10911 runs. It is intended to identify functions which most probably cause
10912 a stack overflow. It is useful to be used in an environment with limited stack
10913 size e.g.@: the linux kernel.
10915 @item -mwarn-dynamicstack
10916 @opindex mwarn-dynamicstack
10917 Emit a warning if the function calls alloca or uses dynamically
10918 sized arrays. This is generally a bad idea with a limited stack size.
10920 @item -mstack-guard=@var{stack-guard}
10921 @item -mstack-size=@var{stack-size}
10922 @opindex mstack-guard
10923 @opindex mstack-size
10924 These arguments always have to be used in conjunction. If they are present the s390
10925 back end emits additional instructions in the function prologue which trigger a trap
10926 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
10927 (remember that the stack on s390 grows downward). These options are intended to
10928 be used to help debugging stack overflow problems. The additionally emitted code
10929 cause only little overhead and hence can also be used in production like systems
10930 without greater performance degradation. The given values have to be exact
10931 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard}.
10932 In order to be efficient the extra code makes the assumption that the stack starts
10933 at an address aligned to the value given by @var{stack-size}.
10937 @subsection SH Options
10939 These @samp{-m} options are defined for the SH implementations:
10944 Generate code for the SH1.
10948 Generate code for the SH2.
10951 Generate code for the SH2e.
10955 Generate code for the SH3.
10959 Generate code for the SH3e.
10963 Generate code for the SH4 without a floating-point unit.
10965 @item -m4-single-only
10966 @opindex m4-single-only
10967 Generate code for the SH4 with a floating-point unit that only
10968 supports single-precision arithmetic.
10972 Generate code for the SH4 assuming the floating-point unit is in
10973 single-precision mode by default.
10977 Generate code for the SH4.
10981 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
10982 floating-point unit is not used.
10984 @item -m4a-single-only
10985 @opindex m4a-single-only
10986 Generate code for the SH4a, in such a way that no double-precision
10987 floating point operations are used.
10990 @opindex m4a-single
10991 Generate code for the SH4a assuming the floating-point unit is in
10992 single-precision mode by default.
10996 Generate code for the SH4a.
11000 Same as @option{-m4a-nofpu}, except that it implicitly passes
11001 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11002 instructions at the moment.
11006 Compile code for the processor in big endian mode.
11010 Compile code for the processor in little endian mode.
11014 Align doubles at 64-bit boundaries. Note that this changes the calling
11015 conventions, and thus some functions from the standard C library will
11016 not work unless you recompile it first with @option{-mdalign}.
11020 Shorten some address references at link time, when possible; uses the
11021 linker option @option{-relax}.
11025 Use 32-bit offsets in @code{switch} tables. The default is to use
11030 Enable the use of the instruction @code{fmovd}.
11034 Comply with the calling conventions defined by Renesas.
11038 Comply with the calling conventions defined by Renesas.
11042 Comply with the calling conventions defined for GCC before the Renesas
11043 conventions were available. This option is the default for all
11044 targets of the SH toolchain except for @samp{sh-symbianelf}.
11047 @opindex mnomacsave
11048 Mark the @code{MAC} register as call-clobbered, even if
11049 @option{-mhitachi} is given.
11053 Increase IEEE-compliance of floating-point code.
11057 Dump instruction size and location in the assembly code.
11060 @opindex mpadstruct
11061 This option is deprecated. It pads structures to multiple of 4 bytes,
11062 which is incompatible with the SH ABI@.
11066 Optimize for space instead of speed. Implied by @option{-Os}.
11069 @opindex mprefergot
11070 When generating position-independent code, emit function calls using
11071 the Global Offset Table instead of the Procedure Linkage Table.
11075 Generate a library function call to invalidate instruction cache
11076 entries, after fixing up a trampoline. This library function call
11077 doesn't assume it can write to the whole memory address space. This
11078 is the default when the target is @code{sh-*-linux*}.
11081 @node SPARC Options
11082 @subsection SPARC Options
11083 @cindex SPARC options
11085 These @samp{-m} options are supported on the SPARC:
11088 @item -mno-app-regs
11090 @opindex mno-app-regs
11092 Specify @option{-mapp-regs} to generate output using the global registers
11093 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
11096 To be fully SVR4 ABI compliant at the cost of some performance loss,
11097 specify @option{-mno-app-regs}. You should compile libraries and system
11098 software with this option.
11101 @itemx -mhard-float
11103 @opindex mhard-float
11104 Generate output containing floating point instructions. This is the
11108 @itemx -msoft-float
11110 @opindex msoft-float
11111 Generate output containing library calls for floating point.
11112 @strong{Warning:} the requisite libraries are not available for all SPARC
11113 targets. Normally the facilities of the machine's usual C compiler are
11114 used, but this cannot be done directly in cross-compilation. You must make
11115 your own arrangements to provide suitable library functions for
11116 cross-compilation. The embedded targets @samp{sparc-*-aout} and
11117 @samp{sparclite-*-*} do provide software floating point support.
11119 @option{-msoft-float} changes the calling convention in the output file;
11120 therefore, it is only useful if you compile @emph{all} of a program with
11121 this option. In particular, you need to compile @file{libgcc.a}, the
11122 library that comes with GCC, with @option{-msoft-float} in order for
11125 @item -mhard-quad-float
11126 @opindex mhard-quad-float
11127 Generate output containing quad-word (long double) floating point
11130 @item -msoft-quad-float
11131 @opindex msoft-quad-float
11132 Generate output containing library calls for quad-word (long double)
11133 floating point instructions. The functions called are those specified
11134 in the SPARC ABI@. This is the default.
11136 As of this writing, there are no SPARC implementations that have hardware
11137 support for the quad-word floating point instructions. They all invoke
11138 a trap handler for one of these instructions, and then the trap handler
11139 emulates the effect of the instruction. Because of the trap handler overhead,
11140 this is much slower than calling the ABI library routines. Thus the
11141 @option{-msoft-quad-float} option is the default.
11143 @item -mno-unaligned-doubles
11144 @itemx -munaligned-doubles
11145 @opindex mno-unaligned-doubles
11146 @opindex munaligned-doubles
11147 Assume that doubles have 8 byte alignment. This is the default.
11149 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
11150 alignment only if they are contained in another type, or if they have an
11151 absolute address. Otherwise, it assumes they have 4 byte alignment.
11152 Specifying this option avoids some rare compatibility problems with code
11153 generated by other compilers. It is not the default because it results
11154 in a performance loss, especially for floating point code.
11156 @item -mno-faster-structs
11157 @itemx -mfaster-structs
11158 @opindex mno-faster-structs
11159 @opindex mfaster-structs
11160 With @option{-mfaster-structs}, the compiler assumes that structures
11161 should have 8 byte alignment. This enables the use of pairs of
11162 @code{ldd} and @code{std} instructions for copies in structure
11163 assignment, in place of twice as many @code{ld} and @code{st} pairs.
11164 However, the use of this changed alignment directly violates the SPARC
11165 ABI@. Thus, it's intended only for use on targets where the developer
11166 acknowledges that their resulting code will not be directly in line with
11167 the rules of the ABI@.
