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 @option{-save-temps}, the compiler will generate multiple
972 (one for each source file), but only one (combined) @file{.o} or
977 Print (on the standard output) a description of the command line options
978 understood by @command{gcc}. If the @option{-v} option is also specified
979 then @option{--help} will also be passed on to the various processes
980 invoked by @command{gcc}, so that they can display the command line options
981 they accept. If the @option{-Wextra} option is also specified then command
982 line options which have no documentation associated with them will also
987 Print (on the standard output) a description of target specific command
988 line options for each tool.
992 Display the version number and copyrights of the invoked GCC.
996 @section Compiling C++ Programs
998 @cindex suffixes for C++ source
999 @cindex C++ source file suffixes
1000 C++ source files conventionally use one of the suffixes @samp{.C},
1001 @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
1002 @samp{.cxx}; C++ header files often use @samp{.hh} or @samp{.H}; and
1003 preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
1004 files with these names and compiles them as C++ programs even if you
1005 call the compiler the same way as for compiling C programs (usually
1006 with the name @command{gcc}).
1010 However, C++ programs often require class libraries as well as a
1011 compiler that understands the C++ language---and under some
1012 circumstances, you might want to compile programs or header files from
1013 standard input, or otherwise without a suffix that flags them as C++
1014 programs. You might also like to precompile a C header file with a
1015 @samp{.h} extension to be used in C++ compilations. @command{g++} is a
1016 program that calls GCC with the default language set to C++, and
1017 automatically specifies linking against the C++ library. On many
1018 systems, @command{g++} is also installed with the name @command{c++}.
1020 @cindex invoking @command{g++}
1021 When you compile C++ programs, you may specify many of the same
1022 command-line options that you use for compiling programs in any
1023 language; or command-line options meaningful for C and related
1024 languages; or options that are meaningful only for C++ programs.
1025 @xref{C Dialect Options,,Options Controlling C Dialect}, for
1026 explanations of options for languages related to C@.
1027 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
1028 explanations of options that are meaningful only for C++ programs.
1030 @node C Dialect Options
1031 @section Options Controlling C Dialect
1032 @cindex dialect options
1033 @cindex language dialect options
1034 @cindex options, dialect
1036 The following options control the dialect of C (or languages derived
1037 from C, such as C++, Objective-C and Objective-C++) that the compiler
1041 @cindex ANSI support
1045 In C mode, support all ISO C90 programs. In C++ mode,
1046 remove GNU extensions that conflict with ISO C++.
1048 This turns off certain features of GCC that are incompatible with ISO
1049 C90 (when compiling C code), or of standard C++ (when compiling C++ code),
1050 such as the @code{asm} and @code{typeof} keywords, and
1051 predefined macros such as @code{unix} and @code{vax} that identify the
1052 type of system you are using. It also enables the undesirable and
1053 rarely used ISO trigraph feature. For the C compiler,
1054 it disables recognition of C++ style @samp{//} comments as well as
1055 the @code{inline} keyword.
1057 The alternate keywords @code{__asm__}, @code{__extension__},
1058 @code{__inline__} and @code{__typeof__} continue to work despite
1059 @option{-ansi}. You would not want to use them in an ISO C program, of
1060 course, but it is useful to put them in header files that might be included
1061 in compilations done with @option{-ansi}. Alternate predefined macros
1062 such as @code{__unix__} and @code{__vax__} are also available, with or
1063 without @option{-ansi}.
1065 The @option{-ansi} option does not cause non-ISO programs to be
1066 rejected gratuitously. For that, @option{-pedantic} is required in
1067 addition to @option{-ansi}. @xref{Warning Options}.
1069 The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
1070 option is used. Some header files may notice this macro and refrain
1071 from declaring certain functions or defining certain macros that the
1072 ISO standard doesn't call for; this is to avoid interfering with any
1073 programs that might use these names for other things.
1075 Functions which would normally be built in but do not have semantics
1076 defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
1077 functions with @option{-ansi} is used. @xref{Other Builtins,,Other
1078 built-in functions provided by GCC}, for details of the functions
1083 Determine the language standard. This option is currently only
1084 supported when compiling C or C++. A value for this option must be
1085 provided; possible values are
1090 ISO C90 (same as @option{-ansi}).
1092 @item iso9899:199409
1093 ISO C90 as modified in amendment 1.
1099 ISO C99. Note that this standard is not yet fully supported; see
1100 @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
1101 names @samp{c9x} and @samp{iso9899:199x} are deprecated.
1104 Default, ISO C90 plus GNU extensions (including some C99 features).
1108 ISO C99 plus GNU extensions. When ISO C99 is fully implemented in GCC,
1109 this will become the default. The name @samp{gnu9x} is deprecated.
1112 The 1998 ISO C++ standard plus amendments.
1115 The same as @option{-std=c++98} plus GNU extensions. This is the
1116 default for C++ code.
1119 Even when this option is not specified, you can still use some of the
1120 features of newer standards in so far as they do not conflict with
1121 previous C standards. For example, you may use @code{__restrict__} even
1122 when @option{-std=c99} is not specified.
1124 The @option{-std} options specifying some version of ISO C have the same
1125 effects as @option{-ansi}, except that features that were not in ISO C90
1126 but are in the specified version (for example, @samp{//} comments and
1127 the @code{inline} keyword in ISO C99) are not disabled.
1129 @xref{Standards,,Language Standards Supported by GCC}, for details of
1130 these standard versions.
1132 @item -aux-info @var{filename}
1134 Output to the given filename prototyped declarations for all functions
1135 declared and/or defined in a translation unit, including those in header
1136 files. This option is silently ignored in any language other than C@.
1138 Besides declarations, the file indicates, in comments, the origin of
1139 each declaration (source file and line), whether the declaration was
1140 implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
1141 @samp{O} for old, respectively, in the first character after the line
1142 number and the colon), and whether it came from a declaration or a
1143 definition (@samp{C} or @samp{F}, respectively, in the following
1144 character). In the case of function definitions, a K&R-style list of
1145 arguments followed by their declarations is also provided, inside
1146 comments, after the declaration.
1150 Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
1151 keyword, so that code can use these words as identifiers. You can use
1152 the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
1153 instead. @option{-ansi} implies @option{-fno-asm}.
1155 In C++, this switch only affects the @code{typeof} keyword, since
1156 @code{asm} and @code{inline} are standard keywords. You may want to
1157 use the @option{-fno-gnu-keywords} flag instead, which has the same
1158 effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
1159 switch only affects the @code{asm} and @code{typeof} keywords, since
1160 @code{inline} is a standard keyword in ISO C99.
1163 @itemx -fno-builtin-@var{function}
1164 @opindex fno-builtin
1165 @cindex built-in functions
1166 Don't recognize built-in functions that do not begin with
1167 @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
1168 functions provided by GCC}, for details of the functions affected,
1169 including those which are not built-in functions when @option{-ansi} or
1170 @option{-std} options for strict ISO C conformance are used because they
1171 do not have an ISO standard meaning.
1173 GCC normally generates special code to handle certain built-in functions
1174 more efficiently; for instance, calls to @code{alloca} may become single
1175 instructions that adjust the stack directly, and calls to @code{memcpy}
1176 may become inline copy loops. The resulting code is often both smaller
1177 and faster, but since the function calls no longer appear as such, you
1178 cannot set a breakpoint on those calls, nor can you change the behavior
1179 of the functions by linking with a different library. In addition,
1180 when a function is recognized as a built-in function, GCC may use
1181 information about that function to warn about problems with calls to
1182 that function, or to generate more efficient code, even if the
1183 resulting code still contains calls to that function. For example,
1184 warnings are given with @option{-Wformat} for bad calls to
1185 @code{printf}, when @code{printf} is built in, and @code{strlen} is
1186 known not to modify global memory.
1188 With the @option{-fno-builtin-@var{function}} option
1189 only the built-in function @var{function} is
1190 disabled. @var{function} must not begin with @samp{__builtin_}. If a
1191 function is named this is not built-in in this version of GCC, this
1192 option is ignored. There is no corresponding
1193 @option{-fbuiltin-@var{function}} option; if you wish to enable
1194 built-in functions selectively when using @option{-fno-builtin} or
1195 @option{-ffreestanding}, you may define macros such as:
1198 #define abs(n) __builtin_abs ((n))
1199 #define strcpy(d, s) __builtin_strcpy ((d), (s))
1204 @cindex hosted environment
1206 Assert that compilation takes place in a hosted environment. This implies
1207 @option{-fbuiltin}. A hosted environment is one in which the
1208 entire standard library is available, and in which @code{main} has a return
1209 type of @code{int}. Examples are nearly everything except a kernel.
1210 This is equivalent to @option{-fno-freestanding}.
1212 @item -ffreestanding
1213 @opindex ffreestanding
1214 @cindex hosted environment
1216 Assert that compilation takes place in a freestanding environment. This
1217 implies @option{-fno-builtin}. A freestanding environment
1218 is one in which the standard library may not exist, and program startup may
1219 not necessarily be at @code{main}. The most obvious example is an OS kernel.
1220 This is equivalent to @option{-fno-hosted}.
1222 @xref{Standards,,Language Standards Supported by GCC}, for details of
1223 freestanding and hosted environments.
1225 @item -fms-extensions
1226 @opindex fms-extensions
1227 Accept some non-standard constructs used in Microsoft header files.
1229 Some cases of unnamed fields in structures and unions are only
1230 accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
1231 fields within structs/unions}, for details.
1235 Support ISO C trigraphs. The @option{-ansi} option (and @option{-std}
1236 options for strict ISO C conformance) implies @option{-trigraphs}.
1238 @item -no-integrated-cpp
1239 @opindex no-integrated-cpp
1240 Performs a compilation in two passes: preprocessing and compiling. This
1241 option allows a user supplied "cc1", "cc1plus", or "cc1obj" via the
1242 @option{-B} option. The user supplied compilation step can then add in
1243 an additional preprocessing step after normal preprocessing but before
1244 compiling. The default is to use the integrated cpp (internal cpp)
1246 The semantics of this option will change if "cc1", "cc1plus", and
1247 "cc1obj" are merged.
1249 @cindex traditional C language
1250 @cindex C language, traditional
1252 @itemx -traditional-cpp
1253 @opindex traditional-cpp
1254 @opindex traditional
1255 Formerly, these options caused GCC to attempt to emulate a pre-standard
1256 C compiler. They are now only supported with the @option{-E} switch.
1257 The preprocessor continues to support a pre-standard mode. See the GNU
1258 CPP manual for details.
1260 @item -fcond-mismatch
1261 @opindex fcond-mismatch
1262 Allow conditional expressions with mismatched types in the second and
1263 third arguments. The value of such an expression is void. This option
1264 is not supported for C++.
1266 @item -funsigned-char
1267 @opindex funsigned-char
1268 Let the type @code{char} be unsigned, like @code{unsigned char}.
1270 Each kind of machine has a default for what @code{char} should
1271 be. It is either like @code{unsigned char} by default or like
1272 @code{signed char} by default.
1274 Ideally, a portable program should always use @code{signed char} or
1275 @code{unsigned char} when it depends on the signedness of an object.
1276 But many programs have been written to use plain @code{char} and
1277 expect it to be signed, or expect it to be unsigned, depending on the
1278 machines they were written for. This option, and its inverse, let you
1279 make such a program work with the opposite default.
1281 The type @code{char} is always a distinct type from each of
1282 @code{signed char} or @code{unsigned char}, even though its behavior
1283 is always just like one of those two.
1286 @opindex fsigned-char
1287 Let the type @code{char} be signed, like @code{signed char}.
1289 Note that this is equivalent to @option{-fno-unsigned-char}, which is
1290 the negative form of @option{-funsigned-char}. Likewise, the option
1291 @option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
1293 @item -fsigned-bitfields
1294 @itemx -funsigned-bitfields
1295 @itemx -fno-signed-bitfields
1296 @itemx -fno-unsigned-bitfields
1297 @opindex fsigned-bitfields
1298 @opindex funsigned-bitfields
1299 @opindex fno-signed-bitfields
1300 @opindex fno-unsigned-bitfields
1301 These options control whether a bit-field is signed or unsigned, when the
1302 declaration does not use either @code{signed} or @code{unsigned}. By
1303 default, such a bit-field is signed, because this is consistent: the
1304 basic integer types such as @code{int} are signed types.
1307 @node C++ Dialect Options
1308 @section Options Controlling C++ Dialect
1310 @cindex compiler options, C++
1311 @cindex C++ options, command line
1312 @cindex options, C++
1313 This section describes the command-line options that are only meaningful
1314 for C++ programs; but you can also use most of the GNU compiler options
1315 regardless of what language your program is in. For example, you
1316 might compile a file @code{firstClass.C} like this:
1319 g++ -g -frepo -O -c firstClass.C
1323 In this example, only @option{-frepo} is an option meant
1324 only for C++ programs; you can use the other options with any
1325 language supported by GCC@.
1327 Here is a list of options that are @emph{only} for compiling C++ programs:
1331 @item -fabi-version=@var{n}
1332 @opindex fabi-version
1333 Use version @var{n} of the C++ ABI. Version 2 is the version of the
1334 C++ ABI that first appeared in G++ 3.4. Version 1 is the version of
1335 the C++ ABI that first appeared in G++ 3.2. Version 0 will always be
1336 the version that conforms most closely to the C++ ABI specification.
1337 Therefore, the ABI obtained using version 0 will change as ABI bugs
1340 The default is version 2.
1342 @item -fno-access-control
1343 @opindex fno-access-control
1344 Turn off all access checking. This switch is mainly useful for working
1345 around bugs in the access control code.
1349 Check that the pointer returned by @code{operator new} is non-null
1350 before attempting to modify the storage allocated. This check is
1351 normally unnecessary because the C++ standard specifies that
1352 @code{operator new} will only return @code{0} if it is declared
1353 @samp{throw()}, in which case the compiler will always check the
1354 return value even without this option. In all other cases, when
1355 @code{operator new} has a non-empty exception specification, memory
1356 exhaustion is signalled by throwing @code{std::bad_alloc}. See also
1357 @samp{new (nothrow)}.
1359 @item -fconserve-space
1360 @opindex fconserve-space
1361 Put uninitialized or runtime-initialized global variables into the
1362 common segment, as C does. This saves space in the executable at the
1363 cost of not diagnosing duplicate definitions. If you compile with this
1364 flag and your program mysteriously crashes after @code{main()} has
1365 completed, you may have an object that is being destroyed twice because
1366 two definitions were merged.
1368 This option is no longer useful on most targets, now that support has
1369 been added for putting variables into BSS without making them common.
1371 @item -fno-const-strings
1372 @opindex fno-const-strings
1373 Give string constants type @code{char *} instead of type @code{const
1374 char *}. By default, G++ uses type @code{const char *} as required by
1375 the standard. Even if you use @option{-fno-const-strings}, you cannot
1376 actually modify the value of a string constant.
1378 This option might be removed in a future release of G++. For maximum
1379 portability, you should structure your code so that it works with
1380 string constants that have type @code{const char *}.
1382 @item -fno-elide-constructors
1383 @opindex fno-elide-constructors
1384 The C++ standard allows an implementation to omit creating a temporary
1385 which is only used to initialize another object of the same type.
1386 Specifying this option disables that optimization, and forces G++ to
1387 call the copy constructor in all cases.
1389 @item -fno-enforce-eh-specs
1390 @opindex fno-enforce-eh-specs
1391 Don't check for violation of exception specifications at runtime. This
1392 option violates the C++ standard, but may be useful for reducing code
1393 size in production builds, much like defining @samp{NDEBUG}. The compiler
1394 will still optimize based on the exception specifications.
1397 @itemx -fno-for-scope
1399 @opindex fno-for-scope
1400 If @option{-ffor-scope} is specified, the scope of variables declared in
1401 a @i{for-init-statement} is limited to the @samp{for} loop itself,
1402 as specified by the C++ standard.
1403 If @option{-fno-for-scope} is specified, the scope of variables declared in
1404 a @i{for-init-statement} extends to the end of the enclosing scope,
1405 as was the case in old versions of G++, and other (traditional)
1406 implementations of C++.
1408 The default if neither flag is given to follow the standard,
1409 but to allow and give a warning for old-style code that would
1410 otherwise be invalid, or have different behavior.
1412 @item -fno-gnu-keywords
1413 @opindex fno-gnu-keywords
1414 Do not recognize @code{typeof} as a keyword, so that code can use this
1415 word as an identifier. You can use the keyword @code{__typeof__} instead.
1416 @option{-ansi} implies @option{-fno-gnu-keywords}.
1418 @item -fno-implicit-templates
1419 @opindex fno-implicit-templates
1420 Never emit code for non-inline templates which are instantiated
1421 implicitly (i.e.@: by use); only emit code for explicit instantiations.
1422 @xref{Template Instantiation}, for more information.
1424 @item -fno-implicit-inline-templates
1425 @opindex fno-implicit-inline-templates
1426 Don't emit code for implicit instantiations of inline templates, either.
1427 The default is to handle inlines differently so that compiles with and
1428 without optimization will need the same set of explicit instantiations.
1430 @item -fno-implement-inlines
1431 @opindex fno-implement-inlines
1432 To save space, do not emit out-of-line copies of inline functions
1433 controlled by @samp{#pragma implementation}. This will cause linker
1434 errors if these functions are not inlined everywhere they are called.
1436 @item -fms-extensions
1437 @opindex fms-extensions
1438 Disable pedantic warnings about constructs used in MFC, such as implicit
1439 int and getting a pointer to member function via non-standard syntax.
1441 @item -fno-nonansi-builtins
1442 @opindex fno-nonansi-builtins
1443 Disable built-in declarations of functions that are not mandated by
1444 ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
1445 @code{index}, @code{bzero}, @code{conjf}, and other related functions.
1447 @item -fno-operator-names
1448 @opindex fno-operator-names
1449 Do not treat the operator name keywords @code{and}, @code{bitand},
1450 @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
1451 synonyms as keywords.
1453 @item -fno-optional-diags
1454 @opindex fno-optional-diags
1455 Disable diagnostics that the standard says a compiler does not need to
1456 issue. Currently, the only such diagnostic issued by G++ is the one for
1457 a name having multiple meanings within a class.
1460 @opindex fpermissive
1461 Downgrade some diagnostics about nonconformant code from errors to
1462 warnings. Thus, using @option{-fpermissive} will allow some
1463 nonconforming code to compile.
1467 Enable automatic template instantiation at link time. This option also
1468 implies @option{-fno-implicit-templates}. @xref{Template
1469 Instantiation}, for more information.
1473 Disable generation of information about every class with virtual
1474 functions for use by the C++ runtime type identification features
1475 (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts
1476 of the language, you can save some space by using this flag. Note that
1477 exception handling uses the same information, but it will generate it as
1482 Emit statistics about front-end processing at the end of the compilation.
1483 This information is generally only useful to the G++ development team.
1485 @item -ftemplate-depth-@var{n}
1486 @opindex ftemplate-depth
1487 Set the maximum instantiation depth for template classes to @var{n}.
1488 A limit on the template instantiation depth is needed to detect
1489 endless recursions during template class instantiation. ANSI/ISO C++
1490 conforming programs must not rely on a maximum depth greater than 17.
1492 @item -fno-threadsafe-statics
1493 @opindex fno-threadsafe-statics
1494 Do not emit the extra code to use the routines specified in the C++
1495 ABI for thread-safe initialization of local statics. You can use this
1496 option to reduce code size slightly in code that doesn't need to be
1499 @item -fuse-cxa-atexit
1500 @opindex fuse-cxa-atexit
1501 Register destructors for objects with static storage duration with the
1502 @code{__cxa_atexit} function rather than the @code{atexit} function.
1503 This option is required for fully standards-compliant handling of static
1504 destructors, but will only work if your C library supports
1505 @code{__cxa_atexit}.
1507 @item -fvisibility-inlines-hidden
1508 @opindex fvisibility-inlines-hidden
1509 Causes all inlined methods to be marked with
1510 @code{__attribute__ ((visibility ("hidden")))} so that they do not
1511 appear in the export table of a DSO and do not require a PLT indirection
1512 when used within the DSO. Enabling this option can have a dramatic effect
1513 on load and link times of a DSO as it massively reduces the size of the
1514 dynamic export table when the library makes heavy use of templates. While
1515 it can cause bloating through duplication of code within each DSO where
1516 it is used, often the wastage is less than the considerable space occupied
1517 by a long symbol name in the export table which is typical when using
1518 templates and namespaces. For even more savings, combine with the
1519 @option{-fvisibility=hidden} switch.
1523 Do not use weak symbol support, even if it is provided by the linker.
1524 By default, G++ will use weak symbols if they are available. This
1525 option exists only for testing, and should not be used by end-users;
1526 it will result in inferior code and has no benefits. This option may
1527 be removed in a future release of G++.
1531 Do not search for header files in the standard directories specific to
1532 C++, but do still search the other standard directories. (This option
1533 is used when building the C++ library.)
1536 In addition, these optimization, warning, and code generation options
1537 have meanings only for C++ programs:
1540 @item -fno-default-inline
1541 @opindex fno-default-inline
1542 Do not assume @samp{inline} for functions defined inside a class scope.
1543 @xref{Optimize Options,,Options That Control Optimization}. Note that these
1544 functions will have linkage like inline functions; they just won't be
1547 @item -Wabi @r{(C++ only)}
1549 Warn when G++ generates code that is probably not compatible with the
1550 vendor-neutral C++ ABI. Although an effort has been made to warn about
1551 all such cases, there are probably some cases that are not warned about,
1552 even though G++ is generating incompatible code. There may also be
1553 cases where warnings are emitted even though the code that is generated
1556 You should rewrite your code to avoid these warnings if you are
1557 concerned about the fact that code generated by G++ may not be binary
1558 compatible with code generated by other compilers.
1560 The known incompatibilities at this point include:
1565 Incorrect handling of tail-padding for bit-fields. G++ may attempt to
1566 pack data into the same byte as a base class. For example:
1569 struct A @{ virtual void f(); int f1 : 1; @};
1570 struct B : public A @{ int f2 : 1; @};
1574 In this case, G++ will place @code{B::f2} into the same byte
1575 as@code{A::f1}; other compilers will not. You can avoid this problem
1576 by explicitly padding @code{A} so that its size is a multiple of the
1577 byte size on your platform; that will cause G++ and other compilers to
1578 layout @code{B} identically.
1581 Incorrect handling of tail-padding for virtual bases. G++ does not use
1582 tail padding when laying out virtual bases. For example:
1585 struct A @{ virtual void f(); char c1; @};
1586 struct B @{ B(); char c2; @};
1587 struct C : public A, public virtual B @{@};
1591 In this case, G++ will not place @code{B} into the tail-padding for
1592 @code{A}; other compilers will. You can avoid this problem by
1593 explicitly padding @code{A} so that its size is a multiple of its
1594 alignment (ignoring virtual base classes); that will cause G++ and other
1595 compilers to layout @code{C} identically.
1598 Incorrect handling of bit-fields with declared widths greater than that
1599 of their underlying types, when the bit-fields appear in a union. For
1603 union U @{ int i : 4096; @};
1607 Assuming that an @code{int} does not have 4096 bits, G++ will make the
1608 union too small by the number of bits in an @code{int}.
1611 Empty classes can be placed at incorrect offsets. For example:
1621 struct C : public B, public A @{@};
1625 G++ will place the @code{A} base class of @code{C} at a nonzero offset;
1626 it should be placed at offset zero. G++ mistakenly believes that the
1627 @code{A} data member of @code{B} is already at offset zero.
1630 Names of template functions whose types involve @code{typename} or
1631 template template parameters can be mangled incorrectly.
1634 template <typename Q>
1635 void f(typename Q::X) @{@}
1637 template <template <typename> class Q>
1638 void f(typename Q<int>::X) @{@}
1642 Instantiations of these templates may be mangled incorrectly.
1646 @item -Wctor-dtor-privacy @r{(C++ only)}
1647 @opindex Wctor-dtor-privacy
1648 Warn when a class seems unusable because all the constructors or
1649 destructors in that class are private, and it has neither friends nor
1650 public static member functions.
1652 @item -Wnon-virtual-dtor @r{(C++ only)}
1653 @opindex Wnon-virtual-dtor
1654 Warn when a class appears to be polymorphic, thereby requiring a virtual
1655 destructor, yet it declares a non-virtual one.
1656 This warning is enabled by @option{-Wall}.
1658 @item -Wreorder @r{(C++ only)}
1660 @cindex reordering, warning
1661 @cindex warning for reordering of member initializers
1662 Warn when the order of member initializers given in the code does not
1663 match the order in which they must be executed. For instance:
1669 A(): j (0), i (1) @{ @}
1673 The compiler will rearrange the member initializers for @samp{i}
1674 and @samp{j} to match the declaration order of the members, emitting
1675 a warning to that effect. This warning is enabled by @option{-Wall}.
1678 The following @option{-W@dots{}} options are not affected by @option{-Wall}.
1681 @item -Weffc++ @r{(C++ only)}
1683 Warn about violations of the following style guidelines from Scott Meyers'
1684 @cite{Effective C++} book:
1688 Item 11: Define a copy constructor and an assignment operator for classes
1689 with dynamically allocated memory.
1692 Item 12: Prefer initialization to assignment in constructors.
1695 Item 14: Make destructors virtual in base classes.
1698 Item 15: Have @code{operator=} return a reference to @code{*this}.
1701 Item 23: Don't try to return a reference when you must return an object.
1705 Also warn about violations of the following style guidelines from
1706 Scott Meyers' @cite{More Effective C++} book:
1710 Item 6: Distinguish between prefix and postfix forms of increment and
1711 decrement operators.
1714 Item 7: Never overload @code{&&}, @code{||}, or @code{,}.
1718 When selecting this option, be aware that the standard library
1719 headers do not obey all of these guidelines; use @samp{grep -v}
1720 to filter out those warnings.
1722 @item -Wno-deprecated @r{(C++ only)}
1723 @opindex Wno-deprecated
1724 Do not warn about usage of deprecated features. @xref{Deprecated Features}.
1726 @item -Wno-non-template-friend @r{(C++ only)}
1727 @opindex Wno-non-template-friend
1728 Disable warnings when non-templatized friend functions are declared
1729 within a template. Since the advent of explicit template specification
1730 support in G++, if the name of the friend is an unqualified-id (i.e.,
1731 @samp{friend foo(int)}), the C++ language specification demands that the
1732 friend declare or define an ordinary, nontemplate function. (Section
1733 14.5.3). Before G++ implemented explicit specification, unqualified-ids
1734 could be interpreted as a particular specialization of a templatized
1735 function. Because this non-conforming behavior is no longer the default
1736 behavior for G++, @option{-Wnon-template-friend} allows the compiler to
1737 check existing code for potential trouble spots and is on by default.
1738 This new compiler behavior can be turned off with
1739 @option{-Wno-non-template-friend} which keeps the conformant compiler code
1740 but disables the helpful warning.
1742 @item -Wold-style-cast @r{(C++ only)}
1743 @opindex Wold-style-cast
1744 Warn if an old-style (C-style) cast to a non-void type is used within
1745 a C++ program. The new-style casts (@samp{static_cast},
1746 @samp{reinterpret_cast}, and @samp{const_cast}) are less vulnerable to
1747 unintended effects and much easier to search for.
1749 @item -Woverloaded-virtual @r{(C++ only)}
1750 @opindex Woverloaded-virtual
1751 @cindex overloaded virtual fn, warning
1752 @cindex warning for overloaded virtual fn
1753 Warn when a function declaration hides virtual functions from a
1754 base class. For example, in:
1761 struct B: public A @{
1766 the @code{A} class version of @code{f} is hidden in @code{B}, and code
1774 will fail to compile.
1776 @item -Wno-pmf-conversions @r{(C++ only)}
1777 @opindex Wno-pmf-conversions
1778 Disable the diagnostic for converting a bound pointer to member function
1781 @item -Wsign-promo @r{(C++ only)}
1782 @opindex Wsign-promo
1783 Warn when overload resolution chooses a promotion from unsigned or
1784 enumerated type to a signed type, over a conversion to an unsigned type of
1785 the same size. Previous versions of G++ would try to preserve
1786 unsignedness, but the standard mandates the current behavior.
1788 @item -Wsynth @r{(C++ only)}
1790 @cindex warning for synthesized methods
1791 @cindex synthesized methods, warning
1792 Warn when G++'s synthesis behavior does not match that of cfront. For
1798 A& operator = (int);
1808 In this example, G++ will synthesize a default @samp{A& operator =
1809 (const A&);}, while cfront will use the user-defined @samp{operator =}.
1812 @node Objective-C and Objective-C++ Dialect Options
1813 @section Options Controlling Objective-C and Objective-C++ Dialects
1815 @cindex compiler options, Objective-C and Objective-C++
1816 @cindex Objective-C and Objective-C++ options, command line
1817 @cindex options, Objective-C and Objective-C++
1818 (NOTE: This manual does not describe the Objective-C and Objective-C++
1819 languages themselves. See @xref{Standards,,Language Standards
1820 Supported by GCC}, for references.)
1822 This section describes the command-line options that are only meaningful
1823 for Objective-C and Objective-C++ programs, but you can also use most of
1824 the language-independent GNU compiler options.
1825 For example, you might compile a file @code{some_class.m} like this:
1828 gcc -g -fgnu-runtime -O -c some_class.m
1832 In this example, @option{-fgnu-runtime} is an option meant only for
1833 Objective-C and Objective-C++ programs; you can use the other options with
1834 any language supported by GCC@.
1836 Note that since Objective-C is an extension of the C language, Objective-C
1837 compilations may also use options specific to the C front-end (e.g.,
1838 @option{-Wtraditional}). Similarly, Objective-C++ compilations may use
1839 C++-specific options (e.g., @option{-Wabi}).
1841 Here is a list of options that are @emph{only} for compiling Objective-C
1842 and Objective-C++ programs:
1845 @item -fconstant-string-class=@var{class-name}
1846 @opindex fconstant-string-class
1847 Use @var{class-name} as the name of the class to instantiate for each
1848 literal string specified with the syntax @code{@@"@dots{}"}. The default
1849 class name is @code{NXConstantString} if the GNU runtime is being used, and
1850 @code{NSConstantString} if the NeXT runtime is being used (see below). The
1851 @option{-fconstant-cfstrings} option, if also present, will override the
1852 @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
1853 to be laid out as constant CoreFoundation strings.
1856 @opindex fgnu-runtime
1857 Generate object code compatible with the standard GNU Objective-C
1858 runtime. This is the default for most types of systems.
1860 @item -fnext-runtime
1861 @opindex fnext-runtime
1862 Generate output compatible with the NeXT runtime. This is the default
1863 for NeXT-based systems, including Darwin and Mac OS X@. The macro
1864 @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
1867 @item -fno-nil-receivers
1868 @opindex fno-nil-receivers
1869 Assume that all Objective-C message dispatches (e.g.,
1870 @code{[receiver message:arg]}) in this translation unit ensure that the receiver
1871 is not @code{nil}. This allows for more efficient entry points in the runtime
1872 to be used. Currently, this option is only available in conjunction with
1873 the NeXT runtime on Mac OS X 10.3 and later.
1875 @item -fobjc-exceptions
1876 @opindex fobjc-exceptions
1877 Enable syntactic support for structured exception handling in Objective-C,
1878 similar to what is offered by C++ and Java. Currently, this option is only
1879 available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
1887 @@catch (AnObjCClass *exc) @{
1894 @@catch (AnotherClass *exc) @{
1897 @@catch (id allOthers) @{
1907 The @code{@@throw} statement may appear anywhere in an Objective-C or
1908 Objective-C++ program; when used inside of a @code{@@catch} block, the
1909 @code{@@throw} may appear without an argument (as shown above), in which case
1910 the object caught by the @code{@@catch} will be rethrown.
1912 Note that only (pointers to) Objective-C objects may be thrown and
1913 caught using this scheme. When an object is thrown, it will be caught
1914 by the nearest @code{@@catch} clause capable of handling objects of that type,
1915 analogously to how @code{catch} blocks work in C++ and Java. A
1916 @code{@@catch(id @dots{})} clause (as shown above) may also be provided to catch
1917 any and all Objective-C exceptions not caught by previous @code{@@catch}
1920 The @code{@@finally} clause, if present, will be executed upon exit from the
1921 immediately preceding @code{@@try @dots{} @@catch} section. This will happen
1922 regardless of whether any exceptions are thrown, caught or rethrown
1923 inside the @code{@@try @dots{} @@catch} section, analogously to the behavior
1924 of the @code{finally} clause in Java.
1926 There are several caveats to using the new exception mechanism:
1930 Although currently designed to be binary compatible with @code{NS_HANDLER}-style
1931 idioms provided by the @code{NSException} class, the new
1932 exceptions can only be used on Mac OS X 10.3 (Panther) and later
1933 systems, due to additional functionality needed in the (NeXT) Objective-C
1937 As mentioned above, the new exceptions do not support handling
1938 types other than Objective-C objects. Furthermore, when used from
1939 Objective-C++, the Objective-C exception model does not interoperate with C++
1940 exceptions at this time. This means you cannot @code{@@throw} an exception
1941 from Objective-C and @code{catch} it in C++, or vice versa
1942 (i.e., @code{throw @dots{} @@catch}).
1945 The @option{-fobjc-exceptions} switch also enables the use of synchronization
1946 blocks for thread-safe execution:
1949 @@synchronized (ObjCClass *guard) @{
1954 Upon entering the @code{@@synchronized} block, a thread of execution shall
1955 first check whether a lock has been placed on the corresponding @code{guard}
1956 object by another thread. If it has, the current thread shall wait until
1957 the other thread relinquishes its lock. Once @code{guard} becomes available,
1958 the current thread will place its own lock on it, execute the code contained in
1959 the @code{@@synchronized} block, and finally relinquish the lock (thereby
1960 making @code{guard} available to other threads).
1962 Unlike Java, Objective-C does not allow for entire methods to be marked
1963 @code{@@synchronized}. Note that throwing exceptions out of
1964 @code{@@synchronized} blocks is allowed, and will cause the guarding object
1965 to be unlocked properly.
1967 @item -freplace-objc-classes
1968 @opindex freplace-objc-classes
1969 Emit a special marker instructing @command{ld(1)} not to statically link in
1970 the resulting object file, and allow @command{dyld(1)} to load it in at
1971 run time instead. This is used in conjunction with the Fix-and-Continue
1972 debugging mode, where the object file in question may be recompiled and
1973 dynamically reloaded in the course of program execution, without the need
1974 to restart the program itself. Currently, Fix-and-Continue functionality
1975 is only available in conjunction with the NeXT runtime on Mac OS X 10.3
1980 When compiling for the NeXT runtime, the compiler ordinarily replaces calls
1981 to @code{objc_getClass("@dots{}")} (when the name of the class is known at
1982 compile time) with static class references that get initialized at load time,
1983 which improves run-time performance. Specifying the @option{-fzero-link} flag
1984 suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
1985 to be retained. This is useful in Zero-Link debugging mode, since it allows
1986 for individual class implementations to be modified during program execution.
1990 Dump interface declarations for all classes seen in the source file to a
1991 file named @file{@var{sourcename}.decl}.
1994 @opindex Wno-protocol
1995 If a class is declared to implement a protocol, a warning is issued for
1996 every method in the protocol that is not implemented by the class. The
1997 default behavior is to issue a warning for every method not explicitly
1998 implemented in the class, even if a method implementation is inherited
1999 from the superclass. If you use the @option{-Wno-protocol} option, then
2000 methods inherited from the superclass are considered to be implemented,
2001 and no warning is issued for them.
2005 Warn if multiple methods of different types for the same selector are
2006 found during compilation. The check is performed on the list of methods
2007 in the final stage of compilation. Additionally, a check is performed
2008 for each selector appearing in a @code{@@selector(@dots{})}
2009 expression, and a corresponding method for that selector has been found
2010 during compilation. Because these checks scan the method table only at
2011 the end of compilation, these warnings are not produced if the final
2012 stage of compilation is not reached, for example because an error is
2013 found during compilation, or because the @option{-fsyntax-only} option is
2016 @item -Wundeclared-selector
2017 @opindex Wundeclared-selector
2018 Warn if a @code{@@selector(@dots{})} expression referring to an
2019 undeclared selector is found. A selector is considered undeclared if no
2020 method with that name has been declared before the
2021 @code{@@selector(@dots{})} expression, either explicitly in an
2022 @code{@@interface} or @code{@@protocol} declaration, or implicitly in
2023 an @code{@@implementation} section. This option always performs its
2024 checks as soon as a @code{@@selector(@dots{})} expression is found,
2025 while @option{-Wselector} only performs its checks in the final stage of
2026 compilation. This also enforces the coding style convention
2027 that methods and selectors must be declared before being used.
2029 @item -print-objc-runtime-info
2030 @opindex print-objc-runtime-info
2031 Generate C header describing the largest structure that is passed by
2036 @node Language Independent Options
2037 @section Options to Control Diagnostic Messages Formatting
2038 @cindex options to control diagnostics formatting
2039 @cindex diagnostic messages
2040 @cindex message formatting
2042 Traditionally, diagnostic messages have been formatted irrespective of
2043 the output device's aspect (e.g.@: its width, @dots{}). The options described
2044 below can be used to control the diagnostic messages formatting
2045 algorithm, e.g.@: how many characters per line, how often source location
2046 information should be reported. Right now, only the C++ front end can
2047 honor these options. However it is expected, in the near future, that
2048 the remaining front ends would be able to digest them correctly.
2051 @item -fmessage-length=@var{n}
2052 @opindex fmessage-length
2053 Try to format error messages so that they fit on lines of about @var{n}
2054 characters. The default is 72 characters for @command{g++} and 0 for the rest of
2055 the front ends supported by GCC@. If @var{n} is zero, then no
2056 line-wrapping will be done; each error message will appear on a single
2059 @opindex fdiagnostics-show-location
2060 @item -fdiagnostics-show-location=once
2061 Only meaningful in line-wrapping mode. Instructs the diagnostic messages
2062 reporter to emit @emph{once} source location information; that is, in
2063 case the message is too long to fit on a single physical line and has to
2064 be wrapped, the source location won't be emitted (as prefix) again,
2065 over and over, in subsequent continuation lines. This is the default
2068 @item -fdiagnostics-show-location=every-line
2069 Only meaningful in line-wrapping mode. Instructs the diagnostic
2070 messages reporter to emit the same source location information (as
2071 prefix) for physical lines that result from the process of breaking
2072 a message which is too long to fit on a single line.
2076 @node Warning Options
2077 @section Options to Request or Suppress Warnings
2078 @cindex options to control warnings
2079 @cindex warning messages
2080 @cindex messages, warning
2081 @cindex suppressing warnings
2083 Warnings are diagnostic messages that report constructions which
2084 are not inherently erroneous but which are risky or suggest there
2085 may have been an error.
2087 You can request many specific warnings with options beginning @samp{-W},
2088 for example @option{-Wimplicit} to request warnings on implicit
2089 declarations. Each of these specific warning options also has a
2090 negative form beginning @samp{-Wno-} to turn off warnings;
2091 for example, @option{-Wno-implicit}. This manual lists only one of the
2092 two forms, whichever is not the default.
2094 The following options control the amount and kinds of warnings produced
2095 by GCC; for further, language-specific options also refer to
2096 @ref{C++ Dialect Options} and @ref{Objective-C and Objective-C++ Dialect
2100 @cindex syntax checking
2102 @opindex fsyntax-only
2103 Check the code for syntax errors, but don't do anything beyond that.
2107 Issue all the warnings demanded by strict ISO C and ISO C++;
2108 reject all programs that use forbidden extensions, and some other
2109 programs that do not follow ISO C and ISO C++. For ISO C, follows the
2110 version of the ISO C standard specified by any @option{-std} option used.
2112 Valid ISO C and ISO C++ programs should compile properly with or without
2113 this option (though a rare few will require @option{-ansi} or a
2114 @option{-std} option specifying the required version of ISO C)@. However,
2115 without this option, certain GNU extensions and traditional C and C++
2116 features are supported as well. With this option, they are rejected.
2118 @option{-pedantic} does not cause warning messages for use of the
2119 alternate keywords whose names begin and end with @samp{__}. Pedantic
2120 warnings are also disabled in the expression that follows
2121 @code{__extension__}. However, only system header files should use
2122 these escape routes; application programs should avoid them.
2123 @xref{Alternate Keywords}.
2125 Some users try to use @option{-pedantic} to check programs for strict ISO
2126 C conformance. They soon find that it does not do quite what they want:
2127 it finds some non-ISO practices, but not all---only those for which
2128 ISO C @emph{requires} a diagnostic, and some others for which
2129 diagnostics have been added.
2131 A feature to report any failure to conform to ISO C might be useful in
2132 some instances, but would require considerable additional work and would
2133 be quite different from @option{-pedantic}. We don't have plans to
2134 support such a feature in the near future.
2136 Where the standard specified with @option{-std} represents a GNU
2137 extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
2138 corresponding @dfn{base standard}, the version of ISO C on which the GNU
2139 extended dialect is based. Warnings from @option{-pedantic} are given
2140 where they are required by the base standard. (It would not make sense
2141 for such warnings to be given only for features not in the specified GNU
2142 C dialect, since by definition the GNU dialects of C include all
2143 features the compiler supports with the given option, and there would be
2144 nothing to warn about.)
2146 @item -pedantic-errors
2147 @opindex pedantic-errors
2148 Like @option{-pedantic}, except that errors are produced rather than
2153 Inhibit all warning messages.
2157 Inhibit warning messages about the use of @samp{#import}.
2159 @item -Wchar-subscripts
2160 @opindex Wchar-subscripts
2161 Warn if an array subscript has type @code{char}. This is a common cause
2162 of error, as programmers often forget that this type is signed on some
2167 Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
2168 comment, or whenever a Backslash-Newline appears in a @samp{//} comment.
2170 @item -Wfatal-errors
2171 @opindex Wfatal-errors
2172 This option causes the compiler to abort compilation on the first error
2173 occurred rather than trying to keep going and printing further error
2178 @opindex ffreestanding
2179 @opindex fno-builtin
2180 Check calls to @code{printf} and @code{scanf}, etc., to make sure that
2181 the arguments supplied have types appropriate to the format string
2182 specified, and that the conversions specified in the format string make
2183 sense. This includes standard functions, and others specified by format
2184 attributes (@pxref{Function Attributes}), in the @code{printf},
2185 @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
2186 not in the C standard) families (or other target-specific families).
2187 Which functions are checked without format attributes having been
2188 specified depends on the standard version selected, and such checks of
2189 functions without the attribute specified are disabled by
2190 @option{-ffreestanding} or @option{-fno-builtin}.
2192 The formats are checked against the format features supported by GNU
2193 libc version 2.2. These include all ISO C90 and C99 features, as well
2194 as features from the Single Unix Specification and some BSD and GNU
2195 extensions. Other library implementations may not support all these
2196 features; GCC does not support warning about features that go beyond a
2197 particular library's limitations. However, if @option{-pedantic} is used
2198 with @option{-Wformat}, warnings will be given about format features not
2199 in the selected standard version (but not for @code{strfmon} formats,
2200 since those are not in any version of the C standard). @xref{C Dialect
2201 Options,,Options Controlling C Dialect}.
2203 Since @option{-Wformat} also checks for null format arguments for
2204 several functions, @option{-Wformat} also implies @option{-Wnonnull}.
2206 @option{-Wformat} is included in @option{-Wall}. For more control over some
2207 aspects of format checking, the options @option{-Wformat-y2k},
2208 @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length},
2209 @option{-Wformat-nonliteral}, @option{-Wformat-security}, and
2210 @option{-Wformat=2} are available, but are not included in @option{-Wall}.
2213 @opindex Wformat-y2k
2214 If @option{-Wformat} is specified, also warn about @code{strftime}
2215 formats which may yield only a two-digit year.
2217 @item -Wno-format-extra-args
2218 @opindex Wno-format-extra-args
2219 If @option{-Wformat} is specified, do not warn about excess arguments to a
2220 @code{printf} or @code{scanf} format function. The C standard specifies
2221 that such arguments are ignored.
2223 Where the unused arguments lie between used arguments that are
2224 specified with @samp{$} operand number specifications, normally
2225 warnings are still given, since the implementation could not know what
2226 type to pass to @code{va_arg} to skip the unused arguments. However,
2227 in the case of @code{scanf} formats, this option will suppress the
2228 warning if the unused arguments are all pointers, since the Single
2229 Unix Specification says that such unused arguments are allowed.
2231 @item -Wno-format-zero-length
2232 @opindex Wno-format-zero-length
2233 If @option{-Wformat} is specified, do not warn about zero-length formats.
2234 The C standard specifies that zero-length formats are allowed.
2236 @item -Wformat-nonliteral
2237 @opindex Wformat-nonliteral
2238 If @option{-Wformat} is specified, also warn if the format string is not a
2239 string literal and so cannot be checked, unless the format function
2240 takes its format arguments as a @code{va_list}.
2242 @item -Wformat-security
2243 @opindex Wformat-security
2244 If @option{-Wformat} is specified, also warn about uses of format
2245 functions that represent possible security problems. At present, this
2246 warns about calls to @code{printf} and @code{scanf} functions where the
2247 format string is not a string literal and there are no format arguments,
2248 as in @code{printf (foo);}. This may be a security hole if the format
2249 string came from untrusted input and contains @samp{%n}. (This is
2250 currently a subset of what @option{-Wformat-nonliteral} warns about, but
2251 in future warnings may be added to @option{-Wformat-security} that are not
2252 included in @option{-Wformat-nonliteral}.)
2256 Enable @option{-Wformat} plus format checks not included in
2257 @option{-Wformat}. Currently equivalent to @samp{-Wformat
2258 -Wformat-nonliteral -Wformat-security -Wformat-y2k}.
2262 Warn about passing a null pointer for arguments marked as
2263 requiring a non-null value by the @code{nonnull} function attribute.
2265 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
2266 can be disabled with the @option{-Wno-nonnull} option.
2268 @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
2270 Warn about uninitialized variables which are initialized with themselves.
2271 Note this option can only be used with the @option{-Wuninitialized} option,
2272 which in turn only works with @option{-O1} and above.
2274 For example, GCC will warn about @code{i} being uninitialized in the
2275 following snippet only when @option{-Winit-self} has been specified:
2286 @item -Wimplicit-int
2287 @opindex Wimplicit-int
2288 Warn when a declaration does not specify a type.
2290 @item -Wimplicit-function-declaration
2291 @itemx -Werror-implicit-function-declaration
2292 @opindex Wimplicit-function-declaration
2293 @opindex Werror-implicit-function-declaration
2294 Give a warning (or error) whenever a function is used before being
2295 declared. The form @option{-Wno-error-implicit-function-declaration}
2300 Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
2304 Warn if the type of @samp{main} is suspicious. @samp{main} should be a
2305 function with external linkage, returning int, taking either zero
2306 arguments, two, or three arguments of appropriate types.
2308 @item -Wmissing-braces
2309 @opindex Wmissing-braces
2310 Warn if an aggregate or union initializer is not fully bracketed. In
2311 the following example, the initializer for @samp{a} is not fully
2312 bracketed, but that for @samp{b} is fully bracketed.
2315 int a[2][2] = @{ 0, 1, 2, 3 @};
2316 int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
2319 @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
2320 @opindex Wmissing-include-dirs
2321 Warn if a user-supplied include directory does not exist.
2324 @opindex Wparentheses
2325 Warn if parentheses are omitted in certain contexts, such
2326 as when there is an assignment in a context where a truth value
2327 is expected, or when operators are nested whose precedence people
2328 often get confused about. Only the warning for an assignment used as
2329 a truth value is supported when compiling C++; the other warnings are
2330 only supported when compiling C@.
2332 Also warn if a comparison like @samp{x<=y<=z} appears; this is
2333 equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different
2334 interpretation from that of ordinary mathematical notation.
2336 Also warn about constructions where there may be confusion to which
2337 @code{if} statement an @code{else} branch belongs. Here is an example of
2352 In C, every @code{else} branch belongs to the innermost possible @code{if}
2353 statement, which in this example is @code{if (b)}. This is often not
2354 what the programmer expected, as illustrated in the above example by
2355 indentation the programmer chose. When there is the potential for this
2356 confusion, GCC will issue a warning when this flag is specified.
2357 To eliminate the warning, add explicit braces around the innermost
2358 @code{if} statement so there is no way the @code{else} could belong to
2359 the enclosing @code{if}. The resulting code would look like this:
2375 @item -Wsequence-point
2376 @opindex Wsequence-point
2377 Warn about code that may have undefined semantics because of violations
2378 of sequence point rules in the C standard.
2380 The C standard defines the order in which expressions in a C program are
2381 evaluated in terms of @dfn{sequence points}, which represent a partial
2382 ordering between the execution of parts of the program: those executed
2383 before the sequence point, and those executed after it. These occur
2384 after the evaluation of a full expression (one which is not part of a
2385 larger expression), after the evaluation of the first operand of a
2386 @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
2387 function is called (but after the evaluation of its arguments and the
2388 expression denoting the called function), and in certain other places.
2389 Other than as expressed by the sequence point rules, the order of
2390 evaluation of subexpressions of an expression is not specified. All
2391 these rules describe only a partial order rather than a total order,
2392 since, for example, if two functions are called within one expression
2393 with no sequence point between them, the order in which the functions
2394 are called is not specified. However, the standards committee have
2395 ruled that function calls do not overlap.
2397 It is not specified when between sequence points modifications to the
2398 values of objects take effect. Programs whose behavior depends on this
2399 have undefined behavior; the C standard specifies that ``Between the
2400 previous and next sequence point an object shall have its stored value
2401 modified at most once by the evaluation of an expression. Furthermore,
2402 the prior value shall be read only to determine the value to be
2403 stored.''. If a program breaks these rules, the results on any
2404 particular implementation are entirely unpredictable.
2406 Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
2407 = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
2408 diagnosed by this option, and it may give an occasional false positive
2409 result, but in general it has been found fairly effective at detecting
2410 this sort of problem in programs.
2412 The present implementation of this option only works for C programs. A
2413 future implementation may also work for C++ programs.
2415 The C standard is worded confusingly, therefore there is some debate
2416 over the precise meaning of the sequence point rules in subtle cases.
2417 Links to discussions of the problem, including proposed formal
2418 definitions, may be found on the GCC readings page, at
2419 @w{@uref{http://gcc.gnu.org/readings.html}}.
2422 @opindex Wreturn-type
2423 Warn whenever a function is defined with a return-type that defaults to
2424 @code{int}. Also warn about any @code{return} statement with no
2425 return-value in a function whose return-type is not @code{void}.
2427 For C, also warn if the return type of a function has a type qualifier
2428 such as @code{const}. Such a type qualifier has no effect, since the
2429 value returned by a function is not an lvalue. ISO C prohibits
2430 qualified @code{void} return types on function definitions, so such
2431 return types always receive a warning even without this option.
2433 For C++, a function without return type always produces a diagnostic
2434 message, even when @option{-Wno-return-type} is specified. The only
2435 exceptions are @samp{main} and functions defined in system headers.
2439 Warn whenever a @code{switch} statement has an index of enumerated type
2440 and lacks a @code{case} for one or more of the named codes of that
2441 enumeration. (The presence of a @code{default} label prevents this
2442 warning.) @code{case} labels outside the enumeration range also
2443 provoke warnings when this option is used.
2445 @item -Wswitch-default
2446 @opindex Wswitch-switch
2447 Warn whenever a @code{switch} statement does not have a @code{default}
2451 @opindex Wswitch-enum
2452 Warn whenever a @code{switch} statement has an index of enumerated type
2453 and lacks a @code{case} for one or more of the named codes of that
2454 enumeration. @code{case} labels outside the enumeration range also
2455 provoke warnings when this option is used.
2459 Warn if any trigraphs are encountered that might change the meaning of
2460 the program (trigraphs within comments are not warned about).
2462 @item -Wunused-function
2463 @opindex Wunused-function
2464 Warn whenever a static function is declared but not defined or a
2465 non\-inline static function is unused.
2467 @item -Wunused-label
2468 @opindex Wunused-label
2469 Warn whenever a label is declared but not used.
2471 To suppress this warning use the @samp{unused} attribute
2472 (@pxref{Variable Attributes}).
2474 @item -Wunused-parameter
2475 @opindex Wunused-parameter
2476 Warn whenever a function parameter is unused aside from its declaration.
2478 To suppress this warning use the @samp{unused} attribute
2479 (@pxref{Variable Attributes}).
2481 @item -Wunused-variable
2482 @opindex Wunused-variable
2483 Warn whenever a local variable or non-constant static variable is unused
2484 aside from its declaration
2486 To suppress this warning use the @samp{unused} attribute
2487 (@pxref{Variable Attributes}).
2489 @item -Wunused-value
2490 @opindex Wunused-value
2491 Warn whenever a statement computes a result that is explicitly not used.
2493 To suppress this warning cast the expression to @samp{void}.
2497 All the above @option{-Wunused} options combined.
2499 In order to get a warning about an unused function parameter, you must
2500 either specify @samp{-Wextra -Wunused} (note that @samp{-Wall} implies
2501 @samp{-Wunused}), or separately specify @option{-Wunused-parameter}.
2503 @item -Wuninitialized
2504 @opindex Wuninitialized
2505 Warn if an automatic variable is used without first being initialized or
2506 if a variable may be clobbered by a @code{setjmp} call.
2508 These warnings are possible only in optimizing compilation,
2509 because they require data flow information that is computed only
2510 when optimizing. If you don't specify @option{-O}, you simply won't
2513 If you want to warn about code which uses the uninitialized value of the
2514 variable in its own initializer, use the @option{-Winit-self} option.
2516 These warnings occur only for variables that are candidates for
2517 register allocation. Therefore, they do not occur for a variable that
2518 is declared @code{volatile}, or whose address is taken, or whose size
2519 is other than 1, 2, 4 or 8 bytes. Also, they do not occur for
2520 structures, unions or arrays, even when they are in registers.
2522 Note that there may be no warning about a variable that is used only
2523 to compute a value that itself is never used, because such
2524 computations may be deleted by data flow analysis before the warnings
2527 These warnings are made optional because GCC is not smart
2528 enough to see all the reasons why the code might be correct
2529 despite appearing to have an error. Here is one example of how
2550 If the value of @code{y} is always 1, 2 or 3, then @code{x} is
2551 always initialized, but GCC doesn't know this. Here is
2552 another common case:
2557 if (change_y) save_y = y, y = new_y;
2559 if (change_y) y = save_y;
2564 This has no bug because @code{save_y} is used only if it is set.
2566 @cindex @code{longjmp} warnings
2567 This option also warns when a non-volatile automatic variable might be
2568 changed by a call to @code{longjmp}. These warnings as well are possible
2569 only in optimizing compilation.
2571 The compiler sees only the calls to @code{setjmp}. It cannot know
2572 where @code{longjmp} will be called; in fact, a signal handler could
2573 call it at any point in the code. As a result, you may get a warning
2574 even when there is in fact no problem because @code{longjmp} cannot
2575 in fact be called at the place which would cause a problem.
2577 Some spurious warnings can be avoided if you declare all the functions
2578 you use that never return as @code{noreturn}. @xref{Function
2581 @item -Wunknown-pragmas
2582 @opindex Wunknown-pragmas
2583 @cindex warning for unknown pragmas
2584 @cindex unknown pragmas, warning
2585 @cindex pragmas, warning of unknown
2586 Warn when a #pragma directive is encountered which is not understood by
2587 GCC@. If this command line option is used, warnings will even be issued
2588 for unknown pragmas in system header files. This is not the case if
2589 the warnings were only enabled by the @option{-Wall} command line option.
2591 @item -Wstrict-aliasing
2592 @opindex Wstrict-aliasing
2593 This option is only active when @option{-fstrict-aliasing} is active.
2594 It warns about code which might break the strict aliasing rules that the
2595 compiler is using for optimization. The warning does not catch all
2596 cases, but does attempt to catch the more common pitfalls. It is
2597 included in @option{-Wall}.
2599 @item -Wstrict-aliasing=2
2600 @opindex Wstrict-aliasing=2
2601 This option is only active when @option{-fstrict-aliasing} is active.
2602 It warns about all code which might break the strict aliasing rules that the
2603 compiler is using for optimization. This warning catches all cases, but
2604 it will also give a warning for some ambiguous cases that are safe.
2608 All of the above @samp{-W} options combined. This enables all the
2609 warnings about constructions that some users consider questionable, and
2610 that are easy to avoid (or modify to prevent the warning), even in
2611 conjunction with macros. This also enables some language-specific
2612 warnings described in @ref{C++ Dialect Options} and
2613 @ref{Objective-C and Objective-C++ Dialect Options}.
2616 The following @option{-W@dots{}} options are not implied by @option{-Wall}.
2617 Some of them warn about constructions that users generally do not
2618 consider questionable, but which occasionally you might wish to check
2619 for; others warn about constructions that are necessary or hard to avoid
2620 in some cases, and there is no simple way to modify the code to suppress
2627 (This option used to be called @option{-W}. The older name is still
2628 supported, but the newer name is more descriptive.) Print extra warning
2629 messages for these events:
2633 A function can return either with or without a value. (Falling
2634 off the end of the function body is considered returning without
2635 a value.) For example, this function would evoke such a
2649 An expression-statement or the left-hand side of a comma expression
2650 contains no side effects.
2651 To suppress the warning, cast the unused expression to void.
2652 For example, an expression such as @samp{x[i,j]} will cause a warning,
2653 but @samp{x[(void)i,j]} will not.
2656 An unsigned value is compared against zero with @samp{<} or @samp{>=}.
2659 Storage-class specifiers like @code{static} are not the first things in
2660 a declaration. According to the C Standard, this usage is obsolescent.
2663 If @option{-Wall} or @option{-Wunused} is also specified, warn about unused
2667 A comparison between signed and unsigned values could produce an
2668 incorrect result when the signed value is converted to unsigned.
2669 (But don't warn if @option{-Wno-sign-compare} is also specified.)
2672 An aggregate has an initializer which does not initialize all members.
2673 This warning can be independently controlled by
2674 @option{-Wmissing-field-initializers}.
2677 A function parameter is declared without a type specifier in K&R-style
2685 An empty body occurs in an @samp{if} or @samp{else} statement.
2688 A pointer is compared against integer zero with @samp{<}, @samp{<=},
2689 @samp{>}, or @samp{>=}.
2692 A variable might be changed by @samp{longjmp} or @samp{vfork}.
2695 Any of several floating-point events that often indicate errors, such as
2696 overflow, underflow, loss of precision, etc.
2698 @item @r{(C++ only)}
2699 An enumerator and a non-enumerator both appear in a conditional expression.
2701 @item @r{(C++ only)}
2702 A non-static reference or non-static @samp{const} member appears in a
2703 class without constructors.
2705 @item @r{(C++ only)}
2706 Ambiguous virtual bases.
2708 @item @r{(C++ only)}
2709 Subscripting an array which has been declared @samp{register}.
2711 @item @r{(C++ only)}
2712 Taking the address of a variable which has been declared @samp{register}.
2714 @item @r{(C++ only)}
2715 A base class is not initialized in a derived class' copy constructor.
2718 @item -Wno-div-by-zero
2719 @opindex Wno-div-by-zero
2720 @opindex Wdiv-by-zero
2721 Do not warn about compile-time integer division by zero. Floating point
2722 division by zero is not warned about, as it can be a legitimate way of
2723 obtaining infinities and NaNs.
2725 @item -Wsystem-headers
2726 @opindex Wsystem-headers
2727 @cindex warnings from system headers
2728 @cindex system headers, warnings from
2729 Print warning messages for constructs found in system header files.
2730 Warnings from system headers are normally suppressed, on the assumption
2731 that they usually do not indicate real problems and would only make the
2732 compiler output harder to read. Using this command line option tells
2733 GCC to emit warnings from system headers as if they occurred in user
2734 code. However, note that using @option{-Wall} in conjunction with this
2735 option will @emph{not} warn about unknown pragmas in system
2736 headers---for that, @option{-Wunknown-pragmas} must also be used.
2739 @opindex Wfloat-equal
2740 Warn if floating point values are used in equality comparisons.
2742 The idea behind this is that sometimes it is convenient (for the
2743 programmer) to consider floating-point values as approximations to
2744 infinitely precise real numbers. If you are doing this, then you need
2745 to compute (by analyzing the code, or in some other way) the maximum or
2746 likely maximum error that the computation introduces, and allow for it
2747 when performing comparisons (and when producing output, but that's a
2748 different problem). In particular, instead of testing for equality, you
2749 would check to see whether the two values have ranges that overlap; and
2750 this is done with the relational operators, so equality comparisons are
2753 @item -Wtraditional @r{(C only)}
2754 @opindex Wtraditional
2755 Warn about certain constructs that behave differently in traditional and
2756 ISO C@. Also warn about ISO C constructs that have no traditional C
2757 equivalent, and/or problematic constructs which should be avoided.
2761 Macro parameters that appear within string literals in the macro body.
2762 In traditional C macro replacement takes place within string literals,
2763 but does not in ISO C@.
2766 In traditional C, some preprocessor directives did not exist.
2767 Traditional preprocessors would only consider a line to be a directive
2768 if the @samp{#} appeared in column 1 on the line. Therefore
2769 @option{-Wtraditional} warns about directives that traditional C
2770 understands but would ignore because the @samp{#} does not appear as the
2771 first character on the line. It also suggests you hide directives like
2772 @samp{#pragma} not understood by traditional C by indenting them. Some
2773 traditional implementations would not recognize @samp{#elif}, so it
2774 suggests avoiding it altogether.
2777 A function-like macro that appears without arguments.
2780 The unary plus operator.
2783 The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating point
2784 constant suffixes. (Traditional C does support the @samp{L} suffix on integer
2785 constants.) Note, these suffixes appear in macros defined in the system
2786 headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
2787 Use of these macros in user code might normally lead to spurious
2788 warnings, however GCC's integrated preprocessor has enough context to
2789 avoid warning in these cases.
2792 A function declared external in one block and then used after the end of
2796 A @code{switch} statement has an operand of type @code{long}.
2799 A non-@code{static} function declaration follows a @code{static} one.
2800 This construct is not accepted by some traditional C compilers.
2803 The ISO type of an integer constant has a different width or
2804 signedness from its traditional type. This warning is only issued if
2805 the base of the constant is ten. I.e.@: hexadecimal or octal values, which
2806 typically represent bit patterns, are not warned about.
2809 Usage of ISO string concatenation is detected.
2812 Initialization of automatic aggregates.
2815 Identifier conflicts with labels. Traditional C lacks a separate
2816 namespace for labels.
2819 Initialization of unions. If the initializer is zero, the warning is
2820 omitted. This is done under the assumption that the zero initializer in
2821 user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
2822 initializer warnings and relies on default initialization to zero in the
2826 Conversions by prototypes between fixed/floating point values and vice
2827 versa. The absence of these prototypes when compiling with traditional
2828 C would cause serious problems. This is a subset of the possible
2829 conversion warnings, for the full set use @option{-Wconversion}.
2832 Use of ISO C style function definitions. This warning intentionally is
2833 @emph{not} issued for prototype declarations or variadic functions
2834 because these ISO C features will appear in your code when using
2835 libiberty's traditional C compatibility macros, @code{PARAMS} and
2836 @code{VPARAMS}. This warning is also bypassed for nested functions
2837 because that feature is already a GCC extension and thus not relevant to
2838 traditional C compatibility.
2841 @item -Wdeclaration-after-statement @r{(C only)}
2842 @opindex Wdeclaration-after-statement
2843 Warn when a declaration is found after a statement in a block. This
2844 construct, known from C++, was introduced with ISO C99 and is by default
2845 allowed in GCC@. It is not supported by ISO C90 and was not supported by
2846 GCC versions before GCC 3.0. @xref{Mixed Declarations}.
2850 Warn if an undefined identifier is evaluated in an @samp{#if} directive.
2852 @item -Wendif-labels
2853 @opindex Wendif-labels
2854 Warn whenever an @samp{#else} or an @samp{#endif} are followed by text.
2858 Warn whenever a local variable shadows another local variable, parameter or
2859 global variable or whenever a built-in function is shadowed.
2861 @item -Wlarger-than-@var{len}
2862 @opindex Wlarger-than
2863 Warn whenever an object of larger than @var{len} bytes is defined.
2865 @item -Wpointer-arith
2866 @opindex Wpointer-arith
2867 Warn about anything that depends on the ``size of'' a function type or
2868 of @code{void}. GNU C assigns these types a size of 1, for
2869 convenience in calculations with @code{void *} pointers and pointers
2872 @item -Wbad-function-cast @r{(C only)}
2873 @opindex Wbad-function-cast
2874 Warn whenever a function call is cast to a non-matching type.
2875 For example, warn if @code{int malloc()} is cast to @code{anything *}.
2879 Warn whenever a pointer is cast so as to remove a type qualifier from
2880 the target type. For example, warn if a @code{const char *} is cast
2881 to an ordinary @code{char *}.
2884 @opindex Wcast-align
2885 Warn whenever a pointer is cast such that the required alignment of the
2886 target is increased. For example, warn if a @code{char *} is cast to
2887 an @code{int *} on machines where integers can only be accessed at
2888 two- or four-byte boundaries.
2890 @item -Wwrite-strings
2891 @opindex Wwrite-strings
2892 When compiling C, give string constants the type @code{const
2893 char[@var{length}]} so that
2894 copying the address of one into a non-@code{const} @code{char *}
2895 pointer will get a warning; when compiling C++, warn about the
2896 deprecated conversion from string constants to @code{char *}.
2897 These warnings will help you find at
2898 compile time code that can try to write into a string constant, but
2899 only if you have been very careful about using @code{const} in
2900 declarations and prototypes. Otherwise, it will just be a nuisance;
2901 this is why we did not make @option{-Wall} request these warnings.
2904 @opindex Wconversion
2905 Warn if a prototype causes a type conversion that is different from what
2906 would happen to the same argument in the absence of a prototype. This
2907 includes conversions of fixed point to floating and vice versa, and
2908 conversions changing the width or signedness of a fixed point argument
2909 except when the same as the default promotion.
2911 Also, warn if a negative integer constant expression is implicitly
2912 converted to an unsigned type. For example, warn about the assignment
2913 @code{x = -1} if @code{x} is unsigned. But do not warn about explicit
2914 casts like @code{(unsigned) -1}.
2916 @item -Wsign-compare
2917 @opindex Wsign-compare
2918 @cindex warning for comparison of signed and unsigned values
2919 @cindex comparison of signed and unsigned values, warning
2920 @cindex signed and unsigned values, comparison warning
2921 Warn when a comparison between signed and unsigned values could produce
2922 an incorrect result when the signed value is converted to unsigned.
2923 This warning is also enabled by @option{-Wextra}; to get the other warnings
2924 of @option{-Wextra} without this warning, use @samp{-Wextra -Wno-sign-compare}.
2926 @item -Waggregate-return
2927 @opindex Waggregate-return
2928 Warn if any functions that return structures or unions are defined or
2929 called. (In languages where you can return an array, this also elicits
2932 @item -Wstrict-prototypes @r{(C only)}
2933 @opindex Wstrict-prototypes
2934 Warn if a function is declared or defined without specifying the
2935 argument types. (An old-style function definition is permitted without
2936 a warning if preceded by a declaration which specifies the argument
2939 @item -Wold-style-definition @r{(C only)}
2940 @opindex Wold-style-definition
2941 Warn if an old-style function definition is used. A warning is given
2942 even if there is a previous prototype.
2944 @item -Wmissing-prototypes @r{(C only)}
2945 @opindex Wmissing-prototypes
2946 Warn if a global function is defined without a previous prototype
2947 declaration. This warning is issued even if the definition itself
2948 provides a prototype. The aim is to detect global functions that fail
2949 to be declared in header files.
2951 @item -Wmissing-declarations @r{(C only)}
2952 @opindex Wmissing-declarations
2953 Warn if a global function is defined without a previous declaration.
2954 Do so even if the definition itself provides a prototype.
2955 Use this option to detect global functions that are not declared in
2958 @item -Wmissing-field-initializers
2959 @opindex Wmissing-field-initializers
2962 Warn if a structure's initializer has some fields missing. For
2963 example, the following code would cause such a warning, because
2964 @code{x.h} is implicitly zero:
2967 struct s @{ int f, g, h; @};
2968 struct s x = @{ 3, 4 @};
2971 This option does not warn about designated initializers, so the following
2972 modification would not trigger a warning:
2975 struct s @{ int f, g, h; @};
2976 struct s x = @{ .f = 3, .g = 4 @};
2979 This warning is included in @option{-Wextra}. To get other @option{-Wextra}
2980 warnings without this one, use @samp{-Wextra -Wno-missing-field-initializers}.
2982 @item -Wmissing-noreturn
2983 @opindex Wmissing-noreturn
2984 Warn about functions which might be candidates for attribute @code{noreturn}.
2985 Note these are only possible candidates, not absolute ones. Care should
2986 be taken to manually verify functions actually do not ever return before
2987 adding the @code{noreturn} attribute, otherwise subtle code generation
2988 bugs could be introduced. You will not get a warning for @code{main} in
2989 hosted C environments.
2991 @item -Wmissing-format-attribute
2992 @opindex Wmissing-format-attribute
2994 If @option{-Wformat} is enabled, also warn about functions which might be
2995 candidates for @code{format} attributes. Note these are only possible
2996 candidates, not absolute ones. GCC will guess that @code{format}
2997 attributes might be appropriate for any function that calls a function
2998 like @code{vprintf} or @code{vscanf}, but this might not always be the
2999 case, and some functions for which @code{format} attributes are
3000 appropriate may not be detected. This option has no effect unless
3001 @option{-Wformat} is enabled (possibly by @option{-Wall}).
3003 @item -Wno-multichar
3004 @opindex Wno-multichar
3006 Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
3007 Usually they indicate a typo in the user's code, as they have
3008 implementation-defined values, and should not be used in portable code.
3010 @item -Wno-deprecated-declarations
3011 @opindex Wno-deprecated-declarations
3012 Do not warn about uses of functions, variables, and types marked as
3013 deprecated by using the @code{deprecated} attribute.
3014 (@pxref{Function Attributes}, @pxref{Variable Attributes},
3015 @pxref{Type Attributes}.)
3019 Warn if a structure is given the packed attribute, but the packed
3020 attribute has no effect on the layout or size of the structure.
3021 Such structures may be mis-aligned for little benefit. For
3022 instance, in this code, the variable @code{f.x} in @code{struct bar}
3023 will be misaligned even though @code{struct bar} does not itself
3024 have the packed attribute:
3031 @} __attribute__((packed));
3041 Warn if padding is included in a structure, either to align an element
3042 of the structure or to align the whole structure. Sometimes when this
3043 happens it is possible to rearrange the fields of the structure to
3044 reduce the padding and so make the structure smaller.
3046 @item -Wredundant-decls
3047 @opindex Wredundant-decls
3048 Warn if anything is declared more than once in the same scope, even in
3049 cases where multiple declaration is valid and changes nothing.
3051 @item -Wnested-externs @r{(C only)}
3052 @opindex Wnested-externs
3053 Warn if an @code{extern} declaration is encountered within a function.
3055 @item -Wunreachable-code
3056 @opindex Wunreachable-code
3057 Warn if the compiler detects that code will never be executed.
3059 This option is intended to warn when the compiler detects that at
3060 least a whole line of source code will never be executed, because
3061 some condition is never satisfied or because it is after a
3062 procedure that never returns.
3064 It is possible for this option to produce a warning even though there
3065 are circumstances under which part of the affected line can be executed,
3066 so care should be taken when removing apparently-unreachable code.
3068 For instance, when a function is inlined, a warning may mean that the
3069 line is unreachable in only one inlined copy of the function.
3071 This option is not made part of @option{-Wall} because in a debugging
3072 version of a program there is often substantial code which checks
3073 correct functioning of the program and is, hopefully, unreachable
3074 because the program does work. Another common use of unreachable
3075 code is to provide behavior which is selectable at compile-time.
3079 Warn if a function can not be inlined and it was declared as inline.
3080 Even with this option, the compiler will not warn about failures to
3081 inline functions declared in system headers.
3083 The compiler uses a variety of heuristics to determine whether or not
3084 to inline a function. For example, the compiler takes into account
3085 the size of the function being inlined and the the amount of inlining
3086 that has already been done in the current function. Therefore,
3087 seemingly insignificant changes in the source program can cause the
3088 warnings produced by @option{-Winline} to appear or disappear.
3090 @item -Wno-invalid-offsetof @r{(C++ only)}
3091 @opindex Wno-invalid-offsetof
3092 Suppress warnings from applying the @samp{offsetof} macro to a non-POD
3093 type. According to the 1998 ISO C++ standard, applying @samp{offsetof}
3094 to a non-POD type is undefined. In existing C++ implementations,
3095 however, @samp{offsetof} typically gives meaningful results even when
3096 applied to certain kinds of non-POD types. (Such as a simple
3097 @samp{struct} that fails to be a POD type only by virtue of having a
3098 constructor.) This flag is for users who are aware that they are
3099 writing nonportable code and who have deliberately chosen to ignore the
3102 The restrictions on @samp{offsetof} may be relaxed in a future version
3103 of the C++ standard.
3106 @opindex Winvalid-pch
3107 Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
3108 the search path but can't be used.
3112 @opindex Wno-long-long
3113 Warn if @samp{long long} type is used. This is default. To inhibit
3114 the warning messages, use @option{-Wno-long-long}. Flags
3115 @option{-Wlong-long} and @option{-Wno-long-long} are taken into account
3116 only when @option{-pedantic} flag is used.
3118 @item -Wvariadic-macros
3119 @opindex Wvariadic-macros
3120 @opindex Wno-variadic-macros
3121 Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
3122 alternate syntax when in pedantic ISO C99 mode. This is default.
3123 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
3125 @item -Wdisabled-optimization
3126 @opindex Wdisabled-optimization
3127 Warn if a requested optimization pass is disabled. This warning does
3128 not generally indicate that there is anything wrong with your code; it
3129 merely indicates that GCC's optimizers were unable to handle the code
3130 effectively. Often, the problem is that your code is too big or too
3131 complex; GCC will refuse to optimize programs when the optimization
3132 itself is likely to take inordinate amounts of time.
3136 Make all warnings into errors.
3139 @node Debugging Options
3140 @section Options for Debugging Your Program or GCC
3141 @cindex options, debugging
3142 @cindex debugging information options
3144 GCC has various special options that are used for debugging
3145 either your program or GCC:
3150 Produce debugging information in the operating system's native format
3151 (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging
3154 On most systems that use stabs format, @option{-g} enables use of extra
3155 debugging information that only GDB can use; this extra information
3156 makes debugging work better in GDB but will probably make other debuggers
3158 refuse to read the program. If you want to control for certain whether
3159 to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
3160 @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
3162 GCC allows you to use @option{-g} with
3163 @option{-O}. The shortcuts taken by optimized code may occasionally
3164 produce surprising results: some variables you declared may not exist
3165 at all; flow of control may briefly move where you did not expect it;
3166 some statements may not be executed because they compute constant
3167 results or their values were already at hand; some statements may
3168 execute in different places because they were moved out of loops.
3170 Nevertheless it proves possible to debug optimized output. This makes
3171 it reasonable to use the optimizer for programs that might have bugs.
3173 The following options are useful when GCC is generated with the
3174 capability for more than one debugging format.
3178 Produce debugging information for use by GDB@. This means to use the
3179 most expressive format available (DWARF 2, stabs, or the native format
3180 if neither of those are supported), including GDB extensions if at all
3185 Produce debugging information in stabs format (if that is supported),
3186 without GDB extensions. This is the format used by DBX on most BSD
3187 systems. On MIPS, Alpha and System V Release 4 systems this option
3188 produces stabs debugging output which is not understood by DBX or SDB@.
3189 On System V Release 4 systems this option requires the GNU assembler.
3191 @item -feliminate-unused-debug-symbols
3192 @opindex feliminate-unused-debug-symbols
3193 Produce debugging information in stabs format (if that is supported),
3194 for only symbols that are actually used.
3198 Produce debugging information in stabs format (if that is supported),
3199 using GNU extensions understood only by the GNU debugger (GDB)@. The
3200 use of these extensions is likely to make other debuggers crash or
3201 refuse to read the program.
3205 Produce debugging information in COFF format (if that is supported).
3206 This is the format used by SDB on most System V systems prior to
3211 Produce debugging information in XCOFF format (if that is supported).
3212 This is the format used by the DBX debugger on IBM RS/6000 systems.
3216 Produce debugging information in XCOFF format (if that is supported),
3217 using GNU extensions understood only by the GNU debugger (GDB)@. The
3218 use of these extensions is likely to make other debuggers crash or
3219 refuse to read the program, and may cause assemblers other than the GNU
3220 assembler (GAS) to fail with an error.
3224 Produce debugging information in DWARF version 2 format (if that is
3225 supported). This is the format used by DBX on IRIX 6. With this
3226 option, GCC uses features of DWARF version 3 when they are useful;
3227 version 3 is upward compatible with version 2, but may still cause
3228 problems for older debuggers.
3232 Produce debugging information in VMS debug format (if that is
3233 supported). This is the format used by DEBUG on VMS systems.
3236 @itemx -ggdb@var{level}
3237 @itemx -gstabs@var{level}
3238 @itemx -gcoff@var{level}
3239 @itemx -gxcoff@var{level}
3240 @itemx -gvms@var{level}
3241 Request debugging information and also use @var{level} to specify how
3242 much information. The default level is 2.
3244 Level 1 produces minimal information, enough for making backtraces in
3245 parts of the program that you don't plan to debug. This includes
3246 descriptions of functions and external variables, but no information
3247 about local variables and no line numbers.
3249 Level 3 includes extra information, such as all the macro definitions
3250 present in the program. Some debuggers support macro expansion when
3251 you use @option{-g3}.
3253 @option{-gdwarf-2} does not accept a concatenated debug level, because
3254 GCC used to support an option @option{-gdwarf} that meant to generate
3255 debug information in version 1 of the DWARF format (which is very
3256 different from version 2), and it would have been too confusing. That
3257 debug format is long obsolete, but the option cannot be changed now.
3258 Instead use an additional @option{-g@var{level}} option to change the
3259 debug level for DWARF2.
3261 @item -feliminate-dwarf2-dups
3262 @opindex feliminate-dwarf2-dups
3263 Compress DWARF2 debugging information by eliminating duplicated
3264 information about each symbol. This option only makes sense when
3265 generating DWARF2 debugging information with @option{-gdwarf-2}.
3267 @cindex @command{prof}
3270 Generate extra code to write profile information suitable for the
3271 analysis program @command{prof}. You must use this option when compiling
3272 the source files you want data about, and you must also use it when
3275 @cindex @command{gprof}
3278 Generate extra code to write profile information suitable for the
3279 analysis program @command{gprof}. You must use this option when compiling
3280 the source files you want data about, and you must also use it when
3285 Makes the compiler print out each function name as it is compiled, and
3286 print some statistics about each pass when it finishes.
3289 @opindex ftime-report
3290 Makes the compiler print some statistics about the time consumed by each
3291 pass when it finishes.
3294 @opindex fmem-report
3295 Makes the compiler print some statistics about permanent memory
3296 allocation when it finishes.
3298 @item -fprofile-arcs
3299 @opindex fprofile-arcs
3300 Add code so that program flow @dfn{arcs} are instrumented. During
3301 execution the program records how many times each branch and call is
3302 executed and how many times it is taken or returns. When the compiled
3303 program exits it saves this data to a file called
3304 @file{@var{auxname}.gcda} for each source file. The data may be used for
3305 profile-directed optimizations (@option{-fbranch-probabilities}), or for
3306 test coverage analysis (@option{-ftest-coverage}). Each object file's
3307 @var{auxname} is generated from the name of the output file, if
3308 explicitly specified and it is not the final executable, otherwise it is
3309 the basename of the source file. In both cases any suffix is removed
3310 (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
3311 @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
3316 Compile the source files with @option{-fprofile-arcs} plus optimization
3317 and code generation options. For test coverage analysis, use the
3318 additional @option{-ftest-coverage} option. You do not need to profile
3319 every source file in a program.
3322 Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
3323 (the latter implies the former).
3326 Run the program on a representative workload to generate the arc profile
3327 information. This may be repeated any number of times. You can run
3328 concurrent instances of your program, and provided that the file system
3329 supports locking, the data files will be correctly updated. Also
3330 @code{fork} calls are detected and correctly handled (double counting
3334 For profile-directed optimizations, compile the source files again with
3335 the same optimization and code generation options plus
3336 @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
3337 Control Optimization}).
3340 For test coverage analysis, use @command{gcov} to produce human readable
3341 information from the @file{.gcno} and @file{.gcda} files. Refer to the
3342 @command{gcov} documentation for further information.
3346 With @option{-fprofile-arcs}, for each function of your program GCC
3347 creates a program flow graph, then finds a spanning tree for the graph.
3348 Only arcs that are not on the spanning tree have to be instrumented: the
3349 compiler adds code to count the number of times that these arcs are
3350 executed. When an arc is the only exit or only entrance to a block, the
3351 instrumentation code can be added to the block; otherwise, a new basic
3352 block must be created to hold the instrumentation code.
3354 @item -ftree-based-profiling
3355 @opindex ftree-based-profiling
3356 This option is used in addition to @option{-fprofile-arcs} or
3357 @option{-fbranch-probabilities} to control whether those optimizations
3358 are performed on a tree-based or rtl-based internal representation.
3359 If you use this option when compiling with @option{-fprofile-arcs},
3360 you must also use it when compiling later with @option{-fbranch-probabilities}.
3361 Currently the tree-based optimization is in an early stage of
3362 development, and this option is recommended only for those people
3363 working on improving it.
3366 @item -ftest-coverage
3367 @opindex ftest-coverage
3368 Produce a notes file that the @command{gcov} code-coverage utility
3369 (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
3370 show program coverage. Each source file's note file is called
3371 @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
3372 above for a description of @var{auxname} and instructions on how to
3373 generate test coverage data. Coverage data will match the source files
3374 more closely, if you do not optimize.
3376 @item -d@var{letters}
3377 @item -fdump-rtl-@var{pass}
3379 Says to make debugging dumps during compilation at times specified by
3380 @var{letters}. This is used for debugging the RTL-based passes of the
3381 compiler. The file names for most of the dumps are made by appending a
3382 pass number and a word to the @var{dumpname}. @var{dumpname} is generated
3383 from the name of the output file, if explicitly specified and it is not
3384 an executable, otherwise it is the basename of the source file.
3386 Most debug dumps can be enabled either passing a letter to the @option{-d}
3387 option, or with a long @option{-fdump-rtl} switch; here are the possible
3388 letters for use in @var{letters} and @var{pass}, and their meanings:
3393 Annotate the assembler output with miscellaneous debugging information.
3396 @itemx -fdump-rtl-bp
3398 @opindex fdump-rtl-bp
3399 Dump after computing branch probabilities, to @file{@var{file}.09.bp}.
3402 @itemx -fdump-rtl-bbro
3404 @opindex fdump-rtl-bbro
3405 Dump after block reordering, to @file{@var{file}.30.bbro}.
3408 @itemx -fdump-rtl-combine
3410 @opindex fdump-rtl-combine
3411 Dump after instruction combination, to the file @file{@var{file}.17.combine}.
3414 @itemx -fdump-rtl-ce1
3415 @itemx -fdump-rtl-ce2
3417 @opindex fdump-rtl-ce1
3418 @opindex fdump-rtl-ce2
3419 @option{-dC} and @option{-fdump-rtl-ce1} enable dumping after the
3420 first if conversion, to the file @file{@var{file}.11.ce1}. @option{-dC}
3421 and @option{-fdump-rtl-ce2} enable dumping after the second if
3422 conversion, to the file @file{@var{file}.18.ce2}.
3425 @itemx -fdump-rtl-btl
3426 @itemx -fdump-rtl-dbr
3428 @opindex fdump-rtl-btl
3429 @opindex fdump-rtl-dbr
3430 @option{-dd} and @option{-fdump-rtl-btl} enable dumping after branch
3431 target load optimization, to to @file{@var{file}.31.btl}. @option{-dd}
3432 and @option{-fdump-rtl-dbr} enable dumping after delayed branch
3433 scheduling, to @file{@var{file}.36.dbr}.
3437 Dump all macro definitions, at the end of preprocessing, in addition to
3441 @itemx -fdump-rtl-ce3
3443 @opindex fdump-rtl-ce3
3444 Dump after the third if conversion, to @file{@var{file}.28.ce3}.
3447 @itemx -fdump-rtl-cfg
3448 @itemx -fdump-rtl-life
3450 @opindex fdump-rtl-cfg
3451 @opindex fdump-rtl-life
3452 @option{-df} and @option{-fdump-rtl-cfg} enable dumping after control
3453 and data flow analysis, to @file{@var{file}.08.cfg}. @option{-df}
3454 and @option{-fdump-rtl-cfg} enable dumping dump after life analysis,
3455 to @file{@var{file}.16.life}.
3458 @itemx -fdump-rtl-greg
3460 @opindex fdump-rtl-greg
3461 Dump after global register allocation, to @file{@var{file}.23.greg}.
3464 @itemx -fdump-rtl-gcse
3465 @itemx -fdump-rtl-bypass
3467 @opindex fdump-rtl-gcse
3468 @opindex fdump-rtl-bypass
3469 @option{-dG} and @option{-fdump-rtl-gcse} enable dumping after GCSE, to
3470 @file{@var{file}.05.gcse}. @option{-dG} and @option{-fdump-rtl-bypass}
3471 enable dumping after jump bypassing and control flow optimizations, to
3472 @file{@var{file}.07.bypass}.
3475 @itemx -fdump-rtl-eh
3477 @opindex fdump-rtl-eh
3478 Dump after finalization of EH handling code, to @file{@var{file}.02.eh}.
3481 @itemx -fdump-rtl-sibling
3483 @opindex fdump-rtl-sibling
3484 Dump after sibling call optimizations, to @file{@var{file}.01.sibling}.
3487 @itemx -fdump-rtl-jump
3489 @opindex fdump-rtl-jump
3490 Dump after the first jump optimization, to @file{@var{file}.03.jump}.
3493 @itemx -fdump-rtl-stack
3495 @opindex fdump-rtl-stack
3496 Dump after conversion from registers to stack, to @file{@var{file}.33.stack}.
3499 @itemx -fdump-rtl-lreg
3501 @opindex fdump-rtl-lreg
3502 Dump after local register allocation, to @file{@var{file}.22.lreg}.
3505 @itemx -fdump-rtl-loop
3506 @itemx -fdump-rtl-loop2
3508 @opindex fdump-rtl-loop
3509 @opindex fdump-rtl-loop2
3510 @option{-dL} and @option{-fdump-rtl-loop} enable dumping after the first
3511 loop optimization pass, to @file{@var{file}.06.loop}. @option{-dL} and
3512 @option{-fdump-rtl-loop2} enable dumping after the second pass, to
3513 @file{@var{file}.13.loop2}.
3516 @itemx -fdump-rtl-sms
3518 @opindex fdump-rtl-sms
3519 Dump after modulo scheduling, to @file{@var{file}.20.sms}.
3522 @itemx -fdump-rtl-mach
3524 @opindex fdump-rtl-mach
3525 Dump after performing the machine dependent reorganization pass, to
3526 @file{@var{file}.35.mach}.
3529 @itemx -fdump-rtl-rnreg
3531 @opindex fdump-rtl-rnreg
3532 Dump after register renumbering, to @file{@var{file}.29.rnreg}.
3535 @itemx -fdump-rtl-regmove
3537 @opindex fdump-rtl-regmove
3538 Dump after the register move pass, to @file{@var{file}.19.regmove}.
3541 @itemx -fdump-rtl-postreload
3543 @opindex fdump-rtl-postreload
3544 Dump after post-reload optimizations, to @file{@var{file}.24.postreload}.
3547 @itemx -fdump-rtl-expand
3549 @opindex fdump-rtl-expand
3550 Dump after RTL generation, to @file{@var{file}.00.expand}.
3553 @itemx -fdump-rtl-sched2
3555 @opindex fdump-rtl-sched2
3556 Dump after the second scheduling pass, to @file{@var{file}.32.sched2}.
3559 @itemx -fdump-rtl-cse
3561 @opindex fdump-rtl-cse
3562 Dump after CSE (including the jump optimization that sometimes follows
3563 CSE), to @file{@var{file}.04.cse}.
3566 @itemx -fdump-rtl-sched
3568 @opindex fdump-rtl-sched
3569 Dump after the first scheduling pass, to @file{@var{file}.21.sched}.
3572 @itemx -fdump-rtl-cse2
3574 @opindex fdump-rtl-cse2
3575 Dump after the second CSE pass (including the jump optimization that
3576 sometimes follows CSE), to @file{@var{file}.15.cse2}.
3579 @itemx -fdump-rtl-tracer
3581 @opindex fdump-rtl-tracer
3582 Dump after running tracer, to @file{@var{file}.12.tracer}.
3585 @itemx -fdump-rtl-vpt
3586 @itemx -fdump-rtl-vartrack
3588 @opindex fdump-rtl-vpt
3589 @opindex fdump-rtl-vartrack
3590 @option{-dV} and @option{-fdump-rtl-vpt} enable dumping after the value
3591 profile transformations, to @file{@var{file}.10.vpt}. @option{-dV}
3592 and @option{-fdump-rtl-vartrack} enable dumping after variable tracking,
3593 to @file{@var{file}.34.vartrack}.
3596 @itemx -fdump-rtl-flow2
3598 @opindex fdump-rtl-flow2
3599 Dump after the second flow pass, to @file{@var{file}.26.flow2}.
3602 @itemx -fdump-rtl-peephole2
3604 @opindex fdump-rtl-peephole2
3605 Dump after the peephole pass, to @file{@var{file}.27.peephole2}.
3608 @itemx -fdump-rtl-web
3610 @opindex fdump-rtl-web
3611 Dump after live range splitting, to @file{@var{file}.14.web}.
3614 @itemx -fdump-rtl-all
3616 @opindex fdump-rtl-all
3617 Produce all the dumps listed above.
3621 Produce a core dump whenever an error occurs.
3625 Print statistics on memory usage, at the end of the run, to
3630 Annotate the assembler output with a comment indicating which
3631 pattern and alternative was used. The length of each instruction is
3636 Dump the RTL in the assembler output as a comment before each instruction.
3637 Also turns on @option{-dp} annotation.
3641 For each of the other indicated dump files (either with @option{-d} or
3642 @option{-fdump-rtl-@var{pass}}), dump a representation of the control flow
3643 graph suitable for viewing with VCG to @file{@var{file}.@var{pass}.vcg}.
3647 Just generate RTL for a function instead of compiling it. Usually used
3648 with @samp{r} (@option{-fdump-rtl-expand}).
3652 Dump debugging information during parsing, to standard error.
3655 @item -fdump-unnumbered
3656 @opindex fdump-unnumbered
3657 When doing debugging dumps (see @option{-d} option above), suppress instruction
3658 numbers and line number note output. This makes it more feasible to
3659 use diff on debugging dumps for compiler invocations with different
3660 options, in particular with and without @option{-g}.
3662 @item -fdump-translation-unit @r{(C and C++ only)}
3663 @itemx -fdump-translation-unit-@var{options} @r{(C and C++ only)}
3664 @opindex fdump-translation-unit
3665 Dump a representation of the tree structure for the entire translation
3666 unit to a file. The file name is made by appending @file{.tu} to the
3667 source file name. If the @samp{-@var{options}} form is used, @var{options}
3668 controls the details of the dump as described for the
3669 @option{-fdump-tree} options.
3671 @item -fdump-class-hierarchy @r{(C++ only)}
3672 @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
3673 @opindex fdump-class-hierarchy
3674 Dump a representation of each class's hierarchy and virtual function
3675 table layout to a file. The file name is made by appending @file{.class}
3676 to the source file name. If the @samp{-@var{options}} form is used,
3677 @var{options} controls the details of the dump as described for the
3678 @option{-fdump-tree} options.
3680 @item -fdump-ipa-@var{switch}
3682 Control the dumping at various stages of inter-procedural analysis
3683 language tree to a file. The file name is generated by appending a switch
3684 specific suffix to the source file name. The following dumps are possible:
3688 Enables all inter-procedural analysis dumps; currently the only produced
3689 dump is the @samp{cgraph} dump.
3692 Dumps information about call-graph optimization, unused function removal,
3693 and inlining decisions.
3696 @item -fdump-tree-@var{switch} @r{(C and C++ only)}
3697 @itemx -fdump-tree-@var{switch}-@var{options} @r{(C and C++ only)}
3699 Control the dumping at various stages of processing the intermediate
3700 language tree to a file. The file name is generated by appending a switch
3701 specific suffix to the source file name. If the @samp{-@var{options}}
3702 form is used, @var{options} is a list of @samp{-} separated options that
3703 control the details of the dump. Not all options are applicable to all
3704 dumps, those which are not meaningful will be ignored. The following
3705 options are available
3709 Print the address of each node. Usually this is not meaningful as it
3710 changes according to the environment and source file. Its primary use
3711 is for tying up a dump file with a debug environment.
3713 Inhibit dumping of members of a scope or body of a function merely
3714 because that scope has been reached. Only dump such items when they
3715 are directly reachable by some other path. When dumping pretty-printed
3716 trees, this option inhibits dumping the bodies of control structures.
3718 Print a raw representation of the tree. By default, trees are
3719 pretty-printed into a C-like representation.
3721 Enable more detailed dumps (not honored by every dump option).
3723 Enable dumping various statistics about the pass (not honored by every dump
3726 Enable showing basic block boundaries (disabled in raw dumps).
3728 Enable showing virtual operands for every statement.
3730 Enable showing line numbers for statements.
3732 Enable showing the unique ID (@code{DECL_UID}) for each variable.
3734 Turn on all options, except @option{raw}, @option{slim} and @option{lineno}.
3737 The following tree dumps are possible:
3741 Dump before any tree based optimization, to @file{@var{file}.original}.
3744 Dump after all tree based optimization, to @file{@var{file}.optimized}.
3747 Dump after function inlining, to @file{@var{file}.inlined}.
3750 @opindex fdump-tree-gimple
3751 Dump each function before and after the gimplification pass to a file. The
3752 file name is made by appending @file{.gimple} to the source file name.
3755 @opindex fdump-tree-cfg
3756 Dump the control flow graph of each function to a file. The file name is
3757 made by appending @file{.cfg} to the source file name.
3760 @opindex fdump-tree-vcg
3761 Dump the control flow graph of each function to a file in VCG format. The
3762 file name is made by appending @file{.vcg} to the source file name. Note
3763 that if the file contains more than one function, the generated file cannot
3764 be used directly by VCG. You will need to cut and paste each function's
3765 graph into its own separate file first.
3768 @opindex fdump-tree-ch
3769 Dump each function after copying loop headers. The file name is made by
3770 appending @file{.ch} to the source file name.
3773 @opindex fdump-tree-ssa
3774 Dump SSA related information to a file. The file name is made by appending
3775 @file{.ssa} to the source file name.
3778 @opindex fdump-tree-alias
3779 Dump aliasing information for each function. The file name is made by
3780 appending @file{.alias} to the source file name.
3783 @opindex fdump-tree-ccp
3784 Dump each function after CCP. The file name is made by appending
3785 @file{.ccp} to the source file name.
3788 @opindex fdump-tree-pre
3789 Dump trees after partial redundancy elimination. The file name is made
3790 by appending @file{.pre} to the source file name.
3793 @opindex fdump-tree-fre
3794 Dump trees after full redundancy elimination. The file name is made
3795 by appending @file{.fre} to the source file name.
3798 @opindex fdump-tree-dce
3799 Dump each function after dead code elimination. The file name is made by
3800 appending @file{.dce} to the source file name.
3803 @opindex fdump-tree-mudflap
3804 Dump each function after adding mudflap instrumentation. The file name is
3805 made by appending @file{.mudflap} to the source file name.
3808 @opindex fdump-tree-sra
3809 Dump each function after performing scalar replacement of aggregates. The
3810 file name is made by appending @file{.sra} to the source file name.