11169 @item -mimpure-text
11170 @opindex mimpure-text
11171 @option{-mimpure-text}, used in addition to @option{-shared}, tells
11172 the compiler to not pass @option{-z text} to the linker when linking a
11173 shared object. Using this option, you can link position-dependent
11174 code into a shared object.
11176 @option{-mimpure-text} suppresses the ``relocations remain against
11177 allocatable but non-writable sections'' linker error message.
11178 However, the necessary relocations will trigger copy-on-write, and the
11179 shared object is not actually shared across processes. Instead of
11180 using @option{-mimpure-text}, you should compile all source code with
11181 @option{-fpic} or @option{-fPIC}.
11183 This option is only available on SunOS and Solaris.
11185 @item -mcpu=@var{cpu_type}
11187 Set the instruction set, register set, and instruction scheduling parameters
11188 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
11189 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
11190 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
11191 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
11192 @samp{ultrasparc3}.
11194 Default instruction scheduling parameters are used for values that select
11195 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
11196 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
11198 Here is a list of each supported architecture and their supported
11203 v8: supersparc, hypersparc
11204 sparclite: f930, f934, sparclite86x
11206 v9: ultrasparc, ultrasparc3
11209 By default (unless configured otherwise), GCC generates code for the V7
11210 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
11211 additionally optimizes it for the Cypress CY7C602 chip, as used in the
11212 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
11213 SPARCStation 1, 2, IPX etc.
11215 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
11216 architecture. The only difference from V7 code is that the compiler emits
11217 the integer multiply and integer divide instructions which exist in SPARC-V8
11218 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
11219 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
11222 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
11223 the SPARC architecture. This adds the integer multiply, integer divide step
11224 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
11225 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
11226 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With
11227 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
11228 MB86934 chip, which is the more recent SPARClite with FPU.
11230 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
11231 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
11232 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
11233 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
11234 optimizes it for the TEMIC SPARClet chip.
11236 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
11237 architecture. This adds 64-bit integer and floating-point move instructions,
11238 3 additional floating-point condition code registers and conditional move
11239 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
11240 optimizes it for the Sun UltraSPARC I/II chips. With
11241 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
11242 Sun UltraSPARC III chip.
11244 @item -mtune=@var{cpu_type}
11246 Set the instruction scheduling parameters for machine type
11247 @var{cpu_type}, but do not set the instruction set or register set that the
11248 option @option{-mcpu=@var{cpu_type}} would.
11250 The same values for @option{-mcpu=@var{cpu_type}} can be used for
11251 @option{-mtune=@var{cpu_type}}, but the only useful values are those
11252 that select a particular cpu implementation. Those are @samp{cypress},
11253 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
11254 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
11255 @samp{ultrasparc3}.
11260 @opindex mno-v8plus
11261 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI. The
11262 difference from the V8 ABI is that the global and out registers are
11263 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
11264 mode for all SPARC-V9 processors.
11270 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
11271 Visual Instruction Set extensions. The default is @option{-mno-vis}.
11274 These @samp{-m} options are supported in addition to the above
11275 on SPARC-V9 processors in 64-bit environments:
11278 @item -mlittle-endian
11279 @opindex mlittle-endian
11280 Generate code for a processor running in little-endian mode. It is only
11281 available for a few configurations and most notably not on Solaris.
11287 Generate code for a 32-bit or 64-bit environment.
11288 The 32-bit environment sets int, long and pointer to 32 bits.
11289 The 64-bit environment sets int to 32 bits and long and pointer
11292 @item -mcmodel=medlow
11293 @opindex mcmodel=medlow
11294 Generate code for the Medium/Low code model: 64-bit addresses, programs
11295 must be linked in the low 32 bits of memory. Programs can be statically
11296 or dynamically linked.
11298 @item -mcmodel=medmid
11299 @opindex mcmodel=medmid
11300 Generate code for the Medium/Middle code model: 64-bit addresses, programs
11301 must be linked in the low 44 bits of memory, the text and data segments must
11302 be less than 2GB in size and the data segment must be located within 2GB of
11305 @item -mcmodel=medany
11306 @opindex mcmodel=medany
11307 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
11308 may be linked anywhere in memory, the text and data segments must be less
11309 than 2GB in size and the data segment must be located within 2GB of the
11312 @item -mcmodel=embmedany
11313 @opindex mcmodel=embmedany
11314 Generate code for the Medium/Anywhere code model for embedded systems:
11315 64-bit addresses, the text and data segments must be less than 2GB in
11316 size, both starting anywhere in memory (determined at link time). The
11317 global register %g4 points to the base of the data segment. Programs
11318 are statically linked and PIC is not supported.
11321 @itemx -mno-stack-bias
11322 @opindex mstack-bias
11323 @opindex mno-stack-bias
11324 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
11325 frame pointer if present, are offset by @minus{}2047 which must be added back
11326 when making stack frame references. This is the default in 64-bit mode.
11327 Otherwise, assume no such offset is present.
11330 These switches are supported in addition to the above on Solaris:
11335 Add support for multithreading using the Solaris threads library. This
11336 option sets flags for both the preprocessor and linker. This option does
11337 not affect the thread safety of object code produced by the compiler or
11338 that of libraries supplied with it.
11342 Add support for multithreading using the POSIX threads library. This
11343 option sets flags for both the preprocessor and linker. This option does
11344 not affect the thread safety of object code produced by the compiler or
11345 that of libraries supplied with it.
11348 @node System V Options
11349 @subsection Options for System V
11351 These additional options are available on System V Release 4 for
11352 compatibility with other compilers on those systems:
11357 Create a shared object.
11358 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
11362 Identify the versions of each tool used by the compiler, in a
11363 @code{.ident} assembler directive in the output.
11367 Refrain from adding @code{.ident} directives to the output file (this is
11370 @item -YP,@var{dirs}
11372 Search the directories @var{dirs}, and no others, for libraries
11373 specified with @option{-l}.
11375 @item -Ym,@var{dir}
11377 Look in the directory @var{dir} to find the M4 preprocessor.
11378 The assembler uses this option.
11379 @c This is supposed to go with a -Yd for predefined M4 macro files, but
11380 @c the generic assembler that comes with Solaris takes just -Ym.
11383 @node TMS320C3x/C4x Options
11384 @subsection TMS320C3x/C4x Options
11385 @cindex TMS320C3x/C4x Options
11387 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
11391 @item -mcpu=@var{cpu_type}
11393 Set the instruction set, register set, and instruction scheduling
11394 parameters for machine type @var{cpu_type}. Supported values for
11395 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
11396 @samp{c44}. The default is @samp{c40} to generate code for the
11401 @itemx -msmall-memory
11403 @opindex mbig-memory
11405 @opindex msmall-memory
11407 Generates code for the big or small memory model. The small memory
11408 model assumed that all data fits into one 64K word page. At run-time
11409 the data page (DP) register must be set to point to the 64K page
11410 containing the .bss and .data program sections. The big memory model is
11411 the default and requires reloading of the DP register for every direct
11418 Allow (disallow) allocation of general integer operands into the block
11419 count register BK@.