3813 @opindex fdump-tree-dom
3814 Dump each function after applying dominator tree optimizations. The file
3815 name is made by appending @file{.dom} to the source file name.
3818 @opindex fdump-tree-dse
3819 Dump each function after applying dead store elimination. The file
3820 name is made by appending @file{.dse} to the source file name.
3823 @opindex fdump-tree-phiopt
3824 Dump each function after optimizing PHI nodes into straightline code. The file
3825 name is made by appending @file{.phiopt} to the source file name.
3828 @opindex fdump-tree-forwprop
3829 Dump each function after forward propagating single use variables. The file
3830 name is made by appending @file{.forwprop} to the source file name.
3833 @opindex fdump-tree-copyrename
3834 Dump each function after applying the copy rename optimization. The file
3835 name is made by appending @file{.copyrename} to the source file name.
3838 @opindex fdump-tree-nrv
3839 Dump each function after applying the named return value optimization on
3840 generic trees. The file name is made by appending @file{.nrv} to the source
3844 @opindex fdump-tree-vect
3845 Dump each function after applying vectorization of loops. The file name is
3846 made by appending @file{.vect} to the source file name.
3849 @opindex fdump-tree-all
3850 Enable all the available tree dumps with the flags provided in this option.
3853 @item -frandom-seed=@var{string}
3854 @opindex frandom-string
3855 This option provides a seed that GCC uses when it would otherwise use
3856 random numbers. It is used to generate certain symbol names
3857 that have to be different in every compiled file. It is also used to
3858 place unique stamps in coverage data files and the object files that
3859 produce them. You can use the @option{-frandom-seed} option to produce
3860 reproducibly identical object files.
3862 The @var{string} should be different for every file you compile.
3864 @item -fsched-verbose=@var{n}
3865 @opindex fsched-verbose
3866 On targets that use instruction scheduling, this option controls the
3867 amount of debugging output the scheduler prints. This information is
3868 written to standard error, unless @option{-dS} or @option{-dR} is
3869 specified, in which case it is output to the usual dump
3870 listing file, @file{.sched} or @file{.sched2} respectively. However
3871 for @var{n} greater than nine, the output is always printed to standard
3874 For @var{n} greater than zero, @option{-fsched-verbose} outputs the
3875 same information as @option{-dRS}. For @var{n} greater than one, it
3876 also output basic block probabilities, detailed ready list information
3877 and unit/insn info. For @var{n} greater than two, it includes RTL
3878 at abort point, control-flow and regions info. And for @var{n} over
3879 four, @option{-fsched-verbose} also includes dependence info.
3883 Store the usual ``temporary'' intermediate files permanently; place them
3884 in the current directory and name them based on the source file. Thus,
3885 compiling @file{foo.c} with @samp{-c -save-temps} would produce files
3886 @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
3887 preprocessed @file{foo.i} output file even though the compiler now
3888 normally uses an integrated preprocessor.
3892 Report the CPU time taken by each subprocess in the compilation
3893 sequence. For C source files, this is the compiler proper and assembler
3894 (plus the linker if linking is done). The output looks like this:
3901 The first number on each line is the ``user time'', that is time spent
3902 executing the program itself. The second number is ``system time'',
3903 time spent executing operating system routines on behalf of the program.
3904 Both numbers are in seconds.
3906 @item -fvar-tracking
3907 @opindex fvar-tracking
3908 Run variable tracking pass. It computes where variables are stored at each
3909 position in code. Better debugging information is then generated
3910 (if the debugging information format supports this information).
3912 It is enabled by default when compiling with optimization (@option{-Os},
3913 @option{-O}, @option{-O2}, ...), debugging information (@option{-g}) and
3914 the debug info format supports it.
3916 @item -print-file-name=@var{library}
3917 @opindex print-file-name
3918 Print the full absolute name of the library file @var{library} that
3919 would be used when linking---and don't do anything else. With this
3920 option, GCC does not compile or link anything; it just prints the
3923 @item -print-multi-directory
3924 @opindex print-multi-directory
3925 Print the directory name corresponding to the multilib selected by any
3926 other switches present in the command line. This directory is supposed
3927 to exist in @env{GCC_EXEC_PREFIX}.
3929 @item -print-multi-lib
3930 @opindex print-multi-lib
3931 Print the mapping from multilib directory names to compiler switches
3932 that enable them. The directory name is separated from the switches by
3933 @samp{;}, and each switch starts with an @samp{@@} instead of the
3934 @samp{-}, without spaces between multiple switches. This is supposed to
3935 ease shell-processing.
3937 @item -print-prog-name=@var{program}
3938 @opindex print-prog-name
3939 Like @option{-print-file-name}, but searches for a program such as @samp{cpp}.
3941 @item -print-libgcc-file-name
3942 @opindex print-libgcc-file-name
3943 Same as @option{-print-file-name=libgcc.a}.
3945 This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
3946 but you do want to link with @file{libgcc.a}. You can do
3949 gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
3952 @item -print-search-dirs
3953 @opindex print-search-dirs
3954 Print the name of the configured installation directory and a list of
3955 program and library directories @command{gcc} will search---and don't do anything else.
3957 This is useful when @command{gcc} prints the error message
3958 @samp{installation problem, cannot exec cpp0: No such file or directory}.
3959 To resolve this you either need to put @file{cpp0} and the other compiler
3960 components where @command{gcc} expects to find them, or you can set the environment
3961 variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
3962 Don't forget the trailing @samp{/}.
3963 @xref{Environment Variables}.
3966 @opindex dumpmachine
3967 Print the compiler's target machine (for example,
3968 @samp{i686-pc-linux-gnu})---and don't do anything else.
3971 @opindex dumpversion
3972 Print the compiler version (for example, @samp{3.0})---and don't do
3977 Print the compiler's built-in specs---and don't do anything else. (This
3978 is used when GCC itself is being built.) @xref{Spec Files}.
3980 @item -feliminate-unused-debug-types
3981 @opindex feliminate-unused-debug-types
3982 Normally, when producing DWARF2 output, GCC will emit debugging
3983 information for all types declared in a compilation
3984 unit, regardless of whether or not they are actually used
3985 in that compilation unit. Sometimes this is useful, such as
3986 if, in the debugger, you want to cast a value to a type that is
3987 not actually used in your program (but is declared). More often,
3988 however, this results in a significant amount of wasted space.
3989 With this option, GCC will avoid producing debug symbol output
3990 for types that are nowhere used in the source file being compiled.
3993 @node Optimize Options
3994 @section Options That Control Optimization
3995 @cindex optimize options
3996 @cindex options, optimization
3998 These options control various sorts of optimizations.
4000 Without any optimization option, the compiler's goal is to reduce the
4001 cost of compilation and to make debugging produce the expected
4002 results. Statements are independent: if you stop the program with a
4003 breakpoint between statements, you can then assign a new value to any
4004 variable or change the program counter to any other statement in the
4005 function and get exactly the results you would expect from the source
4008 Turning on optimization flags makes the compiler attempt to improve
4009 the performance and/or code size at the expense of compilation time
4010 and possibly the ability to debug the program.
4012 The compiler performs optimization based on the knowledge it has of
4013 the program. Optimization levels @option{-O2} and above, in
4014 particular, enable @emph{unit-at-a-time} mode, which allows the
4015 compiler to consider information gained from later functions in
4016 the file when compiling a function. Compiling multiple files at
4017 once to a single output file in @emph{unit-at-a-time} mode allows
4018 the compiler to use information gained from all of the files when
4019 compiling each of them.
4021 Not all optimizations are controlled directly by a flag. Only
4022 optimizations that have a flag are listed.
4029 Optimize. Optimizing compilation takes somewhat more time, and a lot
4030 more memory for a large function.
4032 With @option{-O}, the compiler tries to reduce code size and execution
4033 time, without performing any optimizations that take a great deal of
4036 @option{-O} turns on the following optimization flags:
4037 @gccoptlist{-fdefer-pop @gol
4038 -fmerge-constants @gol
4040 -floop-optimize @gol
4041 -fif-conversion @gol
4042 -fif-conversion2 @gol
4043 -fdelayed-branch @gol
4044 -fguess-branch-probability @gol
4047 @option{-O} also turns on @option{-fomit-frame-pointer} on machines
4048 where doing so does not interfere with debugging.
4052 Optimize even more. GCC performs nearly all supported optimizations
4053 that do not involve a space-speed tradeoff. The compiler does not
4054 perform loop unrolling or function inlining when you specify @option{-O2}.
4055 As compared to @option{-O}, this option increases both compilation time
4056 and the performance of the generated code.
4058 @option{-O2} turns on all optimization flags specified by @option{-O}. It
4059 also turns on the following optimization flags:
4060 @gccoptlist{-fforce-mem @gol
4061 -foptimize-sibling-calls @gol
4062 -fstrength-reduce @gol
4063 -fcse-follow-jumps -fcse-skip-blocks @gol
4064 -frerun-cse-after-loop -frerun-loop-opt @gol
4065 -fgcse -fgcse-lm -fgcse-sm -fgcse-las @gol
4066 -fdelete-null-pointer-checks @gol
4067 -fexpensive-optimizations @gol
4069 -fschedule-insns -fschedule-insns2 @gol
4070 -fsched-interblock -fsched-spec @gol
4073 -freorder-blocks -freorder-functions @gol
4074 -fstrict-aliasing @gol
4075 -funit-at-a-time @gol
4076 -falign-functions -falign-jumps @gol
4077 -falign-loops -falign-labels @gol
4080 Please note the warning under @option{-fgcse} about
4081 invoking @option{-O2} on programs that use computed gotos.
4085 Optimize yet more. @option{-O3} turns on all optimizations specified by
4086 @option{-O2} and also turns on the @option{-finline-functions},
4087 @option{-fweb} and @option{-fgcse-after-reload} options.
4091 Do not optimize. This is the default.
4095 Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
4096 do not typically increase code size. It also performs further
4097 optimizations designed to reduce code size.
4099 @option{-Os} disables the following optimization flags:
4100 @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
4101 -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays}
4103 If you use multiple @option{-O} options, with or without level numbers,
4104 the last such option is the one that is effective.
4107 Options of the form @option{-f@var{flag}} specify machine-independent
4108 flags. Most flags have both positive and negative forms; the negative
4109 form of @option{-ffoo} would be @option{-fno-foo}. In the table
4110 below, only one of the forms is listed---the one you typically will
4111 use. You can figure out the other form by either removing @samp{no-}
4114 The following options control specific optimizations. They are either
4115 activated by @option{-O} options or are related to ones that are. You
4116 can use the following flags in the rare cases when ``fine-tuning'' of
4117 optimizations to be performed is desired.
4120 @item -fno-default-inline
4121 @opindex fno-default-inline
4122 Do not make member functions inline by default merely because they are
4123 defined inside the class scope (C++ only). Otherwise, when you specify
4124 @w{@option{-O}}, member functions defined inside class scope are compiled
4125 inline by default; i.e., you don't need to add @samp{inline} in front of
4126 the member function name.
4128 @item -fno-defer-pop
4129 @opindex fno-defer-pop
4130 Always pop the arguments to each function call as soon as that function
4131 returns. For machines which must pop arguments after a function call,
4132 the compiler normally lets arguments accumulate on the stack for several
4133 function calls and pops them all at once.
4135 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4139 Force memory operands to be copied into registers before doing
4140 arithmetic on them. This produces better code by making all memory
4141 references potential common subexpressions. When they are not common
4142 subexpressions, instruction combination should eliminate the separate
4145 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4148 @opindex fforce-addr
4149 Force memory address constants to be copied into registers before
4150 doing arithmetic on them. This may produce better code just as
4151 @option{-fforce-mem} may.
4153 @item -fomit-frame-pointer
4154 @opindex fomit-frame-pointer
4155 Don't keep the frame pointer in a register for functions that
4156 don't need one. This avoids the instructions to save, set up and
4157 restore frame pointers; it also makes an extra register available
4158 in many functions. @strong{It also makes debugging impossible on
4161 On some machines, such as the VAX, this flag has no effect, because
4162 the standard calling sequence automatically handles the frame pointer
4163 and nothing is saved by pretending it doesn't exist. The
4164 machine-description macro @code{FRAME_POINTER_REQUIRED} controls
4165 whether a target machine supports this flag. @xref{Registers,,Register
4166 Usage, gccint, GNU Compiler Collection (GCC) Internals}.
4168 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4170 @item -foptimize-sibling-calls
4171 @opindex foptimize-sibling-calls
4172 Optimize sibling and tail recursive calls.
4174 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4178 Don't pay attention to the @code{inline} keyword. Normally this option
4179 is used to keep the compiler from expanding any functions inline.
4180 Note that if you are not optimizing, no functions can be expanded inline.
4182 @item -finline-functions
4183 @opindex finline-functions
4184 Integrate all simple functions into their callers. The compiler
4185 heuristically decides which functions are simple enough to be worth
4186 integrating in this way.
4188 If all calls to a given function are integrated, and the function is
4189 declared @code{static}, then the function is normally not output as
4190 assembler code in its own right.
4192 Enabled at level @option{-O3}.
4194 @item -finline-limit=@var{n}
4195 @opindex finline-limit
4196 By default, GCC limits the size of functions that can be inlined. This flag
4197 allows the control of this limit for functions that are explicitly marked as
4198 inline (i.e., marked with the inline keyword or defined within the class
4199 definition in c++). @var{n} is the size of functions that can be inlined in
4200 number of pseudo instructions (not counting parameter handling). The default
4201 value of @var{n} is 600.
4202 Increasing this value can result in more inlined code at
4203 the cost of compilation time and memory consumption. Decreasing usually makes
4204 the compilation faster and less code will be inlined (which presumably
4205 means slower programs). This option is particularly useful for programs that
4206 use inlining heavily such as those based on recursive templates with C++.
4208 Inlining is actually controlled by a number of parameters, which may be
4209 specified individually by using @option{--param @var{name}=@var{value}}.
4210 The @option{-finline-limit=@var{n}} option sets some of these parameters
4214 @item max-inline-insns-single
4215 is set to @var{n}/2.
4216 @item max-inline-insns-auto
4217 is set to @var{n}/2.
4218 @item min-inline-insns
4219 is set to 130 or @var{n}/4, whichever is smaller.
4220 @item max-inline-insns-rtl
4224 See below for a documentation of the individual
4225 parameters controlling inlining.
4227 @emph{Note:} pseudo instruction represents, in this particular context, an
4228 abstract measurement of function's size. In no way, it represents a count
4229 of assembly instructions and as such its exact meaning might change from one
4230 release to an another.
4232 @item -fkeep-inline-functions
4233 @opindex fkeep-inline-functions
4234 In C, emit @code{static} functions that are declared @code{inline}
4235 into the object file, even if the function has been inlined into all
4236 of its callers. This switch does not affect functions using the
4237 @code{extern inline} extension in GNU C. In C++, emit any and all
4238 inline functions into the object file.
4240 @item -fkeep-static-consts
4241 @opindex fkeep-static-consts
4242 Emit variables declared @code{static const} when optimization isn't turned
4243 on, even if the variables aren't referenced.
4245 GCC enables this option by default. If you want to force the compiler to
4246 check if the variable was referenced, regardless of whether or not
4247 optimization is turned on, use the @option{-fno-keep-static-consts} option.
4249 @item -fmerge-constants
4250 Attempt to merge identical constants (string constants and floating point
4251 constants) across compilation units.
4253 This option is the default for optimized compilation if the assembler and
4254 linker support it. Use @option{-fno-merge-constants} to inhibit this
4257 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4259 @item -fmerge-all-constants
4260 Attempt to merge identical constants and identical variables.
4262 This option implies @option{-fmerge-constants}. In addition to
4263 @option{-fmerge-constants} this considers e.g.@: even constant initialized
4264 arrays or initialized constant variables with integral or floating point
4265 types. Languages like C or C++ require each non-automatic variable to
4266 have distinct location, so using this option will result in non-conforming
4269 @item -fmodulo-sched
4270 @opindex fmodulo-sched
4271 Perform swing modulo scheduling immediately before the first scheduling
4272 pass. This pass looks at innermost loops and reorders their
4273 instructions by overlapping different iterations.
4277 Use a graph coloring register allocator. Currently this option is meant
4278 only for testing. Users should not specify this option, since it is not
4279 yet ready for production use.
4281 @item -fno-branch-count-reg
4282 @opindex fno-branch-count-reg
4283 Do not use ``decrement and branch'' instructions on a count register,
4284 but instead generate a sequence of instructions that decrement a
4285 register, compare it against zero, then branch based upon the result.
4286 This option is only meaningful on architectures that support such
4287 instructions, which include x86, PowerPC, IA-64 and S/390.
4289 The default is @option{-fbranch-count-reg}, enabled when
4290 @option{-fstrength-reduce} is enabled.
4292 @item -fno-function-cse
4293 @opindex fno-function-cse
4294 Do not put function addresses in registers; make each instruction that
4295 calls a constant function contain the function's address explicitly.
4297 This option results in less efficient code, but some strange hacks
4298 that alter the assembler output may be confused by the optimizations
4299 performed when this option is not used.
4301 The default is @option{-ffunction-cse}
4303 @item -fno-zero-initialized-in-bss
4304 @opindex fno-zero-initialized-in-bss
4305 If the target supports a BSS section, GCC by default puts variables that
4306 are initialized to zero into BSS@. This can save space in the resulting
4309 This option turns off this behavior because some programs explicitly
4310 rely on variables going to the data section. E.g., so that the
4311 resulting executable can find the beginning of that section and/or make
4312 assumptions based on that.
4314 The default is @option{-fzero-initialized-in-bss}.
4316 @item -fbounds-check
4317 @opindex fbounds-check
4318 For front-ends that support it, generate additional code to check that
4319 indices used to access arrays are within the declared range. This is
4320 currently only supported by the Java and Fortran front-ends, where
4321 this option defaults to true and false respectively.
4323 @item -fmudflap -fmudflapth -fmudflapir
4327 @cindex bounds checking
4329 For front-ends that support it (C and C++), instrument all risky
4330 pointer/array dereferencing operations, some standard library
4331 string/heap functions, and some other associated constructs with
4332 range/validity tests. Modules so instrumented should be immune to
4333 buffer overflows, invalid heap use, and some other classes of C/C++
4334 programming errors. The instrumentation relies on a separate runtime
4335 library (@file{libmudflap}), which will be linked into a program if
4336 @option{-fmudflap} is given at link time. Run-time behavior of the
4337 instrumented program is controlled by the @env{MUDFLAP_OPTIONS}
4338 environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out}
4341 Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to
4342 link if your program is multi-threaded. Use @option{-fmudflapir}, in
4343 addition to @option{-fmudflap} or @option{-fmudflapth}, if
4344 instrumentation should ignore pointer reads. This produces less
4345 instrumentation (and therefore faster execution) and still provides
4346 some protection against outright memory corrupting writes, but allows
4347 erroneously read data to propagate within a program.
4349 @item -fstrength-reduce
4350 @opindex fstrength-reduce
4351 Perform the optimizations of loop strength reduction and
4352 elimination of iteration variables.
4354 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4356 @item -fthread-jumps
4357 @opindex fthread-jumps
4358 Perform optimizations where we check to see if a jump branches to a
4359 location where another comparison subsumed by the first is found. If
4360 so, the first branch is redirected to either the destination of the
4361 second branch or a point immediately following it, depending on whether
4362 the condition is known to be true or false.
4364 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4366 @item -fcse-follow-jumps
4367 @opindex fcse-follow-jumps
4368 In common subexpression elimination, scan through jump instructions
4369 when the target of the jump is not reached by any other path. For
4370 example, when CSE encounters an @code{if} statement with an
4371 @code{else} clause, CSE will follow the jump when the condition
4374 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4376 @item -fcse-skip-blocks
4377 @opindex fcse-skip-blocks
4378 This is similar to @option{-fcse-follow-jumps}, but causes CSE to
4379 follow jumps which conditionally skip over blocks. When CSE
4380 encounters a simple @code{if} statement with no else clause,
4381 @option{-fcse-skip-blocks} causes CSE to follow the jump around the
4382 body of the @code{if}.
4384 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4386 @item -frerun-cse-after-loop
4387 @opindex frerun-cse-after-loop
4388 Re-run common subexpression elimination after loop optimizations has been
4391 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4393 @item -frerun-loop-opt
4394 @opindex frerun-loop-opt
4395 Run the loop optimizer twice.
4397 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4401 Perform a global common subexpression elimination pass.
4402 This pass also performs global constant and copy propagation.
4404 @emph{Note:} When compiling a program using computed gotos, a GCC
4405 extension, you may get better runtime performance if you disable
4406 the global common subexpression elimination pass by adding
4407 @option{-fno-gcse} to the command line.
4409 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4413 When @option{-fgcse-lm} is enabled, global common subexpression elimination will
4414 attempt to move loads which are only killed by stores into themselves. This
4415 allows a loop containing a load/store sequence to be changed to a load outside
4416 the loop, and a copy/store within the loop.
4418 Enabled by default when gcse is enabled.
4422 When @option{-fgcse-sm} is enabled, a store motion pass is run after
4423 global common subexpression elimination. This pass will attempt to move
4424 stores out of loops. When used in conjunction with @option{-fgcse-lm},
4425 loops containing a load/store sequence can be changed to a load before
4426 the loop and a store after the loop.
4428 Enabled by default when gcse is enabled.
4432 When @option{-fgcse-las} is enabled, the global common subexpression
4433 elimination pass eliminates redundant loads that come after stores to the
4434 same memory location (both partial and full redundancies).
4436 Enabled by default when gcse is enabled.
4438 @item -fgcse-after-reload
4439 @opindex fgcse-after-reload
4440 When @option{-fgcse-after-reload} is enabled, a redundant load elimination
4441 pass is performed after reload. The purpose of this pass is to cleanup
4444 @item -floop-optimize
4445 @opindex floop-optimize
4446 Perform loop optimizations: move constant expressions out of loops, simplify
4447 exit test conditions and optionally do strength-reduction as well.
4449 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4451 @item -floop-optimize2
4452 @opindex floop-optimize2
4453 Perform loop optimizations using the new loop optimizer. The optimizations
4454 (loop unrolling, peeling and unswitching, loop invariant motion) are enabled
4457 @item -fcrossjumping
4458 @opindex crossjumping
4459 Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
4460 resulting code may or may not perform better than without cross-jumping.
4462 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4464 @item -fif-conversion
4465 @opindex if-conversion
4466 Attempt to transform conditional jumps into branch-less equivalents. This
4467 include use of conditional moves, min, max, set flags and abs instructions, and
4468 some tricks doable by standard arithmetics. The use of conditional execution
4469 on chips where it is available is controlled by @code{if-conversion2}.
4471 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4473 @item -fif-conversion2
4474 @opindex if-conversion2
4475 Use conditional execution (where available) to transform conditional jumps into
4476 branch-less equivalents.
4478 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4480 @item -fdelete-null-pointer-checks
4481 @opindex fdelete-null-pointer-checks
4482 Use global dataflow analysis to identify and eliminate useless checks
4483 for null pointers. The compiler assumes that dereferencing a null
4484 pointer would have halted the program. If a pointer is checked after
4485 it has already been dereferenced, it cannot be null.
4487 In some environments, this assumption is not true, and programs can
4488 safely dereference null pointers. Use
4489 @option{-fno-delete-null-pointer-checks} to disable this optimization
4490 for programs which depend on that behavior.
4492 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4494 @item -fexpensive-optimizations
4495 @opindex fexpensive-optimizations
4496 Perform a number of minor optimizations that are relatively expensive.
4498 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4500 @item -foptimize-register-move
4502 @opindex foptimize-register-move
4504 Attempt to reassign register numbers in move instructions and as
4505 operands of other simple instructions in order to maximize the amount of
4506 register tying. This is especially helpful on machines with two-operand
4509 Note @option{-fregmove} and @option{-foptimize-register-move} are the same
4512 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4514 @item -fdelayed-branch
4515 @opindex fdelayed-branch
4516 If supported for the target machine, attempt to reorder instructions
4517 to exploit instruction slots available after delayed branch
4520 Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4522 @item -fschedule-insns
4523 @opindex fschedule-insns
4524 If supported for the target machine, attempt to reorder instructions to
4525 eliminate execution stalls due to required data being unavailable. This
4526 helps machines that have slow floating point or memory load instructions
4527 by allowing other instructions to be issued until the result of the load
4528 or floating point instruction is required.
4530 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4532 @item -fschedule-insns2
4533 @opindex fschedule-insns2
4534 Similar to @option{-fschedule-insns}, but requests an additional pass of
4535 instruction scheduling after register allocation has been done. This is
4536 especially useful on machines with a relatively small number of
4537 registers and where memory load instructions take more than one cycle.
4539 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4541 @item -fno-sched-interblock
4542 @opindex fno-sched-interblock
4543 Don't schedule instructions across basic blocks. This is normally
4544 enabled by default when scheduling before register allocation, i.e.@:
4545 with @option{-fschedule-insns} or at @option{-O2} or higher.
4547 @item -fno-sched-spec
4548 @opindex fno-sched-spec
4549 Don't allow speculative motion of non-load instructions. This is normally
4550 enabled by default when scheduling before register allocation, i.e.@:
4551 with @option{-fschedule-insns} or at @option{-O2} or higher.
4553 @item -fsched-spec-load
4554 @opindex fsched-spec-load
4555 Allow speculative motion of some load instructions. This only makes
4556 sense when scheduling before register allocation, i.e.@: with
4557 @option{-fschedule-insns} or at @option{-O2} or higher.
4559 @item -fsched-spec-load-dangerous
4560 @opindex fsched-spec-load-dangerous
4561 Allow speculative motion of more load instructions. This only makes
4562 sense when scheduling before register allocation, i.e.@: with
4563 @option{-fschedule-insns} or at @option{-O2} or higher.
4565 @item -fsched-stalled-insns=@var{n}
4566 @opindex fsched-stalled-insns
4567 Define how many insns (if any) can be moved prematurely from the queue
4568 of stalled insns into the ready list, during the second scheduling pass.
4570 @item -fsched-stalled-insns-dep=@var{n}
4571 @opindex fsched-stalled-insns-dep
4572 Define how many insn groups (cycles) will be examined for a dependency
4573 on a stalled insn that is candidate for premature removal from the queue
4574 of stalled insns. Has an effect only during the second scheduling pass,
4575 and only if @option{-fsched-stalled-insns} is used and its value is not zero.
4577 @item -fsched2-use-superblocks
4578 @opindex fsched2-use-superblocks
4579 When scheduling after register allocation, do use superblock scheduling
4580 algorithm. Superblock scheduling allows motion across basic block boundaries
4581 resulting on faster schedules. This option is experimental, as not all machine
4582 descriptions used by GCC model the CPU closely enough to avoid unreliable
4583 results from the algorithm.
4585 This only makes sense when scheduling after register allocation, i.e.@: with
4586 @option{-fschedule-insns2} or at @option{-O2} or higher.
4588 @item -fsched2-use-traces
4589 @opindex fsched2-use-traces
4590 Use @option{-fsched2-use-superblocks} algorithm when scheduling after register
4591 allocation and additionally perform code duplication in order to increase the
4592 size of superblocks using tracer pass. See @option{-ftracer} for details on
4595 This mode should produce faster but significantly longer programs. Also
4596 without @option{-fbranch-probabilities} the traces constructed may not
4597 match the reality and hurt the performance. This only makes
4598 sense when scheduling after register allocation, i.e.@: with
4599 @option{-fschedule-insns2} or at @option{-O2} or higher.
4601 @item -freschedule-modulo-scheduled-loops
4602 @opindex fscheduling-in-modulo-scheduled-loops
4603 The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
4604 we may want to prevent the later scheduling passes from changing its schedule, we use this
4605 option to control that.
4607 @item -fcaller-saves
4608 @opindex fcaller-saves
4609 Enable values to be allocated in registers that will be clobbered by
4610 function calls, by emitting extra instructions to save and restore the
4611 registers around such calls. Such allocation is done only when it
4612 seems to result in better code than would otherwise be produced.
4614 This option is always enabled by default on certain machines, usually
4615 those which have no call-preserved registers to use instead.
4617 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4620 Perform Partial Redundancy Elimination (PRE) on trees. This flag is
4621 enabled by default at @option{-O} and higher.
4624 Perform Full Redundancy Elimination (FRE) on trees. The difference
4625 between FRE and PRE is that FRE only considers expressions
4626 that are computed on all paths leading to the redundant computation.
4627 This analysis faster than PRE, though it exposes fewer redundancies.
4628 This flag is enabled by default at @option{-O} and higher.
4631 Perform sparse conditional constant propagation (CCP) on trees. This flag
4632 is enabled by default at @option{-O} and higher.
4635 Perform dead code elimination (DCE) on trees. This flag is enabled by
4636 default at @option{-O} and higher.
4638 @item -ftree-dominator-opts
4639 Perform dead code elimination (DCE) on trees. This flag is enabled by
4640 default at @option{-O} and higher.
4643 Perform loop header copying on trees. This is beneficial since it increases
4644 effectiveness of code motion optimizations. It also saves one jump. This flag
4645 is enabled by default at @option{-O} and higher. It is not enabled
4646 for @option{-Os}, since it usually increases code size.
4648 @item -ftree-loop-optimize
4649 Perform loop optimizations on trees. This flag is enabled by default
4650 at @option{-O} and higher.
4652 @item -ftree-loop-linear
4653 Perform linear loop transformations on tree. This flag can improve cache
4654 performance and allow further loop optimizations to take place.
4657 Perform loop invariant motion on trees. This pass moves only invartiants that
4658 would be hard to handle on rtl level (function calls, operations that expand to
4659 nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
4660 operands of conditions that are invariant out of the loop, so that we can use
4661 just trivial invariantness analysis in loop unswitching. The pass also includes
4665 Create a canonical counter for number of iterations in the loop for that
4666 determining number of iterations requires complicated analysis. Later
4667 optimizations then may determine the number easily. Useful especially
4668 in connection with unrolling.
4671 Perform induction variable optimizations (strength reduction, induction
4672 variable merging and induction variable elimination) on trees.
4675 Perform scalar replacement of aggregates. This pass replaces structure
4676 references with scalars to prevent committing structures to memory too
4677 early. This flag is enabled by default at @option{-O} and higher.
4679 @item -ftree-copyrename
4680 Perform copy renaming on trees. This pass attempts to rename compiler
4681 temporaries to other variables at copy locations, usually resulting in
4682 variable names which more closely resemble the original variables. This flag
4683 is enabled by default at @option{-O} and higher.
4686 Perform temporary expression replacement during the SSA->normal phase. Single
4687 use/single def temporaries are replaced at their use location with their
4688 defining expression. This results in non-GIMPLE code, but gives the expanders
4689 much more complex trees to work on resulting in better RTL generation. This is
4690 enabled by default at @option{-O} and higher.
4693 Perform live range splitting during the SSA->normal phase. Distinct live
4694 ranges of a variable are split into unique variables, allowing for better
4695 optimization later. This is enabled by default at @option{-O} and higher.
4697 @item -ftree-vectorize
4698 Perform loop vectorization on trees.
4702 Perform tail duplication to enlarge superblock size. This transformation
4703 simplifies the control flow of the function allowing other optimizations to do
4706 @item -funroll-loops
4707 @opindex funroll-loops
4708 Unroll loops whose number of iterations can be determined at compile
4709 time or upon entry to the loop. @option{-funroll-loops} implies both
4710 @option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
4711 option makes code larger, and may or may not make it run faster.
4713 @item -funroll-all-loops
4714 @opindex funroll-all-loops
4715 Unroll all loops, even if their number of iterations is uncertain when
4716 the loop is entered. This usually makes programs run more slowly.
4717 @option{-funroll-all-loops} implies the same options as
4718 @option{-funroll-loops},
4720 @item -fsplit-ivs-in-unroller
4721 @opindex -fsplit-ivs-in-unroller
4722 Enables expressing of values of induction variables in later iterations
4723 of the unrolled loop using the value in the first iteration. This breaks
4724 long dependency chains, thus improving efficiency of the scheduling passes
4725 (for best results, @option{-fweb} should be used as well).
4727 Combination of @option{-fweb} and CSE is often sufficient to obtain the
4728 same effect. However in cases the loop body is more complicated than
4729 a single basic block, this is not reliable. It also does not work at all
4730 on some of the architectures due to restrictions in the CSE pass.
4732 This optimization is enabled by default.
4734 @item -fvariable-expansion-in-unroller
4735 @opindex -fvariable-expansion-in-unroller
4736 With this option, the compiler will create multiple copies of some
4737 local variables when unrolling a loop which can result in superior code.
4739 @item -fprefetch-loop-arrays
4740 @opindex fprefetch-loop-arrays
4741 If supported by the target machine, generate instructions to prefetch
4742 memory to improve the performance of loops that access large arrays.
4744 These options may generate better or worse code; results are highly
4745 dependent on the structure of loops within the source code.
4748 @itemx -fno-peephole2
4749 @opindex fno-peephole
4750 @opindex fno-peephole2
4751 Disable any machine-specific peephole optimizations. The difference
4752 between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
4753 are implemented in the compiler; some targets use one, some use the
4754 other, a few use both.
4756 @option{-fpeephole} is enabled by default.
4757 @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4759 @item -fno-guess-branch-probability
4760 @opindex fno-guess-branch-probability
4761 Do not guess branch probabilities using a randomized model.
4763 Sometimes GCC will opt to use a randomized model to guess branch
4764 probabilities, when none are available from either profiling feedback
4765 (@option{-fprofile-arcs}) or @samp{__builtin_expect}. This means that
4766 different runs of the compiler on the same program may produce different
4769 In a hard real-time system, people don't want different runs of the
4770 compiler to produce code that has different behavior; minimizing
4771 non-determinism is of paramount import. This switch allows users to
4772 reduce non-determinism, possibly at the expense of inferior
4775 The default is @option{-fguess-branch-probability} at levels
4776 @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4778 @item -freorder-blocks
4779 @opindex freorder-blocks
4780 Reorder basic blocks in the compiled function in order to reduce number of
4781 taken branches and improve code locality.
4783 Enabled at levels @option{-O2}, @option{-O3}.
4785 @item -freorder-blocks-and-partition
4786 @opindex freorder-blocks-and-partition
4787 In addition to reordering basic blocks in the compiled function, in order
4788 to reduce number of taken branches, partitions hot and cold basic blocks
4789 into separate sections of the assembly and .o files, to improve
4790 paging and cache locality performance.
4792 This optimization is automatically turned off in the presence of
4793 exception handling, for linkonce sections, for functions with a user-defined
4794 section attribute and on any architecture that does not support named
4797 @item -freorder-functions
4798 @opindex freorder-functions
4799 Reorder basic blocks in the compiled function in order to reduce number of
4800 taken branches and improve code locality. This is implemented by using special
4801 subsections @code{.text.hot} for most frequently executed functions and
4802 @code{.text.unlikely} for unlikely executed functions. Reordering is done by
4803 the linker so object file format must support named sections and linker must
4804 place them in a reasonable way.
4806 Also profile feedback must be available in to make this option effective. See
4807 @option{-fprofile-arcs} for details.
4809 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4811 @item -fstrict-aliasing
4812 @opindex fstrict-aliasing
4813 Allows the compiler to assume the strictest aliasing rules applicable to
4814 the language being compiled. For C (and C++), this activates
4815 optimizations based on the type of expressions. In particular, an
4816 object of one type is assumed never to reside at the same address as an
4817 object of a different type, unless the types are almost the same. For
4818 example, an @code{unsigned int} can alias an @code{int}, but not a
4819 @code{void*} or a @code{double}. A character type may alias any other
4822 Pay special attention to code like this:
4835 The practice of reading from a different union member than the one most
4836 recently written to (called ``type-punning'') is common. Even with
4837 @option{-fstrict-aliasing}, type-punning is allowed, provided the memory
4838 is accessed through the union type. So, the code above will work as
4839 expected. However, this code might not:
4850 Every language that wishes to perform language-specific alias analysis
4851 should define a function that computes, given an @code{tree}
4852 node, an alias set for the node. Nodes in different alias sets are not
4853 allowed to alias. For an example, see the C front-end function
4854 @code{c_get_alias_set}.
4856 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
4858 @item -falign-functions
4859 @itemx -falign-functions=@var{n}
4860 @opindex falign-functions
4861 Align the start of functions to the next power-of-two greater than
4862 @var{n}, skipping up to @var{n} bytes. For instance,
4863 @option{-falign-functions=32} aligns functions to the next 32-byte
4864 boundary, but @option{-falign-functions=24} would align to the next
4865 32-byte boundary only if this can be done by skipping 23 bytes or less.
4867 @option{-fno-align-functions} and @option{-falign-functions=1} are
4868 equivalent and mean that functions will not be aligned.
4870 Some assemblers only support this flag when @var{n} is a power of two;
4871 in that case, it is rounded up.
4873 If @var{n} is not specified or is zero, use a machine-dependent default.
4875 Enabled at levels @option{-O2}, @option{-O3}.
4877 @item -falign-labels
4878 @itemx -falign-labels=@var{n}
4879 @opindex falign-labels
4880 Align all branch targets to a power-of-two boundary, skipping up to
4881 @var{n} bytes like @option{-falign-functions}. This option can easily
4882 make code slower, because it must insert dummy operations for when the
4883 branch target is reached in the usual flow of the code.
4885 @option{-fno-align-labels} and @option{-falign-labels=1} are
4886 equivalent and mean that labels will not be aligned.
4888 If @option{-falign-loops} or @option{-falign-jumps} are applicable and
4889 are greater than this value, then their values are used instead.
4891 If @var{n} is not specified or is zero, use a machine-dependent default
4892 which is very likely to be @samp{1}, meaning no alignment.
4894 Enabled at levels @option{-O2}, @option{-O3}.
4897 @itemx -falign-loops=@var{n}
4898 @opindex falign-loops
4899 Align loops to a power-of-two boundary, skipping up to @var{n} bytes
4900 like @option{-falign-functions}. The hope is that the loop will be
4901 executed many times, which will make up for any execution of the dummy
4904 @option{-fno-align-loops} and @option{-falign-loops=1} are
4905 equivalent and mean that loops will not be aligned.
4907 If @var{n} is not specified or is zero, use a machine-dependent default.
4909 Enabled at levels @option{-O2}, @option{-O3}.
4912 @itemx -falign-jumps=@var{n}
4913 @opindex falign-jumps
4914 Align branch targets to a power-of-two boundary, for branch targets
4915 where the targets can only be reached by jumping, skipping up to @var{n}
4916 bytes like @option{-falign-functions}. In this case, no dummy operations
4919 @option{-fno-align-jumps} and @option{-falign-jumps=1} are
4920 equivalent and mean that loops will not be aligned.
4922 If @var{n} is not specified or is zero, use a machine-dependent default.
4924 Enabled at levels @option{-O2}, @option{-O3}.
4926 @item -funit-at-a-time
4927 @opindex funit-at-a-time
4928 Parse the whole compilation unit before starting to produce code.
4929 This allows some extra optimizations to take place but consumes
4930 more memory (in general). There are some compatibility issues
4931 with @emph{unit-at-at-time} mode:
4934 enabling @emph{unit-at-a-time} mode may change the order
4935 in which functions, variables, and top-level @code{asm} statements
4936 are emitted, and will likely break code relying on some particular
4937 ordering. The majority of such top-level @code{asm} statements,
4938 though, can be replaced by @code{section} attributes.
4941 @emph{unit-at-a-time} mode removes unreferenced static variables
4942 and functions are removed. This may result in undefined references
4943 when an @code{asm} statement refers directly to variables or functions
4944 that are otherwise unused. In that case either the variable/function
4945 shall be listed as an operand of the @code{asm} statement operand or,
4946 in the case of top-level @code{asm} statements the attribute @code{used}
4947 shall be used on the declaration.
4950 Static functions now can use non-standard passing conventions that
4951 may break @code{asm} statements calling functions directly. Again,
4952 attribute @code{used} will prevent this behavior.
4955 As a temporary workaround, @option{-fno-unit-at-a-time} can be used,
4956 but this scheme may not be supported by future releases of GCC.
4958 Enabled at levels @option{-O2}, @option{-O3}.
4962 Constructs webs as commonly used for register allocation purposes and assign
4963 each web individual pseudo register. This allows the register allocation pass
4964 to operate on pseudos directly, but also strengthens several other optimization
4965 passes, such as CSE, loop optimizer and trivial dead code remover. It can,
4966 however, make debugging impossible, since variables will no longer stay in a
4969 Enabled at levels @option{-O2}, @option{-O3}, @option{-Os},
4970 on targets where the default format for debugging information supports
4973 @item -fno-cprop-registers
4974 @opindex fno-cprop-registers
4975 After register allocation and post-register allocation instruction splitting,
4976 we perform a copy-propagation pass to try to reduce scheduling dependencies
4977 and occasionally eliminate the copy.
4979 Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
4981 @item -fprofile-generate
4982 @opindex fprofile-generate
4984 Enable options usually used for instrumenting application to produce
4985 profile useful for later recompilation with profile feedback based
4986 optimization. You must use @option{-fprofile-generate} both when
4987 compiling and when linking your program.
4989 The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}.
4992 @opindex fprofile-use
4993 Enable profile feedback directed optimizations, and optimizations
4994 generally profitable only with profile feedback available.
4996 The following options are enabled: @code{-fbranch-probabilities},
4997 @code{-fvpt}, @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer}.
5001 The following options control compiler behavior regarding floating
5002 point arithmetic. These options trade off between speed and
5003 correctness. All must be specifically enabled.
5007 @opindex ffloat-store
5008 Do not store floating point variables in registers, and inhibit other
5009 options that might change whether a floating point value is taken from a
5012 @cindex floating point precision
5013 This option prevents undesirable excess precision on machines such as
5014 the 68000 where the floating registers (of the 68881) keep more
5015 precision than a @code{double} is supposed to have. Similarly for the
5016 x86 architecture. For most programs, the excess precision does only
5017 good, but a few programs rely on the precise definition of IEEE floating
5018 point. Use @option{-ffloat-store} for such programs, after modifying
5019 them to store all pertinent intermediate computations into variables.
5023 Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
5024 @option{-fno-trapping-math}, @option{-ffinite-math-only},
5025 @option{-fno-rounding-math} and @option{-fno-signaling-nans}.
5027 This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
5029 This option should never be turned on by any @option{-O} option since
5030 it can result in incorrect output for programs which depend on
5031 an exact implementation of IEEE or ISO rules/specifications for
5034 @item -fno-math-errno
5035 @opindex fno-math-errno
5036 Do not set ERRNO after calling math functions that are executed
5037 with a single instruction, e.g., sqrt. A program that relies on
5038 IEEE exceptions for math error handling may want to use this flag
5039 for speed while maintaining IEEE arithmetic compatibility.
5041 This option should never be turned on by any @option{-O} option since
5042 it can result in incorrect output for programs which depend on
5043 an exact implementation of IEEE or ISO rules/specifications for
5046 The default is @option{-fmath-errno}.
5048 @item -funsafe-math-optimizations
5049 @opindex funsafe-math-optimizations
5050 Allow optimizations for floating-point arithmetic that (a) assume
5051 that arguments and results are valid and (b) may violate IEEE or
5052 ANSI standards. When used at link-time, it may include libraries
5053 or startup files that change the default FPU control word or other
5054 similar optimizations.
5056 This option should never be turned on by any @option{-O} option since
5057 it can result in incorrect output for programs which depend on
5058 an exact implementation of IEEE or ISO rules/specifications for
5061 The default is @option{-fno-unsafe-math-optimizations}.
5063 @item -ffinite-math-only
5064 @opindex ffinite-math-only
5065 Allow optimizations for floating-point arithmetic that assume
5066 that arguments and results are not NaNs or +-Infs.
5068 This option should never be turned on by any @option{-O} option since
5069 it can result in incorrect output for programs which depend on
5070 an exact implementation of IEEE or ISO rules/specifications.
5072 The default is @option{-fno-finite-math-only}.
5074 @item -fno-trapping-math
5075 @opindex fno-trapping-math
5076 Compile code assuming that floating-point operations cannot generate
5077 user-visible traps. These traps include division by zero, overflow,
5078 underflow, inexact result and invalid operation. This option implies
5079 @option{-fno-signaling-nans}. Setting this option may allow faster
5080 code if one relies on ``non-stop'' IEEE arithmetic, for example.
5082 This option should never be turned on by any @option{-O} option since
5083 it can result in incorrect output for programs which depend on
5084 an exact implementation of IEEE or ISO rules/specifications for
5087 The default is @option{-ftrapping-math}.
5089 @item -frounding-math
5090 @opindex frounding-math
5091 Disable transformations and optimizations that assume default floating
5092 point rounding behavior. This is round-to-zero for all floating point
5093 to integer conversions, and round-to-nearest for all other arithmetic
5094 truncations. This option should be specified for programs that change
5095 the FP rounding mode dynamically, or that may be executed with a
5096 non-default rounding mode. This option disables constant folding of
5097 floating point expressions at compile-time (which may be affected by
5098 rounding mode) and arithmetic transformations that are unsafe in the
5099 presence of sign-dependent rounding modes.
5101 The default is @option{-fno-rounding-math}.
5103 This option is experimental and does not currently guarantee to
5104 disable all GCC optimizations that are affected by rounding mode.
5105 Future versions of GCC may provide finer control of this setting
5106 using C99's @code{FENV_ACCESS} pragma. This command line option
5107 will be used to specify the default state for @code{FENV_ACCESS}.
5109 @item -fsignaling-nans
5110 @opindex fsignaling-nans
5111 Compile code assuming that IEEE signaling NaNs may generate user-visible
5112 traps during floating-point operations. Setting this option disables
5113 optimizations that may change the number of exceptions visible with
5114 signaling NaNs. This option implies @option{-ftrapping-math}.
5116 This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
5119 The default is @option{-fno-signaling-nans}.
5121 This option is experimental and does not currently guarantee to
5122 disable all GCC optimizations that affect signaling NaN behavior.
5124 @item -fsingle-precision-constant
5125 @opindex fsingle-precision-constant
5126 Treat floating point constant as single precision constant instead of
5127 implicitly converting it to double precision constant.
5132 The following options control optimizations that may improve
5133 performance, but are not enabled by any @option{-O} options. This
5134 section includes experimental options that may produce broken code.
5137 @item -fbranch-probabilities
5138 @opindex fbranch-probabilities
5139 After running a program compiled with @option{-fprofile-arcs}
5140 (@pxref{Debugging Options,, Options for Debugging Your Program or
5141 @command{gcc}}), you can compile it a second time using
5142 @option{-fbranch-probabilities}, to improve optimizations based on
5143 the number of times each branch was taken. When the program
5144 compiled with @option{-fprofile-arcs} exits it saves arc execution
5145 counts to a file called @file{@var{sourcename}.gcda} for each source
5146 file The information in this data file is very dependent on the
5147 structure of the generated code, so you must use the same source code
5148 and the same optimization options for both compilations.
5150 With @option{-fbranch-probabilities}, GCC puts a
5151 @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
5152 These can be used to improve optimization. Currently, they are only
5153 used in one place: in @file{reorg.c}, instead of guessing which path a
5154 branch is mostly to take, the @samp{REG_BR_PROB} values are used to
5155 exactly determine which path is taken more often.
5157 @item -fprofile-values
5158 @opindex fprofile-values
5159 If combined with @option{-fprofile-arcs}, it adds code so that some
5160 data about values of expressions in the program is gathered.
5162 With @option{-fbranch-probabilities}, it reads back the data gathered
5163 from profiling values of expressions and adds @samp{REG_VALUE_PROFILE}
5164 notes to instructions for their later usage in optimizations.
5166 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5170 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5171 a code to gather information about values of expressions.
5173 With @option{-fbranch-probabilities}, it reads back the data gathered
5174 and actually performs the optimizations based on them.
5175 Currently the optimizations include specialization of division operation
5176 using the knowledge about the value of the denominator.
5178 @item -fspeculative-prefetching
5179 @opindex fspeculative-prefetching
5180 If combined with @option{-fprofile-arcs}, it instructs the compiler to add
5181 a code to gather information about addresses of memory references in the
5184 With @option{-fbranch-probabilities}, it reads back the data gathered
5185 and issues prefetch instructions according to them. In addition to the opportunities
5186 noticed by @option{-fprefetch-loop-arrays}, it also notices more complicated
5187 memory access patterns---for example accesses to the data stored in linked
5188 list whose elements are usually allocated sequentially.
5190 In order to prevent issuing double prefetches, usage of
5191 @option{-fspeculative-prefetching} implies @option{-fno-prefetch-loop-arrays}.
5193 Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
5195 @item -frename-registers
5196 @opindex frename-registers
5197 Attempt to avoid false dependencies in scheduled code by making use
5198 of registers left over after register allocation. This optimization
5199 will most benefit processors with lots of registers. Depending on the
5200 debug information format adopted by the target, however, it can
5201 make debugging impossible, since variables will no longer stay in
5202 a ``home register''.
5204 Not enabled by default at any level because it has known bugs.
5208 Use a graph coloring register allocator. Currently this option is meant
5209 for testing, so we are interested to hear about miscompilations with
5214 Perform tail duplication to enlarge superblock size. This transformation
5215 simplifies the control flow of the function allowing other optimizations to do
5218 Enabled with @option{-fprofile-use}.
5220 @item -funroll-loops
5221 @opindex funroll-loops
5222 Unroll loops whose number of iterations can be determined at compile time or
5223 upon entry to the loop. @option{-funroll-loops} implies
5224 @option{-frerun-cse-after-loop}. It also turns on complete loop peeling
5225 (i.e.@: complete removal of loops with small constant number of iterations).
5226 This option makes code larger, and may or may not make it run faster.
5228 Enabled with @option{-fprofile-use}.
5230 @item -funroll-all-loops
5231 @opindex funroll-all-loops
5232 Unroll all loops, even if their number of iterations is uncertain when
5233 the loop is entered. This usually makes programs run more slowly.
5234 @option{-funroll-all-loops} implies the same options as
5235 @option{-funroll-loops}.
5238 @opindex fpeel-loops
5239 Peels the loops for that there is enough information that they do not
5240 roll much (from profile feedback). It also turns on complete loop peeling
5241 (i.e.@: complete removal of loops with small constant number of iterations).
5243 Enabled with @option{-fprofile-use}.
5245 @item -fmove-loop-invariants
5246 @opindex fmove-loop-invariants
5247 Enables the loop invariant motion pass in the new loop optimizer. Enabled
5248 at level @option{-O1}
5250 @item -funswitch-loops
5251 @opindex funswitch-loops
5252 Move branches with loop invariant conditions out of the loop, with duplicates
5253 of the loop on both branches (modified according to result of the condition).
5255 @item -fprefetch-loop-arrays
5256 @opindex fprefetch-loop-arrays
5257 If supported by the target machine, generate instructions to prefetch
5258 memory to improve the performance of loops that access large arrays.
5260 Disabled at level @option{-Os}.
5262 @item -ffunction-sections
5263 @itemx -fdata-sections
5264 @opindex ffunction-sections
5265 @opindex fdata-sections
5266 Place each function or data item into its own section in the output
5267 file if the target supports arbitrary sections. The name of the
5268 function or the name of the data item determines the section's name
5271 Use these options on systems where the linker can perform optimizations
5272 to improve locality of reference in the instruction space. Most systems
5273 using the ELF object format and SPARC processors running Solaris 2 have
5274 linkers with such optimizations. AIX may have these optimizations in
5277 Only use these options when there are significant benefits from doing
5278 so. When you specify these options, the assembler and linker will
5279 create larger object and executable files and will also be slower.
5280 You will not be able to use @code{gprof} on all systems if you
5281 specify this option and you may have problems with debugging if
5282 you specify both this option and @option{-g}.
5284 @item -fbranch-target-load-optimize
5285 @opindex fbranch-target-load-optimize
5286 Perform branch target register load optimization before prologue / epilogue
5288 The use of target registers can typically be exposed only during reload,
5289 thus hoisting loads out of loops and doing inter-block scheduling needs
5290 a separate optimization pass.
5292 @item -fbranch-target-load-optimize2
5293 @opindex fbranch-target-load-optimize2
5294 Perform branch target register load optimization after prologue / epilogue
5297 @item -fbtr-bb-exclusive
5298 @opindex fbtr-bb-exclusive
5299 When performing branch target register load optimization, don't reuse
5300 branch target registers in within any basic block.
5302 @item --param @var{name}=@var{value}
5304 In some places, GCC uses various constants to control the amount of
5305 optimization that is done. For example, GCC will not inline functions
5306 that contain more that a certain number of instructions. You can
5307 control some of these constants on the command-line using the
5308 @option{--param} option.
5310 The names of specific parameters, and the meaning of the values, are
5311 tied to the internals of the compiler, and are subject to change
5312 without notice in future releases.
5314 In each case, the @var{value} is an integer. The allowable choices for
5315 @var{name} are given in the following table:
5318 @item sra-max-structure-size
5319 The maximum structure size, in bytes, at which the scalar replacement
5320 of aggregates (SRA) optimization will perform block copies. The
5321 default value, 0, implies that GCC will select the most appropriate
5324 @item sra-field-structure-ratio
5325 The treshold ratio (as a percentage) between instantiated fields and
5326 the complete structure size. We say that if the ratio of the number
5327 of bytes in instantiated fields to the number of bytes in the complete
5328 structure exceeds this parameter, then block copies are not used. The
5331 @item max-crossjump-edges
5332 The maximum number of incoming edges to consider for crossjumping.
5333 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
5334 the number of edges incoming to each block. Increasing values mean
5335 more aggressive optimization, making the compile time increase with
5336 probably small improvement in executable size.
5338 @item min-crossjump-insns
5339 The minimum number of instructions which must be matched at the end
5340 of two blocks before crossjumping will be performed on them. This
5341 value is ignored in the case where all instructions in the block being
5342 crossjumped from are matched. The default value is 5.
5344 @item max-delay-slot-insn-search
5345 The maximum number of instructions to consider when looking for an
5346 instruction to fill a delay slot. If more than this arbitrary number of
5347 instructions is searched, the time savings from filling the delay slot
5348 will be minimal so stop searching. Increasing values mean more
5349 aggressive optimization, making the compile time increase with probably
5350 small improvement in executable run time.
5352 @item max-delay-slot-live-search
5353 When trying to fill delay slots, the maximum number of instructions to
5354 consider when searching for a block with valid live register
5355 information. Increasing this arbitrarily chosen value means more
5356 aggressive optimization, increasing the compile time. This parameter
5357 should be removed when the delay slot code is rewritten to maintain the
5360 @item max-gcse-memory
5361 The approximate maximum amount of memory that will be allocated in
5362 order to perform the global common subexpression elimination
5363 optimization. If more memory than specified is required, the
5364 optimization will not be done.
5366 @item max-gcse-passes
5367 The maximum number of passes of GCSE to run. The default is 1.
5369 @item max-pending-list-length
5370 The maximum number of pending dependencies scheduling will allow
5371 before flushing the current state and starting over. Large functions
5372 with few branches or calls can create excessively large lists which
5373 needlessly consume memory and resources.
5375 @item max-inline-insns-single
5376 Several parameters control the tree inliner used in gcc.
5377 This number sets the maximum number of instructions (counted in GCC's
5378 internal representation) in a single function that the tree inliner
5379 will consider for inlining. This only affects functions declared
5380 inline and methods implemented in a class declaration (C++).
5381 The default value is 500.
5383 @item max-inline-insns-auto
5384 When you use @option{-finline-functions} (included in @option{-O3}),
5385 a lot of functions that would otherwise not be considered for inlining
5386 by the compiler will be investigated. To those functions, a different
5387 (more restrictive) limit compared to functions declared inline can
5389 The default value is 120.
5391 @item large-function-insns
5392 The limit specifying really large functions. For functions greater than this
5393 limit inlining is constrained by @option{--param large-function-growth}.
5394 This parameter is useful primarily to avoid extreme compilation time caused by non-linear
5395 algorithms used by the backend.
5396 This parameter is ignored when @option{-funit-at-a-time} is not used.
5397 The default value is 3000.
5399 @item large-function-growth
5400 Specifies maximal growth of large function caused by inlining in percents.
5401 This parameter is ignored when @option{-funit-at-a-time} is not used.
5402 The default value is 200.
5404 @item inline-unit-growth
5405 Specifies maximal overall growth of the compilation unit caused by inlining.
5406 This parameter is ignored when @option{-funit-at-a-time} is not used.
5407 The default value is 150.
5409 @item max-inline-insns-recursive
5410 @itemx max-inline-insns-recursive-auto
5411 Specifies maximum number of instructions out-of-line copy of self recursive inline
5412 function can grow into by performing recursive inlining.
5414 For functions declared inline @option{--param max-inline-insns-recursive} is
5415 taken into acount. For function not declared inline, recursive inlining
5416 happens only when @option{-finline-functions} (included in @option{-O3}) is
5417 enabled and @option{--param max-inline-insns-recursive-auto} is used. The
5418 default value is 500.
5420 @item max-inline-recursive-depth
5421 @itemx max-inline-recursive-depth-auto
5422 Specifies maximum recursion depth used by the recursive inlining.
5424 For functions declared inline @option{--param max-inline-recursive-depth} is
5425 taken into acount. For function not declared inline, recursive inlining
5426 happens only when @option{-finline-functions} (included in @option{-O3}) is
5427 enabled and @option{--param max-inline-recursive-depth-auto} is used. The
5428 default value is 500.
5430 @item max-inline-insns-rtl
5431 For languages that use the RTL inliner (this happens at a later stage
5432 than tree inlining), you can set the maximum allowable size (counted
5433 in RTL instructions) for the RTL inliner with this parameter.
5434 The default value is 600.
5436 @item max-unrolled-insns
5437 The maximum number of instructions that a loop should have if that loop
5438 is unrolled, and if the loop is unrolled, it determines how many times
5439 the loop code is unrolled.
5441 @item max-average-unrolled-insns
5442 The maximum number of instructions biased by probabilities of their execution
5443 that a loop should have if that loop is unrolled, and if the loop is unrolled,
5444 it determines how many times the loop code is unrolled.
5446 @item max-unroll-times
5447 The maximum number of unrollings of a single loop.
5449 @item max-peeled-insns
5450 The maximum number of instructions that a loop should have if that loop
5451 is peeled, and if the loop is peeled, it determines how many times
5452 the loop code is peeled.
5454 @item max-peel-times
5455 The maximum number of peelings of a single loop.
5457 @item max-completely-peeled-insns
5458 The maximum number of insns of a completely peeled loop.
5460 @item max-completely-peel-times
5461 The maximum number of iterations of a loop to be suitable for complete peeling.
5463 @item max-unswitch-insns
5464 The maximum number of insns of an unswitched loop.
5466 @item max-unswitch-level
5467 The maximum number of branches unswitched in a single loop.
5470 The minimum cost of an expensive expression in the loop invariant motion.
5472 @item iv-consider-all-candidates-bound
5473 Bound on number of candidates for induction variables below that
5474 all candidates are considered for each use in induction variable
5475 optimizations. Only the most relevant candidates are considered
5476 if there are more candidates, to avoid quadratic time complexity.
5478 @item iv-max-considered-uses
5479 The induction variable optimizations give up on loops that contain more
5480 induction variable uses.
5482 @item max-iterations-to-track
5484 The maximum number of iterations of a loop the brute force algorithm
5485 for analysis of # of iterations of the loop tries to evaluate.
5487 @item hot-bb-count-fraction
5488 Select fraction of the maximal count of repetitions of basic block in program
5489 given basic block needs to have to be considered hot.
5491 @item hot-bb-frequency-fraction
5492 Select fraction of the maximal frequency of executions of basic block in
5493 function given basic block needs to have to be considered hot
5495 @item tracer-dynamic-coverage
5496 @itemx tracer-dynamic-coverage-feedback
5498 This value is used to limit superblock formation once the given percentage of
5499 executed instructions is covered. This limits unnecessary code size
5502 The @option{tracer-dynamic-coverage-feedback} is used only when profile
5503 feedback is available. The real profiles (as opposed to statically estimated
5504 ones) are much less balanced allowing the threshold to be larger value.
5506 @item tracer-max-code-growth
5507 Stop tail duplication once code growth has reached given percentage. This is
5508 rather hokey argument, as most of the duplicates will be eliminated later in
5509 cross jumping, so it may be set to much higher values than is the desired code
5512 @item tracer-min-branch-ratio
5514 Stop reverse growth when the reverse probability of best edge is less than this
5515 threshold (in percent).
5517 @item tracer-min-branch-ratio
5518 @itemx tracer-min-branch-ratio-feedback
5520 Stop forward growth if the best edge do have probability lower than this
5523 Similarly to @option{tracer-dynamic-coverage} two values are present, one for
5524 compilation for profile feedback and one for compilation without. The value
5525 for compilation with profile feedback needs to be more conservative (higher) in
5526 order to make tracer effective.
5528 @item max-cse-path-length
5530 Maximum number of basic blocks on path that cse considers. The default is 10.
5532 @item global-var-threshold
5534 Counts the number of function calls (N) and the number of
5535 call-clobbered variables (V). If NxV is larger than this limit, a
5536 single artificial variable will be created to represent all the
5537 call-clobbered variables at function call sites. This artificial
5538 variable will then be made to alias every call-clobbered variable.
5539 (done as int * size_t on the host machine; beware overflow).
5541 @item max-aliased-vops
5543 Maximum number of virtual operands allowed to represent aliases
5544 before triggering the alias grouping heuristic. Alias grouping
5545 reduces compile times and memory consumption needed for aliasing at
5546 the expense of precision loss in alias information.
5548 @item ggc-min-expand
5550 GCC uses a garbage collector to manage its own memory allocation. This
5551 parameter specifies the minimum percentage by which the garbage
5552 collector's heap should be allowed to expand between collections.
5553 Tuning this may improve compilation speed; it has no effect on code
5556 The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
5557 RAM >= 1GB. If @code{getrlimit} is available, the notion of "RAM" is
5558 the smallest of actual RAM and RLIMIT_DATA or RLIMIT_AS. If
5559 GCC is not able to calculate RAM on a particular platform, the lower
5560 bound of 30% is used. Setting this parameter and
5561 @option{ggc-min-heapsize} to zero causes a full collection to occur at
5562 every opportunity. This is extremely slow, but can be useful for
5565 @item ggc-min-heapsize
5567 Minimum size of the garbage collector's heap before it begins bothering
5568 to collect garbage. The first collection occurs after the heap expands
5569 by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
5570 tuning this may improve compilation speed, and has no effect on code
5573 The default is the smaller of RAM/8, RLIMIT_RSS, or a limit which
5574 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
5575 with a lower bound of 4096 (four megabytes) and an upper bound of
5576 131072 (128 megabytes). If GCC is not able to calculate RAM on a
5577 particular platform, the lower bound is used. Setting this parameter
5578 very large effectively disables garbage collection. Setting this
5579 parameter and @option{ggc-min-expand} to zero causes a full collection
5580 to occur at every opportunity.
5582 @item max-reload-search-insns
5583 The maximum number of instruction reload should look backward for equivalent
5584 register. Increasing values mean more aggressive optimization, making the
5585 compile time increase with probably slightly better performance. The default
5588 @item max-cselib-memory-location
5589 The maximum number of memory locations cselib should take into acount.
5590 Increasing values mean more aggressive optimization, making the compile time
5591 increase with probably slightly better performance. The default value is 500.
5593 @item reorder-blocks-duplicate
5594 @itemx reorder-blocks-duplicate-feedback
5596 Used by basic block reordering pass to decide whether to use unconditional
5597 branch or duplicate the code on its destination. Code is duplicated when its
5598 estimated size is smaller than this value multiplied by the estimated size of
5599 unconditional jump in the hot spots of the program.
5601 The @option{reorder-block-duplicate-feedback} is used only when profile
5602 feedback is available and may be set to higher values than
5603 @option{reorder-block-duplicate} since information about the hot spots is more
5606 @item max-sched-region-blocks
5607 The maximum number of blocks in a region to be considered for
5608 interblock scheduling. The default value is 10.
5610 @item max-sched-region-insns
5611 The maximum number of insns in a region to be considered for
5612 interblock scheduling. The default value is 100.
5614 @item integer-share-limit
5615 Small integer constants can use a shared data structure, reducing the
5616 compiler's memory usage and increasing its speed. This sets the maximum
5617 value of a shared integer constant's. The default value is 256.
5622 @node Preprocessor Options
5623 @section Options Controlling the Preprocessor
5624 @cindex preprocessor options
5625 @cindex options, preprocessor
5627 These options control the C preprocessor, which is run on each C source
5628 file before actual compilation.
5630 If you use the @option{-E} option, nothing is done except preprocessing.
5631 Some of these options make sense only together with @option{-E} because
5632 they cause the preprocessor output to be unsuitable for actual
5637 You can use @option{-Wp,@var{option}} to bypass the compiler driver
5638 and pass @var{option} directly through to the preprocessor. If
5639 @var{option} contains commas, it is split into multiple options at the
5640 commas. However, many options are modified, translated or interpreted
5641 by the compiler driver before being passed to the preprocessor, and
5642 @option{-Wp} forcibly bypasses this phase. The preprocessor's direct
5643 interface is undocumented and subject to change, so whenever possible
5644 you should avoid using @option{-Wp} and let the driver handle the
5647 @item -Xpreprocessor @var{option}
5648 @opindex preprocessor
5649 Pass @var{option} as an option to the preprocessor. You can use this to
5650 supply system-specific preprocessor options which GCC does not know how to
5653 If you want to pass an option that takes an argument, you must use
5654 @option{-Xpreprocessor} twice, once for the option and once for the argument.
5657 @include cppopts.texi
5659 @node Assembler Options
5660 @section Passing Options to the Assembler
5662 @c prevent bad page break with this line
5663 You can pass options to the assembler.
5666 @item -Wa,@var{option}
5668 Pass @var{option} as an option to the assembler. If @var{option}
5669 contains commas, it is split into multiple options at the commas.
5671 @item -Xassembler @var{option}
5673 Pass @var{option} as an option to the assembler. You can use this to
5674 supply system-specific assembler options which GCC does not know how to
5677 If you want to pass an option that takes an argument, you must use
5678 @option{-Xassembler} twice, once for the option and once for the argument.
5683 @section Options for Linking
5684 @cindex link options
5685 @cindex options, linking
5687 These options come into play when the compiler links object files into
5688 an executable output file. They are meaningless if the compiler is
5689 not doing a link step.
5693 @item @var{object-file-name}
5694 A file name that does not end in a special recognized suffix is
5695 considered to name an object file or library. (Object files are
5696 distinguished from libraries by the linker according to the file
5697 contents.) If linking is done, these object files are used as input
5706 If any of these options is used, then the linker is not run, and
5707 object file names should not be used as arguments. @xref{Overall
5711 @item -l@var{library}
5712 @itemx -l @var{library}
5714 Search the library named @var{library} when linking. (The second
5715 alternative with the library as a separate argument is only for
5716 POSIX compliance and is not recommended.)
5718 It makes a difference where in the command you write this option; the
5719 linker searches and processes libraries and object files in the order they
5720 are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
5721 after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
5722 to functions in @samp{z}, those functions may not be loaded.
5724 The linker searches a standard list of directories for the library,
5725 which is actually a file named @file{lib@var{library}.a}. The linker
5726 then uses this file as if it had been specified precisely by name.
5728 The directories searched include several standard system directories
5729 plus any that you specify with @option{-L}.
5731 Normally the files found this way are library files---archive files
5732 whose members are object files. The linker handles an archive file by
5733 scanning through it for members which define symbols that have so far
5734 been referenced but not defined. But if the file that is found is an
5735 ordinary object file, it is linked in the usual fashion. The only
5736 difference between using an @option{-l} option and specifying a file name
5737 is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
5738 and searches several directories.
5742 You need this special case of the @option{-l} option in order to
5743 link an Objective-C or Objective-C++ program.
5746 @opindex nostartfiles
5747 Do not use the standard system startup files when linking.
5748 The standard system libraries are used normally, unless @option{-nostdlib}
5749 or @option{-nodefaultlibs} is used.
5751 @item -nodefaultlibs
5752 @opindex nodefaultlibs
5753 Do not use the standard system libraries when linking.
5754 Only the libraries you specify will be passed to the linker.
5755 The standard startup files are used normally, unless @option{-nostartfiles}
5756 is used. The compiler may generate calls to @code{memcmp},
5757 @code{memset}, @code{memcpy} and @code{memmove}.
5758 These entries are usually resolved by entries in
5759 libc. These entry points should be supplied through some other
5760 mechanism when this option is specified.
5764 Do not use the standard system startup files or libraries when linking.
5765 No startup files and only the libraries you specify will be passed to
5766 the linker. The compiler may generate calls to @code{memcmp}, @code{memset},
5767 @code{memcpy} and @code{memmove}.
5768 These entries are usually resolved by entries in
5769 libc. These entry points should be supplied through some other
5770 mechanism when this option is specified.
5772 @cindex @option{-lgcc}, use with @option{-nostdlib}
5773 @cindex @option{-nostdlib} and unresolved references
5774 @cindex unresolved references and @option{-nostdlib}
5775 @cindex @option{-lgcc}, use with @option{-nodefaultlibs}
5776 @cindex @option{-nodefaultlibs} and unresolved references
5777 @cindex unresolved references and @option{-nodefaultlibs}
5778 One of the standard libraries bypassed by @option{-nostdlib} and
5779 @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
5780 that GCC uses to overcome shortcomings of particular machines, or special
5781 needs for some languages.
5782 (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
5783 Collection (GCC) Internals},
5784 for more discussion of @file{libgcc.a}.)
5785 In most cases, you need @file{libgcc.a} even when you want to avoid
5786 other standard libraries. In other words, when you specify @option{-nostdlib}
5787 or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
5788 This ensures that you have no unresolved references to internal GCC
5789 library subroutines. (For example, @samp{__main}, used to ensure C++
5790 constructors will be called; @pxref{Collect2,,@code{collect2}, gccint,
5791 GNU Compiler Collection (GCC) Internals}.)
5795 Produce a position independent executable on targets which support it.
5796 For predictable results, you must also specify the same set of options
5797 that were used to generate code (@option{-fpie}, @option{-fPIE},
5798 or model suboptions) when you specify this option.
5802 Remove all symbol table and relocation information from the executable.
5806 On systems that support dynamic linking, this prevents linking with the shared
5807 libraries. On other systems, this option has no effect.
5811 Produce a shared object which can then be linked with other objects to
5812 form an executable. Not all systems support this option. For predictable
5813 results, you must also specify the same set of options that were used to
5814 generate code (@option{-fpic}, @option{-fPIC}, or model suboptions)
5815 when you specify this option.@footnote{On some systems, @samp{gcc -shared}
5816 needs to build supplementary stub code for constructors to work. On
5817 multi-libbed systems, @samp{gcc -shared} must select the correct support
5818 libraries to link against. Failing to supply the correct flags may lead
5819 to subtle defects. Supplying them in cases where they are not necessary
5822 @item -shared-libgcc
5823 @itemx -static-libgcc
5824 @opindex shared-libgcc
5825 @opindex static-libgcc
5826 On systems that provide @file{libgcc} as a shared library, these options
5827 force the use of either the shared or static version respectively.
5828 If no shared version of @file{libgcc} was built when the compiler was
5829 configured, these options have no effect.
5831 There are several situations in which an application should use the
5832 shared @file{libgcc} instead of the static version. The most common
5833 of these is when the application wishes to throw and catch exceptions
5834 across different shared libraries. In that case, each of the libraries
5835 as well as the application itself should use the shared @file{libgcc}.
5837 Therefore, the G++ and GCJ drivers automatically add
5838 @option{-shared-libgcc} whenever you build a shared library or a main
5839 executable, because C++ and Java programs typically use exceptions, so
5840 this is the right thing to do.
5842 If, instead, you use the GCC driver to create shared libraries, you may
5843 find that they will not always be linked with the shared @file{libgcc}.
5844 If GCC finds, at its configuration time, that you have a non-GNU linker
5845 or a GNU linker that does not support option @option{--eh-frame-hdr},
5846 it will link the shared version of @file{libgcc} into shared libraries
5847 by default. Otherwise, it will take advantage of the linker and optimize
5848 away the linking with the shared version of @file{libgcc}, linking with
5849 the static version of libgcc by default. This allows exceptions to
5850 propagate through such shared libraries, without incurring relocation
5851 costs at library load time.
5853 However, if a library or main executable is supposed to throw or catch
5854 exceptions, you must link it using the G++ or GCJ driver, as appropriate
5855 for the languages used in the program, or using the option
5856 @option{-shared-libgcc}, such that it is linked with the shared
5861 Bind references to global symbols when building a shared object. Warn
5862 about any unresolved references (unless overridden by the link editor
5863 option @samp{-Xlinker -z -Xlinker defs}). Only a few systems support
5866 @item -Xlinker @var{option}
5868 Pass @var{option} as an option to the linker. You can use this to
5869 supply system-specific linker options which GCC does not know how to
5872 If you want to pass an option that takes an argument, you must use
5873 @option{-Xlinker} twice, once for the option and once for the argument.
5874 For example, to pass @option{-assert definitions}, you must write
5875 @samp{-Xlinker -assert -Xlinker definitions}. It does not work to write
5876 @option{-Xlinker "-assert definitions"}, because this passes the entire
5877 string as a single argument, which is not what the linker expects.
5879 @item -Wl,@var{option}
5881 Pass @var{option} as an option to the linker. If @var{option} contains
5882 commas, it is split into multiple options at the commas.
5884 @item -u @var{symbol}
5886 Pretend the symbol @var{symbol} is undefined, to force linking of
5887 library modules to define it. You can use @option{-u} multiple times with
5888 different symbols to force loading of additional library modules.
5891 @node Directory Options
5892 @section Options for Directory Search
5893 @cindex directory options
5894 @cindex options, directory search
5897 These options specify directories to search for header files, for
5898 libraries and for parts of the compiler:
5903 Add the directory @var{dir} to the head of the list of directories to be
5904 searched for header files. This can be used to override a system header
5905 file, substituting your own version, since these directories are
5906 searched before the system header file directories. However, you should
5907 not use this option to add directories that contain vendor-supplied
5908 system header files (use @option{-isystem} for that). If you use more than
5909 one @option{-I} option, the directories are scanned in left-to-right
5910 order; the standard system directories come after.
5912 If a standard system include directory, or a directory specified with
5913 @option{-isystem}, is also specified with @option{-I}, the @option{-I}
5914 option will be ignored. The directory will still be searched but as a
5915 system directory at its normal position in the system include chain.
5916 This is to ensure that GCC's procedure to fix buggy system headers and
5917 the ordering for the include_next directive are not inadvertently changed.
5918 If you really need to change the search order for system directories,
5919 use the @option{-nostdinc} and/or @option{-isystem} options.
5921 @item -iquote@var{dir}
5923 Add the directory @var{dir} to the head of the list of directories to
5924 be searched for header files only for the case of @samp{#include
5925 "@var{file}"}; they are not searched for @samp{#include <@var{file}>},
5926 otherwise just like @option{-I}.
5930 Add directory @var{dir} to the list of directories to be searched
5933 @item -B@var{prefix}
5935 This option specifies where to find the executables, libraries,
5936 include files, and data files of the compiler itself.
5938 The compiler driver program runs one or more of the subprograms
5939 @file{cpp}, @file{cc1}, @file{as} and @file{ld}. It tries
5940 @var{prefix} as a prefix for each program it tries to run, both with and
5941 without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}).
5943 For each subprogram to be run, the compiler driver first tries the
5944 @option{-B} prefix, if any. If that name is not found, or if @option{-B}
5945 was not specified, the driver tries two standard prefixes, which are
5946 @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
5947 those results in a file name that is found, the unmodified program
5948 name is searched for using the directories specified in your
5949 @env{PATH} environment variable.
5951 The compiler will check to see if the path provided by the @option{-B}
5952 refers to a directory, and if necessary it will add a directory
5953 separator character at the end of the path.
5955 @option{-B} prefixes that effectively specify directory names also apply
5956 to libraries in the linker, because the compiler translates these
5957 options into @option{-L} options for the linker. They also apply to
5958 includes files in the preprocessor, because the compiler translates these
5959 options into @option{-isystem} options for the preprocessor. In this case,
5960 the compiler appends @samp{include} to the prefix.
5962 The run-time support file @file{libgcc.a} can also be searched for using
5963 the @option{-B} prefix, if needed. If it is not found there, the two
5964 standard prefixes above are tried, and that is all. The file is left
5965 out of the link if it is not found by those means.
5967 Another way to specify a prefix much like the @option{-B} prefix is to use
5968 the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
5971 As a special kludge, if the path provided by @option{-B} is
5972 @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
5973 9, then it will be replaced by @file{[dir/]include}. This is to help
5974 with boot-strapping the compiler.
5976 @item -specs=@var{file}
5978 Process @var{file} after the compiler reads in the standard @file{specs}
5979 file, in order to override the defaults that the @file{gcc} driver
5980 program uses when determining what switches to pass to @file{cc1},
5981 @file{cc1plus}, @file{as}, @file{ld}, etc. More than one
5982 @option{-specs=@var{file}} can be specified on the command line, and they
5983 are processed in order, from left to right.
5987 This option has been deprecated. Please use @option{-iquote} instead for
5988 @option{-I} directories before the @option{-I-} and remove the @option{-I-}.
5989 Any directories you specify with @option{-I} options before the @option{-I-}
5990 option are searched only for the case of @samp{#include "@var{file}"};
5991 they are not searched for @samp{#include <@var{file}>}.
5993 If additional directories are specified with @option{-I} options after
5994 the @option{-I-}, these directories are searched for all @samp{#include}
5995 directives. (Ordinarily @emph{all} @option{-I} directories are used
5998 In addition, the @option{-I-} option inhibits the use of the current
5999 directory (where the current input file came from) as the first search
6000 directory for @samp{#include "@var{file}"}. There is no way to
6001 override this effect of @option{-I-}. With @option{-I.} you can specify
6002 searching the directory which was current when the compiler was
6003 invoked. That is not exactly the same as what the preprocessor does
6004 by default, but it is often satisfactory.
6006 @option{-I-} does not inhibit the use of the standard system directories
6007 for header files. Thus, @option{-I-} and @option{-nostdinc} are
6014 @section Specifying subprocesses and the switches to pass to them
6017 @command{gcc} is a driver program. It performs its job by invoking a
6018 sequence of other programs to do the work of compiling, assembling and
6019 linking. GCC interprets its command-line parameters and uses these to
6020 deduce which programs it should invoke, and which command-line options
6021 it ought to place on their command lines. This behavior is controlled
6022 by @dfn{spec strings}. In most cases there is one spec string for each
6023 program that GCC can invoke, but a few programs have multiple spec
6024 strings to control their behavior. The spec strings built into GCC can
6025 be overridden by using the @option{-specs=} command-line switch to specify
6028 @dfn{Spec files} are plaintext files that are used to construct spec
6029 strings. They consist of a sequence of directives separated by blank
6030 lines. The type of directive is determined by the first non-whitespace
6031 character on the line and it can be one of the following:
6034 @item %@var{command}
6035 Issues a @var{command} to the spec file processor. The commands that can
6039 @item %include <@var{file}>
6041 Search for @var{file} and insert its text at the current point in the
6044 @item %include_noerr <@var{file}>
6045 @cindex %include_noerr
6046 Just like @samp{%include}, but do not generate an error message if the include
6047 file cannot be found.
6049 @item %rename @var{old_name} @var{new_name}
6051 Rename the spec string @var{old_name} to @var{new_name}.
6055 @item *[@var{spec_name}]:
6056 This tells the compiler to create, override or delete the named spec
6057 string. All lines after this directive up to the next directive or
6058 blank line are considered to be the text for the spec string. If this
6059 results in an empty string then the spec will be deleted. (Or, if the
6060 spec did not exist, then nothing will happened.) Otherwise, if the spec
6061 does not currently exist a new spec will be created. If the spec does
6062 exist then its contents will be overridden by the text of this
6063 directive, unless the first character of that text is the @samp{+}
6064 character, in which case the text will be appended to the spec.
6066 @item [@var{suffix}]:
6067 Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
6068 and up to the next directive or blank line are considered to make up the
6069 spec string for the indicated suffix. When the compiler encounters an
6070 input file with the named suffix, it will processes the spec string in
6071 order to work out how to compile that file. For example:
6078 This says that any input file whose name ends in @samp{.ZZ} should be
6079 passed to the program @samp{z-compile}, which should be invoked with the
6080 command-line switch @option{-input} and with the result of performing the
6081 @samp{%i} substitution. (See below.)
6083 As an alternative to providing a spec string, the text that follows a
6084 suffix directive can be one of the following:
6087 @item @@@var{language}
6088 This says that the suffix is an alias for a known @var{language}. This is
6089 similar to using the @option{-x} command-line switch to GCC to specify a
6090 language explicitly. For example:
6097 Says that .ZZ files are, in fact, C++ source files.
6100 This causes an error messages saying:
6103 @var{name} compiler not installed on this system.
6107 GCC already has an extensive list of suffixes built into it.
6108 This directive will add an entry to the end of the list of suffixes, but
6109 since the list is searched from the end backwards, it is effectively
6110 possible to override earlier entries using this technique.
6114 GCC has the following spec strings built into it. Spec files can
6115 override these strings or create their own. Note that individual
6116 targets can also add their own spec strings to this list.
6119 asm Options to pass to the assembler
6120 asm_final Options to pass to the assembler post-processor
6121 cpp Options to pass to the C preprocessor
6122 cc1 Options to pass to the C compiler
6123 cc1plus Options to pass to the C++ compiler
6124 endfile Object files to include at the end of the link
6125 link Options to pass to the linker
6126 lib Libraries to include on the command line to the linker
6127 libgcc Decides which GCC support library to pass to the linker
6128 linker Sets the name of the linker
6129 predefines Defines to be passed to the C preprocessor
6130 signed_char Defines to pass to CPP to say whether @code{char} is signed
6132 startfile Object files to include at the start of the link
6135 Here is a small example of a spec file:
6141 --start-group -lgcc -lc -leval1 --end-group %(old_lib)
6144 This example renames the spec called @samp{lib} to @samp{old_lib} and
6145 then overrides the previous definition of @samp{lib} with a new one.
6146 The new definition adds in some extra command-line options before
6147 including the text of the old definition.
6149 @dfn{Spec strings} are a list of command-line options to be passed to their
6150 corresponding program. In addition, the spec strings can contain
6151 @samp{%}-prefixed sequences to substitute variable text or to
6152 conditionally insert text into the command line. Using these constructs
6153 it is possible to generate quite complex command lines.
6155 Here is a table of all defined @samp{%}-sequences for spec
6156 strings. Note that spaces are not generated automatically around the
6157 results of expanding these sequences. Therefore you can concatenate them
6158 together or combine them with constant text in a single argument.
6162 Substitute one @samp{%} into the program name or argument.
6165 Substitute the name of the input file being processed.
6168 Substitute the basename of the input file being processed.
6169 This is the substring up to (and not including) the last period
6170 and not including the directory.
6173 This is the same as @samp{%b}, but include the file suffix (text after
6177 Marks the argument containing or following the @samp{%d} as a
6178 temporary file name, so that that file will be deleted if GCC exits
6179 successfully. Unlike @samp{%g}, this contributes no text to the
6182 @item %g@var{suffix}
6183 Substitute a file name that has suffix @var{suffix} and is chosen
6184 once per compilation, and mark the argument in the same way as
6185 @samp{%d}. To reduce exposure to denial-of-service attacks, the file
6186 name is now chosen in a way that is hard to predict even when previously
6187 chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
6188 might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
6189 the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
6190 treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
6191 was simply substituted with a file name chosen once per compilation,
6192 without regard to any appended suffix (which was therefore treated
6193 just like ordinary text), making such attacks more likely to succeed.
6195 @item %u@var{suffix}
6196 Like @samp{%g}, but generates a new temporary file name even if
6197 @samp{%u@var{suffix}} was already seen.
6199 @item %U@var{suffix}
6200 Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
6201 new one if there is no such last file name. In the absence of any
6202 @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
6203 the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
6204 would involve the generation of two distinct file names, one
6205 for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
6206 simply substituted with a file name chosen for the previous @samp{%u},
6207 without regard to any appended suffix.
6209 @item %j@var{suffix}
6210 Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
6211 writable, and if save-temps is off; otherwise, substitute the name
6212 of a temporary file, just like @samp{%u}. This temporary file is not
6213 meant for communication between processes, but rather as a junk
6216 @item %|@var{suffix}
6217 @itemx %m@var{suffix}
6218 Like @samp{%g}, except if @option{-pipe} is in effect. In that case
6219 @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
6220 all. These are the two most common ways to instruct a program that it
6221 should read from standard input or write to standard output. If you
6222 need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
6223 construct: see for example @file{f/lang-specs.h}.
6225 @item %.@var{SUFFIX}
6226 Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
6227 when it is subsequently output with @samp{%*}. @var{SUFFIX} is
6228 terminated by the next space or %.
6231 Marks the argument containing or following the @samp{%w} as the
6232 designated output file of this compilation. This puts the argument
6233 into the sequence of arguments that @samp{%o} will substitute later.
6236 Substitutes the names of all the output files, with spaces
6237 automatically placed around them. You should write spaces
6238 around the @samp{%o} as well or the results are undefined.
6239 @samp{%o} is for use in the specs for running the linker.
6240 Input files whose names have no recognized suffix are not compiled
6241 at all, but they are included among the output files, so they will
6245 Substitutes the suffix for object files. Note that this is
6246 handled specially when it immediately follows @samp{%g, %u, or %U},
6247 because of the need for those to form complete file names. The
6248 handling is such that @samp{%O} is treated exactly as if it had already
6249 been substituted, except that @samp{%g, %u, and %U} do not currently
6250 support additional @var{suffix} characters following @samp{%O} as they would
6251 following, for example, @samp{.o}.
6254 Substitutes the standard macro predefinitions for the
6255 current target machine. Use this when running @code{cpp}.
6258 Like @samp{%p}, but puts @samp{__} before and after the name of each
6259 predefined macro, except for macros that start with @samp{__} or with
6260 @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
6264 Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
6265 @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), and
6266 @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
6270 Current argument is the name of a library or startup file of some sort.
6271 Search for that file in a standard list of directories and substitute
6272 the full name found.
6275 Print @var{str} as an error message. @var{str} is terminated by a newline.
6276 Use this when inconsistent options are detected.
6279 Substitute the contents of spec string @var{name} at this point.
6282 Like @samp{%(@dots{})} but put @samp{__} around @option{-D} arguments.
6284 @item %x@{@var{option}@}
6285 Accumulate an option for @samp{%X}.
6288 Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
6292 Output the accumulated assembler options specified by @option{-Wa}.
6295 Output the accumulated preprocessor options specified by @option{-Wp}.
6298 Process the @code{asm} spec. This is used to compute the
6299 switches to be passed to the assembler.
6302 Process the @code{asm_final} spec. This is a spec string for
6303 passing switches to an assembler post-processor, if such a program is
6307 Process the @code{link} spec. This is the spec for computing the
6308 command line passed to the linker. Typically it will make use of the
6309 @samp{%L %G %S %D and %E} sequences.
6312 Dump out a @option{-L} option for each directory that GCC believes might
6313 contain startup files. If the target supports multilibs then the
6314 current multilib directory will be prepended to each of these paths.
6317 Output the multilib directory with directory separators replaced with
6318 @samp{_}. If multilib directories are not set, or the multilib directory is
6319 @file{.} then this option emits nothing.
6322 Process the @code{lib} spec. This is a spec string for deciding which
6323 libraries should be included on the command line to the linker.
6326 Process the @code{libgcc} spec. This is a spec string for deciding
6327 which GCC support library should be included on the command line to the linker.
6330 Process the @code{startfile} spec. This is a spec for deciding which
6331 object files should be the first ones passed to the linker. Typically
6332 this might be a file named @file{crt0.o}.
6335 Process the @code{endfile} spec. This is a spec string that specifies
6336 the last object files that will be passed to the linker.
6339 Process the @code{cpp} spec. This is used to construct the arguments
6340 to be passed to the C preprocessor.
6343 Process the @code{cc1} spec. This is used to construct the options to be
6344 passed to the actual C compiler (@samp{cc1}).
6347 Process the @code{cc1plus} spec. This is used to construct the options to be
6348 passed to the actual C++ compiler (@samp{cc1plus}).
6351 Substitute the variable part of a matched option. See below.
6352 Note that each comma in the substituted string is replaced by
6356 Remove all occurrences of @code{-S} from the command line. Note---this
6357 command is position dependent. @samp{%} commands in the spec string
6358 before this one will see @code{-S}, @samp{%} commands in the spec string
6359 after this one will not.
6361 @item %:@var{function}(@var{args})
6362 Call the named function @var{function}, passing it @var{args}.
6363 @var{args} is first processed as a nested spec string, then split
6364 into an argument vector in the usual fashion. The function returns
6365 a string which is processed as if it had appeared literally as part
6366 of the current spec.
6368 The following built-in spec functions are provided:
6371 @item @code{if-exists}
6372 The @code{if-exists} spec function takes one argument, an absolute
6373 pathname to a file. If the file exists, @code{if-exists} returns the
6374 pathname. Here is a small example of its usage:
6378 crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
6381 @item @code{if-exists-else}
6382 The @code{if-exists-else} spec function is similar to the @code{if-exists}
6383 spec function, except that it takes two arguments. The first argument is
6384 an absolute pathname to a file. If the file exists, @code{if-exists-else}
6385 returns the pathname. If it does not exist, it returns the second argument.
6386 This way, @code{if-exists-else} can be used to select one file or another,
6387 based on the existence of the first. Here is a small example of its usage:
6391 crt0%O%s %:if-exists(crti%O%s) \
6392 %:if-exists-else(crtbeginT%O%s crtbegin%O%s)
6395 @item @code{replace-outfile}
6396 The @code{replace-outfile} spec function takes two arguments. It looks for the
6397 first argument in the outfiles array and replaces it with the second argument. Here
6398 is a small example of its usage:
6401 %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
6407 Substitutes the @code{-S} switch, if that switch was given to GCC@.
6408 If that switch was not specified, this substitutes nothing. Note that
6409 the leading dash is omitted when specifying this option, and it is
6410 automatically inserted if the substitution is performed. Thus the spec
6411 string @samp{%@{foo@}} would match the command-line option @option{-foo}
6412 and would output the command line option @option{-foo}.
6414 @item %W@{@code{S}@}
6415 Like %@{@code{S}@} but mark last argument supplied within as a file to be
6418 @item %@{@code{S}*@}
6419 Substitutes all the switches specified to GCC whose names start
6420 with @code{-S}, but which also take an argument. This is used for
6421 switches like @option{-o}, @option{-D}, @option{-I}, etc.
6422 GCC considers @option{-o foo} as being
6423 one switch whose names starts with @samp{o}. %@{o*@} would substitute this
6424 text, including the space. Thus two arguments would be generated.
6426 @item %@{@code{S}*&@code{T}*@}
6427 Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
6428 (the order of @code{S} and @code{T} in the spec is not significant).
6429 There can be any number of ampersand-separated variables; for each the
6430 wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
6432 @item %@{@code{S}:@code{X}@}
6433 Substitutes @code{X}, if the @samp{-S} switch was given to GCC@.
6435 @item %@{!@code{S}:@code{X}@}
6436 Substitutes @code{X}, if the @samp{-S} switch was @emph{not} given to GCC@.
6438 @item %@{@code{S}*:@code{X}@}
6439 Substitutes @code{X} if one or more switches whose names start with
6440 @code{-S} are specified to GCC@. Normally @code{X} is substituted only
6441 once, no matter how many such switches appeared. However, if @code{%*}
6442 appears somewhere in @code{X}, then @code{X} will be substituted once
6443 for each matching switch, with the @code{%*} replaced by the part of
6444 that switch that matched the @code{*}.
6446 @item %@{.@code{S}:@code{X}@}
6447 Substitutes @code{X}, if processing a file with suffix @code{S}.
6449 @item %@{!.@code{S}:@code{X}@}
6450 Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
6452 @item %@{@code{S}|@code{P}:@code{X}@}
6453 Substitutes @code{X} if either @code{-S} or @code{-P} was given to GCC@.
6454 This may be combined with @samp{!}, @samp{.}, and @code{*} sequences as well,
6455 although they have a stronger binding than the @samp{|}. If @code{%*}
6456 appears in @code{X}, all of the alternatives must be starred, and only
6457 the first matching alternative is substituted.
6459 For example, a spec string like this:
6462 %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
6465 will output the following command-line options from the following input
6466 command-line options:
6471 -d fred.c -foo -baz -boggle
6472 -d jim.d -bar -baz -boggle
6475 @item %@{S:X; T:Y; :D@}
6477 If @code{S} was given to GCC, substitutes @code{X}; else if @code{T} was
6478 given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
6479 be as many clauses as you need. This may be combined with @code{.},
6480 @code{!}, @code{|}, and @code{*} as needed.
6485 The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
6486 construct may contain other nested @samp{%} constructs or spaces, or
6487 even newlines. They are processed as usual, as described above.
6488 Trailing white space in @code{X} is ignored. White space may also
6489 appear anywhere on the left side of the colon in these constructs,
6490 except between @code{.} or @code{*} and the corresponding word.
6492 The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
6493 handled specifically in these constructs. If another value of
6494 @option{-O} or the negated form of a @option{-f}, @option{-m}, or
6495 @option{-W} switch is found later in the command line, the earlier
6496 switch value is ignored, except with @{@code{S}*@} where @code{S} is
6497 just one letter, which passes all matching options.
6499 The character @samp{|} at the beginning of the predicate text is used to
6500 indicate that a command should be piped to the following command, but
6501 only if @option{-pipe} is specified.
6503 It is built into GCC which switches take arguments and which do not.
6504 (You might think it would be useful to generalize this to allow each
6505 compiler's spec to say which switches take arguments. But this cannot
6506 be done in a consistent fashion. GCC cannot even decide which input
6507 files have been specified without knowing which switches take arguments,
6508 and it must know which input files to compile in order to tell which
6511 GCC also knows implicitly that arguments starting in @option{-l} are to be
6512 treated as compiler output files, and passed to the linker in their
6513 proper position among the other output files.
6515 @c man begin OPTIONS
6517 @node Target Options
6518 @section Specifying Target Machine and Compiler Version
6519 @cindex target options
6520 @cindex cross compiling
6521 @cindex specifying machine version
6522 @cindex specifying compiler version and target machine
6523 @cindex compiler version, specifying
6524 @cindex target machine, specifying
6526 The usual way to run GCC is to run the executable called @file{gcc}, or
6527 @file{<machine>-gcc} when cross-compiling, or
6528 @file{<machine>-gcc-<version>} to run a version other than the one that
6529 was installed last. Sometimes this is inconvenient, so GCC provides
6530 options that will switch to another cross-compiler or version.
6533 @item -b @var{machine}
6535 The argument @var{machine} specifies the target machine for compilation.
6537 The value to use for @var{machine} is the same as was specified as the
6538 machine type when configuring GCC as a cross-compiler. For
6539 example, if a cross-compiler was configured with @samp{configure
6540 i386v}, meaning to compile for an 80386 running System V, then you
6541 would specify @option{-b i386v} to run that cross compiler.
6543 @item -V @var{version}
6545 The argument @var{version} specifies which version of GCC to run.
6546 This is useful when multiple versions are installed. For example,
6547 @var{version} might be @samp{2.0}, meaning to run GCC version 2.0.
6550 The @option{-V} and @option{-b} options work by running the
6551 @file{<machine>-gcc-<version>} executable, so there's no real reason to
6552 use them if you can just run that directly.
6554 @node Submodel Options
6555 @section Hardware Models and Configurations
6556 @cindex submodel options
6557 @cindex specifying hardware config
6558 @cindex hardware models and configurations, specifying
6559 @cindex machine dependent options
6561 Earlier we discussed the standard option @option{-b} which chooses among
6562 different installed compilers for completely different target
6563 machines, such as VAX vs.@: 68000 vs.@: 80386.