11425 Enable (disable) generation of code using decrement and branch,
11426 DBcond(D), instructions. This is enabled by default for the C4x. To be
11427 on the safe side, this is disabled for the C3x, since the maximum
11428 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
11429 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
11430 that it can utilize the decrement and branch instruction, but will give
11431 up if there is more than one memory reference in the loop. Thus a loop
11432 where the loop counter is decremented can generate slightly more
11433 efficient code, in cases where the RPTB instruction cannot be utilized.
11435 @item -mdp-isr-reload
11437 @opindex mdp-isr-reload
11439 Force the DP register to be saved on entry to an interrupt service
11440 routine (ISR), reloaded to point to the data section, and restored on
11441 exit from the ISR@. This should not be required unless someone has
11442 violated the small memory model by modifying the DP register, say within
11449 For the C3x use the 24-bit MPYI instruction for integer multiplies
11450 instead of a library call to guarantee 32-bit results. Note that if one
11451 of the operands is a constant, then the multiplication will be performed
11452 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
11453 then squaring operations are performed inline instead of a library call.
11456 @itemx -mno-fast-fix
11458 @opindex mno-fast-fix
11459 The C3x/C4x FIX instruction to convert a floating point value to an
11460 integer value chooses the nearest integer less than or equal to the
11461 floating point value rather than to the nearest integer. Thus if the
11462 floating point number is negative, the result will be incorrectly
11463 truncated an additional code is necessary to detect and correct this
11464 case. This option can be used to disable generation of the additional
11465 code required to correct the result.
11471 Enable (disable) generation of repeat block sequences using the RPTB
11472 instruction for zero overhead looping. The RPTB construct is only used
11473 for innermost loops that do not call functions or jump across the loop
11474 boundaries. There is no advantage having nested RPTB loops due to the
11475 overhead required to save and restore the RC, RS, and RE registers.
11476 This is enabled by default with @option{-O2}.
11478 @item -mrpts=@var{count}
11482 Enable (disable) the use of the single instruction repeat instruction
11483 RPTS@. If a repeat block contains a single instruction, and the loop
11484 count can be guaranteed to be less than the value @var{count}, GCC will
11485 emit a RPTS instruction instead of a RPTB@. If no value is specified,
11486 then a RPTS will be emitted even if the loop count cannot be determined
11487 at compile time. Note that the repeated instruction following RPTS does
11488 not have to be reloaded from memory each iteration, thus freeing up the
11489 CPU buses for operands. However, since interrupts are blocked by this
11490 instruction, it is disabled by default.
11492 @item -mloop-unsigned
11493 @itemx -mno-loop-unsigned
11494 @opindex mloop-unsigned
11495 @opindex mno-loop-unsigned
11496 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
11497 is @math{2^{31} + 1} since these instructions test if the iteration count is
11498 negative to terminate the loop. If the iteration count is unsigned
11499 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
11500 exceeded. This switch allows an unsigned iteration count.
11504 Try to emit an assembler syntax that the TI assembler (asm30) is happy
11505 with. This also enforces compatibility with the API employed by the TI
11506 C3x C compiler. For example, long doubles are passed as structures
11507 rather than in floating point registers.
11513 Generate code that uses registers (stack) for passing arguments to functions.
11514 By default, arguments are passed in registers where possible rather
11515 than by pushing arguments on to the stack.
11517 @item -mparallel-insns
11518 @itemx -mno-parallel-insns
11519 @opindex mparallel-insns
11520 @opindex mno-parallel-insns
11521 Allow the generation of parallel instructions. This is enabled by
11522 default with @option{-O2}.
11524 @item -mparallel-mpy
11525 @itemx -mno-parallel-mpy
11526 @opindex mparallel-mpy
11527 @opindex mno-parallel-mpy
11528 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
11529 provided @option{-mparallel-insns} is also specified. These instructions have
11530 tight register constraints which can pessimize the code generation
11531 of large functions.
11536 @subsection V850 Options
11537 @cindex V850 Options
11539 These @samp{-m} options are defined for V850 implementations:
11543 @itemx -mno-long-calls
11544 @opindex mlong-calls
11545 @opindex mno-long-calls
11546 Treat all calls as being far away (near). If calls are assumed to be
11547 far away, the compiler will always load the functions address up into a
11548 register, and call indirect through the pointer.
11554 Do not optimize (do optimize) basic blocks that use the same index
11555 pointer 4 or more times to copy pointer into the @code{ep} register, and
11556 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
11557 option is on by default if you optimize.
11559 @item -mno-prolog-function
11560 @itemx -mprolog-function
11561 @opindex mno-prolog-function
11562 @opindex mprolog-function
11563 Do not use (do use) external functions to save and restore registers
11564 at the prologue and epilogue of a function. The external functions
11565 are slower, but use less code space if more than one function saves
11566 the same number of registers. The @option{-mprolog-function} option
11567 is on by default if you optimize.
11571 Try to make the code as small as possible. At present, this just turns
11572 on the @option{-mep} and @option{-mprolog-function} options.
11574 @item -mtda=@var{n}
11576 Put static or global variables whose size is @var{n} bytes or less into
11577 the tiny data area that register @code{ep} points to. The tiny data
11578 area can hold up to 256 bytes in total (128 bytes for byte references).
11580 @item -msda=@var{n}
11582 Put static or global variables whose size is @var{n} bytes or less into
11583 the small data area that register @code{gp} points to. The small data
11584 area can hold up to 64 kilobytes.
11586 @item -mzda=@var{n}
11588 Put static or global variables whose size is @var{n} bytes or less into
11589 the first 32 kilobytes of memory.
11593 Specify that the target processor is the V850.
11596 @opindex mbig-switch
11597 Generate code suitable for big switch tables. Use this option only if
11598 the assembler/linker complain about out of range branches within a switch
11603 This option will cause r2 and r5 to be used in the code generated by
11604 the compiler. This setting is the default.
11606 @item -mno-app-regs
11607 @opindex mno-app-regs
11608 This option will cause r2 and r5 to be treated as fixed registers.
11612 Specify that the target processor is the V850E1. The preprocessor
11613 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
11614 this option is used.
11618 Specify that the target processor is the V850E. The preprocessor
11619 constant @samp{__v850e__} will be defined if this option is used.
11621 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
11622 are defined then a default target processor will be chosen and the
11623 relevant @samp{__v850*__} preprocessor constant will be defined.
11625 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
11626 defined, regardless of which processor variant is the target.
11628 @item -mdisable-callt
11629 @opindex mdisable-callt
11630 This option will suppress generation of the CALLT instruction for the
11631 v850e and v850e1 flavors of the v850 architecture. The default is
11632 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
11637 @subsection VAX Options
11638 @cindex VAX options
11640 These @samp{-m} options are defined for the VAX:
11645 Do not output certain jump instructions (@code{aobleq} and so on)
11646 that the Unix assembler for the VAX cannot handle across long
11651 Do output those jump instructions, on the assumption that you
11652 will assemble with the GNU assembler.
11656 Output code for g-format floating point numbers instead of d-format.
11659 @node x86-64 Options
11660 @subsection x86-64 Options
11661 @cindex x86-64 options
11663 These are listed under @xref{i386 and x86-64 Options}.
11665 @node Xstormy16 Options
11666 @subsection Xstormy16 Options
11667 @cindex Xstormy16 Options
11669 These options are defined for Xstormy16:
11674 Choose startup files and linker script suitable for the simulator.
11677 @node Xtensa Options
11678 @subsection Xtensa Options
11679 @cindex Xtensa Options
11681 These options are supported for Xtensa targets:
11685 @itemx -mno-const16
11687 @opindex mno-const16
11688 Enable or disable use of @code{CONST16} instructions for loading
11689 constant values. The @code{CONST16} instruction is currently not a
11690 standard option from Tensilica. When enabled, @code{CONST16}
11691 instructions are always used in place of the standard @code{L32R}
11692 instructions. The use of @code{CONST16} is enabled by default only if
11693 the @code{L32R} instruction is not available.
11696 @itemx -mno-fused-madd
11697 @opindex mfused-madd
11698 @opindex mno-fused-madd
11699 Enable or disable use of fused multiply/add and multiply/subtract
11700 instructions in the floating-point option. This has no effect if the
11701 floating-point option is not also enabled. Disabling fused multiply/add
11702 and multiply/subtract instructions forces the compiler to use separate
11703 instructions for the multiply and add/subtract operations. This may be
11704 desirable in some cases where strict IEEE 754-compliant results are
11705 required: the fused multiply add/subtract instructions do not round the
11706 intermediate result, thereby producing results with @emph{more} bits of
11707 precision than specified by the IEEE standard. Disabling fused multiply
11708 add/subtract instructions also ensures that the program output is not
11709 sensitive to the compiler's ability to combine multiply and add/subtract
11712 @item -mtext-section-literals
11713 @itemx -mno-text-section-literals
11714 @opindex mtext-section-literals
11715 @opindex mno-text-section-literals
11716 Control the treatment of literal pools. The default is
11717 @option{-mno-text-section-literals}, which places literals in a separate
11718 section in the output file. This allows the literal pool to be placed
11719 in a data RAM/ROM, and it also allows the linker to combine literal
11720 pools from separate object files to remove redundant literals and
11721 improve code size. With @option{-mtext-section-literals}, the literals
11722 are interspersed in the text section in order to keep them as close as
11723 possible to their references. This may be necessary for large assembly
11726 @item -mtarget-align
11727 @itemx -mno-target-align
11728 @opindex mtarget-align
11729 @opindex mno-target-align
11730 When this option is enabled, GCC instructs the assembler to
11731 automatically align instructions to reduce branch penalties at the
11732 expense of some code density. The assembler attempts to widen density
11733 instructions to align branch targets and the instructions following call
11734 instructions. If there are not enough preceding safe density
11735 instructions to align a target, no widening will be performed. The
11736 default is @option{-mtarget-align}. These options do not affect the
11737 treatment of auto-aligned instructions like @code{LOOP}, which the
11738 assembler will always align, either by widening density instructions or
11739 by inserting no-op instructions.
11742 @itemx -mno-longcalls
11743 @opindex mlongcalls
11744 @opindex mno-longcalls
11745 When this option is enabled, GCC instructs the assembler to translate
11746 direct calls to indirect calls unless it can determine that the target
11747 of a direct call is in the range allowed by the call instruction. This
11748 translation typically occurs for calls to functions in other source
11749 files. Specifically, the assembler translates a direct @code{CALL}
11750 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
11751 The default is @option{-mno-longcalls}. This option should be used in
11752 programs where the call target can potentially be out of range. This
11753 option is implemented in the assembler, not the compiler, so the
11754 assembly code generated by GCC will still show direct call
11755 instructions---look at the disassembled object code to see the actual
11756 instructions. Note that the assembler will use an indirect call for
11757 every cross-file call, not just those that really will be out of range.
11760 @node zSeries Options
11761 @subsection zSeries Options
11762 @cindex zSeries options
11764 These are listed under @xref{S/390 and zSeries Options}.
11766 @node Code Gen Options
11767 @section Options for Code Generation Conventions
11768 @cindex code generation conventions
11769 @cindex options, code generation
11770 @cindex run-time options
11772 These machine-independent options control the interface conventions
11773 used in code generation.
11775 Most of them have both positive and negative forms; the negative form
11776 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
11777 one of the forms is listed---the one which is not the default. You
11778 can figure out the other form by either removing @samp{no-} or adding
11782 @item -fbounds-check
11783 @opindex fbounds-check
11784 For front-ends that support it, generate additional code to check that
11785 indices used to access arrays are within the declared range. This is
11786 currently only supported by the Java and Fortran 77 front-ends, where
11787 this option defaults to true and false respectively.
11791 This option generates traps for signed overflow on addition, subtraction,
11792 multiplication operations.
11796 This option instructs the compiler to assume that signed arithmetic
11797 overflow of addition, subtraction and multiplication wraps around
11798 using twos-complement representation. This flag enables some optimizations
11799 and disables other. This option is enabled by default for the Java
11800 front-end, as required by the Java language specification.
11803 @opindex fexceptions
11804 Enable exception handling. Generates extra code needed to propagate
11805 exceptions. For some targets, this implies GCC will generate frame
11806 unwind information for all functions, which can produce significant data
11807 size overhead, although it does not affect execution. If you do not
11808 specify this option, GCC will enable it by default for languages like
11809 C++ which normally require exception handling, and disable it for
11810 languages like C that do not normally require it. However, you may need
11811 to enable this option when compiling C code that needs to interoperate
11812 properly with exception handlers written in C++. You may also wish to
11813 disable this option if you are compiling older C++ programs that don't
11814 use exception handling.
11816 @item -fnon-call-exceptions
11817 @opindex fnon-call-exceptions
11818 Generate code that allows trapping instructions to throw exceptions.
11819 Note that this requires platform-specific runtime support that does
11820 not exist everywhere. Moreover, it only allows @emph{trapping}
11821 instructions to throw exceptions, i.e.@: memory references or floating
11822 point instructions. It does not allow exceptions to be thrown from
11823 arbitrary signal handlers such as @code{SIGALRM}.
11825 @item -funwind-tables
11826 @opindex funwind-tables
11827 Similar to @option{-fexceptions}, except that it will just generate any needed
11828 static data, but will not affect the generated code in any other way.
11829 You will normally not enable this option; instead, a language processor
11830 that needs this handling would enable it on your behalf.
11832 @item -fasynchronous-unwind-tables
11833 @opindex fasynchronous-unwind-tables
11834 Generate unwind table in dwarf2 format, if supported by target machine. The
11835 table is exact at each instruction boundary, so it can be used for stack
11836 unwinding from asynchronous events (such as debugger or garbage collector).
11838 @item -fpcc-struct-return
11839 @opindex fpcc-struct-return
11840 Return ``short'' @code{struct} and @code{union} values in memory like
11841 longer ones, rather than in registers. This convention is less
11842 efficient, but it has the advantage of allowing intercallability between
11843 GCC-compiled files and files compiled with other compilers, particularly
11844 the Portable C Compiler (pcc).
11846 The precise convention for returning structures in memory depends
11847 on the target configuration macros.