6565 In addition, each of these target machine types can have its own
6566 special options, starting with @samp{-m}, to choose among various
6567 hardware models or configurations---for example, 68010 vs 68020,
6568 floating coprocessor or none. A single installed version of the
6569 compiler can compile for any model or configuration, according to the
6572 Some configurations of the compiler also support additional special
6573 options, usually for compatibility with other compilers on the same
6576 These options are defined by the macro @code{TARGET_SWITCHES} in the
6577 machine description. The default for the options is also defined by
6578 that macro, which enables you to change the defaults.
6580 @c This list is ordered alphanumerically by subsection name.
6581 @c It should be the same order and spelling as these options are listed
6582 @c in Machine Dependent Options
6590 * DEC Alpha Options::
6591 * DEC Alpha/VMS Options::
6595 * i386 and x86-64 Options::
6607 * RS/6000 and PowerPC Options::
6608 * S/390 and zSeries Options::
6611 * System V Options::
6612 * TMS320C3x/C4x Options::
6616 * Xstormy16 Options::
6622 @subsection ARC Options
6625 These options are defined for ARC implementations:
6630 Compile code for little endian mode. This is the default.
6634 Compile code for big endian mode.
6637 @opindex mmangle-cpu
6638 Prepend the name of the cpu to all public symbol names.
6639 In multiple-processor systems, there are many ARC variants with different
6640 instruction and register set characteristics. This flag prevents code
6641 compiled for one cpu to be linked with code compiled for another.
6642 No facility exists for handling variants that are ``almost identical''.
6643 This is an all or nothing option.
6645 @item -mcpu=@var{cpu}
6647 Compile code for ARC variant @var{cpu}.
6648 Which variants are supported depend on the configuration.
6649 All variants support @option{-mcpu=base}, this is the default.
6651 @item -mtext=@var{text-section}
6652 @itemx -mdata=@var{data-section}
6653 @itemx -mrodata=@var{readonly-data-section}
6657 Put functions, data, and readonly data in @var{text-section},
6658 @var{data-section}, and @var{readonly-data-section} respectively
6659 by default. This can be overridden with the @code{section} attribute.
6660 @xref{Variable Attributes}.
6665 @subsection ARM Options
6668 These @samp{-m} options are defined for Advanced RISC Machines (ARM)
6672 @item -mabi=@var{name}
6674 Generate code for the specified ABI. Permissible values are: @samp{apcs-gnu},
6675 @samp{atpcs}, @samp{aapcs} and @samp{iwmmxt}.
6678 @opindex mapcs-frame
6679 Generate a stack frame that is compliant with the ARM Procedure Call
6680 Standard for all functions, even if this is not strictly necessary for
6681 correct execution of the code. Specifying @option{-fomit-frame-pointer}
6682 with this option will cause the stack frames not to be generated for
6683 leaf functions. The default is @option{-mno-apcs-frame}.
6687 This is a synonym for @option{-mapcs-frame}.
6690 @c not currently implemented
6691 @item -mapcs-stack-check
6692 @opindex mapcs-stack-check
6693 Generate code to check the amount of stack space available upon entry to
6694 every function (that actually uses some stack space). If there is
6695 insufficient space available then either the function
6696 @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} will be
6697 called, depending upon the amount of stack space required. The run time
6698 system is required to provide these functions. The default is
6699 @option{-mno-apcs-stack-check}, since this produces smaller code.
6701 @c not currently implemented
6703 @opindex mapcs-float
6704 Pass floating point arguments using the float point registers. This is
6705 one of the variants of the APCS@. This option is recommended if the
6706 target hardware has a floating point unit or if a lot of floating point
6707 arithmetic is going to be performed by the code. The default is
6708 @option{-mno-apcs-float}, since integer only code is slightly increased in
6709 size if @option{-mapcs-float} is used.
6711 @c not currently implemented
6712 @item -mapcs-reentrant
6713 @opindex mapcs-reentrant
6714 Generate reentrant, position independent code. The default is
6715 @option{-mno-apcs-reentrant}.
6718 @item -mthumb-interwork
6719 @opindex mthumb-interwork
6720 Generate code which supports calling between the ARM and Thumb
6721 instruction sets. Without this option the two instruction sets cannot
6722 be reliably used inside one program. The default is
6723 @option{-mno-thumb-interwork}, since slightly larger code is generated
6724 when @option{-mthumb-interwork} is specified.
6726 @item -mno-sched-prolog
6727 @opindex mno-sched-prolog
6728 Prevent the reordering of instructions in the function prolog, or the
6729 merging of those instruction with the instructions in the function's
6730 body. This means that all functions will start with a recognizable set
6731 of instructions (or in fact one of a choice from a small set of
6732 different function prologues), and this information can be used to
6733 locate the start if functions inside an executable piece of code. The
6734 default is @option{-msched-prolog}.
6737 @opindex mhard-float
6738 Generate output containing floating point instructions. This is the
6742 @opindex msoft-float
6743 Generate output containing library calls for floating point.
6744 @strong{Warning:} the requisite libraries are not available for all ARM
6745 targets. Normally the facilities of the machine's usual C compiler are
6746 used, but this cannot be done directly in cross-compilation. You must make
6747 your own arrangements to provide suitable library functions for
6750 @option{-msoft-float} changes the calling convention in the output file;
6751 therefore, it is only useful if you compile @emph{all} of a program with
6752 this option. In particular, you need to compile @file{libgcc.a}, the
6753 library that comes with GCC, with @option{-msoft-float} in order for
6756 @item -mfloat-abi=@var{name}
6758 Specifies which ABI to use for floating point values. Permissible values
6759 are: @samp{soft}, @samp{softfp} and @samp{hard}.
6761 @samp{soft} and @samp{hard} are equivalent to @option{-msoft-float}
6762 and @option{-mhard-float} respectively. @samp{softfp} allows the generation
6763 of floating point instructions, but still uses the soft-float calling
6766 @item -mlittle-endian
6767 @opindex mlittle-endian
6768 Generate code for a processor running in little-endian mode. This is
6769 the default for all standard configurations.
6772 @opindex mbig-endian
6773 Generate code for a processor running in big-endian mode; the default is
6774 to compile code for a little-endian processor.
6776 @item -mwords-little-endian
6777 @opindex mwords-little-endian
6778 This option only applies when generating code for big-endian processors.
6779 Generate code for a little-endian word order but a big-endian byte
6780 order. That is, a byte order of the form @samp{32107654}. Note: this
6781 option should only be used if you require compatibility with code for
6782 big-endian ARM processors generated by versions of the compiler prior to
6785 @item -mcpu=@var{name}
6787 This specifies the name of the target ARM processor. GCC uses this name
6788 to determine what kind of instructions it can emit when generating
6789 assembly code. Permissible names are: @samp{arm2}, @samp{arm250},
6790 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
6791 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
6792 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
6793 @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
6794 @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
6795 @samp{arm8}, @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
6796 @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
6797 @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
6798 @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
6799 @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
6800 @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
6801 @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
6802 @samp{arm1176jz-s}, @samp{arm1176jzf-s}, @samp{xscale}, @samp{iwmmxt},
6805 @itemx -mtune=@var{name}
6807 This option is very similar to the @option{-mcpu=} option, except that
6808 instead of specifying the actual target processor type, and hence
6809 restricting which instructions can be used, it specifies that GCC should
6810 tune the performance of the code as if the target were of the type
6811 specified in this option, but still choosing the instructions that it
6812 will generate based on the cpu specified by a @option{-mcpu=} option.
6813 For some ARM implementations better performance can be obtained by using
6816 @item -march=@var{name}
6818 This specifies the name of the target ARM architecture. GCC uses this
6819 name to determine what kind of instructions it can emit when generating
6820 assembly code. This option can be used in conjunction with or instead
6821 of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
6822 @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
6823 @samp{armv5}, @samp{armv5t}, @samp{armv5te}, @samp{armv6}, @samp{armv6j},
6824 @samp{iwmmxt}, @samp{ep9312}.
6826 @item -mfpu=@var{name}
6827 @itemx -mfpe=@var{number}
6828 @itemx -mfp=@var{number}
6832 This specifies what floating point hardware (or hardware emulation) is
6833 available on the target. Permissible names are: @samp{fpa}, @samp{fpe2},
6834 @samp{fpe3}, @samp{maverick}, @samp{vfp}. @option{-mfp} and @option{-mfpe}
6835 are synonyms for @option{-mfpu}=@samp{fpe}@var{number}, for compatibility
6836 with older versions of GCC@.
6838 If @option{-msoft-float} is specified this specifies the format of
6839 floating point values.
6841 @item -mstructure-size-boundary=@var{n}
6842 @opindex mstructure-size-boundary
6843 The size of all structures and unions will be rounded up to a multiple
6844 of the number of bits set by this option. Permissible values are 8, 32
6845 and 64. The default value varies for different toolchains. For the COFF
6846 targeted toolchain the default value is 8. A value of 64 is only allowed
6847 if the underlying ABI supports it.
6849 Specifying the larger number can produce faster, more efficient code, but
6850 can also increase the size of the program. Different values are potentially
6851 incompatible. Code compiled with one value cannot necessarily expect to
6852 work with code or libraries compiled with another value, if they exchange
6853 information using structures or unions.
6855 @item -mabort-on-noreturn
6856 @opindex mabort-on-noreturn
6857 Generate a call to the function @code{abort} at the end of a
6858 @code{noreturn} function. It will be executed if the function tries to
6862 @itemx -mno-long-calls
6863 @opindex mlong-calls
6864 @opindex mno-long-calls
6865 Tells the compiler to perform function calls by first loading the
6866 address of the function into a register and then performing a subroutine
6867 call on this register. This switch is needed if the target function
6868 will lie outside of the 64 megabyte addressing range of the offset based
6869 version of subroutine call instruction.
6871 Even if this switch is enabled, not all function calls will be turned
6872 into long calls. The heuristic is that static functions, functions
6873 which have the @samp{short-call} attribute, functions that are inside
6874 the scope of a @samp{#pragma no_long_calls} directive and functions whose
6875 definitions have already been compiled within the current compilation
6876 unit, will not be turned into long calls. The exception to this rule is
6877 that weak function definitions, functions with the @samp{long-call}
6878 attribute or the @samp{section} attribute, and functions that are within
6879 the scope of a @samp{#pragma long_calls} directive, will always be
6880 turned into long calls.
6882 This feature is not enabled by default. Specifying
6883 @option{-mno-long-calls} will restore the default behavior, as will
6884 placing the function calls within the scope of a @samp{#pragma
6885 long_calls_off} directive. Note these switches have no effect on how
6886 the compiler generates code to handle function calls via function
6889 @item -mnop-fun-dllimport
6890 @opindex mnop-fun-dllimport
6891 Disable support for the @code{dllimport} attribute.
6893 @item -msingle-pic-base
6894 @opindex msingle-pic-base
6895 Treat the register used for PIC addressing as read-only, rather than
6896 loading it in the prologue for each function. The run-time system is
6897 responsible for initializing this register with an appropriate value
6898 before execution begins.
6900 @item -mpic-register=@var{reg}
6901 @opindex mpic-register
6902 Specify the register to be used for PIC addressing. The default is R10
6903 unless stack-checking is enabled, when R9 is used.
6905 @item -mcirrus-fix-invalid-insns
6906 @opindex mcirrus-fix-invalid-insns
6907 @opindex mno-cirrus-fix-invalid-insns
6908 Insert NOPs into the instruction stream to in order to work around
6909 problems with invalid Maverick instruction combinations. This option
6910 is only valid if the @option{-mcpu=ep9312} option has been used to
6911 enable generation of instructions for the Cirrus Maverick floating
6912 point co-processor. This option is not enabled by default, since the
6913 problem is only present in older Maverick implementations. The default
6914 can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns}
6917 @item -mpoke-function-name
6918 @opindex mpoke-function-name
6919 Write the name of each function into the text section, directly
6920 preceding the function prologue. The generated code is similar to this:
6924 .ascii "arm_poke_function_name", 0
6927 .word 0xff000000 + (t1 - t0)
6928 arm_poke_function_name
6930 stmfd sp!, @{fp, ip, lr, pc@}
6934 When performing a stack backtrace, code can inspect the value of
6935 @code{pc} stored at @code{fp + 0}. If the trace function then looks at
6936 location @code{pc - 12} and the top 8 bits are set, then we know that
6937 there is a function name embedded immediately preceding this location
6938 and has length @code{((pc[-3]) & 0xff000000)}.
6942 Generate code for the 16-bit Thumb instruction set. The default is to
6943 use the 32-bit ARM instruction set.
6946 @opindex mtpcs-frame
6947 Generate a stack frame that is compliant with the Thumb Procedure Call
6948 Standard for all non-leaf functions. (A leaf function is one that does
6949 not call any other functions.) The default is @option{-mno-tpcs-frame}.
6951 @item -mtpcs-leaf-frame
6952 @opindex mtpcs-leaf-frame
6953 Generate a stack frame that is compliant with the Thumb Procedure Call
6954 Standard for all leaf functions. (A leaf function is one that does
6955 not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
6957 @item -mcallee-super-interworking
6958 @opindex mcallee-super-interworking
6959 Gives all externally visible functions in the file being compiled an ARM
6960 instruction set header which switches to Thumb mode before executing the
6961 rest of the function. This allows these functions to be called from
6962 non-interworking code.
6964 @item -mcaller-super-interworking
6965 @opindex mcaller-super-interworking
6966 Allows calls via function pointers (including virtual functions) to
6967 execute correctly regardless of whether the target code has been
6968 compiled for interworking or not. There is a small overhead in the cost
6969 of executing a function pointer if this option is enabled.
6974 @subsection AVR Options
6977 These options are defined for AVR implementations:
6980 @item -mmcu=@var{mcu}
6982 Specify ATMEL AVR instruction set or MCU type.
6984 Instruction set avr1 is for the minimal AVR core, not supported by the C
6985 compiler, only for assembler programs (MCU types: at90s1200, attiny10,
6986 attiny11, attiny12, attiny15, attiny28).
6988 Instruction set avr2 (default) is for the classic AVR core with up to
6989 8K program memory space (MCU types: at90s2313, at90s2323, attiny22,
6990 at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515,
6991 at90c8534, at90s8535).
6993 Instruction set avr3 is for the classic AVR core with up to 128K program
6994 memory space (MCU types: atmega103, atmega603, at43usb320, at76c711).
6996 Instruction set avr4 is for the enhanced AVR core with up to 8K program
6997 memory space (MCU types: atmega8, atmega83, atmega85).
6999 Instruction set avr5 is for the enhanced AVR core with up to 128K program
7000 memory space (MCU types: atmega16, atmega161, atmega163, atmega32, atmega323,
7001 atmega64, atmega128, at43usb355, at94k).
7005 Output instruction sizes to the asm file.
7007 @item -minit-stack=@var{N}
7008 @opindex minit-stack
7009 Specify the initial stack address, which may be a symbol or numeric value,
7010 @samp{__stack} is the default.
7012 @item -mno-interrupts
7013 @opindex mno-interrupts
7014 Generated code is not compatible with hardware interrupts.
7015 Code size will be smaller.
7017 @item -mcall-prologues
7018 @opindex mcall-prologues
7019 Functions prologues/epilogues expanded as call to appropriate
7020 subroutines. Code size will be smaller.
7022 @item -mno-tablejump
7023 @opindex mno-tablejump
7024 Do not generate tablejump insns which sometimes increase code size.
7027 @opindex mtiny-stack
7028 Change only the low 8 bits of the stack pointer.
7032 Assume int to be 8 bit integer. This affects the sizes of all types: A
7033 char will be 1 byte, an int will be 1 byte, an long will be 2 bytes
7034 and long long will be 4 bytes. Please note that this option does not
7035 comply to the C standards, but it will provide you with smaller code
7040 @subsection CRIS Options
7041 @cindex CRIS Options
7043 These options are defined specifically for the CRIS ports.
7046 @item -march=@var{architecture-type}
7047 @itemx -mcpu=@var{architecture-type}
7050 Generate code for the specified architecture. The choices for
7051 @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
7052 respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX.
7053 Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
7056 @item -mtune=@var{architecture-type}
7058 Tune to @var{architecture-type} everything applicable about the generated
7059 code, except for the ABI and the set of available instructions. The
7060 choices for @var{architecture-type} are the same as for
7061 @option{-march=@var{architecture-type}}.
7063 @item -mmax-stack-frame=@var{n}
7064 @opindex mmax-stack-frame
7065 Warn when the stack frame of a function exceeds @var{n} bytes.
7067 @item -melinux-stacksize=@var{n}
7068 @opindex melinux-stacksize
7069 Only available with the @samp{cris-axis-aout} target. Arranges for
7070 indications in the program to the kernel loader that the stack of the
7071 program should be set to @var{n} bytes.
7077 The options @option{-metrax4} and @option{-metrax100} are synonyms for
7078 @option{-march=v3} and @option{-march=v8} respectively.
7080 @item -mmul-bug-workaround
7081 @itemx -mno-mul-bug-workaround
7082 @opindex mmul-bug-workaround
7083 @opindex mno-mul-bug-workaround
7084 Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
7085 models where it applies. This option is active by default.
7089 Enable CRIS-specific verbose debug-related information in the assembly
7090 code. This option also has the effect to turn off the @samp{#NO_APP}
7091 formatted-code indicator to the assembler at the beginning of the
7096 Do not use condition-code results from previous instruction; always emit
7097 compare and test instructions before use of condition codes.
7099 @item -mno-side-effects
7100 @opindex mno-side-effects
7101 Do not emit instructions with side-effects in addressing modes other than
7105 @itemx -mno-stack-align
7107 @itemx -mno-data-align
7108 @itemx -mconst-align
7109 @itemx -mno-const-align
7110 @opindex mstack-align
7111 @opindex mno-stack-align
7112 @opindex mdata-align
7113 @opindex mno-data-align
7114 @opindex mconst-align
7115 @opindex mno-const-align
7116 These options (no-options) arranges (eliminate arrangements) for the
7117 stack-frame, individual data and constants to be aligned for the maximum
7118 single data access size for the chosen CPU model. The default is to
7119 arrange for 32-bit alignment. ABI details such as structure layout are
7120 not affected by these options.
7128 Similar to the stack- data- and const-align options above, these options
7129 arrange for stack-frame, writable data and constants to all be 32-bit,
7130 16-bit or 8-bit aligned. The default is 32-bit alignment.
7132 @item -mno-prologue-epilogue
7133 @itemx -mprologue-epilogue
7134 @opindex mno-prologue-epilogue
7135 @opindex mprologue-epilogue
7136 With @option{-mno-prologue-epilogue}, the normal function prologue and
7137 epilogue that sets up the stack-frame are omitted and no return
7138 instructions or return sequences are generated in the code. Use this
7139 option only together with visual inspection of the compiled code: no
7140 warnings or errors are generated when call-saved registers must be saved,
7141 or storage for local variable needs to be allocated.
7147 With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
7148 instruction sequences that load addresses for functions from the PLT part
7149 of the GOT rather than (traditional on other architectures) calls to the
7150 PLT. The default is @option{-mgotplt}.
7154 Legacy no-op option only recognized with the cris-axis-aout target.
7158 Legacy no-op option only recognized with the cris-axis-elf and
7159 cris-axis-linux-gnu targets.
7163 Only recognized with the cris-axis-aout target, where it selects a
7164 GNU/linux-like multilib, include files and instruction set for
7169 Legacy no-op option only recognized with the cris-axis-linux-gnu target.
7173 This option, recognized for the cris-axis-aout and cris-axis-elf arranges
7174 to link with input-output functions from a simulator library. Code,
7175 initialized data and zero-initialized data are allocated consecutively.
7179 Like @option{-sim}, but pass linker options to locate initialized data at
7180 0x40000000 and zero-initialized data at 0x80000000.
7183 @node Darwin Options
7184 @subsection Darwin Options
7185 @cindex Darwin options
7187 These options are defined for all architectures running the Darwin operating
7188 system. They are useful for compatibility with other Mac OS compilers.
7193 Add the framework directory @var{dir} to the head of the list of
7194 directories to be searched for header files. These directories are
7195 interleaved with those specified by @option{-I} options and are
7196 scanned in a left-to-right order.
7198 A framework directory is a directory with frameworks in it. A
7199 framework is a directory with a @samp{"Headers"} and/or
7200 @samp{"PrivateHeaders"} directory contained directly in it that ends
7201 in @samp{".framework"}. The name of a framework is the name of this
7202 directory excluding the @samp{".framework"}. Headers associated with
7203 the framework are found in one of those two directories, with
7204 @samp{"Headers"} being searched first. A subframework is a framework
7205 directory that is in a framework's @samp{"Frameworks"} directory.
7206 Includes of subframework headers can only appear in a header of a
7207 framework that contains the subframework, or in a sibling subframework
7208 header. Two subframeworks are siblings if they occur in the same
7209 framework. A subframework should not have the same name as a
7210 framework, a warning will be issued if this is violated. Currently a
7211 subframework cannot have subframeworks, in the future, the mechanism
7212 may be extended to support this. The standard frameworks can be found
7213 in @samp{"/System/Library/Frameworks"} and
7214 @samp{"/Library/Frameworks"}. An example include looks like
7215 @code{#include <Framework/header.h>}, where @samp{Framework} denotes
7216 the name of the framework and header.h is found in the
7217 @samp{"PrivateHeaders"} or @samp{"Headers"} directory.
7221 Emit debugging information for symbols that are used. For STABS
7222 debugging format, this enables @option{-feliminate-unused-debug-symbols}.
7223 This is by default ON.
7227 Emit debugging information for all symbols and types.
7229 @item -mone-byte-bool
7230 @opindex -mone-byte-bool
7231 Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}.
7232 By default @samp{sizeof(bool)} is @samp{4} when compiling for
7233 Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this
7234 option has no effect on x86.
7236 @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
7237 to generate code that is not binary compatible with code generated
7238 without that switch. Using this switch may require recompiling all
7239 other modules in a program, including system libraries. Use this
7240 switch to conform to a non-default data model.
7242 @item -mfix-and-continue
7243 @itemx -ffix-and-continue
7244 @itemx -findirect-data
7245 @opindex mfix-and-continue
7246 @opindex ffix-and-continue
7247 @opindex findirect-data
7248 Generate code suitable for fast turn around development. Needed to
7249 enable gdb to dynamically load @code{.o} files into already running
7250 programs. @option{-findirect-data} and @option{-ffix-and-continue}
7251 are provided for backwards compatibility.
7255 Loads all members of static archive libraries.
7256 See man ld(1) for more information.
7258 @item -arch_errors_fatal
7259 @opindex arch_errors_fatal
7260 Cause the errors having to do with files that have the wrong architecture
7264 @opindex bind_at_load
7265 Causes the output file to be marked such that the dynamic linker will
7266 bind all undefined references when the file is loaded or launched.
7270 Produce a Mach-o bundle format file.
7271 See man ld(1) for more information.
7273 @item -bundle_loader @var{executable}
7274 @opindex bundle_loader
7275 This specifies the @var{executable} that will be loading the build
7276 output file being linked. See man ld(1) for more information.
7278 @item -allowable_client @var{client_name}
7282 @itemx -compatibility_version
7283 @itemx -current_version
7285 @itemx -dependency-file
7287 @itemx -dylinker_install_name
7290 @itemx -exported_symbols_list
7292 @itemx -flat_namespace
7293 @itemx -force_cpusubtype_ALL
7294 @itemx -force_flat_namespace
7295 @itemx -headerpad_max_install_names
7298 @itemx -install_name
7299 @itemx -keep_private_externs
7300 @itemx -multi_module
7301 @itemx -multiply_defined
7302 @itemx -multiply_defined_unused
7304 @itemx -no_dead_strip_inits_and_terms
7305 @itemx -nofixprebinding
7308 @itemx -noseglinkedit
7309 @itemx -pagezero_size
7311 @itemx -prebind_all_twolevel_modules
7312 @itemx -private_bundle
7313 @itemx -read_only_relocs
7315 @itemx -sectobjectsymbols
7319 @itemx -sectobjectsymbols
7322 @itemx -segs_read_only_addr
7323 @itemx -segs_read_write_addr
7324 @itemx -seg_addr_table
7325 @itemx -seg_addr_table_filename
7328 @itemx -segs_read_only_addr
7329 @itemx -segs_read_write_addr
7330 @itemx -single_module
7333 @itemx -sub_umbrella
7334 @itemx -twolevel_namespace
7337 @itemx -unexported_symbols_list
7338 @itemx -weak_reference_mismatches
7341 @opindex allowable_client
7343 @opindex client_name
7344 @opindex compatibility_version
7345 @opindex current_version
7347 @opindex dependency-file
7349 @opindex dylinker_install_name
7352 @opindex exported_symbols_list
7354 @opindex flat_namespace
7355 @opindex force_cpusubtype_ALL
7356 @opindex force_flat_namespace
7357 @opindex headerpad_max_install_names
7360 @opindex install_name
7361 @opindex keep_private_externs
7362 @opindex multi_module
7363 @opindex multiply_defined
7364 @opindex multiply_defined_unused
7366 @opindex no_dead_strip_inits_and_terms
7367 @opindex nofixprebinding
7368 @opindex nomultidefs
7370 @opindex noseglinkedit
7371 @opindex pagezero_size
7373 @opindex prebind_all_twolevel_modules
7374 @opindex private_bundle
7375 @opindex read_only_relocs
7377 @opindex sectobjectsymbols
7381 @opindex sectobjectsymbols
7384 @opindex segs_read_only_addr
7385 @opindex segs_read_write_addr
7386 @opindex seg_addr_table
7387 @opindex seg_addr_table_filename
7388 @opindex seglinkedit
7390 @opindex segs_read_only_addr
7391 @opindex segs_read_write_addr
7392 @opindex single_module
7394 @opindex sub_library
7395 @opindex sub_umbrella
7396 @opindex twolevel_namespace
7399 @opindex unexported_symbols_list
7400 @opindex weak_reference_mismatches
7401 @opindex whatsloaded
7403 These options are available for Darwin linker. Darwin linker man page
7404 describes them in detail.
7407 @node DEC Alpha Options
7408 @subsection DEC Alpha Options
7410 These @samp{-m} options are defined for the DEC Alpha implementations:
7413 @item -mno-soft-float
7415 @opindex mno-soft-float
7416 @opindex msoft-float
7417 Use (do not use) the hardware floating-point instructions for
7418 floating-point operations. When @option{-msoft-float} is specified,
7419 functions in @file{libgcc.a} will be used to perform floating-point
7420 operations. Unless they are replaced by routines that emulate the
7421 floating-point operations, or compiled in such a way as to call such
7422 emulations routines, these routines will issue floating-point
7423 operations. If you are compiling for an Alpha without floating-point
7424 operations, you must ensure that the library is built so as not to call
7427 Note that Alpha implementations without floating-point operations are
7428 required to have floating-point registers.
7433 @opindex mno-fp-regs
7434 Generate code that uses (does not use) the floating-point register set.
7435 @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
7436 register set is not used, floating point operands are passed in integer
7437 registers as if they were integers and floating-point results are passed
7438 in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
7439 so any function with a floating-point argument or return value called by code
7440 compiled with @option{-mno-fp-regs} must also be compiled with that
7443 A typical use of this option is building a kernel that does not use,
7444 and hence need not save and restore, any floating-point registers.
7448 The Alpha architecture implements floating-point hardware optimized for
7449 maximum performance. It is mostly compliant with the IEEE floating
7450 point standard. However, for full compliance, software assistance is
7451 required. This option generates code fully IEEE compliant code
7452 @emph{except} that the @var{inexact-flag} is not maintained (see below).
7453 If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
7454 defined during compilation. The resulting code is less efficient but is
7455 able to correctly support denormalized numbers and exceptional IEEE
7456 values such as not-a-number and plus/minus infinity. Other Alpha
7457 compilers call this option @option{-ieee_with_no_inexact}.
7459 @item -mieee-with-inexact
7460 @opindex mieee-with-inexact
7461 This is like @option{-mieee} except the generated code also maintains
7462 the IEEE @var{inexact-flag}. Turning on this option causes the
7463 generated code to implement fully-compliant IEEE math. In addition to
7464 @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
7465 macro. On some Alpha implementations the resulting code may execute
7466 significantly slower than the code generated by default. Since there is
7467 very little code that depends on the @var{inexact-flag}, you should
7468 normally not specify this option. Other Alpha compilers call this
7469 option @option{-ieee_with_inexact}.
7471 @item -mfp-trap-mode=@var{trap-mode}
7472 @opindex mfp-trap-mode
7473 This option controls what floating-point related traps are enabled.
7474 Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
7475 The trap mode can be set to one of four values:
7479 This is the default (normal) setting. The only traps that are enabled
7480 are the ones that cannot be disabled in software (e.g., division by zero
7484 In addition to the traps enabled by @samp{n}, underflow traps are enabled
7488 Like @samp{su}, but the instructions are marked to be safe for software
7489 completion (see Alpha architecture manual for details).
7492 Like @samp{su}, but inexact traps are enabled as well.
7495 @item -mfp-rounding-mode=@var{rounding-mode}
7496 @opindex mfp-rounding-mode
7497 Selects the IEEE rounding mode. Other Alpha compilers call this option
7498 @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
7503 Normal IEEE rounding mode. Floating point numbers are rounded towards
7504 the nearest machine number or towards the even machine number in case
7508 Round towards minus infinity.
7511 Chopped rounding mode. Floating point numbers are rounded towards zero.
7514 Dynamic rounding mode. A field in the floating point control register
7515 (@var{fpcr}, see Alpha architecture reference manual) controls the
7516 rounding mode in effect. The C library initializes this register for
7517 rounding towards plus infinity. Thus, unless your program modifies the
7518 @var{fpcr}, @samp{d} corresponds to round towards plus infinity.
7521 @item -mtrap-precision=@var{trap-precision}
7522 @opindex mtrap-precision
7523 In the Alpha architecture, floating point traps are imprecise. This
7524 means without software assistance it is impossible to recover from a
7525 floating trap and program execution normally needs to be terminated.
7526 GCC can generate code that can assist operating system trap handlers
7527 in determining the exact location that caused a floating point trap.
7528 Depending on the requirements of an application, different levels of
7529 precisions can be selected:
7533 Program precision. This option is the default and means a trap handler
7534 can only identify which program caused a floating point exception.
7537 Function precision. The trap handler can determine the function that
7538 caused a floating point exception.
7541 Instruction precision. The trap handler can determine the exact
7542 instruction that caused a floating point exception.
7545 Other Alpha compilers provide the equivalent options called
7546 @option{-scope_safe} and @option{-resumption_safe}.
7548 @item -mieee-conformant
7549 @opindex mieee-conformant
7550 This option marks the generated code as IEEE conformant. You must not
7551 use this option unless you also specify @option{-mtrap-precision=i} and either
7552 @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
7553 is to emit the line @samp{.eflag 48} in the function prologue of the
7554 generated assembly file. Under DEC Unix, this has the effect that
7555 IEEE-conformant math library routines will be linked in.
7557 @item -mbuild-constants
7558 @opindex mbuild-constants
7559 Normally GCC examines a 32- or 64-bit integer constant to
7560 see if it can construct it from smaller constants in two or three
7561 instructions. If it cannot, it will output the constant as a literal and
7562 generate code to load it from the data segment at runtime.
7564 Use this option to require GCC to construct @emph{all} integer constants
7565 using code, even if it takes more instructions (the maximum is six).
7567 You would typically use this option to build a shared library dynamic
7568 loader. Itself a shared library, it must relocate itself in memory
7569 before it can find the variables and constants in its own data segment.
7575 Select whether to generate code to be assembled by the vendor-supplied
7576 assembler (@option{-malpha-as}) or by the GNU assembler @option{-mgas}.
7594 Indicate whether GCC should generate code to use the optional BWX,
7595 CIX, FIX and MAX instruction sets. The default is to use the instruction
7596 sets supported by the CPU type specified via @option{-mcpu=} option or that
7597 of the CPU on which GCC was built if none was specified.
7602 @opindex mfloat-ieee
7603 Generate code that uses (does not use) VAX F and G floating point
7604 arithmetic instead of IEEE single and double precision.
7606 @item -mexplicit-relocs
7607 @itemx -mno-explicit-relocs
7608 @opindex mexplicit-relocs
7609 @opindex mno-explicit-relocs
7610 Older Alpha assemblers provided no way to generate symbol relocations
7611 except via assembler macros. Use of these macros does not allow
7612 optimal instruction scheduling. GNU binutils as of version 2.12
7613 supports a new syntax that allows the compiler to explicitly mark
7614 which relocations should apply to which instructions. This option
7615 is mostly useful for debugging, as GCC detects the capabilities of
7616 the assembler when it is built and sets the default accordingly.
7620 @opindex msmall-data
7621 @opindex mlarge-data
7622 When @option{-mexplicit-relocs} is in effect, static data is
7623 accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
7624 is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
7625 (the @code{.sdata} and @code{.sbss} sections) and are accessed via
7626 16-bit relocations off of the @code{$gp} register. This limits the
7627 size of the small data area to 64KB, but allows the variables to be
7628 directly accessed via a single instruction.
7630 The default is @option{-mlarge-data}. With this option the data area
7631 is limited to just below 2GB. Programs that require more than 2GB of
7632 data must use @code{malloc} or @code{mmap} to allocate the data in the
7633 heap instead of in the program's data segment.
7635 When generating code for shared libraries, @option{-fpic} implies
7636 @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
7640 @opindex msmall-text
7641 @opindex mlarge-text
7642 When @option{-msmall-text} is used, the compiler assumes that the
7643 code of the entire program (or shared library) fits in 4MB, and is
7644 thus reachable with a branch instruction. When @option{-msmall-data}
7645 is used, the compiler can assume that all local symbols share the
7646 same @code{$gp} value, and thus reduce the number of instructions
7647 required for a function call from 4 to 1.
7649 The default is @option{-mlarge-text}.
7651 @item -mcpu=@var{cpu_type}
7653 Set the instruction set and instruction scheduling parameters for
7654 machine type @var{cpu_type}. You can specify either the @samp{EV}
7655 style name or the corresponding chip number. GCC supports scheduling
7656 parameters for the EV4, EV5 and EV6 family of processors and will
7657 choose the default values for the instruction set from the processor
7658 you specify. If you do not specify a processor type, GCC will default
7659 to the processor on which the compiler was built.
7661 Supported values for @var{cpu_type} are
7667 Schedules as an EV4 and has no instruction set extensions.
7671 Schedules as an EV5 and has no instruction set extensions.
7675 Schedules as an EV5 and supports the BWX extension.
7680 Schedules as an EV5 and supports the BWX and MAX extensions.
7684 Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
7688 Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
7691 @item -mtune=@var{cpu_type}
7693 Set only the instruction scheduling parameters for machine type
7694 @var{cpu_type}. The instruction set is not changed.
7696 @item -mmemory-latency=@var{time}
7697 @opindex mmemory-latency
7698 Sets the latency the scheduler should assume for typical memory
7699 references as seen by the application. This number is highly
7700 dependent on the memory access patterns used by the application
7701 and the size of the external cache on the machine.
7703 Valid options for @var{time} are
7707 A decimal number representing clock cycles.
7713 The compiler contains estimates of the number of clock cycles for
7714 ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
7715 (also called Dcache, Scache, and Bcache), as well as to main memory.
7716 Note that L3 is only valid for EV5.
7721 @node DEC Alpha/VMS Options
7722 @subsection DEC Alpha/VMS Options
7724 These @samp{-m} options are defined for the DEC Alpha/VMS implementations:
7727 @item -mvms-return-codes
7728 @opindex mvms-return-codes
7729 Return VMS condition codes from main. The default is to return POSIX
7730 style condition (e.g.@ error) codes.
7734 @subsection FRV Options
7741 Only use the first 32 general purpose registers.
7746 Use all 64 general purpose registers.
7751 Use only the first 32 floating point registers.
7756 Use all 64 floating point registers
7759 @opindex mhard-float
7761 Use hardware instructions for floating point operations.
7764 @opindex msoft-float
7766 Use library routines for floating point operations.
7771 Dynamically allocate condition code registers.
7776 Do not try to dynamically allocate condition code registers, only
7777 use @code{icc0} and @code{fcc0}.
7782 Change ABI to use double word insns.
7787 Do not use double word instructions.
7792 Use floating point double instructions.
7797 Do not use floating point double instructions.
7802 Use media instructions.
7807 Do not use media instructions.
7812 Use multiply and add/subtract instructions.
7817 Do not use multiply and add/subtract instructions.
7822 Select the FDPIC ABI, that uses function descriptors to represent
7823 pointers to functions. Without any PIC/PIE-related options, it
7824 implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
7825 assumes GOT entries and small data are within a 12-bit range from the
7826 GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
7827 are computed with 32 bits.
7830 @opindex minline-plt
7832 Enable inlining of PLT entries in function calls to functions that are
7833 not known to bind locally. It has no effect without @option{-mfdpic}.
7834 It's enabled by default if optimizing for speed and compiling for
7835 shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
7836 optimization option such as @option{-O3} or above is present in the
7842 Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
7843 that is known to be in read-only sections. It's enabled by default,
7844 except for @option{-fpic} or @option{-fpie}: even though it may help
7845 make the global offset table smaller, it trades 1 instruction for 4.
7846 With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
7847 one of which may be shared by multiple symbols, and it avoids the need
7848 for a GOT entry for the referenced symbol, so it's more likely to be a
7849 win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
7851 @item -multilib-library-pic
7852 @opindex multilib-library-pic
7854 Link with the (library, not FD) pic libraries. It's implied by
7855 @option{-mlibrary-pic}, as well as by @option{-fPIC} and
7856 @option{-fpic} without @option{-mfdpic}. You should never have to use
7862 Follow the EABI requirement of always creating a frame pointer whenever
7863 a stack frame is allocated. This option is enabled by default and can
7864 be disabled with @option{-mno-linked-fp}.
7867 @opindex mlong-calls
7869 Use indirect addressing to call functions outside the current
7870 compilation unit. This allows the functions to be placed anywhere
7871 within the 32-bit address space.
7873 @item -malign-labels
7874 @opindex malign-labels
7876 Try to align labels to an 8-byte boundary by inserting nops into the
7877 previous packet. This option only has an effect when VLIW packing
7878 is enabled. It doesn't create new packets; it merely adds nops to
7882 @opindex mlibrary-pic
7884 Generate position-independent EABI code.
7889 Use only the first four media accumulator registers.
7894 Use all eight media accumulator registers.
7899 Pack VLIW instructions.
7904 Do not pack VLIW instructions.
7909 Do not mark ABI switches in e_flags.
7914 Enable the use of conditional-move instructions (default).
7916 This switch is mainly for debugging the compiler and will likely be removed
7917 in a future version.
7919 @item -mno-cond-move
7920 @opindex mno-cond-move
7922 Disable the use of conditional-move instructions.
7924 This switch is mainly for debugging the compiler and will likely be removed
7925 in a future version.
7930 Enable the use of conditional set instructions (default).
7932 This switch is mainly for debugging the compiler and will likely be removed
7933 in a future version.
7938 Disable the use of conditional set instructions.
7940 This switch is mainly for debugging the compiler and will likely be removed
7941 in a future version.
7946 Enable the use of conditional execution (default).
7948 This switch is mainly for debugging the compiler and will likely be removed
7949 in a future version.
7951 @item -mno-cond-exec
7952 @opindex mno-cond-exec
7954 Disable the use of conditional execution.
7956 This switch is mainly for debugging the compiler and will likely be removed
7957 in a future version.
7960 @opindex mvliw-branch
7962 Run a pass to pack branches into VLIW instructions (default).
7964 This switch is mainly for debugging the compiler and will likely be removed
7965 in a future version.
7967 @item -mno-vliw-branch
7968 @opindex mno-vliw-branch
7970 Do not run a pass to pack branches into VLIW instructions.
7972 This switch is mainly for debugging the compiler and will likely be removed
7973 in a future version.
7975 @item -mmulti-cond-exec
7976 @opindex mmulti-cond-exec
7978 Enable optimization of @code{&&} and @code{||} in conditional execution
7981 This switch is mainly for debugging the compiler and will likely be removed
7982 in a future version.
7984 @item -mno-multi-cond-exec
7985 @opindex mno-multi-cond-exec
7987 Disable optimization of @code{&&} and @code{||} in conditional execution.
7989 This switch is mainly for debugging the compiler and will likely be removed
7990 in a future version.
7992 @item -mnested-cond-exec
7993 @opindex mnested-cond-exec
7995 Enable nested conditional execution optimizations (default).
7997 This switch is mainly for debugging the compiler and will likely be removed
7998 in a future version.
8000 @item -mno-nested-cond-exec
8001 @opindex mno-nested-cond-exec
8003 Disable nested conditional execution optimizations.
8005 This switch is mainly for debugging the compiler and will likely be removed
8006 in a future version.
8008 @item -mtomcat-stats
8009 @opindex mtomcat-stats
8011 Cause gas to print out tomcat statistics.
8013 @item -mcpu=@var{cpu}
8016 Select the processor type for which to generate code. Possible values are
8017 @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
8018 @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
8022 @node H8/300 Options
8023 @subsection H8/300 Options
8025 These @samp{-m} options are defined for the H8/300 implementations:
8030 Shorten some address references at link time, when possible; uses the
8031 linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
8032 ld, Using ld}, for a fuller description.
8036 Generate code for the H8/300H@.
8040 Generate code for the H8S@.
8044 Generate code for the H8S and H8/300H in the normal mode. This switch
8045 must be used either with @option{-mh} or @option{-ms}.
8049 Generate code for the H8S/2600. This switch must be used with @option{-ms}.
8053 Make @code{int} data 32 bits by default.
8057 On the H8/300H and H8S, use the same alignment rules as for the H8/300.
8058 The default for the H8/300H and H8S is to align longs and floats on 4
8060 @option{-malign-300} causes them to be aligned on 2 byte boundaries.
8061 This option has no effect on the H8/300.
8065 @subsection HPPA Options
8066 @cindex HPPA Options
8068 These @samp{-m} options are defined for the HPPA family of computers:
8071 @item -march=@var{architecture-type}
8073 Generate code for the specified architecture. The choices for
8074 @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
8075 1.1, and @samp{2.0} for PA 2.0 processors. Refer to
8076 @file{/usr/lib/sched.models} on an HP-UX system to determine the proper
8077 architecture option for your machine. Code compiled for lower numbered
8078 architectures will run on higher numbered architectures, but not the
8082 @itemx -mpa-risc-1-1
8083 @itemx -mpa-risc-2-0
8084 @opindex mpa-risc-1-0
8085 @opindex mpa-risc-1-1
8086 @opindex mpa-risc-2-0
8087 Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
8090 @opindex mbig-switch
8091 Generate code suitable for big switch tables. Use this option only if
8092 the assembler/linker complain about out of range branches within a switch
8095 @item -mjump-in-delay
8096 @opindex mjump-in-delay
8097 Fill delay slots of function calls with unconditional jump instructions
8098 by modifying the return pointer for the function call to be the target
8099 of the conditional jump.
8101 @item -mdisable-fpregs
8102 @opindex mdisable-fpregs
8103 Prevent floating point registers from being used in any manner. This is
8104 necessary for compiling kernels which perform lazy context switching of
8105 floating point registers. If you use this option and attempt to perform
8106 floating point operations, the compiler will abort.
8108 @item -mdisable-indexing
8109 @opindex mdisable-indexing
8110 Prevent the compiler from using indexing address modes. This avoids some
8111 rather obscure problems when compiling MIG generated code under MACH@.
8113 @item -mno-space-regs
8114 @opindex mno-space-regs
8115 Generate code that assumes the target has no space registers. This allows
8116 GCC to generate faster indirect calls and use unscaled index address modes.
8118 Such code is suitable for level 0 PA systems and kernels.
8120 @item -mfast-indirect-calls
8121 @opindex mfast-indirect-calls
8122 Generate code that assumes calls never cross space boundaries. This
8123 allows GCC to emit code which performs faster indirect calls.
8125 This option will not work in the presence of shared libraries or nested
8128 @item -mfixed-range=@var{register-range}
8129 @opindex mfixed-range
8130 Generate code treating the given register range as fixed registers.
8131 A fixed register is one that the register allocator can not use. This is
8132 useful when compiling kernel code. A register range is specified as
8133 two registers separated by a dash. Multiple register ranges can be
8134 specified separated by a comma.
8136 @item -mlong-load-store
8137 @opindex mlong-load-store
8138 Generate 3-instruction load and store sequences as sometimes required by
8139 the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
8142 @item -mportable-runtime
8143 @opindex mportable-runtime
8144 Use the portable calling conventions proposed by HP for ELF systems.
8148 Enable the use of assembler directives only GAS understands.
8150 @item -mschedule=@var{cpu-type}
8152 Schedule code according to the constraints for the machine type
8153 @var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
8154 @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
8155 to @file{/usr/lib/sched.models} on an HP-UX system to determine the
8156 proper scheduling option for your machine. The default scheduling is
8160 @opindex mlinker-opt
8161 Enable the optimization pass in the HP-UX linker. Note this makes symbolic
8162 debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
8163 linkers in which they give bogus error messages when linking some programs.
8166 @opindex msoft-float
8167 Generate output containing library calls for floating point.
8168 @strong{Warning:} the requisite libraries are not available for all HPPA
8169 targets. Normally the facilities of the machine's usual C compiler are
8170 used, but this cannot be done directly in cross-compilation. You must make
8171 your own arrangements to provide suitable library functions for
8172 cross-compilation. The embedded target @samp{hppa1.1-*-pro}
8173 does provide software floating point support.
8175 @option{-msoft-float} changes the calling convention in the output file;
8176 therefore, it is only useful if you compile @emph{all} of a program with
8177 this option. In particular, you need to compile @file{libgcc.a}, the
8178 library that comes with GCC, with @option{-msoft-float} in order for
8183 Generate the predefine, @code{_SIO}, for server IO. The default is
8184 @option{-mwsio}. This generates the predefines, @code{__hp9000s700},
8185 @code{__hp9000s700__} and @code{_WSIO}, for workstation IO. These
8186 options are available under HP-UX and HI-UX.
8190 Use GNU ld specific options. This passes @option{-shared} to ld when
8191 building a shared library. It is the default when GCC is configured,
8192 explicitly or implicitly, with the GNU linker. This option does not
8193 have any affect on which ld is called, it only changes what parameters
8194 are passed to that ld. The ld that is called is determined by the
8195 @option{--with-ld} configure option, GCC's program search path, and
8196 finally by the user's @env{PATH}. The linker used by GCC can be printed
8197 using @samp{which `gcc -print-prog-name=ld`}.
8201 Use HP ld specific options. This passes @option{-b} to ld when building
8202 a shared library and passes @option{+Accept TypeMismatch} to ld on all
8203 links. It is the default when GCC is configured, explicitly or
8204 implicitly, with the HP linker. This option does not have any affect on
8205 which ld is called, it only changes what parameters are passed to that
8206 ld. The ld that is called is determined by the @option{--with-ld}
8207 configure option, GCC's program search path, and finally by the user's
8208 @env{PATH}. The linker used by GCC can be printed using @samp{which
8209 `gcc -print-prog-name=ld`}.
8212 @opindex mno-long-calls
8213 Generate code that uses long call sequences. This ensures that a call
8214 is always able to reach linker generated stubs. The default is to generate
8215 long calls only when the distance from the call site to the beginning
8216 of the function or translation unit, as the case may be, exceeds a
8217 predefined limit set by the branch type being used. The limits for
8218 normal calls are 7,600,000 and 240,000 bytes, respectively for the
8219 PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
8222 Distances are measured from the beginning of functions when using the
8223 @option{-ffunction-sections} option, or when using the @option{-mgas}
8224 and @option{-mno-portable-runtime} options together under HP-UX with
8227 It is normally not desirable to use this option as it will degrade
8228 performance. However, it may be useful in large applications,
8229 particularly when partial linking is used to build the application.
8231 The types of long calls used depends on the capabilities of the
8232 assembler and linker, and the type of code being generated. The
8233 impact on systems that support long absolute calls, and long pic
8234 symbol-difference or pc-relative calls should be relatively small.
8235 However, an indirect call is used on 32-bit ELF systems in pic code
8236 and it is quite long.