11849 Short structures and unions are those whose size and alignment match
11850 that of some integer type.
11852 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11853 switch is not binary compatible with code compiled with the
11854 @option{-freg-struct-return} switch.
11855 Use it to conform to a non-default application binary interface.
11857 @item -freg-struct-return
11858 @opindex freg-struct-return
11859 Return @code{struct} and @code{union} values in registers when possible.
11860 This is more efficient for small structures than
11861 @option{-fpcc-struct-return}.
11863 If you specify neither @option{-fpcc-struct-return} nor
11864 @option{-freg-struct-return}, GCC defaults to whichever convention is
11865 standard for the target. If there is no standard convention, GCC
11866 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11867 the principal compiler. In those cases, we can choose the standard, and
11868 we chose the more efficient register return alternative.
11870 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11871 switch is not binary compatible with code compiled with the
11872 @option{-fpcc-struct-return} switch.
11873 Use it to conform to a non-default application binary interface.
11875 @item -fshort-enums
11876 @opindex fshort-enums
11877 Allocate to an @code{enum} type only as many bytes as it needs for the
11878 declared range of possible values. Specifically, the @code{enum} type
11879 will be equivalent to the smallest integer type which has enough room.
11881 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11882 code that is not binary compatible with code generated without that switch.
11883 Use it to conform to a non-default application binary interface.
11885 @item -fshort-double
11886 @opindex fshort-double
11887 Use the same size for @code{double} as for @code{float}.
11889 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11890 code that is not binary compatible with code generated without that switch.
11891 Use it to conform to a non-default application binary interface.
11893 @item -fshort-wchar
11894 @opindex fshort-wchar
11895 Override the underlying type for @samp{wchar_t} to be @samp{short
11896 unsigned int} instead of the default for the target. This option is
11897 useful for building programs to run under WINE@.
11899 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11900 code that is not binary compatible with code generated without that switch.
11901 Use it to conform to a non-default application binary interface.
11903 @item -fshared-data
11904 @opindex fshared-data
11905 Requests that the data and non-@code{const} variables of this
11906 compilation be shared data rather than private data. The distinction
11907 makes sense only on certain operating systems, where shared data is
11908 shared between processes running the same program, while private data
11909 exists in one copy per process.
11912 @opindex fno-common
11913 In C, allocate even uninitialized global variables in the data section of the
11914 object file, rather than generating them as common blocks. This has the
11915 effect that if the same variable is declared (without @code{extern}) in
11916 two different compilations, you will get an error when you link them.
11917 The only reason this might be useful is if you wish to verify that the
11918 program will work on other systems which always work this way.
11922 Ignore the @samp{#ident} directive.
11924 @item -finhibit-size-directive
11925 @opindex finhibit-size-directive
11926 Don't output a @code{.size} assembler directive, or anything else that
11927 would cause trouble if the function is split in the middle, and the
11928 two halves are placed at locations far apart in memory. This option is
11929 used when compiling @file{crtstuff.c}; you should not need to use it
11932 @item -fverbose-asm
11933 @opindex fverbose-asm
11934 Put extra commentary information in the generated assembly code to
11935 make it more readable. This option is generally only of use to those
11936 who actually need to read the generated assembly code (perhaps while
11937 debugging the compiler itself).
11939 @option{-fno-verbose-asm}, the default, causes the
11940 extra information to be omitted and is useful when comparing two assembler
11945 @cindex global offset table
11947 Generate position-independent code (PIC) suitable for use in a shared
11948 library, if supported for the target machine. Such code accesses all
11949 constant addresses through a global offset table (GOT)@. The dynamic
11950 loader resolves the GOT entries when the program starts (the dynamic
11951 loader is not part of GCC; it is part of the operating system). If
11952 the GOT size for the linked executable exceeds a machine-specific
11953 maximum size, you get an error message from the linker indicating that
11954 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11955 instead. (These maximums are 8k on the SPARC and 32k
11956 on the m68k and RS/6000. The 386 has no such limit.)
11958 Position-independent code requires special support, and therefore works
11959 only on certain machines. For the 386, GCC supports PIC for System V
11960 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11961 position-independent.
11965 If supported for the target machine, emit position-independent code,
11966 suitable for dynamic linking and avoiding any limit on the size of the
11967 global offset table. This option makes a difference on the m68k
11970 Position-independent code requires special support, and therefore works
11971 only on certain machines.
11977 These options are similar to @option{-fpic} and @option{-fPIC}, but
11978 generated position independent code can be only linked into executables.
11979 Usually these options are used when @option{-pie} GCC option will be
11980 used during linking.
11982 @item -ffixed-@var{reg}
11984 Treat the register named @var{reg} as a fixed register; generated code
11985 should never refer to it (except perhaps as a stack pointer, frame
11986 pointer or in some other fixed role).
11988 @var{reg} must be the name of a register. The register names accepted
11989 are machine-specific and are defined in the @code{REGISTER_NAMES}
11990 macro in the machine description macro file.
11992 This flag does not have a negative form, because it specifies a
11995 @item -fcall-used-@var{reg}
11996 @opindex fcall-used
11997 Treat the register named @var{reg} as an allocable register that is
11998 clobbered by function calls. It may be allocated for temporaries or
11999 variables that do not live across a call. Functions compiled this way
12000 will not save and restore the register @var{reg}.
12002 It is an error to used this flag with the frame pointer or stack pointer.
12003 Use of this flag for other registers that have fixed pervasive roles in
12004 the machine's execution model will produce disastrous results.
12006 This flag does not have a negative form, because it specifies a
12009 @item -fcall-saved-@var{reg}
12010 @opindex fcall-saved
12011 Treat the register named @var{reg} as an allocable register saved by
12012 functions. It may be allocated even for temporaries or variables that
12013 live across a call. Functions compiled this way will save and restore
12014 the register @var{reg} if they use it.
12016 It is an error to used this flag with the frame pointer or stack pointer.
12017 Use of this flag for other registers that have fixed pervasive roles in
12018 the machine's execution model will produce disastrous results.
12020 A different sort of disaster will result from the use of this flag for
12021 a register in which function values may be returned.
12023 This flag does not have a negative form, because it specifies a
12026 @item -fpack-struct[=@var{n}]
12027 @opindex fpack-struct
12028 Without a value specified, pack all structure members together without
12029 holes. When a value is specified (which must be a small power of two), pack
12030 structure members according to this value, representing the maximum
12031 alignment (that is, objects with default alignment requirements larger than
12032 this will be output potentially unaligned at the next fitting location.
12034 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
12035 code that is not binary compatible with code generated without that switch.
12036 Additionally, it makes the code suboptimal.
12037 Use it to conform to a non-default application binary interface.
12039 @item -finstrument-functions
12040 @opindex finstrument-functions
12041 Generate instrumentation calls for entry and exit to functions. Just
12042 after function entry and just before function exit, the following
12043 profiling functions will be called with the address of the current
12044 function and its call site. (On some platforms,
12045 @code{__builtin_return_address} does not work beyond the current
12046 function, so the call site information may not be available to the
12047 profiling functions otherwise.)
12050 void __cyg_profile_func_enter (void *this_fn,
12052 void __cyg_profile_func_exit (void *this_fn,
12056 The first argument is the address of the start of the current function,
12057 which may be looked up exactly in the symbol table.
12059 This instrumentation is also done for functions expanded inline in other
12060 functions. The profiling calls will indicate where, conceptually, the
12061 inline function is entered and exited. This means that addressable
12062 versions of such functions must be available. If all your uses of a
12063 function are expanded inline, this may mean an additional expansion of
12064 code size. If you use @samp{extern inline} in your C code, an
12065 addressable version of such functions must be provided. (This is
12066 normally the case anyways, but if you get lucky and the optimizer always
12067 expands the functions inline, you might have gotten away without
12068 providing static copies.)
12070 A function may be given the attribute @code{no_instrument_function}, in
12071 which case this instrumentation will not be done. This can be used, for
12072 example, for the profiling functions listed above, high-priority
12073 interrupt routines, and any functions from which the profiling functions
12074 cannot safely be called (perhaps signal handlers, if the profiling
12075 routines generate output or allocate memory).
12077 @item -fstack-check
12078 @opindex fstack-check
12079 Generate code to verify that you do not go beyond the boundary of the
12080 stack. You should specify this flag if you are running in an
12081 environment with multiple threads, but only rarely need to specify it in
12082 a single-threaded environment since stack overflow is automatically
12083 detected on nearly all systems if there is only one stack.
12085 Note that this switch does not actually cause checking to be done; the
12086 operating system must do that. The switch causes generation of code
12087 to ensure that the operating system sees the stack being extended.
12089 @item -fstack-limit-register=@var{reg}
12090 @itemx -fstack-limit-symbol=@var{sym}
12091 @itemx -fno-stack-limit
12092 @opindex fstack-limit-register
12093 @opindex fstack-limit-symbol
12094 @opindex fno-stack-limit
12095 Generate code to ensure that the stack does not grow beyond a certain value,
12096 either the value of a register or the address of a symbol. If the stack
12097 would grow beyond the value, a signal is raised. For most targets,
12098 the signal is raised before the stack overruns the boundary, so
12099 it is possible to catch the signal without taking special precautions.
12101 For instance, if the stack starts at absolute address @samp{0x80000000}
12102 and grows downwards, you can use the flags
12103 @option{-fstack-limit-symbol=__stack_limit} and
12104 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
12105 of 128KB@. Note that this may only work with the GNU linker.
12107 @cindex aliasing of parameters
12108 @cindex parameters, aliased
12109 @item -fargument-alias
12110 @itemx -fargument-noalias
12111 @itemx -fargument-noalias-global
12112 @opindex fargument-alias
12113 @opindex fargument-noalias
12114 @opindex fargument-noalias-global
12115 Specify the possible relationships among parameters and between
12116 parameters and global data.
12118 @option{-fargument-alias} specifies that arguments (parameters) may
12119 alias each other and may alias global storage.@*
12120 @option{-fargument-noalias} specifies that arguments do not alias
12121 each other, but may alias global storage.@*
12122 @option{-fargument-noalias-global} specifies that arguments do not
12123 alias each other and do not alias global storage.
12125 Each language will automatically use whatever option is required by
12126 the language standard. You should not need to use these options yourself.
12128 @item -fleading-underscore
12129 @opindex fleading-underscore
12130 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
12131 change the way C symbols are represented in the object file. One use
12132 is to help link with legacy assembly code.
12134 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
12135 generate code that is not binary compatible with code generated without that
12136 switch. Use it to conform to a non-default application binary interface.
12137 Not all targets provide complete support for this switch.
12139 @item -ftls-model=@var{model}
12140 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
12141 The @var{model} argument should be one of @code{global-dynamic},
12142 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
12144 The default without @option{-fpic} is @code{initial-exec}; with
12145 @option{-fpic} the default is @code{global-dynamic}.
12147 @item -fvisibility=@var{default|internal|hidden|protected}
12148 @opindex fvisibility
12149 Set the default ELF image symbol visibility to the specified option - all
12150 symbols will be marked with this unless overridden within the code.
12151 Using this feature can very substantially improve linking and
12152 load times of shared object libraries, produce more optimized
12153 code, provide near-perfect API export and prevent symbol clashes.
12154 It is @strong{strongly} recommended that you use this in any shared objects
12157 Despite the nomenclature, @code{default} always means public ie;
12158 available to be linked against from outside the shared object.
12159 @code{protected} and @code{internal} are pretty useless in real-world
12160 usage so the only other commonly used option will be @code{hidden}.
12161 The default if -fvisibility isn't specified is @code{default} ie; make every
12162 symbol public - this causes the same behavior as previous versions of
12165 A good explanation of the benefits offered by ensuring ELF
12166 symbols have the correct visibility is given by ``How To Write
12167 Shared Libraries'' by Ulrich Drepper (which can be found at
12168 @w{@uref{http://people.redhat.com/~drepper/}}) - however a superior
12169 solution made possible by this option to marking things hidden when
12170 the default is public is to make the default hidden and mark things
12171 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
12172 and @code{__attribute__ ((visibility("default")))} instead of
12173 @code{__declspec(dllexport)} you get almost identical semantics with
12174 identical syntax. This is a great boon to those working with
12175 cross-platform projects.
12177 For those adding visibility support to existing code, you may find
12178 @samp{#pragma GCC visibility} of use. This works by you enclosing
12179 the declarations you wish to set visibility for with (for example)
12180 @samp{#pragma GCC visibility push(hidden)} and
12181 @samp{#pragma GCC visibility pop}. These can be nested up to sixteen
12182 times. Bear in mind that symbol visibility should be viewed @strong{as
12183 part of the API interface contract} and thus all new code should
12184 always specify visibility when it is not the default ie; declarations
12185 only for use within the local DSO should @strong{always} be marked explicitly
12186 as hidden as so to avoid PLT indirection overheads - making this
12187 abundantly clear also aids readability and self-documentation of the code.
12188 Note that due to ISO C++ specification requirements, operator new and
12189 operator delete must always be of default visibility.
12191 An overview of these techniques, their benefits and how to use them
12192 is at @w{@uref{http://www.nedprod.com/programs/gccvisibility.html}}.
12198 @node Environment Variables
12199 @section Environment Variables Affecting GCC
12200 @cindex environment variables
12202 @c man begin ENVIRONMENT
12203 This section describes several environment variables that affect how GCC
12204 operates. Some of them work by specifying directories or prefixes to use
12205 when searching for various kinds of files. Some are used to specify other
12206 aspects of the compilation environment.
12208 Note that you can also specify places to search using options such as
12209 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
12210 take precedence over places specified using environment variables, which
12211 in turn take precedence over those specified by the configuration of GCC@.