8238 @item -munix=@var{unix-std}
8240 Generate compiler predefines and select a startfile for the specified
8241 UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
8242 and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
8243 is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
8244 11.11 and later. The default values are @samp{93} for HP-UX 10.00,
8245 @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
8248 @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
8249 @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
8250 and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
8251 @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
8252 @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
8253 @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
8255 It is @emph{important} to note that this option changes the interfaces
8256 for various library routines. It also affects the operational behavior
8257 of the C library. Thus, @emph{extreme} care is needed in using this
8260 Library code that is intended to operate with more than one UNIX
8261 standard must test, set and restore the variable @var{__xpg4_extended_mask}
8262 as appropriate. Most GNU software doesn't provide this capability.
8266 Suppress the generation of link options to search libdld.sl when the
8267 @option{-static} option is specified on HP-UX 10 and later.
8271 The HP-UX implementation of setlocale in libc has a dependency on
8272 libdld.sl. There isn't an archive version of libdld.sl. Thus,
8273 when the @option{-static} option is specified, special link options
8274 are needed to resolve this dependency.
8276 On HP-UX 10 and later, the GCC driver adds the necessary options to
8277 link with libdld.sl when the @option{-static} option is specified.
8278 This causes the resulting binary to be dynamic. On the 64-bit port,
8279 the linkers generate dynamic binaries by default in any case. The
8280 @option{-nolibdld} option can be used to prevent the GCC driver from
8281 adding these link options.
8285 Add support for multithreading with the @dfn{dce thread} library
8286 under HP-UX. This option sets flags for both the preprocessor and
8290 @node i386 and x86-64 Options
8291 @subsection Intel 386 and AMD x86-64 Options
8292 @cindex i386 Options
8293 @cindex x86-64 Options
8294 @cindex Intel 386 Options
8295 @cindex AMD x86-64 Options
8297 These @samp{-m} options are defined for the i386 and x86-64 family of
8301 @item -mtune=@var{cpu-type}
8303 Tune to @var{cpu-type} everything applicable about the generated code, except
8304 for the ABI and the set of available instructions. The choices for
8308 Original Intel's i386 CPU.
8310 Intel's i486 CPU. (No scheduling is implemented for this chip.)
8312 Intel Pentium CPU with no MMX support.
8314 Intel PentiumMMX CPU based on Pentium core with MMX instruction set support.
8315 @item i686, pentiumpro
8316 Intel PentiumPro CPU.
8318 Intel Pentium2 CPU based on PentiumPro core with MMX instruction set support.
8319 @item pentium3, pentium3m
8320 Intel Pentium3 CPU based on PentiumPro core with MMX and SSE instruction set
8323 Low power version of Intel Pentium3 CPU with MMX, SSE and SSE2 instruction set
8324 support. Used by Centrino notebooks.
8325 @item pentium4, pentium4m
8326 Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set support.
8328 Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2 and SSE3 instruction
8331 Improved version of Intel Pentium4 CPU with 64-bit extensions, MMX, SSE,
8332 SSE2 and SSE3 instruction set support.
8334 AMD K6 CPU with MMX instruction set support.
8336 Improved versions of AMD K6 CPU with MMX and 3dNOW! instruction set support.
8337 @item athlon, athlon-tbird
8338 AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE prefetch instructions
8340 @item athlon-4, athlon-xp, athlon-mp
8341 Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and full SSE
8342 instruction set support.
8343 @item k8, opteron, athlon64, athlon-fx
8344 AMD K8 core based CPUs with x86-64 instruction set support. (This supersets
8345 MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and 64-bit instruction set extensions.)
8347 IDT Winchip C6 CPU, dealt in same way as i486 with additional MMX instruction
8350 IDT Winchip2 CPU, dealt in same way as i486 with additional MMX and 3dNOW!
8351 instruction set support.
8353 Via C3 CPU with MMX and 3dNOW! instruction set support. (No scheduling is
8354 implemented for this chip.)
8356 Via C3-2 CPU with MMX and SSE instruction set support. (No scheduling is
8357 implemented for this chip.)
8360 While picking a specific @var{cpu-type} will schedule things appropriately
8361 for that particular chip, the compiler will not generate any code that
8362 does not run on the i386 without the @option{-march=@var{cpu-type}} option
8365 @item -march=@var{cpu-type}
8367 Generate instructions for the machine type @var{cpu-type}. The choices
8368 for @var{cpu-type} are the same as for @option{-mtune}. Moreover,
8369 specifying @option{-march=@var{cpu-type}} implies @option{-mtune=@var{cpu-type}}.
8371 @item -mcpu=@var{cpu-type}
8373 A deprecated synonym for @option{-mtune}.
8382 @opindex mpentiumpro
8383 These options are synonyms for @option{-mtune=i386}, @option{-mtune=i486},
8384 @option{-mtune=pentium}, and @option{-mtune=pentiumpro} respectively.
8385 These synonyms are deprecated.
8387 @item -mfpmath=@var{unit}
8389 Generate floating point arithmetics for selected unit @var{unit}. The choices
8394 Use the standard 387 floating point coprocessor present majority of chips and
8395 emulated otherwise. Code compiled with this option will run almost everywhere.
8396 The temporary results are computed in 80bit precision instead of precision
8397 specified by the type resulting in slightly different results compared to most
8398 of other chips. See @option{-ffloat-store} for more detailed description.
8400 This is the default choice for i386 compiler.
8403 Use scalar floating point instructions present in the SSE instruction set.
8404 This instruction set is supported by Pentium3 and newer chips, in the AMD line
8405 by Athlon-4, Athlon-xp and Athlon-mp chips. The earlier version of SSE
8406 instruction set supports only single precision arithmetics, thus the double and
8407 extended precision arithmetics is still done using 387. Later version, present
8408 only in Pentium4 and the future AMD x86-64 chips supports double precision
8411 For i387 you need to use @option{-march=@var{cpu-type}}, @option{-msse} or
8412 @option{-msse2} switches to enable SSE extensions and make this option
8413 effective. For x86-64 compiler, these extensions are enabled by default.
8415 The resulting code should be considerably faster in the majority of cases and avoid
8416 the numerical instability problems of 387 code, but may break some existing
8417 code that expects temporaries to be 80bit.
8419 This is the default choice for the x86-64 compiler.
8422 Attempt to utilize both instruction sets at once. This effectively double the
8423 amount of available registers and on chips with separate execution units for
8424 387 and SSE the execution resources too. Use this option with care, as it is
8425 still experimental, because the GCC register allocator does not model separate
8426 functional units well resulting in instable performance.
8429 @item -masm=@var{dialect}
8430 @opindex masm=@var{dialect}
8431 Output asm instructions using selected @var{dialect}. Supported choices are
8432 @samp{intel} or @samp{att} (the default one).
8437 @opindex mno-ieee-fp
8438 Control whether or not the compiler uses IEEE floating point
8439 comparisons. These handle correctly the case where the result of a
8440 comparison is unordered.
8443 @opindex msoft-float
8444 Generate output containing library calls for floating point.
8445 @strong{Warning:} the requisite libraries are not part of GCC@.
8446 Normally the facilities of the machine's usual C compiler are used, but
8447 this can't be done directly in cross-compilation. You must make your
8448 own arrangements to provide suitable library functions for
8451 On machines where a function returns floating point results in the 80387
8452 register stack, some floating point opcodes may be emitted even if
8453 @option{-msoft-float} is used.
8455 @item -mno-fp-ret-in-387
8456 @opindex mno-fp-ret-in-387
8457 Do not use the FPU registers for return values of functions.
8459 The usual calling convention has functions return values of types
8460 @code{float} and @code{double} in an FPU register, even if there
8461 is no FPU@. The idea is that the operating system should emulate
8464 The option @option{-mno-fp-ret-in-387} causes such values to be returned
8465 in ordinary CPU registers instead.
8467 @item -mno-fancy-math-387
8468 @opindex mno-fancy-math-387
8469 Some 387 emulators do not support the @code{sin}, @code{cos} and
8470 @code{sqrt} instructions for the 387. Specify this option to avoid
8471 generating those instructions. This option is the default on FreeBSD,
8472 OpenBSD and NetBSD@. This option is overridden when @option{-march}
8473 indicates that the target cpu will always have an FPU and so the
8474 instruction will not need emulation. As of revision 2.6.1, these
8475 instructions are not generated unless you also use the
8476 @option{-funsafe-math-optimizations} switch.
8478 @item -malign-double
8479 @itemx -mno-align-double
8480 @opindex malign-double
8481 @opindex mno-align-double
8482 Control whether GCC aligns @code{double}, @code{long double}, and
8483 @code{long long} variables on a two word boundary or a one word
8484 boundary. Aligning @code{double} variables on a two word boundary will
8485 produce code that runs somewhat faster on a @samp{Pentium} at the
8486 expense of more memory.
8488 @strong{Warning:} if you use the @option{-malign-double} switch,
8489 structures containing the above types will be aligned differently than
8490 the published application binary interface specifications for the 386
8491 and will not be binary compatible with structures in code compiled
8492 without that switch.
8494 @item -m96bit-long-double
8495 @itemx -m128bit-long-double
8496 @opindex m96bit-long-double
8497 @opindex m128bit-long-double
8498 These switches control the size of @code{long double} type. The i386
8499 application binary interface specifies the size to be 96 bits,
8500 so @option{-m96bit-long-double} is the default in 32 bit mode.
8502 Modern architectures (Pentium and newer) would prefer @code{long double}
8503 to be aligned to an 8 or 16 byte boundary. In arrays or structures
8504 conforming to the ABI, this would not be possible. So specifying a
8505 @option{-m128bit-long-double} will align @code{long double}
8506 to a 16 byte boundary by padding the @code{long double} with an additional
8509 In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
8510 its ABI specifies that @code{long double} is to be aligned on 16 byte boundary.
8512 Notice that neither of these options enable any extra precision over the x87
8513 standard of 80 bits for a @code{long double}.
8515 @strong{Warning:} if you override the default value for your target ABI, the
8516 structures and arrays containing @code{long double} variables will change
8517 their size as well as function calling convention for function taking
8518 @code{long double} will be modified. Hence they will not be binary
8519 compatible with arrays or structures in code compiled without that switch.
8523 @itemx -mno-svr3-shlib
8524 @opindex msvr3-shlib
8525 @opindex mno-svr3-shlib
8526 Control whether GCC places uninitialized local variables into the
8527 @code{bss} or @code{data} segments. @option{-msvr3-shlib} places them
8528 into @code{bss}. These options are meaningful only on System V Release 3.
8532 Use a different function-calling convention, in which functions that
8533 take a fixed number of arguments return with the @code{ret} @var{num}
8534 instruction, which pops their arguments while returning. This saves one
8535 instruction in the caller since there is no need to pop the arguments
8538 You can specify that an individual function is called with this calling
8539 sequence with the function attribute @samp{stdcall}. You can also
8540 override the @option{-mrtd} option by using the function attribute
8541 @samp{cdecl}. @xref{Function Attributes}.
8543 @strong{Warning:} this calling convention is incompatible with the one
8544 normally used on Unix, so you cannot use it if you need to call
8545 libraries compiled with the Unix compiler.
8547 Also, you must provide function prototypes for all functions that
8548 take variable numbers of arguments (including @code{printf});
8549 otherwise incorrect code will be generated for calls to those
8552 In addition, seriously incorrect code will result if you call a
8553 function with too many arguments. (Normally, extra arguments are
8554 harmlessly ignored.)
8556 @item -mregparm=@var{num}
8558 Control how many registers are used to pass integer arguments. By
8559 default, no registers are used to pass arguments, and at most 3
8560 registers can be used. You can control this behavior for a specific
8561 function by using the function attribute @samp{regparm}.
8562 @xref{Function Attributes}.
8564 @strong{Warning:} if you use this switch, and
8565 @var{num} is nonzero, then you must build all modules with the same
8566 value, including any libraries. This includes the system libraries and
8569 @item -mpreferred-stack-boundary=@var{num}
8570 @opindex mpreferred-stack-boundary
8571 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
8572 byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
8573 the default is 4 (16 bytes or 128 bits), except when optimizing for code
8574 size (@option{-Os}), in which case the default is the minimum correct
8575 alignment (4 bytes for x86, and 8 bytes for x86-64).
8577 On Pentium and PentiumPro, @code{double} and @code{long double} values
8578 should be aligned to an 8 byte boundary (see @option{-malign-double}) or
8579 suffer significant run time performance penalties. On Pentium III, the
8580 Streaming SIMD Extension (SSE) data type @code{__m128} suffers similar
8581 penalties if it is not 16 byte aligned.
8583 To ensure proper alignment of this values on the stack, the stack boundary
8584 must be as aligned as that required by any value stored on the stack.
8585 Further, every function must be generated such that it keeps the stack
8586 aligned. Thus calling a function compiled with a higher preferred
8587 stack boundary from a function compiled with a lower preferred stack
8588 boundary will most likely misalign the stack. It is recommended that
8589 libraries that use callbacks always use the default setting.
8591 This extra alignment does consume extra stack space, and generally
8592 increases code size. Code that is sensitive to stack space usage, such
8593 as embedded systems and operating system kernels, may want to reduce the
8594 preferred alignment to @option{-mpreferred-stack-boundary=2}.
8612 These switches enable or disable the use of built-in functions that allow
8613 direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
8616 @xref{X86 Built-in Functions}, for details of the functions enabled
8617 and disabled by these switches.
8619 To have SSE/SSE2 instructions generated automatically from floating-point
8620 code, see @option{-mfpmath=sse}.
8623 @itemx -mno-push-args
8625 @opindex mno-push-args
8626 Use PUSH operations to store outgoing parameters. This method is shorter
8627 and usually equally fast as method using SUB/MOV operations and is enabled
8628 by default. In some cases disabling it may improve performance because of
8629 improved scheduling and reduced dependencies.
8631 @item -maccumulate-outgoing-args
8632 @opindex maccumulate-outgoing-args
8633 If enabled, the maximum amount of space required for outgoing arguments will be
8634 computed in the function prologue. This is faster on most modern CPUs
8635 because of reduced dependencies, improved scheduling and reduced stack usage
8636 when preferred stack boundary is not equal to 2. The drawback is a notable
8637 increase in code size. This switch implies @option{-mno-push-args}.
8641 Support thread-safe exception handling on @samp{Mingw32}. Code that relies
8642 on thread-safe exception handling must compile and link all code with the
8643 @option{-mthreads} option. When compiling, @option{-mthreads} defines
8644 @option{-D_MT}; when linking, it links in a special thread helper library
8645 @option{-lmingwthrd} which cleans up per thread exception handling data.
8647 @item -mno-align-stringops
8648 @opindex mno-align-stringops
8649 Do not align destination of inlined string operations. This switch reduces
8650 code size and improves performance in case the destination is already aligned,
8651 but GCC doesn't know about it.
8653 @item -minline-all-stringops
8654 @opindex minline-all-stringops
8655 By default GCC inlines string operations only when destination is known to be
8656 aligned at least to 4 byte boundary. This enables more inlining, increase code
8657 size, but may improve performance of code that depends on fast memcpy, strlen
8658 and memset for short lengths.
8660 @item -momit-leaf-frame-pointer
8661 @opindex momit-leaf-frame-pointer
8662 Don't keep the frame pointer in a register for leaf functions. This
8663 avoids the instructions to save, set up and restore frame pointers and
8664 makes an extra register available in leaf functions. The option
8665 @option{-fomit-frame-pointer} removes the frame pointer for all functions
8666 which might make debugging harder.
8668 @item -mtls-direct-seg-refs
8669 @itemx -mno-tls-direct-seg-refs
8670 @opindex mtls-direct-seg-refs
8671 Controls whether TLS variables may be accessed with offsets from the
8672 TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
8673 or whether the thread base pointer must be added. Whether or not this
8674 is legal depends on the operating system, and whether it maps the
8675 segment to cover the entire TLS area.
8677 For systems that use GNU libc, the default is on.
8680 These @samp{-m} switches are supported in addition to the above
8681 on AMD x86-64 processors in 64-bit environments.
8688 Generate code for a 32-bit or 64-bit environment.
8689 The 32-bit environment sets int, long and pointer to 32 bits and
8690 generates code that runs on any i386 system.
8691 The 64-bit environment sets int to 32 bits and long and pointer
8692 to 64 bits and generates code for AMD's x86-64 architecture.
8695 @opindex no-red-zone
8696 Do not use a so called red zone for x86-64 code. The red zone is mandated
8697 by the x86-64 ABI, it is a 128-byte area beyond the location of the
8698 stack pointer that will not be modified by signal or interrupt handlers
8699 and therefore can be used for temporary data without adjusting the stack
8700 pointer. The flag @option{-mno-red-zone} disables this red zone.
8702 @item -mcmodel=small
8703 @opindex mcmodel=small
8704 Generate code for the small code model: the program and its symbols must
8705 be linked in the lower 2 GB of the address space. Pointers are 64 bits.
8706 Programs can be statically or dynamically linked. This is the default
8709 @item -mcmodel=kernel
8710 @opindex mcmodel=kernel
8711 Generate code for the kernel code model. The kernel runs in the
8712 negative 2 GB of the address space.
8713 This model has to be used for Linux kernel code.
8715 @item -mcmodel=medium
8716 @opindex mcmodel=medium
8717 Generate code for the medium model: The program is linked in the lower 2
8718 GB of the address space but symbols can be located anywhere in the
8719 address space. Programs can be statically or dynamically linked, but
8720 building of shared libraries are not supported with the medium model.
8722 @item -mcmodel=large
8723 @opindex mcmodel=large
8724 Generate code for the large model: This model makes no assumptions
8725 about addresses and sizes of sections. Currently GCC does not implement
8730 @subsection IA-64 Options
8731 @cindex IA-64 Options
8733 These are the @samp{-m} options defined for the Intel IA-64 architecture.
8737 @opindex mbig-endian
8738 Generate code for a big endian target. This is the default for HP-UX@.
8740 @item -mlittle-endian
8741 @opindex mlittle-endian
8742 Generate code for a little endian target. This is the default for AIX5
8749 Generate (or don't) code for the GNU assembler. This is the default.
8750 @c Also, this is the default if the configure option @option{--with-gnu-as}
8757 Generate (or don't) code for the GNU linker. This is the default.
8758 @c Also, this is the default if the configure option @option{--with-gnu-ld}
8763 Generate code that does not use a global pointer register. The result
8764 is not position independent code, and violates the IA-64 ABI@.
8766 @item -mvolatile-asm-stop
8767 @itemx -mno-volatile-asm-stop
8768 @opindex mvolatile-asm-stop
8769 @opindex mno-volatile-asm-stop
8770 Generate (or don't) a stop bit immediately before and after volatile asm
8775 Generate code that works around Itanium B step errata.
8777 @item -mregister-names
8778 @itemx -mno-register-names
8779 @opindex mregister-names
8780 @opindex mno-register-names
8781 Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
8782 the stacked registers. This may make assembler output more readable.
8788 Disable (or enable) optimizations that use the small data section. This may
8789 be useful for working around optimizer bugs.
8792 @opindex mconstant-gp
8793 Generate code that uses a single constant global pointer value. This is
8794 useful when compiling kernel code.
8798 Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
8799 This is useful when compiling firmware code.
8801 @item -minline-float-divide-min-latency
8802 @opindex minline-float-divide-min-latency
8803 Generate code for inline divides of floating point values
8804 using the minimum latency algorithm.
8806 @item -minline-float-divide-max-throughput
8807 @opindex minline-float-divide-max-throughput
8808 Generate code for inline divides of floating point values
8809 using the maximum throughput algorithm.
8811 @item -minline-int-divide-min-latency
8812 @opindex minline-int-divide-min-latency
8813 Generate code for inline divides of integer values
8814 using the minimum latency algorithm.
8816 @item -minline-int-divide-max-throughput
8817 @opindex minline-int-divide-max-throughput
8818 Generate code for inline divides of integer values
8819 using the maximum throughput algorithm.
8821 @item -mno-dwarf2-asm
8823 @opindex mno-dwarf2-asm
8824 @opindex mdwarf2-asm
8825 Don't (or do) generate assembler code for the DWARF2 line number debugging
8826 info. This may be useful when not using the GNU assembler.
8828 @item -mfixed-range=@var{register-range}
8829 @opindex mfixed-range
8830 Generate code treating the given register range as fixed registers.
8831 A fixed register is one that the register allocator can not use. This is
8832 useful when compiling kernel code. A register range is specified as
8833 two registers separated by a dash. Multiple register ranges can be
8834 specified separated by a comma.
8836 @item -mearly-stop-bits
8837 @itemx -mno-early-stop-bits
8838 @opindex mearly-stop-bits
8839 @opindex mno-early-stop-bits
8840 Allow stop bits to be placed earlier than immediately preceding the
8841 instruction that triggered the stop bit. This can improve instruction
8842 scheduling, but does not always do so.
8845 @node M32R/D Options
8846 @subsection M32R/D Options
8847 @cindex M32R/D options
8849 These @option{-m} options are defined for Renesas M32R/D architectures:
8854 Generate code for the M32R/2@.
8858 Generate code for the M32R/X@.
8862 Generate code for the M32R@. This is the default.
8865 @opindex mmodel=small
8866 Assume all objects live in the lower 16MB of memory (so that their addresses
8867 can be loaded with the @code{ld24} instruction), and assume all subroutines
8868 are reachable with the @code{bl} instruction.
8869 This is the default.
8871 The addressability of a particular object can be set with the
8872 @code{model} attribute.
8874 @item -mmodel=medium
8875 @opindex mmodel=medium
8876 Assume objects may be anywhere in the 32-bit address space (the compiler
8877 will generate @code{seth/add3} instructions to load their addresses), and
8878 assume all subroutines are reachable with the @code{bl} instruction.
8881 @opindex mmodel=large
8882 Assume objects may be anywhere in the 32-bit address space (the compiler
8883 will generate @code{seth/add3} instructions to load their addresses), and
8884 assume subroutines may not be reachable with the @code{bl} instruction
8885 (the compiler will generate the much slower @code{seth/add3/jl}
8886 instruction sequence).
8889 @opindex msdata=none
8890 Disable use of the small data area. Variables will be put into
8891 one of @samp{.data}, @samp{bss}, or @samp{.rodata} (unless the
8892 @code{section} attribute has been specified).
8893 This is the default.
8895 The small data area consists of sections @samp{.sdata} and @samp{.sbss}.
8896 Objects may be explicitly put in the small data area with the
8897 @code{section} attribute using one of these sections.
8900 @opindex msdata=sdata
8901 Put small global and static data in the small data area, but do not
8902 generate special code to reference them.
8906 Put small global and static data in the small data area, and generate
8907 special instructions to reference them.
8911 @cindex smaller data references
8912 Put global and static objects less than or equal to @var{num} bytes
8913 into the small data or bss sections instead of the normal data or bss
8914 sections. The default value of @var{num} is 8.
8915 The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
8916 for this option to have any effect.
8918 All modules should be compiled with the same @option{-G @var{num}} value.
8919 Compiling with different values of @var{num} may or may not work; if it
8920 doesn't the linker will give an error message---incorrect code will not be
8925 Makes the M32R specific code in the compiler display some statistics
8926 that might help in debugging programs.
8929 @opindex malign-loops
8930 Align all loops to a 32-byte boundary.
8932 @item -mno-align-loops
8933 @opindex mno-align-loops
8934 Do not enforce a 32-byte alignment for loops. This is the default.
8936 @item -missue-rate=@var{number}
8937 @opindex missue-rate=@var{number}
8938 Issue @var{number} instructions per cycle. @var{number} can only be 1
8941 @item -mbranch-cost=@var{number}
8942 @opindex mbranch-cost=@var{number}
8943 @var{number} can only be 1 or 2. If it is 1 then branches will be
8944 preferred over conditional code, if it is 2, then the opposite will
8947 @item -mflush-trap=@var{number}
8948 @opindex mflush-trap=@var{number}
8949 Specifies the trap number to use to flush the cache. The default is
8950 12. Valid numbers are between 0 and 15 inclusive.
8952 @item -mno-flush-trap
8953 @opindex mno-flush-trap
8954 Specifies that the cache cannot be flushed by using a trap.
8956 @item -mflush-func=@var{name}
8957 @opindex mflush-func=@var{name}
8958 Specifies the name of the operating system function to call to flush
8959 the cache. The default is @emph{_flush_cache}, but a function call
8960 will only be used if a trap is not available.
8962 @item -mno-flush-func
8963 @opindex mno-flush-func
8964 Indicates that there is no OS function for flushing the cache.
8968 @node M680x0 Options
8969 @subsection M680x0 Options
8970 @cindex M680x0 options
8972 These are the @samp{-m} options defined for the 68000 series. The default
8973 values for these options depends on which style of 68000 was selected when
8974 the compiler was configured; the defaults for the most common choices are
8982 Generate output for a 68000. This is the default
8983 when the compiler is configured for 68000-based systems.
8985 Use this option for microcontrollers with a 68000 or EC000 core,
8986 including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
8992 Generate output for a 68020. This is the default
8993 when the compiler is configured for 68020-based systems.
8997 Generate output containing 68881 instructions for floating point.
8998 This is the default for most 68020 systems unless @option{--nfp} was
8999 specified when the compiler was configured.
9003 Generate output for a 68030. This is the default when the compiler is
9004 configured for 68030-based systems.
9008 Generate output for a 68040. This is the default when the compiler is
9009 configured for 68040-based systems.
9011 This option inhibits the use of 68881/68882 instructions that have to be
9012 emulated by software on the 68040. Use this option if your 68040 does not
9013 have code to emulate those instructions.
9017 Generate output for a 68060. This is the default when the compiler is
9018 configured for 68060-based systems.
9020 This option inhibits the use of 68020 and 68881/68882 instructions that
9021 have to be emulated by software on the 68060. Use this option if your 68060
9022 does not have code to emulate those instructions.
9026 Generate output for a CPU32. This is the default
9027 when the compiler is configured for CPU32-based systems.
9029 Use this option for microcontrollers with a
9030 CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
9031 68336, 68340, 68341, 68349 and 68360.
9035 Generate output for a 520X ``coldfire'' family cpu. This is the default
9036 when the compiler is configured for 520X-based systems.
9038 Use this option for microcontroller with a 5200 core, including
9039 the MCF5202, MCF5203, MCF5204 and MCF5202.
9044 Generate output for a 68040, without using any of the new instructions.
9045 This results in code which can run relatively efficiently on either a
9046 68020/68881 or a 68030 or a 68040. The generated code does use the
9047 68881 instructions that are emulated on the 68040.
9051 Generate output for a 68060, without using any of the new instructions.
9052 This results in code which can run relatively efficiently on either a
9053 68020/68881 or a 68030 or a 68040. The generated code does use the
9054 68881 instructions that are emulated on the 68060.
9057 @opindex msoft-float
9058 Generate output containing library calls for floating point.
9059 @strong{Warning:} the requisite libraries are not available for all m68k
9060 targets. Normally the facilities of the machine's usual C compiler are
9061 used, but this can't be done directly in cross-compilation. You must
9062 make your own arrangements to provide suitable library functions for
9063 cross-compilation. The embedded targets @samp{m68k-*-aout} and
9064 @samp{m68k-*-coff} do provide software floating point support.
9068 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9069 Additionally, parameters passed on the stack are also aligned to a
9070 16-bit boundary even on targets whose API mandates promotion to 32-bit.
9073 @opindex mnobitfield
9074 Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
9075 and @option{-m5200} options imply @w{@option{-mnobitfield}}.
9079 Do use the bit-field instructions. The @option{-m68020} option implies
9080 @option{-mbitfield}. This is the default if you use a configuration
9081 designed for a 68020.
9085 Use a different function-calling convention, in which functions
9086 that take a fixed number of arguments return with the @code{rtd}
9087 instruction, which pops their arguments while returning. This
9088 saves one instruction in the caller since there is no need to pop
9089 the arguments there.
9091 This calling convention is incompatible with the one normally
9092 used on Unix, so you cannot use it if you need to call libraries
9093 compiled with the Unix compiler.
9095 Also, you must provide function prototypes for all functions that
9096 take variable numbers of arguments (including @code{printf});
9097 otherwise incorrect code will be generated for calls to those
9100 In addition, seriously incorrect code will result if you call a
9101 function with too many arguments. (Normally, extra arguments are
9102 harmlessly ignored.)
9104 The @code{rtd} instruction is supported by the 68010, 68020, 68030,
9105 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
9108 @itemx -mno-align-int
9110 @opindex mno-align-int
9111 Control whether GCC aligns @code{int}, @code{long}, @code{long long},
9112 @code{float}, @code{double}, and @code{long double} variables on a 32-bit
9113 boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
9114 Aligning variables on 32-bit boundaries produces code that runs somewhat
9115 faster on processors with 32-bit busses at the expense of more memory.
9117 @strong{Warning:} if you use the @option{-malign-int} switch, GCC will
9118 align structures containing the above types differently than
9119 most published application binary interface specifications for the m68k.
9123 Use the pc-relative addressing mode of the 68000 directly, instead of
9124 using a global offset table. At present, this option implies @option{-fpic},
9125 allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
9126 not presently supported with @option{-mpcrel}, though this could be supported for
9127 68020 and higher processors.
9129 @item -mno-strict-align
9130 @itemx -mstrict-align
9131 @opindex mno-strict-align
9132 @opindex mstrict-align
9133 Do not (do) assume that unaligned memory references will be handled by
9137 Generate code that allows the data segment to be located in a different
9138 area of memory from the text segment. This allows for execute in place in
9139 an environment without virtual memory management. This option implies
9143 Generate code that assumes that the data segment follows the text segment.
9144 This is the default.
9146 @item -mid-shared-library
9147 Generate code that supports shared libraries via the library ID method.
9148 This allows for execute in place and shared libraries in an environment
9149 without virtual memory management. This option implies @option{-fPIC}.
9151 @item -mno-id-shared-library
9152 Generate code that doesn't assume ID based shared libraries are being used.
9153 This is the default.
9155 @item -mshared-library-id=n
9156 Specified the identification number of the ID based shared library being
9157 compiled. Specifying a value of 0 will generate more compact code, specifying
9158 other values will force the allocation of that number to the current
9159 library but is no more space or time efficient than omitting this option.
9163 @node M68hc1x Options
9164 @subsection M68hc1x Options
9165 @cindex M68hc1x options
9167 These are the @samp{-m} options defined for the 68hc11 and 68hc12
9168 microcontrollers. The default values for these options depends on
9169 which style of microcontroller was selected when the compiler was configured;
9170 the defaults for the most common choices are given below.
9177 Generate output for a 68HC11. This is the default
9178 when the compiler is configured for 68HC11-based systems.
9184 Generate output for a 68HC12. This is the default
9185 when the compiler is configured for 68HC12-based systems.
9191 Generate output for a 68HCS12.
9194 @opindex mauto-incdec
9195 Enable the use of 68HC12 pre and post auto-increment and auto-decrement
9202 Enable the use of 68HC12 min and max instructions.
9205 @itemx -mno-long-calls
9206 @opindex mlong-calls
9207 @opindex mno-long-calls
9208 Treat all calls as being far away (near). If calls are assumed to be
9209 far away, the compiler will use the @code{call} instruction to
9210 call a function and the @code{rtc} instruction for returning.
9214 Consider type @code{int} to be 16 bits wide, like @code{short int}.
9216 @item -msoft-reg-count=@var{count}
9217 @opindex msoft-reg-count
9218 Specify the number of pseudo-soft registers which are used for the
9219 code generation. The maximum number is 32. Using more pseudo-soft
9220 register may or may not result in better code depending on the program.
9221 The default is 4 for 68HC11 and 2 for 68HC12.
9226 @subsection MCore Options
9227 @cindex MCore options
9229 These are the @samp{-m} options defined for the Motorola M*Core
9237 @opindex mno-hardlit
9238 Inline constants into the code stream if it can be done in two
9239 instructions or less.
9245 Use the divide instruction. (Enabled by default).
9247 @item -mrelax-immediate
9248 @itemx -mno-relax-immediate
9249 @opindex mrelax-immediate
9250 @opindex mno-relax-immediate
9251 Allow arbitrary sized immediates in bit operations.
9253 @item -mwide-bitfields
9254 @itemx -mno-wide-bitfields
9255 @opindex mwide-bitfields
9256 @opindex mno-wide-bitfields
9257 Always treat bit-fields as int-sized.
9259 @item -m4byte-functions
9260 @itemx -mno-4byte-functions
9261 @opindex m4byte-functions
9262 @opindex mno-4byte-functions
9263 Force all functions to be aligned to a four byte boundary.
9265 @item -mcallgraph-data
9266 @itemx -mno-callgraph-data
9267 @opindex mcallgraph-data
9268 @opindex mno-callgraph-data
9269 Emit callgraph information.
9272 @itemx -mno-slow-bytes
9273 @opindex mslow-bytes
9274 @opindex mno-slow-bytes
9275 Prefer word access when reading byte quantities.
9277 @item -mlittle-endian
9279 @opindex mlittle-endian
9280 @opindex mbig-endian
9281 Generate code for a little endian target.
9287 Generate code for the 210 processor.
9291 @subsection MIPS Options
9292 @cindex MIPS options
9298 Generate big-endian code.
9302 Generate little-endian code. This is the default for @samp{mips*el-*-*}
9305 @item -march=@var{arch}
9307 Generate code that will run on @var{arch}, which can be the name of a
9308 generic MIPS ISA, or the name of a particular processor.
9310 @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
9311 @samp{mips32}, @samp{mips32r2}, and @samp{mips64}.
9312 The processor names are:
9313 @samp{4kc}, @samp{4kp}, @samp{5kc}, @samp{20kc},
9315 @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
9316 @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, @samp{rm7000},
9320 @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
9321 @samp{vr5000}, @samp{vr5400} and @samp{vr5500}.
9322 The special value @samp{from-abi} selects the
9323 most compatible architecture for the selected ABI (that is,
9324 @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
9326 In processor names, a final @samp{000} can be abbreviated as @samp{k}
9327 (for example, @samp{-march=r2k}). Prefixes are optional, and
9328 @samp{vr} may be written @samp{r}.
9330 GCC defines two macros based on the value of this option. The first
9331 is @samp{_MIPS_ARCH}, which gives the name of target architecture, as
9332 a string. The second has the form @samp{_MIPS_ARCH_@var{foo}},
9333 where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@.
9334 For example, @samp{-march=r2000} will set @samp{_MIPS_ARCH}
9335 to @samp{"r2000"} and define the macro @samp{_MIPS_ARCH_R2000}.
9337 Note that the @samp{_MIPS_ARCH} macro uses the processor names given
9338 above. In other words, it will have the full prefix and will not
9339 abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
9340 the macro names the resolved architecture (either @samp{"mips1"} or
9341 @samp{"mips3"}). It names the default architecture when no
9342 @option{-march} option is given.
9344 @item -mtune=@var{arch}
9346 Optimize for @var{arch}. Among other things, this option controls
9347 the way instructions are scheduled, and the perceived cost of arithmetic
9348 operations. The list of @var{arch} values is the same as for
9351 When this option is not used, GCC will optimize for the processor
9352 specified by @option{-march}. By using @option{-march} and
9353 @option{-mtune} together, it is possible to generate code that will
9354 run on a family of processors, but optimize the code for one
9355 particular member of that family.
9357 @samp{-mtune} defines the macros @samp{_MIPS_TUNE} and
9358 @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the
9359 @samp{-march} ones described above.
9363 Equivalent to @samp{-march=mips1}.
9367 Equivalent to @samp{-march=mips2}.
9371 Equivalent to @samp{-march=mips3}.
9375 Equivalent to @samp{-march=mips4}.
9379 Equivalent to @samp{-march=mips32}.
9383 Equivalent to @samp{-march=mips32r2}.
9387 Equivalent to @samp{-march=mips64}.
9393 Use (do not use) the MIPS16 ISA.
9405 Generate code for the given ABI@.
9407 Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
9408 generates 64-bit code when you select a 64-bit architecture, but you
9409 can use @option{-mgp32} to get 32-bit code instead.
9411 For information about the O64 ABI, see
9412 @w{@uref{http://gcc.gnu.org/projects/mipso64-abi.html}}.
9415 @itemx -mno-abicalls
9417 @opindex mno-abicalls
9418 Generate (do not generate) SVR4-style position-independent code.
9419 @option{-mabicalls} is the default for SVR4-based systems.
9425 Lift (do not lift) the usual restrictions on the size of the global
9428 GCC normally uses a single instruction to load values from the GOT.
9429 While this is relatively efficient, it will only work if the GOT
9430 is smaller than about 64k. Anything larger will cause the linker
9431 to report an error such as:
9433 @cindex relocation truncated to fit (MIPS)
9435 relocation truncated to fit: R_MIPS_GOT16 foobar
9438 If this happens, you should recompile your code with @option{-mxgot}.
9439 It should then work with very large GOTs, although it will also be
9440 less efficient, since it will take three instructions to fetch the
9441 value of a global symbol.
9443 Note that some linkers can create multiple GOTs. If you have such a
9444 linker, you should only need to use @option{-mxgot} when a single object
9445 file accesses more than 64k's worth of GOT entries. Very few do.
9447 These options have no effect unless GCC is generating position
9452 Assume that general-purpose registers are 32 bits wide.
9456 Assume that general-purpose registers are 64 bits wide.
9460 Assume that floating-point registers are 32 bits wide.
9464 Assume that floating-point registers are 64 bits wide.
9467 @opindex mhard-float
9468 Use floating-point coprocessor instructions.
9471 @opindex msoft-float
9472 Do not use floating-point coprocessor instructions. Implement
9473 floating-point calculations using library calls instead.
9475 @item -msingle-float
9476 @opindex msingle-float
9477 Assume that the floating-point coprocessor only supports single-precision
9480 @itemx -mdouble-float
9481 @opindex mdouble-float
9482 Assume that the floating-point coprocessor supports double-precision
9483 operations. This is the default.
9485 @itemx -mpaired-single
9486 @itemx -mno-paired-single
9487 @opindex mpaired-single
9488 @opindex mno-paired-single
9489 Use (do not use) paired-single floating-point instructions.
9490 @xref{MIPS Paired-Single Support}. This option can only be used
9491 when generating 64-bit code and requires hardware floating-point
9492 support to be enabled.
9498 Use (do not use) the MIPS-3D ASE. @xref{MIPS-3D Built-in Functions}.
9499 The option @option{-mips3d} implies @option{-mpaired-single}.
9503 Force @code{int} and @code{long} types to be 64 bits wide. See
9504 @option{-mlong32} for an explanation of the default and the way
9505 that the pointer size is determined.
9509 Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
9510 an explanation of the default and the way that the pointer size is
9515 Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
9517 The default size of @code{int}s, @code{long}s and pointers depends on
9518 the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
9519 uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
9520 32-bit @code{long}s. Pointers are the same size as @code{long}s,
9521 or the same size as integer registers, whichever is smaller.
9525 @cindex smaller data references (MIPS)
9526 @cindex gp-relative references (MIPS)
9527 Put global and static items less than or equal to @var{num} bytes into
9528 the small data or bss section instead of the normal data or bss section.
9529 This allows the data to be accessed using a single instruction.
9531 All modules should be compiled with the same @option{-G @var{num}}
9534 @item -membedded-data
9535 @itemx -mno-embedded-data
9536 @opindex membedded-data
9537 @opindex mno-embedded-data
9538 Allocate variables to the read-only data section first if possible, then
9539 next in the small data section if possible, otherwise in data. This gives
9540 slightly slower code than the default, but reduces the amount of RAM required
9541 when executing, and thus may be preferred for some embedded systems.
9543 @item -muninit-const-in-rodata
9544 @itemx -mno-uninit-const-in-rodata
9545 @opindex muninit-const-in-rodata
9546 @opindex mno-uninit-const-in-rodata
9547 Put uninitialized @code{const} variables in the read-only data section.
9548 This option is only meaningful in conjunction with @option{-membedded-data}.
9550 @item -msplit-addresses
9551 @itemx -mno-split-addresses
9552 @opindex msplit-addresses
9553 @opindex mno-split-addresses
9554 Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
9555 relocation operators. This option has been superceded by
9556 @option{-mexplicit-relocs} but is retained for backwards compatibility.
9558 @item -mexplicit-relocs
9559 @itemx -mno-explicit-relocs
9560 @opindex mexplicit-relocs
9561 @opindex mno-explicit-relocs
9562 Use (do not use) assembler relocation operators when dealing with symbolic
9563 addresses. The alternative, selected by @option{-mno-explicit-relocs},
9564 is to use assembler macros instead.
9566 @option{-mexplicit-relocs} is the default if GCC was configured
9567 to use an assembler that supports relocation operators.
9569 @item -mcheck-zero-division
9570 @itemx -mno-check-zero-division
9571 @opindex mcheck-zero-division
9572 @opindex mno-check-zero-division
9573 Trap (do not trap) on integer division by zero. The default is
9574 @option{-mcheck-zero-division}.
9576 @item -mdivide-traps
9577 @itemx -mdivide-breaks
9578 @opindex mdivide-traps
9579 @opindex mdivide-breaks
9580 MIPS systems check for division by zero by generating either a
9581 conditional trap or a break instruction. Using traps results in
9582 smaller code, but is only supported on MIPS II and later. Also, some
9583 versions of the Linux kernel have a bug that prevents trap from
9584 generating the proper signal (SIGFPE). Use @option{-mdivide-traps} to
9585 allow conditional traps on architectures that support them and
9586 @option{-mdivide-breaks} to force the use of breaks.
9588 The default is usually @option{-mdivide-traps}, but this can be
9589 overridden at configure time using @option{--with-divide=breaks}.
9590 Divide-by-zero checks can be completely disabled using
9591 @option{-mno-check-zero-division}.
9597 Force (do not force) the use of @code{memcpy()} for non-trivial block
9598 moves. The default is @option{-mno-memcpy}, which allows GCC to inline
9599 most constant-sized copies.
9602 @itemx -mno-long-calls
9603 @opindex mlong-calls
9604 @opindex mno-long-calls
9605 Disable (do not disable) use of the @code{jal} instruction. Calling
9606 functions using @code{jal} is more efficient but requires the caller
9607 and callee to be in the same 256 megabyte segment.
9609 This option has no effect on abicalls code. The default is
9610 @option{-mno-long-calls}.
9616 Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
9617 instructions, as provided by the R4650 ISA.
9620 @itemx -mno-fused-madd
9621 @opindex mfused-madd
9622 @opindex mno-fused-madd
9623 Enable (disable) use of the floating point multiply-accumulate
9624 instructions, when they are available. The default is
9625 @option{-mfused-madd}.
9627 When multiply-accumulate instructions are used, the intermediate
9628 product is calculated to infinite precision and is not subject to
9629 the FCSR Flush to Zero bit. This may be undesirable in some
9634 Tell the MIPS assembler to not run its preprocessor over user
9635 assembler files (with a @samp{.s} suffix) when assembling them.
9638 @itemx -mno-fix-r4000
9640 @opindex mno-fix-r4000
9641 Work around certain R4000 CPU errata:
9644 A double-word or a variable shift may give an incorrect result if executed
9645 immediately after starting an integer division.
9647 A double-word or a variable shift may give an incorrect result if executed
9648 while an integer multiplication is in progress.
9650 An integer division may give an incorrect result if started in a delay slot
9651 of a taken branch or a jump.
9655 @itemx -mno-fix-r4400
9657 @opindex mno-fix-r4400
9658 Work around certain R4400 CPU errata:
9661 A double-word or a variable shift may give an incorrect result if executed
9662 immediately after starting an integer division.
9666 @itemx -mno-fix-vr4120
9667 @opindex mfix-vr4120
9668 Work around certain VR4120 errata:
9671 @code{dmultu} does not always produce the correct result.
9673 @code{div} and @code{ddiv} do not always produce the correct result if one
9674 of the operands is negative.
9676 The workarounds for the division errata rely on special functions in
9677 @file{libgcc.a}. At present, these functions are only provided by
9678 the @code{mips64vr*-elf} configurations.
9680 Other VR4120 errata require a nop to be inserted between certain pairs of
9681 instructions. These errata are handled by the assembler, not by GCC itself.
9686 Work around certain SB-1 CPU core errata.
9687 (This flag currently works around the SB-1 revision 2
9688 ``F1'' and ``F2'' floating point errata.)
9690 @item -mflush-func=@var{func}
9691 @itemx -mno-flush-func
9692 @opindex mflush-func
9693 Specifies the function to call to flush the I and D caches, or to not
9694 call any such function. If called, the function must take the same
9695 arguments as the common @code{_flush_func()}, that is, the address of the
9696 memory range for which the cache is being flushed, the size of the
9697 memory range, and the number 3 (to flush both caches). The default
9698 depends on the target GCC was configured for, but commonly is either
9699 @samp{_flush_func} or @samp{__cpu_flush}.
9701 @item -mbranch-likely
9702 @itemx -mno-branch-likely
9703 @opindex mbranch-likely
9704 @opindex mno-branch-likely
9705 Enable or disable use of Branch Likely instructions, regardless of the
9706 default for the selected architecture. By default, Branch Likely
9707 instructions may be generated if they are supported by the selected
9708 architecture. An exception is for the MIPS32 and MIPS64 architectures
9709 and processors which implement those architectures; for those, Branch
9710 Likely instructions will not be generated by default because the MIPS32
9711 and MIPS64 architectures specifically deprecate their use.
9713 @item -mfp-exceptions
9714 @itemx -mno-fp-exceptions
9715 @opindex mfp-exceptions
9716 Specifies whether FP exceptions are enabled. This affects how we schedule
9717 FP instructions for some processors. The default is that FP exceptions are
9720 For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
9721 64-bit code, then we can use both FP pipes. Otherwise, we can only use one
9724 @item -mvr4130-align
9725 @itemx -mno-vr4130-align
9726 @opindex mvr4130-align
9727 The VR4130 pipeline is two-way superscalar, but can only issue two
9728 instructions together if the first one is 8-byte aligned. When this
9729 option is enabled, GCC will align pairs of instructions that it
9730 thinks should execute in parallel.
9732 This option only has an effect when optimizing for the VR4130.
9733 It normally makes code faster, but at the expense of making it bigger.
9734 It is enabled by default at optimization level @option{-O3}.
9738 @subsection MMIX Options
9739 @cindex MMIX Options
9741 These options are defined for the MMIX:
9745 @itemx -mno-libfuncs
9747 @opindex mno-libfuncs
9748 Specify that intrinsic library functions are being compiled, passing all
9749 values in registers, no matter the size.
9754 @opindex mno-epsilon
9755 Generate floating-point comparison instructions that compare with respect
9756 to the @code{rE} epsilon register.
9758 @item -mabi=mmixware
9760 @opindex mabi-mmixware
9762 Generate code that passes function parameters and return values that (in
9763 the called function) are seen as registers @code{$0} and up, as opposed to
9764 the GNU ABI which uses global registers @code{$231} and up.
9767 @itemx -mno-zero-extend
9768 @opindex mzero-extend
9769 @opindex mno-zero-extend
9770 When reading data from memory in sizes shorter than 64 bits, use (do not
9771 use) zero-extending load instructions by default, rather than
9772 sign-extending ones.
9775 @itemx -mno-knuthdiv
9777 @opindex mno-knuthdiv
9778 Make the result of a division yielding a remainder have the same sign as
9779 the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
9780 remainder follows the sign of the dividend. Both methods are
9781 arithmetically valid, the latter being almost exclusively used.
9783 @item -mtoplevel-symbols
9784 @itemx -mno-toplevel-symbols
9785 @opindex mtoplevel-symbols
9786 @opindex mno-toplevel-symbols
9787 Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
9788 code can be used with the @code{PREFIX} assembly directive.
9792 Generate an executable in the ELF format, rather than the default
9793 @samp{mmo} format used by the @command{mmix} simulator.
9795 @item -mbranch-predict
9796 @itemx -mno-branch-predict
9797 @opindex mbranch-predict
9798 @opindex mno-branch-predict
9799 Use (do not use) the probable-branch instructions, when static branch
9800 prediction indicates a probable branch.