12212 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
12213 GNU Compiler Collection (GCC) Internals}.
12218 @c @itemx LC_COLLATE
12220 @c @itemx LC_MONETARY
12221 @c @itemx LC_NUMERIC
12226 @c @findex LC_COLLATE
12227 @findex LC_MESSAGES
12228 @c @findex LC_MONETARY
12229 @c @findex LC_NUMERIC
12233 These environment variables control the way that GCC uses
12234 localization information that allow GCC to work with different
12235 national conventions. GCC inspects the locale categories
12236 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
12237 so. These locale categories can be set to any value supported by your
12238 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
12239 Kingdom encoded in UTF-8.
12241 The @env{LC_CTYPE} environment variable specifies character
12242 classification. GCC uses it to determine the character boundaries in
12243 a string; this is needed for some multibyte encodings that contain quote
12244 and escape characters that would otherwise be interpreted as a string
12247 The @env{LC_MESSAGES} environment variable specifies the language to
12248 use in diagnostic messages.
12250 If the @env{LC_ALL} environment variable is set, it overrides the value
12251 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
12252 and @env{LC_MESSAGES} default to the value of the @env{LANG}
12253 environment variable. If none of these variables are set, GCC
12254 defaults to traditional C English behavior.
12258 If @env{TMPDIR} is set, it specifies the directory to use for temporary
12259 files. GCC uses temporary files to hold the output of one stage of
12260 compilation which is to be used as input to the next stage: for example,
12261 the output of the preprocessor, which is the input to the compiler
12264 @item GCC_EXEC_PREFIX
12265 @findex GCC_EXEC_PREFIX
12266 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
12267 names of the subprograms executed by the compiler. No slash is added
12268 when this prefix is combined with the name of a subprogram, but you can
12269 specify a prefix that ends with a slash if you wish.
12271 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
12272 an appropriate prefix to use based on the pathname it was invoked with.
12274 If GCC cannot find the subprogram using the specified prefix, it
12275 tries looking in the usual places for the subprogram.
12277 The default value of @env{GCC_EXEC_PREFIX} is
12278 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
12279 of @code{prefix} when you ran the @file{configure} script.
12281 Other prefixes specified with @option{-B} take precedence over this prefix.
12283 This prefix is also used for finding files such as @file{crt0.o} that are
12286 In addition, the prefix is used in an unusual way in finding the
12287 directories to search for header files. For each of the standard
12288 directories whose name normally begins with @samp{/usr/local/lib/gcc}
12289 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
12290 replacing that beginning with the specified prefix to produce an
12291 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
12292 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
12293 These alternate directories are searched first; the standard directories
12296 @item COMPILER_PATH
12297 @findex COMPILER_PATH
12298 The value of @env{COMPILER_PATH} is a colon-separated list of
12299 directories, much like @env{PATH}. GCC tries the directories thus
12300 specified when searching for subprograms, if it can't find the
12301 subprograms using @env{GCC_EXEC_PREFIX}.
12304 @findex LIBRARY_PATH
12305 The value of @env{LIBRARY_PATH} is a colon-separated list of
12306 directories, much like @env{PATH}. When configured as a native compiler,
12307 GCC tries the directories thus specified when searching for special
12308 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
12309 using GCC also uses these directories when searching for ordinary
12310 libraries for the @option{-l} option (but directories specified with
12311 @option{-L} come first).
12315 @cindex locale definition
12316 This variable is used to pass locale information to the compiler. One way in
12317 which this information is used is to determine the character set to be used
12318 when character literals, string literals and comments are parsed in C and C++.
12319 When the compiler is configured to allow multibyte characters,
12320 the following values for @env{LANG} are recognized:
12324 Recognize JIS characters.
12326 Recognize SJIS characters.
12328 Recognize EUCJP characters.
12331 If @env{LANG} is not defined, or if it has some other value, then the
12332 compiler will use mblen and mbtowc as defined by the default locale to
12333 recognize and translate multibyte characters.
12337 Some additional environments variables affect the behavior of the
12340 @include cppenv.texi
12344 @node Precompiled Headers
12345 @section Using Precompiled Headers
12346 @cindex precompiled headers
12347 @cindex speed of compilation
12349 Often large projects have many header files that are included in every
12350 source file. The time the compiler takes to process these header files
12351 over and over again can account for nearly all of the time required to
12352 build the project. To make builds faster, GCC allows users to
12353 `precompile' a header file; then, if builds can use the precompiled
12354 header file they will be much faster.
12356 @strong{Caution:} There are a few known situations where GCC will
12357 crash when trying to use a precompiled header. If you have trouble
12358 with a precompiled header, you should remove the precompiled header
12359 and compile without it. In addition, please use GCC's on-line
12360 defect-tracking system to report any problems you encounter with
12361 precompiled headers. @xref{Bugs}.
12363 To create a precompiled header file, simply compile it as you would any
12364 other file, if necessary using the @option{-x} option to make the driver
12365 treat it as a C or C++ header file. You will probably want to use a
12366 tool like @command{make} to keep the precompiled header up-to-date when
12367 the headers it contains change.
12369 A precompiled header file will be searched for when @code{#include} is
12370 seen in the compilation. As it searches for the included file
12371 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
12372 compiler looks for a precompiled header in each directory just before it
12373 looks for the include file in that directory. The name searched for is
12374 the name specified in the @code{#include} with @samp{.gch} appended. If
12375 the precompiled header file can't be used, it is ignored.
12377 For instance, if you have @code{#include "all.h"}, and you have
12378 @file{all.h.gch} in the same directory as @file{all.h}, then the
12379 precompiled header file will be used if possible, and the original
12380 header will be used otherwise.
12382 Alternatively, you might decide to put the precompiled header file in a
12383 directory and use @option{-I} to ensure that directory is searched
12384 before (or instead of) the directory containing the original header.
12385 Then, if you want to check that the precompiled header file is always
12386 used, you can put a file of the same name as the original header in this
12387 directory containing an @code{#error} command.
12389 This also works with @option{-include}. So yet another way to use
12390 precompiled headers, good for projects not designed with precompiled
12391 header files in mind, is to simply take most of the header files used by
12392 a project, include them from another header file, precompile that header
12393 file, and @option{-include} the precompiled header. If the header files
12394 have guards against multiple inclusion, they will be skipped because
12395 they've already been included (in the precompiled header).
12397 If you need to precompile the same header file for different
12398 languages, targets, or compiler options, you can instead make a
12399 @emph{directory} named like @file{all.h.gch}, and put each precompiled
12400 header in the directory, perhaps using @option{-o}. It doesn't matter
12401 what you call the files in the directory, every precompiled header in
12402 the directory will be considered. The first precompiled header
12403 encountered in the directory that is valid for this compilation will
12404 be used; they're searched in no particular order.
12406 There are many other possibilities, limited only by your imagination,
12407 good sense, and the constraints of your build system.
12409 A precompiled header file can be used only when these conditions apply:
12413 Only one precompiled header can be used in a particular compilation.
12416 A precompiled header can't be used once the first C token is seen. You
12417 can have preprocessor directives before a precompiled header; you can
12418 even include a precompiled header from inside another header, so long as
12419 there are no C tokens before the @code{#include}.
12422 The precompiled header file must be produced for the same language as
12423 the current compilation. You can't use a C precompiled header for a C++
12427 The precompiled header file must be produced by the same compiler
12428 version and configuration as the current compilation is using.
12429 The easiest way to guarantee this is to use the same compiler binary
12430 for creating and using precompiled headers.
12433 Any macros defined before the precompiled header is included must
12434 either be defined in the same way as when the precompiled header was
12435 generated, or must not affect the precompiled header, which usually
12436 means that the they don't appear in the precompiled header at all.
12438 The @option{-D} option is one way to define a macro before a
12439 precompiled header is included; using a @code{#define} can also do it.
12440 There are also some options that define macros implicitly, like
12441 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
12444 @item If debugging information is output when using the precompiled
12445 header, using @option{-g} or similar, the same kind of debugging information
12446 must have been output when building the precompiled header. However,
12447 a precompiled header built using @option{-g} can be used in a compilation
12448 when no debugging information is being output.
12450 @item The same @option{-m} options must generally be used when building
12451 and using the precompiled header. @xref{Submodel Options},
12452 for any cases where this rule is relaxed.
12454 @item Each of the following options must be the same when building and using
12455 the precompiled header:
12457 @gccoptlist{-fexceptions -funit-at-a-time}
12460 Some other command-line options starting with @option{-f},
12461 @option{-p}, or @option{-O} must be defined in the same way as when
12462 the precompiled header was generated. At present, it's not clear
12463 which options are safe to change and which are not; the safest choice
12464 is to use exactly the same options when generating and using the
12465 precompiled header. The following are known to be safe:
12467 @gccoptlist{-fpreprocessed -pedantic-errors}
12471 For all of these except the last, the compiler will automatically
12472 ignore the precompiled header if the conditions aren't met. If you
12473 find an option combination that doesn't work and doesn't cause the
12474 precompiled header to be ignored, please consider filing a bug report,
12477 If you do use differing options when generating and using the
12478 precompiled header, the actual behavior will be a mixture of the
12479 behavior for the options. For instance, if you use @option{-g} to
12480 generate the precompiled header but not when using it, you may or may
12481 not get debugging information for routines in the precompiled header.
12483 @node Running Protoize
12484 @section Running Protoize
12486 The program @code{protoize} is an optional part of GCC@. You can use
12487 it to add prototypes to a program, thus converting the program to ISO
12488 C in one respect. The companion program @code{unprotoize} does the
12489 reverse: it removes argument types from any prototypes that are found.
12491 When you run these programs, you must specify a set of source files as
12492 command line arguments. The conversion programs start out by compiling
12493 these files to see what functions they define. The information gathered
12494 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
12496 After scanning comes actual conversion. The specified files are all
12497 eligible to be converted; any files they include (whether sources or
12498 just headers) are eligible as well.
12500 But not all the eligible files are converted. By default,
12501 @code{protoize} and @code{unprotoize} convert only source and header
12502 files in the current directory. You can specify additional directories
12503 whose files should be converted with the @option{-d @var{directory}}
12504 option. You can also specify particular files to exclude with the
12505 @option{-x @var{file}} option. A file is converted if it is eligible, its
12506 directory name matches one of the specified directory names, and its
12507 name within the directory has not been excluded.
12509 Basic conversion with @code{protoize} consists of rewriting most
12510 function definitions and function declarations to specify the types of
12511 the arguments. The only ones not rewritten are those for varargs
12514 @code{protoize} optionally inserts prototype declarations at the
12515 beginning of the source file, to make them available for any calls that
12516 precede the function's definition. Or it can insert prototype
12517 declarations with block scope in the blocks where undeclared functions
12520 Basic conversion with @code{unprotoize} consists of rewriting most
12521 function declarations to remove any argument types, and rewriting
12522 function definitions to the old-style pre-ISO form.
12524 Both conversion programs print a warning for any function declaration or
12525 definition that they can't convert. You can suppress these warnings
12528 The output from @code{protoize} or @code{unprotoize} replaces the
12529 original source file. The original file is renamed to a name ending
12530 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
12531 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
12532 for DOS) file already exists, then the source file is simply discarded.
12534 @code{protoize} and @code{unprotoize} both depend on GCC itself to
12535 scan the program and collect information about the functions it uses.
12536 So neither of these programs will work until GCC is installed.
12538 Here is a table of the options you can use with @code{protoize} and
12539 @code{unprotoize}. Each option works with both programs unless
12543 @item -B @var{directory}
12544 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
12545 usual directory (normally @file{/usr/local/lib}). This file contains
12546 prototype information about standard system functions. This option
12547 applies only to @code{protoize}.
12549 @item -c @var{compilation-options}
12550 Use @var{compilation-options} as the options when running @command{gcc} to
12551 produce the @samp{.X} files. The special option @option{-aux-info} is
12552 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
12554 Note that the compilation options must be given as a single argument to
12555 @code{protoize} or @code{unprotoize}. If you want to specify several
12556 @command{gcc} options, you must quote the entire set of compilation options
12557 to make them a single word in the shell.
12559 There are certain @command{gcc} arguments that you cannot use, because they
12560 would produce the wrong kind of output. These include @option{-g},
12561 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
12562 the @var{compilation-options}, they are ignored.
12565 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
12566 systems) instead of @samp{.c}. This is convenient if you are converting
12567 a C program to C++. This option applies only to @code{protoize}.
12570 Add explicit global declarations. This means inserting explicit
12571 declarations at the beginning of each source file for each function
12572 that is called in the file and was not declared. These declarations
12573 precede the first function definition that contains a call to an
12574 undeclared function. This option applies only to @code{protoize}.
12576 @item -i @var{string}
12577 Indent old-style parameter declarations with the string @var{string}.
12578 This option applies only to @code{protoize}.
12580 @code{unprotoize} converts prototyped function definitions to old-style
12581 function definitions, where the arguments are declared between the
12582 argument list and the initial @samp{@{}. By default, @code{unprotoize}
12583 uses five spaces as the indentation. If you want to indent with just
12584 one space instead, use @option{-i " "}.
12587 Keep the @samp{.X} files. Normally, they are deleted after conversion
12591 Add explicit local declarations. @code{protoize} with @option{-l} inserts
12592 a prototype declaration for each function in each block which calls the
12593 function without any declaration. This option applies only to
12597 Make no real changes. This mode just prints information about the conversions
12598 that would have been done without @option{-n}.
12601 Make no @samp{.save} files. The original files are simply deleted.
12602 Use this option with caution.
12604 @item -p @var{program}
12605 Use the program @var{program} as the compiler. Normally, the name
12606 @file{gcc} is used.
12609 Work quietly. Most warnings are suppressed.
12612 Print the version number, just like @option{-v} for @command{gcc}.
12615 If you need special compiler options to compile one of your program's
12616 source files, then you should generate that file's @samp{.X} file
12617 specially, by running @command{gcc} on that source file with the
12618 appropriate options and the option @option{-aux-info}. Then run
12619 @code{protoize} on the entire set of files. @code{protoize} will use
12620 the existing @samp{.X} file because it is newer than the source file.
12624 gcc -Dfoo=bar file1.c -aux-info file1.X
12629 You need to include the special files along with the rest in the
12630 @code{protoize} command, even though their @samp{.X} files already
12631 exist, because otherwise they won't get converted.
12633 @xref{Protoize Caveats}, for more information on how to use
12634 @code{protoize} successfully.