9802 @item -mbase-addresses
9803 @itemx -mno-base-addresses
9804 @opindex mbase-addresses
9805 @opindex mno-base-addresses
9806 Generate (do not generate) code that uses @emph{base addresses}. Using a
9807 base address automatically generates a request (handled by the assembler
9808 and the linker) for a constant to be set up in a global register. The
9809 register is used for one or more base address requests within the range 0
9810 to 255 from the value held in the register. The generally leads to short
9811 and fast code, but the number of different data items that can be
9812 addressed is limited. This means that a program that uses lots of static
9813 data may require @option{-mno-base-addresses}.
9816 @itemx -mno-single-exit
9817 @opindex msingle-exit
9818 @opindex mno-single-exit
9819 Force (do not force) generated code to have a single exit point in each
9823 @node MN10300 Options
9824 @subsection MN10300 Options
9825 @cindex MN10300 options
9827 These @option{-m} options are defined for Matsushita MN10300 architectures:
9832 Generate code to avoid bugs in the multiply instructions for the MN10300
9833 processors. This is the default.
9836 @opindex mno-mult-bug
9837 Do not generate code to avoid bugs in the multiply instructions for the
9842 Generate code which uses features specific to the AM33 processor.
9846 Do not generate code which uses features specific to the AM33 processor. This
9851 Do not link in the C run-time initialization object file.
9855 Indicate to the linker that it should perform a relaxation optimization pass
9856 to shorten branches, calls and absolute memory addresses. This option only
9857 has an effect when used on the command line for the final link step.
9859 This option makes symbolic debugging impossible.
9863 @subsection NS32K Options
9864 @cindex NS32K options
9866 These are the @samp{-m} options defined for the 32000 series. The default
9867 values for these options depends on which style of 32000 was selected when
9868 the compiler was configured; the defaults for the most common choices are
9876 Generate output for a 32032. This is the default
9877 when the compiler is configured for 32032 and 32016 based systems.
9883 Generate output for a 32332. This is the default
9884 when the compiler is configured for 32332-based systems.
9890 Generate output for a 32532. This is the default
9891 when the compiler is configured for 32532-based systems.
9895 Generate output containing 32081 instructions for floating point.
9896 This is the default for all systems.
9900 Generate output containing 32381 instructions for floating point. This
9901 also implies @option{-m32081}. The 32381 is only compatible with the 32332
9902 and 32532 cpus. This is the default for the pc532-netbsd configuration.
9906 Try and generate multiply-add floating point instructions @code{polyF}
9907 and @code{dotF}. This option is only available if the @option{-m32381}
9908 option is in effect. Using these instructions requires changes to
9909 register allocation which generally has a negative impact on
9910 performance. This option should only be enabled when compiling code
9911 particularly likely to make heavy use of multiply-add instructions.
9914 @opindex mnomulti-add
9915 Do not try and generate multiply-add floating point instructions
9916 @code{polyF} and @code{dotF}. This is the default on all platforms.
9919 @opindex msoft-float
9920 Generate output containing library calls for floating point.
9921 @strong{Warning:} the requisite libraries may not be available.
9923 @item -mieee-compare
9924 @itemx -mno-ieee-compare
9925 @opindex mieee-compare
9926 @opindex mno-ieee-compare
9927 Control whether or not the compiler uses IEEE floating point
9928 comparisons. These handle correctly the case where the result of a
9929 comparison is unordered.
9930 @strong{Warning:} the requisite kernel support may not be available.
9933 @opindex mnobitfield
9934 Do not use the bit-field instructions. On some machines it is faster to
9935 use shifting and masking operations. This is the default for the pc532.
9939 Do use the bit-field instructions. This is the default for all platforms
9944 Use a different function-calling convention, in which functions
9945 that take a fixed number of arguments return pop their
9946 arguments on return with the @code{ret} instruction.
9948 This calling convention is incompatible with the one normally
9949 used on Unix, so you cannot use it if you need to call libraries
9950 compiled with the Unix compiler.
9952 Also, you must provide function prototypes for all functions that
9953 take variable numbers of arguments (including @code{printf});
9954 otherwise incorrect code will be generated for calls to those
9957 In addition, seriously incorrect code will result if you call a
9958 function with too many arguments. (Normally, extra arguments are
9959 harmlessly ignored.)
9961 This option takes its name from the 680x0 @code{rtd} instruction.
9966 Use a different function-calling convention where the first two arguments
9967 are passed in registers.
9969 This calling convention is incompatible with the one normally
9970 used on Unix, so you cannot use it if you need to call libraries
9971 compiled with the Unix compiler.
9974 @opindex mnoregparam
9975 Do not pass any arguments in registers. This is the default for all
9980 It is OK to use the sb as an index register which is always loaded with
9981 zero. This is the default for the pc532-netbsd target.
9985 The sb register is not available for use or has not been initialized to
9986 zero by the run time system. This is the default for all targets except
9987 the pc532-netbsd. It is also implied whenever @option{-mhimem} or
9988 @option{-fpic} is set.
9992 Many ns32000 series addressing modes use displacements of up to 512MB@.
9993 If an address is above 512MB then displacements from zero can not be used.
9994 This option causes code to be generated which can be loaded above 512MB@.
9995 This may be useful for operating systems or ROM code.
9999 Assume code will be loaded in the first 512MB of virtual address space.
10000 This is the default for all platforms.
10004 @node PDP-11 Options
10005 @subsection PDP-11 Options
10006 @cindex PDP-11 Options
10008 These options are defined for the PDP-11:
10013 Use hardware FPP floating point. This is the default. (FIS floating
10014 point on the PDP-11/40 is not supported.)
10017 @opindex msoft-float
10018 Do not use hardware floating point.
10022 Return floating-point results in ac0 (fr0 in Unix assembler syntax).
10026 Return floating-point results in memory. This is the default.
10030 Generate code for a PDP-11/40.
10034 Generate code for a PDP-11/45. This is the default.
10038 Generate code for a PDP-11/10.
10040 @item -mbcopy-builtin
10041 @opindex bcopy-builtin
10042 Use inline @code{movmemhi} patterns for copying memory. This is the
10047 Do not use inline @code{movmemhi} patterns for copying memory.
10053 Use 16-bit @code{int}. This is the default.
10059 Use 32-bit @code{int}.
10062 @itemx -mno-float32
10064 @opindex mno-float32
10065 Use 64-bit @code{float}. This is the default.
10068 @itemx -mno-float64
10070 @opindex mno-float64
10071 Use 32-bit @code{float}.
10075 Use @code{abshi2} pattern. This is the default.
10079 Do not use @code{abshi2} pattern.
10081 @item -mbranch-expensive
10082 @opindex mbranch-expensive
10083 Pretend that branches are expensive. This is for experimenting with
10084 code generation only.
10086 @item -mbranch-cheap
10087 @opindex mbranch-cheap
10088 Do not pretend that branches are expensive. This is the default.
10092 Generate code for a system with split I&D.
10096 Generate code for a system without split I&D. This is the default.
10100 Use Unix assembler syntax. This is the default when configured for
10101 @samp{pdp11-*-bsd}.
10105 Use DEC assembler syntax. This is the default when configured for any
10106 PDP-11 target other than @samp{pdp11-*-bsd}.
10109 @node PowerPC Options
10110 @subsection PowerPC Options
10111 @cindex PowerPC options
10113 These are listed under @xref{RS/6000 and PowerPC Options}.
10115 @node RS/6000 and PowerPC Options
10116 @subsection IBM RS/6000 and PowerPC Options
10117 @cindex RS/6000 and PowerPC Options
10118 @cindex IBM RS/6000 and PowerPC Options
10120 These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
10127 @itemx -mno-powerpc
10128 @itemx -mpowerpc-gpopt
10129 @itemx -mno-powerpc-gpopt
10130 @itemx -mpowerpc-gfxopt
10131 @itemx -mno-powerpc-gfxopt
10133 @itemx -mno-powerpc64
10137 @opindex mno-power2
10139 @opindex mno-powerpc
10140 @opindex mpowerpc-gpopt
10141 @opindex mno-powerpc-gpopt
10142 @opindex mpowerpc-gfxopt
10143 @opindex mno-powerpc-gfxopt
10144 @opindex mpowerpc64
10145 @opindex mno-powerpc64
10146 GCC supports two related instruction set architectures for the
10147 RS/6000 and PowerPC@. The @dfn{POWER} instruction set are those
10148 instructions supported by the @samp{rios} chip set used in the original
10149 RS/6000 systems and the @dfn{PowerPC} instruction set is the
10150 architecture of the Motorola MPC5xx, MPC6xx, MPC8xx microprocessors, and
10151 the IBM 4xx microprocessors.
10153 Neither architecture is a subset of the other. However there is a
10154 large common subset of instructions supported by both. An MQ
10155 register is included in processors supporting the POWER architecture.
10157 You use these options to specify which instructions are available on the
10158 processor you are using. The default value of these options is
10159 determined when configuring GCC@. Specifying the
10160 @option{-mcpu=@var{cpu_type}} overrides the specification of these
10161 options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
10162 rather than the options listed above.
10164 The @option{-mpower} option allows GCC to generate instructions that
10165 are found only in the POWER architecture and to use the MQ register.
10166 Specifying @option{-mpower2} implies @option{-power} and also allows GCC
10167 to generate instructions that are present in the POWER2 architecture but
10168 not the original POWER architecture.
10170 The @option{-mpowerpc} option allows GCC to generate instructions that
10171 are found only in the 32-bit subset of the PowerPC architecture.
10172 Specifying @option{-mpowerpc-gpopt} implies @option{-mpowerpc} and also allows
10173 GCC to use the optional PowerPC architecture instructions in the
10174 General Purpose group, including floating-point square root. Specifying
10175 @option{-mpowerpc-gfxopt} implies @option{-mpowerpc} and also allows GCC to
10176 use the optional PowerPC architecture instructions in the Graphics
10177 group, including floating-point select.
10179 The @option{-mpowerpc64} option allows GCC to generate the additional
10180 64-bit instructions that are found in the full PowerPC64 architecture
10181 and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
10182 @option{-mno-powerpc64}.
10184 If you specify both @option{-mno-power} and @option{-mno-powerpc}, GCC
10185 will use only the instructions in the common subset of both
10186 architectures plus some special AIX common-mode calls, and will not use
10187 the MQ register. Specifying both @option{-mpower} and @option{-mpowerpc}
10188 permits GCC to use any instruction from either architecture and to
10189 allow use of the MQ register; specify this for the Motorola MPC601.
10191 @item -mnew-mnemonics
10192 @itemx -mold-mnemonics
10193 @opindex mnew-mnemonics
10194 @opindex mold-mnemonics
10195 Select which mnemonics to use in the generated assembler code. With
10196 @option{-mnew-mnemonics}, GCC uses the assembler mnemonics defined for
10197 the PowerPC architecture. With @option{-mold-mnemonics} it uses the
10198 assembler mnemonics defined for the POWER architecture. Instructions
10199 defined in only one architecture have only one mnemonic; GCC uses that
10200 mnemonic irrespective of which of these options is specified.
10202 GCC defaults to the mnemonics appropriate for the architecture in
10203 use. Specifying @option{-mcpu=@var{cpu_type}} sometimes overrides the
10204 value of these option. Unless you are building a cross-compiler, you
10205 should normally not specify either @option{-mnew-mnemonics} or
10206 @option{-mold-mnemonics}, but should instead accept the default.
10208 @item -mcpu=@var{cpu_type}
10210 Set architecture type, register usage, choice of mnemonics, and
10211 instruction scheduling parameters for machine type @var{cpu_type}.
10212 Supported values for @var{cpu_type} are @samp{401}, @samp{403},
10213 @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{505},
10214 @samp{601}, @samp{602}, @samp{603}, @samp{603e}, @samp{604},
10215 @samp{604e}, @samp{620}, @samp{630}, @samp{740}, @samp{7400},
10216 @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
10217 @samp{860}, @samp{970}, @samp{common}, @samp{ec603e}, @samp{G3},
10218 @samp{G4}, @samp{G5}, @samp{power}, @samp{power2}, @samp{power3},
10219 @samp{power4}, @samp{power5}, @samp{powerpc}, @samp{powerpc64},
10220 @samp{rios}, @samp{rios1}, @samp{rios2}, @samp{rsc}, and @samp{rs64a}.
10222 @option{-mcpu=common} selects a completely generic processor. Code
10223 generated under this option will run on any POWER or PowerPC processor.
10224 GCC will use only the instructions in the common subset of both
10225 architectures, and will not use the MQ register. GCC assumes a generic
10226 processor model for scheduling purposes.
10228 @option{-mcpu=power}, @option{-mcpu=power2}, @option{-mcpu=powerpc}, and
10229 @option{-mcpu=powerpc64} specify generic POWER, POWER2, pure 32-bit
10230 PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
10231 types, with an appropriate, generic processor model assumed for
10232 scheduling purposes.
10234 The other options specify a specific processor. Code generated under
10235 those options will run best on that processor, and may not run at all on
10238 The @option{-mcpu} options automatically enable or disable the
10239 following options: @option{-maltivec}, @option{-mhard-float},
10240 @option{-mmfcrf}, @option{-mmultiple}, @option{-mnew-mnemonics},
10241 @option{-mpower}, @option{-mpower2}, @option{-mpowerpc64},
10242 @option{-mpowerpc-gpopt}, @option{-mpowerpc-gfxopt},
10243 @option{-mstring}. The particular options set for any particular CPU
10244 will vary between compiler versions, depending on what setting seems
10245 to produce optimal code for that CPU; it doesn't necessarily reflect
10246 the actual hardware's capabilities. If you wish to set an individual
10247 option to a particular value, you may specify it after the
10248 @option{-mcpu} option, like @samp{-mcpu=970 -mno-altivec}.
10250 On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
10251 not enabled or disabled by the @option{-mcpu} option at present, since
10252 AIX does not have full support for these options. You may still
10253 enable or disable them individually if you're sure it'll work in your
10256 @item -mtune=@var{cpu_type}
10258 Set the instruction scheduling parameters for machine type
10259 @var{cpu_type}, but do not set the architecture type, register usage, or
10260 choice of mnemonics, as @option{-mcpu=@var{cpu_type}} would. The same
10261 values for @var{cpu_type} are used for @option{-mtune} as for
10262 @option{-mcpu}. If both are specified, the code generated will use the
10263 architecture, registers, and mnemonics set by @option{-mcpu}, but the
10264 scheduling parameters set by @option{-mtune}.
10267 @itemx -mno-altivec
10269 @opindex mno-altivec
10270 Generate code that uses (does not use) AltiVec instructions, and also
10271 enable the use of built-in functions that allow more direct access to
10272 the AltiVec instruction set. You may also need to set
10273 @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
10278 Extend the current ABI with SPE ABI extensions. This does not change
10279 the default ABI, instead it adds the SPE ABI extensions to the current
10283 @opindex mabi=no-spe
10284 Disable Booke SPE ABI extensions for the current ABI.
10286 @item -misel=@var{yes/no}
10289 This switch enables or disables the generation of ISEL instructions.
10291 @item -mspe=@var{yes/no}
10294 This switch enables or disables the generation of SPE simd
10297 @item -mfloat-gprs=@var{yes/single/double/no}
10298 @itemx -mfloat-gprs
10299 @opindex mfloat-gprs
10300 This switch enables or disables the generation of floating point
10301 operations on the general purpose registers for architectures that
10304 The argument @var{yes} or @var{single} enables the use of
10305 single-precision floating point operations.
10307 The argument @var{double} enables the use of single and
10308 double-precision floating point operations.
10310 The argument @var{no} disables floating point operations on the
10311 general purpose registers.
10313 This option is currently only available on the MPC854x.
10319 Generate code for 32-bit or 64-bit environments of Darwin and SVR4
10320 targets (including GNU/Linux). The 32-bit environment sets int, long
10321 and pointer to 32 bits and generates code that runs on any PowerPC
10322 variant. The 64-bit environment sets int to 32 bits and long and
10323 pointer to 64 bits, and generates code for PowerPC64, as for
10324 @option{-mpowerpc64}.
10327 @itemx -mno-fp-in-toc
10328 @itemx -mno-sum-in-toc
10329 @itemx -mminimal-toc
10331 @opindex mno-fp-in-toc
10332 @opindex mno-sum-in-toc
10333 @opindex mminimal-toc
10334 Modify generation of the TOC (Table Of Contents), which is created for
10335 every executable file. The @option{-mfull-toc} option is selected by
10336 default. In that case, GCC will allocate at least one TOC entry for
10337 each unique non-automatic variable reference in your program. GCC
10338 will also place floating-point constants in the TOC@. However, only
10339 16,384 entries are available in the TOC@.
10341 If you receive a linker error message that saying you have overflowed
10342 the available TOC space, you can reduce the amount of TOC space used
10343 with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
10344 @option{-mno-fp-in-toc} prevents GCC from putting floating-point
10345 constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
10346 generate code to calculate the sum of an address and a constant at
10347 run-time instead of putting that sum into the TOC@. You may specify one
10348 or both of these options. Each causes GCC to produce very slightly
10349 slower and larger code at the expense of conserving TOC space.
10351 If you still run out of space in the TOC even when you specify both of
10352 these options, specify @option{-mminimal-toc} instead. This option causes
10353 GCC to make only one TOC entry for every file. When you specify this
10354 option, GCC will produce code that is slower and larger but which
10355 uses extremely little TOC space. You may wish to use this option
10356 only on files that contain less frequently executed code.
10362 Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
10363 @code{long} type, and the infrastructure needed to support them.
10364 Specifying @option{-maix64} implies @option{-mpowerpc64} and
10365 @option{-mpowerpc}, while @option{-maix32} disables the 64-bit ABI and
10366 implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
10369 @itemx -mno-xl-call
10371 @opindex mno-xl-call
10372 On AIX, pass floating-point arguments to prototyped functions beyond the
10373 register save area (RSA) on the stack in addition to argument FPRs. The
10374 AIX calling convention was extended but not initially documented to
10375 handle an obscure K&R C case of calling a function that takes the
10376 address of its arguments with fewer arguments than declared. AIX XL
10377 compilers access floating point arguments which do not fit in the
10378 RSA from the stack when a subroutine is compiled without
10379 optimization. Because always storing floating-point arguments on the
10380 stack is inefficient and rarely needed, this option is not enabled by
10381 default and only is necessary when calling subroutines compiled by AIX
10382 XL compilers without optimization.
10386 Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
10387 application written to use message passing with special startup code to
10388 enable the application to run. The system must have PE installed in the
10389 standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
10390 must be overridden with the @option{-specs=} option to specify the
10391 appropriate directory location. The Parallel Environment does not
10392 support threads, so the @option{-mpe} option and the @option{-pthread}
10393 option are incompatible.
10395 @item -malign-natural
10396 @itemx -malign-power
10397 @opindex malign-natural
10398 @opindex malign-power
10399 On AIX, Darwin, and 64-bit PowerPC GNU/Linux, the option
10400 @option{-malign-natural} overrides the ABI-defined alignment of larger
10401 types, such as floating-point doubles, on their natural size-based boundary.
10402 The option @option{-malign-power} instructs GCC to follow the ABI-specified
10403 alignment rules. GCC defaults to the standard alignment defined in the ABI.
10406 @itemx -mhard-float
10407 @opindex msoft-float
10408 @opindex mhard-float
10409 Generate code that does not use (uses) the floating-point register set.
10410 Software floating point emulation is provided if you use the
10411 @option{-msoft-float} option, and pass the option to GCC when linking.
10414 @itemx -mno-multiple
10416 @opindex mno-multiple
10417 Generate code that uses (does not use) the load multiple word
10418 instructions and the store multiple word instructions. These
10419 instructions are generated by default on POWER systems, and not
10420 generated on PowerPC systems. Do not use @option{-mmultiple} on little
10421 endian PowerPC systems, since those instructions do not work when the
10422 processor is in little endian mode. The exceptions are PPC740 and
10423 PPC750 which permit the instructions usage in little endian mode.
10428 @opindex mno-string
10429 Generate code that uses (does not use) the load string instructions
10430 and the store string word instructions to save multiple registers and
10431 do small block moves. These instructions are generated by default on
10432 POWER systems, and not generated on PowerPC systems. Do not use
10433 @option{-mstring} on little endian PowerPC systems, since those
10434 instructions do not work when the processor is in little endian mode.
10435 The exceptions are PPC740 and PPC750 which permit the instructions
10436 usage in little endian mode.
10441 @opindex mno-update
10442 Generate code that uses (does not use) the load or store instructions
10443 that update the base register to the address of the calculated memory
10444 location. These instructions are generated by default. If you use
10445 @option{-mno-update}, there is a small window between the time that the
10446 stack pointer is updated and the address of the previous frame is
10447 stored, which means code that walks the stack frame across interrupts or
10448 signals may get corrupted data.
10451 @itemx -mno-fused-madd
10452 @opindex mfused-madd
10453 @opindex mno-fused-madd
10454 Generate code that uses (does not use) the floating point multiply and
10455 accumulate instructions. These instructions are generated by default if
10456 hardware floating is used.
10458 @item -mno-bit-align
10460 @opindex mno-bit-align
10461 @opindex mbit-align
10462 On System V.4 and embedded PowerPC systems do not (do) force structures
10463 and unions that contain bit-fields to be aligned to the base type of the
10466 For example, by default a structure containing nothing but 8
10467 @code{unsigned} bit-fields of length 1 would be aligned to a 4 byte
10468 boundary and have a size of 4 bytes. By using @option{-mno-bit-align},
10469 the structure would be aligned to a 1 byte boundary and be one byte in
10472 @item -mno-strict-align
10473 @itemx -mstrict-align
10474 @opindex mno-strict-align
10475 @opindex mstrict-align
10476 On System V.4 and embedded PowerPC systems do not (do) assume that
10477 unaligned memory references will be handled by the system.
10479 @item -mrelocatable
10480 @itemx -mno-relocatable
10481 @opindex mrelocatable
10482 @opindex mno-relocatable
10483 On embedded PowerPC systems generate code that allows (does not allow)
10484 the program to be relocated to a different address at runtime. If you
10485 use @option{-mrelocatable} on any module, all objects linked together must
10486 be compiled with @option{-mrelocatable} or @option{-mrelocatable-lib}.
10488 @item -mrelocatable-lib
10489 @itemx -mno-relocatable-lib
10490 @opindex mrelocatable-lib
10491 @opindex mno-relocatable-lib
10492 On embedded PowerPC systems generate code that allows (does not allow)
10493 the program to be relocated to a different address at runtime. Modules
10494 compiled with @option{-mrelocatable-lib} can be linked with either modules
10495 compiled without @option{-mrelocatable} and @option{-mrelocatable-lib} or
10496 with modules compiled with the @option{-mrelocatable} options.
10502 On System V.4 and embedded PowerPC systems do not (do) assume that
10503 register 2 contains a pointer to a global area pointing to the addresses
10504 used in the program.
10507 @itemx -mlittle-endian
10509 @opindex mlittle-endian
10510 On System V.4 and embedded PowerPC systems compile code for the
10511 processor in little endian mode. The @option{-mlittle-endian} option is
10512 the same as @option{-mlittle}.
10515 @itemx -mbig-endian
10517 @opindex mbig-endian
10518 On System V.4 and embedded PowerPC systems compile code for the
10519 processor in big endian mode. The @option{-mbig-endian} option is
10520 the same as @option{-mbig}.
10522 @item -mdynamic-no-pic
10523 @opindex mdynamic-no-pic
10524 On Darwin and Mac OS X systems, compile code so that it is not
10525 relocatable, but that its external references are relocatable. The
10526 resulting code is suitable for applications, but not shared
10529 @item -mprioritize-restricted-insns=@var{priority}
10530 @opindex mprioritize-restricted-insns
10531 This option controls the priority that is assigned to
10532 dispatch-slot restricted instructions during the second scheduling
10533 pass. The argument @var{priority} takes the value @var{0/1/2} to assign
10534 @var{no/highest/second-highest} priority to dispatch slot restricted
10537 @item -msched-costly-dep=@var{dependence_type}
10538 @opindex msched-costly-dep
10539 This option controls which dependences are considered costly
10540 by the target during instruction scheduling. The argument
10541 @var{dependence_type} takes one of the following values:
10542 @var{no}: no dependence is costly,
10543 @var{all}: all dependences are costly,
10544 @var{true_store_to_load}: a true dependence from store to load is costly,
10545 @var{store_to_load}: any dependence from store to load is costly,
10546 @var{number}: any dependence which latency >= @var{number} is costly.
10548 @item -minsert-sched-nops=@var{scheme}
10549 @opindex minsert-sched-nops
10550 This option controls which nop insertion scheme will be used during
10551 the second scheduling pass. The argument @var{scheme} takes one of the
10553 @var{no}: Don't insert nops.
10554 @var{pad}: Pad with nops any dispatch group which has vacant issue slots,
10555 according to the scheduler's grouping.
10556 @var{regroup_exact}: Insert nops to force costly dependent insns into
10557 separate groups. Insert exactly as many nops as needed to force an insn
10558 to a new group, according to the estimated processor grouping.
10559 @var{number}: Insert nops to force costly dependent insns into
10560 separate groups. Insert @var{number} nops to force an insn to a new group.
10563 @opindex mcall-sysv
10564 On System V.4 and embedded PowerPC systems compile code using calling
10565 conventions that adheres to the March 1995 draft of the System V
10566 Application Binary Interface, PowerPC processor supplement. This is the
10567 default unless you configured GCC using @samp{powerpc-*-eabiaix}.
10569 @item -mcall-sysv-eabi
10570 @opindex mcall-sysv-eabi
10571 Specify both @option{-mcall-sysv} and @option{-meabi} options.
10573 @item -mcall-sysv-noeabi
10574 @opindex mcall-sysv-noeabi
10575 Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
10577 @item -mcall-solaris
10578 @opindex mcall-solaris
10579 On System V.4 and embedded PowerPC systems compile code for the Solaris
10583 @opindex mcall-linux
10584 On System V.4 and embedded PowerPC systems compile code for the
10585 Linux-based GNU system.
10589 On System V.4 and embedded PowerPC systems compile code for the
10590 Hurd-based GNU system.
10592 @item -mcall-netbsd
10593 @opindex mcall-netbsd
10594 On System V.4 and embedded PowerPC systems compile code for the
10595 NetBSD operating system.
10597 @item -maix-struct-return
10598 @opindex maix-struct-return
10599 Return all structures in memory (as specified by the AIX ABI)@.
10601 @item -msvr4-struct-return
10602 @opindex msvr4-struct-return
10603 Return structures smaller than 8 bytes in registers (as specified by the
10606 @item -mabi=altivec
10607 @opindex mabi=altivec
10608 Extend the current ABI with AltiVec ABI extensions. This does not
10609 change the default ABI, instead it adds the AltiVec ABI extensions to
10612 @item -mabi=no-altivec
10613 @opindex mabi=no-altivec
10614 Disable AltiVec ABI extensions for the current ABI.
10617 @itemx -mno-prototype
10618 @opindex mprototype
10619 @opindex mno-prototype
10620 On System V.4 and embedded PowerPC systems assume that all calls to
10621 variable argument functions are properly prototyped. Otherwise, the
10622 compiler must insert an instruction before every non prototyped call to
10623 set or clear bit 6 of the condition code register (@var{CR}) to
10624 indicate whether floating point values were passed in the floating point
10625 registers in case the function takes a variable arguments. With
10626 @option{-mprototype}, only calls to prototyped variable argument functions
10627 will set or clear the bit.
10631 On embedded PowerPC systems, assume that the startup module is called
10632 @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
10633 @file{libc.a}. This is the default for @samp{powerpc-*-eabisim}.
10638 On embedded PowerPC systems, assume that the startup module is called
10639 @file{crt0.o} and the standard C libraries are @file{libmvme.a} and
10644 On embedded PowerPC systems, assume that the startup module is called
10645 @file{crt0.o} and the standard C libraries are @file{libads.a} and
10648 @item -myellowknife
10649 @opindex myellowknife
10650 On embedded PowerPC systems, assume that the startup module is called
10651 @file{crt0.o} and the standard C libraries are @file{libyk.a} and
10656 On System V.4 and embedded PowerPC systems, specify that you are
10657 compiling for a VxWorks system.
10661 Specify that you are compiling for the WindISS simulation environment.
10665 On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags
10666 header to indicate that @samp{eabi} extended relocations are used.
10672 On System V.4 and embedded PowerPC systems do (do not) adhere to the
10673 Embedded Applications Binary Interface (eabi) which is a set of
10674 modifications to the System V.4 specifications. Selecting @option{-meabi}
10675 means that the stack is aligned to an 8 byte boundary, a function
10676 @code{__eabi} is called to from @code{main} to set up the eabi
10677 environment, and the @option{-msdata} option can use both @code{r2} and
10678 @code{r13} to point to two separate small data areas. Selecting
10679 @option{-mno-eabi} means that the stack is aligned to a 16 byte boundary,
10680 do not call an initialization function from @code{main}, and the
10681 @option{-msdata} option will only use @code{r13} to point to a single
10682 small data area. The @option{-meabi} option is on by default if you
10683 configured GCC using one of the @samp{powerpc*-*-eabi*} options.
10686 @opindex msdata=eabi
10687 On System V.4 and embedded PowerPC systems, put small initialized
10688 @code{const} global and static data in the @samp{.sdata2} section, which
10689 is pointed to by register @code{r2}. Put small initialized
10690 non-@code{const} global and static data in the @samp{.sdata} section,
10691 which is pointed to by register @code{r13}. Put small uninitialized
10692 global and static data in the @samp{.sbss} section, which is adjacent to
10693 the @samp{.sdata} section. The @option{-msdata=eabi} option is
10694 incompatible with the @option{-mrelocatable} option. The
10695 @option{-msdata=eabi} option also sets the @option{-memb} option.
10698 @opindex msdata=sysv
10699 On System V.4 and embedded PowerPC systems, put small global and static
10700 data in the @samp{.sdata} section, which is pointed to by register
10701 @code{r13}. Put small uninitialized global and static data in the
10702 @samp{.sbss} section, which is adjacent to the @samp{.sdata} section.
10703 The @option{-msdata=sysv} option is incompatible with the
10704 @option{-mrelocatable} option.
10706 @item -msdata=default
10708 @opindex msdata=default
10710 On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
10711 compile code the same as @option{-msdata=eabi}, otherwise compile code the
10712 same as @option{-msdata=sysv}.
10715 @opindex msdata-data
10716 On System V.4 and embedded PowerPC systems, put small global and static
10717 data in the @samp{.sdata} section. Put small uninitialized global and
10718 static data in the @samp{.sbss} section. Do not use register @code{r13}
10719 to address small data however. This is the default behavior unless
10720 other @option{-msdata} options are used.
10724 @opindex msdata=none
10726 On embedded PowerPC systems, put all initialized global and static data
10727 in the @samp{.data} section, and all uninitialized data in the
10728 @samp{.bss} section.
10732 @cindex smaller data references (PowerPC)
10733 @cindex .sdata/.sdata2 references (PowerPC)
10734 On embedded PowerPC systems, put global and static items less than or
10735 equal to @var{num} bytes into the small data or bss sections instead of
10736 the normal data or bss section. By default, @var{num} is 8. The
10737 @option{-G @var{num}} switch is also passed to the linker.
10738 All modules should be compiled with the same @option{-G @var{num}} value.
10741 @itemx -mno-regnames
10743 @opindex mno-regnames
10744 On System V.4 and embedded PowerPC systems do (do not) emit register
10745 names in the assembly language output using symbolic forms.
10748 @itemx -mno-longcall
10750 @opindex mno-longcall
10751 Default to making all function calls indirectly, using a register, so
10752 that functions which reside further than 32 megabytes (33,554,432
10753 bytes) from the current location can be called. This setting can be
10754 overridden by the @code{shortcall} function attribute, or by
10755 @code{#pragma longcall(0)}.
10757 Some linkers are capable of detecting out-of-range calls and generating
10758 glue code on the fly. On these systems, long calls are unnecessary and
10759 generate slower code. As of this writing, the AIX linker can do this,
10760 as can the GNU linker for PowerPC/64. It is planned to add this feature
10761 to the GNU linker for 32-bit PowerPC systems as well.
10763 On Darwin/PPC systems, @code{#pragma longcall} will generate ``jbsr
10764 callee, L42'', plus a ``branch island'' (glue code). The two target
10765 addresses represent the callee and the ``branch island''. The
10766 Darwin/PPC linker will prefer the first address and generate a ``bl
10767 callee'' if the PPC ``bl'' instruction will reach the callee directly;
10768 otherwise, the linker will generate ``bl L42'' to call the ``branch
10769 island''. The ``branch island'' is appended to the body of the
10770 calling function; it computes the full 32-bit address of the callee
10773 On Mach-O (Darwin) systems, this option directs the compiler emit to
10774 the glue for every direct call, and the Darwin linker decides whether
10775 to use or discard it.
10777 In the future, we may cause GCC to ignore all longcall specifications
10778 when the linker is known to generate glue.
10782 Adds support for multithreading with the @dfn{pthreads} library.
10783 This option sets flags for both the preprocessor and linker.
10787 @node S/390 and zSeries Options
10788 @subsection S/390 and zSeries Options
10789 @cindex S/390 and zSeries Options
10791 These are the @samp{-m} options defined for the S/390 and zSeries architecture.
10795 @itemx -msoft-float
10796 @opindex mhard-float
10797 @opindex msoft-float
10798 Use (do not use) the hardware floating-point instructions and registers
10799 for floating-point operations. When @option{-msoft-float} is specified,
10800 functions in @file{libgcc.a} will be used to perform floating-point
10801 operations. When @option{-mhard-float} is specified, the compiler
10802 generates IEEE floating-point instructions. This is the default.
10805 @itemx -mno-backchain
10806 @itemx -mkernel-backchain
10807 @opindex mbackchain
10808 @opindex mno-backchain
10809 @opindex mkernel-backchain
10810 In order to provide a backchain the address of the caller's frame
10811 is stored within the callee's stack frame.
10812 A backchain may be needed to allow debugging using tools that do not understand
10813 DWARF-2 call frame information.
10814 For @option{-mno-backchain} no backchain is maintained at all which is the
10816 If one of the other options is present the backchain pointer is placed either
10817 on top of the stack frame (@option{-mkernel-backchain}) or on
10818 the bottom (@option{-mbackchain}).
10819 Beside the different backchain location @option{-mkernel-backchain}
10820 also changes stack frame layout breaking the ABI. This option
10821 is intended to be used for code which internally needs a backchain but has
10822 to get by with a limited stack size e.g.@: the linux kernel.
10823 Internal unwinding code not using DWARF-2 info has to be able to locate the
10824 return address of a function. That will be eased be the fact that
10825 the return address of a function is placed two words below the backchain
10829 @itemx -mno-small-exec
10830 @opindex msmall-exec
10831 @opindex mno-small-exec
10832 Generate (or do not generate) code using the @code{bras} instruction
10833 to do subroutine calls.
10834 This only works reliably if the total executable size does not
10835 exceed 64k. The default is to use the @code{basr} instruction instead,
10836 which does not have this limitation.
10842 When @option{-m31} is specified, generate code compliant to the
10843 GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
10844 code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
10845 particular to generate 64-bit instructions. For the @samp{s390}
10846 targets, the default is @option{-m31}, while the @samp{s390x}
10847 targets default to @option{-m64}.
10853 When @option{-mzarch} is specified, generate code using the
10854 instructions available on z/Architecture.
10855 When @option{-mesa} is specified, generate code using the
10856 instructions available on ESA/390. Note that @option{-mesa} is
10857 not possible with @option{-m64}.
10858 When generating code compliant to the GNU/Linux for S/390 ABI,
10859 the default is @option{-mesa}. When generating code compliant
10860 to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
10866 Generate (or do not generate) code using the @code{mvcle} instruction
10867 to perform block moves. When @option{-mno-mvcle} is specified,
10868 use a @code{mvc} loop instead. This is the default.
10874 Print (or do not print) additional debug information when compiling.
10875 The default is to not print debug information.
10877 @item -march=@var{cpu-type}
10879 Generate code that will run on @var{cpu-type}, which is the name of a system
10880 representing a certain processor type. Possible values for
10881 @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, and @samp{z990}.
10882 When generating code using the instructions available on z/Architecture,
10883 the default is @option{-march=z900}. Otherwise, the default is
10884 @option{-march=g5}.
10886 @item -mtune=@var{cpu-type}
10888 Tune to @var{cpu-type} everything applicable about the generated code,
10889 except for the ABI and the set of available instructions.
10890 The list of @var{cpu-type} values is the same as for @option{-march}.
10891 The default is the value used for @option{-march}.
10894 @itemx -mno-tpf-trace
10895 @opindex mtpf-trace
10896 @opindex mno-tpf-trace
10897 Generate code that adds (does not add) in TPF OS specific branches to trace
10898 routines in the operating system. This option is off by default, even
10899 when compiling for the TPF OS.
10902 @itemx -mno-fused-madd
10903 @opindex mfused-madd
10904 @opindex mno-fused-madd
10905 Generate code that uses (does not use) the floating point multiply and
10906 accumulate instructions. These instructions are generated by default if
10907 hardware floating point is used.
10909 @item -mwarn-framesize=@var{framesize}
10910 @opindex mwarn-framesize
10911 Emit a warning if the current function exceeds the given frame size. Because
10912 this is a compile time check it doesn't need to be a real problem when the program
10913 runs. It is intended to identify functions which most probably cause
10914 a stack overflow. It is useful to be used in an environment with limited stack
10915 size e.g.@: the linux kernel.
10917 @item -mwarn-dynamicstack
10918 @opindex mwarn-dynamicstack
10919 Emit a warning if the function calls alloca or uses dynamically
10920 sized arrays. This is generally a bad idea with a limited stack size.
10922 @item -mstack-guard=@var{stack-guard}
10923 @item -mstack-size=@var{stack-size}
10924 @opindex mstack-guard
10925 @opindex mstack-size
10926 These arguments always have to be used in conjunction. If they are present the s390
10927 back end emits additional instructions in the function prologue which trigger a trap
10928 if the stack size is @var{stack-guard} bytes above the @var{stack-size}
10929 (remember that the stack on s390 grows downward). These options are intended to
10930 be used to help debugging stack overflow problems. The additionally emitted code
10931 cause only little overhead and hence can also be used in production like systems
10932 without greater performance degradation. The given values have to be exact
10933 powers of 2 and @var{stack-size} has to be greater than @var{stack-guard}.
10934 In order to be efficient the extra code makes the assumption that the stack starts
10935 at an address aligned to the value given by @var{stack-size}.
10939 @subsection SH Options
10941 These @samp{-m} options are defined for the SH implementations:
10946 Generate code for the SH1.
10950 Generate code for the SH2.
10953 Generate code for the SH2e.
10957 Generate code for the SH3.
10961 Generate code for the SH3e.
10965 Generate code for the SH4 without a floating-point unit.
10967 @item -m4-single-only
10968 @opindex m4-single-only
10969 Generate code for the SH4 with a floating-point unit that only
10970 supports single-precision arithmetic.
10974 Generate code for the SH4 assuming the floating-point unit is in
10975 single-precision mode by default.
10979 Generate code for the SH4.
10983 Generate code for the SH4al-dsp, or for a SH4a in such a way that the
10984 floating-point unit is not used.
10986 @item -m4a-single-only
10987 @opindex m4a-single-only
10988 Generate code for the SH4a, in such a way that no double-precision
10989 floating point operations are used.
10992 @opindex m4a-single
10993 Generate code for the SH4a assuming the floating-point unit is in
10994 single-precision mode by default.
10998 Generate code for the SH4a.
11002 Same as @option{-m4a-nofpu}, except that it implicitly passes
11003 @option{-dsp} to the assembler. GCC doesn't generate any DSP
11004 instructions at the moment.
11008 Compile code for the processor in big endian mode.
11012 Compile code for the processor in little endian mode.
11016 Align doubles at 64-bit boundaries. Note that this changes the calling
11017 conventions, and thus some functions from the standard C library will
11018 not work unless you recompile it first with @option{-mdalign}.
11022 Shorten some address references at link time, when possible; uses the
11023 linker option @option{-relax}.
11027 Use 32-bit offsets in @code{switch} tables. The default is to use
11032 Enable the use of the instruction @code{fmovd}.
11036 Comply with the calling conventions defined by Renesas.
11040 Comply with the calling conventions defined by Renesas.
11044 Comply with the calling conventions defined for GCC before the Renesas
11045 conventions were available. This option is the default for all
11046 targets of the SH toolchain except for @samp{sh-symbianelf}.
11049 @opindex mnomacsave
11050 Mark the @code{MAC} register as call-clobbered, even if
11051 @option{-mhitachi} is given.
11055 Increase IEEE-compliance of floating-point code.
11059 Dump instruction size and location in the assembly code.
11062 @opindex mpadstruct
11063 This option is deprecated. It pads structures to multiple of 4 bytes,
11064 which is incompatible with the SH ABI@.
11068 Optimize for space instead of speed. Implied by @option{-Os}.
11071 @opindex mprefergot
11072 When generating position-independent code, emit function calls using
11073 the Global Offset Table instead of the Procedure Linkage Table.
11077 Generate a library function call to invalidate instruction cache
11078 entries, after fixing up a trampoline. This library function call
11079 doesn't assume it can write to the whole memory address space. This
11080 is the default when the target is @code{sh-*-linux*}.
11083 @node SPARC Options
11084 @subsection SPARC Options
11085 @cindex SPARC options
11087 These @samp{-m} options are supported on the SPARC:
11090 @item -mno-app-regs
11092 @opindex mno-app-regs
11094 Specify @option{-mapp-regs} to generate output using the global registers
11095 2 through 4, which the SPARC SVR4 ABI reserves for applications. This
11098 To be fully SVR4 ABI compliant at the cost of some performance loss,
11099 specify @option{-mno-app-regs}. You should compile libraries and system
11100 software with this option.
11103 @itemx -mhard-float
11105 @opindex mhard-float
11106 Generate output containing floating point instructions. This is the
11110 @itemx -msoft-float
11112 @opindex msoft-float
11113 Generate output containing library calls for floating point.
11114 @strong{Warning:} the requisite libraries are not available for all SPARC
11115 targets. Normally the facilities of the machine's usual C compiler are
11116 used, but this cannot be done directly in cross-compilation. You must make
11117 your own arrangements to provide suitable library functions for
11118 cross-compilation. The embedded targets @samp{sparc-*-aout} and
11119 @samp{sparclite-*-*} do provide software floating point support.
11121 @option{-msoft-float} changes the calling convention in the output file;
11122 therefore, it is only useful if you compile @emph{all} of a program with
11123 this option. In particular, you need to compile @file{libgcc.a}, the
11124 library that comes with GCC, with @option{-msoft-float} in order for
11127 @item -mhard-quad-float
11128 @opindex mhard-quad-float
11129 Generate output containing quad-word (long double) floating point
11132 @item -msoft-quad-float
11133 @opindex msoft-quad-float
11134 Generate output containing library calls for quad-word (long double)
11135 floating point instructions. The functions called are those specified
11136 in the SPARC ABI@. This is the default.
11138 As of this writing, there are no SPARC implementations that have hardware
11139 support for the quad-word floating point instructions. They all invoke
11140 a trap handler for one of these instructions, and then the trap handler
11141 emulates the effect of the instruction. Because of the trap handler overhead,
11142 this is much slower than calling the ABI library routines. Thus the
11143 @option{-msoft-quad-float} option is the default.
11145 @item -mno-unaligned-doubles
11146 @itemx -munaligned-doubles
11147 @opindex mno-unaligned-doubles
11148 @opindex munaligned-doubles
11149 Assume that doubles have 8 byte alignment. This is the default.
11151 With @option{-munaligned-doubles}, GCC assumes that doubles have 8 byte
11152 alignment only if they are contained in another type, or if they have an
11153 absolute address. Otherwise, it assumes they have 4 byte alignment.
11154 Specifying this option avoids some rare compatibility problems with code
11155 generated by other compilers. It is not the default because it results
11156 in a performance loss, especially for floating point code.
11158 @item -mno-faster-structs
11159 @itemx -mfaster-structs
11160 @opindex mno-faster-structs
11161 @opindex mfaster-structs
11162 With @option{-mfaster-structs}, the compiler assumes that structures
11163 should have 8 byte alignment. This enables the use of pairs of
11164 @code{ldd} and @code{std} instructions for copies in structure
11165 assignment, in place of twice as many @code{ld} and @code{st} pairs.
11166 However, the use of this changed alignment directly violates the SPARC
11167 ABI@. Thus, it's intended only for use on targets where the developer
11168 acknowledges that their resulting code will not be directly in line with
11169 the rules of the ABI@.
11171 @item -mimpure-text
11172 @opindex mimpure-text
11173 @option{-mimpure-text}, used in addition to @option{-shared}, tells
11174 the compiler to not pass @option{-z text} to the linker when linking a
11175 shared object. Using this option, you can link position-dependent
11176 code into a shared object.
11178 @option{-mimpure-text} suppresses the ``relocations remain against
11179 allocatable but non-writable sections'' linker error message.
11180 However, the necessary relocations will trigger copy-on-write, and the
11181 shared object is not actually shared across processes. Instead of
11182 using @option{-mimpure-text}, you should compile all source code with
11183 @option{-fpic} or @option{-fPIC}.
11185 This option is only available on SunOS and Solaris.
11187 @item -mcpu=@var{cpu_type}
11189 Set the instruction set, register set, and instruction scheduling parameters
11190 for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
11191 @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{sparclite},
11192 @samp{f930}, @samp{f934}, @samp{hypersparc}, @samp{sparclite86x},
11193 @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, and
11194 @samp{ultrasparc3}.
11196 Default instruction scheduling parameters are used for values that select
11197 an architecture and not an implementation. These are @samp{v7}, @samp{v8},
11198 @samp{sparclite}, @samp{sparclet}, @samp{v9}.
11200 Here is a list of each supported architecture and their supported
11205 v8: supersparc, hypersparc
11206 sparclite: f930, f934, sparclite86x
11208 v9: ultrasparc, ultrasparc3
11211 By default (unless configured otherwise), GCC generates code for the V7
11212 variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
11213 additionally optimizes it for the Cypress CY7C602 chip, as used in the
11214 SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
11215 SPARCStation 1, 2, IPX etc.
11217 With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
11218 architecture. The only difference from V7 code is that the compiler emits
11219 the integer multiply and integer divide instructions which exist in SPARC-V8
11220 but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
11221 optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
11224 With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
11225 the SPARC architecture. This adds the integer multiply, integer divide step
11226 and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
11227 With @option{-mcpu=f930}, the compiler additionally optimizes it for the
11228 Fujitsu MB86930 chip, which is the original SPARClite, with no FPU. With
11229 @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
11230 MB86934 chip, which is the more recent SPARClite with FPU.
11232 With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
11233 the SPARC architecture. This adds the integer multiply, multiply/accumulate,
11234 integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
11235 but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
11236 optimizes it for the TEMIC SPARClet chip.
11238 With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
11239 architecture. This adds 64-bit integer and floating-point move instructions,
11240 3 additional floating-point condition code registers and conditional move
11241 instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
11242 optimizes it for the Sun UltraSPARC I/II chips. With
11243 @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
11244 Sun UltraSPARC III chip.
11246 @item -mtune=@var{cpu_type}
11248 Set the instruction scheduling parameters for machine type
11249 @var{cpu_type}, but do not set the instruction set or register set that the
11250 option @option{-mcpu=@var{cpu_type}} would.
11252 The same values for @option{-mcpu=@var{cpu_type}} can be used for
11253 @option{-mtune=@var{cpu_type}}, but the only useful values are those
11254 that select a particular cpu implementation. Those are @samp{cypress},
11255 @samp{supersparc}, @samp{hypersparc}, @samp{f930}, @samp{f934},
11256 @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, and
11257 @samp{ultrasparc3}.
11262 @opindex mno-v8plus
11263 With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI. The
11264 difference from the V8 ABI is that the global and out registers are
11265 considered 64-bit wide. This is enabled by default on Solaris in 32-bit
11266 mode for all SPARC-V9 processors.
11272 With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
11273 Visual Instruction Set extensions. The default is @option{-mno-vis}.
11276 These @samp{-m} options are supported in addition to the above
11277 on SPARC-V9 processors in 64-bit environments:
11280 @item -mlittle-endian
11281 @opindex mlittle-endian
11282 Generate code for a processor running in little-endian mode. It is only
11283 available for a few configurations and most notably not on Solaris.
11289 Generate code for a 32-bit or 64-bit environment.
11290 The 32-bit environment sets int, long and pointer to 32 bits.
11291 The 64-bit environment sets int to 32 bits and long and pointer
11294 @item -mcmodel=medlow
11295 @opindex mcmodel=medlow
11296 Generate code for the Medium/Low code model: 64-bit addresses, programs
11297 must be linked in the low 32 bits of memory. Programs can be statically
11298 or dynamically linked.
11300 @item -mcmodel=medmid
11301 @opindex mcmodel=medmid
11302 Generate code for the Medium/Middle code model: 64-bit addresses, programs
11303 must be linked in the low 44 bits of memory, the text and data segments must
11304 be less than 2GB in size and the data segment must be located within 2GB of
11307 @item -mcmodel=medany
11308 @opindex mcmodel=medany
11309 Generate code for the Medium/Anywhere code model: 64-bit addresses, programs
11310 may be linked anywhere in memory, the text and data segments must be less
11311 than 2GB in size and the data segment must be located within 2GB of the
11314 @item -mcmodel=embmedany
11315 @opindex mcmodel=embmedany
11316 Generate code for the Medium/Anywhere code model for embedded systems:
11317 64-bit addresses, the text and data segments must be less than 2GB in
11318 size, both starting anywhere in memory (determined at link time). The
11319 global register %g4 points to the base of the data segment. Programs
11320 are statically linked and PIC is not supported.
11323 @itemx -mno-stack-bias
11324 @opindex mstack-bias
11325 @opindex mno-stack-bias
11326 With @option{-mstack-bias}, GCC assumes that the stack pointer, and
11327 frame pointer if present, are offset by @minus{}2047 which must be added back
11328 when making stack frame references. This is the default in 64-bit mode.
11329 Otherwise, assume no such offset is present.
11332 These switches are supported in addition to the above on Solaris:
11337 Add support for multithreading using the Solaris threads library. This
11338 option sets flags for both the preprocessor and linker. This option does
11339 not affect the thread safety of object code produced by the compiler or
11340 that of libraries supplied with it.
11344 Add support for multithreading using the POSIX threads library. This
11345 option sets flags for both the preprocessor and linker. This option does
11346 not affect the thread safety of object code produced by the compiler or
11347 that of libraries supplied with it.
11350 @node System V Options
11351 @subsection Options for System V
11353 These additional options are available on System V Release 4 for
11354 compatibility with other compilers on those systems:
11359 Create a shared object.
11360 It is recommended that @option{-symbolic} or @option{-shared} be used instead.
11364 Identify the versions of each tool used by the compiler, in a
11365 @code{.ident} assembler directive in the output.
11369 Refrain from adding @code{.ident} directives to the output file (this is
11372 @item -YP,@var{dirs}
11374 Search the directories @var{dirs}, and no others, for libraries
11375 specified with @option{-l}.
11377 @item -Ym,@var{dir}
11379 Look in the directory @var{dir} to find the M4 preprocessor.
11380 The assembler uses this option.
11381 @c This is supposed to go with a -Yd for predefined M4 macro files, but
11382 @c the generic assembler that comes with Solaris takes just -Ym.
11385 @node TMS320C3x/C4x Options
11386 @subsection TMS320C3x/C4x Options
11387 @cindex TMS320C3x/C4x Options
11389 These @samp{-m} options are defined for TMS320C3x/C4x implementations:
11393 @item -mcpu=@var{cpu_type}
11395 Set the instruction set, register set, and instruction scheduling
11396 parameters for machine type @var{cpu_type}. Supported values for
11397 @var{cpu_type} are @samp{c30}, @samp{c31}, @samp{c32}, @samp{c40}, and
11398 @samp{c44}. The default is @samp{c40} to generate code for the
11403 @itemx -msmall-memory
11405 @opindex mbig-memory
11407 @opindex msmall-memory
11409 Generates code for the big or small memory model. The small memory
11410 model assumed that all data fits into one 64K word page. At run-time
11411 the data page (DP) register must be set to point to the 64K page
11412 containing the .bss and .data program sections. The big memory model is
11413 the default and requires reloading of the DP register for every direct
11420 Allow (disallow) allocation of general integer operands into the block
11421 count register BK@.
11427 Enable (disable) generation of code using decrement and branch,
11428 DBcond(D), instructions. This is enabled by default for the C4x. To be
11429 on the safe side, this is disabled for the C3x, since the maximum
11430 iteration count on the C3x is @math{2^{23} + 1} (but who iterates loops more than
11431 @math{2^{23}} times on the C3x?). Note that GCC will try to reverse a loop so
11432 that it can utilize the decrement and branch instruction, but will give
11433 up if there is more than one memory reference in the loop. Thus a loop
11434 where the loop counter is decremented can generate slightly more
11435 efficient code, in cases where the RPTB instruction cannot be utilized.
11437 @item -mdp-isr-reload
11439 @opindex mdp-isr-reload
11441 Force the DP register to be saved on entry to an interrupt service
11442 routine (ISR), reloaded to point to the data section, and restored on
11443 exit from the ISR@. This should not be required unless someone has
11444 violated the small memory model by modifying the DP register, say within
11451 For the C3x use the 24-bit MPYI instruction for integer multiplies
11452 instead of a library call to guarantee 32-bit results. Note that if one
11453 of the operands is a constant, then the multiplication will be performed
11454 using shifts and adds. If the @option{-mmpyi} option is not specified for the C3x,
11455 then squaring operations are performed inline instead of a library call.
11458 @itemx -mno-fast-fix
11460 @opindex mno-fast-fix
11461 The C3x/C4x FIX instruction to convert a floating point value to an
11462 integer value chooses the nearest integer less than or equal to the
11463 floating point value rather than to the nearest integer. Thus if the
11464 floating point number is negative, the result will be incorrectly
11465 truncated an additional code is necessary to detect and correct this
11466 case. This option can be used to disable generation of the additional
11467 code required to correct the result.
11473 Enable (disable) generation of repeat block sequences using the RPTB
11474 instruction for zero overhead looping. The RPTB construct is only used
11475 for innermost loops that do not call functions or jump across the loop
11476 boundaries. There is no advantage having nested RPTB loops due to the
11477 overhead required to save and restore the RC, RS, and RE registers.
11478 This is enabled by default with @option{-O2}.
11480 @item -mrpts=@var{count}
11484 Enable (disable) the use of the single instruction repeat instruction
11485 RPTS@. If a repeat block contains a single instruction, and the loop
11486 count can be guaranteed to be less than the value @var{count}, GCC will
11487 emit a RPTS instruction instead of a RPTB@. If no value is specified,
11488 then a RPTS will be emitted even if the loop count cannot be determined
11489 at compile time. Note that the repeated instruction following RPTS does
11490 not have to be reloaded from memory each iteration, thus freeing up the
11491 CPU buses for operands. However, since interrupts are blocked by this
11492 instruction, it is disabled by default.
11494 @item -mloop-unsigned
11495 @itemx -mno-loop-unsigned
11496 @opindex mloop-unsigned
11497 @opindex mno-loop-unsigned
11498 The maximum iteration count when using RPTS and RPTB (and DB on the C40)
11499 is @math{2^{31} + 1} since these instructions test if the iteration count is
11500 negative to terminate the loop. If the iteration count is unsigned
11501 there is a possibility than the @math{2^{31} + 1} maximum iteration count may be
11502 exceeded. This switch allows an unsigned iteration count.
11506 Try to emit an assembler syntax that the TI assembler (asm30) is happy
11507 with. This also enforces compatibility with the API employed by the TI
11508 C3x C compiler. For example, long doubles are passed as structures
11509 rather than in floating point registers.
11515 Generate code that uses registers (stack) for passing arguments to functions.
11516 By default, arguments are passed in registers where possible rather
11517 than by pushing arguments on to the stack.
11519 @item -mparallel-insns
11520 @itemx -mno-parallel-insns
11521 @opindex mparallel-insns
11522 @opindex mno-parallel-insns
11523 Allow the generation of parallel instructions. This is enabled by
11524 default with @option{-O2}.
11526 @item -mparallel-mpy
11527 @itemx -mno-parallel-mpy
11528 @opindex mparallel-mpy
11529 @opindex mno-parallel-mpy
11530 Allow the generation of MPY||ADD and MPY||SUB parallel instructions,
11531 provided @option{-mparallel-insns} is also specified. These instructions have
11532 tight register constraints which can pessimize the code generation
11533 of large functions.
11538 @subsection V850 Options
11539 @cindex V850 Options
11541 These @samp{-m} options are defined for V850 implementations:
11545 @itemx -mno-long-calls
11546 @opindex mlong-calls
11547 @opindex mno-long-calls
11548 Treat all calls as being far away (near). If calls are assumed to be
11549 far away, the compiler will always load the functions address up into a
11550 register, and call indirect through the pointer.
11556 Do not optimize (do optimize) basic blocks that use the same index
11557 pointer 4 or more times to copy pointer into the @code{ep} register, and
11558 use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
11559 option is on by default if you optimize.
11561 @item -mno-prolog-function
11562 @itemx -mprolog-function
11563 @opindex mno-prolog-function
11564 @opindex mprolog-function
11565 Do not use (do use) external functions to save and restore registers
11566 at the prologue and epilogue of a function. The external functions
11567 are slower, but use less code space if more than one function saves
11568 the same number of registers. The @option{-mprolog-function} option
11569 is on by default if you optimize.
11573 Try to make the code as small as possible. At present, this just turns
11574 on the @option{-mep} and @option{-mprolog-function} options.
11576 @item -mtda=@var{n}
11578 Put static or global variables whose size is @var{n} bytes or less into
11579 the tiny data area that register @code{ep} points to. The tiny data
11580 area can hold up to 256 bytes in total (128 bytes for byte references).
11582 @item -msda=@var{n}
11584 Put static or global variables whose size is @var{n} bytes or less into
11585 the small data area that register @code{gp} points to. The small data
11586 area can hold up to 64 kilobytes.
11588 @item -mzda=@var{n}
11590 Put static or global variables whose size is @var{n} bytes or less into
11591 the first 32 kilobytes of memory.
11595 Specify that the target processor is the V850.
11598 @opindex mbig-switch
11599 Generate code suitable for big switch tables. Use this option only if
11600 the assembler/linker complain about out of range branches within a switch
11605 This option will cause r2 and r5 to be used in the code generated by
11606 the compiler. This setting is the default.
11608 @item -mno-app-regs
11609 @opindex mno-app-regs
11610 This option will cause r2 and r5 to be treated as fixed registers.
11614 Specify that the target processor is the V850E1. The preprocessor
11615 constants @samp{__v850e1__} and @samp{__v850e__} will be defined if
11616 this option is used.
11620 Specify that the target processor is the V850E. The preprocessor
11621 constant @samp{__v850e__} will be defined if this option is used.
11623 If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
11624 are defined then a default target processor will be chosen and the
11625 relevant @samp{__v850*__} preprocessor constant will be defined.
11627 The preprocessor constants @samp{__v850} and @samp{__v851__} are always
11628 defined, regardless of which processor variant is the target.
11630 @item -mdisable-callt
11631 @opindex mdisable-callt
11632 This option will suppress generation of the CALLT instruction for the
11633 v850e and v850e1 flavors of the v850 architecture. The default is
11634 @option{-mno-disable-callt} which allows the CALLT instruction to be used.
11639 @subsection VAX Options
11640 @cindex VAX options
11642 These @samp{-m} options are defined for the VAX:
11647 Do not output certain jump instructions (@code{aobleq} and so on)
11648 that the Unix assembler for the VAX cannot handle across long
11653 Do output those jump instructions, on the assumption that you
11654 will assemble with the GNU assembler.
11658 Output code for g-format floating point numbers instead of d-format.
11661 @node x86-64 Options
11662 @subsection x86-64 Options
11663 @cindex x86-64 options
11665 These are listed under @xref{i386 and x86-64 Options}.
11667 @node Xstormy16 Options
11668 @subsection Xstormy16 Options
11669 @cindex Xstormy16 Options
11671 These options are defined for Xstormy16:
11676 Choose startup files and linker script suitable for the simulator.
11679 @node Xtensa Options
11680 @subsection Xtensa Options
11681 @cindex Xtensa Options
11683 These options are supported for Xtensa targets:
11687 @itemx -mno-const16
11689 @opindex mno-const16
11690 Enable or disable use of @code{CONST16} instructions for loading
11691 constant values. The @code{CONST16} instruction is currently not a
11692 standard option from Tensilica. When enabled, @code{CONST16}
11693 instructions are always used in place of the standard @code{L32R}
11694 instructions. The use of @code{CONST16} is enabled by default only if
11695 the @code{L32R} instruction is not available.
11698 @itemx -mno-fused-madd
11699 @opindex mfused-madd
11700 @opindex mno-fused-madd
11701 Enable or disable use of fused multiply/add and multiply/subtract
11702 instructions in the floating-point option. This has no effect if the
11703 floating-point option is not also enabled. Disabling fused multiply/add
11704 and multiply/subtract instructions forces the compiler to use separate
11705 instructions for the multiply and add/subtract operations. This may be
11706 desirable in some cases where strict IEEE 754-compliant results are
11707 required: the fused multiply add/subtract instructions do not round the
11708 intermediate result, thereby producing results with @emph{more} bits of
11709 precision than specified by the IEEE standard. Disabling fused multiply
11710 add/subtract instructions also ensures that the program output is not
11711 sensitive to the compiler's ability to combine multiply and add/subtract
11714 @item -mtext-section-literals
11715 @itemx -mno-text-section-literals
11716 @opindex mtext-section-literals
11717 @opindex mno-text-section-literals
11718 Control the treatment of literal pools. The default is
11719 @option{-mno-text-section-literals}, which places literals in a separate
11720 section in the output file. This allows the literal pool to be placed
11721 in a data RAM/ROM, and it also allows the linker to combine literal
11722 pools from separate object files to remove redundant literals and
11723 improve code size. With @option{-mtext-section-literals}, the literals
11724 are interspersed in the text section in order to keep them as close as
11725 possible to their references. This may be necessary for large assembly
11728 @item -mtarget-align
11729 @itemx -mno-target-align
11730 @opindex mtarget-align
11731 @opindex mno-target-align
11732 When this option is enabled, GCC instructs the assembler to
11733 automatically align instructions to reduce branch penalties at the
11734 expense of some code density. The assembler attempts to widen density
11735 instructions to align branch targets and the instructions following call
11736 instructions. If there are not enough preceding safe density
11737 instructions to align a target, no widening will be performed. The
11738 default is @option{-mtarget-align}. These options do not affect the
11739 treatment of auto-aligned instructions like @code{LOOP}, which the
11740 assembler will always align, either by widening density instructions or
11741 by inserting no-op instructions.
11744 @itemx -mno-longcalls
11745 @opindex mlongcalls
11746 @opindex mno-longcalls
11747 When this option is enabled, GCC instructs the assembler to translate
11748 direct calls to indirect calls unless it can determine that the target
11749 of a direct call is in the range allowed by the call instruction. This
11750 translation typically occurs for calls to functions in other source
11751 files. Specifically, the assembler translates a direct @code{CALL}
11752 instruction into an @code{L32R} followed by a @code{CALLX} instruction.
11753 The default is @option{-mno-longcalls}. This option should be used in
11754 programs where the call target can potentially be out of range. This
11755 option is implemented in the assembler, not the compiler, so the
11756 assembly code generated by GCC will still show direct call
11757 instructions---look at the disassembled object code to see the actual
11758 instructions. Note that the assembler will use an indirect call for
11759 every cross-file call, not just those that really will be out of range.
11762 @node zSeries Options
11763 @subsection zSeries Options
11764 @cindex zSeries options
11766 These are listed under @xref{S/390 and zSeries Options}.
11768 @node Code Gen Options
11769 @section Options for Code Generation Conventions
11770 @cindex code generation conventions
11771 @cindex options, code generation
11772 @cindex run-time options
11774 These machine-independent options control the interface conventions
11775 used in code generation.
11777 Most of them have both positive and negative forms; the negative form
11778 of @option{-ffoo} would be @option{-fno-foo}. In the table below, only
11779 one of the forms is listed---the one which is not the default. You
11780 can figure out the other form by either removing @samp{no-} or adding
11784 @item -fbounds-check
11785 @opindex fbounds-check
11786 For front-ends that support it, generate additional code to check that
11787 indices used to access arrays are within the declared range. This is
11788 currently only supported by the Java and Fortran 77 front-ends, where
11789 this option defaults to true and false respectively.
11793 This option generates traps for signed overflow on addition, subtraction,
11794 multiplication operations.
11798 This option instructs the compiler to assume that signed arithmetic
11799 overflow of addition, subtraction and multiplication wraps around
11800 using twos-complement representation. This flag enables some optimizations
11801 and disables other. This option is enabled by default for the Java
11802 front-end, as required by the Java language specification.
11805 @opindex fexceptions
11806 Enable exception handling. Generates extra code needed to propagate
11807 exceptions. For some targets, this implies GCC will generate frame
11808 unwind information for all functions, which can produce significant data
11809 size overhead, although it does not affect execution. If you do not
11810 specify this option, GCC will enable it by default for languages like
11811 C++ which normally require exception handling, and disable it for
11812 languages like C that do not normally require it. However, you may need
11813 to enable this option when compiling C code that needs to interoperate
11814 properly with exception handlers written in C++. You may also wish to
11815 disable this option if you are compiling older C++ programs that don't
11816 use exception handling.
11818 @item -fnon-call-exceptions
11819 @opindex fnon-call-exceptions
11820 Generate code that allows trapping instructions to throw exceptions.
11821 Note that this requires platform-specific runtime support that does
11822 not exist everywhere. Moreover, it only allows @emph{trapping}
11823 instructions to throw exceptions, i.e.@: memory references or floating
11824 point instructions. It does not allow exceptions to be thrown from
11825 arbitrary signal handlers such as @code{SIGALRM}.
11827 @item -funwind-tables
11828 @opindex funwind-tables
11829 Similar to @option{-fexceptions}, except that it will just generate any needed
11830 static data, but will not affect the generated code in any other way.
11831 You will normally not enable this option; instead, a language processor
11832 that needs this handling would enable it on your behalf.
11834 @item -fasynchronous-unwind-tables
11835 @opindex fasynchronous-unwind-tables
11836 Generate unwind table in dwarf2 format, if supported by target machine. The
11837 table is exact at each instruction boundary, so it can be used for stack
11838 unwinding from asynchronous events (such as debugger or garbage collector).
11840 @item -fpcc-struct-return
11841 @opindex fpcc-struct-return
11842 Return ``short'' @code{struct} and @code{union} values in memory like
11843 longer ones, rather than in registers. This convention is less
11844 efficient, but it has the advantage of allowing intercallability between
11845 GCC-compiled files and files compiled with other compilers, particularly
11846 the Portable C Compiler (pcc).
11848 The precise convention for returning structures in memory depends
11849 on the target configuration macros.
11851 Short structures and unions are those whose size and alignment match
11852 that of some integer type.
11854 @strong{Warning:} code compiled with the @option{-fpcc-struct-return}
11855 switch is not binary compatible with code compiled with the
11856 @option{-freg-struct-return} switch.
11857 Use it to conform to a non-default application binary interface.
11859 @item -freg-struct-return
11860 @opindex freg-struct-return
11861 Return @code{struct} and @code{union} values in registers when possible.
11862 This is more efficient for small structures than
11863 @option{-fpcc-struct-return}.
11865 If you specify neither @option{-fpcc-struct-return} nor
11866 @option{-freg-struct-return}, GCC defaults to whichever convention is
11867 standard for the target. If there is no standard convention, GCC
11868 defaults to @option{-fpcc-struct-return}, except on targets where GCC is
11869 the principal compiler. In those cases, we can choose the standard, and
11870 we chose the more efficient register return alternative.
11872 @strong{Warning:} code compiled with the @option{-freg-struct-return}
11873 switch is not binary compatible with code compiled with the
11874 @option{-fpcc-struct-return} switch.
11875 Use it to conform to a non-default application binary interface.
11877 @item -fshort-enums
11878 @opindex fshort-enums
11879 Allocate to an @code{enum} type only as many bytes as it needs for the
11880 declared range of possible values. Specifically, the @code{enum} type
11881 will be equivalent to the smallest integer type which has enough room.
11883 @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
11884 code that is not binary compatible with code generated without that switch.
11885 Use it to conform to a non-default application binary interface.
11887 @item -fshort-double
11888 @opindex fshort-double
11889 Use the same size for @code{double} as for @code{float}.
11891 @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate
11892 code that is not binary compatible with code generated without that switch.
11893 Use it to conform to a non-default application binary interface.
11895 @item -fshort-wchar
11896 @opindex fshort-wchar
11897 Override the underlying type for @samp{wchar_t} to be @samp{short
11898 unsigned int} instead of the default for the target. This option is
11899 useful for building programs to run under WINE@.
11901 @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
11902 code that is not binary compatible with code generated without that switch.
11903 Use it to conform to a non-default application binary interface.
11905 @item -fshared-data
11906 @opindex fshared-data
11907 Requests that the data and non-@code{const} variables of this
11908 compilation be shared data rather than private data. The distinction
11909 makes sense only on certain operating systems, where shared data is
11910 shared between processes running the same program, while private data
11911 exists in one copy per process.
11914 @opindex fno-common
11915 In C, allocate even uninitialized global variables in the data section of the
11916 object file, rather than generating them as common blocks. This has the
11917 effect that if the same variable is declared (without @code{extern}) in
11918 two different compilations, you will get an error when you link them.
11919 The only reason this might be useful is if you wish to verify that the
11920 program will work on other systems which always work this way.
11924 Ignore the @samp{#ident} directive.
11926 @item -finhibit-size-directive
11927 @opindex finhibit-size-directive
11928 Don't output a @code{.size} assembler directive, or anything else that
11929 would cause trouble if the function is split in the middle, and the
11930 two halves are placed at locations far apart in memory. This option is
11931 used when compiling @file{crtstuff.c}; you should not need to use it
11934 @item -fverbose-asm
11935 @opindex fverbose-asm
11936 Put extra commentary information in the generated assembly code to
11937 make it more readable. This option is generally only of use to those
11938 who actually need to read the generated assembly code (perhaps while
11939 debugging the compiler itself).
11941 @option{-fno-verbose-asm}, the default, causes the
11942 extra information to be omitted and is useful when comparing two assembler
11947 @cindex global offset table
11949 Generate position-independent code (PIC) suitable for use in a shared
11950 library, if supported for the target machine. Such code accesses all
11951 constant addresses through a global offset table (GOT)@. The dynamic
11952 loader resolves the GOT entries when the program starts (the dynamic
11953 loader is not part of GCC; it is part of the operating system). If
11954 the GOT size for the linked executable exceeds a machine-specific
11955 maximum size, you get an error message from the linker indicating that
11956 @option{-fpic} does not work; in that case, recompile with @option{-fPIC}
11957 instead. (These maximums are 8k on the SPARC and 32k
11958 on the m68k and RS/6000. The 386 has no such limit.)
11960 Position-independent code requires special support, and therefore works
11961 only on certain machines. For the 386, GCC supports PIC for System V
11962 but not for the Sun 386i. Code generated for the IBM RS/6000 is always
11963 position-independent.
11967 If supported for the target machine, emit position-independent code,
11968 suitable for dynamic linking and avoiding any limit on the size of the
11969 global offset table. This option makes a difference on the m68k
11972 Position-independent code requires special support, and therefore works
11973 only on certain machines.
11979 These options are similar to @option{-fpic} and @option{-fPIC}, but
11980 generated position independent code can be only linked into executables.
11981 Usually these options are used when @option{-pie} GCC option will be
11982 used during linking.
11984 @item -ffixed-@var{reg}
11986 Treat the register named @var{reg} as a fixed register; generated code
11987 should never refer to it (except perhaps as a stack pointer, frame
11988 pointer or in some other fixed role).
11990 @var{reg} must be the name of a register. The register names accepted
11991 are machine-specific and are defined in the @code{REGISTER_NAMES}
11992 macro in the machine description macro file.
11994 This flag does not have a negative form, because it specifies a
11997 @item -fcall-used-@var{reg}
11998 @opindex fcall-used
11999 Treat the register named @var{reg} as an allocable register that is
12000 clobbered by function calls. It may be allocated for temporaries or
12001 variables that do not live across a call. Functions compiled this way
12002 will not save and restore the register @var{reg}.
12004 It is an error to used this flag with the frame pointer or stack pointer.
12005 Use of this flag for other registers that have fixed pervasive roles in
12006 the machine's execution model will produce disastrous results.
12008 This flag does not have a negative form, because it specifies a
12011 @item -fcall-saved-@var{reg}
12012 @opindex fcall-saved
12013 Treat the register named @var{reg} as an allocable register saved by
12014 functions. It may be allocated even for temporaries or variables that
12015 live across a call. Functions compiled this way will save and restore
12016 the register @var{reg} if they use it.
12018 It is an error to used this flag with the frame pointer or stack pointer.
12019 Use of this flag for other registers that have fixed pervasive roles in
12020 the machine's execution model will produce disastrous results.
12022 A different sort of disaster will result from the use of this flag for
12023 a register in which function values may be returned.
12025 This flag does not have a negative form, because it specifies a
12028 @item -fpack-struct[=@var{n}]
12029 @opindex fpack-struct
12030 Without a value specified, pack all structure members together without
12031 holes. When a value is specified (which must be a small power of two), pack
12032 structure members according to this value, representing the maximum
12033 alignment (that is, objects with default alignment requirements larger than
12034 this will be output potentially unaligned at the next fitting location.
12036 @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
12037 code that is not binary compatible with code generated without that switch.
12038 Additionally, it makes the code suboptimal.
12039 Use it to conform to a non-default application binary interface.
12041 @item -finstrument-functions
12042 @opindex finstrument-functions
12043 Generate instrumentation calls for entry and exit to functions. Just
12044 after function entry and just before function exit, the following
12045 profiling functions will be called with the address of the current
12046 function and its call site. (On some platforms,
12047 @code{__builtin_return_address} does not work beyond the current
12048 function, so the call site information may not be available to the
12049 profiling functions otherwise.)
12052 void __cyg_profile_func_enter (void *this_fn,
12054 void __cyg_profile_func_exit (void *this_fn,
12058 The first argument is the address of the start of the current function,
12059 which may be looked up exactly in the symbol table.
12061 This instrumentation is also done for functions expanded inline in other
12062 functions. The profiling calls will indicate where, conceptually, the
12063 inline function is entered and exited. This means that addressable
12064 versions of such functions must be available. If all your uses of a
12065 function are expanded inline, this may mean an additional expansion of
12066 code size. If you use @samp{extern inline} in your C code, an
12067 addressable version of such functions must be provided. (This is
12068 normally the case anyways, but if you get lucky and the optimizer always
12069 expands the functions inline, you might have gotten away without
12070 providing static copies.)
12072 A function may be given the attribute @code{no_instrument_function}, in
12073 which case this instrumentation will not be done. This can be used, for
12074 example, for the profiling functions listed above, high-priority
12075 interrupt routines, and any functions from which the profiling functions
12076 cannot safely be called (perhaps signal handlers, if the profiling
12077 routines generate output or allocate memory).
12079 @item -fstack-check
12080 @opindex fstack-check
12081 Generate code to verify that you do not go beyond the boundary of the
12082 stack. You should specify this flag if you are running in an
12083 environment with multiple threads, but only rarely need to specify it in
12084 a single-threaded environment since stack overflow is automatically
12085 detected on nearly all systems if there is only one stack.
12087 Note that this switch does not actually cause checking to be done; the
12088 operating system must do that. The switch causes generation of code
12089 to ensure that the operating system sees the stack being extended.
12091 @item -fstack-limit-register=@var{reg}
12092 @itemx -fstack-limit-symbol=@var{sym}
12093 @itemx -fno-stack-limit
12094 @opindex fstack-limit-register
12095 @opindex fstack-limit-symbol
12096 @opindex fno-stack-limit
12097 Generate code to ensure that the stack does not grow beyond a certain value,
12098 either the value of a register or the address of a symbol. If the stack
12099 would grow beyond the value, a signal is raised. For most targets,
12100 the signal is raised before the stack overruns the boundary, so
12101 it is possible to catch the signal without taking special precautions.
12103 For instance, if the stack starts at absolute address @samp{0x80000000}
12104 and grows downwards, you can use the flags
12105 @option{-fstack-limit-symbol=__stack_limit} and
12106 @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
12107 of 128KB@. Note that this may only work with the GNU linker.
12109 @cindex aliasing of parameters
12110 @cindex parameters, aliased
12111 @item -fargument-alias
12112 @itemx -fargument-noalias
12113 @itemx -fargument-noalias-global
12114 @opindex fargument-alias
12115 @opindex fargument-noalias
12116 @opindex fargument-noalias-global
12117 Specify the possible relationships among parameters and between
12118 parameters and global data.
12120 @option{-fargument-alias} specifies that arguments (parameters) may
12121 alias each other and may alias global storage.@*
12122 @option{-fargument-noalias} specifies that arguments do not alias
12123 each other, but may alias global storage.@*
12124 @option{-fargument-noalias-global} specifies that arguments do not
12125 alias each other and do not alias global storage.
12127 Each language will automatically use whatever option is required by
12128 the language standard. You should not need to use these options yourself.
12130 @item -fleading-underscore
12131 @opindex fleading-underscore
12132 This option and its counterpart, @option{-fno-leading-underscore}, forcibly
12133 change the way C symbols are represented in the object file. One use
12134 is to help link with legacy assembly code.
12136 @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
12137 generate code that is not binary compatible with code generated without that
12138 switch. Use it to conform to a non-default application binary interface.
12139 Not all targets provide complete support for this switch.
12141 @item -ftls-model=@var{model}
12142 Alter the thread-local storage model to be used (@pxref{Thread-Local}).
12143 The @var{model} argument should be one of @code{global-dynamic},
12144 @code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
12146 The default without @option{-fpic} is @code{initial-exec}; with
12147 @option{-fpic} the default is @code{global-dynamic}.
12149 @item -fvisibility=@var{default|internal|hidden|protected}
12150 @opindex fvisibility
12151 Set the default ELF image symbol visibility to the specified option---all
12152 symbols will be marked with this unless overridden within the code.
12153 Using this feature can very substantially improve linking and
12154 load times of shared object libraries, produce more optimized
12155 code, provide near-perfect API export and prevent symbol clashes.
12156 It is @strong{strongly} recommended that you use this in any shared objects
12159 Despite the nomenclature, @code{default} always means public ie;
12160 available to be linked against from outside the shared object.
12161 @code{protected} and @code{internal} are pretty useless in real-world
12162 usage so the only other commonly used option will be @code{hidden}.
12163 The default if @option{-fvisibility} isn't specified is
12164 @code{default}, i.e., make every
12165 symbol public---this causes the same behavior as previous versions of
12168 A good explanation of the benefits offered by ensuring ELF
12169 symbols have the correct visibility is given by ``How To Write
12170 Shared Libraries'' by Ulrich Drepper (which can be found at
12171 @w{@uref{http://people.redhat.com/~drepper/}})---however a superior
12172 solution made possible by this option to marking things hidden when
12173 the default is public is to make the default hidden and mark things
12174 public. This is the norm with DLL's on Windows and with @option{-fvisibility=hidden}
12175 and @code{__attribute__ ((visibility("default")))} instead of
12176 @code{__declspec(dllexport)} you get almost identical semantics with
12177 identical syntax. This is a great boon to those working with
12178 cross-platform projects.
12180 For those adding visibility support to existing code, you may find
12181 @samp{#pragma GCC visibility} of use. This works by you enclosing
12182 the declarations you wish to set visibility for with (for example)
12183 @samp{#pragma GCC visibility push(hidden)} and
12184 @samp{#pragma GCC visibility pop}. These can be nested up to sixteen
12185 times. Bear in mind that symbol visibility should be viewed @strong{as
12186 part of the API interface contract} and thus all new code should
12187 always specify visibility when it is not the default ie; declarations
12188 only for use within the local DSO should @strong{always} be marked explicitly
12189 as hidden as so to avoid PLT indirection overheads---making this
12190 abundantly clear also aids readability and self-documentation of the code.
12191 Note that due to ISO C++ specification requirements, operator new and
12192 operator delete must always be of default visibility.
12194 An overview of these techniques, their benefits and how to use them
12195 is at @w{@uref{http://www.nedprod.com/programs/gccvisibility.html}}.
12201 @node Environment Variables
12202 @section Environment Variables Affecting GCC
12203 @cindex environment variables
12205 @c man begin ENVIRONMENT
12206 This section describes several environment variables that affect how GCC
12207 operates. Some of them work by specifying directories or prefixes to use
12208 when searching for various kinds of files. Some are used to specify other
12209 aspects of the compilation environment.
12211 Note that you can also specify places to search using options such as
12212 @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
12213 take precedence over places specified using environment variables, which
12214 in turn take precedence over those specified by the configuration of GCC@.
12215 @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
12216 GNU Compiler Collection (GCC) Internals}.
12221 @c @itemx LC_COLLATE
12223 @c @itemx LC_MONETARY
12224 @c @itemx LC_NUMERIC
12229 @c @findex LC_COLLATE
12230 @findex LC_MESSAGES
12231 @c @findex LC_MONETARY
12232 @c @findex LC_NUMERIC
12236 These environment variables control the way that GCC uses
12237 localization information that allow GCC to work with different
12238 national conventions. GCC inspects the locale categories
12239 @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
12240 so. These locale categories can be set to any value supported by your
12241 installation. A typical value is @samp{en_GB.UTF-8} for English in the United
12242 Kingdom encoded in UTF-8.
12244 The @env{LC_CTYPE} environment variable specifies character
12245 classification. GCC uses it to determine the character boundaries in
12246 a string; this is needed for some multibyte encodings that contain quote
12247 and escape characters that would otherwise be interpreted as a string
12250 The @env{LC_MESSAGES} environment variable specifies the language to
12251 use in diagnostic messages.
12253 If the @env{LC_ALL} environment variable is set, it overrides the value
12254 of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
12255 and @env{LC_MESSAGES} default to the value of the @env{LANG}
12256 environment variable. If none of these variables are set, GCC
12257 defaults to traditional C English behavior.
12261 If @env{TMPDIR} is set, it specifies the directory to use for temporary
12262 files. GCC uses temporary files to hold the output of one stage of
12263 compilation which is to be used as input to the next stage: for example,
12264 the output of the preprocessor, which is the input to the compiler
12267 @item GCC_EXEC_PREFIX
12268 @findex GCC_EXEC_PREFIX
12269 If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
12270 names of the subprograms executed by the compiler. No slash is added
12271 when this prefix is combined with the name of a subprogram, but you can
12272 specify a prefix that ends with a slash if you wish.
12274 If @env{GCC_EXEC_PREFIX} is not set, GCC will attempt to figure out
12275 an appropriate prefix to use based on the pathname it was invoked with.
12277 If GCC cannot find the subprogram using the specified prefix, it
12278 tries looking in the usual places for the subprogram.
12280 The default value of @env{GCC_EXEC_PREFIX} is
12281 @file{@var{prefix}/lib/gcc/} where @var{prefix} is the value
12282 of @code{prefix} when you ran the @file{configure} script.
12284 Other prefixes specified with @option{-B} take precedence over this prefix.
12286 This prefix is also used for finding files such as @file{crt0.o} that are
12289 In addition, the prefix is used in an unusual way in finding the
12290 directories to search for header files. For each of the standard
12291 directories whose name normally begins with @samp{/usr/local/lib/gcc}
12292 (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
12293 replacing that beginning with the specified prefix to produce an
12294 alternate directory name. Thus, with @option{-Bfoo/}, GCC will search
12295 @file{foo/bar} where it would normally search @file{/usr/local/lib/bar}.
12296 These alternate directories are searched first; the standard directories
12299 @item COMPILER_PATH
12300 @findex COMPILER_PATH
12301 The value of @env{COMPILER_PATH} is a colon-separated list of
12302 directories, much like @env{PATH}. GCC tries the directories thus
12303 specified when searching for subprograms, if it can't find the
12304 subprograms using @env{GCC_EXEC_PREFIX}.
12307 @findex LIBRARY_PATH
12308 The value of @env{LIBRARY_PATH} is a colon-separated list of
12309 directories, much like @env{PATH}. When configured as a native compiler,
12310 GCC tries the directories thus specified when searching for special
12311 linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
12312 using GCC also uses these directories when searching for ordinary
12313 libraries for the @option{-l} option (but directories specified with
12314 @option{-L} come first).
12318 @cindex locale definition
12319 This variable is used to pass locale information to the compiler. One way in
12320 which this information is used is to determine the character set to be used
12321 when character literals, string literals and comments are parsed in C and C++.
12322 When the compiler is configured to allow multibyte characters,
12323 the following values for @env{LANG} are recognized:
12327 Recognize JIS characters.
12329 Recognize SJIS characters.
12331 Recognize EUCJP characters.
12334 If @env{LANG} is not defined, or if it has some other value, then the
12335 compiler will use mblen and mbtowc as defined by the default locale to
12336 recognize and translate multibyte characters.
12340 Some additional environments variables affect the behavior of the
12343 @include cppenv.texi
12347 @node Precompiled Headers
12348 @section Using Precompiled Headers
12349 @cindex precompiled headers
12350 @cindex speed of compilation
12352 Often large projects have many header files that are included in every
12353 source file. The time the compiler takes to process these header files
12354 over and over again can account for nearly all of the time required to
12355 build the project. To make builds faster, GCC allows users to
12356 `precompile' a header file; then, if builds can use the precompiled
12357 header file they will be much faster.
12359 @strong{Caution:} There are a few known situations where GCC will
12360 crash when trying to use a precompiled header. If you have trouble
12361 with a precompiled header, you should remove the precompiled header
12362 and compile without it. In addition, please use GCC's on-line
12363 defect-tracking system to report any problems you encounter with
12364 precompiled headers. @xref{Bugs}.
12366 To create a precompiled header file, simply compile it as you would any
12367 other file, if necessary using the @option{-x} option to make the driver
12368 treat it as a C or C++ header file. You will probably want to use a
12369 tool like @command{make} to keep the precompiled header up-to-date when
12370 the headers it contains change.
12372 A precompiled header file will be searched for when @code{#include} is
12373 seen in the compilation. As it searches for the included file
12374 (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
12375 compiler looks for a precompiled header in each directory just before it
12376 looks for the include file in that directory. The name searched for is
12377 the name specified in the @code{#include} with @samp{.gch} appended. If
12378 the precompiled header file can't be used, it is ignored.
12380 For instance, if you have @code{#include "all.h"}, and you have
12381 @file{all.h.gch} in the same directory as @file{all.h}, then the
12382 precompiled header file will be used if possible, and the original
12383 header will be used otherwise.
12385 Alternatively, you might decide to put the precompiled header file in a
12386 directory and use @option{-I} to ensure that directory is searched
12387 before (or instead of) the directory containing the original header.
12388 Then, if you want to check that the precompiled header file is always
12389 used, you can put a file of the same name as the original header in this
12390 directory containing an @code{#error} command.
12392 This also works with @option{-include}. So yet another way to use
12393 precompiled headers, good for projects not designed with precompiled
12394 header files in mind, is to simply take most of the header files used by
12395 a project, include them from another header file, precompile that header
12396 file, and @option{-include} the precompiled header. If the header files
12397 have guards against multiple inclusion, they will be skipped because
12398 they've already been included (in the precompiled header).
12400 If you need to precompile the same header file for different
12401 languages, targets, or compiler options, you can instead make a
12402 @emph{directory} named like @file{all.h.gch}, and put each precompiled
12403 header in the directory, perhaps using @option{-o}. It doesn't matter
12404 what you call the files in the directory, every precompiled header in
12405 the directory will be considered. The first precompiled header
12406 encountered in the directory that is valid for this compilation will
12407 be used; they're searched in no particular order.
12409 There are many other possibilities, limited only by your imagination,
12410 good sense, and the constraints of your build system.
12412 A precompiled header file can be used only when these conditions apply:
12416 Only one precompiled header can be used in a particular compilation.
12419 A precompiled header can't be used once the first C token is seen. You
12420 can have preprocessor directives before a precompiled header; you can
12421 even include a precompiled header from inside another header, so long as
12422 there are no C tokens before the @code{#include}.
12425 The precompiled header file must be produced for the same language as
12426 the current compilation. You can't use a C precompiled header for a C++
12430 The precompiled header file must be produced by the same compiler
12431 version and configuration as the current compilation is using.
12432 The easiest way to guarantee this is to use the same compiler binary
12433 for creating and using precompiled headers.
12436 Any macros defined before the precompiled header is included must
12437 either be defined in the same way as when the precompiled header was
12438 generated, or must not affect the precompiled header, which usually
12439 means that the they don't appear in the precompiled header at all.
12441 The @option{-D} option is one way to define a macro before a
12442 precompiled header is included; using a @code{#define} can also do it.
12443 There are also some options that define macros implicitly, like
12444 @option{-O} and @option{-Wdeprecated}; the same rule applies to macros
12447 @item If debugging information is output when using the precompiled
12448 header, using @option{-g} or similar, the same kind of debugging information
12449 must have been output when building the precompiled header. However,
12450 a precompiled header built using @option{-g} can be used in a compilation
12451 when no debugging information is being output.
12453 @item The same @option{-m} options must generally be used when building
12454 and using the precompiled header. @xref{Submodel Options},
12455 for any cases where this rule is relaxed.
12457 @item Each of the following options must be the same when building and using
12458 the precompiled header:
12460 @gccoptlist{-fexceptions -funit-at-a-time}
12463 Some other command-line options starting with @option{-f},
12464 @option{-p}, or @option{-O} must be defined in the same way as when
12465 the precompiled header was generated. At present, it's not clear
12466 which options are safe to change and which are not; the safest choice
12467 is to use exactly the same options when generating and using the
12468 precompiled header. The following are known to be safe:
12470 @gccoptlist{-fpreprocessed -pedantic-errors}
12474 For all of these except the last, the compiler will automatically
12475 ignore the precompiled header if the conditions aren't met. If you
12476 find an option combination that doesn't work and doesn't cause the
12477 precompiled header to be ignored, please consider filing a bug report,
12480 If you do use differing options when generating and using the
12481 precompiled header, the actual behavior will be a mixture of the
12482 behavior for the options. For instance, if you use @option{-g} to
12483 generate the precompiled header but not when using it, you may or may
12484 not get debugging information for routines in the precompiled header.
12486 @node Running Protoize
12487 @section Running Protoize
12489 The program @code{protoize} is an optional part of GCC@. You can use
12490 it to add prototypes to a program, thus converting the program to ISO
12491 C in one respect. The companion program @code{unprotoize} does the
12492 reverse: it removes argument types from any prototypes that are found.
12494 When you run these programs, you must specify a set of source files as
12495 command line arguments. The conversion programs start out by compiling
12496 these files to see what functions they define. The information gathered
12497 about a file @var{foo} is saved in a file named @file{@var{foo}.X}.
12499 After scanning comes actual conversion. The specified files are all
12500 eligible to be converted; any files they include (whether sources or
12501 just headers) are eligible as well.
12503 But not all the eligible files are converted. By default,
12504 @code{protoize} and @code{unprotoize} convert only source and header
12505 files in the current directory. You can specify additional directories
12506 whose files should be converted with the @option{-d @var{directory}}
12507 option. You can also specify particular files to exclude with the
12508 @option{-x @var{file}} option. A file is converted if it is eligible, its
12509 directory name matches one of the specified directory names, and its
12510 name within the directory has not been excluded.
12512 Basic conversion with @code{protoize} consists of rewriting most
12513 function definitions and function declarations to specify the types of
12514 the arguments. The only ones not rewritten are those for varargs
12517 @code{protoize} optionally inserts prototype declarations at the
12518 beginning of the source file, to make them available for any calls that
12519 precede the function's definition. Or it can insert prototype
12520 declarations with block scope in the blocks where undeclared functions
12523 Basic conversion with @code{unprotoize} consists of rewriting most
12524 function declarations to remove any argument types, and rewriting
12525 function definitions to the old-style pre-ISO form.
12527 Both conversion programs print a warning for any function declaration or
12528 definition that they can't convert. You can suppress these warnings
12531 The output from @code{protoize} or @code{unprotoize} replaces the
12532 original source file. The original file is renamed to a name ending
12533 with @samp{.save} (for DOS, the saved filename ends in @samp{.sav}
12534 without the original @samp{.c} suffix). If the @samp{.save} (@samp{.sav}
12535 for DOS) file already exists, then the source file is simply discarded.
12537 @code{protoize} and @code{unprotoize} both depend on GCC itself to
12538 scan the program and collect information about the functions it uses.
12539 So neither of these programs will work until GCC is installed.
12541 Here is a table of the options you can use with @code{protoize} and
12542 @code{unprotoize}. Each option works with both programs unless
12546 @item -B @var{directory}
12547 Look for the file @file{SYSCALLS.c.X} in @var{directory}, instead of the
12548 usual directory (normally @file{/usr/local/lib}). This file contains
12549 prototype information about standard system functions. This option
12550 applies only to @code{protoize}.
12552 @item -c @var{compilation-options}
12553 Use @var{compilation-options} as the options when running @command{gcc} to
12554 produce the @samp{.X} files. The special option @option{-aux-info} is
12555 always passed in addition, to tell @command{gcc} to write a @samp{.X} file.
12557 Note that the compilation options must be given as a single argument to
12558 @code{protoize} or @code{unprotoize}. If you want to specify several
12559 @command{gcc} options, you must quote the entire set of compilation options
12560 to make them a single word in the shell.
12562 There are certain @command{gcc} arguments that you cannot use, because they
12563 would produce the wrong kind of output. These include @option{-g},
12564 @option{-O}, @option{-c}, @option{-S}, and @option{-o} If you include these in
12565 the @var{compilation-options}, they are ignored.
12568 Rename files to end in @samp{.C} (@samp{.cc} for DOS-based file
12569 systems) instead of @samp{.c}. This is convenient if you are converting
12570 a C program to C++. This option applies only to @code{protoize}.
12573 Add explicit global declarations. This means inserting explicit
12574 declarations at the beginning of each source file for each function
12575 that is called in the file and was not declared. These declarations
12576 precede the first function definition that contains a call to an
12577 undeclared function. This option applies only to @code{protoize}.
12579 @item -i @var{string}
12580 Indent old-style parameter declarations with the string @var{string}.
12581 This option applies only to @code{protoize}.
12583 @code{unprotoize} converts prototyped function definitions to old-style
12584 function definitions, where the arguments are declared between the
12585 argument list and the initial @samp{@{}. By default, @code{unprotoize}
12586 uses five spaces as the indentation. If you want to indent with just
12587 one space instead, use @option{-i " "}.
12590 Keep the @samp{.X} files. Normally, they are deleted after conversion
12594 Add explicit local declarations. @code{protoize} with @option{-l} inserts
12595 a prototype declaration for each function in each block which calls the
12596 function without any declaration. This option applies only to
12600 Make no real changes. This mode just prints information about the conversions
12601 that would have been done without @option{-n}.
12604 Make no @samp{.save} files. The original files are simply deleted.
12605 Use this option with caution.
12607 @item -p @var{program}
12608 Use the program @var{program} as the compiler. Normally, the name
12609 @file{gcc} is used.
12612 Work quietly. Most warnings are suppressed.
12615 Print the version number, just like @option{-v} for @command{gcc}.
12618 If you need special compiler options to compile one of your program's
12619 source files, then you should generate that file's @samp{.X} file
12620 specially, by running @command{gcc} on that source file with the
12621 appropriate options and the option @option{-aux-info}. Then run
12622 @code{protoize} on the entire set of files. @code{protoize} will use
12623 the existing @samp{.X} file because it is newer than the source file.
12627 gcc -Dfoo=bar file1.c -aux-info file1.X
12632 You need to include the special files along with the rest in the
12633 @code{protoize} command, even though their @samp{.X} files already
12634 exist, because otherwise they won't get converted.
12636 @xref{Protoize Caveats}, for more information on how to use
12637 @code{protoize} successfully.